Sodium Tetrathiocarbonate 

 Summary Document: 

 Registration Review 

December 2007 

Docket Number: EPA-HQ-OPP-2007-1084 

www.regulations.gov

TABLE OF CONTENTS 

 Page # 

I. Preliminary Work Plan (PWP) 4 

II. Fact Sheet 9

III. Ecological Risk Assessment Problem Formulation 13

IV. Human Health Effects Scoping Document 36

V. Glossary of Terms and Abbreviations 46

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I. PRELIMINARY WORK PLAN

Introduction: 

The Food Quality Protection Act of 1996 mandated a new program: registration review. 

All pesticides distributed or sold in the United States generally must be registered by 

EPA, based on scientific data showing that they will not cause unreasonable risks to 

human health, workers, or the environment when used as directed on product labeling. 

The new registration review program is intended to make sure that, as the ability to assess 

risk evolves and as policies and practices change, all registered pesticides continue to 

meet the statutory standard of no unreasonable adverse effects. Changes in science, 

public policy, and pesticide use practices will occur over time. Through the new 

registration review program, the Agency periodically reevaluates pesticides to make sure 

that as change occurs, products in the marketplace can be used safely. Information on this 

program is provided at: http://www.epa.gov/oppsrrd1/registration_review/. 

The Agency has begun to implement the new registration review program and will 

review each registered pesticide every 15 years to determine whether it continues to meet 

the FIFRA standard for registration. The public phase of registration review begins when 

the initial docket is opened for each case. The docket is the Agency’s opportunity to state 

clearly what it knows about the pesticide and what additional risk analyses and data or 

information it believes are needed to make a registration review decision. After 

reviewing and responding to comments and data received in the docket during this initial 

comment period, the Agency will develop and commit to a Final Work Plan and schedule 

for the registration review of sodium tetrathiocarbonate. 

Sodium tetrathiocarbonate (Na2Cs4) is a soil fumigant which acts as a fungicide, 

insecticide, and nematicide. Sodium tetrathiocarbonate degrades to carbon disulfide 

(CS2), hydrogen sulfide (H2S), sodium hydrazide, and elemental sulfur upon contact with 

water. CS2 (PC code 016401) is the major biologically active degradate. Tolerances are 

established for CS2 from the application of sodium tetrathiocarbonate. CS2 from the 

application of sodium tetrathiocarbonate is the residue of concern for risk assessment. 

Sodium tetrathiocarbonate is registered for pre-plant and post-plant soil applications on 

almonds, grapes, lemons, oranges, peaches, prunes, and plums. It provides control of soil 

nematodes (e.g., ring, root-knot), diseases (e.g., phytophthora, armillaria) and insects 

(e.g., grape phylloxera). It cannot be used in greenhouses and other enclosed areas. 

There are no registered residential uses. Sodium tetrathiocarbonate is currently labeled 

for use only in Arizona, California, Oregon, and Washington. 

Anticipated Risk Assessment and Data Needs: 

The Agency will conduct a comprehensive ecological risk assessment, including an 

endangered species assessment, for the registered uses of sodium tetrathiocarbonate. 

Human health occupational and residential bystander risk assessments will also be 

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needed for the registered uses of sodium tetrathiocarbonate. The Agency also anticipates 

conducting a drinking water risk assessment for groundwater. 

Ecological Risk: 

• The environmental fate database for sodium tetrathiocarbonate is largely 

complete. Fate data requirements have been satisfied with data from sodium, 

calcium, or potassium tetrathiocarbonate. Physical and chemical properties are 

available from open literature sources. 

• There are gaps and uncertainties in the ecological effects database for sodium 

tetrathiocarbonate. The following data on freshwater fish and invertebrates, 

terrestrial plants, and honeybees will be required to complete the ecological 

assessment and will be issued in a data call-in (DCI) during the registration 

review process: 

o Early life stage freshwater-fish (850.1400) 

o Freshwater invertebrate lifecycle toxicity (850.1300) 

o Tier I vegetative vigor (850.4150) 

o Tier I seedling emergence (850.4100) 

o Acute oral or contact honeybees (850.3020) 

• The planned ecological risk assessment will allow the Agency to determine if 

sodium tetrathiocarbonate’s use has "no effect" on federally listed threatened or 

endangered species (listed species) or their designated critical habitat. If the 

screening level assessment indicates that sodium tetrathiocarbonate "may affect" a 

listed species or its designated critical habitat, the assessment will be refined. The 

refined assessment will allow the Agency to determine whether use of sodium 

tetrathiocarbonate is “likely to adversely affect” the species or critical habitat or 

"not likely to adversely affect" the species or critical habitat. When an assessment 

concludes that a pesticide's use "may affect" a listed species or its designated 

critical habitat, the Agency will consult with the U.S. Fish and Wildlife Service 

and/or National Marine Fisheries Service (Services), as appropriate. 

Human Health Risk: 

• Human health risk assessments for agricultural workers and handlers and 

residential bystanders potentially exposed to CS2 as a result of agricultural uses of 

sodium tetrathiocarbonate will need to be updated to reflect current policy and 

practice for soil fumigants. 

• The Agency anticipates needing the following study to complete the bystander 

assessment for CS2 as a result of agricultural uses of sodium tetrathiocarbonate: 

o Special study to determine the flux rate of the compound off-site 

• The Agency will also review and consider the available literature on toxicity and 

exposure, air monitoring databases developed by the California Air Resources 

Board (CARB), and other information available on CS2 prior to issuing the Final 

Work Plan. 

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• Dietary assessments were not conducted in the past because in food CS2 residues 

from application of sodium tetrathiocarbonate were considered “de minimus” 

meaning that residues were not detected at levels above natural background. 

• Although dietary risk from food is not a concern, tolerances for CS2 from 

application of sodium tetrathiocarbonate will need to be re-evaluated since the 

existing tolerances were established based on exaggerated application rates. 

 

• The Agency anticipates conducting a drinking water assessment for groundwater. 

• If a drinking water assessment indicates potential exposures to CS2 as a result of 

agricultural uses of sodium tetrathiocarbonate, an aggregate risk assessment 

combining potential residential bystander exposures with dietary and drinking 

water exposures will be needed. 

Timeline: 

EPA has created the following estimated timeline for the completion of the sodium 

tetrathiocarbonate registration review. 

 

Sodium Tetrathiocarbonate – 

Projected Registration Review Timeline 

Activities Estimated 

Year/Month 

Phase 1: Opening the docket 

Open Public Comment Period 2007 – Dec. 

Close Public Comment Period 2008 – Mar. 

Phase 2: Case Development 

Develop Final Work Plan (FWP) 2008 – Apr.-Jun. 

Issue DCI 2009 – Jan.-Mar 

Data Submission 2011 – Jan.-Mar. 

Preliminary Risk Assessment and Public Comment 2012 – Jul.-Sep. 

Close Public Comment Period 2012 – Oct.-Dec. 

Phase 3: Registration Review Decision 

Proposed Registration Review Decision 2013 – Jan.-Mar. 

Public Comment Period 2013 – Apr.-Jun. 

Final Registration Review Decision and 

Begin Post-Decision Follow-up 

2013 – Jul.-Sep. 

Total (years) 6 

Guidance for Commenters: 

The public is invited to comment on EPA’s preliminary registration review work plan 

and rationale. The Agency will carefully consider all comments as well as any additional 

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information or data provided prior to issuing a Final Work Plan for the sodium 

tetrathiocarbonate case. 

• Through the registration review process, the Agency intends to solicit information 

on trade irritants and, to the extent feasible, take steps toward facilitating irritant 

resolution. Growers and other stakeholders are asked to comment on any trade 

irritant issues resulting from lack of Maximum Residue Limits (MRLs) or 

disparities between U.S. tolerances and MRLs in key export markets, providing as 

much specificity as possible regarding the nature of the concern. See page 43 of 

Section IV, Human Health Effects Scoping Document, for a listing of U.S. 

tolerances. 

• Sodium tetrathiocarbonate is not identified as a cause of impairment for any 

waterbodies listed as impaired under section 303(d) of the Clean Water Act, based 

on information provided at 

http://oaspub.epa.gov/tmdl/waters_list.impairments?p_impid=3. The Agency 

invites submission of water quality data for this pesticide. To the extent possible, 

data should conform to the quality standards in Appendix A of the “OPP Standard 

Operating Procedure: Inclusion of Impaired Water Body and Other Water Quality 

Data in OPP’s Registration Review Risk Assessment and Management Process” 

(see: http://www.epa.gov/oppfead1/cb/ppdc/2006/november06/session1-sop.pdf ), 

to ensure they can be used quantitatively or qualitatively in pesticide risk 

assessments. 

• EPA seeks to achieve environmental justice, the fair treatment and meaningful 

involvement of all people, regardless of race, color, national origin, or income, in 

the development, implementation, and enforcement of environmental laws, 

regulations, and policies. To help address potential environmental justice issues, 

the Agency seeks information on any groups or segments of the population who, 

as a result of their location, cultural practices, or other factors, may have atypical, 

unusually high exposure to sodium tetrathiocarbonate, compared to the general 

population. Please comment if you are aware of any such sub-populations. 

Stakeholders are also specifically asked to provide information and data that will assist 

the Agency in refining the ecological risk assessment, including any species-specific 

effects determinations. 

The Agency is interested in the following information regarding the use of sodium 

tetrathiocarbonate: 

1. confirmation on the following label information 

a. sites of application 

b. formulations 

c. application methods and equipment 

d. maximum application rates 

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e. frequency of application, application intervals, and maximum number of 

 applications per season 

f. geographic limitations on use 

2. use or potential use distribution (e.g., acreage and geographical distribution of 

relevant crops) 

3. use history 

4. median and 90th percentile reported use rates (lbs ai/acre) from usage data – 

national, state, and county 

5. application timing (date of first application and application intervals) by crop – 

national, state, and county 

6. sub-county crop location data 

7. usage/use information for non-agricultural uses (e.g., forestry, residential) 

 8. directly acquired county-level usage data (not derived from state level data) 

 a. maximum reported use rate (lbs ai/acre) from usage data – county 

 b. percent crop treated – county 

 c. median and 90th percentile number of applications – county 

 d. total pounds per year – county 

 e. the year the pesticide was last used in the county/sub-county area 

 f. the years in which the pesticide was applied in the county/sub-county area 

9. typical interval (days) 

10. state or local use restrictions 

11. ecological incidents (non-target plant damage and avian, fish, reptilian, amphibian 

and mammalian mortalities) not already reported to the Agency 

12. monitoring data 

Next Steps: 

After the comment period closes, the Agency will prepare a Final Work Plan for this 

pesticide.

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II. FACT SHEET

Background Information: 

• Sodium tetrathiocarbonate [Carbono(dithioperoxo)dithioic acid, disodium salt] 

registration review case number: 7009. 

• Sodium tetrathiocarbonate: PC Code: 128904; CAS#: 7345-69-9. 

• The major biologically active degradate, carbon disulfide (CS2), is also considered 

in the sodium tetrathiocarbonate registration review case. 

• Carbon disulfide (CS2): PC Code: 016401; CAS# 75-15-0. 

• Technical registrant: Arysta LifesSciences North America Corp. 

• Not subject to reregistration; thus, no Reregistration Eligibility Decision (RED) is 

available. 

• Tolerances were reassessed under FQPA to include a new use May 16, 1997 (62 

FR 26946) (FRL – 5716-8).

• Currently, there are two active Section 3 registrations: 66330-63 (ETK-1101) and 

66330-69 (ENZONE). 

• Labeled for use only in Arizona, California, Oregon, and Washington. 

• Currently, there are no active Section 24c registrations. 

• Special Review and Reregistration Division Chemical Review Manager (CRM): 

Katherine St. Clair (stclair.katherine@epa.gov). 

• Registration Division Product Contacts: Tawanda Spears 

(spears.tawanda@epa.gov) and/or Cynthia Giles-Parker (gilesparker.cynthia@epa.gov). 

Use & Usage Information: 

For additional details on label rates and allowed uses, please refer to the BEAD 

Appendix A document in the Sodium tetrathiocarbonate docket. 

• Sodium tetrathiocarbonate is fumigant pesticide which acts as a fungicide, 

nematicide, and insecticide. 

• It is registered for pre-plant and post-plant soil applications on almonds, grapes, 

lemons, oranges, peaches, prunes, and plums. 

• It is used to control soil nematodes (e.g., ring, root-knot), diseases (e.g., 

phytophthora, armillaria) and insects (e.g., grape phylloxera). 

• The pesticidal mode of action of sodium tetrathiocarbonate and carbon disulfide is 

unknown. 

• Sodium tetrathiocarbonate is formulated as an aqueous solution that breaks down 

in the soil to CS2 gas, the major biologically active degradate. 

• Sodium tetrathiocarbonate may be applied through ground injection equipment or 

may be metered into irrigation water used for low-volume irrigation 

(chemigation) or flood and furrow irrigation. 

• Sodium tetrathiocarbonate cannot be used in greenhouses and other enclosed 

areas. 

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• There are no residential uses. 

• Approximately 700,000 pounds of sodium tetrathiocarbonate are used annually 

(lbs a.i./yr.). 

• Nearly 90% (600,000 lbs a.i./yr.) of sodium tetrathiocarbonate usage is on grapes; 

almonds is the crop with the next highest usage at approximately 6% (40,000 lbs 

a.i./yr.). 

Recent Actions:

• A request to expand use directions, add restrictions, and add Florida to EPA reg# 

66330-63 was denied in February 2003 due to data and label deficiencies. 

Ecological Risk Assessment Status: 

Please refer to Section III of this document, Ecological Risk Assessment Problem 

Formulation, for a detailed discussion of the anticipated ecological risk assessment needs. 

The following is a summary of these anticipated needs: 

• The most recent ecological risk assessment for sodium tetrathiocarbonate was 

conducted in 1995 for proposed new uses on almonds, peaches, and prunes. The 

1995 ecological risk assessment concluded that labeled use of sodium 

tetrathiocarbonate was not expected to pose acute or chronic risk to non-target 

avian, mammalian, fish, aquatic invertebrate, or plant species. However, some of 

the risks were assessed qualitatively (i.e., aquatic exposures were not 

quantitatively estimated), and the potential risks to some receptors (terrestrial 

plants and terrestrial invertebrates) were not assessed. 

• An additional uncertainty is the potential for exposure to aquatic organisms 

through release of treated tailwater. Labels state that “tailwater must not be 

allowed to leave the treated field,” but no details, such as trapping methods or 

holding times, are included. The possibility remains, then, that different 

interpretations of this requirement by users could lead to surface water exposure. 

• The environmental fate database for sodium tetrathiocarbonate is largely 

complete. Fate data requirements have been satisfied with data from sodium, 

calcium, or potassium tetrathiocarbonate. Physical and chemical properties are 

available from open literature sources. 

 

• There are gaps and uncertainties in the ecological effects database for sodium 

tetrathiocarbonate. Data on freshwater fish and invertebrates, terrestrial plants, 

and honeybees will be required to complete the ecological assessment and will be 

issued in a data call-in (DCI) during the registration review process. 

• The Agency plans to conduct a comprehensive ecological risk assessment, 

including an endangered species assessment, for the registered uses of sodium 

tetrathiocarbonate. 

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Human Health Risk Assessment Status: 

Please refer to Section IV of this document, Human Health Effects Scoping Document, 

for a detailed discussion of the anticipated risk assessment needs for human health. The 

following is a summary of these anticipated needs: 

Dietary (Food and Water): 

• Dietary assessments were not conducted in the past because in food CS2 residues 

from application of sodium tetrathiocarbonate were considered “de minimus” 

meaning that residues were not detected at levels above natural background. 

• Although dietary risk from food is not a concern, tolerances for CS2 from 

application of sodium tetrathiocarbonate will need to be re-evaluated since the 

existing tolerances were established based on exaggerated application rates. 

• The Agency anticipates conducting a drinking water assessment for groundwater. 

Residential: 

• There are no residential uses for sodium tetrathiocarbonate. However, there is 

potential for residential bystander exposure to CS2 as a result of agricultural uses 

of sodium tetrathiocarbonate. 

• Human health risk assessments for residential bystanders potentially exposed to 

CS2 as a result of agricultural uses of sodium tetrathiocarbonate will need to be 

updated to reflect current policy and practice for soil fumigants.

Occupational: 

• Human health risk assessments for agricultural workers and handlers potentially 

exposed to CS2 as a result of agricultural uses of sodium tetrathiocarbonate will 

need to be updated to reflect current policy and practice for soil fumigants. 

Aggregate: 

• If a drinking water assessment indicates potential exposures to CS2 as a result of 

agricultural uses of sodium tetrathiocarbonate, an aggregate risk assessment 

combining potential residential bystander exposures with dietary and drinking 

water exposures will be needed. 

Overall: 

• The Agency anticipates needing a “flux” study in order to complete a risk 

assessment of occupational and residential bystander exposure to CS2 as a result 

of agricultural uses of sodium tetrathiocarbonate and for use in setting appropriate 

buffer zones to mitigate off-site exposure. 

• The Agency will review and consider the available literature on toxicity and 

exposure, air monitoring databases developed by the California Air Resources 

Board (CARB), and other information available on CS2 prior to issuing the Final 

Work Plan. 

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Incident Reports: 

• Three data bases were searched for incidents reports on sodium 

tetrathiocarbonate: Poison Control Center (PCC) Data, NIOSH SENSOR, and the 

Incidents Data System. No incidents for sodium tetrathiocarbonate were reported 

in the PCC during the period 1993 through 2005 or the Incident Data System from 

1999 to the present. NIOSH SENSOR reported 2 cases of sodium 

tetrathiocarbonate poisonings. Both incidents occurred in California with one in 

1999 and one in 2001. A more detailed summary is provided in the scoping 

document for registration review located in the docket. 

Tolerances: 

U.S. tolerances are listed under 40 CFR 180.467. Tolerances are established for the 

nematicide, insecticide, and fungicide CS2 from the application of sodium 

tetrathiocarbonate. No MRLs for sodium tetrathiocarbonate have been established or 

proposed by Codex for any agricultural commodities. There are no Canadian or Mexican 

tolerances for carbon disulfide. 

Data Call-In Status: 

A DCI has not been issued for sodium tetrathiocarbonate. 

Labels: 

A list of registration numbers is included below and the labels can then be obtained from 

the Pesticide Product Label System (PPLS) website: 

http://oaspub.epa.gov/pestlabl/ppls.home.

These labels were transferred from Entek Corp. to Arysta LifeScience North America 

Corp. and the labels are available under their previous EPA registration numbers, 68891-

9 for 66330-63 and 68891-2 for 66330-69. 

Registration 

Number 

Product Name Company % Active 

Ingredient 

66330-63 ETK-1101 

Arysta LifeScience North 

America Corporation 53 

66330-69 ENZONE 

Arysta LifeScience North 

America Corporation 31.8 

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III. ECOLOGICAL RISK ASSESSMENT PROBLEM FORMULATION

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An additional uncertainty is the potential for exposure to aquatic organisms through 

release of treated tailwater. Labels state that “tailwater must not be allowed to leave the 

treated field,” but no details, such as trapping methods or holding times, are included. 

The possibility remains, then, that different interpretations of this requirement by users 

could lead to surface water exposure.

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1. PRELIMINARY PROBLEM FORMULATION

The purpose of problem formulation is to provide the foundation for the ecological risk 

assessment to be conducted for sodium tetrathiocarbonate. It sets the objectives for the 

risk assessment, evaluates the nature of the problem, and provides a plan for analyzing 

the data and characterizing the risk (US EPA, 1998). 

1.1 Nature of Regulatory Action 

The registration for sodium tetrathiocarbonate is being reviewed under the Registration 

Review program mandated by the Federal Insecticide, Fungicide, and Rodenticide Act in 

order to determine whether it continues to meet the statutory standard for registration. 

The current analysis is based on the original new chemical assessment, the most recent 

new use and drinking water assessments, and an early fate review which includes the 

most complete discussion of available field studies: 

• Review of lysimeter and groundwater monitoring studies (7/27/1988, P. Holden) 

• Section 3 New Chemical Risk Assessment of proposed uses on grapes, citrus, 

orchards, and potatoes (Eco: 9/20/88, J. Ackerman; Fate: 5/16/89, E. Regelman) 

• Section 3 New Use Risk Assessment of proposed uses on almonds, peaches, and 

prunes (Eco: 5/4/1995, DP Barcode D213559; Fate: 7/9/1996, DP Barcodes 

D220367, D223296) 

• Drinking Water Assessment for proposed new use on citrus in Florida (3/19/02, 

A. Clem) 

Additional ecological toxicity studies (MRIDs 46423901, -02, -03, -04) have been 

submitted and will be formally reviewed during the risk assessment process. 

1.2 Stressor Source and Distribution 

 1.2.1 Nature of the Chemical Stressor 

Sodium tetrathiocarbonate (Na2CS4) is a fumigant which acts as a fungicide and 

nematicide. Sodium tetrathiocarbonate has two soluble concentrate formulations, 

EnZone® (3.4 lb a.i./gal, 31.8% a.i., Reg No. 68891-2) and ETK-1101® (6.8 lb a.i./gal, 

53% a.i., Reg. No. 68891-9). Upon mixing with water, Na2CS4 converts readily to 

carbon disulfide (CS2), the compound that is actually responsible for pesticidal activity. 

The pesticidal mode of action of carbon disulfide is unknown. Chemical identification 

information and physical and chemical properties of these compounds are presented in 

Table 1. 

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Table 1. Nature of the Chemical Stressor 

Common name Sodium tetrathiocarbonate 

(parent chemical)

Carbon disulfide 

(major degradate)

Chemical name Carbono(dithioperoxo)dithioic 

acid, disodium salt Carbon disulfide 

Pesticide type fungicide, nematicide fungicide, nematicide 

CAS number 7345-69-9 75-15-0 

PC Code 128904 016401 

Empirical formula Na2CS4 CS2

Chemical Structure S = C = S 

Molecular Mass (g/mol) 186.2 76.1 

Vapor pressure (mm Hg) 4E-10 a,b 359 a

Henry’s Law Constant 

(atm-m3/mol) -- 0.014 a

Solubility in water (g/L) 1E6 a,b 1180 a

Log Kow -4.68 a,b 1.94 a

a

 From the SRC Physical Properties database (http://www.syrres.com/esc/physdemo.htm, accessed 9/07). 

b

 Estimated rather than experimental value. 

 1.2.2 Overview of Pesticide Usage 

 1.2.2.1 Labeled Uses and Application Rates 

Sodium tetrathiocarbonate is a fumigant used on grapes, some citrus crops (oranges, 

grapefruit, lemons) and some orchard crops (almonds, peaches, prunes, and plums). It is 

currently only labeled for use in Arizona, California, Oregon, and Washington. 

In crops established for one year or more and in preplant sites, sodium tetrathiocarbonate 

is used to control nematodes in all labeled crops and to control phytophthera root rot in 

all crops except grapes. It is also used to control oak root fungus in all crops, although 

for grapes and citrus crops, it can only be used in preplant sites. In grapes, sodium 

tetrathiocarbonate is also used to control phylloxera. Sodium tetrathiocarbonate cannot 

be used in greenhouses and other enclosed areas. 

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Sodium tetrathiocarbonate is applied through ground injection or through chemigation, 

where the active ingredient is metered into water used for low-volume irrigation or flood 

and furrow irrigation. Low-volume irrigation systems allowed by the label include drip, 

drip-tape, strip tubing, foggers, jets, misters, and mini-sprinklers, with limits specified for 

pressure and flow rates of the equipment. Ground injection is to a depth of six to nine 

inches and is only used for established crops. Applications to established orchard crops, 

citrus crops, and grapes can generally be made through the entire growing season. 

Preplant applications can be made one to four weeks before planting. 

The label directs application by specific procedures designed for rapid penetration and 

uniform coverage: 1) prior to application, the soil is to be brought to near, but less than, 

field moisture capacity; 2) chemigation is continuously metered for up to 12 hours to 

attain the necessary application rate; 3) finally, the soil is “sealed” by slowly flushing 

lines and emitters for up to 4 hours with sufficient clean water to attain field moisture 

capacity. Chemigation water concentrations are required to be maintained at minimum 

levels of 250 to 2400 ppm, depending on the use. The labels direct that “tailwater must 

not be allowed to leave the treated field” but no holding times or other specific 

instructions are included. 

The maximum annual application rate for sodium tetrathiocarbonate is 340 lb a.i./A (139 

lb CS2/A). For ground injection, it is applied in one to three applications with maximum 

single application rates of up to 170 lb a.i./A (69 lb CS2/A) and minimum application 

intervals of 30 days. For most low-volume or flood and furrow applications, sodium 

tetrathiocarbonate is applied in one to six applications with maximum single application 

rates of 102 to 204 lbs a.i./A (42 to 84 lb CS2/A), depending on the use. For preplant use 

in citrus and orchard crops, though, it can be applied as a single application at 340 lbs 

a.i./A. For flood and furrow irrigation, the minimum application interval is 30 days, 

while for low-volume irrigation, the application interval can be up to 21 days with no 

minimum specified. 

 1.2.2.2 Use Characterization 

The Screening Level Usage Analysis (SLUA) report prepared by the Biological and 

Economics Analysis Division (5/29/07) indicates a national use of sodium 

tetrathiocarbonate of approximately 674,000 lbs a.i./yr. Nearly 90% of this use (600,000 

lbs) is on grapes, with almonds being the next highest use at 6% (40,000 lbs). Other uses 

of sodium tetrathiocarbonate include peaches, prunes and plums, lemons, oranges, 

nectarines, pecans, and cherries. These estimates are based on data from USDA-NASS, 

private market research from 2000 to 2006, the 2000 National Pesticide Use Database, 

and California Department of Pesticide Regulation (CDPR) data. 

Annual data specific to California are available from the Pesticide Use Reports compiled 

by CDPR. In 2005, approximately 330,000 lbs of sodium tetrathiocarbonate were 

applied to 8,000 acres in California. The primary use that year was on grapes (table, 

raisin, and wine), which accounted for 227,000 lbs. Also in 2005, about 90,000 lbs of 

sodium tetrathiocarbonate were used on almonds; this is a dramatic increase in usage on 

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this crop since less than 5,000 lbs were used annually on almonds between 2000 and 

2004. Total sodium tetrathiocarbonate use in California has been dropping since 2000, 

when approximately 600,000 lbs were used (Source: 

http://calpip.cdpr.ca.gov/cfdocs/calpip/prod/main.cfm, accessed 9/07). 

 1.2.3 Environmental Fate and Transport Summary 

The environmental fate database for sodium tetrathiocarbonate (Na2CS4) is largely 

complete. Fate studies show that Na2CS4 degrades rapidly in water (half-lives on the 

order of several hours to one day) through hydrolysis and photolysis. Carbon disulfide 

(CS2) is the active agent released through hydrolysis in water. CS2 has a high vapor 

pressure and a high Henry’s Law constant, physical properties favorable for 

volatilization. CS2 diffuses rapidly through soil air, initially moving downward through 

the soil profile, followed by diffusion upwards and volatilization to the atmosphere. In 

aerobic soil environments, CS2 is oxidized to sulfates through biological degradation 

(half-lives ranging from 3-27 days). Field studies show that contamination of CS2 in 

ground water may occur under normal uses of sodium tetrathiocarbonate. The observed 

contamination was short-lived, but these studies did not represent worst case conditions. 

Air monitoring shows half-lives of hours to several days for dissipation of CS2 in air from 

ground level to five feet about the surface. 

 1.2.3.1 Environmental Fate Assessment 

Some of the available fate studies tested the calcium or potassium salts of 

tetrathiocarbonate rather than the sodium salt. Data from sodium, calcium, and 

potassium tetrathiocarbonate are considered to be equivalent for the purposes of this 

discussion. Aqueous solutions of the salts are essentially totally ionized and the character 

of the solution is dominated by the common anion, CS4

2-, so the nature of the cation has 

little direct effect on the properties of the product (11/20/86, E. Regelman). 

When Na2CS4 is mixed with water, it hydrolyzes rapidly to the volatile degradate CS2 at 

rates dependant on concentration and pH. Below pH 7, hydrolysis is essentially 

immediate, with rates limited only by the rate of mass transfer of CS2 out of solution. At 

a higher pH, hydrolysis is slower, with half-lives from 3 hours to 1 day (MRID 

40375114). Aquatic photolysis of Na2CS4 can also contribute to the formation of CS2, 

with thiosulfate (S2O3

-

) as another major degradate. The photolysis half-life at pH 9 was 

3.8 hours; at lower pHs, hydrolysis is too rapid for measurement of photolysis rates 

(MRIDs 43817201, 40437401). 

Other products of these reactions include sodium hydroxide (NaOH), sulfur (S), and 

hydrogen sulfide (H2S). The environmental chemistry of these sulfur species is complex 

and highly dependent on local conditions. In aerobic conditions, sulfate (SO4

2-) and 

carbon dioxide (CO2) tend to be the ultimate products and in anaerobic conditions, 

degradates can remain as generated or be reduced to lower oxidation states. All of these 

species can be present naturally and are also generated from common agricultural 

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fertilizers. CS2 is the only substance produced in disproportionate environmental 

concentrations that also may be of toxicological concern (3/19/02, A. Clem). 

The major degradate CS2, the active pesticide agent, is a gas with a high vapor pressure 

(359 mm Hg) and a high Henry’s Law constant (0.014 atm-m3

/mol), so rapid 

volatilization is likely1. CS2 is subject to aerobic soil metabolism with half-lives of 3 to 

25 days, leading to sulfate and carbon dioxide as end products (MRID 00152990). 

Aerobic soil metabolism studies were conducted in closed systems and so do not include 

dissipation by volatilization. CS2 is not metabolized in anaerobic soil environments 

(MRID 40375115). Because of the rapid volatilization of CS2, its adsorption to soil 

cannot be measured and is not expected to affect its environmental fate (MRID 

00152991). No laboratory studies of the air or soil photolysis of CS2 are available, 

although based on its known chemistry, carbon disulfide is expected to undergo 

photochemical reactions to yield carbonyl sulfide (COS), sulfur dioxide (SO2) and carbon 

monoxide (CO) (5/16/89, E. Regelman). 

 1.2.3.2 Environmental Transport Assessment 

The labeled application methods are designed to distribute Na2CS4 below the soil surface, 

either through ground injection to a depth of 6 to 9 inches or by application in irrigation 

water to soils near field capacity, followed by “sealing” with additional irrigation water. 

The irrigation methods used for application of Na2CS4 are not expected to result in spray 

drift. Ground injection and chemigation through drip, drip-tape or strip tubing systems or 

through flood and furrow irrigation do not have an opportunity for drift. Other lowvolume irrigation systems including foggers, jets, misters, and mini-sprinklers are 

permitted but labels include equipment specifications for pressure and flow rates 

designed to prevent drift. Drift is therefore not considered here as a likely route for 

aquatic or terrestrial exposure. 

The labeled application methods also have relatively low runoff potential. Na2CS4 labels 

specify that following application, fields should not be irrigated to the point of runoff 

(Reg Nos. 68891-2 and 68891-9), although runoff could still be possible in a situation 

where rainfall occurs right after application. The pathway leading to the greatest 

potential concentrations of carbon disulfide in surface water would be release of 

tailwater from flood and furrow application methods. Labels require that treated 

tailwater be trapped and not allowed to leave the field, but no specifications for 

implementation of this requirement, such as holding times or trapping methods, are 

included. Different interpretations of this requirement by users could therefore lead to 

surface water exposure. 

The high vapor pressure and Henry’s Law constant of CS2 suggest that it will volatilize 

rapidly from surface water, but available aquatic studies show contradictory results and 

rates cannot be quantified based on the available information. Measurements taken in 

concurrence with hydrolysis studies found that, at concentrations from 65 to 1300 ppm 

 

1

 Lyman, W.J., W.F. Reehl, and D.H. Rosenblatt, 1990. Handbook of Chemical Property Estimation 

Methods: Environmental Behavior of Organic Compounds. ACS, Washington D.C. 

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CS2, mass transfer of CS2 out of water took place with a mean half-life of 90 minutes 

(MRID 40375114). A bluegill sunfish acute toxicity study, however, showed rates of 

dissipation that were substantially lower (MRID 40375113). This static 96-hour test, 

conducted in five gallon tanks with nominal concentrations from 4.1 to 41 ppm as CS2, 

showed that after 2 hours, 80% to 95% of the initial concentration remained. After 96 

hours, tests at lower concentrations (≤ 7.4 ppm CS2) showed complete dissipation, but at 

higher doses (13 to 41 ppm), up to 46% of the initial concentration remained. 

Concentrations in these studies are on the same scale as those in irrigation water at the 

time of application but they are much higher than the concentrations likely to reach 

surface water through runoff. At lower concentrations, it is probable that more rapid 

volatilization will occur. 

Field dissipation studies suggest that the CS2 formed by breakdown of CS4

2- initially 

moves downward through the soil profile, followed by diffusion upwards and 

volatilization to the atmosphere (7/9/1996, DP Barcodes D220367, D223296). Initial 

downward diffusion is rapid, with one study detecting CS2 at 20 ft below the surface after 

8 hours. All studies found maximum soil air concentrations, up to 37,500 ppmv, at one 

foot below the surface on the first day after application. Half-lives measured for 

dissipation of CS2 in soil air were one to six days. The relative contributions of 

metabolism and diffusion to CS2 dissipation have not been quantified and may vary 

depending on environmental conditions. 

Under normal uses of sodium tetrathiocarbonate, CS2 may reach groundwater. 

Prospective groundwater (PGW) studies in Florida found CS2 concentrations of up to 215 

ppb with observed dissipation half-lives on the order of several days to one week 

(7/27/1988, P. Holden). The one PGW conducted in California did not detect carbon 

disulfide in groundwater after sodium tetrathiocarbonate application, although terrestrial 

field dissipation studies in California found carbon disulfide reaching the water table in 

soil air. Volatilization, rather than movement off-site, was determined to be the primary 

mechanism for dissipation. Maximum potential concentrations have not been predicted 

because these studies indicate that CS2 occurrence in groundwater is highly dependent on 

recharge conditions, and none of these studies had significant recharge during the times 

when CS2 levels in soil air were at a maximum. 

Volatilization is the primary pathway for transport of CS2. A ground level air monitoring 

study using several application methods at half of the current labeled application rate 

found maximum air concentrations ranging from 2 ppm (furrow) to 24 ppm (minisprinkler) (MRID 42569101). At one hour after application, these levels had dropped to 

1.1 to 5.7 ppm. Higher application rates may result in higher concentrations, but the 

observed dissipation suggests that any exposure will not be long-lived. A second air 

monitoring study measuring CS2 levels at one foot and five feet above the ground surface 

found mean dissipation half-lives of 1.8 days (MRID 42304401). Maximum 

concentrations at one foot off the ground were 4.50 ppmv on the field and 0.252 ppmv 

100 ft off site. The amounts of CS2 and its degradates that may be released to the 

atmosphere as a result of the pesticidal use of sodium tetrathiocarbonate are not expected 

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to be high enough to have any impact on global sulfur cycles (5/4/89, S. Termes; 7/7/89, 

G. Hume). 

1.3 Receptors 

 1.3.1 Aquatic and Terrestrial Effects 

For sodium tetrathiocarbonate and carbon disulfide, the major degradate and active 

pesticide agent, ecological measures of effect are based on a suite of registrant-submitted 

toxicity studies as well as other lines of evidence, including studies from the open 

literature. A scan of the on-line ECOTOX database (http://www.epa.gov/ecotox) shows 

that there are several studies available for carbon disulfide, which will be considered 

during the risk assessment process. Below is a brief summary of currently available 

ecotoxicity information for sodium tetrathiocarbonate and carbon disulfide. Where 

toxicity data gaps exist, the associated uncertainties and the “value added” for new data 

are briefly discussed (see Section 1.6.2 for more details). 

Aquatic Effects

Several of the available freshwater toxicity studies were conducted with calcium 

tetrathiocarbonate (CaCS4) as the test substance, rather than sodium tetrathiocarbonate 

(Na2CS4). Due to the rapid hydrolysis of the parent compound, though, test organisms 

were actually exposed to carbon disulfide (CS2), and it is CS2 concentrations which were 

analytically verified. The nature of the cation, then, is not expected to affect the 

properties of the product. Two bluegill sunfish acute toxicity studies confirmed that the 

aquatic toxicity of sodium tetrathiocarbonate and calcium tetrathiocarbonate are 

equivalent in aquatic toxicity, and the data can be bridged (Acc. # 072331, MRID 

40375113). Available data for the most sensitive species indicate that CS2 is highly toxic 

to freshwater fish based on acute toxicity information for the rainbow trout (96-hr LC50 = 

0.87 mg CS2/L or 6.7 mg CaCS4/L; Acc. # 072331). An acute toxicity test with the 

freshwater invertebrate, Daphnia magna, also indicates that CS2 is highly toxic (48-hr 

EC50 = 0.87 mg CS2/L or 6.6 mg CaCS4/L; Acc. # 072331). 

There are no chronic toxicity data available to assess the potential effects of CS2 on 

freshwater animal growth and/or reproduction. A fish early life stage toxicity test (§72-

4(a)) with rainbow trout, the most acutely sensitive species of those tested, and a 

freshwater invertebrate lifecycle toxicity test (§72-4(b)) with Daphnia magna would 

reduce the uncertainty in the risk assessment. These data gaps have been identified as 

important uncertainties in risk assessments for other fumigant pesticides. 

Acute toxicity data for estuarine and marine organisms are required to support the 

registration of an end use product intended for direct application to the estuarine or 

marine environment or if the product is expected to enter this environment in significant 

concentrations because of its expected use or mobility pattern. Use on citrus represents a 

potential for estuarine exposure. However, since Enzone® labeling prohibits use “in areas 

adjacent to or draining to marine or estuarine waters,” estuarine/marine toxicity testing is 

not required at this time. 

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No aquatic plant toxicity information was available for previous assessments, but an 

additional 72-hour study with Selenastrum capricornutum with the ENZONE formulation 

as the test substance has recently been submitted (MRID 46423901). A preliminary 

review of these data suggests that biomass is the most sensitive endpoint with a NOAEC 

and EC50 of 9.98 and 17 mg ENZONE/L, respectively. Based on the time-weightedaverages of measured concentrations, this is equivalent to a NOAEC and EC50 of 80.1 

and 150 μg CS2/L.2

 The open literature ecotoxicity database indicates that additional 

carbon disulfide toxicity data exist for non-vascular aquatic plants, and this information 

will be considered during the risk assessment process. 

Terrestrial Effects

Given the nature of sodium tetrathiocarbonate and its expected behavior in the 

environment, there is a potential risk to terrestrial animals via drinking contaminated 

water at the application site. A mallard duck drinking water toxicity study revealed no 

mortality among ducklings that drank water contaminated with 2400 ppm sodium 

tetrathiocarbonate3

, the maximum concentration of expected to be the environment 

(MRID 422308501). The study also shows that the birds found the Enzone® treated 

water to be less palatable. These findings are consistent with a drinking water toxicity 

study with rats; no mortality occurred in male or female rats following exposure to 

drinking water with 2000 ppm sodium tetrathiocarbonate (MRID 43185201). This study 

also shows that the rats found the Enzone® treated water to be less palatable. 

Another potential exposure route for terrestrial animals is via inhalation of the degradate, 

carbon disulfide (CS2). A bobwhite quail inhalation toxicity study revealed no mortality, 

clinical signs of toxicity, or effects on food consumption or body-weight following 4 

hours of inhalation exposure to 1060 ppm CS2 (MRID 42531001). For mammals, based 

on the 1995 ecological risk assessment for new uses on almonds, peaches, and prunes, the 

rat acute inhalation LC50 is 1513 ppm CS2 (males) and 1014 ppm CS2 (females) 

(guideline grade) and 736 ppm CS2 (minimum grade) for both male and female rats. 

Potential reproductive and/or developmental toxicity effects in terrestrial animals via 

inhalation of CS2 will be explored, and relevant study reviews from the Health Effects 

Division (HED) will be considered during the risk assessment process. 

Given the method of application of sodium tetrathiocarbonate and its predicted behavior 

in the environment, dietary exposures are unlikely for terrestrial animals. Nevertheless, 

acute oral and dietary toxicity data are available for birds and mammals. A bobwhite 

quail acute oral toxicity test (with calcium tetrathiocarbonate) suggests that sodium 

tetrathiocarbonate (a.i.) is moderately toxic to birds on an acute oral basis (LD50 = 1180 

mg product/kg or 363 mg a.i./kg; Acc. # 260638). Based on information from the HED, 

the rat acute oral LD50 is > 587 mg a.i./kg, which classifies sodium tetrathiocarbonate as 

no more than slightly toxic to mammals on an acute basis. (However, it is unclear if this 

endpoint has been adjusted for the purity of the test substance; this will be explored 

 

2

 Conclusions may change pending formal review of the study. 

3

 Drinking water toxicity is considered in terms of nominal concentrations of parent Na2CS4, rather than 

measured concentrations of CS2. This differs from aquatic toxicity studies in which CS2 was the species 

analytically verified. Due to rapid hydrolysis, actual exposure is likely to a mix of Na2CS4 and CS2. 

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during the risk assessment process). An acute dietary toxicity test is available for the 

bobwhite quail and the mallard duck; both tests suggest that sodium tetrathiocarbonate 

(a.i.) is no more than slightly toxic to birds on an acute dietary basis (LC50 > 5620 ppm 

product or >1731 ppm a.i.; Acc. # 260638). 

Terrestrial invertebrate toxicity information has recently been submitted for earthworms 

and two beneficial insects, the predatory mite and the parasitic wasp.4

 A 14-day 

earthworm (Eisenia foetida) acute toxicity test with the formulation ENZONE suggests 

that the NOAEC and LC50 are 607 and 1300 mg a.i./kg dw soil, respectively (MRID 

46423902). A 7-day acute toxicity test with the predatory mite (Typhlodromus pyri

Scheuten) revealed almost complete mortality (92%) at the lowest level tested, 3.125 L 

ENZONE/ha (MRID 46423903). A 48-hour acute toxicity test with the parasitic wasp 

(Aphidius rhopalosiphi) suggests the NOAEC and LC50 are <0.1 and 0.41 L 

ENZONE/ha, respectively (MRID 46423904). There are no acute oral or contact toxicity 

data available for honey bees (§141-1). These data would be useful for characterizing the 

potential risk of carbon disulfide to non-target beneficial insects. 

There are no terrestrial plant toxicity data available with which to assess the potential risk 

of sodium tetrathiocarbonate. Due to the application methods and fate properties of this 

pesticide, exposure to terrestrial plants through drift and runoff is unlikely. However, 

there is a possibility of vapor phase exposure to terrestrial plants, and adverse ecological 

incidents in which non-target terrestrial plants have been impacted by off-gassing have 

been reported for other fumigants. In addition, the label suggests that phytotoxic effects 

are possible (e.g., ENZONE Reg. No. 68891-2 says that the “crop must be established in 

the field for at least one year prior to treatment or injury may occur”). Tier I seedling 

emergence and vegetative vigor studies (§122-1) using the maximum application rate of 

formulated product would reduce the amount of uncertainty in this risk assessment. Tier 

II phytotoxicity tests would be required if a 25% or greater detrimental effect is found in 

one or more plant species in the Tier I tests. 

 1.3.2 Ecosystems Potentially at Risk 

The ecosystems at risk are often extensive in scope, and as a result, it may not be possible 

to identify specific ecosystems during the development of a baseline risk assessment. 

However, in general terms, terrestrial ecosystems potentially at risk could include the 

treated field and areas immediately adjacent to the treated field that may be impacted by 

drift, runoff, or volatilization of the applied pesticide. This could include the field itself 

as well as other cultivated fields, fencerows and hedgerows, meadows, fallow fields or 

grasslands, woodlands, riparian habitats and other uncultivated areas. For Tier 1 

assessment purposes, risk will be assessed to terrestrial animals that are assumed to feed 

on and otherwise occupy the treated area. Exposure to animals off the treated site is also 

possible, but exposure and risk estimates are not likely to be higher than on the treated 

site. 

 

4

 Conclusions may change pending formal review of these studies. 

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Aquatic ecosystems potentially at risk include water bodies adjacent to, or down stream 

from, the treated field and might include impounded bodies such as ponds, lakes and 

reservoirs, or flowing waterways such as streams or rivers. For uses in coastal areas, 

aquatic habitat also includes marine ecosystems, including estuaries. For Tier 1 

assessment purposes, risk will be assessed to aquatic animals assumed to occur in small, 

static ponds receiving runoff and drift from treated areas. These ponds are used as 

surrogates for a number of small vulnerable water bodies that occur near the headwaters 

of watersheds including swamps, bogs, prairie potholes, vernal pools, playa lakes, and 

first-order streams. 

 

1.4 Assessment Endpoints 

A summary of the assessment endpoints and measures of ecological effect selected to 

characterize potential ecological risks associated with exposure to sodium 

tetrathiocarbonate is provided in Table 2. 

Table 2. Summary of Ecological Risk Assessment Endpoints for Sodium Tetrathiocarbonate and Carbon Disulfide

Assessment Endpoint Effects Measurement Endpoint 

1. Survival, reproduction and growth of birds

(Birds are surrogates for reptiles and terrestrialphase amphibians)

Acute oral LD50 (bobwhite quail) 

Acute dietary LC50 (bobwhite quail, mallard duck) 

Acute inhalation LC50 (bobwhite quail) 

Acute drinking water exposure NOAEC (mallard duck) 

* No chronic bird toxicity data available 

2. Survival, reproduction and growth of 

mammals 

Acute oral LD50 (rat) 

Acute inhalation LC50 (rat) 

Acute drinking water exposure NOAEC (rat) 

* No chronic rat toxicity data available 

3. Survival, reproduction, and growth of 

freshwater fish and invertebrates 

(Fish are surrogates for aquatic-phase 

amphibians) 

Acute fish LC50 (rainbow trout, bluegill sunfish) 

Acute invertebrate EC50 (Daphnia magna) 

* No chronic fish or invertebrate toxicity data available 

4. Survival, reproduction, and growth of 

saltwater fish and invertebrates 

* No acute or chronic toxicity data available. 

5. Survival of beneficial insects Parasitic wasp NOAEC and LC50 

* No honey bee toxicity data available 

6. Perpetuation of individuals and populations of 

non-target terrestrial plant species (crops and 

non-crop plant species) 

* No seedling emergence or vegetative vigor data available 

7. Maintenance and growth of individuals and 

populations of aquatic plants from standing crop

Selenastrum capricornutum NOAEC and EC50 

LC50 = Lethal concentration to 50% of the test population. 

LD50 = Lethal dose to 50% of the test population. 

NOAEC = No observed adverse effect level. 

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1.5 Conceptual Model

For a pesticide to pose an ecological risk, it must reach ecological receptors in 

biologically significant concentrations. An exposure pathway is the means by which a 

pesticide moves in the environment from a source to an ecological receptor. For an 

ecological pathway to be complete, it must have a source, a release mechanism, an 

environmental transport medium, a point of exposure for ecological receptors, and a 

feasible route of exposure. 

A conceptual model provides a written description and visual representation of the 

predicted relationships between the applied pesticide, potential routes of exposure, and 

the predicted effects for the assessment endpoint. A conceptual model consists of two 

major components: risk hypotheses and a conceptual diagram (US EPA, 1998). 

For sodium tetrathiocarbonate, the conceptual model has been developed in terms of 

carbon disulfide. In water, sodium tetrathiocarbonate is rapidly converted to carbon 

disulfide, which is likely to be the stressor in any aquatic exposure route. All aquatic 

toxicity has been measured in terms of carbon disulfide. Carbon disulfide is volatile and 

off-gasses from treated fields and so will also be the stressor in any exposure through air. 

1.5.1 Risk Hypotheses 

For carbon disulfide, the following ecological risk hypothesis is being employed for this 

baseline risk assessment: 

Carbon disulfide, when produced by degradation of sodium tetrathiocarbonate 

used in accordance with the label, results in potential adverse effects upon the 

survival, growth, and reproduction of non-target terrestrial and aquatic 

organisms.

 

1.5.2 Conceptual Diagram 

The conceptual diagram depicts the potential ecological risk associated with carbon 

disulfide by identifying possible exposure routes and receptors and providing a visual 

representation of their relationships. 

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*Dotted lines indicate that although this exposure route was considered, it was not thought to contribute 

significantly to the fate and transport of carbon disulfide. 

Stressor

Receptors

Attribute 

Changes

Source/ 

Transport 

Pathways

Runoff

Leaching 

(Infiltration/ 

Percolation)

Volatilization/

Off-gassing 

from soil

Source/ 

Exposure 

Media

Exposure 

Route

Terrestrial Vertebrates: 

Birds, Mammals, 

Reptiles, Terrestrial 

Phase Amphibians

Aquatic 

Invertebrates, 

Vertebrates

Aquatic 

Plants

Terrestrial

Upland 

Plants

Wetland/ 

Riparian 

Plants

Individual Animals

Reduced survival 

or reproduction

Individual Plants

Reduced survival, 

growth, or reproduction

Individual 

Vertebrates and 

Invertebrates

Reduced survival 

or reproduction

Plant 

Population

Reduced 

population 

growth

Ground Water Irrigation 

Water

Upland 

Foliage/Soil

Riparian/ 

Wetland 

Foliage/Soil

Receiving 

Water Body/ 

Sediment Air

Gill / Integument 

Uptake Ingestion Uptake/ 

Adsorption Inhalation Direct Contact/ Root Uptake

Direct Contact/ 

Root Uptake

CARBON DISULFIDE, formed through rapid 

hydrolysis of sodium tetrathiocarbonate

Sodium Tetrathiocarbonate, applied 

through chemigation or ground injection 

Figure 1. Conceptual model of the environmental transport and effects of carbon 

disulfide. 

Carbon disulfide is released from sodium tetrathiocarbonate applied through ground 

injection or in irrigation water. Spray drift does not occur with these application methods 

and so is not considered in this conceptual model. The major exposure routes of carbon 

disulfide for terrestrial animals are likely via ingestion of irrigation (drinking) water on 

the treated field or via inhalation resulting from off-gassing from the soil. Volatile 

carbon disulfide released by off-gassing may also impact nearby terrestrial plants. Due to 

its physical properties, off-gassing carbon disulfide is not expected to settle on adjacent 

soils, water bodies, or food items so these exposure routes are not considered. Carbon 

disulfide can move off-site through runoff to adjacent upland or riparian/wetland areas, 

where it may affect plants through direct contact or root uptake. Carbon disulfide in 

runoff also may reach adjacent water bodies where it could affect aquatic plants through 

uptake or adsorption and aquatic animals via uptake through the respiratory surface (gills) 

or the integument. Leaching to groundwater may occur but carbon disulfide is expected 

to be too transient to reach surface water through this route. 

1.6 Analysis Plan 

In Registration Review, pesticide ecological risk assessments will follow the Agency’s 

Guidelines for Ecological Risk Assessment, will be in compliance with the paper titled 

“Overview of the Ecological Risk Assessment Process in the Office of Pesticide 

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Programs, U.S. Environmental Protection Agency” (“Overview Document”; Janu

2004), and will be done in accordance with Section 7 of the Endangered Species Act. 

ary 

1.6.1 Conclusions from Previous Risk Assessments 

he original new chemical registration for sodium tetrathiocarbonate was completed in 

he most recent ecological risk assessment for sodium tetrathiocarbonate conducted by 

otential 

he only available drinking water assessment found estimated drinking water 

f 120 ppb 

.2 Preliminary Identification of Data Gaps and Analysis Plan 

 1.6.2.1 Environmental Fate 

The fate database for sodium tetrathiocarbonate is largely complete. All fate data 

s are 

sed by 

S2

• Due to the complexity of environmental sulfur chemistry, the relative 

/HS-/H2-. 

Studies of CS2 photolysis behavior in soil and air have not been submitted, so 

ir 

T

1988 (Eco: 9/20/88, J. Ackerman; Fate: 5/16/89, E. Regelman). Since then, additional 

data for sodium tetrathiocarbonate and its major degradate, carbon disulfide, have been 

received and considered during the risk assessment process for several new uses. 

T

the EFED is the 1995 assessment for the proposed new uses on almonds, peaches, and 

prunes (Eco: 5/4/1995, DP Barcode D213559; Fate: 8/21/1995, DP Barcodes D213560,

D199125, D196916). The application scheme (maximum rates, use areas, general use 

instructions) considered in that assessment is the same as that on the current labels. The 

1995 ecological risk assessment concluded that labeled use of sodium tetrathiocarbonate 

was not expected to pose acute or chronic risk to non-target avian, mammalian, fish, 

aquatic invertebrate or plant species. However, some of the risks were assessed 

qualitatively (i.e., aquatic exposures were not quantitatively estimated), and the p

risks to some receptors (terrestrial plants, terrestrial invertebrates) were not assessed. 

T

concentrations (EDWCs) in groundwater of 1 to 100 ppb and in surface water o

(acute), 1 ppb (chronic, non-cancer) and 0.35 ppb (chronic, cancer), based on modeling 

using PRZM/VADOFT and PRZM/EXAMS (3/19/02, A. Clem). These were estimated 

based on use in Florida at application rates that are half of maximum labeled rates. 

 

 1.6

requirements are satisfied or partially satisfied and physical and chemical propertie

available from open literature sources. Past assessments have identified some 

uncertainties about the fate and transport of carbon disulfide that are not addres

required studies; additional information would help to further characterize the fate of C

but would not be expected to change risk conclusions: 

concentrations of individual degradation products of CS2 have not been

determined, particularly for “H2S,” which really represents a mix of H2S

•

rates and degradation products are uncertain. Studies of photodegradation in a

may be useful in understanding the fate of CS2 in the atmosphere, important 

because air is the ultimate sink for CS2. 

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The relative contributions of degradation and diffusion to dissipation of CS2 from 

 1.6.2.2 Aquatic Exposure 

 previously completed screening level risk assessments for sodium tetrathiocarbonate, 

w: 

• All available ecological aquatic toxicity data are reported as Na2CS4 rather than 

o 

In the most recent (1995) ecological risk assessment, all levels of concern (LOCs) 

For other routes of aquatic exposure, it is likely that substantial dilution and 

 and 

ased on available data, the most sensitive aquatic animal endpoint is the 

ould 

e 

tial 

Previous assessments have concluded that application of sodium 

lfide that 

 and 

•

soil have not been determined. 

In

there has been some uncertainty in risk conclusions for aquatic organisms and for 

drinking water. These uncertainties and potential paths forward are described belo

CS2, which is likely to be the actual stressor. CS2 is formed rapidly in water 

through hydrolysis of Na2CS4, though, and test solutions were aged at least tw

hours. It is likely that these studies are effectively testing CS2 exposure, and in 

fact it was CS2 that was analytically verified. No additional data are therefore 

required. 

•

for aquatic organisms were exceeded based on the assumption of direct exposure 

to treated irrigation water, the maximum possible exposure. This assumption is 

appropriately conservative to estimate the risk if treated tailwater were to reach 

surface water bodies. Labels direct that “tailwater must not be allowed to leave 

the treated field,” but no details such as trapping methods or holding times are 

included, so there is still some possibility for exposure through this route. 

volatilization will occur before irrigation water reaches aquatic environments

so this assumption may be overprotective. For this case, past assessments have 

qualitatively concluded that use of sodium tetrathiocarbonate is unlikely to pose 

significant risk to aquatic organisms, but there has been no quantitative 

assessment of risk. 

B

Daphnia magna EC50 of 0.86 mg CS2/L. An aquatic EEC ≥ 43 μg CS2/L w

be required to exceed the endangered species LOC. Based on the aquatic plant 

NOAEC of 80.1 μg CS2/L, an aquatic EEC ≥ 80.1 μg CS2/L would yield a risk 

quotient that would exceed the acute endangered species LOC for plants. Surfac

water exposure is expected to be low, but at these LOCs, the possibility of risk 

cannot be precluded at this time. For the current risk assessment, aquatic 

exposures will be quantitatively estimated using models to determine poten

risk to aquatic organisms. No additional data are required to complete this 

modeling. 

•

tetrathiocarbonate may result in groundwater levels of carbon disu

exceed background levels, based on prospective groundwater (PGW) studies

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modeling. These sources do not represent worst-case scenarios because of the 

recharge conditions of the PGW studies and the application rate used in modeli

However, both sources are based on environmental conditions in Florida, which 

has higher vulnerability to leaching than would be expected in Arizona, 

California, Oregon, and Washington, the areas where use of sodium 

tetrathiocarbonate is currently supported. 

ng. 

For this assessment, we will characterize the potential for groundwater exposure 

d 

er 

ese 

ng water 

 1.6.2.3 Ecological Effects 

able 3 presents an evaluation of the uncertainty resulting from each ecotoxicity data 

s. 

his 

from current uses based on the Florida PGW studies and modeling, as well as 

several PGW and terrestrial field dissipation studies conducted in California an

Arizona. Additional PGW studies or monitoring data could reduce the 

uncertainty in this characterization by investigating potential groundwat

exposure in worst-case recharge conditions in the areas labeled for use. Th

studies would be rated as being of low value. In the absence of additional data, 

any conclusions of potential exposure for the current uses may lead to a 

recommendation of label language requiring a 100 ft setback from drinki

wells, as has been recommended in past assessments. 

T

gap. There is inherent uncertainty associated with not receiving data to fulfill data gap

However, the submission of some studies to address specific data gaps is unlikely to 

affect conclusions in the risk assessment, whereas some data gaps are more critical. T

determination is made on a case-by-case basis. 

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Table 3. Summary of ecotoxicity data gaps for sodium tetrathiocarbonate

Assessment endpoint with data 

gap

Value of 

Additional 

Data* 

Rationale 

Early life-stage freshwater fish 

toxicity study (72-4a) 

High Persistence of carbon disulfide in surface water bodies 

may be unlikely; however, given the high annual 

application rate of sodium tetrathiocarbonate and the 

potential for multiple applications per year, chronic risk 

to freshwater fish cannot be precluded at this time. This 

data gap has been identified as an important uncertainty 

in risk assessments for other fumigants. 

The value of this chronic study would be in quantifying 

and potentially refining the risks to fish (surrogate for 

aquatic-phase amphibians). Defining an action area for 

endangered species and exploring risk mitigation 

strategies cannot be evaluated without these data. 

Freshwater invertebrate lifecycle 

toxicity study (72-4b) 

High See above. Chronic risk of to freshwater invertebrates 

cannot be precluded at this time. 

The value of this chronic study would be in quantifying 

and potentially refining the risks to aquatic 

invertebrates. Defining an action area for endangered 

species and exploring risk mitigation cannot be 

evaluated without these data. 

Acute toxicity to estuarine/marine 

fish and invertebrates (72-3) 

Low Enzone® labeling prohibits use “in areas adjacent to or 

draining to marine or estuarine waters.” 

Survivorship, reproduction, and 

growth (chronic toxicity) of 

estuarine/marine fish and 

invertebrates (72-4) 

Low Enzone® labeling prohibits use “in areas adjacent to or 

draining to marine or estuarine waters.” 

Perpetuation of non-target terrestrial 

plants, crops and non-crop species 

(122-1, vegetative vigor and 

seedling emergence)* 

High Risk to terrestrial plants has not been considered in 

previous assessments, and no terrestrial plant toxicity 

data are currently available for sodium 

tetrathiocarbonate. Potential exposure routes for 

terrestrial plants include runoff and via off-gassing and 

volatilization. Adverse ecological incidents have been 

reported for other fumigants in which non-target 

terrestrial plants have been impacted by off-gassing. 

At one foot above ground level, the mean dissipation 

half-life for CS2 is 1.8 days, long enough for potential 

exposure. 

The value of these seedling emergence and vegetative 

vigor studies would be in quantifying and potentially 

refining risks to non-target terrestrial plants. Defining 

an action area for endangered species and exploring 

risk mitigation strategies cannot be evaluated without 

these data. 

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Table 3. Summary of ecotoxicity data gaps for sodium tetrathiocarbonate

Maintenance and growth of aquatic 

plants from standing crop or 

biomass (122-2, aquatic plant 

growth) 

High Risk to vascular aquatic plants (e.g., duckweed) has not 

been considered in previous assessments, and no 

vascular aquatic plant toxicity data are currently 

available for sodium tetrathiocarbonate. 

The value of a vascular aquatic plant toxicity study 

would be in quantifying and potentially refining risks 

to non-target terrestrial plants. Defining an action area 

for endangered species and exploring risk mitigation 

strategies cannot be evaluated without these data. 

Acute oral or contact toxicity to 

honeybees (141-1) 

High Non-target terrestrial invertebrates have the potential to 

be exposed to sodium tetrathiocarbonate by direct 

contact and via off-gassing. There are no honey bee 

toxicity data available for sodium tetrathiocarbonate. 

The value of these honey bee studies would be in 

quantifying and potentially refining risks to non-target 

terrestrial invertebrates. Defining an action area for 

endangered species and exploring risk mitigation 

strategies cannot be evaluated without these data. 

Reproduction and growth of birds 

(71-4) 

Moderate Given the method of application of sodium 

tetrathiocarbonate and its predicted behavior in the 

environment, dietary exposures are unlikely. Thus, a 

dietary exposure chronic avian reproduction study 

would be of limited use in this risk assessment. Since 

inhalation is a more likely exposure route for carbon 

disulfide, a non-guideline chronic avian toxicity test 

(with inhalation exposure) would address this 

uncertainty. 

* Tier II phytotoxicity tests would be required if a 25% or greater detrimental effect is found in one or more 

plant species in the Tier I tests. 

 1.6.3 Measures of Effect and Exposure

 1.6.3.1 Exposure 

Exposure estimates will be determined for carbon disulfide, the rapidly formed degradate 

that is the actual active ingredient, rather than for parent sodium tetrathiocarbonate. 

For ecological aquatic exposures, previous assessments have based EECs on the 

minimum concentration of sodium tetrathiocarbonate in irrigation water required by the 

label, a very conservative approach. For drinking water exposure in surface water, 

EDWCs have been estimated for application rates lower than the current labeled 

maximum. Additionally, these estimates have used out of date models which don’t 

account for irrigation. New modeling will therefore be required to quantitatively estimate 

aquatic exposures to assess ecological and human health risk. 

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Tier I aquatic exposure models are not sufficient to estimate exposure from fumigants 

because they do not account for volatilization. New estimates of surface water exposure 

in aquatic environments and in drinking water will be determined using the linked Tier II 

aquatic exposure models, PRZM (v. 3.12.2; May 12, 2005) and EXAMS (v. 2.98.04; 

April 25, 2005), run with the PE5 (v. 5.0; Nov. 15, 2006). Modeling will assume the 

maximum application rate, a single application of 340 lb a.i./A (139 lb CS2/A). 

Potential groundwater exposure will be characterized based on previous model results 

and based on available prospective groundwater studies and terrestrial field dissipation 

studies. 

Drift is not a potential route of exposure from these application methods, so the highest 

exposure to terrestrial species would be from drinking treated irrigation water or from 

exposure to off-gassing carbon disulfide, either through inhalation or direct contact. 

Ecological exposure in drinking water is based on the irrigation concentrations 

recommended by the labels and additional estimates are not needed. For exposure to offgassing CS2, there are acceptable data from field studies which measure concentrations of 

CS2 in air from one inch to five feet above ground level. Further refinement of these 

values will not be needed.

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 1.6.3.2 Effects 

Ecotoxicity data are available for several assessment endpoints. Table 4 summarizes the 

specific toxicity values that will be used to assess acute and chronic risk of carbon 

disulfide to receptors. 

Table 4. Summary of Measure of Effects for Sodium Tetrathiocarbonate (a.i.) and Carbon Disulfide (CS2) 

Assessment Endpoint Effects Measurement Endpoint 

1. Survival, reproduction and 

growth of birds (Birds are 

surrogates for reptiles and 

terrestrial-phase amphibians)

Bobwhite quail acute oral 14-day LD50 = 1180 mg/kg = 363 mg a.i./kg 

Bobwhite quail dietary 8-day LC50 >5620 ppm or >1731 ppm a.i. 

Bobwhite quail acute inhalation 4-hr NOAEC = 1060 ppm CS2

Mallard duck acute drinking water exposure 8-hr NOAEC = 2400 ppm a.i. 

* No chronic bird toxicity data available 

2. Survival, reproduction and 

growth of mammals 

Rat acute oral LD50 >587 mg a.i./kg 

Rat acute inhalation LC50 = 736 ppm CS2

Rat acute drinking water exposure 24-hour NOAEC = 2000 ppm a.i. 

* No chronic rat toxicity data available 

3. Survival, reproduction, and 

growth of freshwater fish and 

invertebrates (Fish are 

surrogates for aquatic-phase 

amphibians) 

Rainbow trout acute 96-hr LC50 = 6.7 mg a.i./L = 0.87 mg CS2/L 

Daphnia magna 48-hr EC50 = 6.6 mg a.i./L = 0.86 mg CS2/L 

* No chronic fish or invertebrate toxicity data available 

4. Survival, reproduction, and 

growth of saltwater fish and 

invertebrates 

* No acute or chronic toxicity data available. 

5. Survival of beneficial insects Parasitic wasp 48-hr NOAEC <0.1 L ENZONE/ha 

and LC50 = 0.41 L ENZONE/ha 

* No honey bee toxicity data available 

6. Perpetuation of individuals 

and populations of non-target 

terrestrial plant species (crops 

and non-crop plant species) 

* No seedling emergence or vegetative vigor data available 

6. Maintenance and growth of 

individuals and populations of 

aquatic plants from standing 

crop

Selenastrum capricornutum biomass 72-hour NOAEC = 80.1 μg CS2/L 

and EC50 = 520 μg CS2/L 

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 1.6.3 Other Information Needs

There is specific information that will assist the Agency in refining the ecological risk 

assessment, including any species-specific effects determinations. The Agency is very 

much interested in obtaining the following information: 

1. confirmation on the following label information 

a. sites of application 

b. formulations 

c. application methods and equipment 

d. maximum application rates 

e. annual frequency of application, date of initial application per year, 

application intervals, and maximum number of applications per year 

f. geographic limitations on use 

2. use or potential use distribution (e.g., acreage and geographical distribution of 

relevant uses) 

3. use history 

4. median and 90th percentile reported use rates (lbs. a.i./acre) from usage data – 

national, state, and county 

5. application timing (date of first application and application intervals) by use – 

national, state, and county 

6. sub-county crop location data 

7. usage/use information for non-agricultural uses (e.g., golf courses, athletic fields, 

ornamentals) 

8. directly acquired county-level usage data (not derived from state level data) 

a. maximum reported use rate (lbs. a.i./acre) from usage data – county 

b. percent crop treated – county 

c. median and 90th percentile number of applications – county 

d. total pounds per year – county 

e. the year the pesticide was last used in the county/sub-county area 

f. the years in which the pesticide was applied in the county/sub-county area 

9. typical application interval (days) 

10. state or local use restrictions 

11. ecological incidents (non-target plant damage and avian, fish, reptilian, amphibian 

and mammalian mortalities) not already reported to the Agency 

12. monitoring data 

The analysis plan will be revisited and may be revised depending upon the data available 

in the open literature and the information submitted by the public in response to the 

opening of the Registration Review docket. 

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IV. HUMAN HEALTH EFFECTS SCOPING DOCUMENT

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reflect current policy and practice for soil fumigants. If an assessment indicates the 

potential for significant exposures to CS2 above naturally-occurring background levels in 

drinking water as a result of registered uses, a drinking water risk assessment will be 

needed. In addition, tolerances for carbon disulfide need to be reassessed and potentially 

lowered. Prior to requiring any new data, a thorough review of relevant and available 

papers, reports, and databases covering worker and bystander exposures, and mammalian 

toxicity should be conducted. 

Introduction: Registration activity on sodium tetrathiocarbonate occurred mainly 

between 1985 and 1995. Although tolerances for CS2 have been reassessed under the 

Food Quality Protection Act (FQPA), neither a Registration Standard nor a Reregistration 

Eligibility Decision (RED) has been developed for it. HED’s databases contain individual 

decision memoranda regarding the history and disposition of data requirements and 

registration actions. Although these memoranda capture the registration process and 

decisions as practiced at the time, no risk assessments in accordance with FQPA have 

been conducted for sodium tetrathiocarbonate or CS2 .

Sodium tetrathiocarbonate is a soil fumigant used for the management of nematodes and 

phytophthora root rot, oak root fungus, and phylloxera. There are two end-use products 

registered for use: Enzone and Entek. It is registered for use on grapes, citrus, almonds, 

peaches, prunes, and plums in Arizona (AZ), California (CA), Oregon (OR), and 

Washington (WA), only. CDPR reports that during the five years from 2001 to 2005, 

between 200,000 and 400,000 pounds of sodium tetrathiocarbonate were used annually in 

CA. There is also a registration for non-bearing fruit and nut trees, considered a non-food 

use and exempt from tolerances. There are no registered residential uses. 

Sodium tetrathiocarbonate is applied through dilution in irrigation water by means of 

low-volume irrigation (chemigation), flood and furrow irrigation, and ground injection 

equipment. The majority of sodium terathiocarbonate used in CA is applied to grapes 

(vineyards) via irrigation. A 14-day post harvest interval (PHI) has been established on 

all labels. Once in water, it rapidly dissolves and then hydrolyzes in moist soil to form 

H2S, CS2, sodium hydroxide, and elemental sulfur. Soil particles rapidly bind and 

immobilize the sulfur ion and H2S components, leaving only CS2 to migrate and act as 

the biocide (nematicide). CS2’s vapor pressure (294 mmHg @ 20C) suggests that it will 

exist as vapor in the air. The degradation half-life is approximately 3 to 25 days. 

Literature searches on sodium tetrathicarbonate revealed no new information. However, 

literature searches on CS2 revealed extensive sources of information on this soil 

fumigant. HED has identified multiple articles and papers published in the open literature 

within the last five years relevant to worker exposure to CS2 and mammalian toxicity of 

CS2. HED has also contacted the California Department of Pesticide Registration (CDPR) 

and will ensure that information and data are exchanged on sodium tetrathiocarbonate 

and CS2. CDPR is actively working on their assessments for sodium tetrathiocabonate 

and CS2. 

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Hazard: CS2 is a neurotoxicant. Headache and nausea are commonly associated with 

exposures to CS2 as well as a range of more severe effects. These effects include obvious 

clinical signs of neurotoxicity, such as, convulsions and death, as well as changes in 

tissues and organs, such as lesions on and swelling of nerves, and brain weight effects, 

respectively. Additional effects observed in developmental and reproduction studies 

include: abortions/resorptions and body weight changes. 

The most recent documents (memoranda) indicate that the available toxicity data on 

sodium tetrathiocarbonate include: acute toxicity studies, oral rat and rabbit 

developmental studies, and several mutagenicity studies. These studies are considered to 

be of either acceptable or “minimum” quality. The developmental studies indicate 

endpoints based on neurotoxicity (including death) in the adults, and increased 

resorptions and post-implantation losses in fetuses. The effects occur in adults at lower 

doses than in fetuses. The mutagenicity studies were negative. A data waiver for a 21-day 

dermal study was granted because of the severe corrosive nature of CS2. 

Available toxicity studies on CS2 include: three inhalation studies (one in mice and two in 

rats) and developmental studies in rats and rabbits using CS2. Inhalation effects included 

epithelial necrosis of the nasal tract and death at the highest doses. 

Requirements for all subchronic and long-term studies, including acute, subchronic, and 

developmental neurotoxicity studies, have been waived because dietary exposures to CS2

were determined to be “de minimus” relevant to background (naturally-occurring) 

concentrations of CS2. Endpoints for risk assessment have not been selected previously. 

Dietary Exposure: Field trial data were submitted in the late 1980s and early 1990s to 

support an Experimental Use Permit (EUP) on citrus and grapes. An extension allowed 

for the inclusion of many trials in 5 states (AZ, CA, OR, WA, and FL). A nature of the 

residue study in plants outlining the metabolism of sodium tetrathiocarbonate in plants 

was submitted, reviewed, and a determination made that the study was adequate. The 

nature of the residue is understood and the primary degradate and residue of concern for 

regulation and risk assessment is CS2. Animal metabolism studies are not required 

because plant metabolism studies indicate that significant, reversibly bound CS2 is only 

detected in root crops, but not in other crops. As there are no registrations of sodium 

tetrathiocarbonate on root crops, HED does not expect any transfer of residues through 

livestock commodities. Consequently, animal feeding studies are not warranted either. 

Issues related to the analytical method used to detect CS2 in plants were resolved; an 

adequate analytical method exists to analyze CS2 in plants. No processing studies were 

required given the volatile nature of the residue of concern (CS2); residues are not 

expected to withstand conditions normally encountered during processing. Storage 

stability data are adequate.

By 1996, HED determined that residue data were adequate to grant permanent tolerances 

of 0.1 ppm for peaches, plums (fresh plums), prunes, citrus, almonds, and grapes. All of 

the residue data on peaches, plums, and almonds were from field trials in CA. Field trial 

data were also submitted for lemons, tomatoes, and apricots. Residue data from the 

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available field trials showed that levels of CS2 were generally either non-detectable or in 

the low parts per billion (ppb), i.e., 1 to 3 ppb. Maximum residues were detected in one 

sample in tomatoes, in which residues were 6 ppb, one sample of peaches, in which 

residues were 18 .4 ppb, and one sample of almond nutmeats, in which residues were 6.8 

ppb. HED concluded that residues of CS2 were likely to be less than 10 ppb on the 

commodities treated, and a tolerance of 0.05 ppm would be appropriate, but retained the 

0.1 ppm tolerance since available residue data from field trials conducted at maximum 

and exaggerated rates were limited. These tolerances should be reassessed and a 

determination made if they can be lowered. 

HED chemists used information on the background levels of CS2 in soils, decaying 

organic matter, plants, and air in making their determination that CS2 is always present in 

the environment, is ubiquitous, and occurs at low levels in the environment. HED 

concluded that CS2 was probably present in the diet of humans at low levels (< 10 ppb). 

Higher levels have been detected in Shitake mushrooms and in the headspace above beer, 

but on average are not expected to exceed 10 ppb. HED concluded that because “residues 

of CS2 in crops do not exceed natural background levels and will be indistinguishable 

from those background levels, the standard approach to dietary [sic] risk assessment is 

not warranted”. 

Previously, OPP concluded that residues of CS2 generated from the use of sodium 

tetrathiocarbonate as a result of registered uses were not likely to impact potable water 

provided labels contain restrictions prohibiting application within 100 feet of a potable 

well. OPP will revisit the potential for exposures to CS2 in drinking water under 

registration review. 

Occupational and Residential Exposures: HED previously determined that worker 

exposures to individuals handling, mixing, and applying products containing sodium 

tetrathiocarbonate will be “de minimus” provided appropriate PPE as per the labels are 

used. The labels state that handlers must wear respirators (NIOSH TC-23C or TC-14G). 

Post-application worker exposures were also determined to be “de minimus” previously 

provided the 4-day REI on the labels was followed. Monitoring data from a field 

volatility/dissipation study representing worst-case conditions for use of the products 

indicated that residues of CS2 are below detectable levels at 96 hours. The detection limit 

for that study was 0.019 ng/m3. Occupational exposure and risk assessments reflecting 

current policy and practice for soil fumigants are necessary to confirm worker safety. 

There are no residential uses of sodium tetrathiocarbonate. However, application 

techniques such as flood and furrow irrigation provide the potential for bystander 

exposure. Current labels state “posting” requirements to address issues of drift that may 

affect bystanders. CA labels provide buffer zones to protect bystanders. However, a risk 

assessment for residential bystanders potentially exposed to CS2 as a result of sodium 

tetrathiocarbonate applications in nearby fields reflecting current policy and practice for 

soil fumigants has not been conducted. A risk assessment for potential bystander 

exposures to CS2 is necessary under registration review and new data may be required to 

support this risk assessment. 

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Incident Reports: Three data bases were searched for incidents reports on sodium 

tetrathiocarbonate: Poison Control Center (PCC) Data, NIOSH SENSOR, and the 

Incidents Data System. No exposures to sodium tetrathiocarbonate were reported in the 

PCC during the period 1993 through 2005 or the Incident Data System from 1999 to the 

present. NIOSH SENSOR reported 2 cases of sodium tetrathiocarbonate poisonings. One 

case took place in CA in 1999. A 31 year-old man was a mechanic exposed to ENZONE; 

he reported headache, diarrhea, and malaise. The second incident also occurred in CA, 

but in 2001, when a 50-year old farm worker inhaled the pesticide and reported nausea, 

palpitations, upper respiratory pain and irritation, and muscle weakness. Both are likely 

attributed to CS2 poisoning.

An additional poisoning incident associated with sodium tetrathiocarbonate was reported 

under Section 6(a)2 of the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA). 

Two workers at Unocal’s West Sacramento Plant in California were exposed to sodium 

tetrathiocarbonate in 1994 and reported headaches lasting two days. The company 

reported the effects to be due to CS2, a known degradation product of Enzone. 

Exposures to sodium tetrathiocarbonate are not reported frequently in the available 

databases capturing poisoning incidents with pesticides. 

Aggregate Risk: There are no dietary exposures anticipated to sodium 

tetrathiocarbonate. Dietary exposures to CS2 have been determined to be “de minimus”. 

As a result, no quantitative dietary risk assessments have been conducted for sodium 

tetrathiocarbonate, or CS2 in food. A drinking water exposure assessment has not been 

conducted. There are no registered residential uses; however, as CS2 is a soil fumigant, 

the potential for residential bystander exposures needs to be assessed under registration 

review. If a drinking water assessment indicates potential exposures to CS2 in drinking 

water, an aggregate risk assessment combining potential residential bystander exposures 

with drinking water exposures may be warranted. 

Cumulative Risk: Sodium tetrathiocarbonate has not been identified as a member of a 

common mechanism group. However, it breaks down to CS2, as do dithiocarbamates. A 

common mechanism of toxicity across these compounds has not been established. 

Environmental Justice 

The Office of Pesticide Programs (OPP) typically considers the highest potential 

exposures from the legal use of a pesticide when conducting human health risk 

assessments, including, but not limited to, people who obtain drinking water from sources 

near agricultural areas, the variability of diets within the U.S. (including different ages, 

regions, and ethnicities), and people who may be exposed when harvesting crops. Should 

these highest exposures indicate potential risks of concern, OPP further refines the risk 

assessments to ensure that the risk estimates are based on the best available information. 

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As part of the California Environmental Justice Action Plan, the CDPR is currently 

conducting an environmental monitoring program in the town of Parlier, CA. Parlier is a 

small agricultural town in the San Joaquin Valley of CA 20 miles southeast of Fresno. 

Fruit orchards and grape vineyards are the dominant crops grown in the area. This 

program is a pilot project designed to measure air quality in the area. CS2 is included in 

the list of pesticides to be monitored under the pilot project. Findings from this project 

related to CS2’s impact on air quality and environmental justice issues will be considered 

in HED’s updated risk assessments for CS2. 

Human Studies. No toxicity studies involving human subjects exposed intentionally to 

sodium tetrathiocarbonate, or CS2 have been used or mentioned in any of the HED 

assessments or memoranda on sodium tetrathiocarbonate to date. A field volatility study 

in which air monitoring was conducted after application of sodium tetrathiocarbonate 

may require an ethics review. Additional ethics reviews may be needed depending on the 

data used to update existing assessments and develop a new residential bystander risk 

assessment. 

Data Requirements: 

New data may be required on CS2. Specifically, a “flux” study for use in setting 

appropriate off-site exposure mitigation buffer zones may be required. However, HED 

believes that available toxicity and exposure data (field volatility and flux studies and air 

monitoring) already identified in the open literature and through the CDPR may be 

sufficient to update existing CS2 assessments to today’s standards for the fumigants. HED 

will wait until the available literature on toxicity and exposure, air monitoring databases 

developed by the California Air Resources Board (CARB), and other information 

available on CS2 have been reviewed prior to determining what data requirements, if any, 

are warranted. 

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Tolerance Harmonization: 

No MRLs for sodium tetrathiocabonate have been established or proposed by Codex for 

any agricultural commodities. There are no Canadian or Mexican tolerances for carbon 

disulfide. Consequently, at this time, there are no harmonization issues. The US 

tolerances for CS2 are listed under 40 CFR 180.467 and summarized in the attached 

tolerance status table. 

US Canada Mexico Codex 

Residue Definition: 

Registrations include 66300-63 and 66330-

69. 

Tolerances established for carbon disulfide

from the use of sodium tetrathiocarbonate, 

40CFR.180.467 

None 

(including both 

sodium 

tetrathiocarbonate 

and sodium 

disulfide) 

None 

(including both 

sodium 

tetrathiocarbonate 

and sodium 

disulfide) 

None 

(including both 

sodium 

tetrathiocarbonate 

and sodium 

disulfide) 

Commodity Tolerance (ppm) /Maximum Residue Limit (mg/kg) 

Almond 0.1 N/A N/A N/A 

Almond, hulls 0.1 

Grapefruit 0.1 

Grape 0.1 

Lemon 0.1 

Orange, sweet 0.1 

Peach 0.1 

Plum, prune, fresh 0.1 

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References 

Blondell, J., “Review of incident reports – sodium tetrathiocarbonate”, August 15, 1994. 

California Air Resources Board, Annual Statewide Toxics Summary, Carbon Disulfide. 

California Department of Pesticide Regulation, Environmental Justice Pilot Project, 

Pesticide Air Monitoring in Parlier, Second Progress Report, December 2006. 

California Department of Pesticide Regulation, Environmental Justice Pilot Project, 

Pesticide Air Monitoring in Parlier, Addendum, ARB Monitoring Results, September 

2007. 

“Carbon Disulfide; Pesticide Tolerances”, Federal Register Notice, Volume 62, Number 

95, 26946-26949, May 16, 1997. 

Dang, W., “Ground-Level Concentrations Study of Carbon Disulfide in Air During and 

After Application of GY-81”, December 31, 1992. 

Hawkins, M., “Review of Sodium Tetrathiocarbonate Incident Reports, DP Barcode 

D343827, Chemical # 128904”, August 31, 2007. 

Morales, J., “PP#5F4482; ID#000612-00005. Sodium Tetrathiocarbonate(GY-81) in/on 

Almonds, Peaches, and Plums (Fresh Prunes), Evaluation of Residue Data and Analytical 

Methodology, MRID# 435717-01, 435901-01 through -05. DP Barcodes: D213554 and 

213557. CBTS Nos. 15344 and 15345”, September 25, 1995. 

Morales, J., “PP#5F4482; ID#000612-00005. Sodium Tetrathiocarbonate(GY-81) in/on 

Almonds, Peaches, and Plums (Fresh Prunes). Amendment in Response to CBTS memo 

of 9/25/95”, April 8, 1996. 

Olinger, C., “PP#9G3800; GY-81 (Sodium Tetrathiocarbonate solution) on Almonds, 

Prunes, Tomatoes, Lemons, And Apricots; Temporary Tolerances and Experimental Use 

Permit; MRID Nos. 412173 – 01 through -06; Record Nos. 250714 and 251358; 612-

EUP-U; DEB nos. 5770 and 5771.”, December 11, 1989. 

Olinger, C., “PP#9G3800; GY-81 (Sodium TEtrathiocarbonate solution) on Almonds, 

Prunes, Tomatoes, Lemons, And Apricots; Temporary Tolerances and Experimental Use 

Permit; Record Nos. 258610 and 258611; EUP-U; DEB nos. 6281 and 6282. February 

16, 1990. 

Roush, T., “Use Information and Air Monitoring Recommendations for the Pesticide 

Active Ingredients Sodium Tetrathiocarbonate”, Environmental Hazards Assessments 

Program, California Department of Pesticide Regulation, September 2006. 

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Segawa, R. “Literature Review of the Environmental Fate of Sodium Tetrathiocarbonate 

(Enzone)”, Environmental Hazards Assessments Program, California Department of 

Pesticide Regulation, January 18, 1991. 

Taylor, L., “GY-81 - Responses to DEB Review Dated August 6, 1990 and NDEB 

Reviews Dated August 2 and 27, 1990”, October 22, 1990. 

Taylor, L., “Carbon Disulfide – 90-Day Inhalation Toxicity Studies in Rats and Mice”, 

December 4, 1990. 

Taylor, L., “Two 90-Day CS2 Inhalation Studies in Rats”, December 23, 1991. 

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V. GLOSSARY of TERMS and ABBREVIATIONS

ai Active Ingredient 

AR Anticipated Residue 

CFR Code of Federal Regulations 

cPAD Chronic Population Adjusted Dose 

CSF Confidential Statement of Formula 

CSFII USDA Continuing Surveys for Food Intake by Individuals 

DCI Data Call-In 

DEEM Dietary Exposure Evaluation Model 

DFR Dislodgeable Foliar Residue 

DNT Developmental Neurotoxicity 

DWLOC Drinking Water Level of Comparison 

EC Emulsifiable Concentrate Formulation 

EDWC Estimated Drinking Water Concentration 

EEC Estimated Environmental Concentration 

EPA Environmental Protection Agency 

EUP End-Use Product 

FDA Food and Drug Administration 

FIFRA Federal Insecticide, Fungicide, and Rodenticide Act 

FFDCA Federal Food, Drug, and Cosmetic Act 

FQPA Food Quality Protection Act 

FOB Functional Observation Battery 

GENEEC Tier I Surface Water Computer Model 

IR Index Reservoir 

LC50 Median Lethal Concentration. A statistically derived concentration of a substance that can be 

expected to cause death in 50% of test animals. It is usually expressed as the 

weight of substance per weight or volume of water, air or feed, e.g., mg/l, 

mg/kg or ppm. 

LD50 Median Lethal Dose. A statistically derived single dose that can be expected to cause death in 50% of 

the test animals when administered by the route indicated (oral, dermal, 

inhalation). It is expressed as a weight of substance per unit weight of animal, 

e.g., mg/kg. 

LOC Level of Concern 

LOAEL Lowest Observed Adverse Effect Level 

μg/g Micrograms Per Gram 

μg/L Micrograms Per Liter 

mg/kg/day Milligram Per Kilogram Per Day 

mg/L Milligrams Per Liter 

MOE Margin of Exposure 

MRID Master Record Identification (number). EPA's system of recording/tracking submitted studies. 

MUP Manufacturing-Use Product 

NA Not Applicable 

NAWQA USGS National Ambient Water Quality Assessment 

NPDES National Pollutant Discharge Elimination System 

NR Not Required 

NOAEL No Observed Adverse Effect Level 

OPP EPA Office of Pesticide Programs 

OPPTS EPA Office of Prevention, Pesticides and Toxic Substances 

PAD Population Adjusted Dose 

PCA Percent Crop Area 

PDP USDA Pesticide Data Program 

PHED Pesticide Handler's Exposure Data 

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Docket Number: EPA-HQ-OPP-2007-1084 

www.regulations.gov

PHI Preharvest Interval 

ppb Parts Per Billion 

PPE Personal Protective Equipment 

ppm Parts Per Million 

PRZM/ Tier II Surface Water Computer Model 

EXAMS 

Q1* The Carcinogenic Potential of a Compound, Quantified by the EPA's Cancer Risk Model 

RAC Raw Agriculture Commodity 

RED Reregistration Eligibility Decision 

REI Restricted Entry Interval 

RfD Reference Dose 

RQ Risk Quotient 

SCI-GROW Tier I Ground Water Computer Model 

SAP Science Advisory Panel 

SF Safety Factor 

SLN Special Local Need (Registrations Under Section 24©) of FIFRA) 

TGAI Technical Grade Active Ingredient 

USDA United States Department of Agriculture 

UF Uncertainty Factor 

WPS Worker Protection Standard 

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