52 Table 4 4. Non Endangered Species Algal Risk Quotients Agricultural and Non Agricultural Uses Use Application Rate Maximum Peak EEC EC50 or LC50 RQ LOC Exceedance Agricultural uses All labeled rates # 0.9 mg/ L 133 mg/ L < 0.01 No LOC exceeded Non Agricultural All labeled rates # 39 mg/ L 133 mg/ L # 0.29 No LOC exceeded Table 4 5. Endangered Species Algal Risk Quotients Agricultural and Non Agricultural Uses Use Application Rate Maximum Peak EECa NOAEC RQ LOC Exceedance Agricultural uses All labeled rates # 0.9 mg/ L 62.5 mg/ L # 0.014 No LOC exceeded Non Agricultural All labeled rates # 39 mg/ L 62.5 mg/ L # 0.62 No LOC exceeded Risk Description  Interpretation of Direct Effects No LOCs were exceeded from chlorate's agricultural or non agricultural uses. Also, the NOAEC from the green algae study was 62.5 mg/ L, which is lower than the peak chlorate EEC of 39 mg/ L. Therefore, risk to endangered species is also presumably lower than the Agency's level of concern. However, risk to algae cannot be precluded. No studies in the following plant species have been submitted, which are required for herbicides: Lemna gibba ( duckweed), Skeletonema costatum ( a marine diatom), Anabaena flos aquae ( a blue green bacterium), and a freshwater diatom.

Also, data located in the open literature suggest that brown algae are considerably more sensitive than green algae to chlorate. A 14 day EC50 of 0.012 mM (. 1 mg/ L) was reported for brown algae ( van Wijk et al., 1997, described in Appendix M). Sufficient detail was not available in the published study report to allow for a comprehensive assessment of data adequacy. 30 However, the EECs for the non agricultural uses ranged from 3.1 to 39 mg/ L, which all exceed the reported EC50 for brown algae of .1 mg/ L. For this reason, there may be risk to some algal species that exceed the Agency's level of concern for aquatic plants. As previously discussed, however, additional data are needed to address the considerable uncertainty in the aquatic EECs and uncertainty in the toxicity data before risk can be definitively assessed. 53 4.1.4. Uncertainties in the Aquatic Organism Risk Assessment There are a number of areas of uncertainty in the aquatic organism risk assessment that merit discussion. These include the following:

Uncertainties that may have caused an under estimation of risk ° The risk assessment only considers the most sensitive species tested. Aquatic acute and chronic risks are based on acceptable toxicity data for the most sensitive fish, invertebrate, and plant species tested. Responses to a toxicant can be expected to be variable across species. Sensitivity differences between species can be considerable ( several orders of magnitude) for some chemicals ( Mayer and Ellersieck 1986). It is uncertain if the tested laboratory species is representative of most species' sensitivities to chlorate toxicity.

Open literature toxicity data were located that suggest that some fish and algal species may be more sensitive to chlorate toxicity than the surrogate species used in this assessment. Therefore, submission of confirmatory studies in non guideline fish and algal species would reduce uncertainty in this assessment ( see Section 3 for additional discussion).

° The risk assessment only considered a subset of possible use scenarios. Although chlorate has a label for a limited number of crops and non agricultural uses, they encompass a large geographic area. Also, the non agricultural uses may presumably be used without geographic limits. Some uses that may pose higher risks include those occurring in sensitive locations ( close proximity to aquatic environments and high runoff potentials).

° The risk quotients assume that exposure only occurs to chlorate. In some environments, chlorate may be reduced to chlorite, which has been shown to be more toxic to aquatic organisms than chlorate. This is of particular concern for invertebrates because the chlorite EC50 for daphnids is 0.15 mg/ L, which is approximately 6000 fold lower than the EC50 for chlorate of 920 mg/ L. Therefore, formation of even small amounts of chlorite could result risk to endangered and non endangered aquatic invertebrates at levels of concern to the agency.

° The effect of pH on chlorate toxicity is uncertain. The available toxicity studies used pH environments that are slightly alkaline. The toxicity of chlorate is expected to be dependent on pH as well as redox condition. Therefore, submission of data that characterizes the effect of pH and redox condition of the media on chlorate toxicity to invertebrates would be of considerable value to this assessment, provided that the chemical species in the test media are adequately characterized ( qualitatively and quantitatively). Submission of such chlorate in toxicity studies for aquatic invertebrates would reduce uncertainty in this assessment because pH conditions as low as 5.5 are not uncommon, particularly in the Northeastern United States. 54 ° Many of the labels do not specify the maximum number of applications or annual load; however, some labels for cotton indicate that multiple applications may be necessary. The Agency has assumed that chlorate may be applied twice annually to cotton at all application rates with a 30 day application interval and is applied once annually for all other uses. This assumption may have resulted in an under estimation of risk if chlorate may be applied more than twice annually ( or at shorter application intervals) to cotton or more than once annually to other crops.

Uncertainties that may have resulted in an over estimation of risk ° As previously discussed, there is considerable uncertainty in the rate of formation/ decline of redox products of chlorate ( i. e., the kinetics of formation/ decline). Redox kinetics of the chlorine system is complex, studies are very difficult, and most of the data available are not suitable for estimating speciation and predominance in terrestrial and aquatic environments. GENEEC 2 and PRZM EXAMS are not ideal simulation models for chemicals in which one of the elements that can exist in more than one oxidation state. Therefore, conservative assumptions were made that likely resulted in an over estimation of exposure to chlorate.

° GENEEC 2 assumes a contiguous drainage basin that flows into a pond that is10 times smaller than the treated area. The application scenarios for the non agricultural uses may not be consistent with the scenario assumed by GENEEC 2.

° GENEEC 2 assumes no foliar interception, which likely resulted in an over estimation of exposure. Foliar interception is likely to occur because chlorate absorbs into plants. Any chlorate that absorbs into the plant will not likely enter surface water.

Uncertainties that may have resulted in an under estimation or an over estimation of risk ° Surrogate species were used to predict potential risks for species with no data ( i. e., reptiles and amphibians). It was assumed that use of surrogate species toxicity data are sufficiently conservative to apply the broad range of species within taxonomic groups. If other species are more or less sensitive to chlorate and its degradates than the surrogates, risks may be under or over estimated, respectively. 31 The application rate for pre paving is 650 lbs a. i./ Acre; however, this use pattern would not likely result in exposure to birds.

55 4.2. Risks to Birds, Acute and Chronic Exposures Summary of Conclusions ° Agricultural Uses: Based on chlorate's low acute and subacute toxicity to birds ( LD50 > 2510 mg/ kg bw; LC50 > 5620 mg/ kg feed), risk to endangered and non endangered birds is presumably lower than the Agency's level of concern for all agricultural uses.

° Non agricultural Uses: Even though chorate is of low acute toxicity to birds, EECs for chlorate's non agricultural uses were as high as 125,000 ppm. Therefore, acute risk to birds cannot be precluded. However, such risks cannot be quantified.

° Absence of reproduction toxicity data precludes a quantitative assessment of chronic risk to birds. However, mammalian data suggest that chlorate's effects are cumulative ( more toxic after repeated exposures). Therefore, the Agency presumes that potential risk to birds exists.

4.2.1. Risk Estimation  Integration of Exposure and Effects Data Acute risk quotients were not calculated because no mortality or signs of toxicity were observed in the submitted subacute or acute toxicity studies at concentrations that are above the limit for these types of studies.

Chronic risk quotients were not calculated because a reproduction toxicity study has not been submitted to the Agency.

4.2.2. Risk Description  Interpretation of Direct Effects No acute risk to birds was identified at levels of concern to the Agency from chlorate's agricultural uses based on its low acute toxicity to birds. However, EFED cannot preclude acute risk from the non agricultural uses. Chlorate is applied at rates of 52 to 520 lbs/ Acre for these uses. 31 The corresponding EECs are 12,500 and 125,000 ppm, respectively, which are approximately 2.5 to 25 fold higher than the highest concentration tested in the subacute bird toxicity studies. Therefore, acute risk to birds from these high application rates cannot be precluded.

EFED cannot preclude chronic risk because no reproduction toxicity data are available. A field dissipation study has not been submitted; therefore, the potential for chronic exposure has not been fully assessed. However, chlorate is expected to be persistent under some environmental conditions; therefore, the Agency assumes that repeated exposure is possible. The available 56 studies in mammals suggest that chlorate is significantly more toxic after repeated exposures compared with single exposures ( i. e., toxicity increases as study duration increases). A similar relationship between exposure duration and toxicity is presumed in birds as well. Therefore, lack of reproduction toxicity data is an important data gap.

4.3. Risk to Mammals, Acute Exposures Summary of Conclusions ° Risk from acute exposure cannot be precluded for chlorate's agricultural or non agricultural uses.

° A 2 generation reproduction toxicity study is not available to allow for derivation of chronic risk quotients, and other studies were considered inappropriate for risk quotient calculations. However, based on subchronic toxicity studies, there appears to be risk to mammals at levels of concern to the Agency from both agricultural and non agricultural uses.

4.3.1. Risk Estimation, Integration of Exposure and Effects Data Acute risk quotients were not calculated for mammals. The LD50 from a core acute oral toxicity study in rats was > 5000 mg/ kg bw ( MRID 418199 01). In this study, 10% ( 1/ 10) of the rats administered 5000 mg/ kg died. Mortality was not observed at any other dose. Therefore, the data were not sufficient to allow for characterization of the dose response relationship, and the proximity of the LD50 to 5000 mg/ kg bw is uncertain. For this reason, formal risk quotients were not calculated. However, Tables 4 6 and 4 7 below, respectively, present a comparison of the body weight adjusted LD50s to the agricultural and non agricultural EECs. These ratios can be used to estimate high end risk to exposed mammals. 57 Table 4 6. Proximity of the lowest observed acute toxic dose in mammals to the upper 90th percentile EEC ( mg/ kg bw) for small ( 15 gram), medium ( 35 gram), and large ( 1000 gram) mammals ( Range of Maximum Application Rate for all Agricultural Uses).

Food Item Size of Mammal ( grams) Adjusted lowest observed toxic dose from MRID 41819901 ( mg/ kg bw) a Range of EECs ( mg/ kg bw) b Ratio of lowest observed toxic dose to the upper 90th percentile EEC ( unitless)

Short grass 15 10,989 1400  2900 0.13  0.26 35 8891 950  2000 0.11  0.22 1000 3846 200  450 0.052  0.12 Tall grass 15 10,989 630  1300 0.057  0.12 35 8891 440  910 0.049  0.10 1000 3846 99  210 0.026  0.055 Broadleaf plants/ small insects 15 10,989 770  1600 0.070  0.15 35 8891 540  1100 0.061  0.12 1000 3846 120  250 0.031  0.065 Fruits, pods, large insects 15 10989 86  180 < 0.01  0.016 35 8891 59  120 < 0.01  0.013 1000 3846 14  28 < 0.01  < 0.01 a The acute oral toxic dose was adjusted for body weight based on the formula recommended by Mineau et al. 1996: Adj. LD50 = LD50 ( TW/ AW) 0.25 : TW= weight of test organism ( reference body weight of adult rat is .350 grams); AW = weight of assessed organism. b EECs were calculated by assuming that small, medium, and large mammals consume 95%, 66%, and 15% of their body weight daily. Only the highest and lowest EECs from chlorate's agricultural uses are used in this assessment. These values are based on EECs presented in Table 3 8. 58 Table 4 7. Proximity of the lowest observed acute toxic dose in mammals to the predicted EEC ( mg/ kg bw) for small ( 15 gram), medium ( 35 gram), and large ( 1000 gram) mammals ( Based on the Range of Maximum Application Rates for all Non Agricultural Uses).

Food Item Size of Mammal ( weight, grams) Adjusted lowest observed toxic dose ( mg/ kg bw) a Range of EECs ( mg/ kg bw) b Ratio of lowest observed toxic dose to the upper 90th percentile EEC ( unitless)

Short grass 15 10989 11,900  119,000 1.1  11 35 8891 8200  82,000 0.93  9.3 1000 3846 1900  19,000 0.49  4.9 Tall grass 15 10989 5400  54,000 0.49  4.9 35 8891 3800  38,000 0.43  4.3 1000 3846 860  8600 0.22  2.2 Broadleaf plants/ small insects 15 10989 6700  67,000 0.61  6.1 35 8891 4600  46,000 0.52  5.2 1000 3846 1100  11,000 0.27  2.7 Fruits, pods, large insects 15 10989 740  7400 0.07  0.7 35 8891 520  5200 0.06  0.6 1000 3846 120  1200 0.03  0.3 a The acute oral toxic dose was adjusted for body weight based on the formula recommended by Mineau et al. 1996 for adjusting LD50s: Adj. LD50 = LD50 ( TW/ AW) 0.25 : TW= weight of test organism ( reference body weight of adult rat is 350 grams); AW = weight of assessed organism. b EECs were calculated by assuming that small, medium, and large mammals consume 95%, 66%, and 15%, respectively, of their body weight daily, and were calculated using the highest and lowest labeled application rates ( 52 lbs a. i./ Acre and 520 lbs a. i./ Acre) that are most likely to result in exposure.

4.3.2. Risk Description  Interpretation of Direct Effects Agricultural Uses For chlorate's agricultural uses, the ratio of the lowest body weight adjusted observed toxic dose in mammals ( 5000 mg/ kg bw) to the upper 90th percentile EEC was as high as 0.26 for small 32Campbell G S. 1985. Soil Physics with BASIC. Developments in Soil Science 14. Elsevier publishers. New York NY, USA. This soil density is considered a representative, mid range value.

33 650 lbs a. i./ Acre × 0.37 kg/ lb = 240.5 kg a. i./ Acre × 1E6 mg/ kg = 2.4E8 mg a. i./ Acre 1.2E8 cm3/ Acre x 1.3 g soil/ cm3 = 1.6 E8 g soil/ Acre ( 1.6E5 kg soil/ Acre) 2.4E8 mg a. i./ Acre ÷ 1.6E5 kg soil/ Acre = 1500 mg a. i./ kg soil 59 mammals, 0.22 for medium sized mammals, and 0.12 for large mammals ( short grass food items). For other food items, the ratios were # 0.15. If the LD50 is in close proximity to 5000 mg/ kgday there may be potential risk at levels of concern to the Agency to non endangered small and medium sized mammals that forage on short grass and potential risk to large ( 1000 grams) endangered mammals that feed on short grass and small and medium sized endangered mammals that forage on several other food items. However, proximity of the LD50 to 5000 mg/ kg day cannot be determined based on the submitted data. Additional uncertainties in this assessment are discussed in Section 4.7.

Non Agricultural Uses, Spray Applications The ratios presented in Table 4 7 above suggest that there could be considerable risk to mammals of all sizes that forage in the area where chlorate is used for the non agricultural applications. However, potential risk was likely over estimated for the following reasons:

° An LD50 has not been established. The highest dose tested in the available toxicity studies ( 5000 mg/ kg bw) induced 10% mortality. The proximity of the LD50 to 5000 mg/ kg bw is uncertain. ° Many of the non agricultural uses will likely result in small contiguously treated areas. Therefore, the likelihood that an animal will consume 100% of its diet from chlorate treated areas is low for some of these uses.

Nonetheless, the EECs were predicted to be up to 11 times higher than the toxic dose of 5000 mg/ kg bw for the non agricultural uses. Therefore, there appears to be risk to mammals at levels of concern to the Agency.

Also, based on the very high application rates associated with the non agricultural uses of chlorate, ingestion of contaminated soil could represent a significant exposure pathway. Therefore, incidental ingestion via contaminated soil was estimated. Based on a maximum application rate of 650 lbs a. i./ Acre and a soil density of 1.3 grams/ cm3 ( Campbell 1985), 32 chlorate concentrations in the first 3 centimeters of soil could be as high as 1500 mg/ kg soil ( ppm). 33 This application rate is only labeled for pre paving, which is not likely to result in exposure. Also, this calculation assumes no foliar interception ( direct application to soil). For these reasons, this calculation represents a high end estimate. Using daily food intake, as estimated by Nagy ( 1987) ( EQ 1), a 20 gram mammal is estimated to consume approximately 3.7 grams of food ( wet weight) daily: 34 Extrapolations from one mammal species to another needs to consider differences in the scaling of toxicity for differences in body weight. Therefore, the acute oral LD50 was adjusted for body weight based on the formula recommended by Mineau et al. 1996: Adj. LD50 = LD50 ( TW/ AW) 0.25 : TW= weight of test organism ( reference body weight of adult rat is .350 grams); AW = weight of assessed organism.

60 F BW W =   0 621 1 0 564 . *

( ) .

where F is the food intake in grams of fresh weight per day, BW is the body mass ( wet weight) of the organism in grams, and W is the mass fraction of water in the food ( assumed to be 0.1). Therefore, the estimated dose of chlorate from dietary consumption of 100% soil would be 5.6 mg/ day ( 3.7 g soil day 1 × 0.001 kg g 1 × 1500 mg a. i. kg 1). This intake level corresponds to a body weight adjusted internal dose of 280 mg/ kg day for a 20 gram mammal ( 5.6 mg/ day ÷ 0.02 kg = 280 mg/ kg day). Direct comparison of this maximum possible soil intake value to the body weight adjusted acute oral LD50 of > 10,989 mg/ kg bw34 would not result in risk to mammals at levels of concern to the Agency.

In addition, Beyer et al. ( 1994) reported that high end mammals with respect to soil consumption ( e. g., armadillos) consume # 17% soil in their diet, and small mammals ( mice and voles) consume less than 2.5% soil in their diet. Therefore, this analysis likely resulted in an over estimation of exposure and risk. However, risk from repeated ingestion of contaminated soil cannot be precluded, because adequate toxicity data are not available for comparison to these exposure values.

Non Agricultural Uses, Granular Applications Risk Estimation Formal risk quotients were not calculated for reasons previously discussed. However, Table 4 8 below presents a comparison of the body weight adjusted lowest observed toxic dose in rats of 5000 mg/ kg day from MRID 41819901 to the granular application EECs ( mg/ ft2). These ratios are used to qualitatively describe potential risk. 61 Table 4 8. Range of Ratios of Chlorate's Body Weight Adjusted LD50 to Granular EECs ( mg/ ft2) for Sodium Chlorate's Non Agricultural Uses ( Granular Formulations)

Use Body Weight ( g) Rat LD50Adj mg/ kg bwa EEC ( mg/ ft2) b Ratio of LD50adj to EECc Parking lots, under asphalt paving, fence lines, building perimeters, ditch banks, picnic areas, vacant lots, wood decks, bleachers, cemeteries, fuel tanks, runways, helo pads, etc. 520 lbs a. i./ Acre 15 10,989 5400 33 35 8891 5400 17 1000 3846 5400 1.4 Around buildings, storage areas, fences, pumps, machinery, fuel tanks, recreational areas, roadways, guard rails, airports, rights of ways. 160 lbs a. i./ Acre 15 10,989 1700 10 35 8891 1700 5.4 1000 3846 1700 0.43 a Adj. LD50 = LD50 ( TW/ AW) 0.25 : TW= weight of test organism ( reference body weight of adult rat is .350 grams); AW = weight of assessed organism. b EEC = Application rate ( lbs/ Acre) x 453,000 mg/ lb ÷ 43,600 sq ft/ Acre c Ratio = EEC ÷ ( LD50adj × bw in kg)

Risk Description Granular applications of chlorate appear to pose risk to small, medium, and large mammals at levels of concern to the Agency. It was estimated that granular applications would result in chlorate concentrations that are between 0.42 and 33 times the mass of chlorate in every ft2 of chlorate treated areas that has been shown to be toxic to mammals. Although the habitat and feeding area of mammals are substantially greater than a ft2, the mg/ ft2 index is used to evaluate whether there is sufficient mass of chlorate within a treated area to potentially cause adverse effects to exposed mammals. U. S. EPA 1992 and U. S. EPA 2004 can be referenced for additional discussion on the LD50/ ft2 index.

The LD50/ ft2 method is used to encompass exposure via all routes ( oral, dermal, inhalation). However, as an ionic salt, chlorate will not likely appreciably absorb through the skin, and its low Henry's law constant and volatility suggest that inhalation will likely be negligible. Therefore, exposure will likely be limited largely to the oral route ( drinking water, contaminated food items, direct consumption of granules, preening activity). Although chlorate is a strong oxidant, it is not a strong irritant; therefore, mammals are not expected to intentionally avoid chlorate. In fact, chlorate could be particularly attractive to salt thirsty mammals resulting in higher chlorate body burdens in these mammals.

Other uncertainties in this assessment are presented in Section 4.7. 62 4.4. Potential Risk to Mammals, Chronic Exposures Sufficient toxicity data are not available to allow for risk quotient calculations. However, the available subchronic data suggest that mammals may be at considerable risk from repeated exposures to chlorate. Chlorate is presumably stable under some environmental conditions; therefore, repeated exposures to chlorate is possible. Subchronic toxicity studies ranging in duration from 21 to 90 days suggest that chlorate may induce effects that could affect the growth, survival, or reproduction in exposed mammals at doses of approximately 100 mg/ kg bw per day, which is a dose that is 50 times lower than the acute oral LD50 of > 5000 mg/ kg bw. Effects observed in the repeated dose toxicity studies included decreased body weight ( up to approximately 30% decrease compared with control ( unexposed) animals), blood toxicity, and pituitary and thyroid effects ( including changes in hormone levels).

4.5. Endocrine Disruption Potential Effects observed in repeated dose toxicity studies in mammals indicate that chlorate could affect the endocrine system. For example, thyroid hormone levels were affected in rats maintained on drinking water supplemented with chlorate for 90 days.

EPA is required under the Federal Food, Drug, and Cosmetic Act ( FFDCA), as amended by the Food Quality Protection Act ( FQPA), to develop a screening program to determine whether certain substances ( including all pesticide active and other ingredients) " may have an effect in humans that is similar to an effect produced by a naturally occurring estrogen, or other such endocrine effects as the Administrator may designate." Following the recommendations of its Endocrine Disruptor Screening and Testing Advisory Committee ( EDSTAC), EPA determined that there was scientific bases for including, as part of the program, the androgen and thyroid hormone systems, in addition to the estrogen hormone system. EPA also adopted EDSTAC's recommendation that the Program include evaluations of potential effects in wildlife. For pesticide chemicals, EPA will use The Federal Insecticide, Fungicide, and Rodenticide Act ( FIFRA) and, to the extent that effects in wildlife may help determine whether a substance may have an effect in humans, FFDCA authority to require the wildlife evaluations. As the science develops and resources allow, screening of additional hormone systems may be added to the Endocrine Disruptor Screening Program ( EDSP). When the appropriate screening and/ or testing protocols being considered under the Agency's EDSP have been developed, chlorate may be subjected to additional screening and/ or testing to better characterize effects related to endocrine disruption.

4.6. Potential Risk to Terrestrial Plants Based on chlorate's non selective mode of action and lack of adequate toxicity data, EFED presumes risk to non target plants at levels above the Agency's level of concern for all uses. However, such risks cannot be quantified based on the currently available data. 63 4.7. Uncertainties in the Terrestrial Organism Risk Assessment There are a number of areas of uncertainty in the terrestrial risk assessment that merit discussion, which were previously discussed in Sections 2 and 3. These are summarized below.

Exposure ° Many of the labels are not clear regarding the maximum allowable annual applications ( number of applications or total load). The Agency assumed a maximum of 2 annual applications ( 30 days apart) for cotton and 1 annual application for all other uses. Risk may be under estimated if these assumptions do not accurately reflect chlorate's applications.

° Stability of chlorate in terrestrial and aquatic environments is uncertain, but it is expected to exhibit wide spatial and seasonal variability.

° There is considerable uncertainty in the rate of formation/ decline of redox products of chlorate ( i. e., the kinetics of formation/ decline).

° Many of the non agricultural uses will likely result in small contiguously treated areas, which would reduce the likelihood that an animal would consume 100% of its diet from chlorate treated areas.

° Chlorate is a dessicant that kills parts of plants that are generally edible to herbivorous organisms. Because the herbicide is absorbed by plants relatively rapidly and kills most exposed plants within several days to several weeks after exposure, some contaminated food items may not be attractive to herbivores for an extended period of time after treatment.

° The risk assessment assumes that 100% of the exposure organism's diet is relegated to single food types foraged only from treated fields. These assumptions are likely to be conservative for many species and will tend to overestimate potential risks. The assumption of 100% diet from a treated area may be realistic for acute exposures, but long term exposures modeled as single food types composed entirely of material from a treated field is uncertain.

Toxicity ° The toxicity database is limited. No chronic or reproductive toxicity data ( aquatic or terrestrial organisms) considered adequate for screening level ecological risk assessment were available.

° Adequate non target terrestrial plant data are not available for this assessment. In the absence of such data, and based on the non specific mode of action of chlorate, EFED presumes considerable risk to non target plants. 35 Hayes, Wayland J., Jr. Pesticides Studied in Man. Baltimore/ London: Williams and Wilkins, 1982..

64 ° None of the submitted acute toxicity studies in rats, mysid shrimp, or fish produced toxicity at or above the LD50 or LC50 (< 50% of tested organisms were affected by exposure) resulting in an over estimation of risk. The available data from these studies do not allow for an approximation of the highest dose or concentration tested to the LD50 or LC50. Therefore, the magnitude of the over estimation of risk on the risk assessment from using these toxicity values is uncertain.

° An LD50 of 1200 mg/ kg day in rats has been reported in secondary sources. 35 However, this study report has not been obtained and evaluated by the Agency. If these data are reliable, then risks characterized in this assessment may have been under estimated.

Scope of Assessment ° Surrogate organisms were used to predict potential risks for species with no data ( i. e., reptiles and amphibians).

° The risk assessment only considers the most sensitive species tested. Terrestrial acute and chronic risks are based on toxicity data for the most sensitive bird, mammal, and plant species tested. Responses to a toxicant can be expected to be variable across species. The position of the tested species relative to the distribution of all species' sensitivities to chlorate is unknown.

° Sodium Chlorate is formulated with other active ingredients and with flame retardants. Potential effects that these other chemicals may have on chlorate's fate or toxicity is not considered in this assessment. The effects of prolonged, year after year use of chlorate in the same field is not known, particularly in semiarid sites that require irrigation ( e. g., Arizona, California), where there is a potential for salt build up over time.

4.8. Potential Risk to Threatened and/ or Endangered Species 4.8.1. Aquatic Organisms There are no geographical limitations on the non agricultural chlorate uses; therefore, the Agency assumes that there is considerable potential for exposure to endangered aquatic species. No chronic toxicity data are available in freshwater or saltwater fish or invertebrates; therefore, chronic risk to these surrogate organisms cannot be precluded. Although levels of concern were not exceeded, potential risk to listed fish, aquatic invertebrates, or aquatic plants cannot be precluded for the following reasons: 36 The 48 hour acute EC50 in daphnids is 0.15 mg/ L ( MRID 940680 09).

65 ° Fish. The data located in the open literature suggest that brown trout could be considerably more sensitive than other fish species that have been tested. Woodiwiss et al. ( 1974) ( summarized in Appendix M) reported a 48 hour LC50 of 7.3 mg/ L in brown trout for chlorate. No other studies in brown trout were located, and sufficient information was not available in the publication to allow for an evaluation of data quality. However, this LC50 would trigger endangered species concerns for all chlorate agricultural and non agricultural uses. Also, it appears that chlorate was tested in the presence of another unspecified flame retardant in this study. Therefore, it is uncertain if the toxicity observed in this study was caused by chlorate, the other unidentified chemical, or a combination of the two. Nonetheless, these data could suggest that there may be considerable variability in species sensitivity to chlorate toxicity. Alternatively, these data could suggest that formulated products are more toxic to fish because all chlorate formulations contain fire retardants.

° Aquatic Invertebrates. Chlorite could form from the reduction of chlorate in the environment. Chlorite is 6000 fold more toxic than chlorate to daphnids. 36 However, the currently available data do not allow for a realistic estimation of the amount of chlorite that may form in the environment. Therefore, submission of data that characterize the potential for chlorate to be reduced to chlorite in natural waters would be of considerable value to this assessment.

° Aquatic Plants. The data located in the open literature suggest that brown algae are considerably more sensitive than green algae to chlorate. A 14 day EC50 of 0.012 mM (. 1 mg/ L) was reported for brown algae ( van Wijk et al., 1997). The EECs for the nonagricultural uses ranged from 3.1 to 39 mg/ L, which exceed the EC50 for brown algae of .1 mg/ L. Therefore, there may be risk to some algal species that exceeds the Agency's level of concern for aquatic plants. As previously discussed, however, additional data are needed to address the considerable uncertainty in the aquatic EECs before risk can be definitively characterized. Also, no studies in the following plant species have been submitted, which are required for herbicides: Lemna gibba ( duckweed), Skeletonema costatum ( a marine diatom), Anabaena flos aquae ( a blue green bacterium), and a freshwater diatom..

Uncertainties in this assessment are equivalent to those presented in Section 4.1.4. Listed species that reside in areas where chlorate may be used were not located because its uses have no geographical restrictions. For example, rights of ways and airport fields are located in virtually every county in the United States. Therefore, the Agency presumes that there is considerable potential for exposure to chlorate by listed species.

4.8.2. Terrestrial Organisms Potential Risk to Endangered Birds 66 No effects were observed in subacute dietary studies in mallard ducks or bobwhite quail at up to 5620 mg/ kg diet. However, acute risk to endangered birds cannot be precluded for chlorate's non agricultural uses because the EECs were significantly higher ( up to 125,000 mg/ kg food item) than the highest concentration tested in subacute dietary toxicity studies.

No reproduction toxicity data are available to allow for an estimation of risk from chronic exposures to chlorate. However, mammalian toxicity data indicate that chlorate is more toxic after repeated exposures. The Agency presumes that chlorate is also more toxic to birds after repeated exposures. Therefore, chronic risk to birds cannot be precluded.

Potential Acute Risk to Endangered Mammals For chlorate's agricultural uses, the ratio of the lowest observed toxic dose to mammals ( 5000 mg/ kg bw) to the upper 90th percentile EEC was as high as 0.26 for small mammals, 0.22 for medium sized mammals, and 0.12 for large mammals ( short grass food items). For other food items, the ratios were # 0.15. If the LD50 is in close proximity to 5000 mg/ kg day, there may be risk at levels of concern to the Agency to endangered small, medium, and large mammals that forage on short grass and risk to small and medium sized endangered mammals that forage on several other food items.

There appears to be considerable potential acute risk to endangered mammals of all sizes that forage in the area where chlorate is used for the non agricultural applications. The EECs were up to 11 times higher than the toxic dose of 5000 mg/ kg bw for the non agricultural uses. Therefore, there appears to be risk to mammals at levels of concern to the Agency.

A number of uncertainties were noted in this assessment, which have previously been described in detail and are summarized in Section 4.7.

Potential Chronic Risk to Endangered Birds and Mammals No chronic toxicity data have been submitted to the Agency or are available in the open literature for any surrogate species used in this assessment; therefore, risk cannot be precluded for any species assessed. The available studies in mammals suggest that chlorate is significantly more toxic after repeated exposures compared with single exposures ( i. e., toxicity increases as study duration increases). A similar relationship between exposure duration and toxicity is presumed in birds as well. Based on the expected persistence of chlorate under some environmental conditions and the demonstrated cumulative toxicity observed in mammals, risk to endangered birds and mammals is presumed to exceed the Agency's level of concern.

The Agency presumes that there is potential for exposure to a large number and large variety of endangered species because these uses would presumably encompass every county in the United States. Therefore, states or counties with endangered species that reside in areas that may be treated with chlorate were not identified as part of this screening level assessment. 67 Potential Risk to Endangered Terrestrial Plants Sufficient toxicity data have not been submitted to the Agency to allow for a characterization of potential risk to terrestrial plants. Based on chlorate's non selective toxicity to plants, the Agency presumes that there is risk to endangered plants at levels of concern to the Agency from the use of chlorate on agricultural and non agricultural areas.

Critical Habitat In the evaluation of pesticide effects on designated critical habitat, consideration is given to the physical and biological features ( constituent elements) of a critical habitat identified by the U. S Fish and Wildlife and National Marine Fisheries Services as essential to the conservation of a listed species and which may require special management considerations or protection. The evaluation of impacts for a screening level pesticide risk assessment focuses on the biological features that are constituent elements and is accomplished using the screening level taxonomic analysis ( risk quotients, RQs) and listed species levels of concern ( LOCs) that are used to evaluate direct and indirect effects to listed organisms.

The screening level risk assessment has identified potential concerns for indirect effects on listed species for those organisms dependant upon species at risk from chlorate exposure. Considerable uncertainty in the potential for direct effects to listed species from chlorate's use identified in this assessment precludes a meaningful analysis of the potential of indirect effects to listed species. In light of the potential for indirect effects, the next step for EPA and the Service( s) is to identify which listed species and critical habitat are potentially implicated. Analytically, the identification of such species and critical habitat can occur in either of two ways. First, the agencies could determine whether the action area overlaps critical habitat or the occupied range of any listed species. If so, EPA would examine whether the pesticide's potential impacts on non endangered species would affect the listed species indirectly or directly affect a constituent element of the critical habitat. Alternatively, the agencies could determine which listed species depend on biological resources, or have constituent elements that fall into, the taxa that may be directly or indirectly impacted by the pesticide. Then EPA would determine whether use of the pesticide overlaps the critical habitat or the occupied range of those listed species. At present, the information reviewed by EPA does not permit use of either analytical approach to make a definitive identification of species that are potentially impacted indirectly or critical habitats that is potentially impacted directly by the use of the pesticide. EPA and the Service( s) are working together to conduct the necessary analysis.

This screening level risk assessment for critical habitat provides a listing of potential biological features that, if they are constituent elements of one or more critical habitats, would be of potential concern. These correspond to the taxa identified above as being of potential concern for indirect effects. This list should serve as an initial step in problem formulation for further assessment of critical habitat impacts outlined above, should additional work be necessary. 68 5. References Fletcher, J. S., J. E. Nellsen, and T. G. Pfleeger. 1994. Literature review and evaluation of the EPA food chain ( Kenaga) nomogram, an instrument for estimating pesticide residues on plants. Env. Toxicol. Chem. 13: 1381 1391.

Heywood R, Sortwell RJ, Kelly PJ, Street AE. Toxicity of sodium chlorate to the dog. Vet Rec. 1972. 90( 15): 416 8.

Hoerger, F. and E. E. Kenaga. 1972. Pesticide residues on plants: correlation of representative data as a basis for estimation of their magnitude in the environment. in: F. Coulston and F. Corte ( editors), Environmental Quality and Safety: Chemistry, Toxicology, and Technology. Vol I. Georg Thieme Publishers, Stuttgart, West Germany, pp. 9 28.

Kurokawa Y, et al. 1985. Lack of promoting effect of potassium chlorate and sodium chlorate in two stage rat renal carcinogenesis. Journal of the American College of Toxicology. 4( 6): 331 337.

McCauley P. T., Robinson M., Daniel F. B., Olson G. R. The effects of subchronic chlorate exposure in Sprague Dawley rats. Drug Chem Toxicol. 1995 18( 2 3): 185 99.

National Toxicology Program ( NTP). 1999. Toxicology and Carcinogenesis Studies of Sodium Chlorate ( CAS No. 7775 09 9) in F344/ N Rats and B6C3F1 Mice ( Drinking Water Studies). TR517. Abstract available on line at http:// ntp. niehs. nih. gov.

U. S. EPA. 1992. Comparative analysis of acute avian risk from granular pesticides. Office of Pesticide Programs. Washington DC. March, 1992.

U. S. EPA. 2000. Wildlife Exposure Factors Handbook. Office of Research and Development, Washington, D. C. EPA/ 600/ R 93/ 187. December 1993.

U. S. EPA. 2004. Overview of the Ecological Risk Assessment Process in the Office of Pesticide Programs, U. S. Environmental Protection Agency. Office of Prevention, Pesticides and Toxic Substances. Office of Pesticide Programs. Washington, D. C. January 23, 2004. Sodium Chlorate Appendices  1 Appendices Environmental Fate and Ecological Risk Assessment for the Reregistration of Sodium Chlorate as an Active Ingredient in Terrestrial Food/ Feed and Non food/ Non feed Uses Sodium Chlorate Appendices  2 Appendix A. Status of Data Requirements for Sodium Chlorate 37 Photoreactions induced by transfer of energy from photosensitizers in natural water and soils may contribute to the transformation of chlorate in the environment ( that is, indirect photolysis contribution). Many chemical reductants present in natural environments may also behave as photoreductants.

Sodium Chlorate Appendices  3 Table A 1. Status of Data Requirements for Sodium Chlorate ( Food/ Feed and Non food/ Non feed Uses. ( Waivers: EFGWB DPBarcode D186156, 03/ 15/ 93; Transmittal Memo to SRRD 05/ 05/ 93)

Data Requirement Status Comment Environmental Fate Data 161 1 Abiotic Hydrolysis Waived The chemistry of chlorate in water is dominated by redox reactions that require the presence of reductants ( inorganic and/ or organic). Because the 161 1 Hydrolysis study is conducted in abiotic media and in types of buffer solutions that are not likely to act as reductants, this study was waived as it was concluded that the study was not going provide any useful or very limited information, unless known environmental reductants were included in the aqueous media. Moreover, the redox chemistry of chlorate in water is extensively documented in the chemical literature.

161 2 Direct Photolysis in Water Waived The 161 2 study is conducted in the absence of chemical photosensitizers. That is, this study is designed to address the role of direct photolysis in aqueous media. A necessary, but not sufficient, condition for direct photolysis in environmentally significant aqueous media is that the chemical must absorb energy ( photon) in the sunlight wavelength range. Chlorate does not absorb energy in this range. Therefore, the 161 2 study was waived because it does not the necessary condition for direct photolysis. 37.

161 3 Photolysis on Soil Waived The 161 2 study is conducted in the absence of chemical photosensitizers. That is, this study is designed to address the role of direct photolysis in aqueous media. A necessary, but not sufficient, condition for direct photolysis in environmentally significant aqueous media is that the chemical must absorb energy ( photon) in the sunlight wavelength range. Chlorate does not absorb energy in this range. Therefore, the 161 2 study was waived because it does not the necessary condition for direct photolysis.. Data Requirement Status Comment 38 Although laboratory studies conducted on soils could, in principle, provide useful information on the persistence of chlorate on soil, there is a major drawback and concern in the case of chlorate because sodium chlorate can react violently with organic material and cause fire. Therefore, performing these studies is not recommended.

The persistence of chlorate in the field remains an issue and an uncertainty. While there are claims that it could persist as long as 5 years, there are no actual data to support this claim. Use of sodium chlorate as a desiccant/ defoliant requires that it is used in conjunction with a fire retardant. Thus, how the fire retardant influences the persistence of chlorate in the field is unknown. Therefore, a field study is recommended according to agree upon protocols. Terrestrial field dissipation studies must be conducted with a typical end use product formulation.

Sodium Chlorate Appendices  4 162 1 Aerobic Soil Metabolism38 Waived This study, if conducted according to existing guidelines, would not likely produce useful information due to sodium chlorate antimicrobial properties that can destroy the microbial populations in soil. If the microbial population is destroyed, the study cannot adequately address the role of microorganisms in the degradation of chlorate. It is more likely that the nature and concentration of redox species control the chemistry of chlorate in soils 162 2 Anaerobic Soil Metabolism Waived This study, if conducted according to existing guidelines, would not likely produce useful information due to sodium chlorate antimicrobial properties that can destroy the microbial populations in soil. If the microbial population is destroyed, the study cannot adequately address the role of microorganisms in the degradation of chlorate. It is more likely that the nature and concentration of redox species control the chemistry of chlorate in soils 162 3 Anaerobic Aquatic Metabolism Waived This study, if conducted according to existing guidelines, would not likely produce useful information due to sodium chlorate antimicrobial properties that can destroy the microbial populations in water sediment systems. If the microbial population is destroyed, the study cannot adequately address the role of microorganisms in the degradation of chlorate. It is more likely that the nature and concentration of redox species control the chemistry of chlorate in water sediment systems.

162 4 Aerobic Aquatic Metabolism Waived This study, if conducted according to existing guidelines, would not likely produce useful information due to sodium chlorate antimicrobial properties that can destroy the microbial populations in water sediment systems. If the microbial population is destroyed, the study cannot adequately address the role of microorganisms in the degradation of chlorate. It is more likely that the nature and concentration of redox species control the chemistry of chlorate in water sediment systems.

163 1 Mobility in Soil Waived Sodium chlorate is fully ionized in water. The chlorate anion is not likely to adsorb onto soils or sediments. Therefore, high mobility was anticipated. Guideline studies would not provide additional information.

163 2/ 3 Volatility from Soil Waived The very low vapor pressure of sodium chlorate ( 9.7 x 10 14 Pa at 25 ° C) does not trigger the volatility from soil data requirement Data Requirement Status Comment Sodium Chlorate Appendices  5 164 1 Terrestrial Field Dissipation Not Waived This data requirement has never been waived. There is major uncertainty on how long sodium chlorate ( formulated) may remain active in the field. Of particular concern is persistence in use sites in semiarid areas. Additional information and/ or actual field studies is needed. The open literature information submitted by the registrant in not sufficient to decrease the uncertainty on field persistence of sodium chlorate products. ( Refer to Footnote 2)

165 4 Bioaccumulation in Fish There is no waiver request for this data requirement. Although this data requirement may be waived, the registrant must formally request the waiver Sodium chlorate is a highly hydrophilic chemical. Its extremely low Log n octanol/ water partition coefficient of  7 does not trigger this data requirement.

Table A 2. Status of Ecotoxicity Data Requirements Data Requirement Does EPA Have Data To Complete a Risk Assessment? ( Yes, No) Bibliographic Citation Are additional data needed? Comment 71 1( a, b) Acute Avian Oral, Quail/ Duck Yes 421494 01 No 71 2( a) Acute Avian Diet, Quail Yes 418199 08 No 71 2( b) Acute Avian Diet, Duck Yes 418199 07 No 71 3 Wild Mammal Toxicity No N/ A No 71 4( a) Avian Reproduction Quail No N/ A Yes 71 4( b) Avian Reproduction Duck No N/ A Yes 71 5( a) Simulated or Actual Terrestrial Field Study No N/ A No 72 1( a, b) Acute Fish Toxicity Rainbow trout and Bluegill Yes 418872 02 418872 03 No 72 2( a, b) Acute Freshwater Invertebrate Toxicity Yes 438748 01; 418872 04 No Table A 2. Status of Ecotoxicity Data Requirements Data Requirement Does EPA Have Data To Complete a Risk Assessment? ( Yes, No) Bibliographic Citation Are additional data needed? Comment Sodium Chlorate Appendices  6 72 3( a) Acute Estuarine/ Marine Toxicity to Fish Yes 418872 07 No 72 3( b) Acute Estu/ Marine Invertebrate Yes 418872 05 418872 06 No 72 4( a) Early Life Stage Fish No N/ A Yes 72 4( b) Life Cycle Aquatic Invertebrate No N/ A Yes 72 5 Life Cycle Fish No N/ A No 72 6 Aquatic Org. Accumulation No N/ A No 72 7( a) Simulated Aquatic Field Study No N/ A No 72 7( b) Actual Aquatic Field Study No N/ A No 122 1( a) Seed Germ./ Seedling Emerg. Tier I Yes 463008 02 No 122 1( b) Vegetative Vigor, Tier I Yes 463008 01 No 122 2 Aquatic Plant Growth, Tier I No N/ A No 123 1( a) Seed Germ./ Seedling Emerg., Tier II No N/ A Yes 123 1( b) Vegetative Vigor , Tier II No N/ A Yes 123 2 Aquatic Plant Growth , Tier II Yes 418872 01 Yes Only data on green algae were submitted. Studies in four other aquatic plant species are required for herbicides.

124 1 Terrestrial Field Study No N/ A No 124 2 Aquatic Field Study No N/ A No 141 1 Honey Bee Acute Contact Yes N/ A Yes Study was submitted; however, a new copy of the study needs to be submitted to the Agency for evaluation because a readable copy no longer exists. Table A 2. Status of Ecotoxicity Data Requirements Data Requirement Does EPA Have Data To Complete a Risk Assessment? ( Yes, No) Bibliographic Citation Are additional data needed? Comment Sodium Chlorate Appendices  7 141 2 Honey Bee Residue on Foliage No N/ A No 141 5 Field Test for Pollinators No N/ A No OECD, Section 2 # 207 Earthworm Acute Toxicity Test No N/ A No Sodium Chlorate Appendices  8 Appendix B 1. The Chemistry of Chlorate 39 The convention of using Roman numerals to express the oxidation state of an element that can exist in more than one oxidation states has the advantage of identifying the oxidation state of oxidants and reductants regardless of their chemical nature. For example, aqua ions, complexes, amorphous or crystalline mineral phase.

40 The most important oxides of chlorine are " Chlorine Monoxide, Cl2O" and " Chlorine Dioxide, ClO2". Both are gases at room temperature. " Cl2O" is the anhydride of hypochlorous acid. Chlorine dioxide is explosive as a liquid or concentrated gas and, for this reason it is generated in situ when it is used as antimicrobial or wood pulp bleaching agents. It is usually prepared by reducing sodium chlorate. The oxidation state of chlorine in chlorine dioxide, ClO2, is IV (+ 4).

Sodium Chlorate Appendices  9 A. Oxidation States of Chlorine Chlorine ( oxidation state 0) can form chemical species that include chlorine in different oxidation states. In aqueous media, the predominant species, their concentration, and reaction kinetics depend on pH, temperature, and the presence and nature of chemical species that can undergo redox reactions. That is, chlorine speciation ( i. e., reduced and oxidized forms) in aqueous media is driven by thermodynamics ( equilibria) as well as by kinetics. Table B 1 shows the oxidation states of chlorine and the names given to these species39.

Table B 1. Chlorine and Chlorine Species in Aqueous Media40.

Oxidation State Name of the Acid Form Chemical Representatiof the Acid Form Chemical Name of the Anion/ Salts Chemical Representation of the Anion 0 Not Applicable Elemental chlorine, Cl2 ( gas) Not Applicable Not Applicable  I ( 1) Hydrochloric acid HCl Chloride/ Chlorides Cl

I (+ 1) Hypochlorous acida HOCl Hypochloriteb/ Hypochlorites " ClO"

III (+ 3) Chlorous acida HOClO Chloriteb/ Chlorites ClO2

V (+ 5) Chloric Acida HOClO2 Chlorateb/ Chlorates ClO3

VII (+ 7) Perchloric Acid HOClO3 Perchlorateb/ Perchlorates ClO4

a Stable only in aqueous solutions; b Oxyanion. The oxidation state of chlorine in chlorine dioxide ( ClO2) is IV Synthesis of Sodium Chlorate Sodium chlorate is not a naturally occurring material. It is prepared by electrolysis of sodium chloride ( NaCl brine) and it is an energy intensive process. It requires 6 Faradays to produce one 41 " H+" represents the hydrated proton, " H3O+".

42 The standard hydrogen electrode ( SHE) is also represented by the symbol " NHE" ( normal hydrogen electrode)

43 Chlorate, an oxidizing agent, accepts electrons and generates Cl species at oxidation states lower than V( i. e, it gets reduced). In all redox reactions there is an electron donor ( reducing agent; reductant) and an electron acceptor ( oxidizing agent;

oxidizer; oxidant). Thus, the electron donor species gets oxidized while the electron acceptor gets reduced. That is, redox processes involves electron transfer.

Sodium Chlorate Appendices  10 mole of chlorate and the reaction is endothermic ( in practice, it takes 5 kW" hr to generate 1 kg of chlorate). The reaction proceeds via intermediates in a higher oxidation state than chloride, such as chlorine ( oxidation state  I) and hypochlorite/ hypochlorous acid ( oxidation state I). The efficiency of chlorate formation by an electrolytic process is controlled by temperature and pH. The efficiency of chlorate formation may also decrease by non electrolytic processes, such as by the presence of some ionic transition metal species that can act as reductants that can reduce chlorate to chloro species in lower oxidation states. Transition metals are metals that can exist in two or more oxidation states, such as Fe and Mn. Chloric acid, the corresponding acid form of chlorate, exists only in solution and it is a strong acid.

The electrochemical reactions involved in the preparation of sodium chlorate are: Anode: Oxidation of Chloride to chlorine ( Cl 6 ½ Cl2 + e); Cathode: H2O + e 6 ½ H2 + OHMixing Cl2 + 2 OH 6 Cl + O Cl + H2O ( disproportionation, i. e., reaction producing chemical species at a lower and a higher oxidation state) Further disproportionation: 3O Cl 6 ClO3  + Cl Further anodic oxidation: O Cl + 2 H2O 6 ClO3  + 2 H2 Source: Kirk Othmer Encyclopedia of Chemical Technology Cotton, F. A. and Wilkinson, G. " Advanced Inorganic Chemistry", 5th Edition, Wiley Interscience, 1988. Greenwood and Earnshaw, " Chemistry of the Elements", Pergamon B. Oxidation Reduction ( Redox) Chemistry of Chlorate Chlorate is a strong oxidizing agent ( oxidant; oxidizer). As such, chlorate can oxidize chemical species considered to be in their " reduced" state. That is, any oxidation requires a reductant. As a result, the oxidizer gets reduced and the reductant gets oxidized. Therefore, an oxidizer is an electron acceptor and the reductant is the electron donor.

The standard electrode potential ( Eo, defined in terms of standard state conditions of reactants and products; Standard state conditions are 25 ° C, 298 ° K , 1 atm, and activity = 1.0 for all reactants and products) represents a redox reaction whose left hand electrode is a hydrogen electrode. By convention, the hydrogen electrode half reaction is represented as H+ ( aqueous 41at activity a= 1) + e at equilibrium with ½ H 2 ( g, 1 atm) and taken as 0.0 Volt42. The redox couples presented here follow the IUPAC convention43 ( Eo is also represented as Eo h ). Thus, the electrode potential of a 44 The activity of ions in water is the effective concentration and it is thermodynamically more precise than the molar concentration. The activity of any ion ai, is related to the concentration ci by the activity coefficient ( i, ( ai, = ( i c i ). Discussion of methods for calculating ( i are beyond the scope of this Appendix.

45 The Nernst equation correlates the emf with the Gibbs Free Energy, ª G. The ª G. is the negative value of the maximum electric work, W ( ª G =  W= q ª E ), where q is related to the amount of charge transferred at the completion of the reaction and q is related to the number of electrons, n, involved in the reaction. Thus, q= nF, where F is the Faraday Constant,

Sodium Chlorate Appendices  11 cell ( E) is taken as the potential of the right hand terminal with respect to that of the left hand terminal. If the cell is written down in the opposite direction, the sign of E must be reversed.

The standard electrode potentials for reactions involving chlorate are presented in Table B 2 Equations 1 through 7 represent potentials at which chlorate is reduced ( i. e., accepts electrons) and which are the reduced products at different electrode potentials. Equations 8 and 9 represent the reduction of perchlorate to chlorate. Note that the nature and redox potential for the reduced products of chlorate are pH and well as temperature dependent.

Table B 2. Standard Electrode Potentials for Redox Reactions of Chlorate ( Half cell Potentials)

Redox Couplea E ° / E ° b, volts ( V) d E ° ( E ° b)/ dT, mVK  1 ( K= ° Kelvin)

ClO3  + 6 3H2O + 6e 6 Cl + 6 OH ( 1) E ° b, = 0.622 dE ° b)/ dT =  1.333 2 ClO3  + 12 H+ + 10e 6 Cl2 ( g) + 6H2O ( 2) E ° = 1.468 dE ° / dT =  0.347 ClO3  + 2H2O + 4e 6 ClO + 4 OH ( 3) E ° b,= 0.488 dE ° b/ dT =  1.467 ClO3  + 3H+ + 3e 6 HClO2 + H2O ( 4) E ° = 1.181 dE ° / dT =  0.180 ClO3  + H2O + 2e 1 6 ClO2  + 2OH ( 5) E ° b, = 0.295 dE ° b/ dT=  1.467 ClO3  + 2 H+ + e 6 ClO2 ( g) + H2O ( 6) E ° = 1.175 dE ° / dT = 1.026 ClO3  + H2O + e 1 6 ClO2 ( g) + 2OH ( 7) E ° b, =  0.481 dE ° b/ dT =  0.646 ClO4  + 2 H++ 2e 1 6 ClO3  + H2O ( 8) E ° = 1.201 dE ° / dT =  0.416 ClO4  + H2O + 2e 1 6 ClO3  + 2OH ( 9) E ° b, = 0.374 dE ° b/ dT =  1.252 a Defined as any pair of the same element in different oxidation states. Source: Standard Potentials in Aqueous Solutions. Edited by Bard, A. J., Parsons, R., and Jordan, J. IUPAC, Commission on Electrochemistry and Electroanalytical Chemistry, Published by Marcel Dekker, Inc., New York, 1985. Most of these redox couples were experimentally determined Redox Reactions General The tendency for a redox reaction to proceed is determined by the electromotive potential ( emf). That is, the emf is the driving force of the reaction. Because redox reactions involve chemical species that get reduced and chemical species that get oxidized, any redox reaction can be written as the sum of two half reactions. Under real conditions, the activity of reactants and products deviate from the unit activity44 of standard conditions. Therefore, Eo needs to be corrected. This is done using the Nernst relationship45. For any redox reaction at 25 ° C ( 298 ° K) which is the charge of each mole of electrons ( F= 96,485 Coulombs/ mole). Therefore, ª G =  nF ª E and ª G ° =  nF ª E ° for standard conditions and " 0.059" applies only to the standard temperature of 298 ° K.

46 Likewise, all reduction reactions result in oxidation of the reductant.

Sodium Chlorate Appendices  12 between a moles of reactant A and b moles of B to produce c moles of C and d moles of D ( i. e, aA + bB = cC + dD),

E = E °  ( 0.059/ n) ln [ C] c [ D] d/ [ A] a [ B] b = E °  ( 0.059/ n) ln K,

where K is the Equilibrium Constant If [ D]= [ H+] and [ B]= [ H 2 ] and since [ H+]= [ H 2 ]= 1, the equation reduces to E = E °  ( 0.059/ n) ln [ C] c/[ A] a where [ C]= [ R]= concentration of the reduced form and [ A]= the concentration of the oxidized form, both corrected for activity ((),

E = E °  ( 0.059/ n) ln [ R]( R /[ O]( O Since all oxidation reactions result in reduction of the oxidizer46, the overall redox has also to consider the half cell of the reductant. The sum of the two half cells ( i. e., the standard reduction and oxidation half cells) give the net potential ( E net ). It is E net what determines the thermodynamic feasibility of specific redox reactions,

ÎG=  nF ( E net )=  nF ( E red + E ox ), where n is the number of electrons exchanged in the net reaction Reactions with a negative ÎG ( ÎG < 0; or E net > 0) can occur spontaneously.

Predominance of Chemical Species in the Environment The effects of pH on the form in which an element in a given oxidation state exists in natural waters can be summarized with chemical species predominance diagrams. Knowledge of the environmental pH is not sufficient for predicting the form ( i. e., oxidation state; chemical species; phase) in which an element, the chlorine system in this case, will exist in natural waters. When a chemical element can exist in two or more oxidation states, it must also be taken into consideration whether the aqueous environment is well aerated ( oxidizing) or polluted with organic wastes ( reducing). Therefore, it becomes necessary to add the redox variable to expand the predominance diagram to include the reduction potential of the environment as well as the pH. 47 Pourbaix, M. Atlas d'équilibres èlectrochimiques à 25 ° C. Gauthier Villars, Paris, 1963. Pourbaix diagrams are routinely used in corrosion and minerals processing work.

48 For example, the conversion of Diamond carbon to Graphite carbon is favored thermodynamically, but has a very slow kinetics.

49 See " Reactions with Organic Matter"

50 For example, surface reactions with minerals that are semiconductors ( galena). For interfacial reactions such as these, the particle size distribution of the mineral phase is an important controlling factor Sodium Chlorate Appendices  13 This type of predominance diagram is known as a Pourbaix diagram or E pH diagram47, which can also be expressed in a pE scale. The pE ( pE=  log E) scale is analogous to that of pH. It represents the concentration of the standard reducing agent and is obtained from the reduction potential by dividing by 0.059. Low E ( pE) values represent a reducing environment, while high E ( pE) values represent an oxidizing environment.

Thermodynamics versus Kinetics The Standard Redox Potentials, as well as the predominance diagrams are based on equilibria relationships ( i. e., thermodynamics). In the environment, particularly in heterogeneous media such as soils, suspended particulates in natural water, redox species are not generally in equilibrium and the concentrations of ionic species deviate from unit activity. In addition, redox potentials do not tell how fast the redox reactions take place ( i. e., the kinetics of the redox reactions). Thus, a redox reaction that may be thermodynamically favored might be kinetically very slow48. In summary, the redox reactions based on thermodynamic equilibria indicates that the reaction can occur, but it does not mean that they will occur and how fast.

Natural Redox Environments A major factor controlling the redox environment is the nature and concentration of redox species. Major chemical species associated with reducing environments are transition metals in low oxidation states ( e. g., Fe( II), Mn( II)), N species in low oxidation states ( NO 2  ; NH 4 +); S( II) ( e. g HS, S 2; polysulfido species), and organic matter49. Major chemical species associated with oxidizing environments are dissolved dioxygen ( O 2; moleular oxygen), transition metals in high oxidation states such as Fe( III); Mn( III, IV), sulfate, and nitrate. In addition to " straight" redox reactions, many of the redox species in natural waters may also act as photosensitizers. Other factors controlling the redox chemistry of a natural environment are the population of aerobic and anaerobic microorganisms. In addition, many of the transition metals may be present as mineral phases that could be involved in surface catalyzed reactions50. The half cell reactions for important environmental reductants are presented below for selected species Nitrogen System Table B 3. Half cell reactions for important environmental reductants Sodium Chlorate Appendices  14 Redox Couple, E ° / E ° b, volts ( V)

NO3  + 2H+ + 2e 1 6 NO2  + H2O E ° = 0.835 = 0.965 ( pH 4 7)

NO3 + + H2O + 2e 1 6 NO2  + 2OH E ° b = 0.01 NO3 + + H2O + 2e 1 6 NO2  + 2OH E ° b = 0.01 NO3  + 10H+ + 6e 1 6 NH4 + + 3 H2O E ° = 0.87 NO2  + 8H+ + 8e 1 6 NH4 + + 2 H2O E ° = 0.897 NO2  + 7H+ + 8e 1 6 NH3( aq) + 2 H2O E ° = 0.806 NO2 + 6H+ + 8e 1 6 NH3 ( g) E ° = 0.789 The Iron System In aqueous solutions, Fe( II) and Fe( III) are the common oxidation states, yet the chemistry of Fe( II)/ Fe( III) is extremely complex. In addition to pH pE dependent reactions, Fe( II)/ Fe( III) can generate a wide range of chemical species than can occur as discreet aqua ions, colloidal species, and distinct mineral phases of varied composition, all of which can undergo specific redox reactions. In acid solutions ( pH < 2 and in the absence of complexing anions, the predominant species is the hexaaqua Fe( II) complex , [ Fe( H 2 O) 6 ] 2+, which hydrolyzes to first form FeOH+ . With increasing pH, oxidation of Fe( II) to Fe( III) species takes place via a series of hydroxo complexes, precipitated hydroxides, and mineral oxides/ hydroxyoxides ( e. g., hematite/ magnetite; goethite). While oxidation involving dioxygen ( molecular oxygen) occurs, other oxidants can also oxidize Fe( II). Given the complexity of natural systems in terms of types and concentration of natural oxidants ( e. g., nitrate/ nitrite), competitive redox reactions are expected to occur in the environment.

In acid solution ( pH 0),

Fe( III) + e 6 Fe ( II), E ° = + 0.771 V In alkaline solution,

Fe ( III) ( as FeO 4 2) + e 6 Fe ( III) ( as FeO 2 ) E ° = + 0.55 V The Sulfur System Like with chlorine, sulfur can exist in more than one oxidation states. The oxidation state of sulfur in the sulfide system is  II. The inorganic sulfide species that might be present in anoxic natural waters are: H 2 S ( hydrogen sulfide, gas; hydrogen sulfide aqueous), HS, and S 2. The predominance of each of these species depends on pH and is governed by the dissociation 51 At 18 ° C in water, K1 = 9.1 x 10 8, H2S ( aq) 6 H+ + HSK2 = 1.2 x 10 12, HS 6 H+ + S 2

Sodium Chlorate Appendices  15 constants, K 1 and K 2 , of hydrogen sulfide in water51. In addition, polysulfides S n 2 may be present in some aqueous environment. Sulfide species are often found as complexes with some metal ions. Higher oxidation states of sulfur ( e. g., II, IV, VI) are more predominant in oxic systems, of which sulfate ( SO 4 2, S( VI)) is an example. Like for chlorine, the higher oxidation states of sulfur are oxyanions, but the sulfur oxyanions are more numerous and complex than those of chlorine.

Organic Material The reactions below are examples of how different functional groups undergo redox reactions. Many of these functional groups are present in natural organic matter, for example, hydroxyl groups in humic acids, but other simpler organic species such as oxalate may also be present in natural water.

Table B 4. Redox Reactions with Organic Functional Groups Type of Oxidation Reactions Type of Reduction Reactions Alkanes to alcohols ( R H 6 R OH) Reductive dehalogenation ( R X 6 R H)

Alcohols to aldehydes ( R OH 6 RCHO) Vicinal dehalogenation ( X R R X6 R= R)

Aldehydes to acids ( RCHO 6 RCOOH) Nitro reduction ( R NO2 6 R NH2)

Dehydrogenation ( CH CH 6  C= C) Azo reduction ( Ar N= N Ar 6 2Ar NH2)

Oxidative coupling ( 2R OH6 R O R) Disulfide to thiol ( R S S R6 2R SH)

Hydroquinones to quinones ( HO Phenyl OH6 O= Phenyl= O) Deoxygenation of sulfoxo and sulfoxides ( R SO2 R6R SO R6R S R)

Thiooxidation ( R S R6 R SO R; R SO2 R) Nitrosamine Reduction ( R2N N= O6R2N H + HNO)

Fomation of disulfide linkages ( 2R SH 6 R S S R) Quinones to hydroquinones ( O= Phenyl= O6HO Phenyl OH)

 Dealkylation ( R Y R' 6 R YH + R'H)

Redox Conditions in Soils and Water Controlling the Behavior of Chlorate in the Environment Soils If a pH= 9 is taken as the upper bound of a soil solution, the lower extreme value of pE is  9 ( assuming that H 2 , gas, is at the state of 1 atm and 298 ° K). The theoretical range of pE in soil is 9 < pE < + 16.6. However, a pE range of  6 < pE < 12 is more realistic. A pE of  6 corresponds to the " strongly reduced" boundary and + 12 to the " strongly oxidized" boundary. Like for 52 Factors contributing to the acidity of natural waters in the Middle Atlantic/ Northeast of the USA are acid mine drainaged and/ or deposition of acid rain.

Sodium Chlorate Appendices  16 natural waters, the redox environment/ behavior of the soil depends on the nature, concentration and E h  pH dependence of redox species.

Table B 5. pE and Redox Conditions of Soils Medium pE Soil, suboxic + 2< p E< + 7 Soil, oxic + 7 < p E Soil, anoxic p E < + 2 Water Chlorate is more stable under alkaline than acidic conditions. Thus, based on pH dependence alone, it would be less persistent in acidic than alkaline natural waters. In general, it could be said that it would be less persistent in areas of the country where the pH of natural water is < 7. Acidic natural waters are predominantly found east of the Mississippi River, with acidity increasing with latitude52. Likewise, chlorate would be more persistent in the more alkaline water bodies West of the Mississippi River.

However, as previously indicated, pH is not the only controlling factor in the persistence of chlorate because pH dependent redox reactions must be taken into consideration. Thus, the redox conditions of the water body also controls the persistence of chlorate. In reducing environments ( i. e., low E; pE), chlorate would be less persistent than in oxidizing environments ( high E; pE).

In general, the variability in persistence of chlorate in natural waters has a spatial and temporal component. Spatial variability would be related to the geographical location of the use site ( pH and nature of redox species) and temporal ( seasonal variations and concentration of redox species). Therefore, where, when, and how the chemical is used are contributing factors to the persistent of chlorate in water. Sodium Chlorate Appendices  17 Table B 6. Spatial and temporal variability related to the geographical location use site pH pE pH of Natural Water Systems Seasonal Variability of pE < 7 Low East of the Mississippi River, particularly in the Mid Atlantic and Northeastern regions Summer; Early Fall ( High concentration of organic species)

< 7 High East of the Mississippi River, particularly in the Mid Atlantic and Northeastern regions Winter; Early spring > 7 Low West of the Mississippi River Summer; Early Fall ( High concentration of organic species)

> 7 High West of the Mississippi River Winter; Early spring A spatial and temporal variability of chlorate is also expected in soils. Factors like pH, organic matter content and type, moisture content, microbial population. Sodium Chlorate Appendices  18 Appendix B 2. Discussion on Chlorate Redox Chemistry as it Relates to Exposure to Aquatic Organisms in the Environment Sodium Chlorate Appendices  19 MEMORANDUM: January 27, 2005 SUBJECT: pE/ pH Predominance and 3D activity ratio diagrams for aqueous chlorine species at thermodynamic equilibrium TO: Daniel Rieder, Chief Environmental Risk Branch 3 Environmental Fate and Effects Division/ Office of Pesticide Programs/ USEPA Silvia Termes, Ph. D., Chemist Environmental Risk Branch 3 Environmental Fate and Effects Division/ Office of Pesticide Programs/ USEPA FROM: Henry Nelson, Ph. D., Chemist Exposure Assessment Division Office of Science and Coordination Policy ( OSCP/ OPPTS/ USEPA)

This memo provides pE/ pH predominance and 3D activity fraction diagrams for aqueous chlorine species at thermodynamic equilibrium. Chlorine species distributions in actual natural waters at any given time may deviate substantially from such equilibrium computations since natural waters are not at equilibrium and very rarely even approach equilibrium.

Aqueous chlorine reactions considered along with associated equilibrium expressions and equations used to generate activity ratios and redox pair boundary lines in the formation of predominance diagrams are listed in Attachment A. A thermodynamic spreadsheet used to compute ) G0 rxn and log K equil = ) G0 rxn /( 2.3RT) ( where K eq = thermodynamic activity based equilibrium constant) for the various reactions listed in Attachment A is provided in Attachment B. The format of the thermodynamic spreadsheet provided in Attachment B was developed by Dr. Jim Hetrick. Free energies of formation are in kJ/ mol. This memo is an extension of Dr. Hetrick's computations of chlorine species mole fractions.

Mixed equilibrium constants are referred to as " mixed" because their expressions contain chemical species concentrations but H+ and e activities. Mixed equilibrium constants are often used in equilibrium computations ( Jensen 2004) because while the use of concepts such as mass balance generally requires the use of chemical species concentrations rather than activities, pH and redox electrodes respond to H+ and e activities rather than concentrations where ( ) ( ) pH H pE e =   =   +   log log Thermodynamic activity based equilibrium constants are equal to the product of the quotient of activity coefficients for the chemical species times mixed equilibrium constants. For example consider the following reaction:

( eq. 1) Cl H O ClO H e     +   +   + + 2 2 2 Sodium Chlorate Appendices  20 The thermodynamic activity based equilibrium constant for the reaction is related to the mixed equilibrium constant for the reaction by:

( eq. 2) ( )( )( ) ( ) [ ]( ) ( ) [ ] K ClO H e Cl ClO H e Cl K eq ClO Cl ClO Cl mixed = = =   +

    +

  2 2 2 2         where ( eq. 3) [ ]( ) ( ) [ ] K ClO H e Cl mixed =   +

  2 2 and ( = activity coefficients ( ) = designates activities [ ] = designates concentrations The construction of predominance diagrams relies on considerations of mass balance and assumptions of equivalence of molar concentrations along redox couple boundaries which in turn requires the use of chemical species concentrations instead of activities. At the same time it is convenient to maintain the H+ and e levels as activities as previously discussed. The most accurate way of generating predominance diagrams is to convert thermodynamic activity based equilibrium constants ( which are computed from standard free energies of formation) to mixed thermodynamic activity based and concentration based equilibrium constants by dividing the activity based equilibrium constants by quotients of the activity coefficients of the chemical species. For example, from eq. 2 above, it can be seen that the K mix for the eq. 1 reaction is given by:

( eq. 4)

( ) K K K mix eq ClO Cl Cl ClO eq = =

          The mixed equilibrium constants are then set equal to mixed quotients that use concentrations for the chemical species but activities for H+ and e. However, predominance diagrams are semiqualitative ( they predict general predominance areas rather than the actual activities or concentrations of various species). Therefore, equations for generating predominance diagrams are often approximations based on the assumption that the expressions for the mixed equilibrium constants are approximately equal to the thermodynamic equilibrium constants. That assumption is used in the generation of the predominance diagrams in this document. The accuracy of that assumption depends upon how close the quotient of activity coefficients is to one. The chlorine species considered here are either neutral or univalent. Most freshwaters have ionic strengths between 0.001 M and 0.01 M ( Jensen 2004). In freshwaters with ionic strengths between 0.001 and 0.01 M, the activity coefficients of neutral species will be close to one. Based on the use of Sodium Chlorate Appendices  21 the Debye Huckel equation for ionic strengths up to 0.005 M and the extended Debye Huckel equation for ionic strengths between 0.005 M and 0.01 M, the activity coefficients of univalent ions range from approximately 0.9 in waters with ionic strength = 0.01 M to close to one in waters with ionic strengths = 0.001 M ( Langmuir 2002). Therefore, the assumption that the expressions for the mixed equilibrium constants are approximately equal to the thermodynamic equilibrium constants are generally adequate for generating semi qualitative pE/ pH predominance diagrams for freshwaters.

In addition to generating predominance diagrams, activity fractions are generated for various chlorine species as a function of pE and pH. This is done by rearranging the equations in Attachment A to give the activity of each chlorine species considered in terms of the activity of a common chlorine species ( Cl is used here but any of the species could have served as the common species). The ratio of the activity of each chlorine species ( in terms of the Cl activity) to the total activity of chlorine species ( in terms of the Cl activity) is then computed. By performing computations for pHs > 4, Cl 2( aq) does not have to be included in the activity ratio computations because the construction of predominance diagrams indicates that Cl 2( aq) will be predominant ( if at all  see discussion of Case 1 versus Case 2 below) at pEs above the stability of water and at pHs < 2 well below the lower pH limit of natural waters ( pH 5) and well below the lower pH limit of our calculations ( pH 4). Not including Cl 2( aq) in the activity fraction computations allows for complete cancellation of the Cl activity from the numerator and denominator of each ratio. The activity fractions are in terms of the thermodynamic activity based equilibrium constants ( computed in the Attachment B thermodynamic spreadsheet), pH, and pE.

Mole fractions could not be computed because they would be in terms of the mixed equilibrium constants which were not computed ( only thermodynamic activity based equilibrium constants were computed). However, for low ionic strength waters, the activity fractions provide an approximate estimate of mole fractions.

Two cases are considered. Case 1 considers only the lower oxidation state chlorine species ( Cl, Cl 2( aq), ClO, and HClO). Case 2 considers higher oxidation state chlorine species ( ClO 2 , ClO 2( aq), ClO 3 , and ClO 4 ) as well as the lower oxidation state chlorine species ( Cl, Cl 2( aq), ClO, and HClO). Case 1 is included in this memo only because it is the case considered by several aquatic chemistry texts. However, Case 1 is misleading because it results in predominance and activity fraction diagrams that shows predominance areas and areas of high activity fractions for ClO, and HClO that are not reflected in the much more accurate Case 2 predominance and activity fraction diagrams that consider higher oxidation state chlorine species as well as lower oxidation state chlorine species.

The more accurate Case 2 shows predominance areas and high activity fractions for only ClO 4

and Cl. Although Case 1 and Case 2 differ substantially for ClO, HClO, and ClO4 , they both show Cl as the only predominant species at thermodynamic equilibrium within the pE and pH ranges of natural waters.

Case 1: Case 1 considers only the lower oxidation state chlorine species ( Cl, Cl 2( aq), ClO, and HClO). A pE/ pH predominance diagram considering only those lower oxidation state chlorine Sodium Chlorate Appendices  22 species is provided in several aquatic chemistry texts ( e. g., Stumm and Morgan 1995; Pankow 1991; Snoeyink 1980; Jensen 2004). That diagram is recreated independently here ( Chart 1a) using a more systematic approach involving the separate determination of predominance areas for each chlorine species ( Attachment C, Charts 1b through 1e) and then combining the separate diagrams into one predominance diagram ( Chart 1a). The general use of such a systematic approach for generating pE/ pH predominance diagrams was recommended by Benjamin ( 2002).

Because of the 2 to 1 chlorine stoichiometry of Cl 2( aq) compared to other aqueous chlorine species considered in Case 1, the development of a predominance area for Cl 2( aq) in an overall pE/ pH predominance diagram for aqueous chlorine species requires consideration of chlorine mass balance and an assumption concerning total chlorine ( Stumm and Morgan 1995; Pankow 1991; Snoeyink 1980; Jensen 2004).

Chart 1a was generated using the same assumption ( total chlorine concentration = 0.04 M) as used in those references. A total chlorine concentration of 0.04 M is somewhat higher than typical chlorine background concentrations in freshwater. However, the use of a higher assumed total chlorine results in a slightly larger Cl 2( aq) predominance area in Chart 1a that is easier to illustrate than when using a smaller assumed total chlorine. It is somewhat academic in that the the Cl 2( aq) predominance area in Chart 1a is still small and still occurs at high pEs/ low pH well outside the pE & pH ranges of natural waters.

In addition to a small predominance area for Cl 2( aq) at high pEs and very low pHs, Chart 1a for Case 1 predicts predominance areas for HClO at high pEs ( outside those of natural waters) and acidic pHs, for ClO at high pEs ( also outside those of natural waters) and alkaline pHs, and for Cl at lower pEs including those within the range of pE and pH of natural waters ( region ABCD in Chart 1a). The Case 1 predominance diagram Chart 1a is misleading because it shows predominance areas for ClO, and HClO that are not reflected in the Case 2 predominance diagram that considers higher oxidation state chlorine species as well as lower oxidation state chlorine species.

Case 1 activity fraction diagrams were generated for Cl, ClO, and HClO for pHs between 4 and 10 and for pEs between  10 and 30. The Case 1 Cl activity fraction was generated from equation 5 below. The Case 1 ClO and HClO activity fractions were generated from equations 2f and 3f, respectively in Attachment A. Sodium Chlorate Appendices  23 ( ) ( ) ( ) ( ) ( )

( ) ( ) ( ) ( ) ( ) ( )( ) ( ) ( ) ( )( )

( )( ) ( )( ) ( )( ) ( )( ) f Cl Cl ClO HClO Cl Cl K Cl H e K Cl H e K H e K H e Cl Case eq eq eq eq K pH pE K pH pE pH pE pH pE eq eq   = + + =

+ + = + + =

+ + = + +

+

+   +   +

    ( )

log log . . 1 2 2 2 3 2 2 2 2 3 2 2 2 58 1 2 2 50 6 2 1 1 1 1 10 10 10 10 10 10 1 1 10 10 10 10 10 10 2 3 ( eq. 5)

As expected, the Case 1 activity fraction diagrams for Cl, ClO, and HClO ( Charts 2a, 2b, and 2c, respectively) are consistent with the Case 1 predominance diagram 1a with high activity fractions approaching 1 in areas of pE and pH where the Case 1 predominance diagram 1a indicates they are the predominant species. However, like Case 1 predominance diagram Chart 1a, Case 1 activity fraction diagrams Charts 2b and 2c are misleading because they show areas of high activity fractions for ClO, and HClO that are not reflected in the Case 2 activity fraction diagrams that consider higher oxidation state chlorine species as well as lower oxidation state chlorine species.

Case 2: Case 2 is much more accurate than Case 1 because it considers higher oxidation state chlorine species ( ClO 2 , ClO 2( aq), ClO 3 , and ClO 4 ) as well as the lower oxidation state chlorine species ( Cl, Cl 2( aq), ClO, and HClO). A pE/ pH predominance diagram considering the higher oxidation state chlorine species as well as the lower oxidation state chlorine species is provided in Chart 3a. A systematic approach was used involving the separate determination of predominance areas for each chlorine species ( Attachment D, Charts 3b through 3i) and then combining the separate diagrams into one predominance diagram ( Chart 3a). As previously indicated, the general use of such a systematic approach for generating pE/ pH predominance diagrams was recommended by Benjamin ( 2002).

Chart 3a for Case 2 predicts predominance areas for only ClO 4  at high pEs ( above those of natural waters), and for Cl at lower pEs including those within the range of pE and pH of natural waters ( region ABCD in Chart 3a).

Case 2 activity fraction diagrams were generated for Cl, ClO, HClO, ClO 2 , ClO 2( aq), ClO 3 , and ClO 4  for pHs between 4 and 10 and for pEs between  10 and 30. The Case 2 Cl activity fraction was generated from equation 6 below. The Case 2 ClO, HClO, ClO 2 , ClO 2( aq), ClO 3 , and ClO 4

activity ratios were generated from equations 2g, 3g, 4f, 5f, 6f, and 7f, respectively, in Attachment A. Sodium Chlorate Appendices  24 ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )

( ) ( ) ( ) ( ) ( ) ( )( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )( ) ( ) ( )( )

( ) ( ) ( )( ) ( ) ( ) ( ) f Cl Cl ClO HClO ClO ClO ClO ClO Cl Cl K Cl H e K Cl H e K Cl H e K Cl H e K Cl H e K Cl H e K H e K H e K H e K H Cl Case aq eq eq eq eq eq eq eq eq eq eq   = + + + + + + =

+ + + + + + =

+ + + +

+

+

+

+

+

+

+   +   +   + ( )

( ) 2 2 2 3 4 2 2 2 3 2 4 4 4 5 4 5 6 6 6 7 8 8 2 2 2 3 2 4 4 4 5 4 1 1 ( ) ( ) ( ) ( )( )

( )( ) ( )( ) ( )( ) ( )( ) ( )( ) ( )( )

( )( ) ( )( ) ( ) e K H e K H e eq eq K pH pE K pH pE K pH pE K pH pE K pH pE K pH pE pH pE pH pE pH eq eq eq eq eq eq   +   +

  + + =

+ + + + + + =

+ + + 5 6 6 6 7 8 8 2 2 2 4 4 4 5 6 6 8 8 58 1 2 2 50 6 2 109 1 1 1 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 1 1 10 10 10 10 10 10 10 10 2 3 4 5 6 7 log log log log log log . . .

( ) ( )( ) ( )( ) ( )( ) 4 4 126 8 4 5 147 1 6 6 187 8 8 8 10 10 10 10 10 10 10 10 10 10

    + + + pE pH pE pH pE pH pE . . .

( eq. 6)

As expected, the Case 2 activity fraction diagrams for predominant species Cl and ClO 4  ( Charts 4a and 4b) are consistent with the Case 2 predominance diagram 3a with high activity fractions approaching 1 in areas of pE and pH where the Case 2 predominance diagram 3a indicates they are the predominant species. The Case 2 activity fraction diagrams for the other species ( ClO, HClO, ClO 2 , ClO 2( aq), and ClO 3 ) ( Charts 4c through 4g in Attachment E) are also consistent with the Case 2 predominance diagram 3a in that none are shown as predominant in Case 2 predominance diagram 3a and none have activity ratios > 10 6. Sodium Chlorate Appendices  25 Chart 1a: Case 1 aqueous chlorine species predominance diagram: ( Considering only Cl, Cl2( aq), ClO, and HClO); Chart 1a from combination of Charts 1b  1e in Attachment C ; Clpredominant in region ABCD representing pE & pH ranges of natural waters.

 10  8  6  4  2 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 pH pE 3a 14a 2b W1 W2 pH5 pH9 1a 2) ClO / Cl  3) HClO/ Cl  14) HClO/ ClO

O2( g)

H2O( l)

H2O( l)

H2( g) HClO predominance ClO  predominance Cl  predominance Cl  predominance in pE & pH ranges of natural waters A B C D 1) Cl2( aq)/ Cl  Cl2( aq) predominance HClO Sodium Chlorate Appendices  26 30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 0  2  4  6  8  10 4 6 8 10 0.000 0.200 0.400 0.600 0.800 1.000 Cl Activity Fraction pE pH Chart 2a: Case 1 Cl activity fraction considering only Cl, HClO, and ClO.

0.800 1.000 0.600 0.800 0.400 0.600 0.200 0.400 0.000 0.200 Sodium Chlorate Appendices  27 30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 0  2  4  6  8  10 4 6 8 10 0.000 0.200 0.400 0.600 0.800 1.000 HClO Activity Fraction pE pH Chart 2b: Case 1 HClO activity fraction considering only Cl, HClO, and ClO.

0.800 1.000 0.600 0.800 0.400 0.600 0.200 0.400 0.000 0.200 Sodium Chlorate Appendices  28 30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 0  2  4  6  8  10 4 6 8 10 0.000 0.200 0.400 0.600 0.800 1.000 ClO Activity Fraction pE pH Chart 2c: Case 1 ClO activity fraction considering only Cl, HClO, and ClO.

0.800 1.000 0.600 0.800 0.400 0.600 0.200 0.400 0.000 0.200 Sodium Chlorate Appendices  29 Chart 3a: Case 2 aq. chlorine species predominance diagram: ( Considering Cl, Cl2( aq), ClO,

HClO, ClO2 , ClO2( aq), ClO3 , and ClO4 ); Based on Charts 3b  3i in Attachment D; Clpredominant in region ABCD representing pE & pH ranges of natural waters.

 10  5 0 5 10 15 20 25 30 2 3 4 5 6 7 8 9 10 11 12 pH pE 7 W1 W2 pH5 pH9 ClO4  predominance Cl

Cl  predominance in pE & pH ranges of natural waters H2O( l) O2( g)

H2O( l)

H2( g) A B C D 7) ClO4 / Cl  Sodium Chlorate Appendices  30 ATTACHMENT A to Appendix B 2:

Primary chlorine species in aqueous solution:

The primary chlorine species in aqueous solution are Cl, Cl 2( aq), ClO, HClO, ClO 2 , ClO 2( aq), ClO 3 , and ClO 4  in which Cl exhibits oxidation states of  I, 0, I, III, IV, V, and VII, respectively. HClO 3 and HClO 4 are completely dissociated strong acids and HClO 2 has a pK a = 2. Therefore they are not further considered here for computations at pHs > 4.

Provided below are:

( a) 28 reactions between each aqueous chlorine species. ( b) Equations for the thermodynamic activity based equilibrium constant for each reaction ( c) Equations for the mixed equilibrium constant for each reaction ( d) The logarithm of the approximate equation for the equilibrium constant for each reaction ( e) Equations for boundary lines used in generating pE/ pH predominance diagrams for aqueous chlorine species. These equations are derived by substituting the value of the logarithm of the equilibrium constant into the previous equation and assuming that along the boundary the concentration of the species on one side of the boundary = the concentration of the species on the other side of the boundary. ( f) Equations for Case 1 and Case 2 activity fractions for each reaction The thermodynamic activity based equilibrium constant computations were performed using the Attachment B Excel spreadsheet. The format of the spreadsheet used for thermodynamic computations was developed by Dr. Jim Hetrick.

Reactions 1  7 ( reactions involving Cl):

Rxn 1: ( eq. 1a) 2 2 2 Cl Cl e aq       + ( )

( eq. 1b) ( )( ) ( ) K Cl e Cl eq aq 1 2 2 2 =

  ( )

( eq. 1c) [ ]( ) [ ] K Cl e Cl mix aq 1 2 2 2 =

  ( )

For generating predominance diagrams, assume that K eq1 ~ K mix1 such that Sodium Chlorate Appendices  31 ( eq. 1d) [ ] [ ] ( ) [ ] [ ] log log log log log ( ) ( ) K K Cl Cl e Cl Cl pE eq mix aq aq 1 1 2 2 2 2   = + =

Along the Cl 2( aq)/ Cl boundary line, it is reasonable to assume that [ Cl tot ] ~ [ Cl] + 2[ Cl 2( aq)]. Therefore, along the boundary for a total chlorine concentration [ Cl tot ] = 0.04 mol/ L, [ Cl] ~ 0.02 mol/ L and [ Cl 2( aq)] ~ 0.01 mol/ L. From the attached thermodynamic spreadsheet, logK eq1 =  47.2. Substituting those values into eq. 1d and rearranging gives the following equation for the Cl 2( aq)

/ Cl boundary line:

[ ] [ ] ( ) 2 472 001 002 47 2 25 47 2 14 48 6 24 3 2 pE pE = + = + = + =   = . log .

. . log . . . .

( eq. 1e)

Rxn 2: ( eq. 2a) Cl H O ClO H e     +   +   + + 2 2 2 ( eq. 2b) ( )( )( ) ( ) K ClO H e Cl eq2 2 2 =   +

( eq. 2c) [ ]( ) ( ) [ ] K ClO H e Cl mix2 2 2 =   +

For generating predominance diagrams, assume that K eq2 ~ K mix2 such that [ ] [ ] ( ) ( ) [ ] [ ] log log log log log log K K ClO Cl H e ClO Cl pH pE eq mix 2 2 2 2 2 2   = + + =

  +

( eq. 2d)

Along the ClO/ Cl boundary line, [ ClO] = [ Cl] so log{[ ClO]/[ Cl]} = log 1 = 0. From the attached thermodynamic spreadsheet, logK eq2 =  58.1. Substituting those values into eq. 2d and rearranging gives the following equation for the ClO/ Cl boundary line:

( eq. 2e) 2 581 2 291 pE pH pE pH =     =   . . Sodium Chlorate Appendices  32 ( ) ( ) ( ) ( ) ( ) ( ) ( )

( ) ( ) ( ) ( ) ( ) ( )( ) ( ) ( )

( ) ( ) ( )( )

( )( )

( )( ) ( )( ) ( )( )

( ) f ClO Cl ClO HClO K Cl H e Cl K Cl H e K Cl H e K H e K H e K H e ClO Case eq eq eq eq eq eq K pH pE K pH pE K pH pE pH pE pH eq eq eq   = + + =

+ + = + + =

+ + = +

+

+

+   +

+   +

  ( )

log log log .

. 1 2 2 2 2 2 2 3 2 2 2 2 2 2 2 3 2 2 2 2 2 58 1 2 2 58 1 1 10 10 10 1 10 10 10 10 10 10 10 10 10 1 10 10 2 2 3 ( ) ( )( ) 2 2 50 6 2 10 10 10 10

    + pE pH pE .

( eq. 2f)

( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )

( ) ( ) ( ) ( ) ( ) ( )( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )( ) ( ) ( ) ( )

( ) ( )

( ) ( ) ( )( ) f ClO Cl ClO HClO ClO ClO ClO ClO K Cl H e Cl K Cl H e K Cl H e K Cl H e K Cl H e K Cl H e K Cl H e K H e K H e K H e ClO Case aq eq eq eq eq eq eq eq eq eq eq   = + + + + + + =

+ + + + + + =

+ +

+

+

+

+

+

+

+

+

+   +   ( )

( ) 2 2 2 3 4 2 2 2 2 2 2 3 2 4 4 4 5 4 5 6 6 6 7 8 8 2 2 2 2 2 2 3 2 1 ( ) ( ) ( ) ( ) ( ) ( ) ( )( )

( )( )

( )( ) ( )( ) ( )( ) ( )( ) ( )( ) ( )( )

( ) + + + + =

+ + + + + + = +   +   +   +

  K H e K H e K H e K H e eq eq eq eq K pH pE K pH pE K pH pE K pH pE K pH pE K pH pE K pH pE pH eq eq eq eq eq eq eq 4 4 4 5 4 5 6 6 6 7 8 8 2 2 2 2 2 4 4 4 5 6 6 8 8 58 1 2 10 10 10 1 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 2 2 3 4 5 6 7 log log log log log log log .

( )

( )( ) ( )( ) ( )( ) ( )( ) ( )( ) ( )( ) 10 1 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 2 58 1 2 2 50 6 2 109 1 4 4 126 8 4 5 147 1 6 6 187 8 8 8

    + + + + + + pE pH pE pH pE pH pE pH pE pH pE pH pE . . . . . .

( eq 2g)

Rxn 3: ( eq. 3a) Cl H O HClO H e   +   +   + + 2 2 ( eq. 3b) ( )( )( ) ( ) K HClO H e Cl eq3 2 = +

( eq. 3c) [ ]( )( ) [ ] K HClO H e Cl mix3 2 = +

  Sodium Chlorate Appendices  33 For generating predominance diagrams, assume that K eq3 ~ K mix3 such that [ ] [ ] ( ) ( ) [ ] [ ] log log log log log log K K HClO Cl H e HClO Cl pH pE eq mix 3 3 2 2   = + + =       +

( eq. 3d)

Along the HClO/ Cl boundary line, [ HClO] = [ Cl] so log{[ HClO]/[ Cl]} = log 1 = 0. From the attached thermodynamic spreadsheet, logK eq3 =  50.6. Substituting those values into eq. 3d and rearranging gives the following equation for the HClO/ Cl boundary line:

( eq. 3e) 2 50 6 253 05 pE pH pE pH =     =   . . .

( ) ( ) ( ) ( ) ( ) ( )( )

( ) ( ) ( ) ( ) ( ) ( )( ) ( )( )

( ) ( ) ( )( )

( )( )

( )( ) ( )( ) ( )( )

( )( ) f HClO Cl ClO HClO K Cl H e Cl K Cl H e K Cl H e K H e K H e K H e HClO Case eq eq eq eq eq eq K pH pE K pH pE K pH pE pH pE pH pE eq eq eq ( )

log log log .

. 1 3 2 2 2 2 3 2 3 2 2 2 2 3 2 2 2 2 50 6 2 58 1 2 2 1 10 10 10 1 10 10 10 10 10 10 10 10 10 1 10 10 10 3 2 3 = + + =

+ + = + + =

+ + = + +

+

+

+   +

+   +

    ( )( ) 10 10 10 50 6 2

    .

pH pE ( eq. 3f)

( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )( )

( ) ( ) ( ) ( ) ( ) ( )( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )( )

( )( )

( ) ( ) ( )( ) f HClO Cl ClO HClO ClO ClO ClO ClO K Cl H e Cl K Cl H e K Cl H e K Cl H e K Cl H e K Cl H e K Cl H e K H e K H e K H e K HClO Case aq eq eq eq eq eq eq eq eq eq eq eq ( )

( ) 2 2 2 3 4 3 2 2 2 2 3 2 4 4 4 5 4 5 6 6 6 7 8 8 3 2 2 2 2 3 2 4 1 = + + + + + + =

+ + + + + + =

+ + +

+

+

+

+

+

+

+

+

+   +   ( ) ( ) ( ) ( ) ( ) ( ) ( )( )

( )( )

( )( ) ( )( ) ( )( ) ( )( ) ( )( ) ( )( )

( )( ) H e K H e K H e K H e eq eq eq K pH pE K pH pE K pH pE K pH pE K pH pE K pH pE K pH pE pH pE eq eq eq eq eq eq eq +   +   +   +

    + + + =

+ + + + + + =

+ 4 4 5 4 5 6 6 6 7 8 8 2 2 2 2 4 4 4 5 6 6 8 8 50 6 2 10 10 10 1 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 1 3 2 3 4 5 6 7 log log log log log log log .

( )( ) ( )( ) ( )( ) ( )( ) ( )( ) ( )( ) 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 58 1 2 2 50 6 2 109 1 4 4 126 8 4 5 147 1 6 6 187 8 8 8

    + + + + + . . . . . .

pH pE pH pE pH pE pH pE pH pE pH pE ( eq. 3g) Sodium Chlorate Appendices  34 Rxn 4: ( eq. 4a) Cl H O ClO H e     +   +   + + 2 4 4 2 2 ( eq. 4b) ( )( ) ( ) ( ) K ClO H e Cl eq4 2 4 4 =   +

( eq. 4c) [ ]( ) ( ) [ ] K ClO H e Cl mix4 2 4 4 =   +

For generating predominance diagrams, assume that K eq4 ~ K mix4 such that [ ] [ ] ( ) ( ) [ ] [ ] log log log log log log K K ClO Cl H e ClO Cl pH pE eq mix 4 4 2 2 4 4 4 4   = + + =

  +

( eq. 4d)

Along the ClO 2 / Cl boundary line, [ ClO 2 ] = [ Cl] so log{[ ClO 2 ]/[ Cl]} = log 1 = 0. From the attached thermodynamic spreadsheet, logK eq4 =  109.1. Substituting those values into eq. 4d and rearranging gives the following equation for the ClO 2 / Cl boundary line:

( eq. 4e) 4 1091 4 27 3 pE pH pE pH =     =   . .

( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )

( ) ( ) ( ) ( ) ( ) ( )( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )( ) ( ) ( ) ( )

( ) ( )

( ) ( ) ( ) f ClO Cl ClO HClO ClO ClO ClO ClO K Cl H e Cl K Cl H e K Cl H e K Cl H e K Cl H e K Cl H e K Cl H e K H e K H e K H e ClO Case aq eq eq eq eq eq eq eq eq eq eq 2 2 2 2 2 3 4 4 4 4 2 2 2 3 2 4 4 4 5 4 5 6 6 6 7 8 8 4 4 4 2 2 2 3 1   = + + + + + + =

+ + + + + + =

+ +

+

+

+

+

+

+

+

+

+   + ( )

( )

( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )( )

( )( )

( )( ) ( )( ) ( )( ) ( )( ) ( )( ) ( )( )   +   +   +   +

  + + + + =

+ + + + + + = 2 4 4 4 5 4 5 6 6 6 7 8 8 4 4 2 2 2 4 4 4 5 6 6 8 8 109 1 10 10 10 1 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 4 2 3 4 5 6 7 K H e K H e K H e K H e eq eq eq eq K pH pE K pH pE K pH pE K pH pE K pH pE K pH pE K pH pE eq eq eq eq eq eq eq log log log log log log log .

( )( )

( )( ) ( )( ) ( )( ) ( )( ) ( )( ) ( )( ) pH pE pH pE pH pE pH pE pH pE pH pE pH pE 4 4 58 1 2 2 50 6 2 109 1 4 4 126 8 4 5 147 1 6 6 187 8 8 8 10 1 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10

    + + + + + + . . . . . .

( eq. 4f) Sodium Chlorate Appendices  35 5 1268 4 254 0 8 pE pH pE pH =     =   . . .

( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )

( ) ( ) ( ) ( ) ( ) ( )( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )( ) ( ) ( )( )

( ) ( )

( ) ( ) f ClO Cl ClO HClO ClO ClO ClO ClO K Cl H e Cl K Cl H e K Cl H e K Cl H e K Cl H e K Cl H e K Cl H e K H e K H e K ClO Case aq aq eq eq eq eq eq eq eq eq eq eq aq 2 2 2 2 2 3 4 5 4 5 2 2 2 3 2 4 4 4 5 4 5 6 6 6 7 8 8 5 4 5 2 2 2 1 ( )( ) ( )

( ) = + + + + + + =

+ + + + + + =

+ +

+

+

+

+

+

+

+

+

+   ( )( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )

( )( )

( )( ) ( )( ) ( )( ) ( )( ) ( )( ) ( )( ) 3 2 4 4 4 5 4 5 6 6 6 7 8 8 4 5 2 2 2 4 4 4 5 6 6 8 8 126 10 10 10 1 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 5 2 3 4 5 6 7 H e K H e K H e K H e K H e eq eq eq eq K pH pE K pH pE K pH pE K pH pE K pH pE K pH pE K pH pE eq eq eq eq eq eq eq +   +   +   +   +

  + + + + =

+ + + + + + = log log log log log log log .

( )( )

( )( ) ( )( ) ( )( ) ( )( ) ( )( ) ( )( ) 8 4 5 58 1 2 2 50 6 2 109 1 4 4 126 8 4 5 147 1 6 6 187 8 8 8 10 10 1 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10

    + + + + + + pH pE pH pE pH pE pH pE pH pE pH pE pH pE . . . . . . Rxn 5: ( eq. 5a) Cl H O ClO H e aq   +   +   + + 2 4 5 2 2( )

( eq. 5b) ( )( ) ( ) ( ) K ClO H e Cl eq aq 5 2 4 5 = +

  ( )

( eq. 5c) [ ]( ) ( ) [ ] K ClO H e Cl mix aq 5 2 4 5 = +

  ( )

For generating predominance diagrams, assume that K eq5 ~ K mix5 such that [ ] [ ] ( ) ( ) [ ] [ ] log log log log log log ( ) ( ) K K ClO Cl H e ClO Cl pH pE eq mix aq aq 5 5 2 2 4 5 4 5   = + + =       +

( eq. 5d)

Along the ClO 2( aq)/ Cl boundary line, [ ClO 2( aq)] = [ Cl] so log{[ ClO 2( aq)]/[ Cl]} = log 1 = 0. From the attached thermodynamic spreadsheet, logK eq5 =  126.8. Substituting those values into eq. 5d and rearranging gives the following equation for the ClO 2( aq)/ Cl boundary line:

( eq. 5e)

( eq. 5f) Sodium Chlorate Appendices  36 Rxn 6: ( eq. 6a) Cl HO ClO H e     +   +   + + 3 6 6 2 3 ( eq. 6b) ( )( ) ( ) ( ) K ClO H e Cl eq6 3 6 6 =   +

( eq. 6c) [ ]( ) ( ) [ ] K ClO H e Cl mix6 3 6 6 =   +

For generating predominance diagrams, assume that K eq6 ~ K mix6 such that [ ] [ ] ( ) ( ) [ ] [ ] log log log log log log K K ClO Cl H e ClO Cl pH pE eq mix 6 6 3 3 6 6 6 6   = + + =

  +

( eq. 6d)

Along the ClO 3 / Cl boundary line, [ ClO 3 ] = [ Cl] so log{[ ClO 3 ]/[ Cl]} = log 1 = 0. From the attached thermodynamic spreadsheet, logK eq6 =  147.1. Substituting those values into eq. 6d and rearranging gives the following equation for the ClO 3 / Cl boundary line:

6 1471 6 24 5 pE pH pE pH =     =   . . ( eq. 6e)

( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )( )

( ) ( ) ( ) ( ) ( ) ( )( ) ( ) ( )( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )

( ) ( )

( ) ( ) ( ) f ClO Cl ClO HClO ClO ClO ClO ClO K Cl H e Cl K Cl H e K Cl H e K Cl H e K Cl H e K Cl H e K Cl H e K H e K H e K H e ClO Case aq eq eq eq eq eq eq eq eq eq eq 3 2 3 2 2 3 4 6 6 6 2 2 2 3 2 4 4 4 5 4 5 6 6 6 7 8 8 6 6 6 2 2 2 3 1   = + + + + + + =

+ + + + + + =

+ +

+

+

+

+

+

+

+

+

+   + ( )

( )

( ) ( ) ( ) ( ) ( ) ( )( ) ( )( )

( )( )

( )( ) ( )( ) ( )( ) ( )( ) ( )( ) ( )( )   +   +   +   +

  + + + + =

+ + + + + + = 2 4 4 4 5 4 5 6 6 6 7 8 8 6 6 2 2 2 4 4 4 5 6 6 8 8 147 8 10 10 10 1 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 6 2 3 4 5 6 7 K H e K H e K H e K H e eq eq eq eq K pH pE K pH pE K pH pE K pH pE K pH pE K pH pE K pH pE eq eq eq eq eq eq eq log log log log log log log .

( )( )

( )( ) ( )( ) ( )( ) ( )( ) ( )( ) ( )( ) pH pE pH pE pH pE pH pE pH pE pH pE pH pE 6 6 58 1 2 2 50 6 2 109 1 4 4 126 8 4 5 147 1 6 6 187 8 8 8 10 1 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10

    + + + + + + . . . . . .

( eq. 6f) Sodium Chlorate Appendices  37 ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )

( ) ( ) ( ) ( ) ( ) ( )( ) ( ) ( )( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )

( ) ( )

( ) ( ) ( ) f ClO Cl ClO HClO ClO ClO ClO ClO K Cl H e Cl K Cl H e K Cl H e K Cl H e K Cl H e K Cl H e K Cl H e K H e K H e K H e ClO Case aq eq eq eq eq eq eq eq eq eq eq 4 2 4 2 2 3 4 7 8 8 2 2 2 3 2 4 4 4 5 4 5 6 6 6 7 8 8 7 8 8 2 2 2 3 1   = + + + + + + =

+ + + + + + =

+ +

+

+

+

+

+

+

+

+

+   + ( )

( )

( ) ( ) ( ) ( ) ( ) ( )( ) ( )( )

( )( )

( )( ) ( )( ) ( )( ) ( )( ) ( )( ) ( )( )   +   +   +   +

  + + + + =

+ + + + + + = 2 4 4 4 5 4 5 6 6 6 7 8 8 8 8 2 2 2 4 4 4 5 6 6 8 8 187 8 10 10 10 1 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 7 2 3 4 5 6 7 K H e K H e K H e K H e eq eq eq eq K pH pE K pH pE K pH pE K pH pE K pH pE K pH pE K pH pE eq eq eq eq eq eq eq log log log log log log log .

( )( )

( )( ) ( )( ) ( )( ) ( )( ) ( )( ) ( )( ) pH pE pH pE pH pE pH pE pH pE pH pE pH pE 8 8 58 1 2 2 50 6 2 109 1 4 4 126 8 4 5 147 1 6 6 187 8 8 8 10 1 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10

    + + + + + + . . . . . . Rxn 7: ( eq. 7a) Cl H O ClO H e     +   +   + + 4 8 8 2 4 ( eq. 7b) ( )( )( ) ( ) K ClO H e Cl eq7 4 8 8 =   +

( eq. 7c) [ ]( )( ) [ ] K ClO H e Cl mix7 4 8 8 =   +

For generating predominance diagrams, assume that K eq7 ~ K mix7 such that [ ] [ ] ( ) ( ) [ ] [ ] log log log log log log K K ClO Cl H e ClO Cl pH pE eq mix 7 7 4 4 8 8 8 8   = + + =

  +

( eq. 7d)

Along the ClO 4 / Cl boundary line, [ ClO 4 ] = [ Cl] so log{[ ClO 4 ]/[ Cl]} = log 1 = 0. From the attached thermodynamic spreadsheet, logK eq7 =  187.8. Substituting those values into eq. 7d and rearranging gives the following equation for the ClO 4 / Cl boundary line:

( eq. 7e) 8 187 8 8 235 pE pH pE pH =     =   . .

( eq. 7f) Sodium Chlorate Appendices  38 Reactions 8  13 ( remaining reactions involving Cl2( aq):

Rxn 8: ( eq. 8a) Cl H O ClO H e aq 2 2 2 2 4 2 ( )+   + +   +

( eq. 8b) ( )( )( ) ( ) K ClO H e Cl eq aq 8 2 4 2 2 =   +

( )

( eq. 8c) [ ]( ) ( ) [ ] K ClO H e Cl mix aq 8 2 4 2 2 =   +

( )

For generating predominance diagrams, assume that K eq8 ~ K mix8 such that [ ] [ ] ( ) ( ) [ ] [ ] log log log log log log ( ) ( ) K K ClO Cl H e ClO Cl pH pE eq mix aq aq 8 8 2 2 2 2 4 2 4 2   = + + =       +

( eq. 8d)

Along the ClO/ Cl 2( aq) boundary line, it is reasonable to assume that [ Cl tot ] ~ [ ClO] + 2[ Cl 2( aq)]. Therefore, along the boundary for a total chlorine concentration [ Cl tot ] = 0.04 mol/ L, [ ClO] ~ 0.02 mol/ L and [ Cl 2( aq)] ~ 0.01 mol/ L. From the attached thermodynamic spreadsheet, logK eq8 =  69.0. Substituting those values into eq. 8d and rearranging gives the following equation for the ClO/ Cl 2( aq) boundary line:

( eq. 8e) [ ] [ ] 2 690 002 001 4 690 14 4 676 4 2 676 4 338 2 2 pE pH pH pH pE pH pE pH = +   =     =

=     =   . log .

. . . .

. .

Rxn 9: ( eq. 9a) Cl H O HClO H e aq 2 2 2 2 2 2 ( )+   + + +

( eq. 9b) ( )( ) ( ) ( ) K HClO H e Cl eq aq 9 2 2 2 2 = +

( ) Sodium Chlorate Appendices  39 ( eq. 9c) [ ]( ) ( ) [ ] K HClO H e Cl mix aq 9 2 2 2 2 = +

( )

For generating predominance diagrams, assume that K eq9 ~ K mix9 such that [ ]

[ ] ( ) ( ) [ ]

[ ] log log log log log log ( ) ( ) K K HClO Cl H e HClO Cl pH pE eq mix aq aq 9 9 2 2 2 2 2 2 2 2   = + + =     +

( eq. 9d)

Along the HClO/ Cl 2( aq) boundary line, it is reasonable to assume that [ Cl tot ] ~ [ HClO] + 2[ Cl 2( aq)]. Therefore, along the boundary for a total chlorine concentration [ Cl tot ] = 0.04 mol/ L, [ HClO] ~ 0.02 mol/ L and [ Cl 2( aq)] ~ 0.01 mol/ L. From the attached thermodynamic spreadsheet, logK eq9 =  53.9. Substituting those values into eq. 9d and rearranging gives the following equation for the HClO/ Cl 2( aq) boundary line:

( eq. 9e) [ ] [ ] 2 539 002 001 2 539 14 2 525 2 2 525 2 263 2 pE pH pH pH pE pH pE pH = +   =     =

=     =   . log .

. . . .

. .

Rxn 10: ( eq. 10a) Cl H O ClO H e aq 2 2 2 4 2 8 6 ( )+   + +   +

( eq. 10b) ( )( )( ) ( ) K ClO H e Cl eq aq 10 2 2 8 6 2 =   +

( )

( eq. 10c) [ ]( ) ( ) [ ] K ClO H e Cl eq aq 10 2 2 8 6 2 =   +

( )

For generating predominance diagrams, assume that K eq10 ~ K mix10 such that [ ] [ ] ( ) ( ) [ ] [ ] log log log log log ( ) ( ) K ClO Cl H e ClO Cl pH pE eq aq aq 10 2 2 2 2 2 2 8 6 8 6   + +         +

( eq. 10d) Sodium Chlorate Appendices  40 Along the ClO 2  / Cl 2( aq) boundary line, it is reasonable to assume that [ Cl tot ] ~ [ ClO 2  ] + 2[ Cl 2( aq)]. Therefore, along the boundary for a total chlorine concentration [ Cl tot ] = 0.04 mol/ L, [ ClO 2  ] ~ 0.02 mol/ L and [ Cl 2( aq)] ~ 0.01 mol/ L. From the attached thermodynamic spreadsheet, logK eq10 =  171.1. Substituting those values into eq. 10d and rearranging gives the following equation for the ClO 2  / Cl 2( aq) boundary line:

( eq. 10e) [ ] [ ] 6 1711 002 001 8 1711 14 8 169 7 8 6 169 7 8 28 3 133 2 pE pH pH pH pE pH pE pH = +   =     =

=     =   . log .

. . . .

. . .

Rxn 11: ( eq. 11a) Cl H O ClO H e aq aq 2 2 2 4 2 8 8 ( ) ( ) +   + + +

( eq. 11b) ( )( )( ) ( ) K ClO H e Cl eq aq aq 11 2 2 8 8 2 = +   ( )

( )

( eq. 11c) [ ]( )( ) [ ] K ClO H e Cl mix aq aq 11 2 2 8 8 2 = +   ( )

( )

For generating predominance diagrams, assume that K eq11 ~ K mix11 such that [ ] [ ] ( ) ( ) [ ] [ ] log log log log log log ( )

( ) ( )

( ) K K ClO Cl H e ClO Cl pH pE eq mix aq aq aq aq 11 11 2 2 2 2 2 2 8 8 8 8   = + + =     +

( eq. 11d)

Along the ClO 2( aq) / Cl 2( aq) boundary line, it is reasonable to assume that [ Cl tot ] ~ [ ClO 2( aq) ] + 2[ Cl 2( aq)]. Therefore, along the boundary for a total chlorine concentration [ Cl tot ] = 0.04 mol/ L, [ ClO 2( aq) ] ~ 0.02 mol/ L and [ Cl 2( aq)] ~ 0.01 mol/ L. From the attached thermodynamic spreadsheet, logK eq11 =  206.3. Substituting those values into eq. 11d and rearranging gives the following equation for the ClO 2( aq) / Cl 2( aq) boundary line: Sodium Chlorate Appendices  41 ( eq. 11e) [ ] [ ] 8 206 3 002 001 8 206 3 14 8 204 9 8 8 204 9 8 25 6 2 pE pH pH pH pE pH pE pH = +   =     =

=     =   . log .

. . . .

. .

Rxn 12: ( eq. 12a) Cl H O ClO H e aq 2 2 3 6 2 12 10 ( )+   + +   +

( eq. 12b) ( )( ) ( ) ( ) K ClO H e Cl eq aq 12 3 2 12 10 2 =   +

( )

( eq. 12c) [ ]( ) ( ) [ ] K ClO H e Cl mix aq 12 3 2 12 10 2 =   +

( )

For generating predominance diagrams, assume that K eq12 ~ K mix12 such that [ ] [ ] ( ) ( ) [ ] [ ] log log log log log log ( ) ( ) K K ClO Cl H e ClO Cl pH pE eq mix aq aq 12 12 3 2 2 3 2 2 12 10 12 10   = + + =       +

( eq. 12d)

Along the ClO 3  / Cl 2( aq) boundary line, it is reasonable to assume that [ Cl tot ] ~ [ ClO 3  ] + 2[ Cl 2( aq)]. Therefore, along the boundary for a total chlorine concentration [ Cl tot ] = 0.04 mol/ L, [ ClO 3  ] ~ 0.02 mol/ L and [ Cl 2( aq)] ~ 0.01 mol/ L. From the attached thermodynamic spreadsheet, logK eq12 =  247.0. Substituting those values into eq. 12d and rearranging gives the following equation for the ClO 3  / Cl 2( aq) boundary line:

[ ] [ ] 10 247 0 002 001 12 247 0 14 12 245 6 12 10 2456 12 24 6 12 2 pE pH pH pH pE pH pE pH = +   =     =

=     =   . log .

. . . .

. . .

( eq. 12e)

Rxn 13: ( eq. 13a) Cl H O ClO H e aq 2 2 4 8 2 16 14 ( )+   + +   +   Sodium Chlorate Appendices  42 ( eq. 13b) ( )( ) ( ) ( ) K ClO H e Cl eq aq 13 4 2 16 14 2 =   +

( )

( eq. 13c) [ ]( ) ( ) [ ] K ClO H e Cl mix aq 13 4 2 16 14 2 =   +

( )

For generating predominance diagrams, assume that K eq13 ~ K mix13 such that [ ] [ ] ( ) ( ) [ ] [ ] log log log log log log ( ) ( ) K K ClO Cl H e ClO Cl pH pE eq mix aq aq 13 13 4 2 2 4 2 2 16 14 16 14   = + + =       +

( eq. 13d)

Along the ClO 4  / Cl 2( aq) boundary line, it is reasonable to assume that [ Cl tot ] ~ [ ClO 4  ] + 2[ Cl 2( aq)]. Therefore, along the boundary for a total chlorine concentration [ Cl tot ] = 0.04 mol/ L, [ ClO 4  ] ~ 0.02 mol/ L and [ Cl 2( aq)] ~ 0.01 mol/ L. From the attached thermodynamic spreadsheet, logK eq13 =  328.3. Substituting those values into eq. 13d and rearranging gives the following equation for the ClO 4  / Cl 2( aq) boundary line:

[ ] [ ] 14 328 3 002 001 16 328 3 14 16 326 9 16 14 326 9 16 234 114 2 pE pH pH pH pE pH pE pH = +   =     =

=     =   . log .

. . . .

. . .

( eq. 13e)

Reactions 14  18 ( remaining reactions involving ClO):

Rxn 14: ( eq. 14a) ClO H HClO   + +

( eq. 14b) ( ) ( )( ) K HClO ClO H eq14 =   +

( eq. 14c) [ ] [ ]( ) K HClO ClO H mix14 =   + Sodium Chlorate Appendices  43 For generating predominance diagrams, assume that K eq14 ~ K mix14 such that ( eq. 14d) [ ] [ ] ( ) [ ] [ ] log log log log log K K HClO ClO H HClO ClO pH eq mix 14 14   =   = +   +

Along the HClO/ ClO boundary line, [ HClO] = [ ClO] so log{[ HClO]/[ ClO]} = log 1 = 0. From the attached thermodynamic spreadsheet, logK eq14 = 7.6. Substituting the values into eq. 14d and rearranging gives the following equation for the HClO/ ClO boundary line:

( eq. 14e) pH = 7 6 .

Rxn 15: ( eq. 15a) ClO H O ClO H e     +   +   + + 2 2 2 2 ( eq. 15b) ( )( ) ( ) ( ) K ClO H e ClO eq15 2 2 2 =   +

( eq. 15c) [ ]( ) ( ) [ ] K ClO H e ClO mix15 2 2 2 =   +

For generating predominance diagrams, assume that K eq15 ~ K mix15 such that [ ] [ ] ( ) ( ) [ ] [ ] log log log log log log K K ClO ClO H e ClO ClO pH pE eq mix 15 15 2 2 2 2 2 2   = + + =

  +

( eq. 15d)

Along the ClO 2 / ClO boundary line, [ ClO 2 ] = [ ClO] so log{[ ClO 2 ]/[ ClO]} = log 1 = 0. From the attached thermodynamic spreadsheet, logK eq15 =  51.0. Substituting the values into eq. 15d and rearranging gives the following equation for the ClO 2 / ClO boundary line:

( eq. 15e) 2 510 2 255 pE pH pE pH =     =   . .

Rxn 16: ( eq. 16a) ClO H O ClO H e aq   +   +   + + 2 2 2 3 ( ) Sodium Chlorate Appendices  44 ( eq. 16b) ( )( ) ( ) ( ) K ClO H e ClO eq aq 16 2 2 3 = +

  ( )

( eq. 16c) [ ]( ) ( ) [ ] K ClO H e ClO mix aq 16 2 2 3 = +

  ( )

For generating predominance diagrams, assume that K eq16 ~ K mix16 such that [ ] [ ] ( ) ( ) [ ] [ ] log log log log log log ( ) ( ) K K ClO ClO H e ClO ClO pH pE eq mix aq aq 16 16 2 2 2 3 2 3   = + + =       +

( eq. 16d)

Along the ClO 2( aq)/ ClO boundary line, [ ClO 2( aq)] = ClO so log{[ ClO 2( aq)]/[ ClO]} = log 1 = 0. From the thermodynamic spreadsheet, logK eq16 =  68.6. Substituting the values into eq. 16d and rearranging gives the following equation for the ClO 2( aq)/ ClO boundary line:

( eq. 16e) 3 68 6 2 22 9 0 67 pE pH pE pH =     =   . . .

Rxn 17: ( eq. 17a) ClO HO ClO H e     +   +   + + 2 4 4 2 3 ( eq. 17b) ( )( ) ( ) ( ) K ClO H e ClO eq17 3 4 4 =   +

( eq. 17c) [ ]( ) ( ) [ ] K ClO H e ClO mix17 3 4 4 =   +

For generating predominance diagrams, assume that K eq17 ~ K mix17 such that [ ] [ ] ( ) ( ) [ ] [ ] log log log log log log K K ClO ClO H e ClO ClO pH pE eq mix 17 17 3 3 4 4 4 4   = + + =

  +

( eq. 17d) Sodium Chlorate Appendices  45 Along the ClO 3 / ClO boundary line, [ ClO 3 ] = [ ClO] so log{[ ClO 3 ]/[ ClO]} = log 1 = 0. From the attached thermodynamic spreadsheet, logK eq17 =  89.0. Substituting those values into eq. 17d and rearranging gives the following equation for the ClO 3 / ClO boundary line:

( eq. 17e) 4 89 0 4 22 3 pE pH pE pH =     =   . .

Rxn 18: ( eq. 18a) ClO H O ClO H e     +   +   + + 3 6 6 2 4 ( eq. 18b) ( )( ) ( ) ( ) K ClO H e ClO eq18 4 6 6 =   +

( eq. 18c) [ ]( ) ( ) [ ] K ClO H e ClO mix18 4 6 6 =   +

For generating predominance diagrams, assume that K eq18 ~ K mix18 such that [ ] [ ] ( ) ( ) [ ] [ ] log log log log log log K K ClO ClO H e ClO ClO pH pE eq mix 18 18 4 4 6 6 6 6   = + + =

  +

( eq. 18d)

Along the ClO 4 / ClO boundary line, [ ClO 4 ] = [ ClO] so log{[ ClO 4 ]/[ ClO]} = log 1 = 0. From the attached thermodynamic spreadsheet, logK eq18 =  129.7. Substituting those values into eq. 18d and rearranging gives the following equation for the ClO 4 / ClO boundary line:

( eq. 18e) 6 129 7 6 216 pE pH pE pH =     =   . .

Reactions 19  22 ( remaining reactions involving HClO):

Rxn 19: ( eq. 19a) HClO H O ClO H e +   + +   +   2 2 3 2 ( eq. 19b) ( )( )( ) ( ) K ClO H e HClO eq19 2 3 2 =   +   Sodium Chlorate Appendices  46 ( eq. 19c) [ ]( )( ) [ ] K ClO H e HClO mix19 2 3 2 =   +

For generating predominance diagrams, assume that K eq19 ~ K mix19 such that [ ] [ ] ( ) ( ) [ ] [ ] log log log log log log K K ClO HClO H e ClO HClO pH pE eq mix 19 19 2 2 3 2 3 2   = + + =       +

( eq. 19d)

Along the ClO 2  / HClO boundary line, [ ClO 2 ] = [ HClO] so log{[ ClO 2 ]/[ HClO]} = log 1 = 0. From the attached thermodynamic spreadsheet, logK eq19 =  58.6. Substituting the values into eq. 19d and rearranging gives the following equation for the ClO 2  / HClO boundary line:

( eq. 19e) 2 58 6 3 29 3 15 pE pH pE pH =     =   . . .

Rxn 20: ( eq. 20a) HClO H O ClO H e aq +   + ++   2 2 3 3 ( )

( eq. 20b) ( )( )( ) ( ) K ClO H e HClO eq aq 20 2 3 3 = +   ( )

( eq. 20c) [ ]( )( ) [ ] K ClO H e HClO mix aq 20 2 3 3 = +   ( )

For generating predominance diagrams, assume that K eq20 ~ K mix20 such that [ ] [ ] ( ) ( ) [ ] [ ] log log log log log log ( ) ( ) K K ClO HClO H e ClO HClO pH pE eq mix aq aq 20 20 2 2 3 3 3 3   = + + =     +

( eq. 20d)

Along the ClO 2( aq) / HClO boundary line, [ ClO 2( aq)] = [ HClO] so log{[ ClO 2( aq)]/[ HClO]} = log 1 = 0. From the attached thermodynamic spreadsheet, logK eq20 =  76.2. Substituting the values into eq. 20d and rearranging gives the following equation for the ClO 2( aq) / HClO boundary line:

( eq. 20e) 3 76 2 3 254 pE pH pE pH =     =   . . Sodium Chlorate Appendices  47 Rxn 21: ( eq. 21a) HClO H O ClO H e +   + +   +   2 5 4 2 3 ( eq. 21b) ( )( )( ) ( ) K ClO H e HClO eq21 3 5 4 =   +

( eq. 21c) [ ]( )( ) [ ] K ClO H e HClO mix21 3 5 4 =   +

For generating predominance diagrams, assume that K eq21 ~ K mix21 such that [ ] [ ] ( ) ( ) [ ] [ ] log log log log log log K K ClO HClO H e ClO HClO pH pE eq mix 21 21 3 3 5 4 5 4   = + + =       +

( eq. 21d)

Along the ClO 3  / HClO boundary line, [ ClO 3 ] = [ HClO] so log{[ ClO 3 ]/[ HClO]} = log 1 = 0. From the attached thermodynamic spreadsheet, logK eq21 =  96.6. Substituting the values into eq. 21d and rearranging gives the following equation for the ClO 3  / HClO boundary line:

( eq. 21e) 4 96 6 5 24 2 125 pE pH pE pH =     =   . . .

Rxn 22: ( eq. 22a) HClO H O ClO H e +   + +   +   3 7 6 2 4 ( eq. 22b) ( )( ) ( ) ( ) K ClO H e HClO eq22 4 7 6 =   +

( eq. 22c) [ ]( ) ( ) [ ] K ClO H e HClO mix22 4 7 6 =   +

For generating predominance diagrams, assume that K eq22 ~ K mix22 such that [ ] [ ] ( ) ( ) [ ] [ ] log log log log log log K K ClO HClO H e ClO HClO pH pE eq mix 22 22 4 4 7 6 7 6   = + + =       +

( eq. 22d) Sodium Chlorate Appendices  48 Along the ClO 4  / HClO boundary line, [ ClO 4 ] = [ HClO] so log{[ ClO 4 ]/[ HClO]} = log 1 = 0. From the attached thermodynamic spreadsheet, logK eq22 =  137.2. Substituting the values into eq. 22c and rearranging gives the following equation for the ClO 4  / HClO boundary line:

( eq. 22e) 6 137 2 7 22 9 117 pE pH pE pH =     =   . . .

Reactions 23  25 ( remaining reactions involving ClO2  ):

Rxn 23: ( eq. 23a) ClO ClO e aq 2 2       + ( )

( eq. 23b) ( )( ) ( ) K ClO e ClO eq aq 23 2 2 =

  ( )

( eq. 23c) [ ]( ) [ ] K ClO e ClO mix aq 23 2 2 =

  ( )

For generating predominance diagrams, assume that K eq23 ~ K mix23 such that [ ] [ ] ( ) [ ] [ ] log log log log log ( ) ( ) K K ClO ClO e ClO ClO pE eq mix aq aq 23 23 2 2 2 2   = + =

( eq. 23d)

Along the ClO 2( aq) / ClO 2  boundary line, [ ClO 2( aq)] = [ ClO 2 ] so log{[ ClO 2( aq)]/[ ClO 2 ]} = log 1 = 0. From the attached thermodynamic spreadsheet, logK eq23 =  17.6. Substituting the values into eq. 23d and rearranging gives the following equation for the ClO 2( aq) / ClO 2  boundary line:

( eq. 23e) pE = 17 6 .

Rxn 24: ( eq. 24a) ClO HO ClO H e 2 2 3 2 2     +   +   + +

( eq. 24b) ( )( ) ( ) ( ) K ClO H e ClO eq24 3 2 2 2 =   +

  Sodium Chlorate Appendices  49 ( eq. 24c) [ ]( ) ( ) [ ] K ClO H e ClO mix24 3 2 2 2 =   +

For generating predominance diagrams, assume that K eq24 ~ K mix24 such that [ ] [ ] ( ) ( ) [ ] [ ] log log log log log log K K ClO ClO H e ClO ClO pH pE eq mix 24 24 3 2 3 2 2 2 2 2   = + + =

  +

( eq. 24d)

Along the ClO 3  / ClO 2  boundary line, [ ClO 3 ] = [ ClO 2 ] so log{[ ClO 3 ]/[ ClO 2 ]} = log 1 = 0. From the attached thermodynamic spreadsheet, logK eq24 =  38.0. Substituting the values into eq. 24d and rearranging gives the following equation for the ClO 3  / ClO 2  boundary line:

( eq. 24e) 2 38 0 2 19 0 pE pH pE pH =     =   . .

Rxn 25: ( eq. 25a) ClO HO ClO H e 2 2 4 2 4 4     +   +   + +

( eq. 25b) ( )( ) ( ) ( ) K ClO H e ClO eq25 4 4 4 2 =   +

( eq. 25c) [ ]( ) ( ) [ ] K ClO H e ClO mix25 4 4 4 2 =   +

For generating predominance diagrams, assume that K eq25 ~ K mix25 such that [ ] [ ] ( ) ( ) [ ] [ ] log log log log log log K K ClO ClO H e ClO ClO pH pE eq mix 25 25 4 2 4 2 4 4 4 4   = + + =

  +

( eq. 25d)

Along the ClO 4  / ClO 2  boundary line, [ ClO 4 ] = [ ClO 2 ] so log{[ ClO 4 ]/[ ClO 2 ]} = log 1 = 0. From the attached thermodynamic spreadsheet, logK eq25 =  78.6. Substituting the values into eq. 25c and rearranging gives the following equation for the ClO 4  / ClO 2  boundary line:

( eq. 25e) 4 78 6 4 19 7 pE pH pE pH =     =   . . Sodium Chlorate Appendices  50 Reactions 26  27 ( remaining reactions involving ClO2( aq) ):

Rxn 26: ( eq. 26a) ClO H O ClO H e aq 2 2 3 2 ( )+   + +   +

( eq. 26b) ( )( ) ( ) ( ) K ClO H e ClO eq aq 26 3 2 2 =   +

( )

( eq. 26c) [ ]( ) ( ) [ ] K ClO H e ClO mix aq 26 3 2 2 =   +

( )

For generating predominance diagrams, assume that K eq26 ~ K mix26 such that [ ] [ ] ( ) ( ) [ ] [ ] log log log log log log ( ) ( ) K K ClO ClO H e ClO ClO pH pE eq mix aq aq 26 26 3 2 3 2 2 2   = + + =       +

( eq. 26d)

Along the ClO 3  / ClO 2( aq) boundary line, [ ClO 3 ] = [ ClO 2( aq)] so log{[ ClO 3 ]/[ ClO 2( aq)]} = log 1 = 0. From the attached thermodynamic spreadsheet, logK eq26 =  20.4. Substituting the values into eq. 26d and rearranging gives the following equation for the ClO 3  / ClO 2( aq) boundary line:

( eq. 26e) pE pH =   20 4 2 .

Rxn 27: ( eq. 27a) ClO H O ClO H e aq 2 2 4 2 4 3 ( )+   + +   +

( eq. 27b) ( )( ) ( ) ( ) K ClO H e ClO eq aq 27 4 4 3 2 =   +

( )

( eq. 27c) [ ]( ) ( ) [ ] K ClO H e ClO mix aq 27 4 4 3 2 =   +

( )

For generating predominance diagrams, assume that K eq27 ~ K mix27 such that Sodium Chlorate Appendices  51 [ ] [ ] ( ) ( ) [ ] [ ] log log log log log log ( ) ( ) K K ClO ClO H e ClO ClO pH pE eq mix aq aq 27 27 4 2 4 2 4 3 4 3   = + + =       +

( eq. 27d)

Along the ClO 4  / ClO 2( aq) boundary line, [ ClO 4 ] = [ ClO 2( aq)] so log{[ ClO 4 ]/[ ClO 2( aq)]} = log 1 = 0. From the attached thermodynamic spreadsheet, logK eq27 =  61.0. Substituting the values into eq. 27d and rearranging gives the following equation for the ClO 4  / ClO 2( aq) boundary line:

( eq. 27e) 3 610 4 20 3 133 pE pH pE pH =     =   . . .

Reaction 28 ( last remaining reaction involving ClO3  ):

Rxn 28: ( eq. 28a) ClO H O ClO H e 3 2 4 2 2     +   +   + +

( eq. 28b) ( )( ) ( ) ( ) K ClO H e ClO eq28 4 2 2 3 =   +

( eq. 28c) [ ]( ) ( ) [ ] K ClO H e ClO mix28 4 2 2 3 =   +

For generating predominance diagrams, assume that K eq28 ~ K mix28 such that [ ] [ ] ( ) ( ) [ ] [ ] log log log log log log K K ClO ClO H e ClO ClO pH pE eq mix 28 28 4 3 4 3 2 2 2 2   = + + =

  +

( eq. 28d)

Along the ClO 4  / ClO 3  boundary line, [ ClO 4 ] = [ ClO 3 ] so log{[ ClO 4 ]/[ ClO 3 ]} = log 1 = 0. From the attached thermodynamic spreadsheet, logK eq28 =  40.6. Substituting the values into eq. 28d and rearranging gives the following equation for the ClO 4  / ClO 3 boundary line:

( eq. 28e) 2 40 6 2 20 3 pE pH pE pH =     =   . .

See Next Page Sodium Chlorate Appendices  52 Water oxidation and reduction reactions ( Benjamin 2002):

Rxn 1W Oxidation of Water: ( eq. 1Wa) 2 4 4 2 2 H O O H e g   + ++   ( )

( eq. 1Wb) ( )( ) ( ) K O H e eqW aq 1 2 4 4 = +   ( )

( ) ( ) ( ) ( ) log log log log log ( ) ( ) K O H e O pH pE eqW g g 1 2 2 4 4 4 4 = + + =     +

( eq. 1Wc)

( eq. 1Wd) ( ) 4 831 021 4 206 pE pH pE pH = +     =   . log . .

Rxn 2W Reduction of Water: ( eq. 2Wa) 2 2 2 2 2 H O e H OH g +   +     ( )

( eq. 2Wb) ( )( ) ( ) K H OH e eqW g 2 2 2 2 =

  ( )

( ) ( ) ( ) ( ) ( ) log log log( ) log log log ( ) log ( ) ( )

( ) ( ) K H OH e H pOH pE H pH pE H pH pE eqW g g g g 2 2 2 2 2 2 2 2 2 2 14 2 2 2 28 = +   =   + =

    + = + +

( eq. 2Wc)

( eq. 2Wd) ( ) 2 5 10 2 2 6 30 2 32 7 pE pH pE pH pE pH =   ×     =

  =     log .

. Sodium Chlorate Appendices  53 Attachment B: Computations of delta G0 of reactions and equilbrium constants for aqueous chlorine species reactions and for oxidation and reduction of water reactions. ( Spreadsheet format developed by Dr. Jim Hetrick).