Drinking Water Criteria Document for Cyanogen Chloride and Potential Metabolites EPA/ OW/ OST/ HECD Final draft III 1 Chapter III. Toxicokinetics Limited data on the toxicokinetics of cyanogen chloride are available, primarily from old studies conducted prior to the development of modern toxicology methods, and from basic principles of chemistry.

A. Absorption No data were located on the rate or degree of absorption of inhaled cyanogen chloride.

However, based on the rapid onset of systemic symptoms in animals exposed to cyanogen chloride via the inhalation route ( Aldridge and Evans, 1946), it appears that absorption via this route is rapid. No information on the absorption of cyanogen chloride via the oral or dermal routes was located. It is likely, however, that oral absorption of cyanogen chloride is rapid, based on analogy to cyanide. Hydrogen cyanide is moderately lipid soluble, and at least 50% of an oral dose is absorbed within 24 hours of ingestion ( ATSDR, 1997). Cyanogen chloride would be expected to remain in the parent form ( rather than the hydrolyzed form) in the acidic conditions of the stomach ( see Section III. C), and so have absorption characteristics similar to those of hydrogen cyanide. Based on analogy to cyanide, it is also likely that cyanogen chloride can be absorbed following dermal exposure.

Because the generation of cyanogen chloride metabolites, such as cyanide, thiocyanate,

cyanate, cyanamide, or chloride, occurs from cyanogen chloride that has already been absorbed,

absorption of metabolites was not investigated in detail for this project. However, absorption can Drinking Water Criteria Document for Cyanogen Chloride and Potential Metabolites EPA/ OW/ OST/ HECD Final draft III 2 be relevant to the assessment for two reasons. First, the degree or rate of absorption may be greater under certain dosing conditions, which may affect the toxicity. For example, food delays the absorption of cyanide, reducing its toxicity ( reviewed in NTP, 1993) compared to dosing in drinking water. Slower absorption means that the cyanide would be less likely to overwhelm the detoxification capacity of the enzyme rhodanese in the liver, and thus less likely to have toxic effects. The other way in which absorption may be relevant to the assessment is if cyanogen chloride and a metabolite have markedly different degrees of absorption. For example, imagine that absorption via the oral route is 90% for cyanogen chloride, but 20% for the metabolite used as a surrogate to estimate cyanogen chloride toxicity. Not taking into account the differences in absorption would result in an underestimate of the toxicity ( based on ingested amount) of cyanogen chloride. As noted above, however, the close chemical similarity of hydrogen cyanide and cyanogen chloride suggests that their absorption is quantitatively similar.

B. Distribution Cyanogen chloride. No information on the distribution of cyanogen chloride following oral, inhalation, or dermal exposure was located. However, cyanogen chloride is rapidly metabolized in blood, as discussed in Section III. C. This indicates that cyanogen chloride metabolites may be distributed systemically, but it suggests the parent compound would be unlikely to reach tissues beyond the portal of entry and immediately adjacent blood stream.

Cyanide. The distribution of cyanide has been discussed in detail by ATSDR ( 1997) and is summarized here. Small levels of cyanide are normally present in blood plasma, and cyanide Drinking Water Criteria Document for Cyanogen Chloride and Potential Metabolites EPA/ OW/ OST/ HECD Final draft III 3 appears to rapidly distribute throughout the body following absorption. Cyanide has been found in the lung, heart, blood, kidney, and brain of people who died following cyanide inhalation. In dogs exposed to cyanide by inhalation, the highest concentrations of cyanide were found in the lungs, blood, and heart. In rats exposed by inhalation, the highest tissue concentrations were detected in the lungs, blood, liver, brain, and spleen. In rabbits exposed by inhalation, the highest tissue concentrations were detected in the heart, lung, brain, spleen, and kidney. Following oral exposure in humans, stomach contents appear to contain the highest concentration of cyanide.

Other tissues containing cyanide include brain, blood, lungs, kidney, and liver. In rats exposed by the oral route, the highest tissue concentrations of cyanide were in the liver, lung, blood, spleen,

and brain. In rabbits exposed dermally, the highest tissue concentrations of cyanide were in the lungs, heart, brain, liver, and spleen.

Thiocyanate. Data on thiocyanate distribution show that thiocyanate distributes freely throughout the body, but does not cross the blood brain barrier ( Wood, 1975). Thiocyanate occurs in the saliva of unexposed humans, possibly from the metabolism of cyanide produced in the digestion of protein ( as reviewed by Anderson and Chen, 1940). In mice, thiocyanate was found in greater amounts in the walls of large blood vessels, in stomach, thyroid, and salivary glands ( route and compound of exposure not specified, Wood, 1975). Because thiocyanate has an ionic size similar to that of iodide, it competitively inhibits iodide binding at the Na/ I symporter ( Wolff and Maurey, 1963). Therefore it is expected that thiocyanate would be actively taken up into tissues that take up iodide, including the thyroid, mammary gland, skin, and gastrointestinal tract. Drinking Water Criteria Document for Cyanogen Chloride and Potential Metabolites EPA/ OW/ OST/ HECD Final draft III 4 Thiocyanate can cross the placenta to a limited degree. Kreutler et al. ( 1978) administered sodium thiocyanate in drinking water to pregnant rats at 0  160 mg SCN/ L during gestation, and then measured plasma thiocyanate levels in the dams and pups at 5 and 10 days postpartum.

Plasma thiocyanate increased from 0.25 mg/ 100 mL in the control dams to 1.5 mg/ 100 mL at the high dose at postpartum day 5. Plasma thiocyanate also increased in a dose related manner in the pup, but to a much lower degree. On day 5, the control pups had 0.15 mg SCN/ 100 mL, while the high dose pups had only 0.28 mg SCN/ 100 mL plasma. These general results are supported by the findings of Boulos et al. ( 1973). These authors administered sodium thiocyanate intravenously to goats, and found that the plasma concentration in the fetus reached steady state approximately 90 minutes after maternal dosing, and was about 33% of the maternal plasma concentration.

Cyanate. Only one study regarding the distribution of cyanate was located. Following intraperitoneal injection of 160 mg/ kg [ 14C] potassium cyanate in male Swiss Webster mice, peak blood levels were observed within 5 minutes ( Johnson et al., 1985). At 10 minutes after administration, 0.25

mol [ 14C] cyanate was bound per mL of blood. This dropped to 0.01

mol/ mL during the 60 to 210 minute post administration time period. The authors concluded that this bound activity reflected carbamylated hemoglobin.

Cyanamide. Very limited information on the distribution of cyanamide is available.

Following administration of 35 mg/ kg cyanamide by oral gavage, peak plasma concentrations of cyanamide occurred at 6 minutes in fasted rats and at 15 minutes in unfasted rats ( Obach et al.,

1986a). Following administration of 2 mg/ kg cyanamide to rats or 4 mg/ kg cyanamide to dogs by Drinking Water Criteria Document for Cyanogen Chloride and Potential Metabolites EPA/ OW/ OST/ HECD Final draft III 5 oral gavage, peak plasma cyanamide concentrations occurred at 5 minutes in rats and 33 minutes in dogs ( Obach et al., 1989). In contrast, peak plasma levels of calcium cyanamide occurred 1 hour after oral administration ( Loomis and Brien, 1983; not available for review, cited in Obach et al., 1986a).

HCl. Under physiological conditions, HCl rapidly dissociates into hydrogen and chloride ions. These physiological ions are freely soluble in water, and are readily dispersed throughout the body.

C. Metabolism Cyanogen chloride. Although the data on cyanogen chloride metabolism are based primarily on older studies using outdated methods, the key results of these studies are supported by a recent in vitro study ( Midwest Research Institute, 1997).

Aldridge and Evans ( 1946) reported that injection of 1.9 mg cyanogen chloride into the portal vein of a cat produced minimal or no effects ( based on measurements of respiration and arterial pressure), perhaps due to the rapid detoxification in the liver. By contrast, injection of 0.95 mg cyanogen chloride into the femoral artery produced marked effects ( transitory rise and then a fall in arterial pressure, and acceleration followed by slowing in heart rate). This difference between injection sites was attributed to the greater distance traveled before the compound reached the liver for detoxification. The authors remarked that direct evidence from perfusion Drinking Water Criteria Document for Cyanogen Chloride and Potential Metabolites EPA/ OW/ OST/ HECD Final draft III 6 studies showed detoxification of cyanogen chloride in the liver, although it was not rapid. No further quantitation and no supporting data were provided.

Other experiments by these authors ( Aldridge and Evans, 1946) provide information on cyanogen chloride metabolism by comparing the relative potency of cyanogen chloride and cyanide in affecting the arterial pressure and respiration rate under various exposure conditions.

The comparisons were semi quantitative, based on visual evaluation of data tracings. When equivalent amounts of cyanogen chloride and hydrogen cyanide ( HCN) ( based on molar equivalents of cyanide) were injected intravenously, less severe effects were seen with cyanogen chloride. This result suggests that a portion of the cyanogen chloride was metabolized to a product( s) other than cyanide. Alternatively, the difference in toxicity may have been related to the difference in injection volumes ( 4 mL of cyanogen chloride, compared to 0.35 mL of HCN).

The study authors calculated that the toxic effect of intravenously administered cyanogen chloride on respiration rate was approximately 30% that of HCN. This estimate was confirmed by quantitatively comparing the effect of injecting cats with 0.95 mg cyanogen chloride or with 0.122 or 0.144 mg HCN ( equivalent to 30 35% of the CNCl dose on a moles cyanide basis, injection volumes not reported); similar toxic effects were observed. In contrast with this estimate,

Aldridge and Evans ( 1946) used a comparison of intravenous LD 50 values to estimate that approximately 75% of high doses of cyanogen chloride are converted to cyanide. The intravenous LD 50 for HCN in rabbits was 0.8 mg/ kg, while the LD 50 for cyanogen chloride was approximately 2.5 mg/ kg. The reason for the apparent inconsistency between the two estimates of the degree of conversion of cyanogen chloride to cyanide is unclear. Although an effect endpoint was measured in these studies, the quantitative differences can be attributed to the Drinking Water Criteria Document for Cyanogen Chloride and Potential Metabolites EPA/ OW/ OST/ HECD Final draft III 7 degree of cyanogen chloride conversion to cyanide. Differences in the magnitude of the effect cannot be attributed to toxicodynamic differences, because the measured endpoint in both cases is related to cyanide and because exposure in these studies was via injection.

Aldridge and Evans ( 1946) exposed anesthetized animals ( species not reported, but apparently cat) to 3000 mg/ m3 cyanogen chloride and analyzed the blood for cyanogen chloride and HCN at 30 seconds through 6 minutes ( Table III 1). No cyanogen chloride was found at any time point, but HCN was found, beginning at 1 minute of exposure. The level of HCN in the blood rose rapidly and showed a slower increase through the end of sampling ( and apparently the end of exposure) at 6 minutes. In a further experiment, a cat inhaled 1000 mg/ m3 hydrogen cyanide, a concentration that is chemically equivalent ( on a moles cyanide basis) to 75% of the cyanogen chloride concentration in the previous experiment. Therefore, if all of the cyanogen chloride had been converted to HCN, the HCN concentration in blood following cyanide exposure would have been approximately 75% of that following cyanogen chloride exposure.

Instead, exposure to HCN resulted in a blood HCN concentration ( following 4 minutes of exposure) that was approximately twice the blood HCN concentration after exposure to cyanogen chloride ( at the 6 minute time point) ( Table III 1). This suggests that the concentrations would have been equivalent if the authors had exposed the cat to half as much HCN as was actually used. Based on these considerations, the authors concluded that approximately 30% of the cyanogen chloride ( 0.75 × 0.5) was converted to HCN.

Follow up in vitro experiments with defibrinated rabbit blood supported the conclusion that cyanogen chloride is metabolized via routes other than HCN. The authors found that Drinking Water Criteria Document for Cyanogen Chloride and Potential Metabolites EPA/ OW/ OST/ HECD Final draft III 8 Table III 1. HCN and HSCN Levels Following Inhalation of CNCl or HCN1 Time Point ( minutes) HCN Content of Blood (

g/ mL) HSCN Content of Plasma (

g/ mL)

CNCl Inhalation ( at 3000 mg/ m3)

Pre exposure 0 NE 0.5 ND NE 1 3.0 NE 3.5 4.1 NE 6 4.4 NE HCN Inhalation ( at 1000 mg/ m3)

Pre exposure 0 3.9 0.58 3.0 4.2 4 9.8 4.4 4.4  Exposure ended, no blood sampling 6.25 6.2 5.0 1Data from Aldridge and Evans, 1946 ND= Not detected NE = Not evaluated approximately 30 39% of the cyanogen chloride was converted to HCN at cyanogen chloride concentrations of 21 130

g/ mL. However, when only 9.6

g/ mL cyanogen chloride was added to blood, 59% was converted to cyanide, suggesting that formation of cyanide is dose related, and is saturated at high doses. No HCN or thiocyanate were produced when cyanogen chloride was added to serum alone. Instead, the reaction of cyanogen chloride with serum or plasma resulted in the rapid conversion of cyanogen chloride into an unidentified metabolite( s) that was not cyanide. The absence of cyanide conversion to thiocyanate in the study with serum is consistent Drinking Water Criteria Document for Cyanogen Chloride and Potential Metabolites EPA/ OW/ OST/ HECD Final draft III 9 with the finding that an enzyme that converts cyanide to thiocyanate is found in red blood cells, as discussed below in the context of cyanide metabolism.

The experiments of Aldridge and Evans ( 1946) with cyanogen chloride in vivo and with rabbit blood provided very little information on levels of thiocyanate. In the study described above in which blood levels of cyanogen chloride and HCN were monitored in the blood of a cat exposed via inhalation to 3000 mg/ m3, the study authors reported that blood thiocyanate levels were approximately double the background level, but they did not provide additional quantitative information or any information on the time point evaluated. The study authors also noted that thiocyanate could not be accurately estimated in whole blood. Thiocyanate was also found in the blood and saliva ( concentrations not specified) of a dog exposed to cyanogen chloride via inhalation ( approximately 50 mg/ m3 for about 3.75 hours, followed by approximately 100 mg/ m3 for 2.75 hours).

Based on the above results, the authors concluded that conversion of cyanogen chloride into cyanide is not quantitative. They estimated the conversion at 30% in vitro, but stated that there may be more conversion in isolated red blood cells or in vivo. However, interpretation of their data is limited by the absence of mass balance data, particularly the absence of information on the amount of thiocyanate formed. Although 30% conversion at the doses tested is plausible,

an alternative interpretation of the data is that, in addition to the thiocyanate formation from cyanide, there is a pathway by which thiocyanate can be formed directly from cyanogen chloride.

This hypothesis is consistent with the limited quantitative data available from the experiment described above and presented in Table III 1. Thiocyanate levels in blood doubled following Drinking Water Criteria Document for Cyanogen Chloride and Potential Metabolites EPA/ OW/ OST/ HECD Final draft III 10 exposure of a cat to 3000 mg/ m3 cyanogen chloride. If concentrations in blood and plasma are similar, consideration of the background level in Table III 1 suggests that thiocyanate levels in blood were increased by approximately 3.9

g/ mL. Following exposure of a cat to 1000 mg/ m3 HCN ( equivalent to 75% of the cyanogen chloride exposure, on a moles cyanide basis),

thiocyanate levels in plasma increased from a background level of 3.9

g/ mL to 4.4

g/ mL, an increase of 0.5

g/ mL, instead of the 2.9

g/ mL ( i. e., 0.75 × 3.9) expected based on comparison to cyanogen chloride. This rough quantitation is limited, however, by any differences between thiocyanate levels in blood and plasma, the inaccuracy of thiocyanate estimates in plasma, and the small sample size. In addition, although cyanogen chloride can react with nucleophiles to form thiocyanate, it is unclear whether this reaction would occur under physiological conditions. A third hypothesis is that the lower concentration of HCN following cyanogen chloride exposure is due to rapid conversion of HCN to thiocyanate ( SCN). However, in light of the nearinstantaneous disappearance of injected cyanogen chloride from blood ( as described above), there is no clear reason why this reaction would be faster following inhalation exposure to cyanogen chloride than following inhalation exposure to HCN. Regardless of the exact quantitation, these data indicate that the disposition of high doses of cyanogen chloride in vivo involves other reactions besides the reduction to cyanide. As described below, the unidentified reaction products may also result from reaction with other cellular nucleophiles.

In confirmation of the results of Aldridge and Evans ( 1946), Aldridge ( 1951) found that cyanogen chloride reacts rapidly with rat hemoglobin, with less than 1% of the cyanogen chloride detectable within 5 seconds. This study also found that: the conversion of cyanogen chloride to cyanide was higher in a red blood cell suspension than in whole blood, the percent conversion Drinking Water Criteria Document for Cyanogen Chloride and Potential Metabolites EPA/ OW/ OST/ HECD Final draft III 11 was further increased by reduction of the blood hemoglobin ( by treatment with nitrogen), and the percent conversion was decreased by dialysis of the blood, which removed small molecules such as glutathione. ( All solutions were normalized to the same hemoglobin content.) Aldridge and Evans ( 1946) found that the degree of conversion of cyanogen chloride to cyanide by washed red cells decreased with increasing concentration of cyanogen chloride, and ranged from 73% at 9.7

g cyanogen chloride/ mL, to 25% at 126

g/ mL, indicating saturation of the capacity for converting cyanogen chloride to cyanide. In more detailed studies with high concentrations ( 50

100

g/ mL) of cyanogen chloride, a rapid reaction with hemoglobin was followed by a slower reaction. Cyanide was not liberated during the initial reaction, but cyanide was released when hemolysed red cells were added to the products of the initial reaction. This release of cyanide was not produced by the addition of plasma or serum. In other words, cyanide is produced in a 2

stage reaction in which the first stage is a rapid reaction of cyanogen chloride with oxy,

carboxyor reduced hemoglobin. In the second stage, the product produced in the first stage reacts more slowly with a material present in red blood cells, but not in plasma, to produce cyanide.

Cyanogen chloride reacts with methemoglobin, but produces cyanomethemoglobin, rather than cyanide. The authors noted that cyanide is not produced if cyanogen chloride is mixed first with serum, and then hemolysed red cells are added. The chemical nature of the product formed by reaction of cyanogen chloride with hemoglobin was not identified. However, based on the observation that the formation of cyanomethemoglobin from cyanogen chloride and methemoglobin is much slower, and occurs in much lower yields than the reaction of methemoglobin and cyanide, the authors concluded that cyanogen chloride does not react with the heme portion of hemoglobin. The authors suggested that glutathione was the key component of the second phase of the reaction. They noted, however, that glutathione also reacts directly with Drinking Water Criteria Document for Cyanogen Chloride and Potential Metabolites EPA/ OW/ OST/ HECD Final draft III 12 cyanogen chloride, reducing the amount of cyanogen chloride to 1% of the initial amount within 5 seconds. Cyanide is also slowly liberated from the reaction of cyanogen chloride and glutathione.

The study authors concluded that cyanogen chloride may be converted to cyanide both by direct reaction with hemoglobin, and by reaction with glutathione. The reaction of cyanogen chloride with glutathione was further characterized and a reaction pathway was proposed ( Figure III 1).

In the initial fast reaction, cyanogen chloride reacts with one molecule of glutathione. The production of free cyanide requires the supply of additional free SH groups. Cysteine could also react with cyanogen chloride, but no cyanide was produced, even in the presence of excess glutathione, suggesting that the ring structure formed with cysteine is more stable than that formed with glutathione. Metabolism of cyanide is discussed below and shown in Figure III 2.

The rapid disappearance of cyanogen chloride from blood was confirmed in a study conducted using modern toxicology methods. Midwest Research Institute ( 1997) investigated the toxicokinetics of cyanogen chloride in blood in an unpublished in vitro experiment conducted according to GLP guidelines. In preliminary experiments, cyanogen chloride was added to rat blood at 10 or 58 µ g/ mL; cyanogen chloride levels were at the background value by the time of the first measurement ( 1 minute). This was followed by time course experiments, in which cyanogen chloride was added to rat blood at 9.3 or 50 µ g/ mL, and samples were removed at 30,

60, 120, 300, and 600 seconds. As in the preliminary experiment, cyanogen chloride rapidly reacted with blood components, and was not detected at levels found in blank samples of untreated blood. To analyze free cyanide levels, the authors also treated the timed samples with Drinking Water Criteria Document for Cyanogen Chloride and Potential Metabolites EPA/ OW/ OST/ HECD Final draft III 13 CNCl RSCN ROCN R OH R SH SH CH NH CH 2 NH CH NH S CH 2 C SH CH NH CH 2 HCN RNHCN RNH 2 HCl HCl HCl R 1 R 2 R1 R 2 HCl 2 GSH R 1 R 2 See Figure 2 ( 8) ( 7) ( 1)

( 10) ( 9) ( 11)

( 12) ( 2) ( 3) ( 4) ( 5) ( 2) ( 6)

Figure III 1. Reactions of cyanogen chloride ( 1) with various nucleophiles. Cyanogen chloride can react with the  SH group of the cysteine moiety in hemoglobin or glutathione ( 2), producing HCl ( 3) and an intermediate ( 4). This intermediate then reacts with glutathione ( 5), regenerating the original  SH group donor and producing hydrogen cyanide ( 6). In other reactions, cyanogen chloride can react with sulfhydryls ( 7) to produce thiocyanates ( 8) and HCl. Cyanogen chloride can react with alcohols or phenoxy groups ( 9)

to produce cyanates ( 10) and HCl. ( In the simplest form, this reaction is hydrolysis under basic conditions, forming cyanate.)

Cyanogen chloride can also react with ammonia and amines ( 11) to produce cyanamide and substituted cyanamides ( 12). All of these latter reactions also produce HCl as a product. Drinking Water Criteria Document for Cyanogen Chloride and Potential Metabolites EPA/ OW/ OST/ HECD Final Draft III 14 chloramine T, which converts free cyanide to cyanogen chloride, followed by barbituric acid,

which forms a colored product that can be measured spectraphotometrically. In the samples treated with 10 µ g/ mL cyanogen chloride, cyanide was present at all time points, with the peak cyanide concentration at 300 seconds after dosing, and blood cyanide concentrations decreasing thereafter. The peak blood concentration of cyanide was 80% of the theoretical maximum. When blood was spiked with 50 µ g/ mL, however, the free cyanide accounted for only about 25%

percent of expected peak concentration, suggesting that conversion of cyanogen chloride to cyanide is dose dependent. Free cyanide levels were generally constant at all sampling times after mixing the blood with 50 µ g/ mL cyanogen chloride, although the highest levels were measured at the 300 second and 600 second time points. The study authors concluded that cyanogen chloride rapidly reacts in blood, and that some of the cyanogen chloride is converted to free cyanide. Both cyanogen chloride and cyanide were presumed to react with protein, primarily hemoglobin.

However, no other cyanide metabolites or reaction products were evaluated, and no mass balance analysis was conducted. Although an accompanying memorandum ( Boorman, 1998) indicates that the results indicate that an evaluation of cyanogen chloride would be " essentially an evaluation of cyanide," the data do not address that conclusion, since no other metabolites or reaction products were evaluated.

Two studies, Aldridge and Evans ( 1946) and Midwest Research Institute ( 1997), both examined the quantitative relationship between cyanogen chloride concentration and the formation of cyanide, and found that the amount of cyanogen chloride found as cyanide ranged from about 25% to 80%. It is reasonable to question the reasons for the wide variation in cyanogen chloride metabolism. Aldridge and Evans ( 1946) added cyanogen chloride to Drinking Water Criteria Document for Cyanogen Chloride and Potential Metabolites EPA/ OW/ OST/ HECD Final Draft III 15 defibrinated rabbit blood and observed about 60% was converted to cyanide at cyanogen chloride concentrations of about 10 µ g/ mL, compared to 30 40% converted at cyanogen chloride concentrations of 21 130 µ g/ mL. When washed red blood cells from rabbits were used, the degree of conversion was slightly increased, with 73% of the cyanogen chloride converted to cyanide at a cyanogen chloride concentration of about 10 µ g/ mL, decreasing to 25% of cyanogen chloride converted to cyanide at a cyanogen chloride concentration of 126 µ g/ mL. Midwest Research Institute ( 1997) also observed an inverse relationship between cyanogen chloride concentration added to blood and the degree of conversion of cyanogen chloride to cyanide.

When cyanogen chloride was added to rat whole blood at concentrations of about 10 µ g/ mL,

approximately 80% was converted to cyanide. However, when cyanogen chloride was added at concentrations of about 60 µ g/ mL, only 25% of cyanogen chloride was converted to cyanide.

These data suggest that three variables could be contributing to the wide variation in cyanogen chloride: species differences, the type of blood components used, or dose. Although the Aldridge and Evans ( 1946) studies were in rabbit blood and the Midwest Research Institute ( 1997) studies were in rat blood, there is a reasonable agreement in the results, with the suggestion that rat blood may convert cyanogen chloride to a slightly higher degree at low doses. On the other hand,

Aldridge and Evans clearly demonstrated that the type of blood component studied also contributes to the amount of cyanogen chloride converted to cyanide. No cyanide was produced when serum alone was used, cyanide conversion increased when whole blood was used, and conversion was the highest when concentrated red blood cells were used. Thus, although it is possible that species differences contribute to the differences between the two studies, the differences could also be plausibly explained by the fact that in the rabbit defibrinated blood or washed red blood cells were used, while in the rat, whole blood was used. Nonetheless, all of the Drinking Water Criteria Document for Cyanogen Chloride and Potential Metabolites EPA/ OW/ OST/ HECD Final Draft III 16 experiments, regardless of species or type of blood component used, clearly described a concentration dependent relationship for the conversion of cyanogen chloride to cyanide, in which 2 to 3 fold more cyanide is produced at cyanogen chloride concentrations of approximately 10 µ g/ mL than when cyanogen chloride concentrations were higher. Thus, while the maximum capacity for conversion of cyanogen chloride to cyanide may be related to the species tested or the blood component studied, there is a consistently observed concentration dependence.

Although cyanide and thiocyanate are the only metabolites of cyanogen chloride that have been detected to date in biological systems, studies of the aqueous chemistry of cyanogen chloride suggest that several other compounds are potential metabolites. Price et al. ( 1947) investigated the reactivity of dilute cyanogen chloride with a variety of compounds. In both alkali solution ( pH 10) and tap water, cyanogen chloride was hydrolyzed by hydroxyl ion to form cyanate ( HOCN) and chloride ion. This reaction can be expressed by the equation:

ClCN + OH

HOCN + Cl

The rate appeared to be the same for both solutions, 6 x 102/ mmol/ min. Hydrolysis in tap water appeared to be complete in about 48 hours. At pH 8, there was no measurable reaction between cyanogen chloride and up to 4.1E 4M ammonia; at 8.8E 4 M ammonia the reaction was slightly accelerated. The authors concluded that the reaction of cyanogen chloride with ammonia to form cyanamide ( NH 2 CN) is very slow because free ammonia is only a small percentage of the total ammonia present. In contrast, the reaction of cyanogen chloride with sulfide ion ( as sodium sulfide) to form thiocyanate was complete in less than 30 minutes. Finally, cyanogen chloride reacts with hypochlorite to form hydrogen chloride, carbon dioxide, and nitrogen gas; this reaction was complete within 5 minutes. Drinking Water Criteria Document for Cyanogen Chloride and Potential Metabolites EPA/ OW/ OST/ HECD Final Draft III 17 Edwards et al. ( 1986) evaluated the rate of cyanogen chloride hydrolysis at a range of pHs in order to obtain a complete pH rate profile. The hydrolysis rate was constant in the pH range 1

5, with an average of 5.7 x 10 7/ second at 25  C. The hydrolysis rate increased with increasing pH up to pH 10. This suggests that the rate of cyanogen chloride hydrolysis would be lower under the acidic conditions of the stomach than in the respiratory tract or other regions of the body. The authors also reported that nucleophilic compounds, such as amines, attack the carbon in cyanogen chloride, resulting in the release of the chloride ion.

Cyanogen chloride also reacts with a variety of nucleophiles ( Migridichian, 1946). The general equation for these reactions is:

Nu   H + ClCN

Nu   CN + HCl Cyanogen chloride may react in this manner with ammonia, alkyl amines, and aromatic amines, to form cyanamide and substituted cyanamides. For example:

NH 3 + ClCN

NH 2 CN + HCl RNH 2 + ClCN

RNHCN + HCl The rate of this reaction is pH dependent, since the form reacting with cyanogen chloride is the free base. Therefore, at pH 7, weak bases ( pKa < 7) are more reactive than strong bases.

Cyanogen chloride also reacts with sulfhydryls, alcohols, and phenoxy compounds to form thiocyanates and cyanates:

R   SH + ClCN

RSCN + HCl R   OH + ClCN

ROCN + HCl Drinking Water Criteria Document for Cyanogen Chloride and Potential Metabolites EPA/ OW/ OST/ HECD Final Draft III 18 In summary, no information is available on the metabolism of orally administered cyanogen chloride, but information on the metabolic pathway can be deduced from inhalation and injection data, as well as in vitro studies. Cyanogen chloride is rapidly metabolized in the blood to cyanide. This reaction occurs by reduction of cyanogen chloride via interaction with the  SH group in glutathione or hemoglobin; direct reaction with the  SH group in proteins may also occur. It appears that this reaction is so rapid that all of the metabolism after injection of cyanogen chloride takes place in the blood itself, rather than in the liver or other organs; it is not known whether first pass metabolism in the liver following oral exposure is also important.

Thiocyanate was also observed in the blood of animals exposed to cyanogen chloride, but quantitative measurements are not available. It is not known whether the thiocyanate was produced directly from the cyanogen chloride or as a metabolite of cyanide. As discussed below,

cyanide is metabolized to thiocyanate in the liver, kidneys, blood, and other organs. Thus,

thiocyanate might have been produced in the in vitro studies in which cyanogen chloride was mixed with blood, but thiocyanate levels were not evaluated in those studies. Measurements of blood cyanide levels after mixing cyanogen chloride with blood indicate that only approximately 30 40% of the cyanogen chloride is observed as cyanide at higher doses, while the percent present as cyanide increases to approximately 60 80% at lower doses. If a constant percentage of the cyanide is converted to thiocyanate, these data suggest that metabolism of cyanogen chloride to cyanide is capacity limited at high doses. The degree of conversion of cyanogen chloride to cyanide at environmentally relevant doses is not known. However, it would be expected that conversion to cyanide at these lower doses would be > 80%. It is also not known whether the unidentified material represents cyanogen chloride that was converted into other metabolites, or whether the rest of the cyanide was converted to thiocyanate. The increasing percent cyanide Drinking Water Criteria Document for Cyanogen Chloride and Potential Metabolites EPA/ OW/ OST/ HECD Final Draft III 19 yield at decreasing doses suggests, however, that other metabolites are formed. No in vitro or in vivo studies have been conducted to identify the other possible metabolites, but water chemistry data indicate that cyanogen chloride can be converted ( non reductively) to cyanate, cyanamide,

and chloride. Production of these compounds is higher in basic solution, and so would not be expected to occur in the stomach in the absence of enzyme catalysis. Some of this conversion may occur, however, in tap water.

Based on the in vivo data from cyanogen chloride inhalation and injection, and the in vitro data, the following pathway may be hypothesized for ingested cyanogen chloride. Since the rate of cyanogen chloride hydrolysis is slow under acidic and neutral conditions, little reaction would occur in the stomach or intestine. The degree and rate of cyanogen chloride reaction with nucleophiles ( e. g., thiols or amines in proteins) in vivo is not known, but such reactions with nucleophiles would be slower in the stomach ( where the acidic conditions would protonate the nucleophile) than in the neutral conditions of the intestine. This suggests that cyanogen chloride is absorbed from the stomach and/ or intestine as the parent chemical. The products of cyanogen chloride reaction with macromolecules in the intestinal contents may also be absorbed, but these products would not react further. Absorbed cyanogen chloride would enter the blood stream,

where it would be rapidly reduced to cyanide by glutathione. Other reactions with blood constituents may also occur. All parent compound would be expected to disappear within seconds of entering the blood. Some absorption of cyanogen chloride would occur directly from the stomach to the portal vein, where it would enter the liver. It is likely that any cyanogen chloride that is still present in the blood entering the liver would rapidly react with the high concentrations of glutathione present in zone 1 ( the portion of the liver adjacent to the portal Drinking Water Criteria Document for Cyanogen Chloride and Potential Metabolites EPA/ OW/ OST/ HECD Final Draft III 20 vein). Cyanide entering the liver or formed in the liver could then be converted to thiocyanate.

Since high levels of rhodanese ( the enzyme that metabolizes cyanide  see the next section) are found in the liver and the lung, metabolism at the portal of entry is important for cyanogen chloride exposure via both the oral and inhalation routes. In light of this hypothesized mechanism, it is of interest that injection of cyanogen chloride into the portal vein produced minimal acute toxicity compared to intravenous injection ( Aldridge and Evans, 1946, see beginning of this section).

This hypothesized metabolic pathway for cyanogen chloride suggests that much of the ingested cyanogen chloride is metabolized in the gastrointestinal tract or the liver, primarily in the portal vein and liver, with some metabolism possibly occurring in the blood after absorption from the intestine. Similarly, HCl formation as a byproduct of cyanogen chloride metabolism is likely to be limited to these tissues. The HCl produced might result in transient decreases in pH of the blood or liver, but it appears that systemic acidosis would be unlikely at environmentally relevant doses ( see Appendix E, Section III).

Cyanide. The major metabolic pathway for cyanide is conversion to thiocyanate by either rhodanese or 3 mercaptopyruvate sulfur transferase. This pathway accounts for 60 80% of a cyanide dose. Minor pathways include incorporation into a 1 carbon metabolic pool, or conversion to 2 aminothiazoline 4 carboxylic acid ( ATSDR, 1997). These pathways are shown in Figure III 2. Drinking Water Criteria Document for Cyanogen Chloride and Potential Metabolites EPA/ OW/ OST/ HECD Final draft III 21 CO 2  HCN Hydrogen Cyanide ( in expired air) Carbon dioxide H + CN

CNCyanide 2 Aminothiazoline 4 carboxylic acid &

2 Iminothiazolidine 4 carboxylic acid Minor Path ( Pool) Thiocyanate ( SCN)

Major Path ( 80%) Urinary Excretion HCNO Cyanate HCOOH Formic Acid Metabolism of onecarbon compounds Some excreted in urine Formates +

Figure III 2. Cyanide Primary Metabolic Pathways. Adapted from ATSDR ( 1997). Drinking Water Criteria Document for Cyanogen Chloride and Potential Metabolites EPA/ OW/ OST/ HECD Final draft III 22 Rhodanese, a mitochondrial enzyme that converts cyanide to thiocyanate, facilitates transfer of a sulfur atom to cyanide from a sulfane sulfur donor such as thiosulfate. Rhodanese is widely distributed throughout the body. Through immunohistochemical staining techniques,

rhodanese in rabbits has been located in the liver, where it is most abundant in the hepatocytes near blood vessels ( Sylvester and Sander, 1990). It was also found in the lung, localized in epithelial cells that formed the barrier between inhaled air and blood vessels. In the kidney,

rhodanese was found in tubules closest to the glomeruli. Therefore, these authors noted that the most abundant sites of rhodanese are located to maximize conversion of cyanide to thiocyanate following both oral and inhalation exposure ( Sylvester and Sander, 1990).

Devlin et al. ( 1989a) evaluated rhodanese activity in rat liver and skeletal muscle. Using histochemical staining techniques, the authors noted that only low levels of rhodanese activity were present in the blood vessels. In contrast, high levels of rhodanese were detected in the liver and skeletal muscle. Although, the concentration of rhodanese in muscle was lower than in liver,

the authors concluded that total skeletal body mass of muscle makes a significant contribution to the whole body metabolism of cyanide. In a follow up study in perfused liver and hindlimb muscle, Devlin et al. ( 1989b) observed that liver extracted 80% of the available cyanide compared to 18% for hindlimbs. However, when the hindlimb data were extrapolated to total muscle mass,

muscle cleared cyanide 2.6 fold faster than liver, in the absence of exogenous thiosulfate.

Lewis et al. ( 1991) observed the presence of rhodanese in the epithelium of human maxilloturbinates. Compared to rhodanese in human liver, the rhodanese in nasal tissue exhibited a higher affinity ( lower Km) for cyanide and a lower maximum velocity ( lower Vmax). The EPA/ OW/ OST/ HECD Final draft III 23 human enzymes exhibited a lower affinity ( higher Km) and lower maximum velocity ( lower Vmax) than rhodanese in rats. In addition, rhodanese activity in human nasal epithelium was higher in nonsmokers than smokers.

The tissue distribution of rhodanese is highly variable among species. Himwich and Saunders ( 1948) observed that in dogs, the highest activity of rhodanese was observed in the adrenal glands, followed by liver. Brain, spinal cord, kidney, and testes also had large amounts of rhodanese. Monkeys, rats, and rabbits, in general, had much higher concentrations of rhodanese than dogs, with liver and kidney containing the highest activity of rhodanese. Drawbaugh and Marrs ( 1987) also studied the tissue distribution of rhodanese in several species, including marmoset, rats, hamster, rabbit, guinea pig, dog, and pigeon. In general, rhodanese activity was higher in the liver than in the kidney of various species, except for rabbits. The highest rhodanese activities were found in rats, hamsters and guinea pigs; the lowest in pigeon, marmoset, and dogs.

A second enzyme which converts cyanide to thiocyanate is mercaptopyruvate sulfurtransferase ( MPST). This enzyme differs from rhodanese in that it catalyzes the transfer of sulfur from an organic thiol to cyanide ( Wing and Baskin, 1992). Therefore, this enzyme breaks a carbon sulfur bond to facilitate transfer of sulfur to cyanide, compared to rhodanese, which breaks a sulfur sulfur bond. MPST is located in the red blood cells and kidney, and thus appears to have a different tissue distribution from that of rhodanese. MPST is located in both the mitochondria and the cytosol, making it more accessible than rhodanese for conversion of cyanide ( Wing and Baskin, 1992). Support for the role of MPST in cyanide detoxification was provided by Huang et al. ( 1998). These authors demonstrated that addition of L or D cysteine to hepatocytes in vitro EPA/ OW/ OST/ HECD Final draft III 24 prevented cyanide cytotoxicity and enhanced the formation of thiocyanate. Mercaptopyruvate and thiocystine, metabolites of L and D cysteine, are substrates of MPST. Huang et al. ( 1998)

observed that when formation of these metabolites was prevented, the formation of thiocyanate was also inhibited. However, it is not clear whether MPST directly transfers sulfur to cyanide or whether it acts indirectly by transferring sulfur to albumin in the liver. The modified albumin could then be excreted to form a sulfane sulfur pool that is available to react with cyanide via rhodanese ( Wing and Baskin, 1992).

Thiocyanate. Thiocyanate and cyanide are in equilibrium in the body; thiocyanate is converted back to cyanide and sulfate by the action of thiocyanate oxidase located in the red blood cells, lymphocytes, mammary gland, and thyroid ( Wood, 1975). These enzymes catalyze the reaction of hydrogen peroxide and thiocyanate to form cyanide and sulfate. In addition, these enzymes produce an intermediate oxidation product of thiocyanate ( OSCN), which reacts with cyanide to form cyanate, which is then hydrolyzed to ammonia and carbon dioxide ( Wood, 1975).

Cyanate. Holtham and Schutz ( 1948, not available for review, cited in Johnson et al.,

1985) have shown that cyanate is hydrolyzed to carbon dioxide and ammonia by the enzyme cyanase, which is present in kidney, liver, and red blood cells. When mice were injected intraperitoneally with 160 mg/ kg [ 14C] potassium cyanate, 70% of the activity was recovered in expired air as 14CO 2 ( Johnson et al., 1985). The authors concluded that the conversion of cyanate to CO 2 follows first order kinetics and is dependent on the blood levels of cyanate. EPA/ OW/ OST/ HECD Final draft III 25 Cyanamide. Cyanamide appears to be metabolized by two pathways. The major metabolite is N acetylcyanamide. Shirota et al. ( 1984, cited in Obach et al., 1989) demonstrated that after giving [ 14C] cyanamide to dogs, 87% of the radioactivity was recovered in the urine as N acetylcyanamide and 11% was recovered in the urine as cyanamide. Mertschenk et al. ( 1991)

demonstrated that in Wistar rats administered 10 mg/ kg cyanamide by oral gavage, 43% of the administered dose was excreted in the urine as N acetlycyanamide within 22 hours. In humans who ingested a single dose of 0.25 mg/ kg, 40% of the administered dose was excreted in the urine as N acetylcyanamide ( Mertschenk et al., 1991).

A second potential pathway for the metabolism of cyanamide involves the interaction of hydrogen peroxide and cyanamide via the enzyme catalase to form the unstable intermediate Nhydroxycyanamide which then spontaneously decomposes to cyanide and nitroxyl ( HNO). In support of this theory, Shirota et al. ( 1987) demonstrated that cyanide is produced in vitro when cyanamide is incubated with bovine liver catalase and a glucose/ glucose oxidase system to generate a steady supply of hydrogen peroxide. The amount of cyanide formed was directly related to the cyanamide and catalase concentrations. However, in an investigation of human volunteers who ingested 0.25 mg/ kg cyanamide, Mertschenk et al. ( 1991) did not detect cyanide in the blood, or increased thiocyanate in the urine.

HCl. The hydrogen and chloride ions are not subject to enzymatic metabolism. However,

the hydrogen ion readily interacts with, and is neutralized by, physiological bases such as the bicarbonate ion ( HCO 3 ). The acid and base levels in blood and tissues are tightly controlled ( reviewed in Chan, 1983). The body rapidly responds to metabolic acidosis by increasing the EPA/ OW/ OST/ HECD Final draft III 26 respiration rate and increasing carbon dioxide expiration. If the acidosis is not corrected, the kidney follows with stepwise increments of increased net acid excretion over 3 to 4 days, until maximal renal acidification occurs.

D. Excretion Cyanogen chloride. No information on the excretion of cyanogen chloride following oral or dermal exposure was located. Thiocyanate levels in saliva were elevated several days following a 6.5 hour exposure of a single dog to 50 100 mg/ m3 cyanogen chloride, suggesting that elimination occurs over at least several days ( Aldridge and Evans, 1946).

Cyanide. Cyanide is primarily excreted in the urine as thiocyanate following both inhalation and oral exposure. Following occupational exposure to 0.19 0.75 ppm hydrogen cyanide, urinary thiocyanate levels in exposed workers were approximately twice the levels in controls ( 5.4 vs 2.2

g/ mL; Chandra et al., 1980, as cited in ATSDR, 1997). Following a single subcutaneous injection of rats with [ 14C] potassium cyanide, 89% of the radioactivity was detected as thiocyanate in urine within 24 hours; about 4% was expired in air as carbon dioxide ( Okoh, 1983, cited in ATSDR).

Leuschner et al. ( 1991) evaluated the elimination of potassium cyanide following both acute and subchronic exposure. For the acute study, three male Sprague Dawley rats were treated by gavage with 1 mg/ kg potassium cyanide. Blood was collected at regular intervals for up to 1 hour following administration. A peak blood level of 6.2 nmol cyanide/ mL blood was observed 2 EPA/ OW/ OST/ HECD Final draft III 27 minutes after treatment; by 60 minutes the blood levels had dropped to the detection limit. The authors calculated an elimination half life of 14.1 minutes.

For the subchronic study, male Sprague Dawley rats ( 26 40/ group) received potassium cyanide in their drinking water at doses of 0, 40, 80, or 140/ 160 mg/ kg day for 13 weeks ( Leuschner et al., 1991). Blood was collected every two weeks for analysis of cyanide and thiocyanate levels. Urine was collected over a 16 hour period during weeks 6 and 13 of the study for analysis of cyanide and thiocyanate levels. For both cyanide and thiocyanate, blood levels were dose related; although within each dose group, the levels of both cyanide and thiocyanate remained fairly constant over the 13 week exposure period. Cyanide levels in the blood were 16

25 nmol CN/ mL blood; thiocyanate levels were 341 877 nmoles thiocyanate/ mL plasma. ( The study authors did not report why cyanide levels were reported in blood, whereas thiocyanate levels were reported in plasma, although this may relate to better methods for measuring thiocyanate in plasma than in blood.) Small amounts of thiocyanate were also detected in the control animals at concentrations of 11 53 nmol thiocyanate/ mL plasma. The same patterns were observed for excretion of cyanide and thiocyanate in urine. A dose response relationship was observed for the concentration of both cyanide and thiocyanate in urine, and a small amount of thiocyanate was observed in the urine of the controls. The levels of cyanide in the urine were much lower than the thiocyanate levels; the ratio of cyanide to thiocyanate was about 1 to 1000.

Approximately 11% of the administered cyanide was eliminated per day as thiocyanate in the urine during the dosing period, while only about 0.003% was excreted per day unchanged. The study authors did not report how they estimated the percent of total dose eliminated; radiolabeled material was not used. The authors also did not address the disposition of the ~ 90% of the EPA/ OW/ OST/ HECD Final draft III 28 administered cyanide that was not accounted for. Although no elimination half life was calculated under the subchronic conditions, these results suggest that the elimination half life is longer under subchronic than acute exposure conditions. Blood levels of cyanide and thiocyanate were fairly consistent with time. Some elimination may have occurred as exhaled HCN, but HCN is reported to account for < 10% of an ingested cyanide dose ( ATSDR, 1997). The study authors noted,

however, that the percent administered cyanide excreted via the urine was unchanged between weeks 6 and 13, indicating that detoxification pathways were not saturated and the mode of cyanide excretion was not affected over this duration.

Blood cyanide and plasma thiocyanate levels were monitored in a patient during hospital treatment for a lethal case of cyanide poisoning ( Singh et al., 1989). Sampling was done at 0.5, 2,

4, 12, 18, and 24 hours after admission. The highest blood cyanide level of 819

mol/ L was measured at 2 hours, and had decreased to 23

mol/ L by 12 hours, following cobalt edetate therapy. Plasma thiocyanate levels peaked at 345

mol/ L, at 12 hours post admission.

In Cynomolgus monkeys exposed for up to 30 minutes to approximately 100 170 mg CN/ m3, blood cyanide levels remained nearly constant after approximately the first 10 15 minutes of exposure, and for 60 minutes after the termination of exposure ( Purser et al., 1984). These data indicate a relatively long half life in monkeys, based on the slow decrease in blood levels after exposure was terminated.

Thiocyanate. Thiocyanate is primarily excreted unchanged in the urine. In humans administered 1.2 to 1.5 g of sodium thiocyanate, 96 99% was excreted in the urine within 5 14 EPA/ OW/ OST/ HECD Final draft III 29 days ( Wood, 1975). In rats injected with 9 15 mg of [ 35S] potassium thiocyanate, 81% of the radiolabel was recovered unchanged in the urine. Sulfate in the urine accounted for 4.5% of the label and less than 1% was found in the feces over a 23 day period ( Wood, 1975).

Considerable variability, on the order of 4 5 fold, has been reported in the daily excretion of thiocyanate by human subjects ( Gorman et al., 1949). This variability may be due to both interindividual variability and changes in the excretion rate with continued dosing. In addition, renal disease can be related to hypertension, and would have affected the excretion rate in the subjects studied. A human clinical study found that ( thio) cyanate clearance through the kidney increased as subjects were exposed repeatedly to thiocyanate ( Barker, 1936). This meant that higher administered doses were required to maintain the target blood concentration of thiocyanate.

Similar results were found in an animal study. Kreutler et al. ( 1978) administered radiolabeled SCN intraperitoneally to control lactating rats and to lactating rats that had been exposed to sodium thiocyanate in drinking water during gestation and lactation. In contrast to the elevated levels of unlabeled thiocyanate in the plasma of the exposed rats, the radiolabeled material appeared at decreased levels in the plasma and milk, compared to the controls. The authors suggested that this reflected increased urinary clearance of thiocyanate after repeated dosing.

Limited data are available on the rate of thiocyanate excretion. Anderson and Chen ( 1940) administered 100 mg/ kg of sodium or potassium thiocyanate to rabbits, and found that thiocyanate levels in blood peaked within 6 hours for sodium thiocyanate, and within 6 24 hours for potassium thiocyanate. Thiocyanate was still detectable in the blood 1 week after rabbits were dosed with 300 mg/ kg sodium thiocyanate. Boulos et al. ( 1973) found that the half life of sodium EPA/ OW/ OST/ HECD Final draft III 30 thiocyanate in non pregnant goats was 16 hours. Although the species used is not a standard laboratory species and the dose was administered intravenously, this study still provides a general estimate of the half life of absorbed thiocyanate in other species.

Cyanate. Johnson et al. ( 1985) determined that the primary route of excretion for cyanate is through the lungs as CO 2. When mice were injected intraperitoneally with 160 mg/ kg [ 14C] potassium cyanate, 70% of the activity was recovered in expired air as 14CO 2 . Peak recovery of CO 2 occurred within 10 minutes, and the elimination half life was estimated to be 43 minutes.

Cyanamide. Cyanamide is primarily excreted in the urine as the metabolite Nacetylcyanamide Dietrich et al. ( 1976, not available for review, cited in Mertschenk et al., 1991)

determined that when [ 14C] cyanamide was administered intraperitoneally to rats, 93.9% of the applied dose was excreted in the urine within 6 hours and 1.39% of the dose was excreted in the expired CO 2. Obach et al. ( 1989) studied the excretion of cyanamide in rats and dogs following oral administration. Male Sprague Dawley rats received 2 mg/ kg cyanamide by either intravenous injection or oral gavage. Male beagle dogs received either 1, 2, or 4 mg/ kg cyanamide by intravenous injection or 4 mg/ kg cyanamide by oral gavage. Blood samples were collected at regular intervals following treatment and were analyzed for plasma cyanamide concentrations. In dogs, the elimination half life increased with increasing dose; the measured half life was 39, 47,

and 61 minutes following doses of 1, 2, and 4 mg/ kg respectively. However, the elimination halflife was constant regardless of route of exposure. In dogs treated with 4 mg/ kg, the half life was 61 minutes following intravenous injection and 62 minutes following oral gavage. In rats treated EPA/ OW/ OST/ HECD Final draft III 31 with 2 mg/ kg, the half life was 33 minutes following intravenous injection and 27 minutes following oral gavage. In contrast, the elimination half life for calcium cyanamide following oral administration is reported to be 92 minutes ( Loomis and Brien, 1983, not available for review,

cited in Obach et al., 1989)

E. Bioaccumulation, Retention, and Body Burden Little information is available on the bioaccumulation of cyanogen chloride or its metabolites.

Cyanogen chloride. The limited available data ( Aldridge and Evans, 1946) indicate that elimination may be slower than intake at moderate doses, leading to some accumulation.

Elevated thiocyanate levels were observed in the saliva of a single dog for several days after a single 6 hour inhalation exposure to cyanogen chloride ( Aldridge and Evans, 1946); interpretation of this result is limited by the small sample size. There is no information in the available literature on the body burden of cyanogen chloride.

Hydrogen cyanide and thiocyanate. These two chemicals are discussed together, since they readily interconvert. A study on the toxicokinetics of subchronic oral exposure of rats to cyanide found that only ~ 10% of the cyanide dose was eliminated per day ( Leuschner et al.,

1991). The authors did not conduct a mass balance analysis, but this result suggests that the detoxified cyanide was retained to some degree, and that the cyanide half life following subchronic exposure was longer than the half life following acute exposure. Data from a study of EPA/ OW/ OST/ HECD Final draft III 32 monkeys exposed to cyanide via inhalation also indicate a relatively long half life ( Purser et al.,

1984). The conclusion of slower excretion is supported by the finding that thiocyanate was still detectable in the blood one week following a single exposure ( Anderson and Chen, 1940).

Information on the body burden of cyanide is available from the ATSDR ( 1997)

Toxicological Profile for Cyanide.

Concentrations of HCN and its metabolite thiocyanate in blood serum and plasma, urine,

and saliva have been used as indicators of HCN exposure, particularly with populations with potentially high exposures ( workers at risk of occupational exposure, smokers, nonsmokers exposed to sidestream smoke, and those exposed to high dietary levels of HCN). In a study conducted by Chandra et al. ( 1988), workers exposed to approximately 0.2 to 0.8 ppm ( 0.2  0.9 mg/ m3) HCN in air and controls exposed to 0 to 14

g/ 100 mL, had blood HCN concentrations ranging from 0.54 to 28.4

g/ 100 mL for both workers and for controls. Urinary thiocyanate levels ranged from 0.05 to 2.8 mg/ mL for exposed workers, and 0.02 to 0.88 mg/ mL for the controls.

A number of investigators studied HCN levels in the blood serum and thiocyanate levels in the blood serum and plasma, urine, and saliva of smokers and nonsmokers. In general, serum HCN levels and plasma, serum, and saliva thiocyanate levels could distinguish between the two populations. The authors concluded that plasma thiocyanate levels below 20

mole/ L ( 1200

g/ L) indicated that passive smoking was unlikely, and concentrations above 80 to 85

mole/ L ( 4600  4900

g/ L) were a reliable indication of active smoking. However, Yamanaka et al. EPA/ OW/ OST/ HECD Final draft III 33 ( 1991) found that urine thiocyanate concentrations of smokers and nonsmokers were not significantly different. Chen et al. ( 1990) found that serum thiocyanate levels in 18 month old infants exposed to heavy environmental tobacco smoke (> 20 cigarettes a day smoked in the home) were significantly higher than those of unexposed infants ( p < 0.05). Mean concentrations were 36.2

mole/ L and 27.7

mole/ L for the exposed and unexposed infants, respectively.

Bottoms et al. ( 1982) and Hauth et al. ( 1984) found positive correlations between fetal umbilical serum thiocyanate levels and serum thiocyanate levels of smoking mothers. Hauth et al.

( 1984) found that the mean serum thiocyanate level of smoking mothers ( 95

mole/ L; 5.5

g/ mL) was significantly higher ( p < 0.001) than that of mothers exposed to passive smoke ( 35.9

mole/ L; 2.1

g/ mL) or that of nonsmoking mothers ( 32.3

mole/ L; 1.9

g/ mL). Similarly, the mean umbilical serum thiocyanate concentration ( 72

mole/ L; 4.8

g/ mL) in newborn infants of smoking mothers was significantly higher than the concentrations in newborn infants of passive smokers ( 25

mole/ L; 1.5

g/ mL) and nonsmokers ( 23

mole/ L; 1.3

g/ mL).

Data on elevated levels of thiocyanate in body fluids resulting from consumption of cyanide containing foods come primarily for populations in tropical regions that may consume large quantities of improperly processed food. Mlingi et al. ( 1992, 1993) and Tylleskar et al.

( 1992) reported urinary thiocyanate levels in the normal population of less than 100

mole/ L ( 5.8

g/ L) as compared to concentrations ranging from 350 to 1,120

mole/ L ( 20 to 265

g/ L)

among 4 populations exposed to high levels of dietary HCN caused by incomplete processing of cassava during drought. EPA/ OW/ OST/ HECD Final draft III 34 Cyanate and Cyanamide. Little information is available on the bioaccumulation of cyanate and cyanamide. The half life for cyanate and cyanamide following a single oral dose was less than two hours ( Johnson et al., 1985; Obach et al., 1989). These data suggest that these metabolites would be unlikely to be retained, but information on their half lives following repeated dosing would also be useful. No information was identified on the body burden of cyanate and cyanamide.

F. Summary of Toxicokinetics No data were located regarding the absorption of cyanogen chloride by the oral or dermal routes of exposure, although cyanogen chloride appears to be rapidly absorbed following inhalation exposure ( Aldridge and Evans, 1946). The absorption of known or potential metabolites of cyanogen chloride is not of concern, since these would be formed after cyanogen chloride has already been absorbed. No data were located regarding the distribution of cyanogen chloride. Both cyanide and thiocyanate appear to distribute freely through the body following absorption. Following absorption via all routes of exposure, cyanide has been found in the lung,

heart, blood, liver, brain, spleen, and kidney ( ATSDR, 1997). Thiocyanate does not cross the blood brain barrier ( Wood, 1975), but can cross the placenta ( Kreutler et al., 1978). Very little data are available on the distribution of cyanate and cyanamide. Both compounds were detected in the blood within minutes of administration in mice, rats, or dogs ( Johnson et al., 1985; Obach et al., 1986a). However, the calcium form of cyanamide appears to distribute more slowly,

peaking in the blood by 1 hour following oral administration ( Loomis and Brien, 1983). EPA/ OW/ OST/ HECD Final draft III 35 Early studies of cyanogen chloride ( Aldridge and Evans, 1946; Aldridge, 1951) indicate that, in animals exposed to cyanogen chloride by either intravenous injection or inhalation,

cyanogen chloride was not detected in the blood, but cyanide ( CN ) was detected as soon as 1 minute following the start of exposure. In addition, thiocyanate ( SCN ) was detected at double the background levels in blood and in saliva. Further studies characterizing the reaction products showed that cyanogen chloride is rapidly reduced to cyanide by glutathione in the blood ( Aldridge, 1951). These early studies concluded that at least 30 40% of the cyanogen chloride had been converted to cyanide at higher doses, while at least 60 80% was converted to cyanide at lower doses ( Aldridge and Evans, 1946; Midwest Research Institute, 1997). It is possible that the test system ( species differences or the specific blood component studied) affected the observed range of results. However, a consistent dose dependence of the amount of cyanogen chloride converted to cyanide has been observed regardless of the species from which blood was drawn or the component of blood studied. The degree of conversion to cyanide can not be determined more precisely, because none of the authors determined how much of the cyanogen chloride had been converted to thiocyanate ( either directly, or via cyanide). In addition, the authors did not determine if the total amount of cyanide and thiocyanate accounted for the total cyanogen chloride dose or if additional, unidentified metabolites were present. The degree of conversion of cyanogen chloride to cyanide at environmentally relevant doses is not known, but it would be expected that conversion to cyanide at these lower doses would be > 80%. Based on limited information regarding the aqueous chemistry of cyanogen chloride, other potential metabolites of cyanogen chloride include cyanate ( OCN ), cyanamide ( H 2 NCN), and chloride ion ( Cl), as well as the products of reactions with a variety of other cellular nucleophiles. Note, however, that no EPA/ OW/ OST/ HECD Final draft III 36 studies have been conducted to determine if these compounds are detected in vivo following cyanogen chloride administration.

The major metabolic pathway for cyanide is conversion to thiocyanate by either rhodanese or 3 mercaptopyruvate sulfur transferase. This pathway accounts for 60 80% of a cyanide dose.

Minor pathways include incorporation into a 1 carbon metabolic pool, or conversion to 2

aminothiazoline 4 carboxylic acid ( ATSDR, 1997). Rhodanese is a mitochondrial enzyme that is widely distributed throughout the body. It has been found in liver, lung, nasal passages, kidney,

and muscle ( Sylvester and Sander, 1990; Devlin et al., 1989a, b; Lewis et al., 1991); although the distribution of rhodanese among tissues varies widely in different species ( Himwich and Saunders,

1948; Drawbaugh and Marrs, 1987). Cyanide appears to be in equilibrium with thiocyanate in the body. Although the action of rhodanese is not reversible, there is an enzyme system, thiocyanate oxidase, that catalyzes the reaction of thiocyanate and hydrogen peroxide to form cyanide and sulfate ( Wood, 1975). Cyanate appears to be hydrolyzed to carbon dioxide and ammonia by the enzyme cyanase, which is located in the kidney, liver, and red blood cells ( Johnson et al., 1985).

The primary metabolic pathway for cyanamide is acetylation to form N acetylcyanamide ( Mertschenk et al., 1991). A second pathway has been demonstrated in vivo, but not in vitro. In this pathway, the enzyme catalase facilitates the interaction of cyanamide and hydrogen peroxide to form an unstable intermediate, which spontaneously decomposes to form cyanide and nitroxyl ( Shirota et al., 1987).

No information is available regarding the excretion of cyanogen chloride. Cyanide is primarily excreted in the urine as thiocyanate, although a small amount appears to be excreted in EPA/ OW/ OST/ HECD Final draft III 37 expired air as carbon dioxide ( ATSDR, 1997). The elimination half life in rats following acute oral administration has been estimated to be 14 minutes, with an undetermined longer half life following subchronic exposure ( Leuschner et al., 1991). Data in monkeys suggest a longer halflife based on the slow decrease in blood levels following a 30 minute inhalation exposure ( Purser et al., 1984). Thiocyanate appears to be excreted in the urine unchanged ( Wood et al., 1975).

Thiocyanate has a long half life; it was still detectable in the blood one week following exposure ( Anderson and Chen, 1940). The half life in nonpregnant goats was 16 hours ( Boulos et al.,

1973). Cyanate is primarily excreted in expired air as carbon dioxide, with a half life of 43 minutes ( Johnson et al, 1985). Cyanamide is primarily excreted in the urine as Nacetylcyanamide although a small amount is excreted in expired air as carbon dioxide ( Dietrich et al., 1976). The elimination half life is reported to be 62 minutes in dogs, and 27 minutes in rats following oral exposure ( Obach et al., 1989). No information was available on the half life of cyanate or cyanamide following repeated exposures. Overall, these data suggest the potential for some degree of thiocyanate retention after repeated exposure to sufficiently high levels of cyanogen chloride. Information on body burden was available only for cyanide and its metabolite thiocyanate. Concentrations of cyanide and its metabolite thiocyanate in blood serum and plasma,

urine, and saliva have been used as indicators of cyanide exposure, and are elevated in cigarette smokers and populations consuming large quantities of food containing cyanide ( e. g., improperly processed cassava).

Based on consideration of cyanogen chloride biochemistry and that of its known and putative metabolites, it is plausible that ingested cyanogen chloride is absorbed from the stomach and/ or intestine as the parent compound, and that most of its metabolism occurs in the EPA/ OW/ OST/ HECD Final draft III 38 gastrointestinal tract and liver. Metabolism in the blood after absorption from the intestine is also possible, as is reaction with nucleophiles in the intestine, or its contents. The high concentration of rhodanese in the liver would enhance the rate of conversion to thiocyanate from cyanide that is produced in the portal vein or liver. HCl production might result in transient pH decreases, but it appears that systemic acidosis would be unlikely at environmentally relevant doses.

Significant uncertainties exist in the kinetic data for cyanogen chloride, particularly in the studies which are relied upon to provide key conclusions regarding the metabolism of cyanogen chloride. These studies ( Aldridge and Evans, 1946; Aldridge, 1951) were conducted long before Good Laboratory Practices ( GLP) were implemented and before modern technology afforded the opportunity for sophisticated measurements. As a result, these authors' conclusions regarding cyanogen chloride metabolism in vivo are based on physiological responses rather than a more accurate measurement of tissue concentrations or metabolites. These uncertainties are compounded by the more modern study ( Midwest Research Institute, 1997), which was only a screening level in vitro assay and also did not quantify all possible metabolites. Nonetheless, the body of data do provide certain data that allow risk assessment conclusions to be drawn with a reasonable degree of confidence.

Once cyanogen chloride reaches the blood stream, it is rapidly metabolized ( within one minute) and the parent compound is no longer detected. Both cyanide and thiocyanate have been identified as metabolites following cyanogen chloride exposure. Although thiocyanate production could not be measured, cyanide production has been roughly quantified. An in vivo assay that measured physiological response to cyanogen chloride exposure compared to cyanide exposure EPA/ OW/ OST/ HECD Final draft III 39 suggested that about 30% of cyanogen chloride is converted to cyanide ( Aldridge and Evans,

1946). In vitro studies that measured cyanide production when cyanogen chloride was added to either whole blood or washed red blood cells confirmed that at the doses tested, at least 30% of cyanogen chloride is converted to cyanide in the blood ( actually, in the red blood cells) ( Aldridge and Evans, 1946; Midwest Research Institute, 1997). The in vitro studies also indicate that cyanide production is dependent on cyanogen chloride concentration. When 10 µ g/ L cyanogen chloride was added to blood, 60 80% was converted to cyanide; when  50 µ g/ L cyanogen chloride 30 40% was converted to cyanide. Species differences ( rabbit vs. rat) or different blood components ( whole blood vs. washed red blood cells) could be contributing to the wide range of responses. Metabolites other than cyanide and thiocyanate have not been identified, but may have been formed.

Given the available kinetic data for cyanogen chloride, the following risk assessment assumptions are reasonable for the development of health values for cyanogen chloride ( e. g.,

Health Advisories and reference dose). First, toxicity of cyanogen chloride is likely to be due to metabolites rather than the parent compound. Therefore, it is reasonable to base a risk assessment on metabolites given the lack of toxicity data on cyanogen chloride itself. Second, cyanide and thiocyanate are known, observed metabolites of cyanogen chloride. Therefore, it is reasonable to consider these chemicals as surrogates for cyanogen chloride in a quantitative risk assessment,

even though the exact quantitative relationship between cyanogen chloride and cyanide or thiocyanate production has not been adequately determined. The health protective nature of this approach, and associated uncertainties, are discussed in the context of the quantitation in Chapter 8, and the risk characterization in Chapter 9. EPA/ OW/ OST/ HECD Final draft III 40 It is plausible that additional metabolites are formed following cyanogen chloride exposure, in light of the limited available quantitative data on metabolism. Given the available information on water chemistry and metabolic pathways, three additional chemicals ( cyanate,

cyanamide, HCl) have been discussed here as potential metabolites. However, these chemicals have been dropped from the remainder of this document as potential surrogates for cyanogen chloride, primarily because they have not been identified experimentally. In addition, a preliminary toxicity assessment of these chemicals ( see results in Appendices C, D, and E)

indicates that a quantitative assessment based on data from cyanide or thiocyanate will be more conservative. Therefore, the remainder of this document focuses only on cyanogen chloride,

cyanide, and thiocyanate.


[Federal Register Volume 77, Number 181 (Tuesday, September 18, 2012)]
[Proposed Rules]
[Pages 57529-57531]
[FR Doc No: 2012-22890]

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2012-0937; Directorate Identifier 2011-NM-270-AD]
RIN 2120-AA64

Airworthiness Directives; The Boeing Company Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of proposed rulemaking (NPRM).

-----------------------------------------------------------------------

SUMMARY: We propose to adopt a new airworthiness directive (AD) for
certain The Boeing Company Model 737-800 series airplanes. This
proposed AD was prompted by reports of early fatigue cracks at chem-
mill areas on the crown skin panels. This proposed AD would require
repetitive inspections for cracking of the fuselage skin along chem-
mill steps at certain crown skin and shear wrinkle areas, and repair if
necessary. We are proposing this AD to detect and correct fatigue
cracking of the skin panel at the specified chem-mill step locations,
which could result in rapid decompression of the airplane.

DATES: We must receive comments on this proposed AD by November 2,
2012.

ADDRESSES: You may send comments, using the procedures found in 14 CFR
11.43 and 11.45, by any of the following methods:
     Federal eRulemaking Portal: Go to http://www.regulations.gov. Follow the instructions for submitting comments.
     Fax:<PHONE_NUMBER>.
     Mail: U.S. Department of Transportation, Docket
Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New
Jersey Avenue SE., Washington, DC 20590.
     Hand Delivery: Deliver to Mail address above between 9
a.m. and 5 p.m., Monday through Friday, except Federal holidays.
    For service information identified in this proposed AD, contact
Boeing Commercial Airplanes, Attention: Data & Services Management,
P.O. Box 3707, MC 2H-65, Seattle, WA 98124-2207; telephone 206-544-
5000, extension 1; fax<PHONE_NUMBER>; Internet https://www.myboeingfleet.com. You may review copies of the referenced service
information at the FAA, Transport Airplane Directorate; 1601 Lind
Avenue SW., Renton, Washington. For information on the availability of
this material at the FAA, call<PHONE_NUMBER>.

Examining the AD Docket

    You may examine the AD docket on the Internet at  http://www.regulations.gov; or in person at the Docket Management Facility
between 9 a.m. and 5 p.m., Monday through Friday, except Federal
holidays. The AD docket contains this proposed AD, the regulatory
evaluation, any comments received, and other information. The street
address for the Docket Office (phone:<PHONE_NUMBER>) is in the ADDRESSES
section. Comments will be available in the AD docket shortly after
receipt.

FOR FURTHER INFORMATION CONTACT: Wayne Lockett, Aerospace Engineer,
Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office,
1601 Lind Avenue SW., Renton, Washington 98057-3356; phone: (425) 917-
6447; fax:<PHONE_NUMBER>; email<EMAIL_ADDRESS>
SUPPLEMENTARY INFORMATION:

Comments Invited

    We invite you to send any written relevant data, views, or
arguments about this proposal. Send your comments to an address listed
under the ADDRESSES section. Include ``Docket No. FAA-2012-0937;
Directorate Identifier 2011-NM-270-AD'' at the beginning of your
comments. We specifically invite comments on the overall regulatory,
economic, environmental, and energy aspects of this proposed AD. We
will consider all comments received by the closing date and may amend
this proposed AD because of those comments.
    We will post all comments we receive, without change, to  http://www.regulations.gov, including any personal information you provide. We
will also post a report summarizing each substantive verbal contact we
receive about this proposed AD.

Discussion

    We received reports of early fatigue cracks near chem-mill areas on
the crown skin panels of Model 737-300, -400, and -500 series
airplanes. The cracks resulted from high stresses in the areas where
chem-mill pockets are adjacent to non-chem-mill areas. Although we have
not received any reports of this type of fuselage fatigue cracks on
Model 737-600, -700, -700C, -800, -900, or -900ER series airplanes, a
full-scale fatigue test article was inspected for skin cracks at
similar structural details and two chem-mill cracks were found that
occurred late in the testing program. This condition, if not detected
and corrected, could result in rapid decompression of the airplane.

Relevant Service Information

    We reviewed Boeing Service Bulletin 737-53-1311, dated October 21,
2011, for Model 737-800 series airplanes. That service bulletin
describes, among other things, procedures for doing repetitive external
detailed inspections and external non-destructive inspections (medium
frequency eddy current (MFEC), magneto optic imager (MOI), C-scan, or
ultrasonic phased array (UTPA) inspections) of the fuselage skin at
specified locations where chem-mill areas are adjacent to non-chem-mill
areas at antenna and door bearstrap installations, and shear wrinkle
areas at stringers 9 and 10 between stations 500E and 500G; and repairs
if necessary.
    Boeing Service Bulletin 737-53-1311, dated October 21, 2011, also
describes procedures for installing modification doublers in certain
locations, which involves an external detailed inspection and an
external non-destructive (MFEC, MOI, C-scan, or UTPA) inspection for
any cracking of the area to be modified prior to the doubler being
placed on that area, a high frequency eddy current inspection of all
existing holes for cracking as applicable, and contacting Boeing if
necessary. That service bulletin also specifies that when a
modification is accomplished, the repetitive inspection for the area
under the modification is no longer necessary.
    Boeing Service Bulletin 737-53-1311, dated October 21, 2011,
specifies an initial compliance time of 43,000 total flight cycles, or
1,500 to 2,100 flight cycles (depending on group/configuration) after
the original issue date of that service bulletin, whichever occurs
later. That service bulletin specifies a repetitive interval not to
exceed 1,500 flight cycles, 2,100 flight cycles, or 2,700 flight cycles
depending on inspection method and group configuration.
    For airplanes that have incorporated Boeing Business Jet (BBJ)
lower cabin altitude supplemental type certificate (STC) ST010697SE,
Boeing Service Bulletin 737-53-1311, dated October 21, 2011, specifies
that all initial compliance times specified in flight cycles must be
reduced to half of those specified in that service bulletin, and all
repeat interval compliance times specified in flight cycles must be
reduced to one-quarter of those specified in that service bulletin.

FAA's Determination

    We are proposing this AD because we evaluated all the relevant
information and determined the unsafe condition described previously is
likely to exist or

develop in other products of the same type design.

Proposed AD Requirements

    This proposed AD would require accomplishing the actions specified
in the service information described previously, except as discussed
under ``Differences Between the Proposed AD and the Service
Information.''

Similar Rulemaking

    The crown skin panels on Model 737-800 series airplanes are of a
similar design to those on Model 737-300, -400, -500, -600, -700, -
700C, -900, and -900ER series airplanes. Therefore, all these models
may be subject to the identified unsafe condition. We are considering
similar rulemaking for these additional models.

Differences Between the Proposed AD and the Service Information

    Boeing Service Bulletin 737-53-1311, dated October 21, 2011,
specifies to contact the manufacturer for disposition of certain repair
conditions, but this proposed AD would require repairing those
conditions in one of the following ways:
     In accordance with a method that we approve; or
     Using data that meet the certification basis of the
airplane, and that have been approved by the Boeing Commercial
Airplanes Organization Designation Authorization (ODA) whom we have
authorized to make those findings.
    Tables 3 and 4 in paragraph 1.E., ``Compliance,'' of Boeing Service
Bulletin 737-53-1311, dated October 21, 2011, specify post-modification
inspections at certain chem-mill step locations, which may be used in
support of compliance with section 121.1109(c)(2) or 129.109(c)(2) of
the Federal Aviation Regulations (14 CFR 121.1109(c)(2) or
129.109(c)(2)). However, this NPRM does not propose to require those
post-modification inspections. This difference has been coordinated
with Boeing.

Costs of Compliance

    We estimate that this proposed AD affects 441 airplanes of U.S.
registry.
    We estimate the following costs to comply with this proposed AD:

                                                 Estimated Costs
----------------------------------------------------------------------------------------------------------------
                                                                                Cost on U.S.
             Action                  Labor cost           Parts cost       Cost per  product       operators
----------------------------------------------------------------------------------------------------------------
Inspection of chem-mill step     30 work-hours x     None...............  $2,550 per          $1,124,550 per
 locations.                       $85 per hour =                           inspection cycle.   inspection cycle.
                                  $2,550 per
                                  inspection cycle.
----------------------------------------------------------------------------------------------------------------

    We have received no definitive data that would enable us to provide
cost estimates for the on-condition actions specified in this proposed
AD.

Authority for This Rulemaking

    Title 49 of the United States Code specifies the FAA's authority to
issue rules on aviation safety. Subtitle I, section 106, describes the
authority of the FAA Administrator. Subtitle VII: Aviation Programs,
describes in more detail the scope of the Agency's authority.
    We are issuing this rulemaking under the authority described in
Subtitle VII, Part A, Subpart III, Section 44701: ``General
requirements.'' Under that section, Congress charges the FAA with
promoting safe flight of civil aircraft in air commerce by prescribing
regulations for practices, methods, and procedures the Administrator
finds necessary for safety in air commerce. This regulation is within
the scope of that authority because it addresses an unsafe condition
that is likely to exist or develop on products identified in this
rulemaking action.

Regulatory Findings

    We determined that this proposed AD would not have federalism
implications under Executive Order 13132. This proposed AD would not
have a substantial direct effect on the States, on the relationship
between the national Government and the States, or on the distribution
of power and responsibilities among the various levels of government.
    For the reasons discussed above, I certify this proposed
regulation:
    (1) Is not a ``significant regulatory action'' under Executive
Order 12866,
    (2) Is not a ``significant rule'' under the DOT Regulatory Policies
and Procedures (44 FR 11034, February 26, 1979),
    (3) Will not affect intrastate aviation in Alaska, and
    (4) Will not have a significant economic impact, positive or
negative, on a substantial number of small entities under the criteria
of the Regulatory Flexibility Act.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Incorporation by
reference, Safety.

The Proposed Amendment

    Accordingly, under the authority delegated to me by the
Administrator, the FAA proposes to amend 14 CFR part 39 as follows:

PART 39--AIRWORTHINESS DIRECTIVES

    1. The authority citation for part 39 continues to read as follows:

    Authority:  49 U.S.C. 106(g), 40113, 44701.

Sec.  39.13  [Amended]

    2. The FAA amends Sec.  39.13 by adding the following new
airworthiness directive (AD):
The Boeing Company: Docket No. FAA-2012-0937; Directorate Identifier
2011-NM-270-AD.

(a) Comments Due Date

    We must receive comments by November 2, 2012.

(b) Affected ADs

    None.

(c) Applicability

    This AD applies to The Boeing Company Model 737-800 series
airplanes, certificated in any category, as identified in Boeing
Service Bulletin 737-53-1311, dated October 21, 2011.

(d) Subject

    Joint Aircraft System Component (JASC)/Air Transport Association
(ATA) of America Code 53; Fuselage.

(e) Unsafe Condition

    This AD was prompted by reports of early fatigue cracks at chem-
mill areas on the crown skin panels. We are issuing this AD to
detect and correct fatigue cracking of the skin panel at the
specified chem-mill step locations, which could result in rapid
decompression of the airplane.

(f) Compliance

    Comply with this AD within the compliance times specified,
unless already done.

(g) Inspections of Crown Skin Areas

    At the applicable time specified in paragraph 1.E.,
``Compliance,'' of Boeing Service Bulletin 737-53-1311, dated
October 21, 2011, except as required by paragraph (k) of this AD: Do
an external detailed inspection and an external non-destructive
inspection (a medium frequency eddy current (MFEC), magneto optic
imager (MOI), C-scan, or ultrasonic phased array (UTPA) inspection)
for cracking in the fuselage skin along the chem-mill steps at
certain locations specified in, and in accordance with, Boeing
Service Bulletin 737-53-1311, dated October 21, 2011. Repeat the
inspections thereafter at the applicable times specified in
paragraph 1.E., ``Compliance,'' of Boeing Service Bulletin 737-53-
1311, dated October 21, 2011.

(h) Inspections of Shear Wrinkle Areas

    For Groups 2, 5, and 6 airplanes as identified in Boeing Service
Bulletin 737-53-1311, dated October 21, 2011: At the applicable time
specified in paragraph 1.E., ``Compliance,'' of Boeing Service
Bulletin 737-53-1311, dated October 21, 2011, except as required by
paragraph (k) of this AD, do an external detailed inspection and an
external non-destructive inspection (MFEC, MOI, C-scan, or UTPA) for
cracking in the fuselage skin along the chem-mill steps at certain
shear wrinkle locations specified in, and in accordance with, Boeing
Service Bulletin 737-53-1311, dated October 21, 2011. Repeat the
inspections required by paragraph (h) of this AD thereafter at the
applicable times specified in paragraph 1.E., ``Compliance,'' of
Boeing Service Bulletin 737-53-1311, dated October 21, 2011.

(i) Repairs

    If any cracking is found during any inspection required by
paragraphs (g) and (h) of this AD, before further flight, repair the
cracking using a method approved in accordance with the procedures
specified in paragraph (m) of this AD. Accomplishing the repair
approved in accordance with the procedures specified in paragraph
(m) of this AD terminates the repetitive inspection requirement for
that area under the repair only.

(j) Optional Terminating Modification

    Modification of an inspection area specified in paragraph (g) of
this AD, including doing an external detailed inspection and an
external non-destructive inspection (MFEC, MOI, C-scan, or UTPA) for
cracking of the area to be modified, and a high frequency eddy
current inspection of all existing holes for cracking as applicable,
in accordance with the Accomplishment Instructions of Boeing Service
Bulletin 737-53-1311, dated October 21, 2011, terminates the
repetitive inspections required by paragraph (g) of this AD for that
area only. If any cracking is found during any inspection described
by this paragraph, before further flight, repair the cracking using
a method approved in accordance with the procedures specified in
paragraph (m) of this AD.

(k) Service Bulletin Exception

    Boeing Service Bulletin 737-53-1311, dated October 21, 2011,
specifies compliance times ``after the original issue date of this
service bulletin.'' However, this AD requires compliance within the
specified compliance times ``after the effective date of this AD.''

(l) Post-Modification Inspections

    The post-modification inspections specified in Tables 3 and 4 of
paragraph 1.E., ``Compliance,'' of Boeing Service Bulletin 737-53-
1311, dated October 21, 2011, are not required by this AD.

    Note 1 to paragraph (l) of this AD:  The damage tolerance
inspections specified in Tables 3 and 4 of paragraph 1.E.,
``Compliance,'' of Boeing Service Bulletin 737-53-1311, dated
October 21, 2011, may be used in support of compliance with section
121.1109(c)(2) or 129.109(c)(2) of the Federal Aviation Regulations
(14 CFR 121.1109(c)(2) or 14 CFR 129.109(c)(2)). The actions
specified in Part 5 of the Accomplishment Instructions and
corresponding figures of Boeing Service Bulletin 737-53-1311, dated
October 21, 2011, are not required by this AD.

(m) Alternative Methods of Compliance (AMOCs)

    (1) The Manager, Seattle Aircraft Certification Office (ACO),
FAA, has the authority to approve AMOCs for this AD, if requested
using the procedures found in 14 CFR 39.19. In accordance with 14
CFR 39.19, send your request to your principal inspector or local
Flight Standards District Office, as appropriate. If sending
information directly to the manager of the ACO, send it to the
attention of the person identified in the Related Information
section of this AD. Information may be emailed to<EMAIL_ADDRESS>    (2) Before using any approved AMOC, notify your appropriate
principal inspector, or lacking a principal inspector, the manager
of the local flight standards district office/certificate holding
district office.
    (3) An AMOC that provides an acceptable level of safety may be
used for any repair required by this AD if it is approved by the
Boeing Commercial Airplanes Organization Designation Authorization
(ODA) that has been authorized by the Manager, Seattle ACO, to make
those findings. For a repair method to be approved, the repair must
meet the certification basis of the airplane, and the approval must
specifically refer to this AD.

(n) Related Information

    (1) For more information about this AD, contact Wayne Lockett,
Aerospace Engineer, Airframe Branch, ANM-120S, FAA, Seattle Aircraft
Certification Office, 1601 Lind Avenue SW., Renton, Washington
98057-3356; phone:<PHONE_NUMBER>; fax:<PHONE_NUMBER>; email:
<EMAIL_ADDRESS>    (2) For service information identified in this AD, contact
Boeing Commercial Airplanes, Attention: Data & Services Management,
P.O. Box 3707, MC 2H-65, Seattle, WA 98124-2207; telephone 206-544-
5000, extension 1; fax<PHONE_NUMBER>; Internet https://www.myboeingfleet.com. You may review copies of the referenced
service information at the FAA, Transport Airplane Directorate, 1601
Lind Avenue SW., Renton, Washington. For information on the
availability of this material at the FAA, call<PHONE_NUMBER>.

    Issued in Renton, Washington, on September 4, 2012.
Ali Bahrami,
Manager, Transport Airplane Directorate, Aircraft Certification
Service.
[FR Doc. 2012-22890 Filed 9-17-12; 8:45 am]
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[Federal Register Volume 85, Number 19 (Wednesday, January 29, 2020)]
[Notices]
[Page 5204]
[FR Doc No: 2020-01541]

-----------------------------------------------------------------------

ENVIRONMENTAL PROTECTION AGENCY

[EPA-HQ-OECA-2013-0342; FRL-10004-80-OMS]

Information Collection Request Submitted to OMB for Review and
Approval; Comment Request; NESHAP for Lime Manufacturing (Renewal)

AGENCY: Environmental Protection Agency (EPA).

ACTION: Notice.

-----------------------------------------------------------------------

SUMMARY: The Environmental Protection Agency (EPA) has submitted an
information collection request (ICR), NESHAP for Lime Manufacturing (40
CFR part 63, subpart AAAAA) (EPA ICR Number 2072.08, OMB Control Number
2060-0544), to the Office of Management and Budget (OMB) for review and
approval in accordance with the Paperwork Reduction Act. This is a
proposed extension of the ICR, which is currently approved through
March 31, 2020. Public comments were previously requested, via the
Federal Register, on May 6, 2019 during a 60-day comment period. This
notice allows for an additional 30 days for public comments. A fuller
description of the ICR is given below, including its estimated burden
and cost to the public. An agency may neither conduct nor sponsor, and
a person is not required to respond to, a collection of information
unless it displays a currently valid OMB control number.

DATES: Additional comments may be submitted on or before February 28,
2020.

ADDRESSES: Submit your comments, referencing Docket ID Number EPA-HQ-
OECA-2013-0342, to: (1) EPA online using www.regulations.gov (our
preferred method), or by email to<EMAIL_ADDRESS>or by mail to:
EPA Docket Center, Environmental Protection Agency, Mail Code 28221T,
1200 Pennsylvania Ave. NW, Washington, DC 20460; and (2) OMB via email
to<EMAIL_ADDRESS>Address comments to OMB Desk Officer
for EPA.
    EPA's policy is that all comments received will be included in the
public docket without change, including any personal information
provided, unless the comment includes profanity, threats, information
claimed to be Confidential Business Information (CBI), or other
information whose disclosure is restricted by statute.

FOR FURTHER INFORMATION CONTACT: Patrick Yellin, Monitoring,
Assistance, and Media Programs Division, Office of Compliance, Mail
Code 2227A, Environmental Protection Agency, 1200 Pennsylvania Ave. NW,
Washington, DC 20460; telephone number:<PHONE_NUMBER>; fax number:
(202) 564-0050; email address<EMAIL_ADDRESS>
SUPPLEMENTARY INFORMATION: Supporting documents which explain in detail
the information that the EPA will be collecting are available in the
public docket for this ICR. The docket can be viewed online at
www.regulations.gov, or in person at the EPA Docket Center, WJC West,
Room 3334, 1301 Constitution Ave. NW, Washington, DC. The telephone
number for the Docket Center is<PHONE_NUMBER>. For additional
information about EPA's public docket, visit: http://www.epa.gov/dockets.
    Abstract: The National Emission Standards for Hazardous Air
Pollutants (NESHAP) for Lime Manufacturing (40 CR Part 63, Subpart
AAAAA) apply to existing facilities and new facilities that either emit
or has the potential to emit any single hazardous air pollutant (HAP)
at a rate of 9.07 megagrams (10 tons) or more per year or any
combination of HAP at a rate of 22.68 megagrams (25 tons) or more per
year from all emission sources at the plant site. This subpart covers
lime kilns, their associated coolers, and processed stone handling
(PSH) operation systems located at a lime manufacturing plant that is a
major source. New facilities include those that commenced construction,
modification or reconstruction after the date of proposal. The EPA
proposed revised standards to the NESHAP for Lime Manufacturing on
September 16, 2019 (84 FR 48708), however, the proposed amendments have
not been finalized; therefore, the burden reflected in this ICR does
not consider burden from the proposed amendments, but is based on the
existing standards. This information is being collected to assure
compliance with 40 CFR part 63, subpart AAAAA.
    In general, all NESHAP standards require initial notifications,
performance tests, and periodic reports by the owners/operators of the
affected facilities. They are also required to maintain records of the
occurrence and duration of any startup, shutdown, or malfunction in the
operation of an affected facility, or any period during which the
monitoring system is inoperative. These notifications, reports, and
records are essential in determining compliance, and are required of
all affected facilities subject to NESHAP.
    Form Numbers: None.
    Respondents/affected entities: New and existing lime manufacturing
facilities that are major sources of HAP.
    Respondent's obligation to respond: Mandatory (40 CFR part 63,
subpart AAAAA).
    Estimated number of respondents: 37 (total).
    Frequency of response: Initially, occasionally, and semiannually.
    Total estimated burden: 9,700 hours (per year). Burden is defined
at 5 CFR 1320.3(b).
    Total estimated cost: $1,460,000 (per year), which includes
$335,000 in annualized capital/startup and/or operation & maintenance
costs.
    Changes in the Estimates: There is a decrease in the total
estimated burden as currently identified in the OMB Inventory of
Approved Burdens. This decrease is not due to any program changes. The
change in the burden and cost estimates occurred due to several
factors. First, as part of a recent inventory of facilities subject to
the NESHAP for Lime Manufacturing by OAQPS, including consultations
with industry representatives and industry trade associations, EPA has
concluded that the number of sources subject to the regulation has
decreased. Second, the recent inventory revealed an increase in the
number of sources using bag leak detectors to comply with regulations,
leading to an increase in O&M costs. The overall result is a decrease
in burden hours and costs.

Courtney Kerwin,
Director, Regulatory Support Division.
[FR Doc. 2020-01541 Filed 1-28-20; 8:45 am]
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