2 

fate, endangered species, and drinking water assessments to be conducted as part of the 

registration review for metam sodium, metam potassium, and MITC. The problem formulation 

draws on information from both open literature and studies submitted by the technical registrants 

in response to data requirements. This document is intended to provide an overview of what is 

currently known and the uncertainties regarding the environmental fate and ecological effects 

associated with metam sodium, metam potassium, and MITC. It describes the conceptual model 

and the processes that will be used during the completion of drinking water exposure and 

ecological risk assessments in support of registration review. This document also recommends 

studies that may be included in a data call-in (DCI) to address uncertainties surrounding the 

environmental fate and potential ecological effects of the three compounds.
Page 3 of 79 

 

 

Problem Formulation for the Environmental Fate, 

Ecological Risk, Endangered Species, and 

Drinking Water Exposure Assessments in Support 

of the Registration Review of Metam Sodium, 

Metam Potassium, and MITC 

Metam Sodium Metam Potassium MITC 

CAS No. 137-42-8 CAS No. 137-41-7 CAS No. 556-61-6 

PC Code 039003 PC Code 039002 PC Code 068103 

Prepared by:

Justin Housenger, M.S., Biologist 

Gabe Rothman, M.S., Environmental Scientist 

U.S. Environmental Protection Agency 

Office of Pesticide Programs 

Environmental Fate and Effects Division 

Environmental Risk Branch IV

1200 Pennsylvania Ave., NW 

Mail Code 7507P 

Washington, DC 20460

Reviewed by: 

Mah Shamim, Ph.D., Chief ERB5

June 18, 2013 

 
Page 4 of 79 

Table of Contents 

1. Executive summary ........................................................................................... 5

2. Introduction ....................................................................................................... 8

3. Use Characterization ........................................................................................ 9

4. Conclusions from Previous Risk Assessments ............................................. 13

4.1 Ecological Risk Assessments ............................................................................. 14

4.2 Drinking Water Exposure Assessments ............................................................. 15

4.3 Clean Water Act Programs ................................................................................. 15

5. Environmental Fate and Transport .............................................................. 16

6. Receptors .......................................................................................................... 24

6.1 Effects to Aquatic Organisms ............................................................................ 25

6.2 Effects to Terrestrial Organisms ........................................................................ 28

6.3 Ecological Incidents ........................................................................................... 28

7. Exposure Pathways of Concern ..................................................................... 32

8. . Analysis Plan ................................................................................................. 35

8.1 Stressors of Concern........................................................................................... 35

8.2 Measures of Exposure ........................................................................................ 35

8.3 Measures of Effect ............................................................................................. 38

8.4 Endangered Species Assessments ...................................................................... 39

8.5 Endocrine Disruptor Screening Program ........................................................... 39

8.6 Drinking Water Assessment ............................................................................... 39

9 Preliminary Identification of Data Gaps ...................................................... 39

9.1 Environmental Fate ............................................................................................ 39

9.2 Effects ................................................................................................................. 43

9. References ........................................................................................................ 47

Appendix A - California Department of Pesticide Regulation Report on Train 

Derailment and Metam Sodium Release to Sacramento River and MITC Dissipation 

Analysis......................................................................................................................... 49

Appendix B – Evaluation of Toxic Degradates of Concern ......................................... 53

Appendix C – STIR Model Run to Establish Drinking Water and Dietary Exposure 

Conceptual Model for Birds and Mammals .................................................................. 66

Appendix D – SIP Model Run to Establish Drinking Water Exposure Conceptual 

Model for Birds and Mammals ..................................................................................... 67

Appendix E – Earthworm Fugacity Model Results to Establish Dietary Exposure 

Conceptual Model for Birds and Mammals .................................................................. 68

Appendix F – Detailed Environmental Fate Summary and Degradate Tables for Metam 

Sodium, Metam Potassium, and MITC......................................................................... 69
Page 5 of 79 

1. Executive summary 

The Environmental Fate and Effects Division (EFED) and Antimicrobials Division (AD) 

have completed the preliminary problem formulation for the ecological risk, 

environmental fate, endangered species, and drinking water assessments to be conducted 

as part of the registration review of metam sodium, metam potassium, and methyl 

isothiocyanate (hereafter referred to as MITC). The problem formulation describes the 

methods planned to be used during the completion of drinking water and ecological risk 

assessments in support of registration review and provides an overview of the 

environmental fate, ecological effects, and potential risks associated with the uses of the 

above mentioned chemicals and related uncertainties unique to the risk assessment. This 

document also identifies additional studies that would recommend conducting an 

ecological risk assessment. 

MITC is considered the main stressor in this risk assessment. Metam sodium and metam 

potassium are similar salts and therefore, they are both expected to behave similarly in 

the environment. Metam sodium and metam potassium, as conventional pesticides, are 

incorporated to bare soil in pre-plant applications to control fungi, weeds, insects, 

nematodes, microbes and diseases. It is also applied in sewer lines for root control. 

Amongst the major antimicrobial uses are: oil drilling muds, packers fluids, cooling 

water systems, pulp/paper, and remedial wood treatment including poles /pilings, and 

large timber. The only registered use for direct MITC applications are for remedial wood 

treatment as well. 

Once applied, metam sodium and metam potassium degrade to MITC with a half-life of 

23 minutes in aerobic soil. In soil, an 83 percent conversion of metam sodium and 

metam potassium to MITC occurs. As a result, it is not expected that metam sodium and 

metam potassium will be bioavailable to terrestrial or aquatic organisms in any 

environmentally relevant concentration. 

MITC is volatile and resides mainly in the vapor phase once converted from metam 

sodium or metam potassium in the environment. For soil uses, post-application soil 

sealing methods (e.g., tarps, water, or soil) will be the largest factor determining off-site 

movement of dissolved MITC vapors via runoff to water bodies or MITC vapors to air. 

Given its high water solubility, leaching of dissolved MITC to ground water is also 

possible in well-draining sandy soils in areas where the water table is shallow, under all 

application scenarios. Once in water, MITC aquatic dissipation will be mediated by 

hydrolysis and volatilization. 

Exposure to aquatic organisms is predicated by runoff of MITC from treated fields. The 

PRZM/EXAMS model Georgia Farm Pond scenario will be used to quantify EECs in 

surface water. The aquatic exposure modeling will account for MITC loss from soil 

through the use of the PRZM volatilization algorithm. For MITC and terrestrial animals, 

the main route of exposure is expected to be via inhalation. For terrestrial plants, 

exposure to vapor phase MITC is also expected. To estimate exposures for MITC vapor, 
Page 6 of 79 

a tiered approach will be used. Both AERSCREEN and PERFUM can predict the upper 

bound air EEC at a point nearby the edge of the treated field directly downwind from the 

application site. In addition, both models can predict fumigant air concentrations at 

specified points downwind from the treated field. AERSCREEN, which considers worstcase meteorological conditions coupled with a peak flux rate, will be used as a screen. If 

LOCs are exceeded using AERSCREEN, PERFUM, which has the capability of 

producing a distribution of air EECs from a range of different meteorological conditions, 

will be used to refine the potential exposure values for animals and plants (vegetative 

vigor). For exposure to plant seedlings, TerrPlant will be used. Although TerrPlant 

EECs are based on runoff, TerrPlant will capture the overall exposure of plant seedlings 

whether it occurs from diffusion in the gas phase or runoff of dissolved MITC. 

Additional background information on the models is provided in Section 8.2. 

The assessment for antimicrobial uses will also focus on MITC as the main stressor. The 

EFAST (PDM module) will be used to estimate the EECs in surface water from the 

releases from uses in recirculating cooling towers and paper and pulp systems. Metam 

sodium, metam potassium, and their degradation product MITC are also used for 

remedial treatment of wooden poles, timbers by inserting metam sodium into the holes 

and use the product from 1⁄4 pint to 2 pints, depending upon the severity of wood decay. 

The holes are plugged with treated wooden plugs. Therefore, no exposure from metam 

sodium, metam potassium, or MITC is likely with this treatment. Metam sodium and 

metam potassium are also used to treat animal waste products in storage that are 

eventually used outdoors. Aquatic and terrestrial exposure associated with this use will 

be addressed consistent with the soil fumigant uses. Surface water exposure estimates 

will rely on the PRZM/EXAMS model calculations. Air exposure estimates will rely on 

AERSCREEN and PERFUM if necessary. Other uses are indoor uses, and exposure 

from these uses will likely be addressed by way of Down-the-Drain (DtD, and PDM 

modules) of E-FAST model. 

There are several sources of uncertainty for the aquatic exposure assessment for MITC. 

These include the following points: 

1. The largest uncertainty in quantifying exposure in this assessment will be 

considering the impact of tarps, especially bedded tarps, on MITC’s ability to 

runoff. MITC may become available to runoff by possibly moving into the soil 

space between the bedded strips. It is intended that the estimated exposure 

concentrations (EECs) of MITC in surface water for untarped applications would 

result in an upper-bound estimate of exposure for the overall usage of metam 

sodium and metam potassium. 

2. The EECs for MITC are highly sensitive to rainfall events that occur close to 

applications, given high application rates of metam sodium and metam potassium 

and that MITC volatilization in runoff water is not accounted for. However, there 

is also little experimental data on MITC’s overall retention time in water in the 

environment. In order to account for this source of uncertainty, aquatic EECs will 

be corroborated using monitoring data, associated with various incidents due to 
Page 7 of 79 

pesticide applications, as well as a train derailment leading to a metam sodium 

spill into the Sacramento River in California (CALDPR, 1991). While many of 

these lines of evidence such as the train incident may not be tied to registered 

pesticide uses, they provide evidence for the ability of MITC to be transported to 

water bodies nearby releases which may occur over exposed treated fields not 

covered by a tarp. Furthermore, an aerobic aquatic metabolism study will be 

requested to address uncertainties related to MITC’s retention time in water. 

There is also limited information on the role of how biodegradation mediates levels of 

MITC in the soil. Terrestrial field studies conducted in California and Mississippi 

indicate that MITC is not detected in soil 7 days after the application at both sites. A 

robust database of field volatility studies indicate that large but variable amounts of 

MITC escape to the atmosphere. However, the mediation of biodegradation on MITC is 

unknown. Nonetheless, EECs in aquatic environments will incorporate all available data 

regarding the loss of MITC from treated soil. 

Furthermore, there are several sources of uncertainty for the terrestrial exposure 

assessment for MITC. These include the following points: 

1. For terrestrial exposure, EECs in air will conservatively assume that birds and 

mammals are not transient and are always being exposed to emissions of MITC 

downwind from the treated field. Such an assumption is perhaps more 

representative for plants since they are not transient. However, EECs will still 

assume that plants are always being exposed to MITC downwind from the treated 

field. 

2. One uncertainty for air EECs is the propensity for large exposures to occur on 

timescales less than one hour. Such conditions are often associated with 

temperature inversions when light and variable wind speeds and highly stagnant 

air with limited mixing can occur. Therefore, peak air concentrations may be 

underestimated. However, it is not expected that these conditions would 

significantly impact the expected frequency of exposure events since these 

conditions may only occur within a few hours of certain days after fumigant 

applications. In addition, current labels contain specific language restricting 

applications during temperature inversions citing a number of criteria indicating 

the presence or forecasted temperature inversion. 

3. Another uncertainty includes the consideration of field size for the quantification 

of air EECs. Air EECs will be based on emissions occurring from a maximum 

field size of 80 acres. 80 acres is considered to be the upper-bound field size for 

the maximum area that is typically treated in one day. However, in some 

applications such as in center pivot chemigation, applications occur over much 

larger fields over multiple days. Therefore, a separate scenario addressing center 

pivot applications will be evaluated to quantify air EECs. Please refer to Section 

8.2.2. for further details. 
Page 8 of 79 

The major data needs for environmental fate are listed below:

 Aerobic Aquatic Metabolism: MITC (835.4300) 

 Environmental Chemistry Methods (ECMs)/Independent Laboratory Validation 

(ILVs) in Air and Water: MITC (850.6100) 

The major data needs for ecological effects are listed below:

 Acute vapor exposure study for the honey bee (non-guideline study): MITC 

 Tier I/II Seedling Emergence Study (850.4100): MITC 

The environmental fate requirements mentioned above are outstanding data needs to 

address the conventional and antimicrobial uses of metam sodium and metam potassium. 

The ecological effects data needs are requested to address the conventional uses of 

metam sodium and metam potassium. Please refer to Section 9 on the rationale for the 

data requests. 

2. Introduction 

For this Problem Formulation (PF), EFED and AD evaluated the most recent ecological 

risk assessments for metam sodium, metam potassium, and MITC in association with any 

updated toxicity, exposure, and use and usage information to determine if sufficient data 

are available and if further updates are needed to support registration review. Recent risk 

assessments include a 2004 ecological risk assessment conducted for the Re-registration 

Eligibility Decision (RED) (DP Barcode 2016938, dated August 18, 2004). In addition, 

EFED considered the latest Agency science policies and risk assessment methodologies. 

The structures of metam sodium, metam potassium, and MITC as well as the chemical 

names and other identifiers can be found in Table 2 of this document. 

Metam sodium, metam potassium, and MITC products are all available as emulsifiable 

concentrates. Metam sodium and metam potassium degrade rapidly to MITC via 

hydrolysis and biodegradation. Once MITC is formed, it readily changes phase to a gas 

due to its high volatility. Acting as a fumigant, MITC controls a wide spectrum of pests 

such as fungi, weeds, insects, nematodes, microbes and diseases, and used as root control 

as well. MITC exhibits nematicidal, bactericidal, algaecidal, herbicidal, fungicidal, and 

insecticidal activity. MITC accounts for most of the fumigant activity by diffusing, either 

as a gas or volatile liquid, upward through the interstitial spaces and killing living 

organisms with which it comes in contact. MITC is highly toxic and results in the 

disruption of biological functions of both target and non-target organisms. For example, 

MITC is highly reactive with the nucleophilic centers such as thiol groups in vital 

enzymes of nematodes (Cremlyn, 1991). 

 
Page 9 of 79 

3. Use Characterization 

Conventional Uses

There are currently 14 active registered metam sodium end-use products and 3 active 

registered metam potassium end-use products.. Two metam sodium products are coformulated with dichlobenil. The majority of metam sodium and metam potassium 

products are applied to bare soil in pre-plant applications for a wide variety of crops as 

well as turf greens1

. Up to 320 lbs. metam sodium/A and 360 lbs. metam potassium/A 

are allowed on the labels. This translates to MITC equivalent maximum application rates 

of 150.31 lbs./A and 150.38 lbs./A from metam sodium and metam potassium 

applications, respectively2. In general, metam sodium and metam potassium are applied 

as frequently as once per year for soil uses. 

There are also eleven Section 24c Special Local Needs registrations for conventional uses 

of metam sodium. Two of the registrations in Georgia and South Carolina are for preplant applications for peanuts at a maximum application rate of 63.9 lbs. a.i./A. Two 

other Section 24c Special Local Needs registrations in North Carolina and Virginia are 

also for pre-plant applications for peanuts at a maximum application rate of 63.6 lbs. 

a.i./A. Six other Special Local Needs registrations were recently registered in North 

Carolina and Virginia. These labels will further be evaluated at a later date and 

incorporated into the registration review risk assessment These labels are equivalent to 

the labels with the fore mentioned Special Local Needs registered in Virginia and North 

Carolina except they contain buffer zones for application rates lower than those found on 

the section 3 labels. 

Metam sodium and metam potassium soil uses may be applied by surface applications 

such as chemigation (e.g., drip, solid set sprinkler, or center pivot chemigation), and 

flooded applications. Soil incorporated applications include shank injection, spray blade, 

and rotary tiller. Labels require metam sodium and metam potassium to be injected to a 

minimum depth of 4 inches. For all methods, metam sodium and metam potassium is 

required to be applied 14 days before planting (plant back interval). No maximum field 

size for metam sodium and metam potassium applications is specified on labels. 

However, worker and bystander buffer zones address applications occurring up to 160 

 

11 Listed crops on labels include apples, artichokes, asparagus, beans (all types), berries (all types), 

broccoli, brussel sprouts, cabbage, carrots, cauliflower, celery, cherries, cover crops, guava, okra, corn, 

cilantro, corn (all types), cotton, cucumber, currant (all types), dandelion, dill, eggplant, endive, fennel, 

garlic, grapefruit, grapes, honeysuckle, kale, kiwi, kohlrabi, kumquat, leeks, lemon, lime, lettuce, oranges, 

mangoes, melons (all types), squash (all types), gourds (all types), mint, nectarines, pears, peaches, plums, 

nuts (all types), peanuts, nursery plants, onions, radicchio, radish, rhubarb, soybeans, rye, spinach, sugar 

beets, potatoes, sweet potatoes, peppers, tobacco, tomatoes, turnips, wheat, and yams. 2

 MITC Application Rate from Metam Sodium (lbs./A) = 320 lbs./A x 0.83 transformation factor x 

(73.12 g-mol-1/129.2 g-mol-1) 

 MITC Application Rate from Metam Potassium (lbs./A) = 360 lbs./A x 0.83 transformation factor x 

(73.12 g-mol-1/129.2 g-mol-1) 
Page 10 of 79 

acre fields for center pivot applications; 120 acre fields for overhead chemigation, spray 

blade, rotary tiller, and shank injection applications; and 80 acre fields for drip 

chemigation applications. 

For all methods, minimum Good Agricultural Practices (GAPs) include using an 

adequate sealing method including the incorporation of soil or water over the applied 

metam sodium or metam potassium solution. GAPs are specified to optimize the efficacy 

of the fumigant by maximizing retention of the fumigant in the top soil that is treated. 

The sealing of the fumigant may be reinforced using tarps, but tarps are not required on 

labels. Therefore, it is important to note that while GAPs are required for metam sodium 

and metam potassium soil applications, and the application of tarps is one of the nonmandatory GAPs specified, untarped applications using other GAPs are allowed. In 

addition, surface and incorporated metam sodium and metam potassium applications are 

allowed to occur under a variety of field cultivation settings. For example, broadcast 

applications (e.g., flat fume) or applications within bedded strips are allowed. The photos 

showing the variations on incorporated application methods for metam sodium and 

metam potassium soil uses are shown in Figure 1 and Figure 2 below. Surface 

chemigation applications (e.g., solid set sprinkler) are not shown below. Moreover, all of 

the application methods shown in the figures below may also be used with water and soil 

sealing methods without the application of tarps. 

Credit: http://www.goodfruit.com

Figure 1. Photograph showing flat fume or broadcast shank injection application 

followed by tarp covering. 
Page 11 of 79 

Credit: EPA, 2005 

Figure 2. Photograph showing shank injection application to raised beds followed 

by tarp covering. 

There is also one metam sodium product that can be used for root control uses in sewage 

pipes. The maximum application rate for these uses is 0.212 lbs. of metam sodium per 

gallon of solution. No maximum number of applications are specified on the label for 

sewer uses. 

National pesticide usage data from the United States Geological Survey indicate that an 

average of 42 million pounds of metam sodium and 12 million pounds of metam 

potassium was applied per year to agricultural crops in the United States from 2006 to 

2011. It is expected that metam sodium and metam potassium usage will increase in the 

future in response to the phase-out of methyl bromide given the use of metam sodium and 

metam potassium products as an alternative to methyl bromide (; USEPA, 2012). The 

average fraction treated of crops was reported to be between 5 to 15 percent for most 

registered crops, with a maximum of up to 30% for potatoes and cantaloupes and 60% for 

carrots (USEPA, 2012). 

Antimicrobial Uses

There are an additional 16 registered antimicrobial products. Metam sodium 

antimicrobial uses include remedial treatment of wooden poles and timbers, and 

treatment of sewer sludge and animal waste. For metam potassium the uses include 

tanning drum leather, pulp and paper, recirculating cooling water systems, and industrial 

water purification systems. For MITC, the only antimicrobial is for remedial treatment of 

wooden poles and timbers. Table 1 below lists the antimicrobial products, application 

type, and application rates of the products. There is also a Section 24c registration exists 

in California for industrial waste stream uses. 

 
Page 12 of 79 

Table 1. Anitmicrobial uses of metam sodium, metam potassium, and MITC.

No Application type Reg. No %AI Application. Rate 

1 Oil drilling muds, packer 

fluids 

1448-52 Metam-K: 

32.5 

0.05 to 0.2% 

500 ppm-2000ppm 

2 Leather manufacture 100-750 ppm 

3 Animal Glue solution 75-150 ppm 

4 Clay slurries, phosphate 

dispersed 

50-100 ppm 

5 Coating formulation, protein 

binders, starch binders, 

starch slurries and solutions 

150-400 ppm 

6 Cooling Water systems 1448-115 Metam Na: 

3.69 

Metam-K: 

5.07 

6.9-13.9 fl oz/1000 

gallons of system 

7 Industrial Water purification 24.5-49.0 fl.oz/1000 

gallons of water 

8 Cooling water system 1448-128 Metam Na: 

14.7 

Metam 

K:20.3 

1.5-3 fl.oz/1000 

gallons of system 

water 

9 Industrial water purification 

system 

5.0-10 floz/1000 

gallons water 

10 Industrial and commercial 

Cooling towers 

1448-180 Metam-Na: 

7.35 

Metam-K: 

10.15 

3.3-6.6 fl.oz/1000 

gallons of water 

system 

11 Industrial Water purification 11.5-23.0 fl.oz/1000 

gallons of water 

12 Pulp/Paper mills 1448-53 Metam-Na: 

14.7 

Metam-K: 

20.3 

0.4 lbs-2.0 lbs/ton of 

pulp (dry basis) 

13 Petroleum secondary 

recovery operations 

1-1.5 fl.oz/1000 

gallons of water 

14 Cooling water systems 1.5-3.0 fl.oz/1000 

gallons of water 

15 Wood and wood products 1448-107 Metam-Na: 

42.5 

No application rate 

provided 

16 Brine cured hides/skins 

Preservation of salt-cured 

hides/skins 

1448-371 Metam-Na: 

33 

4000-10,000 ppm 

100-250 ppm 

17 Leather 125-500 ppm 

18 Wood treatment: 

poles/pilings, large timbers 

1448-437 Metam-Na: 

33 

Bore 4-5 holes of 3⁄4 

inch in diameter; 

apply 1 pint of/pole. 

Plug holes with 

treated wood plugs 
Page 13 of 79 

No Application type Reg. No %AI Application. Rate 

19 Douglas fir poles, western 

red cedar poles, southern 

pine poles; 

Wood chips can also be 

treated by dipping 0.3%/100 

gallons of water, and 0.8 % 

in 100 gallons of water 

10182-196 Metam-Na: 

32.7 

Drill 9/16 inch holes 

and apply 1 pint to all 

holes; If severe 

conditions, apply 2 

pints. Plug the holes 

with treated wood 

plugs; 

In 500 gallons of 

water and increase 

these amounts 

accordingly 

20 Sewage sludge (biosolids) 

and animal waste 

5481-477 Metam-Na: 

42.0 

1-3 gallons /ton of 

sludge or animal 

waste; store in a 

protected area for 14-

21 days until the tests 

show it is safe to use 

in agricultural and 

horticulture purposes 

21 Remedial treatment of 

wooden poles/timbers 

75341-2 Metam-Na: 

33.0 

Drill 7/8 inch holes, 

and apply 1⁄4 pint of 

the product (36 inch 

diameter size poles; 

for larger size poles, 

1.5-2.0 pints for all 

holes. Plug the holes 

with plugs that are 

treated with the 

product. Also can use 

plastic plugs. 

22 Remedial treatment of 

wooden poles/timbers 

69850-1 MITC Drill 9 holes, 30 g per 

hole 

4. Conclusions from Previous Risk Assessments 

The following serves as the basis for this scoping document covering metam sodium, 

metam potassium, and MITC: 
Page 14 of 79 

 The Reregistration Eligibility Decision (RED) science chapter (DP Barcode 

2016938, dated August 18, 2004) 

 AD Memo from Heather Garvie to Mark Hartman May 11, 2008 

Two other risk assessments were conducted for metam sodium after 2004 addressing 

local endangered species litigation for the Red Legged Frog (dated July 19, 2007) and 

California Tiger Salamander (dated December 29, 2010). The RED document for metam 

sodium, metam potassium, and MITC was originally signed in 2008, but was amended 

and the revision was signed in 2009 (USEPA, 2009). The RED was amended to 

incorporate public comments; however, the Agency’s risk conclusions did not change. 

The major ecological risk conclusions presented in the RED are described below. 

4.1 Ecological Risk Assessments 

The reregistration eligibility decision (RED) outlined the potential ecological risks 

associated with the soil fumigant pesticide uses and the antimicrobial uses of metam 

sodium, metam potassium, and MITC, which were assessed separately. 

Conventional Uses

The environmental fate and effects risk assessment conducted for the soil fumigant 

pesticidal uses of metam sodium and metam potassium (USEPA, 2009), was based 

completely on the risk from MITC as the stressor of concern3

. For MITC, no risks to 

mammals were identified as it was determined that downwind air estimated exposure 

concentrations (EECs) from a single 80-acre field4 did not exceed acute levels of concern 

(LOCs) for inhalation. Inhalation toxicity data were not available for MITC and other 

taxa (including birds and terrestrial plants) at the time of the RED, and therefore these 

taxa were not assessed. Acute aquatic LOCs are exceeded for both aquatic invertebrates 

and freshwater fish, based on MITC surface water EECs in the modeled pond. The effect 

of tarps were not included quantitatively in estimating aquatic concentrations, so aquatic 

EECs would especially represent upper-bound events for those scenarios. However, tarps 

are not exclusively requriedon labels. No LOCs were exceeded for aquatic plant 

exposure to MITC, based on a partially complete data set for related toxicity data. Table 

2 below summarizes the previous risk conclusions from the RED.

Table 2. Summary of risk concerns identified in previous assessments of metam 

sodium and metam potassium, and MITC

Birds Mammals Terr. 

Plants 

Terr. 

Inverts Fish Aq. Inverts BCF 

Aq. 

Plants 

Groundwater 

Contamination Persistence Degradates of Concern 

--* None --* --* √ √ None √ √ None MITC 

*Toxicity data were not available at the time of the risk assessment to estimate risk.

 

3

 The risk assessment for the RED was not conducted for sewer uses. 

4

 Air EECs from field sizes between 80 acres and 120 acres were not calculated. 
Page 15 of 79 

In 2007, risk to the federally threatened California Red Legged Frog (Rana aurora 

draytonii - CRLF), was assessed from the use of metam sodium. In that assessment, 

inhalation exposure was cited as the primary route of exposure for terrestrial organisms. 

Birds normally serve as a surrogate for terrestrial phase amphibians like the CRLF but 

there were no avian inhalation data available and so mammals served as a surrogate to the 

CRLF. This assessment considered MITC to be the stressor of concern in both the 

terrestrial and aquatic phases. Direct effects to the aquatic phase CRLF on survival were 

predicted as a likely to adversely affect determination for most uses of metam sodium as 

a sprinkler irrigation method. Indirect effects caused by direct effects on prey for the 

CRLF were similar for those scenarios that predicted direct effects. No effect 

determinations were made for direct effects to survival for the CRLF for certain uses, for 

effects on reproduction and growth, and for indirect effects to the CRLF mediated by 

direct effects on prey for certain uses. No effects determinations were indicated to the 

terrestrial phase CRLF for any use of metam sodium. 

In 2010, risk to the federally threatened California Tiger Salamander (Ambystoma 

californiense - CTS), was assessed from the use of metam sodium. As in the previous 

assessment to the CRLF, MITC was considered the stressor of concern for both the 

aquatic and terrestrial phase CTS. For the potential for direct and indirect effects to the 

aquatic phase CTS was determined as likely to adversely effect. For direct effects to the 

terrestrial phase CTS, a determination of no effect was made, again using the mammalian 

rat inhalation data as a surrogate for the CTS. 

Antimicrobial Uses

In the RED document, AD determined that metam sodium, metam potasium and MITC 

antimicrobial uses do not pose an unreasonable risks or adverse effects to humans or 

environment, provided that the risk mitigation measures and label changes outlined in the 

RED (July 2009) are implemented and therefore products containing metamsodium,metam-potassium and MITC for these uses are eligible for reregistration. 

4.2 Drinking Water Exposure Assessments 

A drinking water exposure assessment was conducted and the estimated drinking water 

concentrations (EDWCs) were calculated and submitted (DP Barcode D293341, dated 

September 16, 2003) to support HED’s human health risk assessment for the RED. 

Exposure estimates of MITC from metam sodium labeled uses maximum exposure (FL 

Tomato) were 73.22 μg/L (acute: 1-in-10-year peak), and 2.99 g/L for both chronic 

and cancer EDWCs (1-in-10-year annual mean and 30-year mean, respectively). A 

concentration of 0.72 μg/L was calculated for ground water using the SCIGROW model. 

It is important to note that SCIGROW does not account for volatility. In addition, there 

are uncertainties with using the SCIGROW model for mobile compounds such as MITC. 

4.3 Clean Water Act Programs 
Page 16 of 79 

MITC is not identified as a cause of impairment for any water bodies listed as impaired 

under section 303(d) of the Clean Water Act, based on information provided at 

http://iaspub.epa.gov/tmdl_waters10/attains_nation_cy.cause_detail_303d?p_cause_grou

p_id=885. No Total Maximum Daily Load (TMDL) criteria have been developed for 

MITC, based on information provided at 

http://iaspub.epa.gov/tmdl_waters10/attains_nation.tmdl_pollutant_detail?p_pollutant_gr

oup_id=885&p_pollutant_group_name=PESTICIDES. More information on impaired 

water bodies and TMDLs can be found at http://www.epa.gov/owow/tmdl/. 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/oppsrrd1/registration_review/water_quality_sop.htm), in order to 

ensure they can be used quantitatively or qualitatively in pesticide risk assessments. 

5. Environmental Fate and Transport 

Metam sodium and metam potassium are non-volatile and readily soluble (722 g/L @ 

200C for both compounds) in water and degrade very rapidly to MITC in soil (soil 

photolysis and aerobic degradation half lives range from 23 to 63 minutes) and in water 

(hydrolysis half-life = 2 days at pH 7). Unlike the parent compounds metam sodium and 

metam potassium, MITC has a high vapor pressure (19 mm Hg at 200C) and Henry’s 

Law Constant of 1.79 x 10-4 atm·m3/mol, which suggests that it will be volatilized from 

fields treated with metam sodium or metam potassium in a dry environment. However, 

its Henry’s Law Constant suggests that the retention time of MITC will probably be 

longer in moist soils. Table 3 lists the physical-chemical properties of metam 

sodium/metam potassium and MITC. Metam sodium and metam potassium possess the 

same physical chemical properties since they are salt analogues of each other. 

 
Page 17 of 79 

Table 3. Physical and chemical properties of metam sodium/metam potassium and 

MITC.

Property 

Metam Sodium and Metam Potassium MITC 

Value and units MRID or Source Value and units MRID or 

Source 

Structure, 

Molecular 

Formula, and 

Molecular 

Weight 

Metam Sodium

C2H4NNaS2

129.2 g/mol 

Metam Potassium

C2H4NKS2

145.3 g/mol 

EPISUITE 

MITC

C2H3NS 

73.12 g/mol 

EPISUITE 

Vapor 

Pressure 

(25°C) 

4.53 x 10-9 torr EPISuite 

(MPBPVP) 16 torr CDPR, 2002 

Henry’s Law 

Constant 7.7 x 10-16 atm·m3

/mol 

Calculated from 

Vapor 

Pressure/Solubility 

1.79 x10-4 atm·m3/mol CDPR, 2002 

Water 

Solubility 722,000 mg/L Tomlin, 1997 (ed.) 

(20°C) 

8,610 mg/L 

(25°C) 

CDPR, 2002 

Octanol – 

water partition 

coefficient 

(log KOW)

0.46 EPISUITE 0.98 MRID 

43540903 

Aerobic soil metabolism, photodegradation in water, and hydrolysis studies suggest that 

parent metam sodium and metam potassium are very unstable in the environment and 

degrade rapidly to MITC and other minor degradates. Metam sodium and metam 

potassium both degrade to MITC with a half-life of 23 minutes in aerobic soil. In soil, an 

83 percent conversion of metam sodium and metam potassium to MITC occurs. For 

MITC, degradation in soil and water appears to be dependent on hydrolysis and 

microbially-mediated degradation, and MITC appears to persist longer than metam 

sodium in the environment. The dissipation of MITC in aquatic and terrestrial 

environments appears to be predominantly dependent on volatilization and to a lesser 

extent on leaching and degradation. Photolytic degradation is the major loss pathway of 

MITC in atmosphere (half-life of 1.21 – 1.60 days). Table 4 and Table 5 list the 

environmental fate properties and degradate formation of metam sodium/metam 

potassium and MITC, respectively. Table 6 shows the amount of MITC escaping to the 

atmosphere from field volatility studies with metam sodium and metam potassium 

applications. The open literature has been used to fulfill many outstanding data gaps 
Page 18 of 79 

related to the environmental fate, especially for MITC. Detailed information on the 

environmental fate of metam sodium, metam potassium, and MITC may be found in 

Appendix F. Furthermore, degradate structures can be found in Tables F-1 and Table 

F-2 of Appendix F for metam sodium/metam potassium and MITC, respectively. 

Table 4. Summary of metam sodium/metam potassium environmental fate 

properties.

Study3 Value and unit Major Degradates 

MRID # 

or 

Citation 

Study 

Classification, 

Comment 

Abiotic Hydrolysis 

t 1⁄2 = 2.0 days (pH 

5) 

t 1⁄2 = 2.0 days (pH 

7) 

t 1⁄2 = 4.5 days (pH 

9) 

MITC (pH 5 and 7) 

Methylamine (pH 5, 7, 

and 9) 

MCDT (pH 9) 

DMTU (pH 5, 7, and 

9) 

DMU (pH 5, 7, and 9) 

41631101 Acceptable 

Aqueous Photolysis t 1⁄2 = 28 minutes 

MITC 

Methylamine 

MCDT 

NMethylthioformamide 

41517701 Acceptable 

Soil Photolysis t 1⁄2 = 63 minutes - 42978701 Supplemental 

Degradation t1/2 in air No Data - NA NA 

Aerobic Soil Metabolism t 1⁄2 = 23 minutes MITC 40198502 Acceptable 

Anaerobic Soil 

Metabolism No Data - NA NA 

Aerobic Aquatic 

Metabolism No Data - NA NA 

Anaerobic Aquatic 

Metabolism No Data - NA NA 

Mobility, unaged 

leaching, 

adsorption/desorption 

and aged leaching soil 

column 

Koc = 4.04 ml/g - EPISUITE NA 

Volatility from Soil 

(Laboratory) No Data 1

 - NA NA 

Volatility from Soil 

(Field) No Data 1

 - NA NA 

Terrestrial Field 

Dissipation 

Metam Sodium 

residues were not 

detected after 

application in 

Mississippi Silt 

Loam and 

California Sandy 

Loam Soils 

MITC 

DMU 

41514402 

41514401 

Supplemental 

Supplemental 
Page 19 of 79 

Table 4. Summary of metam sodium/metam potassium environmental fate 

properties.

Study3 Value and unit Major Degradates 

MRID # 

or 

Citation 

Study 

Classification, 

Comment 

Bioconcentration Factor 

(BCF)- Species Name No Data 2

 - NA NA 

1 Metam sodium/metam potassium possess a low vapor pressure of 4.53 x 10-9 torr, therefore no data are 

necessary. 

2 Metam sodium/metam potassium Log Kow < 3. therefore no data are necessary. 

3 All studies used metam sodium as the test substance. 

4

 Dashes mean no constituents found or measured. 

5

 NA means not applicable. 

Table 5. Summary of MITC environmental fate properties.

Study 2 Value and unit Major Degradates 

MRID # 

or 

Citation 

Study 

Classification, 

Comment6

Abiotic Hydrolysis 

t 1⁄2 = 3.5 days (pH 5) 

t 1⁄2 = 20.4 days (pH 

7) 

t 1⁄2 = 4.6 days (pH 9) 

Methylamine (pH 5, 

7, and 9) 

DMTU (pH 9) 

00158162 Acceptable 

Aqueous Photolysis t 1⁄2 = 51.6 days - CALDPR, 

2002 NA 

Soil Photolysis - - - NA 

Degradation t1/2 in 

air 1.21 – 1.60 days 

MIC5

Methyl Isocyanide5

Sulfur Dioxide5

Hydrogen Sulfide5

Carbonyl Sulfur5

Nmethylthioformamide5

Methylamine5

Geddes et 

al., 1995 NA 

Aerobic Soil 

Metabolism 3.3 – 9.9 days - Gerstl et al., 1997 NA 

Anaerobic Soil 

Metabolism No Data - NA NA 

Aerobic Aquatic 

Metabolism No Data - NA NA 

Anaerobic Aquatic 

Metabolism 21 Days - 43596501 Supplemental 

Mobility, unaged 

leaching, 

adsorption/desorption 

and aged leaching 

soil column 

Kd = 0.26 ml/g 

(mean value) - Gerstl et 

al., 1977 NA 

Volatility from Soil 

(Laboratory) No Data - NA NA 
Page 20 of 79 

Table 5. Summary of MITC environmental fate properties.

Study 2 Value and unit Major Degradates 

MRID # 

or 

Citation 

Study 

Classification, 

Comment6

Volatility from Soil 

(Field) 

See Table 6 for field 

volatility study 

descriptions and 

volatile flux 

measurements 

- 

45703702 

45703704 

47131601 

47314301 

47732801 

46379201 

47820001 

47813901 

48011601 

48005901 

48115101 

47956701 

48467601 

Acceptable 

Acceptable 

Acceptable 

Acceptable 

Supplemental 

Pending 

Pending 

Pending 

Pending 

Pending 

Pending 

Pending 

Pending 

Terrestrial Field 

Dissipation 

Leland, MD Silt 

Loam Soil

t 1⁄2 < 24 hours 

MITC residues were 

not detected after 7 

days 

Visalia, CA Sandy 

Loam Soil

t 1⁄2 < 24 hours 

MITC residues were 

not detected after 7 

days 

- 

41514402 

41514401 

Supplemental 

Supplemental 

Bioconcentration 

Factor (BCF)- 

Species Name 

No data 1 - NA NA 

1 MITC’s Log Kow < 3, therefore no data are needed. 

2 All studies used MITC as the test substance except for the field dissipation and field volatility studies, 

where metam sodium was used. 

3

 Dashes means no constituents found or measured. 

4

 NA means not applicable. 

5 Degradates detected in field volatility from Geddes et al., 1995. Limited information regarding material 

balance. 

6 For studies with finalized classification pending, cursory review found studies adequate for risk 

assessments. Finalized review with formal DER pending.

 
Page 21 of 79 

Table 6. Description of MITC field volatility studies and volatile flux 

measurements. 

Parent 

Chemical 

Applied 

Field Volatility 

Study 

(Application 

Rate) 

Time 

Applied MRID 

Study 

Classification 1

Peak Flux 

Rate 2,3

(mass 

loss) 

Cumulative 

Mass Loss 2

(% mass loss) 

Metam 

Sodium 

Bakersfield, CA 

Sandy Loam 

Sprinkler 

Chemigation 

with water seal 

(320 lbs. a.i./A) 

August 21 

5:00 am 

45703702 Acceptable 4.22 15.86 percent 

through 96 

hours postapplication 

Metam 

Sodium 

Lost Hills, CA 

Clay Loam

Shank Injection 

to Raised Beds to 

>16 inch depth 

with water seal 

(320 lbs. a.i./A) 

June 13 

6:50 am 

45703704 Acceptable 2.39 7.45 percent 

through 96 

hours postapplication 

Metam 

Sodium

Helm, CA Sandy 

Loam

Shank Injection 

to Raised Beds to 

4 inch depth 

with soil seal 

(297 lbs. a.i./A) 

February 3 

9:30 am 

47131601 Acceptable 1.11 6.38 percent 

through 72 

hours postapplication 

Metam 

Sodium

Brawley, CA

Flooded 

Application 

(320 lbs. a.i./A) 

September 

15 

12:05 pm 

47314301 Acceptable 4.53 14.64 percent 

through 68 

hours postapplication 

Metam 

Sodium

Franklin County, 

WA

Broadcast Shank 

Injection to 9 

inch depth with 

water seal 

(219.44 lbs. 

a.i./A) 

October 9 

12:10 pm 

47732801 Supplemental 1.39 9.68 percent 

through 94 

hours postapplication 

Metam 

Sodium

Mount Vernon, 

WA Clay Loam

Broadcast Shank 

Injection (depth 

unspecified) with 

Soil Compaction 

(285.76 lbs. 

a.i./A) 

July 21 

8:27 am 

46379201 Finalized 

Classification 

Pending 

TBD TBD
Page 22 of 79 

Parent 

Chemical 

Applied 

Field Volatility 

Study 

(Application 

Rate) 

Time 

Applied MRID 

Study 

Classification 1

Peak Flux 

Rate 2,3

(mass 

loss) 

Cumulative 

Mass Loss 2

(% mass loss) 

Metam 

Sodium 

Tifton, GA 

Loamy Sand

Virtually 

Impermeable 

Film Tarped 

Shank Injection 

to Raised Beds to 

4 inch depth 

(712.6 lbs. a.i./A) 

February 7 

4:30 pm 

47820001 

(Field 1) 

Finalized 

Classification 

Pending

TBD TBD

Metam 

Sodium 

Tifton, GA 

Loamy Sand

Polytarp Film 

Shank Injection 

to Raised Beds to 

4 inch depth 

(728.9 lbs. a.i./A) 

February 7 

4:30pm 

47820001 

(Field 2) 

Finalized 

Classification 

Pending

TBD TBD

Metam 

Sodium 

Tifton, GA Sand

Polytarp Film 

Shank Injection 

to Raised Beds to 

4 inch depth 

(709.1 lbs. a.i./A) 

February 7 

4:30pm 

47820001 

(Field 3) 

Finalized 

Classification 

Pending

TBD TBD

Metam 

Potassium 

Duette, FL Sand

Metalized Tarped 

Shank Injection 

to Raised Beds to 

4 inch depth 

(311 lbs. a.i./A) 

January 14 

10:43 am 

47813901 

(Field 1) 

Finalized 

Classification 

Pending 

TBD TBD

Metam 

Potassium 

Duette, FL Sand

Virtually 

Impermeable 

Film Shank 

Injection to 

Raised Beds to 4 

inch depth 

(300.1 lbs. a.i./A) 

January 14 

1:22 pm 

47813901 

(Field 2) 

Finalized 

Classification 

Pending 

TBD TBD

Metam 

Potassium 

Duette, FL Sand

Metalized Tarped 

Shank Injection 

to Raised Beds to 

4 inch depth 

(305.8 lbs. a.i./A) 

January 14 

4:03 pm 

47813901 

(Field 3) 

Finalized 

Classification 

Pending 

TBD TBD

Metam 

Sodium 

Coloma, WI

Loamy Sand

Broadcast Shank 

Injection with 

water seal to 5.5 

inch and 9.5 inch 

depths 

(287 lbs. a.i./A) 

September 

25 

10:27 am 

48011601 

(Field 1) 

Finalized 

Classification 

Pending

TBD TBD
Page 23 of 79 

Parent 

Chemical 

Applied 

Field Volatility 

Study 

(Application 

Rate) 

Time 

Applied MRID 

Study 

Classification 1

Peak Flux 

Rate 2,3

(mass 

loss) 

Cumulative 

Mass Loss 2

(% mass loss) 

Metam 

Sodium 

Coloma, WI

Loamy Sand

Broadcast Shank 

Injection with 

water seal to 5.5 

inch and 9.5 inch 

depths (270.1 lbs. 

a.i./A) 

September 

25 

8:15 am 

48011601 

(Field 3) 

Finalized 

Classification 

Pending

TBD TBD

Metam 

Sodium

Howard City, MI 

Loamy Sand

Broadcast Shank 

Injection to 12 

inch depth with 

Soil Compaction 

(318.2 lbs. a.i./A) 

October 28 

4:10 pm 

48005901 

(Field 1) 

Finalized 

Classification 

Pending

TBD TBD

Metam 

Sodium

Howard City, MI 

Sand

Broadcast Shank 

Injection to 12 

inch depth with 

Soil Compaction 

and Water Seal 

(321.1 lbs. a.i./A) 

October 28 

2:34 pm 

48005901 

(Field 2) 

Finalized 

Classification 

Pending

TBD TBD

Metam 

Sodium

Pasco, WA

Sandy Loam

Broadcast Shank 

Injection to 9 

inch depth with 

Soil Compaction 

(823.3 lbs. a.i./A) 

March 24 

9:40 am 

48115101 

(Field 1) 

Finalized 

Classification 

Pending

TBD TBD

Metam 

Sodium

Pasco, WA

Sandy Loam

Broadcast Shank 

Injection to 9 

inch depth with 

Soil Compaction 

and Water Seal 

(880.46 lbs. 

a.i./A) 

October 28 

8:30 am 

48115101 

(Field 2) 

Finalized 

Classification 

Pending

TBD TBD

Metam 

Potassium 

Modesto, CA 

Sandy Loam

Drench 

Application with 

Water Seal 

(49.15 lbs. 

a.i./A) 

August 20 

7:30 am 

47956701 Finalized 

Classification 

Pending

TBD TBD
Page 24 of 79 

Parent 

Chemical 

Applied 

Field Volatility 

Study 

(Application 

Rate) 

Time 

Applied MRID 

Study 

Classification 1

Peak Flux 

Rate 2,3

(mass 

loss) 

Cumulative 

Mass Loss 2

(% mass loss) 

Metam 

Sodium 

Prosser, WA 

Sandy Loam

Center Pivot 

Chemigation 

with Water Seal 

(422 lbs. a.i./A) 

October 13 

9:40 am – 

2:05 pm 

48467601 

(Field 1) 

Finalized 

Classification 

Pending

TBD TBD

Metam 

Sodium

Prosser, WA 

Sandy Loam

Center Pivot 

Chemigation 

with Water Seal 

(633.33 lbs. 

a.i./A) 

October 13 

3:10 pm – 

6:23 pm 

48467601 

(Field 2) 

Finalized 

Classification 

Pending

TBD TBD

Metam 

Sodium

Prosser, WA 

Sandy Loam

Center Pivot 

Chemigation 

with Water Seal 

(623.53 lbs. 

a.i./A)

October 13 

9:55 pm – 

October 14 

3:40 am 

48467601 

(Field 3)

Finalized 

Classification 

Pending

TBD TBD

Metam 

Sodium

Prosser, WA 

Sandy Loam

Center Pivot 

Chemigation 

with Water Seal 

(520 lbs. a.i./A) 

October 14 

2:25 am – 

5:35 am 

48467601 

(Field 4) 

Finalized 

Classification 

Pending

TBD TBD

1. For studies with finalized classification pending, cursory review found studies adequate for risk 

assessments. Finalized review with formal DER pending. 2 TBD means peak flux rates to be determined pending finalization of study reviews. 

3

 Peak flux rate refers to the average over ~ 4 hours as per the sampling periods in the field volatility 

studies.

6. Receptors 

Since metam sodium and metam potassium rapidly hydrolyze to MITC, and degrade by 

microbial degradation and by soil photolysis quickly, the toxicity data for MITC will be 

used to assess risk to fish, aquatic invertebrates, and aquatic plants. Terrestrial exposure 

to birds, mammals, invertebrates can occur by inhalation of MITC. Additionally, 

exposure to terrestrial plants can occur via MITC vapors or runoff exposure of MITC. 

Therefore, for aquatic and terrestrial organisms, toxicity data for only MITC will be 

considered. Table 7 and Table 8 provide a summary of the MITC aquatic toxicity data 

and terrestrial toxicity data, respectively. The most sensitive species tested in each taxon 

is reported and will be used to characterize the potential acute and chronic ecological 

effects of MITC to terrestrial and aquatic organisms. 
Page 25 of 79 

6.1 Effects to Aquatic Organisms 

Table 7. Summary of the most sensitive endpoints from aquatic toxicity studies for 

MITC (degradate of metam sodium and metam potassium) 

Taxonomic 

Group 

Study 

Type Surrogate Species Toxicity Value 

MRID and 

Classification 

Acute 

Toxicity 

Classification 

Freshwater fish1

Acute 

Rainbow Trout 

(Oncorhynchus 

mykiss) 

LC50 = 94 μg 

a.i./L 

(slope = 

N/A) 

42058002 

Acceptable 

Very highly 

toxic 

LC50 = 53 μg 

a.i./L 

(slope = 

N/A) 

45919420 

Supplemental 

(due to 

(hydrolytic 

instability and 

insufficient 

sampling of the 

test chemical) 

Very highly 

toxic 

Chronic 

(Early 

LifeStage) 

No data available 

Freshwater 

invertebrates 

Acute Water Flea 

(Daphnia magna) 

EC50 = 55 μg 

a.i/L 

(slope not 

available) 

41819302 

Acceptable 

Very highly 

toxic 

Chronic Water Flea 

NOAEC = 25 

μg a.i./L 

LOAEC = 

>25 μg a.i./L 

(based on 

parental 

mortality and 

reproduction) 

45634001 

Supplemental 

(based on mean 

measured 

concentrations 

not determined, 

stability of 

chemical not 

assessed, 

terminal growth 

measurements 

not obtained, two 

highest treatment 

concentrations 

excluded from 

analysis to 

reproduction 

endpoint due to 

100% mortality) 

N/A 

Estuarine/marine 

fish Acute 

Sheepshead 

Minnow 

(Cyprinodon 

variegatus) 

Study in 

review 48731101 Study in review 
Page 26 of 79 

Taxonomic 

Group 

Study 

Type Surrogate Species Toxicity Value 

MRID and 

Classification 

Acute 

Toxicity 

Classification 

Estuarine/marine 

invertebrates Acute 

Eastern Oyster 

(Crassostrea 

virginica) 

Study in 

review 48985201 Study in 

review 

Saltwater mysid 

(Americamysis 

bahia) 

Study in 

review 48649301 Study in 

review 

Aquatic plants 

and algae 

Vascular Duckweed 

(Lemna gibba) 

7-day EC50

(frond 

number) = 

0.59 mg a.i/L 

NOAEC 

(frond 

number and 

growth rate) = 

0.09 mg a.i/L 

45919421 Acceptable 

Nonvascular2

Freshwater Algae 

(Scenedesmus 

subspicatus) 

96-hour EC50 

(cell density) 

= 0.2 mg a.i/L 

NOAEC = 

0.13 mg a.i/L 

44588903 

Supplemental 

(non-guideline 

species used) 

Freshwater algae 

Pseudokirchnerella 

subcapita (99 % 

a.i) 

72-hour EC50

(area under 

the curve)= 

0.3 mg a.i/L 

(95% C.I = 

0.26 – 0.34) 

NOAEC(cell 

density, 

growth rate, 

area under the 

curve) = 0.21 

mg a.i/L 

45919416 Supplemental 

(72-hour 

exposure 

instead of 

guideline 

recommended 

96-hour 

exposure 

conducted) 

Cyanobacteria 

Anabaena flosaquae ( 99.6 % a.i.) 

72 hour-EC50

(cell density) 

= 1.5 mg a.i/L 

(95% C.I = 

1.1 – 2.0) 

NOAEC (cell 

density, 

growth rate, 

area under the 

curve) = 5.0 

mg a.i/L 

45919422 Supplemental 

(72-hour 

exposure 

instead of 

guideline 

recommended 

96-hour 

exposure 

conducted) 

Freshwater diatom 

Navicula 

pelliculosa (99.7% 

a.i) 

N/A 48733401 

Study in 

review 
Page 27 of 79 

Taxonomic 

Group 

Study 

Type Surrogate Species Toxicity Value 

MRID and 

Classification 

Acute 

Toxicity 

Classification 

Marine diatom 

Skeletonema 

costatum (99.7% 

a.i) 

N/A 48733501 

Study in 

review 

Cyanobacteria 

Anabaena flosaquae (99.7 % a.i.) 

N/A 48733601 Study in 

review 

Freshwater algae 

Pseudokirchnerella 

subcapita (99.7 % 

a.i) 

N/A 48733701 

Study in 

review 

1 Freshwater fish may be surrogates for aquatic-phase amphibians. 

2

 Several additional aquatic non-vascular plants studies have been submitted for MITC and are currently 

under review (MRIDs: 48733401, 48733501, 48733601, and 48733701). 

 
Page 28 of 79 

6.2 Effects to Terrestrial Organisms 

Table 8. Summary of the most sensitive endpoints from terrestrial toxicity studies 

for MITC 

Taxonomic 

Group 

Study 

Type 

Surrogate 

Species 

Toxicity Value 

(all units in 

terms of 

measured active 

ingredient) 

MRID and 

Classification 

Acute Toxicity 

Classification 

Birds1 Acute 

(Inhalation) 

Bobwhite quail 

(Colinus 

virginianus) 

Study in review 48788401 Study in review 

Mammals 

Acute 

(Inhalation) 

Laboratory rat 

(Rattus 

norvegicus) 

4 hour LC50 = 

<0.0296 mg a.i/L 42365605 Acceptable 

Acute 

(oral) 

Laboratory rat 

(Rattus 

norvegicus) 

14-d LD50 = 55 

mg ai/kg bw 00162331 Acceptable 

Insects Acute 

contact 

Honey bee 

(Apis mellifera 

L.) 

No data 

available N/A -- 

Terrestrial 

plants 

Vegetative 

Vigor (Tier 

II) 

Various species Study in review 49058001 Study in review 

Seedling 

Emergence Various species No data available N/A 

This study was 

previously waived 

(see USEPA, 2012) 

1 Birds represent surrogates for terrestrial-phase amphibians and reptiles. 

6.3 Ecological Incidents 

A review of the Ecological Incident Information System (EIIS, version 2.1), the 

Aggregate Summary Module (ASM) (v.1.0) of Office of Pesticide Program’s Incident 

database maintained by the Information Technology and Resource Management Division, 

and the Avian Monitoring Information System (AIMS) for ecological incidents involving 

MITC from metam sodium applications was completed. The results of this review for 

terrestrial, plant, and aquatic incidents are discussed below. 

Incidents from the EIIS Database: 

Incidents are reported separately for MITC in the EIIS database. Metam sodium use has 

been linked to six reported adverse ecological incidents in aquatic systems from the EIIS 

system, which included mortality (Table 9). Amphibians are not among the reported 

mortalities; however, this does not necessarily mean that they have not occurred. No 

aquatic or terrestrial incidents for MITC were reported in the EIIS database. 
Page 29 of 79 

Table 9. Reported aquatic ecological incidents for metam sodium.

EIIS 

Incident 

No. (Date) 

Location Species 

Affected 

Magnitude 

of Effect 

(number of 

organisms) 

Incident Summary Certainty 

Index 

I006515-

001 

(01 June 

1991) 

Sacramento 

River, CA 

Fish 1,000 A railroad tank car spill in which 

thousands of fish (as well as 

most insects and some plants) 

were killed in a 42-mile stretch 

of the Sacramento River in 

California in 1991. While not 

representative of agricultural 

applications, this incident shows 

clearly that metam-sodium has 

the ability to kill large numbers 

of aquatic organisms if the 

chemical gets into water in large 

quantities. 

(3) 

Probable 

I005525-

016 (July 

17 1991) 

Sacramento 

River, CA 

Trout, 

suckers, 

squawfish 

and sculpin 

and other 

fish 

1,000 

This incident report is a 

summary report only, but cites 

the death of over 1000 fish, 

including trout, suckers, 

squawfish, and sculpin in 

Siskiyou and Shasta counties in 

California in 1991. It very likely 

refers to the same railroad tank 

car spill cited above. It provides 

the additional information of fish 

species involved.

I012648-

001 (Nov 1 

1994) 

St Johns, 

FL 

Fish Unknown This incident report involved a 

phone call in which a Florida fish 

farm representative claimed that 

the use of metam-sodium nearby 

resulted in several fish kills from 

1994 - 2001. 

(2) 

Possible 

I008259-

001 

(December 

23 1998) 

Hastings, 

FL 

Bass 2,700 This incident report under 6(a)(2) 

(from a registrant) cites a claim 

from a Florida fish farm owner 

that 2700 hybrid bass were killed 

after metam-sodium was applied 

within 300 feet of the fish tanks. 

The owner suspected that drift 

occurred (i.e., of MITC, the toxic 

degradate of metam-sodium that 

off-gasses) and that his aeration 

system picked it up and redissolved it into the fish tanks. 

Also cited in the report is a pump 

malfunction that apparently 

interrupted water and oxygen 

circulation. 

(2) 

Possible 
Page 30 of 79 

EIIS 

Incident 

No. (Date) 

Location Species 

Affected 

Magnitude 

of Effect 

(number of 

organisms) 

Incident Summary Certainty 

Index 

I008275-

003 (Nov 

30 1998) 

NR Fish NR This incident report under 6(a)(2) 

(from a registrant) cites a 

reported pond contamination and 

a fish kill following metamsodium application. There was 

no report of application method 

or if there was a misapplication. 

Very few details were provided, 

although it states that USFWS 

was notified when the incident 

occurred. 

(2) 

Possible 

I011162-

001 (Jan 6 

2001) 

Hastings, 

FL 

Bass >400 This incident report under 6(a)(2) 

(from a registrant) cites a claim 

from a Florida fish farm owner 

that approximately 400 striped 

bass were killed after metamsodium was applied within about 

600 feet of the fish tank. 

Although reportedly most of the 

tanks receive air from a common 

source, mortality was reported in 

only one of 94 tanks 

(1) 

Not 

probable 

The aquatic incidents reported in this assessment include agriculture applications based 

on the conceptual model. The incidents I012648-001 and I008259-001 report applications 

to adjacent areas with drift impacting fish. The distances reported vary from 300 feet to 1⁄4 

mile. These reports were assigned an uncertainty index of possible (2 out of 4). Both of 

these reports fail to provide sufficient information to exclude other causes for the fish 

mortality and therefore are not used in the assessment. However, since fish tanks at fish 

farms were impacted, it is unlikely that the incidents occurred as a result of runoff of 

MITC residues. In addition, a recent newspaper article in the Tribune Weekly Chronicle 

(October 5, 2010) reported that small levels of MITC were detected in a canal in the 

Sonoran Desert town of Holtville, CA. Additional details were provided by Nelson Perez 

of the County of Imperial Office of the Agriculture Commissioner (Personal 

Communication).The levels of MITC were attributed to cases of human exposure and a 

fish kill in the area possibly associated with metam sodium applications in the region 

which occurred throughout late September and early October 2010. MITC was detected 

at a level of 1.62 μg/L (Nelson Perez, County of Imperial Office of the Agriculture 

Commissioner, Personal Communication). The resulting RQ=0.03 for both fish and 

Daphnia would indicate a “No Effect” determination. There is uncertainty regarding 

when measurements were taken relative to the suspected application and in the distance 

from the source of release to the measurement site. This incident report is not available 

in the EIIS database at this time. 

There are several other incidents which are not tied to the agricultural use of metam 
Page 31 of 79 

sodium, metam potassium, or MITC. I005525-016, the tank car spill incident, does not 

reflect an agricultural labeled use or method of application. Incident I008275-003 did not 

include extensive information in the report. The county or state was not identified, and 

the number of dead fish and the application method or if this was a misapplication was 

not reported. Incident I011162-001 was assigned certainty index assigned, of 1, 

indicating a classification of not probable. 

Table 10 shows five terrestrial incidents reports involving metam sodium included in the 

agency’s Ecological Incident Information System (EIIS) database. They have certainty 

indices ranging from 1 (unlikely) to 4 (highly probable). 

Table 10. Adverse terrestrial ecological incidents for metam sodium. 

EIIS 

Incident 

No. (Date)

Location Species 

Affected 

Magnitude 

of Effect Incident Summary Certainty Index 

I011510-

001 

(12 

November 

1999) 

Bullard, TX 

Pine 

30 acres This incident report under 

6(a)(2) (from a registrant) cites 

an incident in which 30 acres of 

pine seedlings in Texas were 

alleged to be damaged by drift 

(presumably of MITC) from a 

metam-sodium application in 

which no water seal was used. 

(3) 

Probable 

I011838-

056 (22 

May 2001) 

Robersonville 

River, NC Peanuts 80 acres 

This incident report under 6(a)2 

cites an incident in which 80 

acres of peanuts were damaged 

in North Carolina. Metam 

sodium was one of five products 

applied 

(2) 

Possible 

I012457-

005 (22 

May 2001) 

Robersonville 

River, NC Peanuts 120 acres 

This incident report under 

6(a)(2) (from a registrant) cites 

an incident in which 120 acres of 

peanuts were damaged in North 

Carolina. Metam-sodium was 

apparently one of two pesticides 

applied. 

(2) 

Possible 

I014405-

002 (23 

May 1996) 

Grant County, 

WA 

Potato NR This incident reported in the 

Washington State Department of 

Health 1997 Annual Report. 

Misapplication of metam sodium 

damaged potato crop. Complaint 

was withdrawn. 

(2) 

Possible 

I016107-

001 (23 

September 

2004) 

Broad 

Brook,CT 

Spruce 

and 

Cherry 

trees 

Several A complaint was received by the 

State of Connecticut Department 

of Environmental Protection 

citing damage to spruce trees as 

well as a cherry tree. 

(2) 

Possible 

Incident I016107-001 reported application on according to label instructions with a 

certainty index of 2 (possible). This demonstrates the possible adverse effect of MITC 

exposure from metam sodium applications to vegetation or crops off-site treated fields. 

No distance off the treated field was reported, the application rate of metam sodium used 
Page 32 of 79 

and the concentration of MITC was not reported, and no other pesticide use was reported. 

Incidents I011510-001 and I014405-002 were not used in this assessment due to 

misapplication of metam sodium. Both I011838-056 and I012457-005 reported use of 

multiple pesticides. No percentages of the mixture were reported. 

Incidents from the AIMS Database: 

Bird incidents for metam sodium and MITC were reviewed in the Avian Incident 

Monitoring System (AIMS). No avian incidents for metam sodium or MITC were 

reported in the AIMS database. 

7. Exposure Pathways of Concern 

Conventional Uses 

Given MITC’s volatile and soluble physical chemical properties, broad spectrum mode of 

action as a fumigant, application methods, and application to soil at most once per year, 

the following lists the pathways of exposure anticipated for MITC associated with metam 

sodium and metam potassium applications: 

 Inhalation exposure for mammals, birds, and terrestrial invertebrates (honey 

bee) (acute) 

 Air exposure for plants (full-grown) 

MITC has been shown to escape to the atmosphere from soil in large quantities over short 

time frames close to the time of application from the collection of field volatility studies 

from metam sodium and metam potassium applications submitted to the Agency. 

Despite previous risk assessments not showing risk due to MITC exposure, more recent 

field volatility studies will be utilized to evaluate MITC air exposure to mammals, birds, 

plants, and terrestrial invertebrates. For mammals, birds and terrestrial organisms, 

chronic exposure may occur due to repeat exposure of applied fumigants from multiple 

applications across an airshed. Since metam sodium and metam potassium are expected 

to rapidly convert to MITC in the environment, spray drift is not expected to be of 

concern for terrestrial organisms. In addition, MITC vapor-phase exposure to plants will 

only be evaluated as it is expected to be the dominate exposure route compared exposure 

of MITC dissolved in runoff water. 

 Soil exposure for plant seedlings (acute) 

MITC exposure to plant seedlings is expected from metam sodium and metam potassium 

applications off the treated field. MITC’s broad spectrum mode of action as a fumigant, 

metam sodium and metam potassium large application rates to soil, and the mobile and 

diffuse nature of MITC as a vapor in soil all justify this exposure pathway. 
Page 33 of 79 

 Aquatic exposure for freshwater fish, estuarine marine organisms, aquatic 

invertebrates, and aquatic plants (acute and chronic) 

Although not the dominant route of exposure, MITC aquatic exposure can occur from 

metam sodium and metam potassium soil applications. When rain events occur close to 

the time of metam sodium and metam potassium applications, the large amounts of MITC 

that is present on the field can dissolve and runoff to neighboring water bodies. 

Infiltration and runoff of MITC may occur particularly with untarped applications. It is 

important to note that only runoff will predicate exposure to aquatic organisms for soil 

uses. Since MITC is the primary stressor of concern and conversion from metam sodium 

and metam potassium occurs rapidly beneath the soil, the spray drift contribution to 

aquatic exposure is not of concern. MITC discharges to water bodies from sewer uses for 

root control will also be evaluated. 

A train derailment resulted in a metam sodium spill over the Sacramento River in 1991. 

Up to 27,000 kg of metam sodium was released into the river. MITC was detected 

transporting downstream about 40 miles from the derailment site to the inlet of Lake 

Shasta where monitored concentrations of up to 5,800 ppb were detected two days after 

the spill (CALDPR, 1991). This demonstrates that 1.) though not resulting from a 

pesticide application, there is a potential for MITC from pesticide applications to be 

transported into a nearby watershed from a release site and 2.) that significant quantities 

of MITC may remain in water long enough for acute exposure to occur. Based on a time 

series of monitoring data at the inlet to Lake Shasta, a DT50 value of 3.75 hours was 

calculated. It is important to note that this short DT50 may be due to volatilization of 

MITC as well as due to flow through the inlet into Lake Shasta. The CALDPR report 

concerning the train derailment leading to the metam sodium spill to the Sacramento 

River and resulting dissipation analysis using the monitoring data at Lake Shasta is 

provided in Appendix A. 

MITC is shown to dissipate significantly over time in the water column. An inspection of 

previous PRZM/EXAMS modeling indicates that MITC in the receiving water body from 

runoff volatilizes to very low levels (< 0.1 ppb) between 15 – 30 days as controlled by 

Henry’s Law Constant. However, laboratory studies show that volatilization from water 

for other fumigants with similar physical chemical properties indicate that volatilization 

may occur at an even more rapid rate than what Henry’s Law Constant shows. 

A previously submitted chronic life cycle toxicity study to the freshwater invertebrate 

Daphnia magna MRID 45634001) shows that the NOEAC (for mortality and 

reproductive endpoints) was determined to be 25 μg a.i/L, based on initial nominal 

concentrations. However, given the high peak MITC aquatic exposure concentration 

possible and the short exposure duration for sub-lethal adverse effects to occur, the 

lethality resulting from acute MITC peak exposure concentrations will be the primary 

endpoint of concern. Therefore, a chronic early life stage test for freshwater fish is not 

being requested at this time. 
Page 34 of 79 

 Drinking water exposure for mammals and birds

While dietary and drinking water exposures are possible for mammals and birds, acute 

risk from inhalation is determined to be primary route of exposure for several reasons. 

For birds, based on MITC’s vapor pressure and calculations using STIR, the maximum 1-

hour vapor inhalation dose for birds is 7914 mg/kg. By contrast, based on MITCs 

solubility limit and calculations using SIP, the upper bound daily drinking water intake 

dose for a bird is 6974 mg/kg bw. Multiplying the STIR estimate of one hour by 12 (to 

match the daily exposure duration of the SIP estimate) yields 94968 mg/kg which is 2 

orders of magnitude more than the SIP drinking water dose. For MITC, this suggests that 

the potential daily inhalation exposure of a bird is substantially greater than the potential 

daily drinking water exposure of a bird indicating that inhalation exposure may be of 

more concern. 

Additionally, acute oral and acute inhalation toxicity data are available for the laboratory 

rat (MRIDs 00162331 and 42365605, respectively). The acute inhalation study did not 

achieve a definitive toxicity endpoint with an inhalation LC50 of <0.0296 mg/L. Using 

the STIR model, which estimates an inhalation LD50 from an oral LD50 endpoint, the rat 

inhalation LD50 value would be 0.80 mg/L. This indicates that MITC is at least 2 orders 

of magnitude more toxic on an acute inhalation basis than for an acute oral one (although 

this estimate is non-definitive as the rat inhalation study did not achieve a definitive 

endpoint). 

Therefore, while the potential for drinking water exposure exists to birds and mammals, 

inhalation exposure is determined to be the one of primary concern for the terrestrial risk 

assessment. By being protective of birds and mammals via the inhalation route of 

exposure, EFED believes that the dietary and drinking water routes of exposure will be 

protected as well. 

 Dietary exposure for mammals and birds

Like drinking water exposure described above, inhalation exposure is expected to be the 

dominate exposure route for mammals and birds. First, residues are not expected to be 

present on crops due to pre-planting application methods for metam sodium and metam 

potassium and plant back interval specified on the label. Second, once applied, birds and 

mammals are expected to be much more sensitive to inhalation than to any ingested soil 

borne food material exposed to MITC. The dominance of the inhalation exposure over 

dietary exposure is confirmed by analysis comparing upper bound inhalation exposure 

dose to dietary exposure doses using STIR and the Earthworm Fugacity Model, 

respectively. This analysis is shown in Appendix E.

Antimicrobial Uses 

The antimicrobial metam sodium uses for remedial treatment of wooden poles may be of 

a concern, but the pesticide is inserted into a hole in the pole and then is sealed off. 

Therefore, the environmental risk is minimal for this use. 
Page 35 of 79 

The antimicrobial metam potassium use in pulp and paper, and cooling water systems 

may trigger risk to aquatic ecosystems. In addition, there may be risks associated with 

aquatic exposure and air exposure with animal waste products treated with metam sodium 

and metam potassium. Other antimicrobial uses are considered as indoor uses, but may 

be discharged through storm drains. Therefore, these uses may also trigger aquatic risks. 

8. . Analysis Plan 

The ecological risk assessment will focus on MITC as the main stressor of concern for 

air, soil, and aquatic exposure. This determination is discussed further in Section 8.1

below. EECs will be calculated for air, soil, and water using various environmental fate 

and transport models discussed in Section 8.2 below. The EECs will be compared with 

toxicological endpoints from various aquatic and terrestrial taxa to quantitatively 

compute a risk quotient (RQ). The RQ will be compared to the Agency’s levels of 

concern (LOC) to determine the risk to organisms resulting from MITC exposure from 

metam sodium and metam potassium applications. 

8.1 Stressors of Concern 

Table 5 and Table F-1 in Appendix F shows degradates which form in soil, water, and 

air resulting from the application of metam sodium and metam potassium and subsequent 

conversion to MITC in soil. Structural activity relationships (SARs) of the degradates 

and the resulting estimated toxicity endpoint values for various aquatic and terrestrial 

taxa were compared to MITC’s measured toxicity values to the same organisms to 

identify the toxic residues of concern. This analysis was conducted using ECOSAR 

version 1 (February 2, 2009) and is shown in Appendix B. Among the major degradates 

found in environmental fate studies, none have been identified as being potentially of 

toxicological concern compared to MITC. Therefore, MITC is considered the primary 

stressor of concern in the ecological risk assessment. 

8.2 Measures of Exposure 

Measures of exposure of MITC to the aquatic and terrestrial organisms are derived from 

the utilization of environmental fate and transport models. Section 8.2.1 and Section 

8.2.2 describe the exposure estimation methodology in the aquatic and terrestrial 

environments, respectively. Exposures to aquatic and terrestrial organisms will be 

estimated based on maximum application rates and all application methods cited in 

Section 3. MITC equivalent application rates will be calculated considering appropriate 

transformation scaling factors from environmental fate studies and the ratio of molecular 

weights from MITC to parent metam sodium or metam potassium. Please see Section 3

on the determination of appropriate MITC application rates by use. 
Page 36 of 79 

8.2.1 Estimating Exposure in the Aquatic Environment 

The models used to predict aquatic EECs are the Pesticide Root Zone Model coupled 

with the Exposure Analysis Modeling System (PRZM/EXAMS) publically available at: 

http://www.epa.gov/oppefed1/models/water/pe5_user_manual.htm. The PRZM/EXAMS 

Georgia Farm Pond scenario will be used to estimate the aquatic EECs in surface water 

resulting from both soil fumigant and animal waste product uses. Since both surface 

chemigation and incorporated chemigation and injection application methods for metam 

sodium and metam potassium application exist, two separate runs will be conducted for 

each crop scenario addressing the surface and incorporated applications. The PRZM 

volatilization algorithm will be used to address both MITC’s upward movement in soil to 

the runoff extraction zone and escape to the atmosphere. 

The PDM module of EFAST model to estimate the concentrations of metam sodium, 

metam potassium in water for use in paper and pulp and recalculating cooling water 

systems. Sewer root control uses and indoor uses requiring discharges down drainage 

pipes will be addressed through the EFAST using the DtD, and PDM modules for 

exposure determination. 

8.2.2 Estimating Exposure in the Terrestrial Environment 

MITC acute exposures of the birds, mammals, terrestrial invertebrates, and plants through 

inhalation exposure for metam sodium and metam potassium soil fumigant applications 

and treatment for animal waste products are determined using the EECs from 

atmospheric dispersion models. Consistent with the aquatic exposure assessment, the 

ecological risk assessment will assess two separate scenarios addressing surface and 

incorporated application of metam sodium and metam potassium. The Agency’s 

recommended screening dispersion model for the near field, the American 

Meteorological Society/EPA Regulatory Screening Model (AERSCREEN), will be used 

to generate Tier I EECs. The Tier I analysis will consider the maximum flux rate for 

each application method from the collection of MITC flux studies and worst-case 

meteorological conditions (light winds and stagnant conditions) to calculate peak air 

EECs, representing one-hour average concentrations. Documentation on the 

AERSCREEN model is available at 

http://www.epa.gov/scram001/dispersion_screening.htm. The exposure scenario 

evaluated in the Tier 1 analysis will assume that the terrestrial receptors are directly 

downwind from the emissions source. This is illustrated in Figure 3 below. 
Page 37 of 79 

Figure 3. Schematic showing soil fumigant air exposure scenario due to volatilization 

and subsequent release from soil evaluated in Tier 1 analysis. 

If the Tier 1 EECs for either surface or incorporated applications result in an exceedance 

with the LOC, EECs will be further examined using the Tier 2 model, the Probabilistic 

Exposure and Risk Model for Fumigants (PERFUM). PERFUM is parameterized by a 

time series of flux data obtained from field volatility studies. PERFUM considers these 

flux values with a robust statistical sampling of meteorological data from points within 

rings surrounding a treated field (usually 5 years of hourly meteorological data). The 

current version of PERFUM processes estimated air concentrations from EPA’s 

previously recommended atmospheric dispersion model in the near field, the Industrial 

Source Complex Short-Range Model, Version 3 (ISCST3). The framework for 

PERFUM is illustrated in Figure 4 below. Estimated air concentrations are calculated 

and binned by percentile distributions within each ring and averaging time period. First, 

a peak one-hour averaging period will be used to calculate air EECs. If necessary, a 

higher averaging period equivalent to the exposure duration in toxicity studies will be 

used to characterize the RQs resulting from utilizing the one-hour peak EECs. The 

highest 90th percentile estimated air concentration from all averaging periods from the 

receptor ring closest to the edge of the field will be considered as the upper-bound EEC 

to determine the RQ. The PERFUM model is publically available on the web from the 

follow link: 

http://www.exponent.com/projectdetail.aspx?project=450. For this soil fumigant 

assessment, maximum air exposure will occur at the edge of the field corresponding to 

the where MITC mass emissions from the treated field will accumulate to maximum 

levels along the fetch of wind blowing over the treated field. 

Wind, Dispersion, 

and 

Accumulation 

of Vapors or Gas

Volatilization of 

residues in soil

Soil incorporated and 

chemigation fumigant 

application 
Page 38 of 79 

Figure 4. Illustration of the spatial and temporal aspects of the source to receptor 

configuration in PERFUM. The wind rose (left) illustrates the frequency distribution of 

variations in wind speed and wind direction that PERFUM accounts for in the transport 

of the vapor plume from the treated source to receptors (right). 

All modeling scenarios will be parameterized based on field volatility flux data 

normalized to an 80 acre field for drip chemigation applications and 120 acre field for 

overhead chemigation, shank injection, rotary tiller, and spray blade applications. Other 

applications such as center pivot chemigation, can be applied to larger areas over multiple 

days. Therefore, a separate scenario will account for MITC emissions occurring within a 

circular field over areas which increase over time as treatment occurs. 

For exposure to plant seedlings, TerrPlant will be used. Although TerrPlant EECs are 

based on runoff, TerrPlant will capture the overall exposure of plant seedlings whether it 

occurs from diffusion in the gas phase or runoff of dissolved MITC. Terrplant EECs can 

only be calculated at the edge of the field. 

8.3 Measures of Effect 

Toxicity data presented in Sections 6.1 and 6.2 of this problem formulation will be used 

with EECs to calculate risk quotients. Any additional information submitted by the 

registrant or found in the open literature prior to conducting the risk assessment will also 

be considered. The open literature studies are identified using EPA’s ECOTOXicology 

database (ECOTOX) (USEPA, 2007c), which employs a literature search engine for 

locating chemical toxicity data for aquatic life, terrestrial plants, and wildlife. The 

evaluation of both sources of data can also provide insight into the direct and indirect 

efects of pesticides on biotic communities from loss of species that are sensitive to the 

chemicals and from changes in structure and functional characteristics of the affected 

communities. 

Treated 

Field 

Receptor 

Rings 
Page 39 of 79 

8.4 Endangered Species Assessments 

Consistent with the Agency’s responsibility under the Endangered Species Act (ESA), 

the Agency will evaluate risks to federally threatened and/or endangered (listed) species 

from registered uses of pesticides in registration review. These assessments will be 

conducted in accordance with standard EPA procedures.. 

8.5 Endocrine Disruptor Screening Program

Metam sodium, metam potassium and MITC were not included in the first group of 67 

chemicals issued an order to conduct Tier 1 EDSP testing. For additional information the 

EDSP program, visit http://www.epa.gov/endo/. 

8.6 Drinking Water Assessment

For soil fumigation, runoff of MITC to reservoirs after rain events may occur shortly 

after soil treatments given the option for untarped application methods of metam sodium 

and metam potassium,. In addition, leaching of MITC to ground water and wells nearby 

treated fields are possible due to MITC’s high water solubility. The relative importance 

of MITC drinking water dosing concentrations with MITC inhalation doses resulting 

from metam sodium and metam potassium application will be determined. As a result of 

this determination, drinking water assessments addressing metam sodium and metam 

potassium applications will be conducted on an as needed basis. In case that a drinking 

water assessment is conducted, the PRZM-GW model accounting for volatility from soil 

will be used to calculate the EDWCs. 

For sewer root control uses, there is reportedly (Martyn, P., 2004) a contaminant 

(NDMA, nnitrosodimethylamine) in the Vaporooter product for which there is a National 

Recommended Water Quality Criteria of 0.00069 :g/L (current/potential drinking water) 

and 3.0 :g/L (no potential for drinking water). Any water quality data for NDMA and 

MITC submitted at the discharge point in sewage treatment plants where MITC use in 

sewers occurs will also be considered in any drinking water assessment. 

Drinking water exposure of parent compounds metam sodium and metam potassium are 

not expected due to the large transformation of these compounds to MITC 

(transformation fraction = 83 percent) and transformation of the parent compounds in the 

environment to MITC (half life = 23 minutes). 

9 Preliminary Identification of Data Gaps 

9.1 Environmental Fate

Table 11 and Table 12 identify environmental fate studies for metam sodium and 

MITC, respectively, by MRID that offer data for each guideline requirement, as well as 
Page 40 of 79 

study classifications and whether or not further data are needed in order to support risk 

assessment. 

Table 11. Submitted and requested environmental fate data for metam sodium. 

OCSPP 

Guideline 

Data 

Requirement 

Submitted 

Studies 

(MRID) 

Study 

Classifications

Are data 

needed to 

conduct 

risk 

assessment?

Current Additional Data Need 

835.2120 Hydrolysis 41631101 Acceptable No -- 

835.2240 Aqueous 

photolysis 

41517701 Acceptable No -- 

835.2410 Soil photolysis 42978701 Supplemental No -- 

835.4100 Aerobic soil 

metabolism 

40198502 Acceptable No -- 

835.4200 Anaerobic soil 

metabolism 

(None) (Not 

applicable) 

No -- 

835.4300 Aerobic aquatic 

metabolism 

(None) (Not 

applicable) 

No -- 

835.4400 Anaerobic 

aquatic 

metabolism 

(None) (Not 

applicable) 

No -- 

835.1230 

835.1240 

Adsorption/ 

desorption and 

leaching 

(None) (Not 

applicable) 

No -- 

835.1410 Volatility – 

laboratory 

(None) (Not 

applicable) 

No -- 

835.6100 

850.6100 

Terrestrial field 

dissipation 

41514401 Supplemental No -- 

41514402 Supplemental 

Analytical 

method in soil 

(None) (Not 

applicable) 

835.8100 

850.6100 

Volatility - 

Field 

(None) (Not 

applicable) 

No -- 

Analytical 

method in air 

(None) (Not 

applicable) 

 

835.6200 

850.6100 

Aquatic field 

dissipation 

(None) (Not 

applicable) 

No -- 

Analytical 

method in water 

(None) (Not 

applicable) 

 850.1730 Fish 

bioconcentration 

(None) (Not 

applicable) 

No -- 

A Metam potassium is expected to possess similar environmental fate properties since it is an analogue salt 

of metam sodium. 

B All studies were conducted with metam sodium as the test substance and provided information on 

environmental degradation of metam sodium. 
Page 41 of 79 

Table 12. Submitted and requested environmental fate data for MITC from metam 

sodium/potassium pre-plant soil products.. 

OCSPP 

Guideline 

Data 

Requirement 

Submitted 

Studies 

(MRID) 

Study 

Classifications

Are data 

needed to 

conduct risk 

assessment?

Current Additional Data Need 

835.2120 Hydrolysis 00158162 Acceptable No -- 

835.2240 Aqueous 

photolysis 

(None) (Not 

applicable) 

No -- 

835.2410 Soil photolysis (None) (Not 

applicable) 

No -- 

835.4100 Aerobic soil 

metabolism 

(None) (Not 

applicable) 

No

-- 

835.4200 Anaerobic soil 

metabolism 

(None) (Not 

applicable) 

No -- 

835.4300 Aerobic aquatic 

metabolism4

(None) (Not 

applicable) 

Yes A laboratory aquatic study is needed to 

determine MITC’s residence time in 

water. 

835.4400 Anaerobic 

aquatic 

metabolism 

43596501 Supplemental No -- 

835.1230 

835.1240 

Adsorption/ 

desorption and 

leaching 

(None) (Not 

applicable) 

No -- 

835.1410 Volatility – 

laboratory 

(None) (Not 

applicable) 

No -- 

835.6100 Terrestrial field 

dissipation 

(None) (Not 

applicable) 

No -- 

Analytical 

method in soil 

(None) (Not 

applicable) 

835.8100 Volatility - 

Field 

45703702 

45703704 

47131601 

47314301 

47732801 

48552102 

48552101 

47956901 

45703708 

45703701 

46969601 

46379201 

47820001 

47813901 

48011601 

48005901 

48115101 

47956701 

48467601 

Acceptable 

Acceptable 

Acceptable 

Acceptable 

Supplemental 

Supplemental 

Supplemental 

Supplemental 

Supplemental 

Supplemental 

Supplemental 

Supplemental 

Supplemental 

Pending 

Pending 

Pending 

Pending 

Pending 

Pending 

No -- 
Page 42 of 79 

OCSPP 

Guideline 

Data 

Requirement 

Submitted 

Studies 

(MRID) 

Study 

Classifications

Are data 

needed to 

conduct risk 

assessment?

Current Additional Data Need 

860.6100 

Analytical 

method in air 

(None) (Not 

applicable) 

Yes Environmental chemistry methods 

(ECMs) and independent laboratory 

validation (ILVs) are needed to support 

all methods used in each MITC field 

volatility study. 

835.6200 

850.6100 

Aquatic field 

dissipation 

(None) (Not 

applicable) 

No - 

Analytical 

method in water 

(None) (Not 

applicable) 

Yes Although MITC is volatile in water, an 

ILV/ECM in water is needed because of 

MITC’s high acute aquatic toxicity and 

its potential to reach surface water.

 850.1730 Fish 

bioconcentration 

(None) (Not 

applicable) 

No -- 

1. For studies with finalized classification pending, cursory review found studies adequate for risk 

assessments. Finalized review with formal DER pending. 2. With the exception of field volatility studies, all studies were conducted with MITC as the test substance 

and provided information on the environmental degradation of MITC in the environment. 3. Field volatility studies were conducted with either metam sodium or metam potassium as the test 

substance (see Table 5 for further details). MITC flux is measured in all field volatility studies. 4 The aerobic aquatic laboratory study for MITC is being requested to address both conventional and 

antimicrobial uses of metam sodium and metam potassium. 

835.4300: Aerobic Aquatic Metabolism: MITC 

An aerobic aquatic metabolism study with MITC as the test substance is being requested 

at this time. This study will enable the determination of MITCs residence time in water 

to address the potential of MITC to reach water sheds and water bodies adjacent to fields 

treated with metam sodium and metam potassium. The DT50 and residence time from 

this study will be used quantitatively in PRZM/EXAMS surface water acute EEC 

calculations. Since volatilization is expected to be the dominate loss route and that 

sorption to sediment is expected to be minimal, this study should only address measuring 

MITC concentrations in water and in the headspace. However, known degradates should 

be quantified to recover and track the complete material balance over the course of the 

study.

850.6100: Environmental Chemistry Methods (ECMs)/Independent Laboratory 

Validation (ILVs) in Air and Water: MITC

There are no ECMs or ILVs available for any of the MITC field volatility studies. 

Therefore, ECMs and ILVs for air should be submitted to support the field volatility 

studies. In addition, although MITC is volatile, an ECM and ILV is being requested for 

water since it is highly toxic on an acute basis and it may reach water bodies at a very 
Page 43 of 79 

large initial level. The ECM and ILV in water will help validate the aerobic aquatic 

study that is also being requested for MITC. 

9.2 Effects 

Table 13 and Table 14 identify ecological effects studies by MRID that offer data for 

each guideline requirement, as well as study classifications and whether or not further 

data are needed in order to support risk assessment. Rationale for the additional data 

requested is presented below the tables. 

The adequacy of the current toxicity data submitted to assess MITC will largely depend 

on the review of recently submitted data that were submitted in response to a RED data 

call-in (DCI). These studies are listed as ‘in review’ in the following tables. If these 

studies are found to be adequate for use in risk assessment, EFED recommends 

requesting the following studies to assess the environmental risks associated with the use 

of MITC: a honey bee vapor exposure study with MITC and a terrestrial plant seedling 

emergence study with MITC. The justifications for recommending the request of these 

studies are provided below. 

Table 13. Submitted and requested aquatic ecological effects data for MITC.

OCSPP 

Guideline 

Data 

Requirement 

Submitted 

Studies 

(MRID) 

Study 

Classifications 

Are data 

needed to 

conduct 

risk 

assessment? 

Current Additional Data Need 

850.1010 

Freshwater 

invertebrate 

acute toxicity 

41819302 Acceptable 

No -- 

45919419 Supplemental 

850.1025 

850.1035 

850.1045 

850.1055 

Saltwater 

invertebrate 

acute toxicity 

48985201 In review 

Yes

Depending on the results of the 

review of the recently submitted 

study. 48649301 In review 

850.1075 

Freshwater 

fish acute 

toxicity 

44523412 Acceptable 

44523413 Acceptable No -- 

45919420 Supplemental 

850.1075 Saltwater fish 

acute toxicity 48731101 In review Yes

Depending on the results of the 

review of the recently submitted 

study. 

850.1300 

Freshwater 

invertebrate 

life cycle 

45634001 Supplemental No -- 
Page 44 of 79 

OCSPP 

Guideline 

Data 

Requirement 

Submitted 

Studies 

(MRID) 

Study 

Classifications 

Are data 

needed to 

conduct 

risk 

assessment? 

Current Additional Data Need 

850.1350 

Saltwater 

invertebrates 

life cycle 

(None) (N/A) No 

850.1400 

Freshwater 

fish 

early-life 

stage 

(None) (N/A) No 

MITC shown to dissipate 

rapidly from the water column. 

See Section 7.

850.1400 

Saltwater fish 

early-life 

stage 

(None) (N/A) No -- 

850.1500 Fish life 

cycle (None) (N/A) No -- 

850.4400 

Aquatic plant 

growth: 

Tier II 

vascular 

plants 

45919421 Acceptable No -- 

850.5400 

Aquatic Plant 

Growth: 

Tier II algae 

44588903 Supplemental 

Yes

Depending on the results of the 

review of the recently submitted 

study. 

45919416 Supplemental 

45919422 Supplemental 

48733401 In review 

48733501 In review 

48733601 In review 

48733701 In review 

N/A = Not applicable 

Table 14. Submitted and requested terrestrial ecological effects data for MITC.

OCSPP 

Guideline 

Data 

Requirement 

Submitted 

Studies 

(MRID) 

Study 

Classifications 

Are data 

needed for 

risk 

assessment? 

Current Additional Data 

Need 

850.2100 Avian oral 

toxicity (None) (N/A) No 

Nonguideline 

Avian 

inhalation 

toxicity 

48788401 In review Yes

Depending on the results 

of the review of the 

recently submitted study.

850.2200 Avian dietary 

toxicity (None) (N/A) No -- 

850.2300 Avian 

reproduction (None) (N/A) No -- 
Page 45 of 79 

OCSPP 

Guideline 

Data 

Requirement 

Submitted 

Studies 

(MRID) 

Study 

Classifications 

Are data 

needed for 

risk 

assessment? 

Current Additional Data 

Need 

850.3020 

Honey bee 

acute contact 

toxicity 

00018842 Acceptable No -- 

850.3030 

Honey bee 

residue on 

foliage 

(None) (N/A) No -- 

Nonguideline 

Acute honey 

bee vapor 

exposure study 

(None) (N/A) Yes 

This study is needed to 

quantitatively determine 

risk to terrestrial 

invertebrates. 

850.3040 Field testing 

for pollinators (None) (N/A) No -- 

850.4100 

Terrestrial 

plant toxicity: 

Tier II seedling 

emergence 

41280801 (N/A) Yes

The requirement was 

previously waived (see 

USEPA 2012, D395875); 

however, upon further 

evaluation, it was 

determined that exposure 

to MITC via runoff is a 

potential risk concern. 

850.4150 

Terrestrial 

plant toxicity: 

Tier II 

vegetative 

vigor 

49058001 In Review Yes 

Depending on the results 

of the review of the 

recently submitted study. 

N/A = Not applicable 

Non-Guideline Study: Acute honey bee vapor exposure study with MITC

As discussed further in this assessment, inhalation exposure is determined to be the 

primary route of exposure for the terrestrial risk assessment. Inhalation studies are 

available for mammals (MRID 41277004) and birds (MRID 48788401) and given the 

volatile nature of MITC, inhalation risk would also be applicable to terrestrial 

invertebrates using the honey bee as a surrogate. A protocol should be submitted to the 

Agency for review prior to conducting the study. See the justification table below for 

more information. 

850.4100: Tier I/II Seedling Emergence Study: MITC

Section 7 of this assessment details the exposure pathways for MITC. Included in these 

pathways is one of soil exposure to plant seedlings on and off the treated field. The broad 

spectrum mode of action of MITC, the large application rates of metam sodium and 

metam potassium, and mobile and diffuse nature of the MITC as a vapor in soil justify 
Page 46 of 79 

this exposure pathway. The guideline study method will adequately capture the effects 

occurring from MITC movement off-site resulting either from runoff in the dissolved 

phase or diffusion in the gas phase. 

Guideline Number:  N/A  (Non‐Guideline Study)

Study Title:  Acute Honey Bee Vapor Exposure Study

Rationale for Requiring the Data

Due to the fate properties of fumigants, in particular their high volatility, it is expected

that honey bees and other insect pollinators will be exposed to fumigants in the vapor

phase.  Neither of the standard Tier I toxicity studies with honey bees (i.e., acute contact

or acute oral toxicity study for honey bees) account for exposure to vapor phase

pesticides. Therefore, to assess risks of MITC to bees, EFED recommends that the

Agency require a non‐guideline acute honey bee vapor exposure study for MITC, to be

conducted in lieu of the normally required acute honey bee contact study that would

fulfill guideline 850.3020 and the newly proposed requirements for oral toxicity tests

including adult and larval honey bees.   

Practical Utility of the Data

How will the data be used?

Data from an acute honey bee vapor exposure study will be used to determine the

potential for MITC to affect non‐target terrestrial invertebrates in the terrestrial

environment. Of particular interest is quantification of a toxicity endpoint, i.e., a 4‐hour

LC50, that can be used to derive risk quotients. In the absence of vapor exposure data

specific for honey bees, risk to terrestrial invertebrates, including listed species, will be

assumed.

How could the data impact the Agency’s future decision‐making?

If future ecological risk assessments are performed without these data, the Agency

would have to presume risk to non‐target terrestrial invertebrates, including honey

bees, from use of MITC. Therefore, use of MITC and its formulated products may need

to be restricted in areas where terrestrial invertebrates, including honey bees, could be

exposed. The lack of these data will limit the flexibility the Agency and registrants have

in mitigating potential risks and could result in use restrictions for MITC that are

unnecessarily severe.
Page 47 of 79 

9. References 

Alvarez, R. and C.B. Moore. 1994. Quantum yield for production of CH3NC in the 

photolysis of CH3NCS. Science263: 205-207. 

ARB, 1997. Ambient air monitoring for MIC and MITC after a soil injection application 

of metam sodium in Kern County during August 1995. Test Report No. C94-046, May 

20, 1997. Air Resources Board, Sacramento, CA. 

ARB, 1999. Lompoc pesticide monitoring program-phase I; System evaluation report of 

Trace Analytical Laboratory, University of California, Davis; Center for Environmental 

Sciences and Engineering, University of Nevada, Reno; and Inorganics Laboratory 

Section, Air Resources Board. March 3, 1999. Monitoring and Laboratory Division, 

Quality Assurance Section, Air Resources Board, Sacramento, CA. 

Ashley, M.G., B.L. Leigh, and L.S. Llyod. 1963. The action of metam sodium in soil. II. 

Factors affecting removal of methyl isothiocyanate residues. J. Sci. Food Agric. 14: 153-

161. 

Boesten, J.J.T.I., L.J.T. Van Der Pas, J.H. Smelt, and M. Leistra. 1991. Transformation 

rate of methyl isothiocyanate and 1,3-dichloropropane in water-saturated sandy subsoils. 

Netherlands Jour. of Agric. Sci. 30: 170-190. 

CDPR (California Dept. of Pesticide Regulation). 2002. Evaluation of Methyl 

Isothiocyanate as a Toxic Air Contaminant, Part A-Environmental Fate. California 

Environmental Protection Agency, Sacramento, CA. 

Cremlyn, R.J. 1991. Agrochemicals: Preparation and Mode of Action. p. 283-307. John 

Wiley and Sons. New York, NY. 

Dungan, R.S. and S.R. Yates. Degradation of fumigant Pesticides. 2003. 1,3-

Dichloropropane, methyl isothiocyanate, and methyl bromide. Vodose Zone Jour. 2: 279-

286. 

Geddes, J.D., G.C. Miller, and G. E. Taylor Jr. 1995. Gas phase photolysis of methyl 

isothiocyanate. Environ. Sci. Technol. 29:2590-2594. 

Gerstl, Z., U. Mingelgrin, B. Yaron. 1977. Behavior of Vapam and Methylisothiocyanate 

in soils. Soil Sci. Soc. Am. J. 41: 545-548. 

Martyn, P. 2004. 7/27/04 Letter to Metam-Sodium Docket. County Sanitation Districts 

of Los Angeles County. 
Page 48 of 79 

Segawa, R.T., S.J. Marade, N.K. Miller, and P.Y. Lee. 1991. Monitoring of the Cantara 

metam-sodium spill. Environmental Hazards Assessment Program, Report Number EH 

91-09. Department of Pesticide Regulation. Sacramento, CA. 

 

Seiber, J.N., J.E. Woodrow, R.I. Krieger, and T. Dinoff. 1999. Determination of ambient 

MITC residues in indoor and outdoor air in townships near fields treated with metam 

sodium. June 1999. Amvec Chemical Corporation, Newport Beach, CA. 

Smelt, J.H., S.J.H. Crum, and W. Teinissen. 1989. Accelerated transformation of the 

fumigant methyl isocyanate in soil after repeated application of metam sodium. J. 

Environ. Sci. Health B24: 437-455. 

Tomlin, C.D.S. (ed.) 1997. The Pesticide Manual. Eleventh Ed. P 335-339. British Crop 

Protection Council, Surrey, GU9 7PH, UK 

U.S. EPA, 2005. Overview of the use and usage of soil fumigants. Biological and 

Economic Analysis Division. Office of Pesticide Programs. Washington, D.C. 

U.S. EPA. 2009. Amended Reregistration Eligibility Decision (RED) for the 

Methyldithiocarbamate Salts (Metam sodium, Metam-potassium) and Methyl 

Isothiocyanate (MITC). Office of Pesticide Programs. Washington, D.C. 

USEPA, 2012. Screening Level Estimates of Agricultural Uses of Metam Sodium. 

Office of Pesticide Programs. Washington, D.C. 

Warton, B. and J.N. Matthiessen. 2000. Enhanced biodegradation of metham sodium soil 

fumigant in Australia. Proc. BCPC Conf.-Pest and Diseases 4C-4:377-380. 

Wofford, P.L., K.P. Bennett, J. Hernandez, and P. Lee. 1994. Air monitoring for Methyl 

isothiocyanate driung a sprinkler application of metam sodium. Report No. EH 94-02, 

Environmental Hazards Assessment Program, Dept. of Pesticide Regulation, Sacramento, 

CA. 
Page 49 of 79 

Appendix A - California Department of Pesticide Regulation 

Report on Train Derailment and Metam Sodium Release to 

Sacramento River and MITC Dissipation Analysis
SlAlE OF CALIkORNIA . ENVIRONMENTAL PHOTECTION AGENCY PETE WILSON, Governor 

DEPARTMENT OF PESTICIDE REGULATION 

EXECUTIVE SUMMARY 

Of Report EH-91-8 Entitled 

"Monitoring of the Cantara Metam-Sodium Spill" 

Environmental Monitoring and Pest Management Branch 

Department of Pesticide Regulation 

On July 14, 1991, a railroad car derailed north of Dunsmuir, 

California, releasing 49,000 to 72,000 liters (13,000-19,000 

gallons) of metam-sodium into the Sacramento River. Metam-sodium is 

the active ingredient in 18 pesticide products registered in 

California. Metam-sodium is a soil fumigant effective against 

weeds, soil diseases, nematodes and insects. The product that was 

spilled is 32.7% metam-sodium in an inert ingredient that is not of 

toxicological concern. The principal breakdown product, methyl isothiocyanate (MITC), causes most of the pesticidal activity. Breakdown to MITC in normal use situations occurs very rapidly, 

within a few hours. 

Since the release of metam-sodium into the Sacramento River was 

caused by an accident during transport and not by its use as a 

pesticide, the Department of Pesticide Regulation of the California 

Environmental Protection Agency does not have regulatory oversight. 

However, because of the Department's experience in monitoring the 

environment for pesticide residues, Department personnel from the 

Environmental Monitoring :and Pest Management Branch were asked to 

assist other state and federal agencies in documenting the changes 

in concentrations of MITC in the waters of Shasta Lake at two 

sampling sites from July 16 through July 23, 1991. 

Studv: 

Water samples were collected at two sites in Shasta Lake twice 

daily, in the morning and evening, for eight days. After this, 

other agencies continued monitoring at these sites. The 

northernmost site was a boat launching area at Antlers Campground 

located on the Sacramento River inlet to Shasta Lake, 62 kilometers 

(39 miles) downstream of the spill. The other was located at the 

Centimudi Boat Ramp approximately 800 meters (875 yards) northeast 

of Shasta Dam, 87 kilometers (54 miles) downstream of the spill, and 

24 kilometers (15 miles) south of the sampling site at Antlers 

Campground. 

Samples were analyzed for MITC by two laboratories: Chemistry 

Laboratory Services of the California Department of Food and 

Agriculture, and a private laboratory, the Agricultural and Priority 

Pollutants Laboratory (APPL), Inc. In normal use, metam-sodium 

would not be expected to enter surface water: therefore, neither 

laboratory was experienced in analyzing for either metam-sodium or 

its breakdown product, MITC. This meant that special care had to be 

taken in collecting samples and in conducting the analyses. 
Metam-Sodium Long term 0.02 milligramdliter (mg/L) = 20 ppb 

Short term 0.35 mg/L = 350 ppb 

MITC Long term 0.05 mg/L = 50 ppb 

Short term 1.0 mg/L = 1000 ppb 

Levels of MITC in the lake exceeded the short-term action level for 

one day and the long-term action level for three days during the 

eight-day sampling period. However, water from the Sacramento River 

from the point where the. spill occurred to the area above Centimudi 

Boat,Ramp in Shasta Lake is not used for drinking. In addition, 

fishing (eating fish would be another source of exposure) was not 

allowed in Shasta Lake from July 22 to August 5, 1991. 

Ronald J, Oshima 

Branch Chief 

-2- 

October, 1991 
MONITORING OF THE CANTARA METAM-SODIUM SPILL 

BY 

R .T. Segawa' , S. J. Maradel, N.K. Miller' and P .Y. Lee2 

September 1991 

' California Department of Pesticide Regulation, 

Environmental Hazards Assessment Program 

California Department of Food and Agriculture, 

Chemistry Laboratory Services 
ABSTRACT 

On July 14, 1991 a railroad car derailed at the Cantara Loop, north of 

Dunsmuir, California and spilled between 49,000 and 72,000 liters of a 

product containing the pesticide metam-sodium (19,000 - 27,000 kg active 

ingredient) into the Sacramento River. This spill posed a threat to 

public health and the environment. Therefore, monitoring was conducted by 

several agencies including the California Department of Pesticide 

Regulation (CDPR). Most of the pesticidal activity of metam-sodium is 

produced by its primary breakdown product methyl isothiocyanate (MITC). 

In cooperation with the California Department of Fish and Game, the 

Environmental Hazards Assessment Program of CDPR collected surface water 

samples to help characterize the temporal distribution of MITC residues in 

Shasta Lake, downstream of the spill. MITC water concentrations were 

monitored at Antlers Campground (62 km downstream of spill) and the 

Centimudi boat ramp (87 km downstream of spill) between July 16 and 23, 

1991. 

MITC concentrations at the north end (closest to the spill) of Shasta Lake 

at Antlers Campground reached a maximum of 5500 ppb three days after the 

spill. MITC levels decreased to 8 ppb six days later, No MITC was 

detected at the Centimudi Boat Ramp located at the southern end of Shasta 

Lake (detection limit 5 ppb). 

This monitoring alone is not enough to assess the movement, dissipation 

and possible effects of the metam-sodium spill. When the data from all 

monitoring groups are available, such an assessment will be possible. 

i 
ACKNOWLEDGEMENTS 

The authors wish to thank the hard-working members of the Environmental 

Hazards Assessment Program's field group and the the California Department 

of Food and Agriculture Chemistry Lab's environmental monitoring section. 

Thanks also to Linda Heath for preparing the graphics and to the owners of 

the Antlers Campground. 

DISCLAIMER 

The mention of commercial products, their source or use in connection with 

material reported herein is not to be construed as an actual or implied 

endorsement of those products. 

ii 
TABLE OF CONTENTS 

Page 

ABSTRACT .............................................................. i 

ACKNOWLEGEMENTS. ..................................................... ii 

DISCLAIMER ........................................................... ii 

TABLE OF CONTENTS.. ................................................. iii 

LIST OF FIGURES ..................................................... iii 

LIST OF TABLES ...................................................... iii 

INTRODUCTION .......................................................... 1 

MATERIALS AND METHODS .................................................3 

RESULTS AND DISCUSSION .................................,.,............5 

MONITORING BY OTHER AGENCIES ......................................,,..g 

Appendix 1 - Environmental Fate of Metam-Sodium 

Appendix 2 - Chemical Analysis Methods 

Appendix 3 - Quality Control Data 

LIST OF FIGURES 

Figure 1. Location of metam-sodium spill and downstream areas ........ 2 

Figure 2. MITC at Antlers Campground ................................. 8 

LIST OF TABLES 

Table 1. Results of the Cantara metam-sodium spill water monitoring 

at Antlers Campground, Shasta Lake .......................... 6 

Table 2. Results of the Cantara metam-sodium spill water monitoring 

at the Centimudi Boat Ramp, Shasta Lake ..................... 7 

iii 
INTRODUCTION 

On July 14, 1991 a Southern Pacific railroad car carrying Alco Metam 

Sodium"' derailed at the Cantara Loop, north of Dunsmuir, California and 

spilled between 49,000 and 72,000 liters (13,000 - 19,000 gal) of the 

product into the Sacramento River. The spilled material degraded to 

several toxic and volatile chemicals which could pose a threat to public 

health and the environment. Of particular concern were the people living 

in small communities adjacent to this part of the river, the aquatic organisms in the river, and Shasta Lake, downstream ofthe spill which is a 

major recreation area and drinking water reservoir. For these and other 

reasons monitoring was conducted by several agencies, including the 

California Department of Pesticide Regulation (CDPR). 

Alco Metam Sodium", formulated by the Amvac Chemical Corporation, contains 

32.7% metam-sodium (by weight) as the active ingredient. Assuming 49,000 

- 72,000 L of the product were released into the river, 19,000 - 27,000 kg 

(42,000 - 60,000 lbs) of active ingredient would have been spilled into 

the river. This chemical is used agriculturally as a fungicide, herbicide, insecticide, nematicide and soil fumigant. Most of its pesticidal 

action is produced by its primary breakdown product, methyl isothiocyanate 

(MITC). Breakdown to MITC normally occurs very rapidly, within a few 

hours. Other chemicals are also produced from the breakdown of rnetarnsodium, including hydrogen sulfide, carbon disulfide, and methylamine. 

See Appendix 1 for references and more details about the environmental 

fate of metam-sodium. 

Monitoring by the CDPR was conducted by the Environmental Hazards 

Assessment Program (EHAP) in cooperation with the California Department of 

Fish and Game, Water was sampled over time at two locations on Shasta 

Lake (Figure 1). The purpose of the monitoring by the EHAP was to characterize the temporal distribution of MITC in Shasta Lake. 

1 
Figure 1. Location of metam-sodium spill and downstream areas 

2 
MATERIALS AND METHODS 

Sample Collection 

Water samples were collected from two sites in Shasta Lake (Figure 1) 

twice daily. Site 1 was a boat launching area at Antlers Campground located on the Sacramento River inlet to Shasta Lake, 62 km (39 mi, by 

river) downstream of the spill site. It is a narrow channel at the north 

end of the lake which expands into a wide bend to the south. Site 2 was 

located at the Centimudi boat ramp which is located approximately 800 m 

northeast of Shasta Dam, 87 km (54 mi, by river) downstream of the spill 

site. Sampling was initiated on July 16, 1991 at 9:05 in the morning. 

Samples continued to be collected twice a day, once in the morning and 

once in the evening. The last set of samples was collected the morning of 

July 23. 

One-liter amber glass bottles and 40 mL glass vials were submerged approximately two meters from the lake edge and 50 cm below the water 

surface to collect the samples. The containers were filled to capacity 

and then capped under water with teflon-lined lids. This procedure 

reduced the possibility of trapping air inside the containers. Containers 

were checked to determine if air was trapped inside by inverting the 

sample. Each sample was accompanied by a chain of custody which documented its history. The pH and water temperature of each sample were also 

measured. 

The samples were placed on wet ice (4°C) immediately after sample collection. Samples were kept under refrigeration during transport until 

delivery to the CDPR West Sacramento facility. Samples were checked in at 

the West Sacramento facility and then delivered to the laboratory for 

analysis. 

3 
Chemical Analysis and Quality Control 

Samples were analyzed for MITC by two laboratories, the California 

Department of Food and Agriculture, Chemistry Laboratory Services Branch 

(CDFA) and the Agricultural and Priority Pollutants Laboratory, Inc. 

(APPL). The primary method, by CDFA, consisted of direct sample injection 

into a high pressure liquid chromatograph with a post-column reactor and a 

fluorescence detector. Samples that were positive using this method were 

confirmed by the CDFA laboratory by extracting the water samples with a 

minimum amount of carbon disulfide and injecting the extract into a gas 

chromatograph equipped with a nitrogen-phosphorous detector. APPL confirmed all samples using a purge and trap apparatus equipped with 

photoionization and flame ionization detectors. Details of the MITC 

analytical methods are given in Appendix 2. 

Analysis for other chemicals was attempted. The CDFA laboratory analyzed 

for a combination of metam-sodium and carbon disulfide. Their method incorporated a step to convert metam-sodium to carbon disulfide and 

analyzing for total carbon disulfide. No distinction was made between 

true carbon disulfide present in the sample and carbon disulfide that was 

present as the result of metam-sodium conversion. 

Several measures were taken to insure valid results were obtained. To 

protect against sample tampering, each bottle wasaccompanied with a chain 

of custody form which was signed by every individual who handled the 

sample. Laboratory results and field notes were also written on the chain 

of custody forms. To check for sample contamination, blank samples were 

created in the field and in the laboratory. Field blanks were created by 

pouring distilled water into sample bottles at the same time and place as 

the actual samples. Additional blanks were created in the laboratory. 

For a qualitative check, all positive samples were confirmed using the 

solvent extraction method described above; this method was not used to 

quantitate. To check for quantitation, spiked samples (known amount of 

MITC added to a sample) were submitted to the laboratory disguised as real 

4 
samples. In addition, the purge and trap method described above was used 

to quantitate concentrations. To check for possible dissipation during 

storage, a storage stability test was conducted. This test consisted of 

storing a set of spiked samples under the same conditions as real samples 

and analyzing them over a period of six days. 

RESULTS AND DISCUSSION 

Results of the water monitoring are shown in Tables 1 and 2 and Figure 2. 

The highest MITC concentration, 5500 ppb, was detected at the Antlers 

Campground site on July 17. Concentrations declined from the peak, to 8 

ppb six days later. No MITC was detected in any sample collected from the 

Centimudi site (detection limit 5 ppb). These results agree with preliminary results obtained by other agencies. 

Results of the quality control analyses were good. None of the blank 

samples were positive and there was good agreement between laboratories. 

Recoveries of the two blind spike samples were both 100%. The storage 

stability test indicated that no dissipation occurred during the time between sampling and analysis. The quality control raw data are shown in 

Appendix 3. 

Thirteen samples that were positive for MITC were also analyzed for metamsodium/carbon disulfide, as described earlier. Only one which 

corresponded to the sample that contained 5500 ppb of MITC was able to be 

quantified at 1240 ppb of carbon disulfide. If all of the carbon disulfide detected was converted metam-sodium, then the original metam-sodium 

concentration would have been 2100 ppb (adjusted for stoichiometric change 

in molecular weight). The CDFA laboratory also attempted to analyze for 

hydrogen sulfide, but could not develop an adequate method. 

This monitoring alone is not enough to assess the movement, dissipation 

and possible effects of the metam-sodium spill. When the data from all 

monitoring groups are available, such an assessment will be possible. 
Table 1. Results of the Cantara metam-sodium spill water monitoring at 

Antlers Campground, Shasta Lake. 

Methyl Isothiocyanate (ppb) Temperature 

Date T ime CDFA APPL pH ("C) 

7/16/91 0905 None Detecteda 7.2 21.1 

1830 None Detected 7.6 21.8 

7/17/91 0825 5500 5800 7.8 19.8 

1805 1580 1600 7.9 25.4 

7/18/91 0850 454 474 7.2 20.3 

1815 242 170 7.4 25.4 

7/ 1919 1 0645 134 broken 7.4 21.2 

1830 85 70 7.4 25.6 

7/20/9 1 0700 61 54 7.4 21.6 

1800 44 36 7.9 25.4 

7/21/91 0645 35 27 7.5 21.7 

1740 22 20 7.6 26.4 

7/22/51 1 0700 20 

1830 12 

16 7.5 22.3 

12 7.6 26.1 

7/23/9 1 0730 8.0 8.3 7.4 22.1 

a - CDFA detection limit = 5.0 ppb, APPL detection limit = 2.0 ppb 

6 
Table 2. Results of the Cantara metam-sodium spill water monitoring at 

the Centimudi Boat Ramp, Shasta Lake. 

Methyl Isothiocyanate (ppb) Temperature 

Date Time CDFA APPL pH ("C) 

7/16/91 1010 None Detecteda 7.6 25.7 

1925 None Detected 7.8 25.8 

71 1719 1 0945 None Detectedb 8.0 25.6 

1920 None Detected 8.2 28.0 

7/ 18/9 1 1010 None Detected 7.9 26.3 

1945 None Detected 7.8 27.7 

71 1919 1 0830 None Detected 7.6 26.4 

1945 None Detected 7.8 26.5 

b 

7/20/9 1 0815 None Detected 7.8 25.8 

1915 None Detected 7.6 25.9 

7/21/91 0800 None Detected 7.4 25.3 

1840 None Detected 7.8 28.9 

7/22/9 1 0800 None Detected 7.9 26.9 

a - CDFA detection limit = 5.0 ppb, APPL detection limit = 2.0 ppb 

b - APPL sample broken, no analysis 

7 
z 

 

-i 

0 

n 

TI 

TI 

u 

Y 
MONITORING BY OTHER AGENCIES 

The CDPR monitoring program was very minimal, Extensive monitoring has 

been and continues to be conducted by other agencies, particularly by the 

Regional Water Quality Control Board. In addition, the Cal EPA Office of 

Environmental Health Hazard Assessment is acting as a central repository 

for all monitoring data. Listed below are the agencies conducting 

monitoring; the list may not be complete. 

U.S. Bureau of Reclamation: water monitoring 

Cal EPA - Regional Water Quality Control Board, Central Valley Region: 

water, soil, and sediment monitoring 

Cal EPA - Air Resources Board: air monitoring 

Cal EPA - State Water Resources Control Board: air monitoring 

Cal EPA - Department of Toxic Substances Control: water, soil, and sediment monitoring 

California Department of Fish and Game: water, sediment, and biota 

monitoring 

California Occupational Safety and Health: air monitoring 

California Department of Health Services: water monitoring 

Shasta County Department of Environmental Health: groundwater monitoring 

(public and private drinking water wells) 

Southern Pacific - Terra and OHM (under contract): water, air, soil, and 

sediment monitoring 

In addition, the California Department of Fish and Game is conducting 

biological surveys for impacts to fish, wildlife and vegetation. 

9 
Appendix 1 - Environmental Fate of Metam-Sodium 
Degradation Pathways for Metam-Sodium 

n 

CH,NHC Na+ 43 

\n 

3- 

Metam-Sodium 

(MW 129.1 7) 

s=c=s 

Carbon Disulfide 

(MW 76.1 3) 

+ 

_I____, CH,NH2 

Methylamine 

(MW 31.06) 

+ 

- CH,N=C=S 

Methyl Isothiocyanate 

(MW 73.11) 

+ 

- H2S 

Hydrogen Sulfide 

(MW 34.08) 

Molecular weight is shown in parentheses 

1-1 
State of California 

Memorandum 

TO : Don Weaver : November 20, 1990 

Sr. Environmental Research Scientist 

Environmental Hazards Assessment Program I Sacramento 

From : Department of Food and Agriculture Chris Collison, Assoc. Env. Research Scientist 

Environmental Hazards Assessment Program 

Subject: LITERATURE REVIEW OF THE ENVIRONMENTAL FATE OF METAM-SODIUM (VAPAMm) 

This review was based on data from the CDFA pesticide registration 

packages cited as Stauffer Chemical Company and IC1 Americas, Inc., 

and from open literature articles. 

Metam-sodium (sodium methyldithiocarbamate) is the active ingredient 

in Vapamo, a broad-spectrum soil fumigant produced by Stauffer 

Chemical Company. It is commonly applied as a preplant fumigant 

incorporated into the irrigation system. 

Metam-sodium degrades rapidly to methyl isothiocyanate (MITC) when ---, 

in contact with moist soil. Smelt and Lcistra (1974) found that the 

conversion of metarn-sodium to MITC (>go%) took only a few hours. In 

experiments using spiked moist soil in glass septum flasks incubated 

at 1Z0C, conversion was complete ino 3 hours in loamy soils and in G 

hours in a humic sandy soil. At 21 C in the sandy soil, a period of 

3-4 hours was sufficient for conversion to MITC. 

The decomposition rate of MITC in moist soil was also investigated 

(Smelt and Leistra, 1974). Depending on the soil type, half-lives 

for MITC were in the range of 8-14 days. The most rapid 

decomposition occurred in heavy, loamy soils at higher temperatures. 

Smelt et al. (1989) also investigated decomposition rates of MITC in 

"problem" soils (those demonstrating inadequate pest control by 

fumigation with metam-sodium). MITC in amounts ranging from 1.5 to 

2.0 mg (equivalent to'150 kg/ha) was added to glass flasks partially 

filled with moist soil and incubated in the dark at 15OC. A 

comparison of the decomposition patterns of MITC in previously 

treated and untreated soils showed that, in general, MITC degraded 

much faster in the previously treated soils. This suggested that 

repeated applications of metam-sodium induced microbial adaptation 

resulting in enhanced biotransformation of MITC. In this study, 

MITC half-lives ranged from 0.5 to 50 days. The study results also 

indicated that the decomposition rate of MITC greatly depends on the 

initial content of the fumigant. 

1-2 
Don Weaver 

November 20, 1990 

Page 2 

In two field studies conducted "under normal agricultural conditions" in Mississippi and California by IC1 Americas, Inc. 

(1989), MITC was found no deeper than 9 inches in soil and 

undetected at any depth 13 days after application. Vapam was 

applied to bare fallow soil at a rate of 100 gallons of formulated 

material (32.7% AI) per acre by chemigation with an overhead 

sprinkler. The respective zero-time MITC residues were 18 and 42 

ppm in the upper 6 inches of soil in Mississippi and California. 

Half-lives were 13 and 26 hours in loam soil near Visalia, 

California and loam/silt-loam soil near Leland, Mississippi 

respectively. Four days post application, maximum residues of the 

degradation product 1,3-dimethylurea were from 0.13 to 0.51 ppm. ' 

Leaching experiments were performed by Stauffer Chemical Company 

(1985a) using 32-37 cm Aong glass and steel columns hand packed with 

soil. A radiolabeled C metam-sodium solution was used to spike 

the columns at concentrations equivalent to 1 quart/100 sq ft and, 

at the highest application rate recommended, 2 quarts/100 sq ft. 

Four soil types ranging from sand to loamy sand to sandy clay were 

tested. In each case, about 60% of the applied 14C leached from the 

columns after 48 mL of water were poured on the soil (equivalent to 

20 inches X thlT cross sectional area of the columns). About 90% of 

the leached C was iqtntified as MITC. Results indicated that the 

bulk of the soluble C leached out of the soil soon after the 

volume of water necessarX for soil saturation was added. Between 11 

and 14% of the applied C remained bound to the soil and 23 to 30% 

was assumed to have been lost as volatile degradation products, 

mainly MITC. 

Emissions of MITC from greenhouse soil were studied by Leistra and 

Crum, (199Oj. Concentrations of MITC in treated soil were measured 

and the data was used in.a computer model to simulate emissions from 

the soil. The experimental fumigation was conducted in a greenhouse 

with wetted, sandy soil cultivated to a depth of 0.25 m. Two 

hundred and forty liters of the trade product (510 g metam-sodium 

per liter), which corresponds to 1950 L/ha of the trade product, was 

applied with a small self-propelled shank injector to a depth of 

0.05-0.10 m. A 30 vm thick low density polyethene .film was used to 

completely cover the soil after application and was left on the soil 

surface for 7 days. Refore removal of the cover, the cumulative 

emission of MITC from the greenhouse soil was computed to be about 

45% of the applied dosage. At day 14, seven days after removal. of 

the cover, the total cumulative emission was 50% of the applied 

dosage. 

1-3 
Don Weaver 

November 20, 1990 

Page 3 

The highest rate of emission from the film-covered soil ocurred on 

the first day after application. Concentrations in greenhouse air 

were computed to be around 50 mg/m on the first day and exceeded 10 

mg/m during the first 4 days after injection. When the model was 

modified to exclude the factor of a film cover, the computed MITC 

emission rate one day after application was 2.5 times greater than 

the rate with a film cover. The cumulative emission after 14 days 

without a film cover was computed to be 648 sf the applied dosage. 

The vapor pressure of MITC is 2.7 kPa at 20 C (Hartly and Kidd, 

1983) . The emission model was further modified to simulate the homogeneous 

incorporation of metam-sodium into the soil to a depth of 0.24 m 

after a surface application. The results indicated a somewhat lower 

emission rate in the first 3-4 days. After about 4 days, the 

emission rate was similar to that for injection. At the end of the 

14 day period, the computed cumulative emission corresponded to 38% 

of the applied dosage. Without a film cover, the emission was 49% 

of the equivalent dosage. 

Half-lives for metam-sodium at 2OoC in dilute solutions at pH 5, 7, 

and 9 were 23, 180, and 46 hours respectively. The major products 

of hydrolytic degradation at pH 5 were methylamine, MITC, and carbon 

disulfide. Minor hydrolytic degradation products included elemental 

sulfur and 1,3-dimethylthiourea (Stauffer Chemical Company, 198513). 

The major products arising from pohotolysis of metam-sodium in 

aqueous solution (120 ppm) at 25 C and pH 7 were MITC, Nmethylthioformamide, methylamine, and elemental sulfur. Minor 

photolytic degradation products included N-methylformamide, carbon 

disulfide, carbon oxide sulfide, and hydrogen sulfide. Under these 

conditions, the half-life for metam-sodium was 1.6 hours (Stauffer 

Chemical Company, 1985b) 

References Cited 

Hartley, 0. and H. Kidd. 1983. The agrochemicals handbook. Royal 

Society of Chemistry. 

IC1 Americas Inc. 1989. RR2021: Two field dissipation studies for 

terrestrial USCS. CDFA Doc. 5015-025. 

Leistra, M. , and S.J.1-l. Crum. 1990. Emission of MITC to the air 

after application of metam-sodium to greenhouse soil. Water, Air 

and Soil Pollution 50:109-121. 

1-4 
Don Weaver 

November 20, 1990 

Page 4 

Smelt, J.HOI S.J.H. Crum and W. Teunissen. 1989. Accelerated 

transformation of the fumigant MITC in soil after repeated 

application of metham-sodium. J. Environ. Sci. Health B24(5) 

437-455 . Smelt, J.H. and M. Leistra. 1974. Conversion of metham-sodium to 

MITC and basic data on the behavior of MITC in soil. Pestic. 

Sci. 5:401-407. 

Stauffer Chemical Company. 1985a. Vapam soil mobility. CDFA Doc. 

50150-006. 

Stauffer Chemical Company. 1985b. Hydrolysis and photolysis of 

metam-sodium. CDFA Doc. 50150-006. 

cc: Ronald J. Oshima .. , , 

John Sanders 

Randy Segawa 

Kean Goh 

1-5 
Appendix 2 - Chemical Analysis Methods 
CALIFORNIA DEPT. OF FOOD & ACRIC. 

ENVIRONMENTAL MONITORING SECTION 

CHEMISTRY LABORATORY SERVICES 

3292 Meadowview Road 

Sacramento, CA 95832 

(916)+427-4408 

Original Date: July 17, 1991 

Supersedes: .New 

Current Date: August 14, 1991 

Method #: 17 

METHYL ISOTHIOCYMATE IN RIVER WATER BY HPIX: AND GC 

SCOPE: 

This method is for the determination of methyl isothiocyanate (MITC) in river 

water. Its sensitivity is 5 ppb. 

PRINCIPLE: 

HPLC method : 

The water samples are directly injected to HPLC, separated on A reverse phase 

octadecyl bonded column. The eluant: is derivatizod with OPA by post column 

reaction and detected with a fluorescence detector (Excltatlon-340 nm, Emission-450 nm). 

GC method: 

MITC in water is extracted with a minimum amount of carbon disulfide. The 

extracts are analyzed by GC with a nitrogen specific detector. 

REAGENTS AND EQUIPMENT: 

Distilled water, HPLC grade 

Acetonitrile, HPLC grade 

Carbon disulfide, residue grade 

Disposable filters 0.2 micron (Nylon Acrodisc). 

HPLC - Hewlett Packard HP 1090 Liquid Chromatoghaph controlled by HP 79994A 

Fluorescence Detector - Hewlett Packard HP 1046A 

Post Column derivatization system - Pickering Laboratory CRX 390 high 

HPLC ChemStationTH 

temperature reaction control device, 

two Milton Roy miniPumpsTH with 

pressure readout devices and an ambient 

temperature reaction coil. 

Reagent A, 0.2% NaOH/H 0 

Reagent B; Dissolve 0.5 gram of o-Phthalaldehyde in 10 mL of methanol, add 

1 mL 2-mercaptoethanol, then add 50 mL of pH 10.4 buffer (1 M of 

-Potassium borate), and dilute to 1 L with distilled water. 

ANALYSIS : 

PRIHARY ANALYSIS (HPLC) 

Sample Preparati.on: 

1. Filter the water sample, using a 10 mL hypodermic syringe, through a 0.2 

micron nylon Acrodisc filter into an autosampler vial. Seal the top with a 

crimp top cap. 

2- 1 

\ 
MITC in river water by HPLC and GC Page 2 

PRIWY ANALYSIS (HPLC) 

Sample Preparation: continued. 

2. The content of the autosampler vials is ready for HPLC analysis. . 

Instrument Conditions: 

Column: Beckman Ultrasphere ODS C-18, 5 micron 4.6 mm X 25 cm. 

Sample Loop: 250 microliter 

Sample injection: 250 microliter (same volume of standard and sample injected) 

Mobile Phase: Gradient 

Time (minutes) % Water % Acetonitrile 

0.0 YO 10 

1.0 90 10 

6.0 30 70 

10.0 30 70 

13.0 90 10 

Retention time of MITC: 9.624 min (SD=O.O18min, n-20) 

Flow: 1.0 ml/min 

Post Column System: 

Flow: Reagent A 0.2 ml/mfn 

Reagent B 0.2 ml/min 

Detector: Fluorescence Excitation - 340 nm Emission - 450 nm 

METHOD VALIDATION: 

This method for water analysis does not require solvent extraction. Samples 

are directly injected to the HPLC system. Thus, the method recovery is at 

about 100% level. The varfation in recoveries is mainly due to the performance 

of the instrument. 

Spike Level MITC SD Percent n 

PPb % Recovery Variation 

5 

20 

100 

500 

1000 

92.6 0.32 6.5 5 

105.2 0 .*74 3.7 5 

102.2 1.5 1.5 5 

97.5 4.0 0.8 5 

102.2 5.0 0.5 5 

\ 

2-2 
MITC in river water by HPLC and GC Page 3 

CONFIRMATION ANALYSIS (CC) 

Sample preparation: 

1. Remove sample from refrigerated storage. 

.2. Shake sample and weigh out 500 g by difference and transfer this aliquot 

to a 1 L separatory funnel. 

3. Extract sample by adding 10 mL of carbon disulfide and shake vigorously 

for 1 minute. 

4. Allow the layers to separate and drain the lower layer into a 25 mL test 

tube. 

5. Repeat the extraction one more time using 10 mL carbon disulfide. Combine 

the extracts. 

6. Add approximately 1 g sodium sulfate and shake to remove water. 

7. The extract is ready for CC analysis. 

Instrument conditionr: 

Varian 3700 GC with NPD 

Column: HP-FFAP (cross-linked polyethylene glycol-TPA modified) 10 m x 0.53 mm x 1.0 um 

Column temperature: 5O0C/1 minute, program at lO'C/mInute to 110°C 

Retention time: 2.60 min 

Injector temperature: 200'C 

Detector base temperature: 220°C 

DISCUSSION: 

MITC is very volatile, Rotary vacuum evaporation and open beaker evaporation 

yields no' recovery. Kuderna-Danish solvent evaporation which is very tedious 

can produce approximately 60% recovery. Thus, to avoid these problems we chose 

to use a minimum amount of solvent for extraction and not to concentrate the 

extract. The average recovery of this solvent extraction method is 60-70%. 

The HPLC method is superior to the GC iethod. It requires no solvent 

extraction, The recoveries are approximately 100%. 

2-3 
NX'X in river water by HPLC and GC Page 4 

REFERENCE: 

Lee, P, RPLC determination of Aldicarb, Afdfcarb sulfoxide, and Aldicarb sulfone 

in Groundwater, September 28, 1989, Environmental Monitoring Method, California 

Department of Food and Agriculture. 

MIlTEN BY: PAUL LEE 

REVIELED BY: Catherine Cooper 

APPROVED BY: Terry Jackson 1 

APPROVED BY: Mark Lee 

K 

T1TLE:Reseerch'Agricultural Chemist 

2-4 
WTC in water by Modified EPA Method 602 

Equipment: 

1) Gas chromatograph: HP Model 5890 

2) Detector: 01 Tandem PID/FID 

3) Column: 30m DB624 

Temperature program: 50*C for 3 minutes; 8'C/Min. to 200.C. 

Hold 0.25 min. Run time - 22 minutes RT MITC = 7.1 min. 

Trap: 1 cm 3kSP-2100, 23 cm Tenax. Supelco #2-0295M 

Purge Time: 11 min. at <30'C 

Desorb Time: 3 min. at 180'C 

Brake Time: 6 min. at 225.C 

4) Purge and Trap: Tekmar Model 4000 

5) Autosampler: Dynatech Precision Sampling .FTA3O-WS 

Procedure: 

Prepare a aalibration curve from a 1000 ppm MITC stock 

solution in methanol. A five point curve is run at 5, 10, 25, 

50 and 100 pg/L. Prepare spikes at 10-25 pg/L. 

Load autosampler with standards and samples in 40 ml VOA vials 

in the following order: Blank, calibration curve, spikes, 10 

samples, midpoint standard (25 pg/L), spikes, 10 samples, 

blank, midpoint standard, etc. 

Set the autosampler to purge 10 ml aliquots in the water mode 

using internal standard addition. The internal standard 

solution is 100 ppm of Volatiles Internal Standards Mix 502 

(Supelco) 

The Turbochrom 111 calculates spike and sample amounts off the 

calibration curve. Peak area and internal standard 

calculation is used. Linearity must be 2 0.997. A new 

calibration curve is run whenever the midpoint standard has a 

linearity below 0.997. Samples containing MITC > 100 pg/L are 

diluted and rerun. 

pg/L MITC in chromatography report times the dilution is pg/L 

MITC in sample. 

.. 

2-5 
Appendix 3 - Quality Control Data 
Comparison of CDFA and APPL Results 

MITC Water Concentrations 

1 10 100 1000 

CDFA (ppb) 

10000 

Line shows ideal slope of 1 
Table 3-1. Method validation data (% recoveries) for the Metam Sodium Study. 

Study: X56 

Analyte: MlTC 

MDL 5ppb 

Date of Report: 8/1/91 

Sample Type: Surface water 

Lab: CDFA 

Chemist: Paul Lee 

Method: GC/NPD 

Lab Sample Results Spike Level covery cv 

Y @pb) @p b) % X SD (%) 

134 3.81 5.0 76 

134 3.33 0 

134 3.33 5.0 67 70 5.2 7.4 

136 7.13 10.0 71 

136 7.56 .0 

136 7.56 0.0 

135 30.51 50.0 77 

135 41.84 50.0 a3 

135 43.95 50.0 87 82 5.0 6.1 

- 

OVERALL 76 6.7 8.8 

Table 3-11. Method validation data (% recoveries) for the Metam Sodium Study. 

Study: X56 

Analyte: MlTC 

MDL 5ppb 

Date of Report: 8/1/91 

Sample Type: Surface water 

Lab: CDFA 

Chemist: Paul Lee 

Method: HPLC/ post column/ fluorescence 

Lab Sample Results Spike Level covery cv 

# (ppb) @pb) % X SD (%) 

- 

390 4.4 5.0 80 

390 5.0 5.0 100 

390 5.0 5.0 100 

390 4.4 5.0 88 

390 4.5 5.0 90 93 6.3 6.7 

389 22 20 110 

389 21 20 105 

389 21 20 105 

389 20 20 100 

389 21 20 105 105 3.54 3.37 

388 100 100 100 

388 101 100 101 

388 104 100 104 

388 103 100 103 

388 102 100 102 1 02 1.58 1.55

387 493.3500 98.6 

387 485.6 500 97.1 

387 486.2500 97.2 

387 482.9500 96.6 

387 489.5500 97.9 97 0.8 0.8 

386 1028 lo00 102.8

386 1027 lo00 102.7 

386 1023 lo00 102.3

386 1015 lo00 101.5 

386 1020 lo00 102.0 102 0.53 0.52 

OVERALL 100 5.225.22 

3-2 
Table 3-111. Continuing quality control data for the Metam Sodium Study. 

Study: X56 

Analyte: MlTC 

MDL 5ppb 

Date of Report: 8/1/91 

Sample Type: Surface water 

Lab: CDFA 

Chemist: Paul Lee 

Method: GC/NPD 

Extraction Lab Results Spike 

- cv 

Set No:s x (ppb) (ppb) % X SD (%) 

31,43,49,55 305 - 15 20 75 

7 303 7.27 10 73 

OVERALL: 74 1.4 1.9 

Table 3-IV. Continuing quality control data for the Metam Sodium Study. 

Study: X56 

Analyte: MlTC 

MDL: 5ppb 

Date of Report: 0/1/91 

Sample Type: Surface water 

Lab: CDFA 

Chemist: Paul Lee 

Method: HPLC/ post column/ fluorescence 

Extraction Lab Results Spike Level Recovery cv 

Set No.'s x (ppb) (PPb) % X SD (%) 

- 

25 380 lo00 lo00 100 

1, 13 378 1012 lo00 101 

221,233,239,227,245,197, 377 98.3 100 98 

137,167,140,142,209,250, 375 100 100 100 

364,370,155,302,394,161, 

127 

251,376,413,407,501,455, 367 97.2 100 97 

308,479,482,504,450,391, 

381,256,410,412 

417,425,431,437,424,507, 373 99.3 100 99 

226,202,232,230 

430,436,442 

401,406,449,454,508 370 97.20 100 97 

OVERALL 99 1.6 1.6 

3-3 
Table 34. Storage dissipation data for the Metam Sodium Study (room temperature, pH 7.5). 

Study: X56 

Analyte: MlTC 

MDL: Sppb 

Date of Report: 0/1/91 

Sample Type: Surface water 

Lab: CDFA 

Chemist: Jean Hsu 

Method: GC/NPD 

Lab Sample Date Oat8 Results Spike Level Recovery - cv 

# Day Extracted Analyzed (ppb) (ppb) 96 X SD (%) 

202 0 7/19/91 7/19/91 156 200 78 

203 0 7/19/91 7/19/91 154 200 77 78 0.71 0.91 

21 1 1 7/20/91 7/20/91 159 200 79 

212 1 7/20/91 7/20/91 140 200 74 77 3.5 4.6 

220 2 7/21/91 7/21/91 152 200 76 

222 2 7/21/91 7/21/91 149 200 72 74 2.0 3.0 

230 3 7/22/91 7/22/91 156 200 76 

23 1 3 7/22/91 7/22/91 138* 200 69 73 4.9 6.8 

267 4 7/23/91 7/23/91 145 200 73 

276 5 7/24/91 7/24/91 131 200 66 

277 5 7/24/91 7/24/91 131 200 66 66 0.0 0.0 

260 4 7/23/91 7/23/91 152 200 76 75 2.1 2.0 

303 6 7/25/91 7/25/91 134 200 67 

304 6 7/25/91 7/25/91 120 200 64 66 2.1 3.2 

OVERALL 72 5.0 7.0 

Low recovery due to leak during extraction. 

Table %VI. Storage dissipation data for the Metam Sodium Study (refrigerated, pH 7.5). 

Study: X56 

Analyte: MlTC 

MDL: 5 ppb 

Date of Report: 0/1/91 

Sample Type: Surface water 

Lab: CDFA 

Chemist: Jean Hsu 

Method: GC/NPD 

Lab Sample Date Date  

Recovery cv 

# Day Extracted Analyzed @pb) (ppb) % X SD (%) 

204 0 7/19/91 7/19/91 151 200 76 

205 0 7/19/91 7/19/91 156 200 70 77 1.41 1.04 

- 

213 1 7/20/91 7/20/91 145 200 72 

214 1 7/20/91 7/20/91 146 200 73 73 0.7 1 0.96 

223 2 7/21/91 7/21/91 124* 200 62 

224 2 7/21/91 7/21/91 141 200 71 67 6.4 9.6 

233 3 7/22/91 7/22/91 156 200 76 76 0.0 0.0 

232 3 7/22/91 7/22/91 156 200 76 

269 4 7/23/91 7/23/91 141 200 71 

270 4 7/23/91 7/23/91 145 200 72 72 0.71 0.99 

279 5 7/24/91 7/24/91 140 200 74 73 1.4 1.9 

278 5 7/24/91 7/24/91 145 200 72 

305 6 7/25/91 7/25/91 124. 200 62 

306 6 7/25/91 7/25/91 152 200 76 69 9.9 14 

* Low recovery due to leak during extraction. 

OVERALL 72 4.9 6.7 

3-4 
Table 3-Vll. Storage dissipation data for the Metam Sodium Study (room temperature, pH 10). 

Study: X56 

Analyte: MlTC 

MDL: 5 ppb 

Date of Report: 8/1/91 

Sample Type: Surface water 

Lab: CDFA 

Chemist: Jean Hsu 

Method: GC/NPD 

Lab Sample Date Date  cv 

# Day Extracted Analyzed (ppb) (ppb) % X SD (%) 

- 

206 0 7/19/91 7/19/91 129 200 64 

207 0 7/19/91 7/19/91 120 200 60 62 3 5 

21 5 1 7/20/91 7/20/91 93 200 47 

216 1 7/20/91 7/20/91 90 200 45 46 1.4 3.1 

225 2 7/21/91 7/21/91 48 200 24 

226 2 7/21/91 7/21/91 50 200 25 25 0.71 2.9 

234 3 7/22/91 7/22/91 27.6 200 14 

235 3 7/22/91 7/22/91 27.6 200 14 14 0.0 0.0 

27 1 4 7/23/91 7/23/91 9.5 200 4.7 

272 4 7/23/91 7/23/91 9.0 200 4.5 5 0.1 3.1 

28 1 5 7/24/91 7/24/91 8 200 4.2 4 0.0 0.0 

280 5 7/24/91 7/24/91 8 200 4.2 

307 6 7/25/91 7/25/91 nd 200 0 

308 6 7/25/91 7/25/91 nd 200 0 0 0.0 0.0 

OVERALL 22 23 102 

Table 3-Vlll. Storage dissipation data for the Metam Sodium Study (refrigerated, pH 10). 

Study: X56 

Analyte: MlTC 

MDL 5ppb 

Date of Report: 8/1/91 

Sample Type: Surface water 

Lab: CDFA 

Chemist: Jean Hsu 

Method: GC/NPD 

Lab Sample Date Date cv 

# Day Extracted Analyzed @p b) (ppb) % X SD (%) 

208 0 7/19/91 7/19/91 133 200 67 

209 0 7/19/91 7/19/91 116 200 58 63 6.4 10 

- 

217 1 7120191 7/20/91 110 200 55 

218 1 7/20/91 7/20/91 114 200 57 56 1.4 2.5 

227 2 7/21/91 7/21/91 106 200 53 

228 2 7/21/91 7/21/91 106 200 53 53 0.0 0.0 

237 3 7/22/91 7/22/91 103 200 52 50 2.8 5.7 

273 4 7/23/91 7/23/91 89.7 200 45 

274 4 7/23/91 7/23/91 89.7 200 45 45 0.00 0.00 

282 5 7/24/91 7/24/91 90 200 45 

236 3 2/91 7/22/91 97 200 48 

283 5 7/24/91 7/24/91 93 200 47 46 1.4 3.1 

309 6 7/25/91 7/25/91 83 200 41 

310 6 7/25/91 7/25/91 79 200 40 41 0.71 1.7 

OVERALL 50 7.4 15 

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Page 51 of 79 

Figure A-1. Dissipation curve and analysis of MITC in Lake Shasta inlet (Antlers 

Campground) monitoring site 

 
Page 52 of 79 

Nonlinear Regression Friday, March 29, 2013, 12:36:49 PM 

Data Source: Data 1 in Notebook2 

Equation: Exponential Decay, Single, 2 Parameter 

f = a*exp(-b*x) 

R Rsqr Adj Rsqr Standard Error of Estimate 

0.9869 0.9739 0.9728 256.2562 

 Coefficient Std. Error t P 

a 5642.2748 181.1738 31.1429 <0.0001 

b 0.1848 0.0198 9.3232 <0.0001 

Analysis of Variance: 

 DF SS MS 

Regression 2 65463774.2748 32731887.1374 

Residual 23 1510346.6152 65667.2441 

Total 25 66974120.8900 2678964.8356 

Corrected for the mean of the observations: 

 DF SS MS F P 

Regression 1 56410535.7752 56410535.7752 859.0361 <0.0001 

Residual 23 1510346.6152 65667.2441 

Total 24 57920882.3904 2413370.0996 

Statistical Tests: 

Normality Test (Shapiro-Wilk) Failed (P = <0.0001) 

W Statistic= 0.7539 Significance Level = 0.0500 

Constant Variance Test Failed (P = <0.0001) 

Fit Equation Description: 

[Variables] 

x = col(1) 

y = col(2) 

reciprocal_y = 1/abs(y) 

reciprocal_ysquare = 1/y^2 

reciprocal_pred = 1/abs(f) 

reciprocal_predsqr = 1/f^2 

'Automatic Initial Parameter Estimate Functions 

F(q) = if(size(x)>1, if(total(abs(y))>0, ape(x,log(abs(y)),1,0,1), -306), 0) 

asign(q) = if(mean(q)>=0,1,-1) 

[Parameters] 

a = if(F(0)[1]< 307, if(F(0)[1]>-307, asign(y)*10^F(0)[1], asign(y)*10^(-307)), asign(y)*10^307) ''Auto {{previous: 5642.27}} {{MinRange: 

-3}} {{MaxRange: 9}} 

b = if(x50(x,y)-min(x)=0, 1, -ln(.5)/(x50(x,y)-min(x))) ''Auto {{previous: 0.184804}} {{MinRange: 0}} {{MaxRange: 1}} 

[Equation] 

f = a*exp(-b*x) 

fit f to y 

''fit f to y with weight reciprocal_y 

''fit f to y with weight reciprocal_ysquare 

''fit f to y with weight reciprocal_pred 

''fit f to y with weight reciprocal_predsqr 

[Constraints] 

b>0 

[Options] 

tolerance=0.0000000001 

stepsize=1 

iterations=200 
Page 53 of 79 

Appendix B – Evaluation of Toxic Degradates of Concern 
Page 54 of 79 

Structural activity relationship models such as ECOSAR are used to characterize 

major degradates and identify toxic degradates of concern by comparing degradate 

modeled toxicities to MITC, which is the stressor of concern in this risk assessment. 

ECOSAR, a utility under EPISuite 4, estimates the toxicity of chemicals discharged to 

water. ECOSAR predicts toxicity to fish, aquatic invertebrates and algae using an 

extensive set of structure-activity relationships (SARs). The program estimates a 

chemical's acute (short-term) toxicity and, when available, and chronic (long-term or 

delayed) toxicity (USEPA, 2010[2]). Table B-1 shows that ECOSAR estimated MITC 

toxicities are underpredicted with the exception of freshwater, which is slightly 

overpredicted. However, Table B-2 shows that the margins of the underprediction are 

generally surpassed by the margin that ECOSAR predicts higher toxicity for parent 

MITC as compared to all of the major degradates as shown in Table C-2. The only 

exception to this is DMU toxicity for green algae, which ECOSAR predicts is lower than 

the measured toxicity for MITC. However, inclusion of DMU as a degradate of concern 

based on green algae toxicity is not expected to significantly impact the existing risk 

determinations. The ECOSAR RUNS for MITC, methylamine, DMTU, DMU, and synmethylthioformamide/anti-methylformamide are shown in Figures B-1, B-2, B-3, B-4, 

and B-5, respectively. 

Table B-1. MITC measured versus ECOSAR predicted toxicity. 

Taxa Endpoint 

MITC Measured 

Toxicity 

(ppm) 

MITC ECOSAR 

Toxicity 

(ppm) 

ECOSAR 

Departure 

Factor 2

Freshwater Fish1 96-hr LC50

(Acute) 0.0512 0.079 0.556 

Daphnid 48-hr LC50

(Acute) 0.055 1.207 21.945 

Green Algae 96-hr EC50

(Acute) 0.254 1.412 5.559 

1. The lowest toxicity value between rainbow trout and bluegill sunfish shown in the 

table. 

2. ECOSAR Departure Factor = MITC ECOSAR Toxicity/MITC Measured Toxicity. 

Table B-2. MITC versus ECOSAR predicted toxicity for methylamine (deg. 1), 

DMTU (deg. 2), DMU (deg. 3), syn-N-methylthioformamide (deg. 4), and anti-Nmethylthioformamide (deg. 5) (departure factors in parenthesis). 

Taxa Endpoint 

MITC 

ECOSAR 

Toxicity 

(ppm) 

Deg. 1 

ECOSAR 

Toxicity 

(ppm) 

Deg. 2 

ECOSAR 

Toxicity 

(ppm) 

Deg. 3 

ECOSAR 

Toxicity 

(ppm) 

Deg. 4 

ECOSAR 

Toxicity 

(ppm) 

Deg. 5 

ECOSAR 

Toxicity 

(ppm) 

Freshwater 

Fish1

96-hr 

LC50 

(Acute) 

0.079 210.956 

(2,670.3) 

56,266.277 

(712,231.2) 

306.85 

(3,884.2) 

17,844.49 

(225,879.6) 

17,844.49 

(225,879.6) 

Daphnid 48-hr 

LC50 

(Acute) 

1.207 12.337 

(10.2) 

6.720 

(5.6) 

6,171.71 

(5,113.3) 

6,623.911 

(5,487.9) 

6,623.911 

(5,487.9) 

Green 

Algae 

96-hr 

LC50 

1.412 2.247 

(1.6) 

4.617 

(3.27) 

0.075 

(0.05) 

920.575 

(652.0) 

920.575 

(652.0) 
Page 55 of 79 

Taxa Endpoint 

MITC 

ECOSAR 

Toxicity 

(ppm) 

Deg. 1 

ECOSAR 

Toxicity 

(ppm) 

Deg. 2 

ECOSAR 

Toxicity 

(ppm) 

Deg. 3 

ECOSAR 

Toxicity 

(ppm) 

Deg. 4 

ECOSAR 

Toxicity 

(ppm) 

Deg. 5 

ECOSAR 

Toxicity 

(ppm) 

(Acute) 

1. The lowest toxicity value between rainbow trout and bluegill sunfish shown in the 

table. 

2. ECOSAR Departure Factor = Degradate ECOSAR Toxicity/MITC Measured Toxicity. 
Page 56 of 79 

Figure B-1. MITC ECOSAR run. 

SMILES : N(=C=S)C 

CHEM : Methane, isothiocyanatoCAS Num: 

ChemID1: 

ChemID2: 

ChemID3: 

MOL FOR: C2 H3 N1 S1 

MOL WT : 73.11 

Log Kow: 1.30 (KowWin estimate) 

Melt Pt: 

Wat Sol: 7600 mg/L (experimental database) 

ECOSAR v1.00 Class(es) Found 

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

Thiocyanates 

 Predicted 

ECOSAR Class Organism Duration End Pt mg/L (ppm) 

=========================== ================== ======== ====== 

========== 

Thiocyanates : Fish 96-hr LC50 0.079 

Thiocyanates : Daphnid 48-hr LC50 1.207 

Thiocyanates : Green Algae 96-hr EC50 1.412 

Thiocyanates : Fish ChV 0.013 ! 

Thiocyanates : Daphnid ChV 0.180 ! 

Thiocyanates : Green Algae ChV 0.333 

=========================== ================== ======== ====== 

========== 

Neutral Organic SAR : Fish 96-hr LC50 220.353 

(Baseline Toxicity) : Daphnid 48-hr LC50 116.832 

 : Green Algae 96-hr EC50 37.792 

 : Fish ChV 21.244 

 : Daphnid ChV 9.534 

 : Green Algae ChV 12.036 

 Note: * = asterisk designates: Chemical may not be soluble 

 enough to measure this predicted effect. 

 

 Note: ! = exclamation designates: The toxicity value was determined from 

 a predicted SAR using established acute-to-chronic ratios and ECOSAR 

 regression techniques which are documented in the supporting Technical 

 Reference Manual. When possible, this toxicity value should be 

 considered in a weight of evidence approach. 

 
Page 57 of 79 

Thiocyanates: 

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

 For All Acute and Chronic Toxicity Values: If the log Kow of the chemical 

is greater than the value listed below, or if the compound is solid and the 

LC50, EC50 or ChV exceeds the water solubility by 10X, no effects at 

saturation are predicted for these endpoints. 

 

ECOSAR v1.00 SAR Limitations: 

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

Maximum LogKow: 6.0 (Fish 96-hr LC50) 

Maximum LogKow: 5.0 (Daphnid LC50) 

Maximum LogKow: 6.4 (Green Algae EC50 

Maximum LogKow: 8.0 (ChV) 

Maximum Mol Wt: 1000 

 

Baseline Toxicity SAR Limitations: 

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

Maximum LogKow: 5.0 (Fish 96-hr LC50; Daphnid LC50) 

Maximum LogKow: 6.4 (Green Algae EC50) 

Maximum LogKow: 8.0 (ChV) 

Maximum Mol Wt: 1000 

 

------------------------------------------------------------------------------ 
Page 58 of 79 

Figure B-2. Methylamine ECOSAR run. 

SMILES : NC 

CHEM : Methanamine 

CAS Num: 

ChemID1: 

ChemID2: 

ChemID3: 

MOL FOR: C1 H5 N1 

MOL WT : 31.06 

Log Kow: -0.64 (KowWin estimate) 

Melt Pt: 

Wat Sol: 1.08E+006 mg/L (experimental database) 

ECOSAR v1.00 Class(es) Found 

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

Aliphatic Amines 

 Predicted 

ECOSAR Class Organism Duration End Pt mg/L (ppm) 

=========================== ================== ======== ====== 

Aliphatic Amines : Fish 96-hr LC50 210.956 

Aliphatic Amines : Daphnid 48-hr LC50 12.337 

Aliphatic Amines : Green Algae 96-hr EC50 2.247 

Aliphatic Amines : Fish ChV 2.907 

Aliphatic Amines : Daphnid ChV 0.007 

Aliphatic Amines : Green Algae ChV 1.794 

Aliphatic Amines : Fish (SW) 96-hr LC50 219.921 

Aliphatic Amines : Mysid Shrimp (SW) 96-hr LC50 12.503 

Aliphatic Amines : Green Algae (SW) 96-hr EC50 2.224 

Aliphatic Amines : Fish (SW) ChV 2.907 

Aliphatic Amines : Mysid Shrimp (SW) ChV 0.007 

Aliphatic Amines : Green Algae (SW) ChV 1.575 

=========================== ================== ======== ====== 

========== 

Neutral Organic SAR : Fish 96-hr LC50 4088.551 

(Baseline Toxicity) : Daphnid 48-hr LC50 1714.937 

 : Green Algae 96-hr EC50 250.419 

 : Fish ChV 411.433 

 : Daphnid ChV 99.337 

 : Green Algae ChV 55.980 

 Note: * = asterisk designates: Chemical may not be soluble 

 enough to measure this predicted effect. 

 

Aliphatic Amines: 
Page 59 of 79 

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

 For Fish 96-hr LC50: For aliphatic amines with log Kow greater than 7.0, 

a test duration of greater than 96 hrs may be required for proper 

expression of toxicity. Also, if the toxicity value obtained by the use 

of this equation exceeds the water solubility (measured or estimated), 

mortalities greater than 50% would not be expected in a saturated 

solution during an exposure period of 96 hrs. 

 

 For Daphnid 48-hr LC50: For aliphatic amines with log Kow greater than 

5.0, a test duration of greater than 48 hrs may be required for proper 

expression of toxicity. Also, if the toxicity value obtained by the use 

of this equation exceeds the water solubility (measured or estimated), 

significant mortalities would not be expected in a saturated solution 

during an exposure period of 48 hrs. 

 

 For Green Algae Acute Toxicity Values: If the log Kow of the chemical is 

greater than 7, or if the compound is solid and the EC50 exceeds the water 

solubility by 10X, no effects at saturation are predicted for these endpoints. 

 

 For Mysid Shrimp Acute Toxicity Values: If the log Kow of the chemical is 

greater than 6, or if the compound is solid and the EC50 exceeds the water 

solubility by 10X, no effects at saturation are predicted for these endpoints. 

 

 For Fish and Daphnid Chronic Toxicity Values: If the log Kow of the chemical 

is greater than 8.0, or if the compound is solid and the ChV exceeds the water 

solubility by 10X, no effects at saturation are predicted for these endpoints. 

 

 For Green Algae Chronic Toxicity Values: If the log Kow of the chemical 

is greater than 7.0, or if the compound is solid and the ChV exceeds the water 

solubility by 10X, no effects at saturation are predicted for these endpoints. 

 

ECOSAR v1.00 SAR Limitations: 

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

Maximum LogKow: 6.0 (Fish, Mysid LC50) 

Maximum LogKow: 5.0 (Daphnid LC50) 

Maximum LogKow: 7.0 (Green Algae EC50) 

Maximum LogKow: 8.0 (Fish, Daphnid ChV) 

Maximum LogKow: 7.0 (Green Algae ChV) 

Maximum Mol Wt: 1000 

 

Baseline Toxicity SAR Limitations: 

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

Maximum LogKow: 5.0 (Fish 96-hr LC50; Daphnid LC50) 

Maximum LogKow: 6.4 (Green Algae EC50) 

Maximum LogKow: 8.0 (ChV) 

Maximum Mol Wt: 1000 
Page 60 of 79 

Figure B-3. DMTU ECOSAR run. 

SMILES : N(C(=S)NC)C 

CHEM : Thiourea, N,N'-dimethylCAS Num: 000534-13-4 

ChemID1: 

ChemID2: 

ChemID3: 

MOL FOR: C3 H8 N2 S1 

MOL WT : 104.17 

Log Kow: -0.38 (KowWin estimate) 

Melt Pt: 

Wat Sol: 1E+006 mg/L (experimental database) 

ECOSAR v1.00 Class(es) Found 

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

Thioureas 

 Predicted 

ECOSAR Class Organism Duration End Pt mg/L (ppm) 

=========================== ================== ======== ====== 

========== 

Thioureas : Fish 96-hr LC50 56266.277 

Thioureas : Daphnid 48-hr LC50 6.720 

Thioureas : Green Algae 96-hr EC50 4.617 

Thioureas : Fish ChV 4731.437 ! 

Thioureas : Daphnid ChV 0.523 ! 

Thioureas : Green Algae ChV 0.338 

=========================== ================== ======== ====== 

========== 

Neutral Organic SAR : Fish 96-hr LC50 8259.677 

(Baseline Toxicity) : Daphnid 48-hr LC50 3575.216 

 : Green Algae 96-hr EC50 580.884 

 : Fish ChV 826.408 

 : Daphnid ChV 216.845 

 : Green Algae ChV 136.173 

 Note: * = asterisk designates: Chemical may not be soluble 

 enough to measure this predicted effect. 

 

 Note: ! = exclamation designates: The toxicity value was determined from 

 a predicted SAR using established acute-to-chronic ratios and ECOSAR 

 regression techniques which are documented in the supporting Technical 

 Reference Manual. When possible, this toxicity value should be 

 considered in a weight of evidence approach. 

 
Page 61 of 79 

Thioureas : 

---------- 

 For Fish and Daphnid Acute Toxicity Values: If the log Kow of the chemical 

is greater than 5.0, or if the compound is solid and the LC50 exceeds the 

water solubility by 10X, no effects at saturation are predicted for these 

endpoints. 

 

 For Green Algae Acute Toxicity Values: If the log Kow of the chemical is 

greater than 6.4, or if the compound is solid and the EC50 exceeds the water 

solubility by 10X, no effects at saturation are predicted for these endpoints. 

 

 For All Chronic Toxicity Values: If the log Kow of the chemical is greater 

than 8.0, or if the compound is solid and the ChV exceeds the water solubility 

by 10X, no effects at saturation are predicted for these endpoints. 

 

ECOSAR v1.00 SAR Limitations: 

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

Maximum LogKow: 5.0 (LC50) 

Maximum LogKow: 6.4 (EC50) 

Maximum LogKow: 8.0 (ChV) 

Maximum Mol Wt: 1000 

 

Baseline Toxicity SAR Limitations: 

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

Maximum LogKow: 5.0 (Fish 96-hr LC50; Daphnid LC50) 

Maximum LogKow: 6.4 (Green Algae EC50) 

Maximum LogKow: 8.0 (ChV) 

Maximum Mol Wt: 1000 

 
Page 62 of 79 

Figure B-4. DMU ECOSAR run. 

SMILES : O=C(NC)NC 

CHEM : Urea, N,N -dimethylCAS Num: 000096-31-1 

ChemID1: 

ChemID2: 

ChemID3: 

MOL FOR: C3 H8 N2 O1 

MOL WT : 88.11 

Log Kow: -0.62 (KowWin estimate) 

Melt Pt: 

Wat Sol: 1.615E+004 mg/L (WskowWin estimate) 

ECOSAR v1.00 Class(es) Found 

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

Substituted Ureas 

Amides 

 Predicted 

ECOSAR Class Organism Duration End Pt mg/L (ppm) 

=========================== ================== ======== ====== 

========== 

Substituted Ureas : Fish 96-hr LC50 2055.694 

Substituted Ureas : Daphnid 48-hr LC50 6171.706 

Substituted Ureas : Green Algae 96-hr EC50 0.075 

Substituted Ureas : Fish ChV 24.377 

Substituted Ureas : Daphnid ChV 308.215 

Substituted Ureas : Green Algae ChV 0.026 ! 

Amides : Fish 96-hr LC50 1348.192 

Amides : Daphnid 48-hr LC50 306.850 

Amides : Green Algae 96-hr EC50 1.042 

Amides : Fish ChV 7.970 

Amides : Daphnid ChV 4.048 ! 

Amides : Green Algae ChV 0.147 

=========================== ================== ======== ====== 

========== 

Neutral Organic SAR : Fish 96-hr LC50 11265.005 

(Baseline Toxicity) : Daphnid 48-hr LC50 4733.666 

 : Green Algae 96-hr EC50 695.488 

 : Fish ChV 1133.227 

 : Daphnid ChV 274.924 

 : Green Algae ChV 155.900 

 Note: * = asterisk designates: Chemical may not be soluble 
Page 63 of 79 

 enough to measure this predicted effect. 

 

 Note: ! = exclamation designates: The toxicity value was determined from 

 a predicted SAR using established acute-to-chronic ratios and ECOSAR 

 regression techniques which are documented in the supporting Technical 

 Reference Manual. When possible, this toxicity value should be 

 considered in a weight of evidence approach. 

 

Substituted Ureas: 

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

 For Fish and Daphnid Acute Toxicity Values: If the log Kow of the chemical 

is greater than 5.0, or if the compound is solid and the LC50 exceeds the 

water solubility by 10X, no effects at saturation are predicted for these 

endpoints. 

 

 For Green Algae Acute Toxicity Values: If the log Kow of the chemical is 

greater than 6.4, or if the compound is solid and the EC50 exceeds the water 

solubility by 10X, no effects at saturation are predicted for these endpoints. 

 

 For All Chronic Toxicity Values: If the log Kow of the chemical is greater 

than 8.0, or if the compound is solid and the ChV exceeds the water solubility 

by 10X, no effects at saturation are predicted for these endpoints. 

 

ECOSAR v1.00 SAR Limitations: 

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

Maximum LogKow: 5.0 (LC50) 

Maximum LogKow: 6.4 (EC50) 

Maximum LogKow: 8.0 (ChV) 

Maximum Mol Wt: 1000 

 

Amides : 

------- 

No limitations known at this time. 

 

ECOSAR v1.00 SAR Limitations: 

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

Maximum LogKow: >8.5 (LC50) 

Maximum LogKow: >8.0 (EC50,ChV) 

Maximum Mol Wt: 1000 

 

Baseline Toxicity SAR Limitations: 

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

Maximum LogKow: 5.0 (Fish 96-hr LC50; Daphnid LC50) 

Maximum LogKow: 6.4 (Green Algae EC50) 

Maximum LogKow: 8.0 (ChV) 

Maximum Mol Wt: 1000 
Page 64 of 79 

Figure B-5. syn-N-methylthioformamide (deg. 4), and anti-N-methylthioformamide 

ECOSAR run. 

SMILES : NC(=S)C 

CHEM : Ethanethioamide 

CAS Num: 000062-55-5 

ChemID1: 

ChemID2: 

ChemID3: 

MOL FOR: C2 H5 N1 S1 

MOL WT : 75.13 

Log Kow: -0.83 (KowWin estimate) 

Melt Pt: 

Wat Sol: 1.63E+005 mg/L (experimental database) 

ECOSAR v1.00 Class(es) Found 

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

Neutral Organics 

 Predicted 

ECOSAR Class Organism Duration End Pt mg/L (ppm) 

=========================== ================== ======== ====== 

========== 

Neutral Organics : Fish 96-hr LC50 17844.490 

Neutral Organics : Fish 14-day LC50 17238.707 

Neutral Organics : Daphnid 48-hr LC50 6623.911 

Neutral Organics : Green Algae 96-hr EC50 920.575 

Neutral Organics : Fish 30-day ChV 1538.136 

Neutral Organics : Daphnid ChV 490.584 

Neutral Organics : Green Algae ChV 219.521 

Neutral Organics : Fish (SW) 96-hr LC50 30757.049 

Neutral Organics : Mysid Shrimp 96-hr LC50 1.34e+005 

Neutral Organics : Fish (SW) ChV 511.459 

Neutral Organics : Mysid Shrimp (SW) ChV 26748.623 

Neutral Organics : Earthworm 14-day LC50 256.639 

 Note: * = asterisk designates: Chemical may not be soluble 

 enough to measure this predicted effect. 

 

Neutral Organics: 

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

 For Fish LC50 (96-h), Daphnid LC50, Mysid: If the log Kow is greater 

than 5.0, or if the compound is solid and the LC50 exceeds the water 

solubility by 10X, no effects at saturation are predicted. 

 

 For Fish LC50 (14-day) and Earthworm LC50: If the log Kow is greater 

than 6.0, or if the compound is solid and the LC50 exceeds the water 
Page 65 of 79 

solubility by 10X, no effects at saturation are predicted. 

 

 For Green Algae Acute Toxicity Values: If the log Kow of the chemical is 

greater than 6.4, or if the compound is solid and the EC50 exceeds the water 

solubility by 10X, no effects at saturation are predicted for these endpoints. 

 

 For All Chronic Toxicity Values: If the log Kow of the chemical is greater 

than 8.0, or if the compound is solid and the ChV exceeds the water solubility 

by 10X, no effects at saturation are predicted for these endpoints. 

 

ECOSAR v1.00 SAR Limitations: 

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

Maximum LogKow: 5.0 (Fish 96-hr LC50; Daphnid LC50, Mysid LC50) 

Maximum LogKow: 6.0 (Fish 14-day LC50; Earthworm LC50) 

Maximum LogKow: 6.4 (Green Algae EC50) 

Maximum LogKow: 8.0 (ChV) 

Maximum Mol Wt: 1000 

 
Page 66 of 79 

Appendix C – STIR Model Run to Establish Drinking Water and 

Dietary Exposure Conceptual Model for Birds and Mammals 

 
Page 67 of 79 

Appendix D – SIP Model Run to Establish Drinking Water 

Exposure Conceptual Model for Birds and Mammals 

Table 1. Inputs 

Parameter Value 

Chemical name 

Solubility (in water at 25oC; mg/L) 8610 

 

Mammalian LD50 (mg/kg-bw) 55 

Mammalian test species laboratory rat 

Body weight (g) of "other" mammalian species 

 

Mammalian NOAEL (mg/kg-bw) 

Mammalian test species 

Body weight (g) of "other" mammalian species 

 

Avian LD50 (mg/kg-bw) 0 

Avian test species northern bobwhite quail 

Body weight (g) of "other" avian species 

Mineau scaling factor 

 

Mallard NOAEC (mg/kg-diet) 

Bobwhite quail NOAEC (mg/kg-diet) 

NOAEC (mg/kg-diet) for other bird species 

Body weight (g) of other avian species 

NOAEC (mg/kg-diet) for 2nd other bird species 

Body weight (g) of 2nd other avian species 

 

Table 2. Mammalian Results 

Parameter Acute Chronic 

Upper bound exposure (mg/kg-bw) 1480.9200 1480.9200 

Adjusted toxicity value (mg/kg-bw) 42.3038 0.0000 

Ratio of exposure to toxicity 35.0068 0.0000 

Conclusion* 

Exposure through 

drinking water alone 

is a potential concern 

for mammals 

Due to insufficient 

data, risk cannot be 

precluded 

 

Table 3. Avian Results 

Parameter Acute Chronic 

Upper bound exposure (mg/kg-bw) 6974.1000 6974.1000 

Adjusted toxicity value (mg/kg-bw) 0.0000 0.0000 

Ratio of exposure to acute toxicity 0.0000 0.0000 

Conclusion* 

Due to insufficient 

data, risk cannot be 

precluded 

Due to insufficient 

data, risk cannot be 

precluded 
Page 68 of 79 

Appendix E – Earthworm Fugacity Model Results to Establish 

Dietary Exposure Conceptual Model for Birds and Mammals 

Parameter MITC 

Application Rate 

(lbs. a.i./A) 

219.41

Molecular Weight 

(g/mol) 

73.12 

Vapor Pressure 

(torr) 

16 

Kd (L/kg) 0.260 

Log Kow 1.30 

Earthworn Conc 

g/kg 

0.00014 

Mammal Diet Dose 

mg/kg 

0.14 

Avian Diet Dose 

mg/kg 

0.16 

Air conc. 6.3EE4 

Mammal Inhaled 

Dose mg/kg 

9.95EE3 

Avian Inhaled 

Dose mg/kg 

7.91EE3 

15 g mammal, 20g bird. Results based on STIR model and Earthworm Fugacity Model. 

Depth 10 cm for earthworm exposure zone. 

1

Dazomet maximum application rate results in highest MITC equivalent application rate of MITC 

generators (from Metam Sodium = 150.31 lbs. a.i./A, from Metam Potassium = 150.38 lbs. a.i./A).
Page 69 of 79 

Appendix F – Detailed Environmental Fate Summary and 

Degradate Tables for Metam Sodium, Metam Potassium, and 

MITC
Page 70 of 79 

Hydrolysis

Metam sodium degrades rapidly due to hydrolysis, especially under acid and neutral 

conditions. The hydrolysis of metam sodium half-lives were 2 days at pH 5 and 7, and 

4.5 days at pH 9 (Table ). In the hydrolysis study, the degradates identified in all test 

solutions were MITC, methylamine, 1,3-dimethylthiourea (DMTU) and 1,3 dimethylurea 

(DMU). Methylcarbamo (dithioperoxo) thioate (MCDT) was identified in the pH 9 test 

solutions. The major degradate formed at pH 5 and 7 was MITC (16% to 65% 

respectively). At pH 9, two major degradates formed, with 20 % of MITC and 16% of 

MCDT. The formation of methylamine was favored under acidic conditions compared to 

neutral or alkaline conditions. MITC is moderately persistent with hydrolysis half-lives 

of 3.5 days at pH 5, 20.4 days at pH 7, and 4.6 days at pH 9 (MRID 00158162). 

Methylamine was the main degradatee of MITC identified in all pHs. One other 

degradate, 1,3-dimethylthiourea was isolated in the pH 9 only, comprised a maximum 

22.1% of the recovered at 13.04 days post-treatment. 

Photolysis in Water

The photodegradation of metam sodium in aqueous solution is very rapid with a half-life 

of 28 minutes. Except for N-methylthioformamide, the degradates identified in the 

photodegradation study were also identified in the hydrolysis study. Nmethylthioformamide were at a maximum concentration of 22.3% by the end of the study 

interval; methylamine increased to 17.5%, MITC increased to 16%, and MCDT increased 

to 14.1%. The placement of metam sodium below the soil surface (except surface 

applications), and rapid degradation of metam sodium in soil to volatile MITC suggest 

that photolysis on soil would be a negligible route of dissipation in the environment. 

Microbial Degradation

In an aerobic soil metabolism study (MRID 401985-02), metam sodium degrades very 

rapidly in soil with a half-life of 23 minutes. The majority of the residues had been 

volatilized: 83% of the applied as MITC; 0.2% as other organic volatiles, and 0.9% as 

CO2. The major nonvolatile degradate was DMU at a maximum of 0.45 ppm at 3 and 7 

days. The degradation rates of MITC in soils have been reported in number of studies 

(Ashley et al., 1963, Gerstl et al., 1977). These studies generally found that MITC 

degradation in soil was dominated by microbial processes and followed first-order 

degradation kinetics. Gerstl et al. (1977) demonstrated that metam sodium breakdown to 

MITC was rapid and generally less than 30 minutes at moisture contents below 

saturation. They also reported that MITC was found to persist longer than metam 

sodium, with half-lives ranging from 3.3 to 9.9 days depending on soil composition. 

Since MITC is a volatile compound, very little information is available on the metabolites 

of MITC degradation in soil. Smelt et al. (1989) investigated the accelerated 

decomposition rates of MITC in previously metam sodium treated soil and suggested that 

repeated application of metam sodium induced microbial adaptation, resulting in 

enhanced biotransformation of MITC. Dungan and Yates (2003) reported that the 

microorganisms responsible for enhanced degradation of MITC specifically target the