UNITED STATES ENVIRONMENTAL PROTECTION AGENCY WASHINGTON, D. C. 20460 OFFICE OF PREVENTION, PESTICIDES AND TOXIC SUBSTANCES MEMORANDUM July 10, 2006 SUBJECT: Sodium Cyanide Revised HED Risk Assessment for Tolerance Reassessment Eligibility Decision ( TRED) Document PC Code No. 074002; DP Barcode No. 318015 FROM: Becky Daiss Environmental Health Scientist Reregistration Branch 4 Health Effects Division ( 7509C)

THROUGH: Susan V. Hummel Branch Senior Scientist Reregistration Branch 4 Health Effects Division ( 7509C)

TO: Wilhelmena Livingston Chemical Review Manager Reregistration Branch 1 Special Review and Registration Division ( 7508C)

Attached is Health Effects Division's ( HED's) revised risk assessment of sodium cyanide for purposes of issuing a Tolerance Reassessment Eligibility Decision ( TRED) Document for this active ingredient. The risk assessment has been revised to incorporate new residue data submitted by the registrant and water monitoring data provided by the Arizona Department of Environmental Quality. The disciplinary science chapters and other supporting documentation are incorporated into the risk assessment or included as appendices as follows:

Hazard Identification Assessment; Bill Dykstra  Section 4 and Appendices 1 & 2 Residue Chemistry Assessment; Thurston Morton ( D30275, 6/ 29/ 06) Dietary Exposure and Risk Assessment; Becky Daiss  Section 6 Occupational and Residential Exposure Assessment, David Jaquith ( D318017, 4/ 4/ 06) Drinking Water Assessment; Faruque Khan ( D318020, 2/ 7/ 06) Page 2 of 44 TABLE OF CONTENTS pg. 1.0 EXECUTIVE SUMMARY ............................................................................................. 4 2.0 INGREDIENT PROFILE................................................................................................ 8 2.1 Summary of Registered and Proposed Uses ..................................................................... 8 2.2 Structure, Nomenclature and Physical/ Chemical Properties .............................................. 9 3.0 METABOLISM ASSESSMENT..................................................................................... 9 3.1 Comparative Metabolic Profile ........................................................................................ 9 3.1.1 Metabolism in Mammals....................................................................................... 9 3.1.2 Plant Metabolism ............................................................................................... 10 3.1.3 Livestock Metabolism ....................................................................................... 10 3.2 Environmental Degradation .......................................................................................... 10 3.3 Metabolites and Degradates .......................................................................................... 11 3.4 Summary of Residues for Tolerance Expression and Risk Assessment ........................... 11 4.0 HAZARD CHARACTERIZATION/ ASSESSMENT .................................................... 11 4.1 Hazard Characterization ............................................................................................... 11 4.2 FQPA Hazard Considerations ....................................................................................... 19 4.2.1 Adequacy of the Toxicity Data Base .................................................................. 19 4.2.2 Evidence of Neurotoxicity ................................................................................. 19 4.2.3 Developmental Toxicity Studies ........................................................................ 21 4.2.4 Reproductive Toxicity Studies ........................................................................... 23 4.2.5 Pre and/ or Postnatal Toxicity ............................................................................ 25 4.2.6 Recommendation for a Developmental Neurotoxicity Study ............................... 25 4.3 FQPA Safety Factor ...................................................................................................... 25 4.4 Hazard Identification and Toxicity Endpoint Selection ................................................... 26 4.4.1 Acute Reference Dose  General Population....................................................... 26 4.4.2 Chronic Reference Dose..................................................................................... 27 4.4.3 Dermal Absorption............................................................................................. 29 4.4.4 Dermal Exposure All Durations.......................................................................... 29 4.4.5 Inhalation Exposure All Durations...................................................................... 29 4.4.6 Margins of Exposure.......................................................................................... 30 4.4.7 Recommendation for Aggregate Exposure Risk Assessments ............................. 30 4.4.8 Classification of Carcinogenic Potential.............................................................. 30 4.4.9 Summary of Endpoints Selected for Risk Assessment ......................................... 31 4.5 Endocrine Disruption..................................................................................................... 31 5.0 PUBLIC HEALTH DATA............................................................................................ 32 6.0 DIETARY EXPOSURE ASSESSMENT ...................................................................... 32 6.1 Dietary Profile ............................................................................................................... 32 6.1.1 Magnitude of the Residue in Plants and Animals................................................. 32 Page 3 of 44 6.1.2 Residue Analytical Method................................................................................. 33 6.2 Drinking Water Profile................................................................................................... 33 6.3 Dietary Exposure and Risk............................................................................................. 33 7.0 OCCUPATIONAL EXPOSURE AND RISK................................................................ 36 7.1 Regulatory Standards..................................................................................................... 36 7.2 Exposure Monitoring Study........................................................................................... 36 7.3 Inhalation Exposure and Risk......................................................................................... 37 7.4 Dermal Exposure and Risk............................................................................................. 38 8.0 AGGREGATE EXPOSURE AND RISK ...................................................................... 38 9.0 CUMULATIVE RISK................................................................................................... 38 10.0 DATA NEEDS.............................................................................................................. 38 10.1 Residue Chemistry Data Requirements........................................................................... 38 10.2 Toxicology Data Requirements...................................................................................... 39 APPENDICES 1.0 GUIDELINE TOXICOLOGY DATA SUMMARY....................................................... 40 2.0 NON CRITICAL TOXICOLOGY STUDIES ............................................................... 41 3.0 REFERENCES.............................................................................................................. 41 Page 4 of 44 1.0 EXECUTIVE SUMMARY This assessment provides information to support the issuance of a risk management decision document known as a Tolerance Reassessment Eligibility Decision ( TRED) Document for sodium cyanide. EPA's pesticide reregistration process provides for the review of older pesticides ( those initially registered prior to November 1984) under the Federal Insecticide, Fungicide, and Rodenticide Act ( FIFRA) to ensure that they meet current scientific and regulatory standards. The process considers the human health and ecological effects of pesticides and incorporates a reassessment of tolerances ( pesticide residue limits in food) to ensure that they meet the safety standard established by the Food Quality Protection Act ( FQPA) of 1996. This document addresses the exposures and risks associated with dietary, drinking water, and residential uses of cyanide. Occupational exposures were partially addressed in Reregistration Eligibility Decision ( RED) for Sodium Cyanide published in 1994. Occupational exposures not addressed in the RED are also assessed in this document.

Use Profile Sodium cyanide is used as a predacide/ rodenticide and as a pesticide. As a predacide/ rodenticide, it is used as a single dose poison in the M 44 ejector device to control animals that prey upon livestock and threatened or endangered species or that are vectors of communicable disease. For application, each capsule is loaded into an ejector mechanism of an M 44 device which has been pounded into the ground for use. The capsule holder is treated with a scent used to attract canids to the unit. When an animal tugs at the capsule holder, a springdriven plunger ejects the sodium cyanide capsule into its mouth. This product is limited to use only by trained and certified applicators under the direct supervision of a government agency.

As an insecticide, sodium cyanide is used a source of hydrocyanic gas for quarantine fumigation of surface pests on citrus. Currently, there are no active registrations for sodium cyanide with food/ feed uses. However, there is one Special Local Needs ( SLN) food/ feed use registration for sodium cyanide. The SLN end use product is formulated as a granular containing 98% sodium cyanide as the active ingredient ( ai). Sodium cyanide is applied to citrus as a postharvest fumigant. It used as a source of hydrogen cyanide gas. Sodium cyanide is used in California to control red scale on fresh market citrus bound for Arizona. It is applied by professional applicators only. A tolerance for residues of the insecticide hydrogen cyanide from postharvest fumigation as a result of application of sodium cyanide is established at 50 ppm in or on citrus fruit ( 40 CFR § 180.130). There are no products available for residential application. OPP's Biological and Economical Analysis Division ( BEAD) estimates that approximately 2800 pounds of sodium cyanide are used annually on agricultural crops ( i. e., fresh citrus commodities) in California ( personal communication, Bill Chism, BEAD). Page 5 of 44 Regulatory History Sodium Cyanide is a FIFRA List C reregistration pesticide. The 1994 RED assessed only the use of sodium cyanide as a predacide/ rodenticide. The Agency issued a Data Call In ( DCI) for sodium cyanide in September, 1992 requiring additional product chemistry and ecological effects data. The 1994 RED reflects a reassessment of all data submitted in response to the 1992 DCI. The 1994 RED determined that the data were sufficient to allow the Agency to assess the registered predacide uses of sodium cyanide and to determine that sodium cyanide could be used without resulting in unreasonable adverse effects to humans and the environment. This TRED addresses the FQPA requirement for reassessment of tolerances for hydrogen cyanide and provides an assessment of worker exposure associated with use of sodium cyanide as a source of hydrocyanic gas for fumigation of surface pests on citrus.

Hazard Identification The toxicology database for hydrogen cyanide is incomplete. No guideline studies are available. All of the critical studies are cited from the open literature. Data on all forms of cyanide ( e. g., hydrogen, sodium, potassium cyanide etc.) have been used to identify hydrogen cyanide toxicity for this assessment. Hydrogen cyanide is extremely acutely toxic by all exposure routes.

All forms of cyanide, hydrogen, sodium, and potassium, are extremely acutely toxic by the oral route. Based on an analysis of case history data the lowest fatal oral dose of hydrogen cyanide for an average adult human is estimated by FDA to be 1 mg/ kg. The lowest reported fatal dose of cyanide ( unspecified form) in humans was estimated to be 0.56 mg/ kg based on incidence data published in 1938. The acute oral fatal dose of potassium cyanide in rats is 10 15 mg/ kg, which is equivalent to 4 6 mg/ kg hydrogen cyanide. Results of clinical trials of Laetrile to treat cancer also provide evidence of the acute oral toxicity of hydrogen cyanide. Laetrile, also known as amygdalin, is a plant compound that produces cyanide. Use of Laetrile has been shown to produce side effects of cyanide poisoning  which can produce a range of symptoms, including death. In a clinical trial of Laetrile to treat human cancer, the single dose of 0.5 g of amygdalin was determined to be minimally toxic; a single dose of 0.5 g of amygdalin is equivalent to 0.4 mg/ kg hydrogen cyanide/ day. The double dose ( two 0.5 g doses at an administration) was generally regarded as frankly toxic producing increased blood levels and associated increase in the incidence and severity of some of the toxic signs and symptoms.

The dose effect curve of the acute inhalation effects in humans is steep. Slight effects occur at exposure levels of 20 40 mg/ m3, 150 mg/ m3 is likely to be fatal within 30 minutes, 200 mg/ m3 is likely to be fatal after 10 minutes, and 300 mg/ m3 is immediately fatal.

An average LD50 value for human dermal exposure is estimated to be 100 mg/ kg HCN ( Toxicity Category I). Air concentrations of 7000 12,000 mg/ m3 HCN were estimated to be fatal after a 5 minute exposure of workers with self contained respirators without effective skin Page 6 of 44 protection. Cyanides are weakly irritating to the skin and eye. No data are available on sensitizing properties.

The primary effects of acute cyanide exposure in humans are central nervous system and cardiovascular disturbances. Typical signs of acute cyanide poisoning include tachypnea, headache, vertigo, lack of motor coordination, weak pulse, cardiac arrhythmias, vomiting, stupor, convulsions, and coma.

Hydrogen cyanide exhibits relatively low subchonic and chronic toxicity by the oral route. In a 13 week repeated dose toxicity study in which sodium cyanide was administered in the drinking water, there were no mortalities, no clinical signs, and no histopathological effects in the brain, thyroid, or other organs of rats and mice exposed to doses up to 12.5 and 26 mg/ kg/ day. A 2 year rat feeding study with hydrogen cyanide fumigated food containing residues up to 10.8 mg/ kg/ day showed no treatment related effects. In this 2 year study, rats ingested 2 to 3 times the fatal acute dose of hydrogen cyanide each day throughout their lifetime without any measurable effects. Significantly, animals in the subchronic and chronic studies showed definite increases in thiocyanate concentrations indicating that metabolic detoxification of hydrogen cyanide had occurred. Thiocyanate is the less toxic primary metabolite of cyanide. Hydrogen cyanide is readily converted to thiocyanate in the liver by the enzyme rhodanese. This metabolic conversion is the major detoxification mechanism for hydrogen cyanide. Results of both animal and human FDA studies indicate that as long as the oral intake of hydrogen cyanide does not exceed the body

s detoxification mechanisms via the formation of thiocyanate, hydrogen cyanide can be ingested in the form of dietary residues for prolonged periods without harm.

There are neurotoxicity, developmental and reproductive studies available with naturally occurring cyanides or cyanide salts in the open literature. However, there are no EPA guideline studies of these types of studies available. Based on literature studies, neurotoxic effects are a major occurrence across species from exposure to cyanide in its various forms. There are no developmental or reproductive toxicity studies for hydrogen cyanide. Developmental and reproductive studies with other forms of cyanide were available and reviewed for this assessment. The weight of the evidence of available data indicates that cyanide induces developmental effects only at doses or concentrations that are overtly toxic to the maternal animals.

Because there are no EPA guideline neurotoxicity, developmental and reproductive studies available, an assessment of FQPA hazard considerations are based on the available open literature citations. Based on the available data, there was no qualitative or quantitative increased susceptibility in postnatal offspring toxicity and there is a low degree of concern for residual uncertainties for pre and/ or post natal susceptibility. Therefore, it is recommended that the FQPA safety factor be reduced to 1x for the hydrogen cyanide risk assessment.

There are no guideline studies and no available open literature studies on the carcinogenic potential of cyanide. However, acute lethal effects of cyanide likely preclude the need for Page 7 of 44 carcinogenic evaluation. Hydrogen cyanide has been evaluated for mutagenic potential with mixed results.

Cyanide gas and salts are rapidly absorbed following inhalation and oral exposure. They are more slowly absorbed by dermal exposure. Animal studies have shown that cyanide does not accumulate in the blood and tissues following chronic oral exposure. Cyanide metabolites are mainly excreted in the urine, with small amounts excreted through the lungs ( ATSDR, 2004). Following inhalation, cyanide is rapidly distributed throughout the body, with measurable levels detected in all organs.

Cyanide is a rapid acting blocker of oxygen utilization at the cellular level. Hydrogen cyanide binds with cytochrome oxidase ( a ferric enzyme) in the electron transport system and inhibits the exchange of oxygen from the blood to the tissues by the mechanism of competitive inhibition.

Dose Response Assessment Toxicological endpoints were selected for dietary and occupational exposure via inhalation, the relevant scenarios for exposure to hydrogen cyanide for this TRED. The acute RfD for the general population was selected based on published data from a clinical trial of amygdalin ( Laetrile) to treat human cancer. Hydrogen cyanide is extremely acutely toxic at doses lower than doses at which chronic effects are observed. Therefore, the acute endpoint is considered protective for chronic toxicity and a chronic RfD was not selected. An inhalation exposure endpoint for all durations was selected from a subchronic hydrogen cyanide inhalation toxicity study in rats based on the effect of mortality.

An uncertainty factor ( UF) of 100 was applied to the acute RfD based on application of a 10X for intraspecies variations, and 10X for lack of a LOAEL, steep dose response curve, and severity of toxic effect. The target level of concern ( LOC) or margin of exposure ( MOE) for occupational exposure via inhalation is 30X ( 3X interspecies factor and 10x intraspecies factor).

Exposure/ Risk Assessment and Risk Characterization Risk assessments were conducted for acute dietary and occupational exposure pathways only based on label prescribed uses. Chronic dietary exposure was not assessed because hydrogen cyanide is severely acutely toxic at doses lower than those at which chronic effects are observed i. e., protecting for acute effects will also protect against chronic toxicity. Drinking water exposures were not assessed because the Environmental Fate and Effects Division ( EFED) does not anticipate significant exposure from hydrogen cyanide in surface or ground water based on the use pattern. An aggregate assessment of risk from the combined food and non food exposures was not conducted because there are no residential uses of hydrogen cyanide. Residential exposures resulting from citrus fumigation are not expected based on monitoring data from the single facility at which hydrogen cyanide fumigation occurs. HED conducted a somewhat refined Page 8 of 44 acute probabilistic dietary assessment for hydrogen cyanide. Recently submitted field trial data were used to assess potential exposure and risk from consumption of citrus treated with hydrogen cyanide. HED's acute dietary assessment indicates that acute dietary exposure estimates are below HED's level of concern. Data from a worker exposure inhalation monitoring study on fumigations conducted at the hydrogen cyanide fumigation facility were used to assess occupational exposure and risk from citrus fumigation. Dermal exposures are not expected based on the limited use pattern and were therefore not assessed. Worker exposure and risk estimates indicate that occupational exposures are below HED's level of concern.

Use of Human Studies This risk assessment relies in part on data from studies in which adult human subjects were intentionally exposed to a pesticide or other chemical. These studies, listed below, have been determined to require a review of their ethical conduct. They are also subject to review by the Human Studies Review Board ( HSRB). All of the listed studies have received the appropriate review by the HSRB and have been determined to be ethically and scientifically acceptable.

Moertel, CG et al ( 1982) A Clinical Trial of Amygdalin ( Laetrile) in the Treatment of Human Cancer. New England Journal of Medicine, Vol. 306, No. 4: 201 206 ( MRID 46769602).

Moertel, CG et al ( 1981) A Pharmacologic and Toxicological Study of Amygdalin. JAMA, Vol. 245, No. 6: 591 594 ( MRID 46769601)

2.0 INGREDIENT PROFILE 2.1 Summary of Registered and Proposed Uses There are eight active registrations for sodium cyanide and one SLN according to the Office of Pesticide Programs Information Network ( OPPIN). Table 1 provides summary information on registered products and uses.

Table 1. Active Label Registrations for Sodium Cyanide Reg # Name Formulation Government Entity/ Company % ai 13808 8 M 44 Cyanide Capsules Capsule South Dakota Dept of Agriculture 91.06 33858 2 M 44 Cyanide Capsules Capsule Texas Department of Agriculture 91.06 35975 2 M 44 Cyanide Capsules Capsule Montana Department of Livestock 91.06 35978 1 M 44 Cyanide Capsules Capsule Wyoming Dept of Agriculture 91.06 39260 1 M 44 Cyanide Capsules Capsule Navajo Fish & Wildlife Department 91.06 39508 1 M 44 Cyanide Capsules Capsule New Mexico Department of Agriculture 91.06 56228 15 M 44 Cyanide Capsules Capsule U. S. Department of Agriculture 91.06 56228 32 M 44 Cyanide Capsules Capsule U. S. Department of Agriculture 91.06 CA840006 Sodium Cyanide Powder Washburn & Sons 98 Page 9 of 44 2.2 Structure, Nomenclature, and Physical/ Chemical Properties The nomenclature and physicochemical properties of hydrogen cyanide are provided in Tables 2 and 3.

TABLE 2. Test Compound Nomenclature Compound Sodium Cyanide Hydrogen Cyanide Chemical Structure NaCN HC= N Common Name sodium cyanide hydrogen cyanide Synonyms Hydrocyanic acid, prussic acid, formonitrile, formic anammonide, carbon hydride nitride, cyclon cyanobrik, cyanogran, sodium cyanide, hydrocyanic acid sodium salt, cymag CAS # 74 90 8 143 33 9 PC Code 045801 074002 Current Food/ Feed Site Registration Citrus Citrus Source: OSHA, 2004 TABLE 3. Physicochemical Properties of the Technical Grade Test Compound Parameter Sodium Cyanide Hydrogen Cyanide Molecular Weight 49.01 27.03 Boiling Point 1496 C at 760 mm Hg 26 C at 760 mm Hg Melting Point 564 C  13.4 C Specific Gravity 1.7 0.7 at 20 C Vapor Density  0.94 Vapor Pressure Negligible 620 mm Hg at 20C Solubility Soluble in water ( 37 g/ 100mL) Miscible with water and alcohol, slightly soluble in ether.

pKa  9.22 Source: OSHA, 2004 3.0 METABOLISM ASSESSMENT 3.1 Comparative Metabolic Profile 3.1.1 Metabolism in Mammals Cyanide gas and salts such as sodium and potassium cyanide are rapidly absorbed following inhalation and oral exposure, but are more slowly absorbed by dermal exposure. Following inhalation, cyanide is rapidly distributed throughout the body, with measurable levels detected in all organs. Cyanide can be distributed in the body within seconds and death can occur within minutes. Animal studies have shown that cyanide per se does not accumulate in the blood and tissues following chronic oral exposure, however. This is due to the fact that cyanide is transformed to the much less toxic thiocyanate in the body, with a plasma half life of 20 minutes to 1 hour. Hydrogen cyanide is readily converted to thiocyanate in the liver by the enzyme rhodanese and this metabolic conversion is the major detoxification mechanism for hydrogen Page 10 of 44 cyanide. Once thiocyanate is formed, it is not converted back to cyanide. Cyanide metabolites are mainly excreted in the urine, with small amounts excreted through the lungs.

3.1.2 Plant Metabolism The nature of the residue in citrus is adequately defined. The residue of concern is hydrogen cyanide per se. Hydrogen cyanide is rapidly absorbed by fresh citrus, and depending upon conditions, between 70 to 95% of available hydrogen cyanide is absorbed within one hour. Upon aeration, less than 5 percent of the sorbed hydrogen cyanide is desorbed. After 48 hours, most of the sorbed hydrogen cyanide is " irreversibly bound." There is no evidence that any of the sorbed hydrogen cyanide is degraded; hydrogen cyanide is stable under acidic conditions. The available data show that over 90% of the hydrogen cyanide can be accounted for as such in the treated citrus or as unsorbed hydrogen cyanide. A study subsequently obtained from University of California, Riverside indicates that when citrus is fortified with hydrogen cyanide about 10% of the hydrogen cyanide is unrecoverable. The studies and data, which the petition response cites, were not available, however, to verify these claims ( PP# 1E1124; 2/ 17/ 71; W. Cox).

3.1.3 Livestock Metabolism The nature of the residue in livestock has not been defined. However, there is limited potential for exposure to livestock though feed items because citrus treated with hydrogen cyanide is destined for fresh market only. ( Personal communication, Bill Chism, BEAD). Additionally, the Agency response to PP# 1E1124 indicates that hydrogen cyanide, when ingested by animals at subtoxic levels, is rapidly detoxified into carbon dioxide and thiocyanate, which is largely excreted by the kidneys ( 2/ 17/ 71; W. Cox).

3.2 Environmental Degradation Sodium cyanide hydrolyzes readily to gaseous hydrogen cyanide when dissolved in water or in contact with moisture. This reaction is the primary reaction in the environment. EFED does not anticipate significant exposure from sodium cyanide or hydrogen cyanide in surface water and ground water, when it is used as a fumigant under controlled delivery system of gaseous hydrogen cyanide into an airtight enclosure as described in the sodium cyanide label ( SLA CA 840006). Residual hydrogen cyanide will be vented from the treated containers through a exhaust system. In a recent air monitoring study ( MRID # 46648901), eight hour time weighted average concentration of hydrogen cyanide in ambient air after fumigation of citrus truck trailers was zero ppm. Based on the nature of the fumigation operation, and due to the high vapor pressure ( 620 mm Hg at 20C) and Henry's Law Constant ( 1.33 x 10 4 atm m3/ mole) of hydrogen cyanide, redeposition of volatilized hydrogen cyanide in surface water does not appear to be significant, thus suggesting that contamination of surface waters and ground water by hydrogen cyanide is unlikely. Page 11 of 44 3.3 Metabolites and Degradates A summary of hydrogen cyanide parent and metabolite matrices is provided in Table 4.

Table 4. Tabular Summary of Metabolites and Degradates Chemical Name Commodity Matrices Major Residue (> 10% TRR) Matrices Minor Residue (< 10% TRR) Chemical Structure Citrus 90% NA Ruminants NA NA Hydrogen Cyanide Poultry NA NA HC= N 3.4 Summary of Residues for Tolerance Expression and Risk Assessment A summary of metabolites and degradates included in the risk assessment and tolerance expression is provided in Table 5. The Agency concluded in the response to petition PP# 1E1124 that feed uses of treated citrus are of little concern because the proposed use is for fruit destined for the fresh market only. Therefore livestock commodities were not included in the dietary risk assessment and tolerances for ruminant and poultry commodities are not required. Based on available data, the established tolerance for this commodity is adequate ( Table 6). Codex maximum residue limits ( MRLs) do not currently exist for hydrogen cyanide; therefore, no questions of compatibility with U. S. tolerances exist.

Table 5. Metabolites and Degradates to be included in the Risk Assessment and Tolerance Expression Matrix Residues included in Risk Assessment Residues included in Tolerance Expression Plant Citrus Hydrogen Cyanide Hydrogen Cyanide Ruminant NA NA Livestock Poultry NA NA Drinking Water NA NA Table 6. Tolerance Summary for Hydrogen Cyanide Commodity Established Tolerance ( ppm) Recommended Tolerance ( ppm) Comments ( correct commodity definition) Fruit, citrus 50 50 Fruit, citrus, group 10 4.0 HAZARD CHARACTERIZATION/ ASSESSMENT 4.1 Hazard Characterization The toxicology database for hydrogen cyanide is incomplete. No guideline studies are available. All of the critical studies are cited from the open literature. Data on all forms of cyanide ( e. g., hydrogen, sodium, potassium cyanide etc.) have been used to identify hydrogen cyanide toxicity for this assessment. Hydrogen cyanide is extremely acutely toxic by all exposure routes. Page 12 of 44 All forms of cyanide, hydrogen, sodium, and potassium, are extremely acutely toxic by the oral route. Based on an analysis of case history data the lowest fatal oral dose of hydrogen cyanide for an average adult human is estimated by FDA to be 1 mg/ kg ( FDA, 1956). The lowest reported fatal dose of cyanide ( unspecified form) in humans was estimated to be 0.56 mg/ kg based on incidence data published in 1938 ( Gettler and Baine, 1938). It is important to note that analytical measurements at the time these studies were conducted lack the precision of current technology. Both sodium and potassium cyanide have lethal doses of 200 mg total, representing 81 and 110 mg total hydrogen cyanide, respectively. The acute oral fatal dose of potassium cyanide in rats is 10 15 mg/ kg, which is equivalent to a 4 6 mg/ kg hydrogen cyanide.

Results of clinical trials of Laetrile to treat cancer also provide evidence of the acute oral toxicity of hydrogen cyanide. Laetrile, also known as amygdalin, is a plant compound that produces cyanide. Use of Laetrile has been shown to produce side effects of cyanide poisoning  which can produce a range of symptoms, including death. In a clinical trial of Laetrile to treat human cancer, the single dose of 0.5 g of amygdalin was determined to be minimally toxic; a single dose of 0.5 g of amygdalin is equivalent to 0.4 mg/ kg hydrogen cyanide/ day ( Moertel et al, 1982). Blood levels of cyanide rose when the single 0.5 g dose was doubled to two 0.5 g doses at an administration. These increased blood levels were associated with an increase in the incidence and severity of some of the toxic signs and symptoms due to the release of hydrogen cyanide from amygdalin by the enzymatic action of B glucosidase, an intestinal enzyme. Therefore, the single dose of 0.5 g of amygdalin was determined to be a minimally toxic dose, whereas the double dose was generally regarded as frankly toxic.

Hydrogen cyanide is also acutely toxic via inhalation. The dose effect curve of the acute inhalation effects in humans is steep. Whereas slight effects occur at exposure to hydrogen cyanide levels of 20 40 mg/ m3, 50 60 mg/ m3 can be tolerated without immediate or late effects for 20 minutes to 1 hour, 120 150 mg/ m3 is dangerous to life and may lead to death after 0.5 1 hour, 150 mg/ m3 is likely to be fatal within 30 minutes, 200 mg/ m3 is likely to be fatal after 10 minutes, and 300 mg/ m3 is immediately fatal. It should be emphasized that this represents crude average exposure estimates, based on various studies ( WHO, 2004).

An average LD50 value for dermal exposure of 100 mg/ kg was estimated for humans ( Rieders, 1971). Concentrations of 7000 12,000 mg/ m3 were estimated to be fatal after a 5 minute exposure of workers with self contained respirators without effective skin protection ( Minkina, 1988). Cyanides are weakly irritating to the skin and eye. No data are available on sensitizing properties.

The primary effects of acute cyanide exposure in humans are central nervous system and cardiovascular disturbances. Typical signs of acute cyanide poisoning include tachypnea, headache, vertigo, lack of motor coordination, weak pulse, cardiac arrhythmias, vomiting, stupor, convulsions, and coma. Page 13 of 44 Hydrogen cyanide exhibits relatively low subchronic and chronic toxicity by the oral route. A 2 year rat feeding study ( Howard and Hanzal, 1955) with hydrogen cyanide fumigated food containing residues up to 300 ppm ( 10.8 mg/ kg/ day) showed no treatment related effects in clinical signs, body weight, food consumption, hematology, gross necropsy or histopathological changes in the organs examined ( heart, lung, liver, spleen, gastrointestinal tract, kidneys, adrenal, thyroid, testes, uterus, ovaries, cerebrum, cerebellum, and brain). The rats in the 2 year study ingested 2 to 3 times the fatal acute dose of hydrogen cyanide in rats each day throughout their lifetime without any measurable effects. In a 13 week repeated dose toxicity study in which sodium cyanide was administered in the drinking water, there were no mortalities, clinical signs or histopathological effects in the brain, thyroid, or other organs of rats and mice exposed to doses up to 12.5 and 26 mg/ kg/ day respectively.

Hydrogen cyanide is readily converted to thiocyanate in the liver by the enzyme rhodanese. This metabolic conversion is the major detoxification mechanism for hydrogen cyanide. The conversion of cyanide to thiocyanate was first demonstrated in 1894. Conversion of cyanide to thiocyanate is enhanced when cyanide poisoning is treated by intravenous administration of a sulfur donor ( e. g., sodium thiosulfate). Definite increases in thiocyanate concentrations were found in the treated tissues of the experimental animals indicating that metabolic detoxification of hydrogen cyanide had occurred ( Howard and Hanzal, 1956). Residues of thiocyanate, the less toxic primary metabolite of cyanide, increased 3.5 fold in plasma, 3.5 fold in erythrocytes, 1.3 fold in liver, and 2.5fold in kidneys of the rats exposed to hydrogen cyanide in the diet. The rapidity of this conversion was demonstrated in a case of humans where one twentieth the lethal dose ( 0.1 0.2 mg/ kg BW) of soluble cyanide was injected intravenously every ten minutes. In this case, more than the equivalent of an acutely fatal dose was administered without any apparent harm to the individual ( FDA, 1956). Based on the FDA study, as long as the oral intake of hydrogen cyanide does not exceed the body's detoxification mechanisms via the formation of thiocyanate, hydrogen cyanide can be ingested in the form of dietary residues for prolonged periods without harm. Once thiocyanate is formed, it is not converted back to cyanide. It has been estimated that based on established tolerances and percentage in the daily diet, the TMRC for the total daily diet could represent about 14 ppm hydrogen cyanide ( FDA, 1956).

Cyanogenic glycosides are present in major edible plants ( WHO, 2004). Amygdalin occurs in almonds, dhurrin in sorghum, linamarin in cassava, lotaustralin in cassava and lima beans, prunasin in stone fruit, and taxiphyllin in bamboo shoots ( WHO, 2004). Cassava is an important subsistence crop for 450 500 million people in 26 tropical countries in the expanding populations of Africa and South America. World production in 1980 was estimated to be 118 million tons. Cassava has been suspected as a cause of human congenital defects ( ATSDR, 2004).

There are neurotoxicity, developmental and reproductive studies available with naturally occurring cyanides or cyanide salts in the open literature, but there are no EPA guideline studies of these types of studies in the available database. Neurotoxic effects are a major occurrence across species and in humans from exposure to cyanide in its various forms. In several animal Page 14 of 44 studies, developmental CNS and heart malformations occur in the presence of overt maternal toxicity ( including death), whereas, parental findings ( mortality) occur at slightly higher doses in the absence of reported reproductive results in inhalation studies with acetone cyanohydrin ( ACH) in rats. ACH rapidly converts to hydrogen cyanide at physiological pH. The effects of acute cyanide exposure in humans are dominated by CNS and cardiovascular disturbances ( ATSDR, 2004). Typical signs of acute cyanide poisoning include tachypnea, headache, vertigo, lack of motor coordination, weak pulse, cardiac arrhythmias, vomiting, stupor, convulsions, and coma. No additive or synergistic effect was observed in the fatalities between cyanide and other factors, such as carbon monoxide, alcohol, age of victims, and presence of heart disease ( WHO, 2004)

There are no guideline studies of carcinogenicity of hydrogen cyanide or its alkali salts. There are no available open literature studies on the carcinogenic potential of cyanide. The classification of the carcinogenic potential could not be determined due to the absence of acceptable cancer studies in rats and mice. Because of cyanide's high toxicity, it would be difficult to conduct a meaningful cancer study in rats and mice over a two year period. Hydrogen cyanide has been evaluated for mutagenic potential with mixed results and several open literature references are available.

Cyanide gas and salts such as sodium and potassium cyanide are rapidly absorbed following inhalation and oral exposure. Cyanide compounds are more slowly absorbed by dermal exposure. Cyanide can be distributed in the body within seconds and death can occur within minutes. Following oral exposure, the highest levels have been detected in lungs and blood. Following inhalation, cyanide is rapidly distributed throughout the body, with measurable levels detected in all organs. Animal studies have shown that cyanide does not accumulate in the blood and tissues following chronic oral exposure. Cyanide is transformed to the much less toxic thiocyanate in the body, with a plasma half life of 20 minutes to 1 hour. Cyanide metabolites are mainly excreted in the urine, with small amounts excreted through the lungs ( ATSDR, 2004).

Hydrogen cyanide does not react with bivalent iron of hemoglobin ( Fe++). It does however, bind with cytochrome oxidase ( a ferric enzyme) in the electron transport system and inhibits the exchange of oxygen from the blood to the tissues by the mechanism of competitive inhibition. Cyanide can also inhibit approximately 40 enzymes, including a number of other metalloenzymes containing, for the most part, iron, copper, or molybdenum ( e. g, alkaline phosphatase, carbonic anhydrase, catalase, peroxidase, ascorbic acid oxidase, xanthine oxidase, and succinic dehydrogenase). These reactions may also contribute to cyanide toxicity ( WHO, 2004). Due to its high dependency on oxidative metabolism and limited anaerobic capacity, the central nervous system is particularly vulnerable to cyanide intoxication. The CNS symptoms observed in cyanide toxicity parallel those observed following accumulation of calcium in the brain and cytosolic calcium ion overload has been implicated as an intracellular mediator of cellular injury during and after anoxic hypoxia ( WHO, 2004).

Tables 7 and 8 provide the toxicity profile for hydrogen cyanide. Page 15 of 44 Table 7. Acute Toxicity Profile  Hydrogen Cyanide Guideline No. Study Type MRID( s) Results Toxicity Category 870.1100 Acute oral [ rat] Potassium Cyanide expressed as equivalents of hydrogen cyanide N/ A* LD50 = 4 6 mg/ kg I * Handbook of Toxicology, ( 1956), Vol. 1, Ed. William S. Spector, p. 242, Toxicity of Potassium Cyanide; W. B. Saunders Co., Philadelphia and London.

Table 8. Subchronic, Chronic and Other Toxicity Profile  Hydrogen Cyanide Guideline No./ Study Type MRID No. ( year)/ Classification / Doses Results 870.3100 90 Day oral toxicity ( rats, mice) ( NTP, 1993) Acceptable/ Non guideline 0, 0.2, 0.5, 1.4, 4.5, 12.5 mg NaCN/ kg/ day ( M) and 0, 0.2, 1.7, 4.9, 12.5 mg NaCN/ kg/ day ( F) in rats in drinking water and 0, 0.3, 1, 3, 9, and 26 mg NaCN/ kg/ day in mice in drinking water NOAEL = 2.5 mg/ HCNkg/ day LOAEL = 8.9 mg/ HCNkg/ day based on slight changes in the reproductive tract in male rats. No adverse effects in female rats or mice.

870.3465 4 Week inhalation toxicity ( rat) Monsanto Co. ( 1985), Acceptable/ Nonguideline Dose: 207 mg acetone cyanohydrin ( ACH)/ m3 calculated as 71 mg HCN/ m3. NOAEL = not established LOAEL = 71 mg HCN/ m3 produced 30% mortality ( 3/ 10) among rats exposed part of one day.

870.3465 14 week dietary toxicity study ( dogs) Kamalu ( 1993) Unacceptable/ Non guideline, Doses: ( 1) control ( zero mg HCN/ kg rice diet), ( 2) cassava [" gari"] ( believed to liberate 10.8 mg HCN/ kg cassava diet), ( 3) rice + added NaCN ( 10.8 mg NaCN added/ kg rice diet) 10.8 mg HCN/ kg diet calculated as 1.08 mg HCN/ kg BW NOAEL = not established LOAEL = 1.08 mg HCN/ kg BW ( NaCN + rice) based on altered profile of free amino acids, but no effects on histology of liver, kidney or heart, although serum enzymes ( plasma glutamyl transferase, ALAT, isocitrate dehydrogenase) were altered. Adrenal hyperplasia and hypertrophy, and pancreatic nephrosis and fibrosis were observed with rice + NaCN. Additionally, a significantly reduced frequency of testicular tubules in Stage 8 of sperm cycle as well as marked germ sloughing off and testicular degeneration was also seen in the rice + NaCN test animals ( 6 dogs/ group). Thiocyanate levels in NaCN + rice treated dogs increased during the study. In contrast, results of the " gari" diet ( cassava) showed generalized congestion and hemorrhage, liver vacuolation, kidney vacuolation, myocardial degeneration, adrenal gland degeneration, pancreatic necrosis, decreased T3 and thyroid effects consistent with goiter. 870.3465 90 Day inhalation toxicity ( rat) Monsanto Co. ( 1984a), Acceptable/ Non guideline, Doses 0, 36, 101, 204 mg/ m3 acetone cyanohydrin ( ACH) calculated as 0, 11, 32, 65 mg HCN/ m3 NOAEL = 65 mg HCN/ m3 or 15 mg HCN/ kg/ day LOAEL = not established.

870.3465 6 Month inhalation toxicity ( monkey, rat) Lewis et al ( 1984) Acceptable/ Nonguideline Doses 0, 11 ppm, 25 ppm cyanogen calculated as 25, or 56 mg HCN/ m3. NOAEL = 25 ppm HCN LOAEL = 56 ppm HCN based on doubling of the rate of responding on a variable interval 2.9 min schedule of reinforcements and decreased lung moisture content in monkeys and decreased body weights in rats. 870.3700a Prenatal Doherty et al ( 1982) Acceptable/ Nonguideline Maternal NOAEL = 0.07 mmol/ kg HCN BW/ hour Maternal LOAEL = 0.073 mmol/ kg HCN BW/ hr Page 16 of 44 Table 8. Subchronic, Chronic and Other Toxicity Profile  Hydrogen Cyanide Guideline No./ Study Type MRID No. ( year)/ Classification / Doses Results developmental in ( golden hamster) Doses 0, 0.125, 0.133 mmol NaCN/ kg BW/ hour using osmotic minipumps ( preliminary study) given on days 6 9 of gestation based on maternal deaths and dyspnea, incoordination, reduced body temperature, and loss of body weight Developmental NOAEL = 0.07 mmol/ kg HCN BW/ hour Developmental LOAEL = 0.073 mmol/ kg HCN BW/ hr based on 100% resorptions 870.3700a Prenatal developmental in ( golden hamster) Doherty et al ( 1982) Acceptable/ Nonguideline Doses: 0, 0.126, 0.1275, or 0.1295 mmol NaCN/ kg BW/ hour using osmotic minipumps equivalent to 0, 78.7, 79.6, and 80.9 mg NaCN/ kg BW/ day given on days 6 9 of gestation Maternal NOAEL = not established Maternal LOAEL = 0.126 mmol NaCN/ kg BW/ hr based on salivation, shortness of breath, ataxia, reduced body temperature, and loss of body weight Developmental NOAEL = not established Developmental LOAEL = 0.126 mmol NaCN/ kg BW/ hr based on resorptions, non closure of neural tube, exencephaly, encephalocoele, and malformations of the heart, limb, or tail. Co administration of thiosulfate eliminated the teratogenic effect, protecting the dams and fetuses from the toxic effects of cyanide 870.3700a Prenatal developmental in ( rats) Monsanto Co. ( 1982, 1983a) Acceptable/ Guideline Doses: 0, 1, 3, 10 mg Acetone cyanohydrin/ kg BW ( equivalent to 0, 0.3, 0.9, or 3 mg cyanide/ kg BW/ day) during days 6 15 of gestation Maternal NOAEL = 0.3 mg HCN/ kg BW/ day Maternal LOAEL = 0.9 mg HCN/ kg BW/ day based on slight reductions in weight gain and significant decreases in high dose group plus decrease in implantations Developmental NOAEL = 3 mg HCN/ kg BW/ day Developmental LOAEL = not established 870.3700a Prenatal developmental in ( rats) Singh ( 1981) Unacceptable/ Nonguideline Doses: 50% and 80% milled cassava powder in diet given during first 15 days of gestation ( CN content not specified) Maternal LOAEL = 50% milled cassava resulted in decreased weight gain Developmental LOAEL = 50% milled cassava resulted in increased resorptions, decreased body weight, and open eye, microcephaly, limb defects at 80% milled cassava 870.3700a Prenatal developmental in ( golden hamster) Willhite ( 1982) Unacceptable/ Nonguideline Doses of 200, 250, or 275 mg/ kg BW of d/ l amygdalin or 177 mg/ kg BW of d prunasin equivalent to 11, 14, or 16 mg CN/ kg BW, respectively, or 16 mg CN/ kg BW administered orally on day 8 of gestation or 16 mg CN/ kg BW/ day given intravenously Maternal oral LOAEL = 11 mg HCN/ kg BW / day, effects not specified. Developmental oral LOAEL = 11 mg HCN/ kg BW/ day based on exencephaly, encephalocoele, skeletal malformations No developmental effects were seen at 16 mg HCN/ kg BW/ day given intravenously 870.3700a Prenatal developmental in ( golden hamster) Frakes et al ( 1985) Acceptable/ Nonguideline Doses: 0, 70, 100, 120, or 140 mg linamarin/ kg BW/ day on day 8 of gestation ( primitive streak) Maternal NOAEL = 70 mg linamarin/ kg/ day LOAEL = 100 mg/ kg/ day based on dyspnea, tremors, and ataxia, Developmental NOAEL = 100 mg linamarin / kg/ day LOAEL = 120 mg linamarin / kg/ day based on vertebral and rib anomalies and Encephalocoele. 870.3700a Prenatal developmental in ( golden hamsters) Frakes et al ( 1986) Unacceptable/ Nonguideline Doses of high cyanide ( bitter cassava, 7.9 mmol CN/ kg)) and low cyanide ( sweet cassava, 0.7 mmol CN/ kg)) mixed in an 20: 80 ratio given on days 3 14 of gestation to pregnant hamsters Maternal LOAEL = based on significant decreases in weight gain. Developmental LOAEL = based on decreased fetal body weight, reduced ossification of sacrocaudal vertebrae, metatarsals, and sternebrae. Page 17 of 44 Table 8. Subchronic, Chronic and Other Toxicity Profile  Hydrogen Cyanide Guideline No./ Study Type MRID No. ( year)/ Classification / Doses Results 870.3800 Reproduction and fertility effects ( rat) Olusi et al ( 1979) Acceptable/ Nonguideline Doses of 1000 or 2000 mg CN/ kg BW/ day administered to females ( 10/ sex) for 2 weeks and then mated to untreated males Parental/ Systemic NOAEL = not established LOAEL = 1000 mg HCN / kg/ day based on decreased weight gain, blood hemoglobin, serum T4 concentration. Reproductive NOAEL = not established LOAEL = 1000 mg HCN/ kg/ day based on no pregnancies. 870.3800 Reproduction and fertility effects ( male rat) Monsanto Co. ( 1985a) Acceptable/ Non guideline, Inhalation doses of 0, 35, 101, or 202 mg acetone cyanohydrin ( ACH)/ m3 equivalent to 0, 11, 32, or 64 mg HCN/ m3 for 6 hours/ day, 5 days/ week during a period of 69 days ( 48 exposure days). Following exposure, the males were mated with 3 untreated females/ male Parental/ Systemic NOAEL = 64 mg HCN/ m3 based on no deaths, clinical signs of toxicity LOAEL = not established. Reproductive NOAEL = 64 mg HCN/ m3 based on mating efficiency, number of live implants, and pre and post implantation loss LOAEL = not established. Offspring NOAEL = not established LOAEL = not established.

870.3800 Reproduction and fertility effects ( rat) Monsanto Co. ( 1985b) Acceptable/ Non guideline, Inhalation doses of 0, 38, 108, or 207 mg acetone cyanohydrin ( ACH)/ m3 equivalent to 0, 12, 34, or 66 mg HCN/ m3 for 6 hours/ day, 7 days/ week up to day of mating ( 34 36 exposures). Following exposure, the females were mated with untreated males; females were sacrificed at gestation days 13 15. Parental/ Systemic NOAEL = 66 mg HCN/ m3 based on absence of clinical signs, except for red nasal discharge, mortality, weight gain and necropsy, LOAEL = not established. Reproductive NOAEL = 66 mg HCN/ m3 based on no effect on fertility, LOAEL = not established. Offspring NOAEL = not established, LOAEL = not established.

870.3800 Reproduction and fertility effects ( rat) Tewe and Maner ( 1981a) Unacceptable/ Non guideline, Doses: 0, 500 ppm dietary KCN added to cassava flour fed to pregnant female rats during gestation and lactation Parental/ Systemic LOAEL = 207 HCN ppm in diet based on decreased body weight gain during lactation. Reproductive NOAEL = 207 KCN ppm in diet did not cause marked effect in gestation and lactation performance Offspring LOAEL = 207 HCN ppm in diet based on decreased food consumption and body weight during lactation. 870.3800 Reproduction and fertility effects ( Yorkshire pigs) Tewe and Maner ( 1981b) Acceptable/ Non guideline Doses: 0, 250, 500 ppm KCN added to fresh cassava diets and fed to maternal animals during gestation and lactation Parental/ Systemic NOAEL = 104 HCN ppm in diet LOAEL = 500 ppm in diet based on increased thyroid weight and thyroid and kidney histopathology. Reproductive NOAEL = 207 HCN ppm in diet did not affect the production or lactation of the first litter of offspring and did not affect either the number or weight of 110 day old fetuses LOAEL not established Offspring NOAEL = 104 HCN ppm in diet LOAEL = 207 HCN ppm in diet based on increased fetal serum thiocyanate levels, increased relative fetal spleen and heart weight. 870.4100a Chronic toxicity ( rat) Howard and Hanzal, 1955, Acceptable/ Non guideline, Doses: 0, 100, 300 ppm calculated as 0, 4.3, 10.8 mg/ kg/ day of HCN NOAEL = 10.8 mg HCN / kg/ day ( HDT) LOAEL = not established.

870.6200a Acute Neurotoxicity ( rats) Fechter et al ( 2002), Acceptable/ Nonguideline Dose: 34 mg HCN/ m3 for 3.5 hours HCN plus noise produced impaired auditory function by producing significant oxidative stress in the cochlea. HCN alone did not cause significant hearing loss or hair cell loss. 870.6200b Mathangi & Namasivayam ( 2000), Reductions of memory ( T maze test), along with reductions in the Page 18 of 44 Table 8. Subchronic, Chronic and Other Toxicity Profile  Hydrogen Cyanide Guideline No./ Study Type MRID No. ( year)/ Classification / Doses Results Subchronic neurotoxicity ( rats) Acceptable/ Non guideline, Dose: 2 mg NaCN/ kg given intraperitoneally followed by 25 ip doses which was 25% of LD50. level of dopamine and 5 hydroxytryptamine and increases in norepinephrine and epinephrine levels in the hippocampus, measured after a month of treatment.

870.6200b Subchronic neurotoxicity ( dogs) Hertting et al ( 1960) Unacceptable/ Nonguideline Doses: 0, 0.5, 2, 1 4 mg NaCN capsule/ kg/ day for 13 15 months ( only one dog at each dose level) NOAEL = not established LOAEL = 0.27 mg HCN/ kg/ day based on degenerative changes in the ganglia cells of CNS, interpreted to be caused by multiple episodes of acute cerebral hypoxia. 870.6200b Subchronic neurotoxicity ( miniature pigs) Jackson ( 1988) Acceptable/ Nonguideline Doses: 0, 0.4, 0.7, 1.2 KCN/ kg/ day dosed by gavage once daily for 24 weeks NOAEL = not established LOAEL = 0.5 mg HCN/ kg/ day based on dose related decreased T3 and T4 and increased fasting blood sugar plus decreased exploration and aggression, slower eating, more frequent drinking and shivering consistent with decreased thyroid activity. 870.3100 Subchronic oral ( human) FDA ( 1956) Administration of NaCN to measure thiocyanate in saliva Oral NOAEL = 0.2 mg HCN/ kg/ day 870.3100 Subchronic oral and intravenous ( human) Moertel et al ( 1982), MRIDs 46769601 46769602 A clinical trial of amygdalin ( laetrile) in the treatment of human cancer and Moertel et al ( 1981) A pharmacological and toxicological study of amygdalin Oral LOAEL = 0.4 mg HCN/ kg/ day based on symptoms and clinical signs of hydrogen cyanide toxicity Mutagenicity Test System Endpoint Result With Activation Result Without Activation Reference Form S. typhimurium TA82, TA102 Reverse Mutation  Not tested DeFlora et al, 1984 KCN S. typhimurium TA98, TA100, TA1535, TA1537, TA1538 Reverse Mutation   DeFlora 1981 KCN S. typhimurium TA98, TA100 Reverse Mutation  (+)  + Kushi et al, 1983 HCN S. typhimurium TA98, TA100 Reverse Mutation   Kubo et al, 2002 KCN S. typhimurium TA97, TA98, TA100, TA1535 Reverse Mutation   NTP 1993 NaCN E. coli WP67, CM871, WP2 DNA Repair Test   DeFlora et al, 1984 KCN HeLa cells DNA Synthesis Inhibition   Painter and Howard, 1982 KCN Human A549 lung carcinoma cells DNA Breakage +( cyt) Vock et al, 1998 KCN Human TK6 lymphoblastoma cells DNA Breakage +( cyt) Henderson et al, 1998 KCN Rat thymocytes DNA Breakage +( cyt) Bhattachrya et al, 1997 KCN Hamster BHK 21 cells DNA Breakage +( cyt) Bhattachrya et al, 1997 KCN Rat hepatocytes DNA Breakage +( cyt) Storer et al, 1996 KCN Mitochondrial fraction from brain of male ddy mice Mitochondrial DNA Breakage + Yamamoto, 2002 KCN  = negative result, + = positive result, (+) = weakly positive result, +( cyt) = DNA breakage associated with cytotoxicity; DNA = deoxyribonucleic acid, HCN = hydrogen cyanide, KCN = potassium cyanide, NaCN = sodium cyanide Page 19 of 44 4.2 FQPA Hazard Considerations 4.2.1 Adequacy of the Toxicity Data Base The toxicology database for hydrogen cyanide is not complete. No guideline studies are available. All of the critical studies are cited from the open literature. Data on all forms of cyanide ( e. g., hydrogen, sodium, potassium cyanide etc) have been used to identify hydrogen cyanide toxicity for this assessment.

4.2.2 Evidence of Neurotoxicity There is a concern for neurotoxicity resulting from exposure to cyanide, since several of the reviewed literature studies show signs of neurotoxic clinical effects or neuropathology. The assessment of hydrogen cyanide neurotoxicity was based on studies conducted with hydrogen cyanide, potassium cyanide, sodium cyanide, and cyanogen.

<IP_ADDRESS> Behavioral Study in Pigs The effects of cyanide on behavior were studied in fasted 25 week old miniature pigs ( 12 litter mates: 5 females and 7 castrated males) randomized in four groups ( Jackson, 1988). The animals were dosed daily for 24 weeks with a single bolus of cyanide as aqueous potassium cyanide just prior to daily feeding. The doses were 0, 0.4, 0.7, or 1.2 mg cyanide/ kg BW, chosen to be equivalent to those consumed by West Africans in their diet. Every six weeks, thyroid function ( T3 and T4) and fasting blood glucose were measured, but not thyroid stimulating hormone ( TSH). Daily observations were made of clinical signs and various behavioral measurements, including social, antagonistic, exploratory, learning, feeding, and excretory behavior. In all treatment groups, dose related decreases were evident from week 6 in blood levels of T3 and T4 and an increase in fasting blood glucose was noted, particularly in top dose animals. Statistical analysis was not provided for each dose group versus the control, but changes in top dose animals appeared significant by week 18; by week 24, decreases of 35% for T3 and 15% for T4 and an increase of 60% in fasting blood glucose were observed. Behavioral observations revealed a picture of decreased high energy demanding behavior, such as exploration and aggression, slower eating, more frequent drinking, and shivering consistent with the decreased thyroid activity. A LOAEL of 0.5 mg HCN/ kg BW/ day could be suggested from this study. It is important to note major weaknesses of this study. The study used a bolus dose with consequent high peaks of cyanide concentration in the organism and involved a very small number of animals ( three animals in four groups) and limited statistical analysis. Page 20 of 44 <IP_ADDRESS> Chronic Toxicity Study in Dogs Dogs administered sodium cyanide in capsules at levels of 0, 0.5, 2, or 1 4 mg/ kg BW ( one dog at each dose level) daily for 13 15 months showed severe signs of acute cyanide poisoning right after the daily dosing ( the dog at the lowest dose died). In the autopsy, the only significant finding were degenerative changes in the ganglia cells of the central nervous system, interpreted to be caused by multiple episodes of acute cerebral hypoxia ( Hertting et al, 1960).

<IP_ADDRESS> Inhalation Toxicity Study in Monkeys and Rats In a 6 month inhalation toxicity study in rhesus monkeys and CD rats, Lewis, Anger and Vault ( 1984) exposed groups of 5 rhesus monkeys and 30 male rats for 6 hr/ day, 5 days/ week to ( A) Control group ( B) 11 ppm cyanogen or ( C) 25 ppm cyanogen. This corresponded to 25, or 56 mg hydrogen cyanide/ m3. At the outset of exposures, there was a doubling of the rate of responding on a variable interval 2.9 min schedule of reinforcement in monkeys exposed to 25 ppm cyanogen, and increases were also seen in the monkeys receiving 11 ppm exposures; the increases were transitory as the rate returned to control levels before exposures were terminated. At the end of the 6 month exposure period, there were no effects in hematologic or clinical chemistry parameters attributable to the inhalation exposure to cyanogen. The electrocardiograms, and gross pathologic and histopathologic examinations of test animals were normal when compared to the control animals. Total lung moisture content was significantly lower in monkeys exposed to either 11 or 25 ppm cyanogen than in control animals. Body weights were significantly lower in rats exposed to 25 ppm cyanogen than in controls. The results suggest that subchronic 25 ppm cyanogen exposures are marginally toxic, but that 11 ppm cyanogen may be considered a no adverse effect level ( NOAEL). The 11 and 25 ppm cyanogen concentrations corresponds to 25 and 56 mg HCN/ m3.

<IP_ADDRESS> Other Indications of Neurotoxic Effects Potentiation to noise induced hearing loss by exposure of rats to low concentrations of hydrogen cyanide was reported by Fechter et al ( 2002). It was suggested that hydrogen cyanide ( 34 mg/ m3 for 3.5 hours) plus noise produced impaired auditory function by producing significant oxidative stress in the cochlea. Hydrogen cyanide alone did not cause significant hearing loss or hair cell loss ( WHO, 2004). A single intraperitoneal dose and 25 repeated intraperitoneal doses of sodium cyanide ( 2 mg/ kg ( 1 mg hydrogen cyanide/ kg)), stated to represent 25% of the LD50, administered to Wistar strain albino rats resulted in similar reductions of memory ( T maze test), along with reductions in the level of dopamine and 5 hydroxytryptamine and increases in norepinephrine and epinephrine levels in the hippocampus, measured after a month of treatment ( Mathangi & Namasivayam, 2000). There is also a neuropathological study in goats ( Soto Blanco et al, 2002), which reported ultrastructural changes in animals given > 0.48 mg cyanide/ kg BW/ day in drinking water for 5 months. However this study did not present quantitative data or statistical analysis, since it was essentially a morphometric evaluation. Page 21 of 44 4.2.3 Developmental Toxicity Studies There are no developmental toxicity studies available for hydrogen cyanide. Developmental studies with sodium cyanide, cassava meal/ powder ( cassava plant contains a cyanogen called linamarin), cyanogenic glycoside linamarin, amygdalin, and acetone cyanohydrin were available and reviewed for this assessment. The weight of the evidence of available data indicates that cyanide induces developmental effects only at doses or concentrations that are overtly toxic to the maternal animals.

<IP_ADDRESS> Developmental Toxicity Studies in Hamsters Preliminary experiments with sodium cyanide given to pregnant Golden Syrian hamsters using osmotic minipumps implanted subcutaneously, showed that at a dose rate of 0.125 mmol/ kg BW/ hour, no effects on the fetus were observed, while at a dose rate of 0.133 mmol/ kg BW/ hour or more, there was a 100% resorption rate and maternal deaths. Toxicity to dams increased with increasing dose levels and included dyspnea, ataxia, reduced body temperature, and loss of body weight. Co administration of thiosulfate eliminated the teratogenic effect, protecting the dams and fetuses from the toxic effects of cyanide ( Doherty et al, 1982).

In a follow up experiment, pregnant Golden Syrian hamsters ( 5 7 per group) were continuously exposed to sodium cyanide from day 6 to day 9 of gestation at 0, 0.126, 0.1275, or 0.1295 mmol/ kg BW/ hour using osmotic minipumps implanted subcutaneously. These doses are equivalent to 0, 78.7, 79.6, and 80.9 mg/ kg BW/ day. Toxicity to dams increased with increasing dose levels and included salivation, dyspnea, ataxia, reduced body temperature, and loss of body weight. The treatment induced a remarkable increase in resorptions as well as fetal malformations. These included non closure of the neural tube, exencephaly, encephalocoele, and malformations of the heart, limbs or tail. Co administration of thiosulfate eliminated the teratogenic effect, protecting the dams and fetuses from the toxic effects of cyanide ( Doherty et al, 1982).

Groups of pregnant hamsters were fed diets consisting of two types of cassava meal, either a " low cyanide" ( sweet cassava meal) or a " high cyanide" ( bitter cassava meal) variety. These were mixed ( 80: 20) with laboratory chow and administered on days 3 14 of gestation ( Frakes et al, 1986). The cyanide concentration of the sweet cassava meals was 0.6 0.7 mmol/ kg; that of the bitter cassava meal was 5 11 ( mean 7.9) mmol/ kg. Cassava fed dams gained significantly less weight than did control animals ( fed diet similar in nutritional values as cassava, but without cyanogenic glycosides) and their offspring showed evidence of fetotoxicity ( reduced fetal body weight and reduced ossification of sacrocaudal vertebrae, metatarsals and sternebrae). The bitter cassava also produced a significant increase in the number of runts compared with litters from dams fed either low protein or laboratory stock diets. The only teratogenic effects noted were hydrocephalus in three animals in the low cyanide ( sweet cassava) test group and one encephalocoele found in one animal at the high cyanide ( bitter cassava) test group. Page 22 of 44 Additionally, Frakes et al ( 1985) studied the developmental toxicity of the cyanogenic glycoside linamarin in the golden hamster at doses of 0, 70, 100, 120, or 140 mg/ kg. This dosing regiment resulted in an increased incidence of vertebral and rib anomalies as well as the production of encephalocoele in the offspring at a dose of 120 or 140 mg/ kg BW, which was a maternally toxic dose. The developmental LOAEL was estimated to be 120 mg/ kg/ day based on skeletal effects and the maternal LOAEL was estimated to be 100 mg/ kg concentration based on cyanide intoxication ( dyspnea, tremors, ataxia, etc.). A NOAEL was established for linamarin fetal and maternal effects at 100 mg/ kg and 70 mg/ kg, respectively, in the study. Frakes et al ( 1985) estimates that a 50 kg person would have to consume about 2.7 kg of cassava flour containing 200 mg/ kg HCN in order to receive a dose of linamarin equal to the 100 mg/ kg dose used in the study. Therefore, ingestion of a toxic/ teratogenic dose of linamarin by a human female seems unlikely.

A single oral dose of d/ l amygdalin at gestational day 8 resulted in exencephaly, encephalocoele, and skeletal malformations at doses of > 250 mg/ kg (> 14 mg cyanide/ kg) in hamsters ( these doses were also clearly toxic to the mothers). At the lowest dose tested, 200 mg/ kg ( 11 mg cyanide/ kg), fused ribs were observed in two offspring of one mother ( maternal toxicity not reported). Encephalocoele and rib anomalies were also reported after a dose of dprunasin ( 177 mg/ kg ( 16 mg cyanide/ kg)) in the absence of maternal toxicity in hamsters. No teratogenic effects were noted when hamsters received d/ l amygdalin ( 275 mg/ kg ( 16 mg cyanide/ kg)) intravenously ( WHO, 2004). The teratogenic effects found were considered to be due to cyanide released by bacterial beta glucosidase in the gastrointestinal tract ( Willhite, 1982).

<IP_ADDRESS> Developmental Toxicity Study in Rats Singh ( 1981) reported a 28% increased incidence of open eye, microcephaly, limb defects, and growth retardation in the offspring of pregnant rats fed 80% milled cassava powder during the first 15 days of gestation. In the preliminary study with limited experimental detail, pregnant albino rats were fed milled cassava powder as 50% and 80% of their diet during the fifteen days of gestation. Growth retardation and an increased frequency of resorptions were observed at both dose levels; in addition, limb defects were observed at the high dose. The weight gain of the dams was lowered from day 6 onward; no further information on maternal toxicity was given. No indication of the cyanide content of the cassava was given.

Groups of 25 pregnant Sprague Dawley rats were dosed by gavage on days 6 15 of gestation with 0, 1, 3, or 10mg acetone cyanohydrin / kg BW ( equivalent to 0, 0.3, 0.9, or 3 mg cyanide/ kg) ( Monsanto Co., 1982). Maternal toxicity was evidenced by slight reductions in body weight gain in the mid and high exposure groups, and statistically significant differences between the high dose group and controls were found for the number of corpora lutea implantations per dam. There were no comparable differences in the number of viable fetuses per dam, postimplantation losses per dam, mean fetal body weight, or fetal sex distribution for all dose groups and the controls. The incidences of fetal malformations and developmental variations for all fetuses of treated animals and controls were also comparable. It was concluded that 10 mg Page 23 of 44 ACH/ kg BW ( 3 mg cyanide/ kg) was not teratogenic in the rat in the presence of maternal toxicity ( Monsanto Co., 1982, 1983a, WHO, 2004).

4.2.4 Reproductive Toxicity Studies There are relatively few data available on the reproductive toxicity of cyanides. There are no reproductive toxicity studies available for hydrogen cyanide. Reproductive studies with sodium cyanide, potassium cyanide, cassava, and acetone cyanohydrin were available and reviewed for this assessment.

<IP_ADDRESS> Reproductive Toxicity Studies in Rats A subchronic, 13 week repeated dose toxicity study was conducted in which sodium cyanide was administered in the drinking water ( NTP, 1993) at doses of 0, 0.2, 0.5, 1.4, 4.5, and 12.5 mg/ kg BW/ day for males and 0, 0.2, 1.7, 4.9, and 12.5 mg/ kg BW/ day for female rats and 0, 0.3, 1, 3, 9, and 26 mg/ kg BW/ day for mice. There were no deaths, clinical signs associated with CNS effects, body or organ weights, or histopathological effects in the brain or thyroid of rats exposed to doses up to 12.5 mg/ kg BW/ day, respectively. At the LOAEL of 12.5 mg/ kg BW/ day in rats, there were slight changes in the reproductive tract of male rats including decreased left epididymis weight, left caudal epididymis weight, left testis weight, spermatids heads, and spermatid counts which, although they apparently did not affect the fertility in rats, are possibly significant to humans. The NOAEL for these effects in male rats was 4.5 mg/ kg BW/ day. The examination of neurotoxicity in this study was limited to clinical observations and optical microscopy at autopsy. At 4.9 and 12.5 mg/ kg BW/ day, there was an increase in the time spent by female rats in proestrus and diestrus relative to estrus and metestrus. The finding in female rats were not considered adverse. In male mice, there was a statistically significant decrease in epidiymidis weight at 26 mg/ kg BW/ day, but no changes in sperm motility or spermatid head density were observed. No estrus effects were seen in female mice. The overall NOAEL for the NTP study was selected as 4.5 mg/ kg BW/ day, based on findings in the male reproductive tract at the LOAEL of 12.5 mg/ kg BW/ day After 2 weeks on a diet containing 5 or 10 g potassium cyanide / 100 g of diet, female rats ( 10/ group) were mated with untreated males ( Olusi et al, 1979). No pregnancies resulted. The dose corresponds to roughly 1000 and 2000 mg cyanide/ kg BW / day. There was a dosedependent decrease in body weight gain, blood hemoglobin ( 18% and 23%) and serum T4 concentration ( 54% and 75%).

In a male fertility study ( Monsanto Co., 1985a), Sprague Dawley rats ( n = 15) were exposed by inhalation to acetone cyanohydrin ( 0, 35, 101, or 202 mg/ m3; 0, 11, 32, or 64 mg HCN/ m3) 6 hours/ day, 5 days/ week, during a period of 69 days ( i. e., 48 exposure days). After the treatment period, the males were mated with three non exposed females each. There were no deaths, clinical signs of toxicity, changes in body weight, or changes in gross necropsy after 48 exposures to up to 202 mg acetone cyanohydrin ( 64 mg hydrogen cyanide/ m3). The mating Page 24 of 44 efficiency, number of live implants, and pre and post implantation losses were not different between treated and control groups ( WHO, 2004).

Female Sprague Dawley rats were exposed by inhalation ( 6 hours/ day, 7 days/ week) for 21 days to acetone cyanohydrin at 38, 108, and 207 mg/ m3 and then mated to untreated males. Exposure of the females, which was equivalent to 12, 34, and 66 mg hydrogen cyanide/ m3, was continued until the day of mating, and the females were sacrificed at mid gestation ( gestation days 13 15). No treatment related effects on female clinical signs of toxicity, mortality, body weight gain or gross necropsy during or after 34 36 exposures up to 207 mg acetone cyanohydrin/ m3 ( 66 mg hydrogen cyanide/ m3). Additionally, no treatment related effects on female fertility were observed in any of the exposure groups. The only frequently observed clinical sign post exposure was red nasal discharge or encrustation. The highest exposure in the study ( 207 mg acetone cyanohydrin/ m3) could be considered as the NOAEL for female reproductive effects ( Monsanto, 1985b, WHO, 2004).

In a study on the long term and carry over effect of control and 500 ppm dietary potassium added to a cassava root flour based basal diet in the life cycle performance and metabolism of Wistar rats, Tewe and Maner ( 1981a) demonstrated that there was no marked effect in gestation and lactation performance in female rats. No carry over effect of the cyanide treated diet fed during gestation was observed on lactation performance of female rats, although females exposed to fortified diets gained less weight than controls. However, the high cyanidecontaining diet significantly reduced the food consumption and growth of offspring when fed during the post weaning growth period. Serum thiocyanate was significantly increased in the potassium cyanide group in lactating rats and their offspring during lactation and in the postweaning growth phase of the pups. Rhodenase, the enzyme which converts cyanide to thiocyanate, activity in liver and kidney was unaffected by feeding the high cyanide diet during gestation, lactation, and/ or during post weaning growth.

<IP_ADDRESS> Reproductive Toxicity Study in Pigs In a second study by Tewe and Maner ( 1981b), groups of six pregnant Yorkshire pigs were fed fresh cassava diets containing 0, 250, and 500 ppm of potassium cyanide. Dietary cyanide level had no significant effect on either the number or weight of 110 day old fetuses. Serum thiocyanate concentration was slightly but not significantly increased in the 500 ppm cyanide group and serum PBI decreased during gestation in all maternal groups, including controls. Fetal serum thiocyanate concentration was significantly higher ( p< 0.05) in the group fed 500 ppm added cyanide. A small increase in maternal thyroid weight with increasing level of cyanide was observed. Pathological studies showed proliferation of glomerular cells of the kidney in maternal animals in all groups, including controls. Both slaughtered 500 ppm " gilts"  maternal animals  had thyroid glands with epithelial follicular cells which were low in height and had an accumulation of colloid. In the presence of maternal histopathologic effects to the thyroid and kidney, fetal spleen and heart to body weight ratios were decreased. Cyanide fed during gestation did not affect the production or lactation of the first litter of offspring, although metabolic and Page 25 of 44 pathologic differences did occur. Milk thiocyanate and colostrum iodine concentrations were significantly higher ( p< 0.05) in the group fed 500 ppm cyanide.

4.2.5 Pre and/ or Postnatal Toxicity <IP_ADDRESS> Determination of Susceptibility Significant developmental effects from exposure to cyanides have been observed across species, but appear in the presence of serious overt maternal toxicity, including death. There is no quantitative or qualitative increased susceptibility of fetuses and offspring across species in comparison to maternal and parental animals. Serious offspring developmental effects of the CNS have also been associated with acute maternal CNS clinical findings, as well as other maternal effects ( death, dyspnea, tremors, ataxia, decreased body weight, etc.). There was no qualitative or quantitative increased susceptibility in postnatal offspring toxicity, since both offspring and parental effects occurred at similar toxic dose levels.

<IP_ADDRESS> Degree of Concern Analysis and Residual Uncertainties for Pre and/ or Post natal Susceptibility There are no quantitative or qualitative increased susceptibilities associated with the serious offspring and parental findings resulting from exposure to cyanides. These results indicate low residual concern due to the fact that the developmental and postnatal findings occurred in the presence of maternal/ parental effects.

4.2.6 Recommendation for a Developmental Neurotoxicity Study There is not a concern for developmental neurotoxicity resulting from exposure to Hydrogen cyanide. There is a concern for serious neurotoxic findings in both offspring and maternal animals i. e., hydrogen cyanide is a neurotoxic chemical which produces neurotoxic clinical signs in both offspring and maternal animals and there is evidence of neuropathology resulting from exposure to hydrogen cyanide in both offspring and maternal animals. However, there is no evidence of increased susceptibility in the several developmental and reproduction studies. Therefore, since the neuropathology seen in offspring in both developmental and reproduction studies is a result of the acute effects of cyanide which are also seen in adult animals a developmental neurotoxicity study is not required for hydrogen cyanide at this time. Page 26 of 44 4.3 FQPA Safety Factor There was no qualitative or quantitative increased susceptibility in postnatal offspring toxicity, since both offspring and parental effects occurred at similar toxic dose levels. Similarly, there is low residual concern due to the fact that the developmental and postnatal findings occurred in the presence of maternal/ parental effects. Additionally, the mechanism of action for hydrogen cyanide toxicity is well established. Hydrogen cyanide binds with cytochrome oxidase in the electron transport system and inhibits the exchange of oxygen from the blood to the tissues by competitive inhibition. Since the cytochrome oxidase system is fully functional in newborns, offspring and parental effects would occur at similar toxic dose levels. Therefore, it is recommended that the FQPA safety factor be reduced to 1x for the hydrogen cyanide risk assessment.

4.4 Hazard Identification and Toxicity Endpoint Selection 4.4.1 Acute Reference Dose ( aRfD)  General Population Selection of an acute RfD for hydrogen cyanide was based on published data from a clinical trial of amygdalin ( Laetrile) in the treatment of human cancer ( Moertel, CG et al. 1982 ( MRIDs Nos 46769602, 46769601). One hundred seventy eight patients with cancer were treated with amygdalin ( Laetrile) plus a " metabolic therapy" program consisting of diet, enzymes and vitamins. Amygdalin was administered at an intravenous dose of 4.5 g/ m2 of body surface area / day for 21 days in the Standard Dose or 7 g/ m2 of body surface area / day for 21 days at the High Dose. Following intravenous treatment, amygdalin was administered orally at 0.5 g, three times daily at the Standard Dose Regimen or 0.5 g, four times daily at the High Dose Regimen. All patients were fully informed about the experimental and unorthodox nature of the treatment program as well as any possible alternative treatment available to them. No placebo group was administered. Clinical signs and symptoms consisting of nausea, vomiting, headaches, dizziness, mental obtundation and, on a few occasions, dermatitis, occurred in some patients on occasion following a single 0.5 g oral dose of amygdalin or when two 0.5 g oral doses were administered at the same time, or shortly apart, to compensate for a missed dose or in one patient who consumed raw almonds following oral therapy ( Moertel et al, 1981). Blood levels of patients who received a single dose ranged between 1 2 µ gCN/ ml whole blood. Blood levels of cyanide rose to 2 3 µ gCN/ ml when the single 0.5 g dose was doubled to two 0.5 g doses at an administration. These increased blood levels were associated with an increase in the incidence and severity of some of the toxic signs and symptoms due to the release of Hydrogen cyanide from amygdalin by the enzymatic action of B glucosidase, an intestinal enzyme. If the blood cyanide level was found to be 3 µ gCN/ ml or greater at any time, therapy was permanently discontinued. Therefore, the single dose of 0.5 g of amygdalin was determined to be a minimally toxic dose, whereas the double dose was generally regarded as frankly toxic. No substantive benefit was observed in terms of cure, improvement, or stabilization of cancer, or extension of life span. Amygdalin ( laetrile) is a toxic drug that is not effective as a cancer treatment. In the Standard Dose study, a single dose 0.5 g of amygdalin results in 29.4 mg of Hydrogen cyanide ( 500 mg/ 17.1 mw of laetrile/ hydrogen Page 27 of 44 cyanide = 29.4 mg of HCN). When the Hydrogen cyanide content is divided by the approximate BW of 70 kg, the result is 0.4 mg/ kg BW/ day.

Supporting evidence comes from the 1956 Quarterly Report of the FDA, which demonstrates that total oral doses of 20 to 30 mg NaCN ( the equivalent of 11.0 to 16.5 mg hydrogen cyanide or 0.2 mg HCN/ kg BW) have been administered to man to demonstrate thiocyanate in saliva. This total oral dose level ( 0.2 mg/ kg BW) has been estimated as a NOAEL in comparison to the human LOAEL for mortality of 0.56  1.0 mg/ kg BW.

The single oral dose level of 0.4 mg/ kg/ BW for HCN has therefore been identified as a LOAEL in comparison to the estimated hydrogen cyanide human NOAEL of 0.2 mg/ kg BW for thiocyanate determinations in human saliva ( FDA 1956) and the LOAEL for cyanide mortality of 0.56 1.0 mg/ kg BW.

Dose and Endpoint for Establishing aRfD: 0.4 mg/ kg BW/ day LOAEL based on symptoms and clinical signs of hydrogen cyanide toxicity Uncertainty Factor ( UF): 100 ( 10X for intraspecies variations and 10X for steep doseresponse curve, severity of effects, and lack of a NOAEL.

Comments about Study/ Endpoint/ Uncertainty Factor: The Moertel clinical trial study arrived at the dose of amygdalin ( 0.5 g) that results in clinical signs in humans. The estimated human dose of 0.4 mg/ kg BW can be used for risk assessment purposes. The uncertainty factor of 100 incorporates 10X for intraspecies variations and 10X for lack of a NOAEL, severity of effects, and a steep dose response curve.

4.4.2 Chronic Reference Dose ( cRfD)

A chronic RfD was not selected because the range of appropriate systemic NOAELs in mammalian species is from 4.5  15 mg HCN/ kg BW/ day. These NOAELs far exceed the estimated human LOAEL of 0.4 mg/ kg BW used for the acute dietary RfD. If these substantially higher NOAELs were used for the cRfD, they would result in chronic exposures which would be greater than and possibly lethal in comparison to an acute dose. A summary of these mammalian studies is presented as follows:

The chronic ingestion of food fumigated with Hydrogen cyanide and containing residues up to 300 ppm has been fed to 10 rats/ sex/ dose in a 2 year feeding study ( Howard and Hanzal, 1955). There were no systemic effects, including neurotoxicity, up to the highest dose tested of 300 ppm in the food. Based on the food intake and body weight of young and old rats, the Acute RfD ( General population) = 0.4 mg/ kg ( LOAEL) = 0.004 mg/ kg 100 ( UF) Page 28 of 44 estimated dietary NOAEL was 10.8 mg/ kg BW/ day. Since the acute oral fatal dose of potassium cyanide for rats is between 10 15 mg/ kg BW ( Handbook of Toxicology, ( 1956)), yielding 4.0 to 6.0 mg/ kg BW Hydrogen cyanide, the rats in the 2 year study ingested 1.8 to 2.7 times the fatal dose of hydrogen cyanide each day throughout their lifetime without any measurable effects. Virtually no cyanide was found in plasma and kidneys. Low levels were found in erythrocytes ( mean of 1.9 µ g/ 100g). In the 2 year rat feeding study, residues of thiocyanate, the less toxic primary liver metabolite of cyanide, increased 3.5 fold in plasma, 3.3 fold in erythrocytes, 1.3 fold in liver, and 2.5 fold in kidneys of the rats exposed to Hydrogen cyanide in the diet ( Howard and Hanzal, 1955).

The systemic NOAEL of 10.8 mg/ kg BW/ day in the 2 year study in rats provides data which are supported by the results and NOAELs of other available studies.

In the 13 week repeated dose toxicity study ( NTP, 1993) in which sodium cyanide was administered in the drinking water, there were no mortalities or clinical signs ( associated with central nervous system effects) or histopathological effects in the brain, thyroid, or other organs of rats and mice exposed to doses up to 12.5 and 26 mg/ kg BW/ day, respectively. The reproductive tract in males was the most sensitive organ to cyanide exposure in this study: In rats at 12.5 mg/ kg BW/ day, there were lowered weight of testis and epididymis, together with a decrease in the number of spermatid heads in the testis and decreased motility of epididymal sperm. The NOAEL in this study, 4.5 mg/ kg BW/ day, is consistent with the 2 year study in rats which had a NOAEL of 10.8 mg/ kg BW/ day ( Howard and Hanzal, 1955).

These results are also roughly consistent with the NOAEL in the 14 week inhalation study ( Monsanto Co., 1984a) in which the airborne systemic no effect level of 204 mg acetone cyanohydrin ( ACH)/ m3 can be estimated to correspond to a daily dose of approximately 15 mg HCN/ kg BW/ day.

The other available studies specifically intended to investigate neurotoxicity or other effects of cyanides have major weaknesses: the study in miniature pigs ( Jackson, 1988), which reported slight functional thyroid changes and behavioral aberrations at 1.2 mg cyanide/ kg BW/ day, used a bolus dose with consequent high peaks of cyanide concentration in the organism and involved a very small number of animals ( three animals in four groups) and limited statistical analysis. Similarly, the neuropathological study in goats ( Soto Blanco et al, 2002), which reported ultrastructural changes in animals given > 0.48 mg cyanide/ kg BW/ day in drinking water for 5 months, did not present quantitative data or statistical analysis, since it was essentially a morphometric evaluation.

Studies by Philbrick et al ( 1979) showed decreased weight gain and thyroxin levels and myelin degeneration in rats ( 10 males/ dose, females were not investigated) fed CN for one year at the LOAEL of 30 mg/ kg BW/ day ( only dose tested). A NOAEL was not established. Page 29 of 44 4.4.3 Dermal Absorption Dermal absorption of Hydrogen cyanide is much slower than pulmonary absorption, and the amount and speed of absorption through human skin are dependent on the amount of skin moisture and duration of skin contact. There are no adequate dermal penetration studies with hydrogen cyanide. Since dermal exposure is not expected based on the use pattern, a dermal assessment was not conducted and a dermal absorption factor was not required for this assessment.

4.4.4 Dermal Exposure ( All Durations)

Worker and residential dermal exposures are not expected based on use patterns and restrictions and were therefore not assessed for this TRED.

4.4.5 Inhalation Exposure ( All Durations)

The inhalation endpoint for all exposure durations was selected based on a subchronic inhalation toxicity study in rats. In this study, Sprague Dawley rats ( 15/ sex/ dose) were exposed to acetone cyanohydrin ( ACH) [ which is rapidly hydrolyzed to hydrogen cyanide at physiological pH] at concentrations of 0, 36, 101, or 204 mg ACH/ m3 for 6 hours/ day, 5 days/ week, for 14 weeks. The exposures were equivalent to 0, 11, 32, and 65 mg HCN/ m3 ( Monsanto Co., 1984a). There were no treatment related deaths or effects in body weight or hematology. Irritation of the nose and eyes was observed, but no more in exposed than in non exposed animals. A decrease in blood glucose was recorded in mid and high dose females and a decrease in total serum protein and globulin was noted in mid and low dose females. There were no effects in serum T3 or T4 and histopathology. The NOAEL reported from the study was 204 mg ACH/ m3, corresponding to 65 mg HCN/ m3. This can be estimated to correspond to a daily dose of 15 mg cyanide/ kg BW/ day. However, in a similar 4 week inhalation study at an average ACH concentration of 211 mg m3 ( 67 mg hydrogen cyanide/ m3), no systemic effects were observed, except on the first day of exposure, when the concentrations in the chamber fluctuated and reached values of 225 mg ACH/ m3 ( 71 mg hydrogen cyanide/ m3) at which dose 3 out of 10 animals died ( Monsanto Co., 1984a, 1985c).

Dose/ Endpoint for Risk Assessment: The NOAEL of 65 mg HCN/ m3 based on mortality in 3 of 10 rats at the LOAEL of 71 mg/ m3 ( HDT). For occupational exposures, the inhalation study NOAEL of 65 mg HCN/ m3 ( 60 ppm) would be converted to human equivalent dose of 50 mg HCN/ m3 ( 65 mg HCN/ m3 x ( 6h/ 8h) assuming similar Regional Gas Distribution Ratio ( RGDR) between animals and humans ( USEPA, 1994).

Comments about Study/ Endpoint: The NOAEL/ LOAEL for the inhalation endpoint is based on the effect of mortality for hydrogen cyanide. The MOE is based on the uncertainty factor of 30X ( 3x interspecies factor and 10x intraspecies factor). The traditional interspecies factor of 10X is reduced to 3X since the doses are expressed as air concentrations and the Page 30 of 44 pharmacokinetics is assumed similar between animals and humans. The interspecies factor of 3x is considered sufficient to account for only pharmacodynamic differences between animals and humans. An additional 10X for steepness of dose response/ severity of effect was considered unnecessary due to the conservative nature of the selected endpoint, i. e., a subchronic exposure endpoint is used to assess intermittent short term exposure.

4.4.6 Margins of Exposure A summary of target Levels of Concern for risk assessment is provided in Table 9.

Table 9. Target Levels of Concern/ Margin of Exposure for Hydrogen Cyanide Route/ Duration Short Term ( 1 30 Days) Intermediate Term ( 1  6 Months) Long Term (> 6 Months) Occupational ( Worker) Exposure Dermal N/ A N/ A N/ A Inhalation 30 30 30 Residential ( Non Dietary) Exposure Oral N/ A N/ A N/ A Dermal N/ A N/ A N/ A Inhalation N/ A N/ A N/ A The uncertainty factor for inhalation exposure is 30X ( 3x interspecies factor and 10x intraspecies factor). For inhalation, the traditional interspecies factor of 10X is reduced to 3X since the doses are expressed as air concentrations and the pharmacokinetics is assumed similar between animals and humans. The interspecies factor of 3x is considered sufficient to account for only pharmacodynamic differences between animals and humans.

4.4.7 Recommendation for Aggregate Exposure Risk Assessments Under FQPA, when there are potential residential exposures to the pesticide, aggregate risk assessment must consider exposures from three major sources: oral, dermal and inhalation exposures. Since there are no residential uses, an assessment of aggregate exposure from risk from food and non food sources is not required.

4.4.8 Classification of Carcinogenic Potential The classification of the carcinogenic potential could not be determined due to the absence of acceptable cancer studies in rats and mice. Because of cyanide's high toxicity, it would be difficult to conduct a meaningful cancer study in rats and mice over a two year period. In addition, regulation of cyanide's acute toxicity is considered to be protective for potential carcinogenicity by the same rationale outlined in Section 4.4.2. Hydrogen cyanide has been evaluated for mutagenic potential with mixed results and several open literature references are available ( Table 8). Page 31 of 44 4.4.9 Summary of Endpoints Selected for Risk Assessment Toxicological doses/ endpoints selected for the hydrogen cyanide risk assessment are provided in Table 10.

Table 10. Summary of Toxicological Doses and Endpoints for Chemical for Use in Human Risk Assessments Exposure Scenario Dose Used in Risk Assessment, UF FQPA SF* and Level of Concern for Risk Assessment Study and Toxicological Effects Acute Dietary ( general population) Oral dose of 29.4 mg HCN calculated as single dose LOAEL of 0.4 mg/ kg/ day; UF = 100; aRfD = 0.004 mg/ kg/ day FQPA Safety Factor = 1 aPAD = 0.004 mg/ kg/ day Clinical trial study in humans, Moertel et al ( 1982). LOAEL of 0.4 mg/ kg/ day based on symptoms and clinical signs of hydrogen cyanide toxicity Inhalation ( all durations) NOAEL of 65 mg HCN/ m3 ( 60 ppm) ( 50 mg/ m3 or 46 ppm adjusted for occupational exposure) MOE requirement = 30 Subchronic ( 14 weeks) inhalation study with LOAEL of 71 mg HCN/ m3 ( 64 ppm) based on mortality in 3 of 10 rats after a single dose Cancer ( oral, dermal, inhalation) Classification: No available studies UF = uncertainty factor, FQPA SF = FQPA safety factor, NOAEL = no observed adverse effect level, LOAEL = lowest observed adverse effect level, PAD = population adjusted dose ( a = acute, c = chronic) RfD = reference dose, MOE = margin of exposure, LOC = level of concern, NA = Not Applicable Note: Study NOAEL is adjusted to human equivalent doses for occupational scenario only e. g., animal NOAEL of 65 mg/ m3 ( 6h/ day, 5d/ week) is adjusted to human NOAEL of 50 mg/ m3 ( 8 h/ day, 5d/ week), assuming the regional gas dose ratio ( RGDR) is similar between animals and humans ( 65 ppm x 6h/ 8h = 50 ppm) ( USEPA, 1994). * Refer to Section 4.3 4.5 Endocrine Disruption EPA is required under the FFDCA, as amended by FQPA, to develop a screening program to determine whether certain substances ( including all pesticide active and other ingredients) " may have an effect in humans that is similar to an effect produced by a naturally occurring estrogen, or other such endocrine effects as the Administrator may designate." Following recommendations of its Endocrine Disruptor and Testing Advisory Committee ( EDSTAC), EPA determined that there was a scientific basis for including, as part of the program, the androgen and thyroid hormone systems, in addition to the estrogen hormone system. EPA also adopted EDSTAC's recommendation that the Program include evaluations of potential effects in wildlife. For pesticide chemicals, EPA will use FIFRA and, to the extent that effects in wildlife may help determine whether a substance may have an effect in humans, FFDCA authority to require the wildlife evaluations. As the science develops and resources allow, screening of additional hormone systems may be added to the Endocrine Disruptor Screening Program ( EDSP).

In the available toxicity studies on hydrogen cyanide, there was no estrogen or androgen, mediated toxicity. Thyroid effects in the presence of liver toxicity were seen in both sexes at the highest dose tested in the chronic dog study. When additional appropriate screening and/ or Page 32 of 44 testing protocols being considered under the Agency's EDSP have been developed, hydrogen cyanide may be subjected to further screening and/ or testing to better characterize effects related to endocrine disruption.

5.0 PUBLIC HEALTH DATA Only five reports have been submitted by USDA APHIS concerning mishaps with M 44 Capsules containing sodium cyanide since 1992 when EPA set up the Incident Data System. None of the mishaps resulted in serious medical outcomes. All resulted in transient symptoms which were minor to moderate. Poison Control Centers have tracked rodenticide use of cyanide over the years since 1985, however, their system does not specify the form of the cyanide ( e. g., calcium cyanide, sodium cyanide, or hydrogen cyanide). On average Poison Control Centers receive only one report per year. Most listed the outcome as not determined or, at most, minor medical outcome.

6.0 DIETARY EXPOSURE ASSESSMENT 6.1 Dietary Profile A tolerance of 50 ppm for citrus has been established under 40 CFR § 180.130 for residues of hydrogen cyanide from postharvest fumigation as a result of application of sodium cyanide. There are no active national registrations for sodium cyanide with food/ feed uses. However, there is one SLN for California for food/ feed use registration for sodium cyanide. Sodium cyanide is used in California as a source of hydrogen cyanide gas to control red scale on fresh market citrus bound for Arizona. The SLN end use product is formulated as a granular containing 98% sodium cyanide and is used on citrus as a post harvest fumigant.

6.1.1 Magnitude of the Residue in Plants and Animals In a recently submitted study ( MRID 46868001), residues of hydrogen cyanide in orange peel averaged 1.2 ppm 8 hours after fumigation with 1 ounce sodium cyanide/ 100 ft3, 0.9 ppm 24 hours after fumigation, and 0.45 ppm 48 hours after fumigation. Residues of hydrogen cyanide in orange pulp averaged 0.06 ppm 8 hours after fumigation, 0.02 ppm 24 hours after fumigation, and < 0.01 ppm 48 hours after fumigation. Residues in whole oranges were not determined. Additional data are required for this study. Residue data from an additional two trials are required along with residue data on whole oranges. A detailed explanation of the modifications to EPA 335.2 along with validation of this method at the reported LOD of 0.01 ppm is required.

Since the use on citrus is for citrus destined for the fresh market in Arizona only, the 8 hour samples were not used in the dietary exposure analysis. The residue data for the 24 and 48 hour samples will be used to refine the dietary exposure analysis. The average residue input for citrus peel in DEEM FCID   model is 0.69 ppm and the residue input for citrus pulp is 0.013 ppm. This recently submitted residue data for citrus peel and citrus edible pulp should be used for Page 33 of 44 the dietary exposure analysis instead of previously submitted data which did not reflect residues which would be incurred in/ on pulp and peel.

6.1.2 Residue Analytical Method The residue data for citrus were obtained by a GLC procedure using a Coulson electrolytic nitrogen detector cell. No recovery data as such were reported, but the report notes that virtually all the Hydrogen cyanide gas was accounted for either as unabsorbed gas or as residues in the treated citrus. In effect, recoveries were well in excess of 95%. Background values were also not reported as such, but data in the studies indicated blanks ( residue values at 0  10 minutes) to be of the order of 1 ppm or less. EPA's response to the citrus petition notes that the method is adequate for obtaining residue data or as an alternate enforcement method ( PP# 1E1124; 2/ 17/ 71; W. Cox).

The enforcement in PAM, Vol II is a titrimetric method. This method involves the distillation of Hydrogen cyanide from acidified substrate into an alkaline solution followed by titration with silver nitrate. This method is considered adequate to determine residues of 1 ppm or more ( PP# 1E1124; 2/ 17/ 71; W. Cox).

6.2 Drinking Water Profile EFED does not anticipate significant exposure from sodium cyanide or hydrogen cyanide in surface water and ground water when it is used as a fumigant under controlled delivery system of gaseous hydrogen cyanide into an airtight enclosure as described in the sodium cyanide label ( SLA CA 840006) ( F. Kahn, D318020, 2/ 7/ 06). HED also evaluated potential exposure and risk from cyanide in drinking water sources in Arizona. Potential sources of cyanide drinking water contamination in Arizona include mining, metal finishing, and organic chemical industries. HED obtained monitoring data on total cyanide levels in public drinking water systems throughout the State of Arizona from the Arizona Department of Environmental Quality ( ADEQ). ADEQ provided drinking water monitoring data for a 13 year period  from January, 1993 through June, 2006. These data indicate that total cyanide concentrations are non detectable throughout the monitoring period ( Personal communication, John Calkins, ADEQ, 7/ 10/ 06). Based on this information, drinking water exposure is expected to be negligible and was therefore not assessed for this TRED.

6.3 Acute Dietary Exposure and Risk Dietary risk assessment incorporates both exposure and toxicity of a given pesticide. For acute assessments, the risk is expressed as a percentage of a maximum acceptable dose ( i. e., the dose which HED has concluded will result in no unreasonable adverse health effects). This dose is referred to as the population adjusted dose ( PAD). The PAD is equivalent to the reference dose ( RfD) divided by the Food Quality Protection Act ( FQPA) Safety Factor. Page 34 of 44 For acute exposures, HED is concerned when estimated dietary risk exceeds 100% of the PAD. References which discuss the acute and chronic risk assessments in more detail are available on the EPA/ pesticides web site: " Available Information on Assessing Exposure from Pesticides, A User's Guide," 6/ 21/ 2000, web link: http:// www. epa. gov/ fedrgstr/ EPAPEST 2000/ July/ Day 12/ 6061. pdf ; or see SOP 99.6 ( 8/ 20/ 99).

The acute dietary exposure assessment for hydrogen cyanide was conducted using the Dietary Exposure Evaluation Model software with the Food Commodity Intake Database ( DEEM FCID   , Version 2.03), which incorporates consumption data from USDA's Continuing Surveys of Food Intakes by Individuals ( CSFII), 1994 1996 and 1998. The 1994 96, 98 data are based on the reported consumption of more than 20,000 individuals over two non consecutive survey days. Foods " as consumed" ( e. g., apple pie) are linked to EPA defined food commodities ( e. g. apples, peeled fruit  cooked; fresh or N/ S; baked; or wheat flour  cooked; fresh or N/ S, baked) using publicly available recipe translation files developed jointly by USDA/ ARS and EPA. For chronic exposure assessment, consumption data are averaged for the entire U. S. population and within population subgroups, but for acute exposure assessment are retained as individual consumption events. Based on analysis of the 1994 96, 98 CSFII consumption data, which took into account dietary patterns and survey respondents, HED concluded that it is most appropriate to report risk for the following population subgroups: the general U. S. population, all infants (< 1 year old), children 1 2, children 3 5, children 6 12, youth 13 19, adults 20 49, females 13 49, and adults 50+ years old.

For acute exposure assessments, individual one day food consumption data are used on an individual by individual basis. The reported consumption amounts of each food item can be multiplied by a residue point estimate and summed to obtain a total daily pesticide exposure for a deterministic exposure assessment, or " matched" in multiple random pairings with residue values and then summed in a probabilistic assessment. The resulting distribution of exposures is expressed as a percentage of the aPAD on both a user ( i. e., only those who reported eating relevant commodities/ food forms) and a per capita ( i. e., those who reported eating the relevant commodities as well as those who did not) basis. In accordance with HED policy, per capita exposure and risk are reported for all tiers of analysis. However, for tiers 1 and 2, any significant differences in user vs. per capita exposure and risk are specifically identified and noted in the risk assessment.

HED conducted a somewhat refined probabilistic acute dietary exposure analysis using recently submitted field trial data for the hydrogen cyanide DEEM acute analysis. The recently submitted data for residues of hydrogen cyanide in orange peel and orange pulp were used for the dietary exposure analysis as it better reflects actual residues in the edible pulp and peel portions of the treated citrus. Previously submitted data provided whole fruit residues but did not provide residues in/ on pulp and peel. Citrus commodities are treated as non blended for this assessment because fumigation occurs post harvest. Therefore, blending of treated and non treated commodities is not likely to occur. Since treated fresh citrus commodities are non blended, residue distribution files ( RDFs) created using field trial data were used for this analysis. Two Page 35 of 44 RDFs were used, one for edible pulp residues and one for peel residues. Since there are so few commodities, all commodities are non blended, and only narrow range of residue values are available for each type of treated commodity, and treated citrus is destined for the fresh market in Arizona only, percent crop treated information is not a factor in the analysis. Since citrus destined for the fresh market only is fumigated, only fresh citrus commodities were used in the dietary analysis. Since citrus is treated in California and but shipped to and consumed only in Arizona, 8 hour residue samples were not used the dietary exposure analysis; only the residue data for the 24 and 48 hour samples were used. Based on the new data, residues included in the dietary analysis for edible citrus pulp ranged from < 0.005   0.04 ppm and residues in citrus peel ranged from 0.3   1.3 ppm.

The results of the acute dietary exposure analyses at the 95th, 99th, and 99.9th percentiles of exposure for consumption of fresh citrus ( edible pulp and peel) are presented in Tables 11 and 12. Data from the food diaries provided in the Food Commodity Intake Database ( FCID) can be used to characterize assumptions regarding fresh citrus consumption used in the DEEM analysis. Based on FCID data, young children ( 1 2 years, 3 5 years) are estimated to consume approximately 1 orange per day at the 95th percentile. For the general population, 95th percentile consumption is estimated to be 2 to 3 peeled oranges per day. As required in the HED policy, any significant differences in user vs. per capita exposure/ risk should be specifically identified and noted in the risk assessment. A user is a survey participant who consumes a treated target food during the period of analysis. The per capita measure estimates exposure risk in the subpopulation of interest as a whole, not just consumers of the treated commodity. Given that only treated citrus commodities are likely to be consumed during a single day, the period of analysis for acute dietary exposure, user exposure is considered the most appropriate risk measure for this analysis. These assessments conclude that acute dietary exposure estimates are below HED's level of concern.

Table 11. Hydrogen Cyanide DEEM Acute Dietary Exposure Analysis  Per Capita Exposure Population Subgroup aPAD ( mg/ kg/ day) 95th % ile Exposure ( mg/ kg/ day) % aPAD. ( 95th %) 99th % ile Exposure ( mg/ kg/ day) % aPAD ( 99th %) 99.9th % ile Exposure ( mg/ kg/ day) % aPAD ( 99.9th %)

General U. S. Population 0.004 0.0001 1 0.0002 4 0.0004 11 All Infants (< 1 year old) 0.004 > 0.0001 > 1 0.0001 1 0.0003 9 Children 1 2 years old 0.004 0.0001 3 0.0004 10 0.0009 23 Children 3 5 years old 0.004 0.0001 3 0.0003 9 0.0008 21 Children 6 12 years old 0.004 0.0001 2 0.0002 5 0.0005 11 Youth 13 19 years old 0.004 0.0001 1 0.0002 4 0.0004 10 Adults 20 49 years old 0.004 > 0.0001 > 1 0.0001 3 0.0003 7 Females 13 49 years old 0.004 > 0.0001 > 1 0.0001 3 0.0003 7 Adults 50+ years old 0.004 > 0.0001 > 1 0.0001 2 0.0002 5 Table 12. Hydrogen Cyanide DEEM Acute Dietary Exposure Analysis  Per User Exposure Population Subgroup aPAD ( mg/ kg/ day) 95th % ile Exposure ( mg/ kg/ day) % aPAD. ( 95th %) 99th % ile Exposure ( mg/ kg/ day) % aPAD ( 99th %) 99.9th % ile Exposure ( mg/ kg/ day) % aPAD ( 99.9th %) Page 36 of 44 Table 12. Hydrogen Cyanide DEEM Acute Dietary Exposure Analysis  Per User Exposure Population Subgroup aPAD ( mg/ kg/ day) 95th % ile Exposure ( mg/ kg/ day) % aPAD. ( 95th %) 99th % ile Exposure ( mg/ kg/ day) % aPAD ( 99th %) 99.9th % ile Exposure ( mg/ kg/ day) % aPAD ( 99.9th %)

General U. S. Population 0.004 0.0001 3 0.0003 7 0.0006 16 All Infants (< 1 year old) 0.004 0.0003 7 0.0005 11 0.0009 20 Children 1 2 years old 0.004 0.0004 9 0.0007 18 0.0014 37 Children 3 5 years old 0.004 0.0003 7 0.0006 15 0.0013 32 Children 6 12 years old 0.004 0.0002 5 0.0004 9 0.0006 14 Youth 13 19 years old 0.004 0.0002 5 0.0003 8 0.0005 14 Adults 20 49 years old 0.004 0.0001 3 0.0002 5 0.0005 12 Females 13 49 years old 0.004 0.0001 3 0.0002 5 0.0004 10 Adults 50+ years old 0.004 0.0001 2 0.0001 3 0.0002 7 7.0 OCCUPATIONAL EXPOSURE AND RISK Workers are potentially exposed to hydrogen cyanide from its use in post harvest fumigation of citrus contained in closed transport trailers. Sodium cyanide is used only in California to control red scale on fresh market citrus bound for Arizona under the restrictions of the SLN label. Consequently, fumigation of citrus with hydrogen cyanide is limited to a single facility in California. Worker exposure monitoring data from fumigations conducted at this facility were used to assess occupational exposure and risk to hydrogen cyanide resulting from citrus fumigation.

7.1 Regulatory Standards The current Occupational Safety and Health Administration ( OSHA) permissible exposure limit ( PEL) for hydrogen cyanide is 10 ppm ( 11 milligrams per cubic meter ( mg/ m3)) as an 8 hour time weighted average ( TWA) concentration. The OSHA PEL also bears a " skin" notation, which indicates that the cutaneous route of exposure ( including mucus membranes and eyes) contributes to overall exposure. The National Institute for Occupational Safety and Health ( NIOSH) has established a recommend exposure limit ( REL) for hydrogen cyanide of 4.7 ppm ( 5 mg/ m3) as a short term exposure limit ( STEL) or level at which an unprotected worker can be exposed for 15 minutes without harm. NIOSH also assigns a " skin" notation to hydrogen cyanide.

7.2 Exposure Monitoring Study A monitoring study of worker exposure to hydrogen cyanide was conducted in 1999 ( MRID 46648901) ( D. Jaquith, D318017, 3/ 30/ 06). The study monitored air concentrations of cyanide in the breathing zone of the applicators and in the ambient air resulting from fumigation of citrus contained in transport trailers. Monitoring was conducted at Washburn and Sons, Highgrove, CA, the only operators of a trailer/ truck citrus hydrogen cyanide fumigation facility. Air monitoring was conducted on 2 days during routine fumigation operations. Citrus containing trailers were treated in a closed system at label specified rates. The trailers were fumigated for 1 hour followed by aeration with more than 10 air changes for ½ to 1 hour. Following fumigation, the trailers were Page 37 of 44 ventilated for 1 hour through a ventilation stack with a height of 20 feet 6 inches at a rate of 800 ft3/ minute. A total of 10 fumigation/ ventilations were monitored during the study.

Airborne hydrogen cyanide concentrations were measured using Safelog 100 datalogging monitors. One monitor was carried in the breast pocket of the fumigator. One ambient monitor was located 50 feet from the trailer, somewhat farther than the 20 foot buffer zone required by the label. Additional area monitors were located downwind at distances of 50, 100, and 200 feet from the trailer. The detection range was 0 50 ppm in increments of 0.1 ppm with + 5% sensor accuracy and < 2% drift. The high alarm for Hydrogen cyanide is 10 ppm, the STEL and TWA Alarm is 4.7 ppm.

Hydrogen cyanide levels of the personal monitor worn by the fumigator are presented in Table 13. Exposure was low and no alarms were noted at any time. Peak 1 minute levels were 4.7 and 5.6 ppm for the two days. The peak STEL was 0.4 for each of the days The results of the ambient air monitoring are presented in Table 14. The TWAs were all zero. The peak 15 minute STEL ranged from 0 to 0.6. The latter was judged to be the result of displacement of a sunshade during monitoring.

Table 13. Gas Detection Report for the Fumigator Hydrogen cyanide Levels ( ppm) Date Time Start Stop # of Trailers Peak( 1min) Average STEL1 TWA2 2/ 18/ 99 10: 27 am  5: 31 pm 3 4.7 0 0.4 0 3/ 3/ 99 9: 00 am  8: 19 pm 7 5.6 0 0.4 0 1 The Short Term Exposure Limit ( STEL) to which an unprotected worker may be exposed over a 15 min periods 2 The time weighted average ( TWA) is the average air concentration taken over an eight hour period Table 14. Ambient Air Monitoring Results Hydrogen cyanide Levels ( ppm) Monitor No. Month Distance from Trailer ( ft) Peak ( 1 min) Avg STEL TWA 2 February 50 2.3 0 0 0 3 February 100 0.5 0 0 0 4 February 200 0.3 0 0 0 5 February 45 5.9 0 0.3 0 2 March 50 2.2 0 0 0 3 March 100 1.2 0 0 0 4 March 200 0.9 0 0.6 0 5 March 45 1 0 0.1 0 7.3 Inhalation Exposure and Risk A NOAEL of 65 mg/ m3 ( 60 ppm) has been established based on a continuous 6 hour exposure for 14 weeks. Adjusted for occupational exposure, the inhalation exposure endpoint for hydrogen cyanide is 50 mg/ m3 ( 46 ppm). The target LOC or MOE for inhalation exposure to hydrogen cyanide is 30. The peak 15 minute STEL for worker exposure from the monitoring study was 0.4 ppm ( 0.36 mg/ m3). It is important to note that, based on the fumigation process and as Page 38 of 44 indicated in the monitoring study, worker exposure from hydrogen cyanide fumigation is likely to be short term and intermittent rather than continuous. Therefore, use of an endpoint based on continuous exposure will result in a conservative estimate of risk. The MOE calculated using the highest worker STEL from the monitoring study is 115. Based on this analysis, calculated inhalation MOEs are below HED's level of concern.

7.4 Dermal Exposure and Risk Sodium cyanide is delivered to the container ( transport trailer) without handling by the fumigator and hydrogen cyanide is produced in a closed system. Dermal exposure and risks to hydrogen cyanide residues following sterilization cannot be fully determined without further information regarding the nature and extent of post sterilization activities ( e. g., post treatment handling of citrus). However, based on the fumigation method and the physical/ chemical nature of the fumigant, it is reasonable to assume that handling of and exposure to treated citrus during poststerilization activities is limited and dermal exposure is negligible.

8.0 AGGREGATE EXPOSURE AND RISK Aggregate exposure is assessed when there are potential residential exposures to the pesticide, aggregate risk assessment must consider exposures from three major sources: oral, dermal and inhalation exposures. Since there are no residential uses, an aggregate exposure risk assessments was not conducted.

9.0 CUMULATIVE RISK Section 408( b)( 2)( D)( v) of FFDCA requires that, when considering whether to establish, modify, or revoke a tolerance, the Agency consider " available information" concerning the cumulative effects of a particular pesticide's residues and " other substances that have a common mechanism of toxicity."

EPA does not have, at this time, available data to determine whether hydrogen cyanide has a common mechanism of toxicity with other substances. Unlike other pesticides for which EPA has followed a cumulative risk approach based on a common mechanism of toxicity, EPA has not made a common mechanism of toxicity finding as to hydrogen cyanide and any other substances and, hydrogen cyanide does not appear to produce a toxic metabolite produced by other substances which have tolerances in the U. S. For the purposes of this tolerance reassessment action, therefore, EPA has not assumed that hydrogen cyanide has a common mechanism of toxicity with other substances. For information regarding EPA's efforts to determine which chemicals have a common mechanism of toxicity and to evaluate the cumulative effects of such chemicals, see the policy statements released by EPA's OPP concerning common mechanism determinations and procedures for cumulating effects from substances found to have a common mechanism on EPA's website at http:// www. epa. gov/ fedrgstr/ EPA_ PEST/ 2002/ January/ Day_ 16/. Page 39 of 44 10.0 DATA NEEDS 10.1 Residue Chemistry Data Requirements  Storage stability data for citrus are required  Guideline 860.1380  Analytical standards for sodium and hydrogen cyanide are not currently available in the National Pesticide Standards Repository. Analytical Reference standards of sodium and hydrogen cyanide must be supplied and supplies replenished as requested by the Repository  Guideline 860.1650  Additional data are required to validate newly submitted residue data ( MRID 46868001). Residue data from an additional two trials are required along with residue data on whole oranges. A detailed explanation of the modifications to EPA 335.2 along with validation of this method at the reported LOD of 0.01 ppm is required.

10.2 Toxicology Data Requirements  None. The classification of the carcinogenic potential could not be determined due to the absence of acceptable cancer studies in rats and mice. However, because of cyanide's high toxicity, it would be difficult to conduct a meaningful cancer study in rats and mice over a twoyear period. Page 40 of 44 APPENDICES 1.0 GUIDELINE TOXICOLOGY DATA SUMMARY Data requirements ( 40CFR 158.340) for hydrogen cyanide are provided in the following table. Use of new GL numbers does not imply that new ( 1998) guideline protocols were used.

Technical Test Required Satisfied 870.1100 Acute Oral Toxicity.......................................................... 870.1200 Acute Dermal Toxicity ..................................................... 870.1300 Acute Inhalation Toxicity ................................................. 870.2400 Primary Eye Irritation ....................................................... 870.2500 Primary Dermal Irritation ................................................. 870.2600 Dermal Sensitization......................................................... yes yes yes yes yes yes yes yes yes yes yes yes 870.3100 Oral Subchronic ( rodent).................................................. 870.3150 Oral Subchronic ( nonrodent)............................................ 870.3200 21 Day Dermal ................................................................. 870.3250 90 Day Dermal ................................................................. 870.3465 90 Day Inhalation ............................................................. yes yes no no yes yes yes no no yes 870.3700a Developmental Toxicity ( rodent) ..................................... 870.3700b Developmental Toxicity ( nonrodent) ............................... 870.3800 Reproduction..................................................................... yes yes yes yes yes yes 870.4100a Chronic Toxicity ( rodent) ................................................. 870.4100b Chronic Toxicity ( nonrodent) ........................................... 870.4200a Oncogenicity ( rat) ............................................................. 870.4200b Oncogenicity ( mouse)....................................................... 870.4300 Chronic/ Oncogenicity....................................................... yes yes yes yes yes no yes no no no 870.5100 Mutagenicity Gene Mutation  bacterial......................... 870.5300 Mutagenicity Gene Mutation  mammalian.................... 870.5xxx Mutagenicity Structural Chromosomal Aberrations....... 870.5xxx Mutagenicity Other Genotoxic Effects ........................... yes yes yes yes yes yes yes yes 870.6100a Acute Delayed Neurotox. ( hen)........................................ 870.6100b 90 Day Neurotoxicity ( hen).............................................. 870.6200a Acute Neurotox. Screening Battery ( rat).......................... 870.6200b 90 Day Neuro. Screening Battery ( rat)............................. 870.6300 Develop. Neuro................................................................. no no yes yes no   yes yes no 870.7485 General Metabolism ......................................................... 870.7600 Dermal Penetration........................................................... yes yes yes yes Special Studies for Ocular Effects Acute Oral ( rat)................................................................. Subchronic Oral ( rat)........................................................ Six month Oral ( dog) ....................................................... no no no no no no Page 41 of 44 2.0 NON CRITICAL TOXICOLOGY STUDIES None 3.0 REFERENCES MRID 00129726 Clemedson, C.; Hultman, H.; Sorbo, B. ( 1955) A combination of rhodanese and ethanethiosulfonate as an antidote in experimental cyanide poisoning. Acta. Phys. Scandinav. 35: 31 35. ( Also In unpublished submission received Jul 8, 1975 under 6704 75; submitted by U. S. Fish and Wildlife Service, Washington, DC; CDL: 221264 R)

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