1 

Appendix A. Environmental Fate and Transport Data

835-2120 Hydrolysis (MRID# 46903532)

Dimethyl disulfide remained stable to hydolysis at a test concentration of approximately 15 ppm. 

[

14C] Dimethyl disulfide was tested at aqueous buffered pH 4 (0.01M phthalate), pH 7 (0.01M 

phosphate) and pH 9 (0.01M borate) solutions. The study was conducted in darkness at 50°C. 

Samples of dimethyl disulfide were taken at Days 0, 1, 2, 3, 4, and 5 posttreatment and 

conentrations ranged from 16.55 ppm to 15.39 in the pH 4 phthalate buffer solution, from 14.22 

to 14.76 ppm in the pH 7 phosphate buffer solution, and from 14.78 ppm to 13.70 ppm in the pH 

9 borate buffer solution. The pH of the buffer solutions remained steady throughout the study, 

ranging from 4.039 - 4.069, 7.056 - 7.090, and 9.044 - 9.088. Based on the results reported by 

the registrant, a typical study environment of 25°C is not necessary in this case since dimethyl 

disulfide did not degrade substantially in this experimental environment. However, the study 

was only conducted for five days; a study duration of at least 30 days or one half-life should be 

conducted for hydrolysis studies per OPPTS Guidelines 835-2120. Therefore, this study is 

classified Supplemental. 

835-2240 Phototdegradation in Water (MRID# 47052818)

Approximately 0.2 ppm of [14C] dimethyl disulfide in sterile ultrapure water solution was 

exposed to 4 days of continuous artificial irradiation from a xenon arclamp with a wavelength 

spectrum of 295 – 800 nm. The study author indicated that the level of irradiation in the study 

was the equivalent exposure of natural irradiation for a 30, 12-hour day and 12-hour night cycle. 

The half-life was determined to be 28.125 hours based on the experimental half-life, subtracted 

from the half-life observed in the dark control, and adjusted to the 12-hour day-night cycle. 

Samples were collected at 0, 1, 2, 5, and 24 hours posttreatment. 

The registrant proposed a degradation pathway from aqueous photolysis of parent dimethyl 

disulfide (see figure below). DMDS can initially degrade to the methyl thiyl radical (CH3S·). A 

series of oxidation and recombination reactions can result in the formation of the methyl thiyl 

peroxy radical (CH3SOO·) and the methyl thiyl oxy radical (CH3SO·). The methyl thiyl oxy 

radical can then decompose to the methyl radical (CH3·) and sulfur dioxide and subsequent 

recombination with the methyl thiyl radical can form methane sulfonic acid (CH3SCH3). In a 

more oxygen rich environment, the methyl radical can further oxidize to form the the methyl 

peroxy radical (CH3OO·) and recombine with a second methyl peroxy radical and a methyl thiyl 

radical to form formic acid (CH2O2) with hydride ion reaction, formaldehyde (CH2O) with 

hydroxide ion reaction, and methyl peroxide (CH3OOH) with hydrogen radical reaction. 

The registrant identified but did not quantify three possible major degradates. The registrant 

attributed one peak on the HPLC plot, designated Deg-1, to three polar transformation products 

accounting for 59.3 percent of the applied residue peaking on Day 1 posttreatment, in one 

replicate. Two of the three products accounted for major components of the material balance (> 

10 percent of the applied). The registrant identified that methanesulfonic acid, methanesulfinic 

acid, and sulfuric acid could have corresponded to the two major degradates detected in the Deg-
1 region. Two additional peaks on the HPLC plot, designated as Reg-1 and Reg-2 accounting for 

26.3 and 24.5 percent of the applied residue, were comprised of multiple unidentified minor 

transformation products. Residues in association with these regions on the HPLC plot peaked on 

Day 1 posttreatment. 

This study is classified Supplemental due to high retrieved material balances up to 121 percent 

by 24-hours posttreatment, indicating the potential for possible contamination. In addition, the 

sampling intervals were too infrequent between hours 5 and 24 hours posttreatment. This gap in 

sampling leads to uncertainty in the formation and decline of degradation products. 

835-2240 Photodegradation in Water (MRID# 47052802)

2 
3 

This study followed the Tier I procedure proposed OECD Guideline, “Phototransformation of 

Chemicals in Water – Direct and Indirect Photolysis”. A solution of 275 mg/L of [14C] dimethyl 

disulfide in ultrapure water was irradiated polychromatically in the UV and Visible spectra. 

However, it is unclear from the study the type of irradiation that dimethyl disulfide was exposed 

to. Regardless, an aquatic photolysis half-life was obtained through the cumulative calculated 

molar absorption coefficient over the 295 to 800 nm spectrum window and the average daily 

solar photon flux irradiance assuming a quantum yield of one. Molar absorption coefficients 

were calculated using the Beer-Lambert Law based on the polychromatic absorbances measured 

by a dual-beam Varian 100-Bio UV-VIS Spectrophotometer, the measured concentration of 

DMDS residues, and the photon path length of 1 cm. The average daily solar photon flux 

irradiance was set to the equivalent seasonal value at 50oN latitude with clear sky conditions. 

The minimum aqueous photolysis half lives calculated were 1.7, 1.3, 3.3, and 7.5 hours for 

spring, summer, fall, and winter, respectively. The theoretical maximum percent aqueous 

photolysis over a 30-day period was 100 percent over all seasons. According to the proposed 

OECD guideline, aqueous photolysis is significant enough of a process for which a refined 

aqueous photolysis study is needed since the theoretical percentages photolysis of dimethyl 

disulfide residues are greater than 50 percent. Therefore, this study is classified Supplemental. 

The registrant submitted a refined study in MRID No. 47052818, “Dimethyl diulfide photolysis 

in the environment”. 

835.2370 Photodegradation in Air (MRID# 47052803)

The registrant provided the value of the photoysis in air half-life of 0.047 days (1.1. hours) 

calculated from the AOPWIN v1.91 software. This submittal will be classified as Supplemental

for the purposes of satisfying the data requirement at this time. However, a photolysis in air 

study utilizing field or laboratory methods may be requested in the future pending revision of the 

OPPTS guidelines. 

835.2370 Photodegradation in Soil

All proposed labels require immediate tarping after application. Therefore, this study is waived 

since the tarping material is expected to minimize direct solar radiation reaching the soil.

835.4300 Aerobic Soil Metabolism (MRID#47052819) 

Aerobic soil metabolism was tested under darkness with 390 mg/kg of [14C] dimethyl disulfide 

on two domestic soils, California loamy sand and Florida sand as well as on two foreign soils, 

Swiss Clay and France clay loam. FAO soil classifications were also provided to discern the 

chemical and mineralogical representativeness of these foreign soils to domestic soils. The 

France and Switzerland soils were classified as Dystric Cambisol and Calcaric Cambisol, 

respectively. Cambisols fall under the category of the Inceptisol U.S. Taxonomic Classification, 

which are found domestically in the Southwest. Therefore, the mineral and chemical properties 

of these soils can be considered representative of that which is found domestically. 

The California loamy sand test was sampled on days 0, 1, 7, 14, 21, 62; and 120 days 
4 

posttreatment; the Florida sand test was sampled on days 0, 1, 4, 7, 14, 21, 60, and 120 days 

posttreatment; the France clay loam test was sampled on 0, 1, 4, 7, 11, 14, 21, and 59 days 

posttreatment; and the Switzerland clay soil test was sampled on days 0, 1, 4, 7, 11, 14, 21, 59, 

and 120 days posttreatment. 

In each of the four test soils, most of the total residue of DMDS in the soil diffused rapidly to the 

solid-phase carbon trap within 5 minutes postapplication. However, over time, residues of the 

major degradate, Methanesulfonic Acid, accumulated in the acetonitrile and aqueous soil extracts 

over time to levels of 3.26 percent for California sandy loam soil by Day 120 posttreatment, 4.95 

percent for Florida sandy soil by Day 120 posttreatment, 33.17 percent France clay loam soil by 

Day 14 posttreatment, and 32.86 percent in the Switzerland clay soil by Day 21 posttreatment. 

In addition, residues of volatile organic compounds and carbon dioxide accumulated in the KOH 

trapping solution to 27.24 percent of the applied parent. Although unclear, the reviewer 

postulates that the build up of the degradate over time in the soil is due to gaseous deposition of 

dimethyl disulfide in the equilibrium process of the experimental system and subsequent 

formation of degradation products. This is unclear since only trace amounts of dimethyl 

disulfide in the soil were detected. 

The aerobic soil metabolism half-life of DMDS was estimated from soil degradate 

(methanesulfonic acid, unidentified extractable residue, non-extractable residue, and CO2) 

formation rates in soil because of the high volatility of DMDS; DMDS was only detected in the 

head space of the biometer flask. Additionally, the aerobic soil metabolism studies for DMDS 

were designed as closed-head space test systems. The combination of the high volatility of 

DMDS and the closed-head space of the test systems led to no detection of DMDS in the soil as 

well as possible sterilization of the soil in the test system from a fumigation effect. 

The DMDS concentration in soil was approximated in aerobic soil metabolism data (MRID 

47052819) using the following equation: 

DMDS estimate = 1.00 – ∑(soil degradation products)time

Soil degradation product = methanesulfonic acid + unidentified extractable residue + 

unextractable residue + CO2 (% of applied radioactivity) at each time interval. 

The table below shows the estimated concentration of DMDS from the aerobic soil metabolism 

studies using a total system mass balance. 
5 

DMDS Concentration Estimate in Soil in the Aerobic Soil Metabolism Study (MRID 

47052819) Using a Total System Mass Balance 

Time Switzerland clay France clay loam 

(Days) Soil 

Degradation 

Products 

Estimate DMDS Soil 

Degradation 

Products 

Estimate DMDS 

0 2.46 97.54 2.18 97.82 

1 21.79 78.21 8.86 91.14 

4 23.17 76.83 37.83 62.17 

7 34.65 65.35 47.8 52.2 

11 41.25 58.75 49.7 50.3 

14 44.64 55.36 50.97 49.03 

21 47.14 52.86 47.68 52.32 

59 47.35 52.65 75.18 24.82 

120 42.7 57.3 

For modeling purposes, the 90th percentile of the mean half-life was calculated using the total 

mass balance estimated DMDS half-lives in soil. The 90th percentile of the mean half-life for 

total mass balance DMDS is 4.07 days (mean=3.607151, Standard deviation=0.214651 days, t90, 

n-1= 3.078). 

Fitted Parameters for Exponential Decay Model for DMDS in Aerobic Soil Metabolism 

Study (MRID 47052819) Using a Total System Mass Balance. 

Soil Model Yo 

(% applied) 

a 

(% applied) 

b 

(days-1) 

Estimated 

Half-life 

(days) 

Adjusted 

R2 

France Clay 

Loam 

48.0940 47.6464 0.2006 3.45 0.8022 

Switzerland 

Clay 

3-parameter 

exponential 

decay 53.9264 38.9367 0.1844 3.75 0.9325 

Another approach was to assume the degradation of DMDS can be indirectly modeled from the 

formation of methanesulfonic acid. Methanesulfonic acid forms through the breaking of the 

disulfide bond in DMDS. The DMDS concentration in soil was approximated in aerobic soil 

metabolism data (MRID 47052819) using the following equation: 

[DMDS] estimate = 1.00 – [methanesulfonic acid] time

The table below shows the estimated concentration of DMDS from the aerobic soil metabolism 

studies using the residue soil data for methanesulfonic acid. 

DMDS Concentration Estimate in Soil in the Aerobic Soil Metabolism Study (MRID 
6 

47052819) Using Methanesulfonic acid formation 

Time Switzerland clay France clay loam 

(Days) Methanesulfonic 

acid 

Estimate DMDS Methanesulfonic 

acid 

Estimate DMDS 

0 1.42 98.58 1.45 98.55 

1 8.09 91.91 6.17 93.83 

4 17.47 82.53 21.68 78.32 

7 25.67 74.33 29.1 70.9 

11 30.34 69.66 32.5 67.5 

14 32.16 67.84 33.17 66.83 

21 32.86 67.14 32.97 67.03 

59 26.8 73.2 35.3 64.7 

120 5.76 94.24 

Bolded values were not included in the degradation kinetic analysis because they indicate DMDS formation. This situation is likely an artifact of 

from the degradation of methanesulfonic acid in soil. 

For modeling purposes, the 90th percentile of the mean half-life was calculated using the 

estimated methanesulfonic acid (MS)-DMDS half-lives in soil. The 90th percentile of the mean 

half-life for total mass balance MS-DMDS is 4.66 days (mean= 3.3032, Standard 

deviation=0.6242 days, t90, n-1= 3.078). 

Fitted Parameters for Exponential Decay Model for DMDS in Aerobic Soil Metabolism 

Study (MRID 47052819). 

Soil Model Yo 

(% applied) 

a 

(% applied) 

b 

(days-1) 

Estimated 

Half-life 

(days) 

Adjusted 

R2

France Clay 

Loam 

65.4818 34.1053 0.2422 2.86 0.80 

Switzerland 

Clay 

3-parameter 

exponential 

decay 65.8673 32.38 0.1851 3.74 0.9948 

The registrant proposed a degradation pathway for aerobic soil metabolism below. The enzyme 

methanethiol oxidase as well as protein disulfide isomerases and oxido reductases may act as 

catalysts to degrade dimethyl disulfide to methane thiol, methane sulfenic acid, methane sulfinic 

acid, and methanesulfonic acid. Further degradation to formaldehyde can occur due to 

methanesulfonic activation with a mono-oxygenase enzyme. Multi-step CO2 mineralization can 

cause further degradation to formic acid and the hydrocarboxyl radical. 
This study is classified as Supplemental. Since dimethyl disulfide residues were detected in the 

headspace immediately upon the beginning of the study, the route of degradation, as observed 

with the accumulation of degradate products in the soil over time, is unclear. Furthermore, in the 

European soil tests, material balances were incomplete with up to 18-23% of the applied 

unaccounted for at study termination. 

835.4200 Anaerobic Soil Metabolism (MRID# 43759301) 

Dimethyl disulfide was applied in California sandy loam soil under anaerobic conditions as the 

the system was flushed with Nitrogen gas in the headspace and then flooded with a layer of 2 - 3 

cm of Nitrogen-sparged deionized water. [14C] Dimethyl disulfide was applied at a 

concentration of 280 mg/L. Samples were extracted on Days 0, 3, 7, 14, 21, and 71 days 

posstreatment, and the experiment was conducted under darkness. The majority of dimethyl 

disulfide residues diffused from the test system and was detected in solid-phase carbon traps and 

the KOH solution traps (including the pre-cartridge KOH trapping solution) within 4 hours 

posttreatment. Since there is evidence that volatilization is the major route of dissipation for 

dimethyl disulfide in the anaerobic environment, a total system half-life of 19.6 days was 

determined considering the formation of metabolites. However, this is an undefinitive value as 

there was an undetermined detection of diemthyl disulfide residues in the water layer and KOH 

solution traps as well throughout most of the study period. A DT50 of 14.3 days was determined 

by the registrant using kinetic modeling KinGui Software. 

The major degradates detected included methanethiol detected at a maximum level of 16 percent 

of the applied parent residue extracted 14 days posstreatment from the KOH trapping solutions, 

and methanesulfonic acid which was definitively detected at a maximum level of 16.2 percent 21 

days postreatment. However, methanesulfonic acid may have accounted for as much as 38.5 

percent of the material balance on 21 days posttreatment extracted from one other replicate KOH 

trapping solution samples and from the water column sample with undefinitive levels of 

methanesulfonic acid residues detected. 

7 
The registrant proposed a degradation pathway shown below. In the mircrobial metabolism 

process, dimethyl disulfide can interact with with enzyme methionine-γ-lyase to form 

methanethiol which can reoxidize to dimethyl disulfide. Methanethiol can also interact with the 

methyl-transferase enzyme to form dimethyl sulfide in saline marine waters. Further microbial 

metabolism can result in the breakdown to methane from dimethyl sulfide or from methanethiol. 

Methanethiol can also further be metabolized through through cynergistic interaction between 

the oxidase and dehyrogenase enzymes to form formaldehyde. Subsequent CO2 mineralization 

can occur due to activation with the formaldehyde hyrdrogenase enzyme and intermediate 

hydrolysis processes can cause the formation formic acid. Further CO2 mineralization can occur 

due to activation with the dehydrogenase enzyme resulting in oxidation for the formation of 

formic acid and the hydrocarobxyl radical. Methanesulfonic acid can also form directly from the 

degradation of dimethyl disulfide in an oxic environment. 

This study is classified as Supplemental. First, the cause of degradation is unclear given the 

study was conducted in darkness and degradates were definitively detected in the KOH trap 

solutions. Second, parent and metabolite residues, detected in the water layer, were not 

quantified. Third, the material balance was incomplete with up to 29.8 percent of the applied 

material unaccounted for in one replicate of the Day 3 sample with an additional 19.4 percent of 

residues unidentified or undefinitively determined (e.g., DMDS in KOH traps or DMDS and 

8 
9 

Methanesulfonic acid in initial water layer). Fourth, verification of the anaerobic environment 

throughout the duration of the experiment by the determination of dissolved oxygen 

concentrations or redox potential was not completed. Fifth, multiple samples of widely 

distributed soil types should be tested to obtain a sufficient database of anaerobic soil 

metabolism rates.

835.1230 Leaching and Adsoprtion/Desorption – Batch Equilibrium (MRID Nos. 46917014 

and 46917015)

The adsorption and desorption of dimethyl disulfide was determined in four foreign soils: and 

one domestic soil was determined (Speyer, Germany sandy loam soil, pH 5.6, organic carbon 

2.3 %; Mechtildshausen, Germany loam soil, pH 7.4, organic carbon 1.3 %; Mussig, France 

clay loam soil, pH 7.6, organic carbon 3.0%; Bretagne 1b, France silt loam soil, pH 5.4, organic 

carbon 2.0%; and California sandy loam soil, pH 7.8, organic carbon 0.6%). These studies are 

Acceptable and were conducted in accordance with USEPA 835.1230 guidelines. FAO soil 

classifications were provided by the registrant. The Speyer, Germany, Mussig, France, and 

Bretagne, France soils are all classified as cambisols which are equivalent to Inceptisols in the 

U.S. Taxonomic Classification system. The Mechtildshausen, Germany soil is classified as 

Luvic Phaeozem which is equivalent to the Chernozemic soils in the U.S. Taxonomic 

Classification system. Therefore, the mineral and chemical properties of these soils can be 

considered representative of that which is found domestically. 

For all soils tested in the studies, [14C] dimethyl disulfide was applied at concentrations of 

0.001, 0.002, 0.011, 0.021, and 0.102 μg a.i./ml in 14.5 ml CaCl2 supernatant over a 14.5 g layer 

of air-dried and sieved (2 mm) soil. The samples were shaken by a rotary shaker for a 24 hour 

period followed by an equilibration time of 24 hours. Residues were then extracted from the 

supernatant by centrifuge at 2800 rpm. The residues in the supernatant were quantified using 

LSC, and the mass that was left over in the soil were indirectly determined considering the initial 

mass of dimethyl disulfide in the system. The temperature of the study environment was 

maintained at 20 + 2°C. 

A desorption phase experiment was also carried out. Following equilibrium from the adsorption 

phase, the supernatant was removed and replaced with an equivalent volume of CaCl2 solution. 

The desorption phase was then initiated as samples were shaken by a rotary shaker for a 44 hour 

period followed by an equilibration time of 44 hours. Residues were then extracted from the 

supernatant by centrifuge at 2800 rpm. The residues in the supernatant were quantified using 

LSC, and the mass that was left over in the soil were indirectly determined considering the initial 

mass of dimethyl disulfide in the system. The temperature of the study environment was 

maintained at 20 + 2°C. 

For the Speyer, Germany sandy loam soil, mass balances were 100.6-102.1 percent of the 

applied residue in the preliminary study. Dimethyl disulfide residues accounted for 27.4 - 30.3 

percent adsorbed in the soil. The resulting adsorption partition coefficients ranged from 0.538 – 

0.774 ml/g for all test concentrations with an average of 0.678 ml/g. The Freundlich adsorption 

partition coefficient based on all five concentrations was nearly equivalent at 0.719 ml/g with a 
10 

1/n value of 1.011. In the desorption phase of the experiment, dimethyl disulfide residues 

accounted for 21.7 – 25.0 percent desorbed of adsorbed in the soil. The desorption partition 

coefficients ranged from 3.0 – 4.0 ml/g for all test concentrations with an average of 3.377 ml/g. 

The Freundlich desorption partition coefficient based on all five test concentrations was nearly 

equivalent at 2.531 ml/g with a 1/n value of 0.9535. 

For the Mechtildshausen, Germany loam soil, mass balances were 100.3-101.1 percent of the 

applied residue in the preliminary study. Dimethyl disulfide residues accounted for 25.6 – 38.8 

percent adsorbed in the soil. The resulting adsorption partition coefficients ranged from 0.451 – 

0.667 ml/g for all test concentrations with an average of 0.597 ml/g. The Freundlich adsorption 

partition coefficient based on all five concentrations was not nearly equivalent 0.297 ml/g with a 

1/n value of 0.867. Desorption properties of the soil were not determined since all dimethyl 

disulfide residues degraded by 44 hours of equilibrium time during the desorption phase of the 

experiment. 

For the Mussig, France clay loam soil, mass balances were 102.0-102.1 percent of the applied 

residue in the preliminary study. Dimethyl disulfide residues accounted for 24.7 – 39.6 percent 

adsorbed in the soil. The resulting adsorption partition coefficients ranged from 0.415 – 0.667 

ml/g for all test concentrations with an average of 0.554 ml/g. The Freundlich adsorption 

partition coefficient based on all five concentrations was not nearly equivalent 0.300 ml/g with a 

1/n value of 0.883. Desorption properties of the soil were not determined since all dimethyl 

disulfide residues degraded by 44 hours of equilibrium time during the desorption phase of the 

experiment. 

For the Bretagne 1b, France silt loam soil, mass balances were 102.0-102.1 percent of the 

applied residue in the preliminary study. In the desorption phase of the experiment, dimethyl 

disulfide residues accounted for 25.7 - 32.9 percent adsorbed in the soil. The resulting 

adsorption partition coefficients ranged from 0.670 – 1.00 ml/g for all test concentrations with an 

average of 0.860 ml/g. The Freundlich adsorption partition coefficient based on all five 

concentrations was nearly equivalent at 1.36 ml/g with a 1/n value of 1.087. Dimethyl disulfide 

residues accounted for 16.2 – 17.3 percent desorbed of adsorbed in the soil. The desorption 

partition coefficients ranged from 3.0 – 4.0 ml/g for all test concentrations with an average of 

3.181 ml/g. The Freundlich desorption partition coefficient representative of all five 

concentrations was nearly equivalent at 1.891 ml/g with a 1/n value of 0.9535. 

For the California sandy loam soil, mass balances were 100.3-101.2 percent of the applied 

residue in the preliminary study. Dimethyl disulfide residues accounted for 16.1 – 47.6 percent 

adsorbed in the soil. The resulting adsorption partition coefficients ranged from 0.270 – 1.00 

ml/g for all test concentrations with an average of 0.537 ml/g. The Freundlich adsorption 

partition coefficient based on all five concentrations was not nearly equivalent at 0.083 ml/g with 

a 1/n value of 0.656. In the desorption phase of the experiment, dimethyl disulfide residues 

accounted for 5.6 – 11.5 percent desorbed of adsorbed in the soil. The desorption partition 

coefficients ranged from 7.7 – 19.0 ml/g for all test concentrations with an average of 12.621 

ml/g. The Freundlich desorption partition coefficient based on all five initial sampled 
11 

concentrations was not nearly equivalent at 1.272 ml/g with a 1/n value of 0.687. 

The percent organic carbon of each soil, percent clay content of each soil, and pH of each soil do 

not show a clear relation to the average partition coefficients of each soil with correlation 

coefficients of 0.792, 0.329, and 0.010, respectively. 

835.8100 Field Volatility (MRID Nos. 47052821, 47052822, 47052823, 47052824, and 

47377801)

All above field volatility studies studies are Acceptable, and no significant deviations from good 

scientific practices were noted. 

Yuma, AZ Loamy Sand – Shank Injection to Raised Beds with Polyethylene Tarp

784 lbs. of 99.5 percent dimethyl disulfide per acre was applied by shank injection to depth of 8 

inches to raised beds followed by immediate tarping with 1.5 mm plastic material. The treated 

field had dimensions of 330 feet by 330 feet with raised beds 67 inches wide, 4-6 inches tall. A 

total of 16 air samplers were symmetrically distributed about radial distances of 10, 50, and 200 

feet completely surrounding the center of the treated field at 5-feet above ground-level. Wind 

and air temperature observations at 1.5 meters and 10 meters above ground level were collected 

and were sampled every minute at for the duration of the field study. 

The field air samples were fortified with 1.0, 100, 500, and 1,000 μg of dimethyl disulfide. On 

the day of treatment, sample periods included Hours 0-7, Hours 7-11, Hours 11-17, and hours 

17-23. On Days 1 – 8, samples were collected every six hours. On Days 8 – 14, samples were 

collected every 12 hours. The Day 0 – 2 average field spike recoveries were 85 percent, 93 

percent, 91 percent, and 104 percent for the 1.0, 100, 500, and 1,000 μg fortifications, 

respectively. The Day 3 – 14 average field spike recoveries were 86 percent, 96 percent, 84 

percent, and 92 percent for the 1.0, 100, 500, and 1,000 μg fortifications, respectively. 

Flux of dimethyl disulfide was back-calculated using monitored off-field concentrations and the 

meteorological data using the ISCST3 model. Flux profiles were developed from the 

comparison of monitored concentrations to modeled concentrations from a unit flux rate of 0.001 

g/m2

s. The relationship between monitored versus modeled concentrations used in the 

determination of the flux was statistically significant for the first 12 sampling periods. 

The total calculated cumulative flux was 3,811 μg/m2

s over the 71 hour period posttreatment. 

Since 784 lbs. a.i./acre was applied, the calculated flux accounts for approximately 81.43 percent 

of the applied residue while tarped. Temporal peak flux rates of 1,660 μg/m2s (Day 0, Hours 7 – 

11) and 37 μg/m2

s (Day 1, Hours 11 – 17) were calculated. 

Nipomo Lake, CA Sandy Loam – Drip Irrigation to Raised Beds with Polyethylene 

Tarp

573 lbs. of 95 percent dimethyl disulfide per acre was applied to raised beds via two drip 
12 

irrigation tapes, separated by 12 inches at a depth of two inches below the surface followed by 

immediate tarping with 1.5 mm plastic material. The treated field had dimensions of 330 feet by 

330 feet with raised beds 51 inches wide, 14 inches tall. The tarp was cut and removed five days 

post-application. 

A total of 20 air samplers were symmetrically distributed about radial distances of 100, 150, and 

250 feet completely surrounding the center of the treated field at 5-feet above ground-level. In 

addition, there were measurements taken from a mast located at the center of the treated field 

with concentration at the 1, 3, 6, and 10 feet levels above ground level, as well as wind and 

temperature measurements at the 1, 3, and 10 feet levels above ground level. Wind speed and 

direction data were also collected at the 20-feet level above ground level as well. 

The field air samples were fortified with 0.2, 1.0, 5.0, 100, and 5,000 μg of dimethyl disulfide. 

On Days 0 - 8 posttreatment, samples were collected every four hours. On Days 9 – 15, samples 

were collected every 12 hours. The average field spike recoveries were 298 percent, 128 

percent, 96 percent, 104 percent, and 91 percent for the 0.2, 1.0, 5.0, 100, and 5,000 μg 

fortification samples, respectively. 

Flux of dimethyl disulfide was back-calculated using monitored off-field concentrations and the 

meteorological data using the ISCST3 model. Flux profiles were developed from the 

comparison of monitored concentrations to modeled concentrations from a unit flux rate of 0.001 

g/m2

s. The relationship between monitored versus modeled concentrations used in the 

determination of the flux was statistically significant for the first 18 sampling periods. 

The total calculated cumulative flux determined by the indirect method was 1,295 μg/m2s over 

the 72 hour period posttreatment. Temporal peak flux rates of 515 μg/m2

s (Day 0, Hours 4 – 8), 

119 μg/m2s (Day 1, Hours 4 – 8), and 48 μg/m2s (Day 2, Hours 8 – 12) were calculated. 

Flux of dimethyl disulfide was also calculated using the aerodynamic method. This method 

incorporates atmospheric stability along with vertical gradients of temperature, concentration, 

and wind speed using monitored profiled data at four or five height levels at the center of the 

treated field. 

In general, the aerodynamic method calculation of dimethyl disulfide flux showed a similar trend 

in values to the indirect method, although the indirect method generally showed higher flux rates. 

However, the data necessary to complete the flux calculation was limited to Hours 4 – 8 of Day 1 

to Hours 1 – 4 of Day 2 posttreatment as temperature data was not available at any time outside 

of this period. 

Since 602 lbs. a.i./acre was applied and based on the indirect and aerodynamic flux calculations, 

dimethyl disulfide flux accounts for at least 27.64 percent of the applied residue while tarped.

Cantua Creek, CA Clay Loam – Broadcast Shank Injection with Polyethylene Tarp

580 lbs. of 95 percent dimethyl disulfide per acre was broadcast applied by shank injection at 
13 

depth of 12 inches followed by immediate tarping with 1.0 mm plastic material. The tarp was 

cut and removed five days post-application. 

The treated field had dimensions of 660 feet by 660 feet. A total of 24 air samplers were 

symmetrically distributed about radial distances of 100, 150, and 250 feet completely 

surrounding the center of the treated field at 5-feet above ground-level. In addition, there were 

measurements taken from four masts located at the center of the treated field with concentration 

at the 1, 3, 6, and 10 feet levels above ground level, as well as wind and temperature 

measurements at the 1, 3, and 10 feet levels above ground level. Wind speed and direction data 

were also collected at the 20-feet level above ground level as well. 

The field air samples were fortified with 0.2, 1.0, 5.0, 100, and 5,000 μg of dimethyl disulfide. 

On Days 0 - 8 posttreatment, samples were collected every four hours. On Days 9 – 15, samples 

were collected every 12 hours. The average field spike recoveries were 219 percent, 99 percent, 

91 percent, 88 percent, and 77 percent for the 0.2, 1.0, 5.0, 100, and 5,000 μg fortification 

samples, respectively. 

Flux of dimethyl disulfide was back-calculated using monitored off-field concentrations and the 

meteorological data using the ISCST3 model. Flux profiles were developed from the 

comparison of monitored concentrations to modeled concentrations from a unit flux rate of 0.001 

g/m2

s. The relationship between monitored versus modeled concentrations used in the 

determination of the flux was statistically significant for the first 18 sampling periods. 

The total calculated cumulative flux determined by the indirect method was 2,451 μg/m2

s over 

the 72 hour period posttreatment. Temporal peak flux rates of 312 μg/m2s (Day 0, Hours 12 – 

16), 296 μg/m2

s (Day 1, Hours 0 – 4), 268 μg/m2s (Day 1, Hours 8 – 12), 83.0 μg/m2s (Day 1, 

Hours 20 – 24), and 112 μg/m2s (Day 2, Hours 8 – 12) were calculated. 

Flux of dimethyl disulfide was also calculated using the aerodynamic method. This method 

incorporates atmospheric stability along with vertical gradients of temperature, concentration, 

and wind speed using monitored profiled data at four or five height levels at the center of the 

treated field. 

In general, flux rates determined using the aerodynamic method showed a similar general 

temporal trend compared to the indirect method except for the maximum peak of ca. 502 μg/m2

s 

occurred much later between Hours 1 – 4 of Day 2. . The data necessary to complete the flux 

calculation was limited to Hours 8 – 12 of Day 0 to Hours 18 – 24 of Day 2 posttreatment as 

temperature, concentration, and wind data was not available at any time outside of this period.

Since 580 lbs. a.i./acre was applied and based on the indirect and aerodynamic flux calculations, 

the calculated flux accounts for at least 54.29 percent of the applied residue while tarped. 

Bradenton, FL Sand - Shank Injection to Raised Beds with Polyethylene Tarp

633 lbs. of 99 percent dimethyl disulfide per acre was applied to 82 raised beds, with height of 6 
14 

- 8 inches and width of 28 inches, by shallow shank injection at depth of 8 to 10 inches followed 

by immediate tarping with 1.5 – 2.0 mm plastic material. The treated field had dimensions of 

333 feet by 530 feet. The tarp was cut and removed five days post-application. 

A total of 14 air samplers were symmetrically distributed about radial distances of 100, 250, and 

500 ft completely surrounding the center of the treated field at 5-feet above ground-level. In 

addition, there were measurements taken from three masts located at the center of the treated 

field with concentration at the 0.5, 1, 3, 6, and 10 feet levels above ground level, as well as wind 

and temperature measurements at the 1, 3, and 10 feet levels above ground level. 

The field air samples were fortified with 0.2, 1.0, 5.0, 100, and 5,000 μg of dimethyl disulfide. 

On Days 0 - 8 posttreatment, samples were collected every four hours. On Days 9 – 15, samples 

were collected every 12 hours. The average field spike recoveries for all fortifications ranged 

between 78.7 - 92 percent with an overall average recovery of 81.4 percent. 

Flux of dimethyl disulfide was back-calculated using monitored off-field concentrations and the 

meteorological data using the ISCST3 model. Flux profiles were developed from the 

comparison of monitored concentrations to modeled concentrations from a unit flux rate of 0.001 

g/m2

s. The relationship between monitored versus modeled concentrations used in the 

determination of the flux was statistically significant for the first 18 sampling periods. 

The total calculated cumulative flux determined by the indirect method was 2,849 μg/m2s over 

the 48 hour period posttreatment. Temporal peak flux rates of 1,189 μg/m2s (Day 0, Hours 20 – 

24), and 117 μg/m2s (Day 1, Hours 20 – 24) were calculated. 

Flux of dimethyl disulfide was also calculated using the aerodynamic method. This method 

incorporates atmospheric stability along with vertical gradients of temperature, concentration, 

and wind speed using monitored profiled data at four or five height levels at the center of the 

treated field. 

In general, flux rates determined using the aerodynamic method showed a similar temporal trend 

compared to the indirect method. . The data necessary to complete the flux calculation was 

limited to Hours 0 – 4 of Day 1 to Hours 20 -24 of Day 1 posttreatment as temperature and 

concentration data was not available at any time outside of this period.

Since 633 lbs. a.i./acre was applied and based on the indirect and aerodynamic flux calculations, 

the calculated flux accounts for 57.82 percent of the applied residue while tarped.

Dover, FL Loamy Sand - Shank Injection to Raised Beds with Metalized Tarp

608.2 lbs. of 99 percent dimethyl disulfide per acre was applied to 82 raised beds, with height of 

6 - 8 inches and width of 28 inches, by shallow shank injection at depth of 8 to 10 inches 

followed by immediate tarping with 1.5 – 2.0 mm plastic material. The treated field had 

dimensions of 333 feet by 530 feet. The tarp was cut and removed five days post-application. 
15 

A total of 14 air samplers were symmetrically distributed about radial distances of 100, 250, and 

500 ft completely surrounding the center of the treated field at 5-feet above ground-level. In 

addition, there were measurements taken from three masts located at the center of the treated 

field with concentration at the 0.5, 1, 3, 6, and 10 feet levels above ground level, as well as wind 

and temperature measurements at the 1, 3, and 10 feet levels above ground level. 

The field air samples were fortified with 0.2, 1.0, 5.0, 100, and 5,000 μg of dimethyl disulfide. 

On Days 0 - 8 posttreatment, samples were collected every four hours. On Days 9 – 15, samples 

were collected every 12 hours. The average field spike recoveries for all fortifications ranged 

between 78.0 – 94.6 percent with an overall average recovery of 84.1 percent. 

Flux of dimethyl disulfide was back-calculated using monitored off-field concentrations and the 

meteorological data using the ISCST3 model. Flux profiles were developed from the 

comparison of monitored concentrations to modeled concentrations from a unit flux rate of 0.001 

g/m2

s. The relationship between monitored versus modeled concentrations used in the 

determination of the flux was statistically significant for the first 18 sampling periods with the 

exception of the Day 0, Hours 16 – 24 and Day 1, Hours 1 - 4 samples. 

The total calculated cumulative flux determined by the indirect method was 383.53 μg/m2s over 

the 48 hour period posttreatment. Temporal peak flux rates of 128.62 μg/m2s (Day 0, Hours 20 – 

24), and 19.12 μg/m2

s (Day 1, Hours 16 – 20) were calculated. 

Flux of dimethyl disulfide was also calculated using the aerodynamic method. This method 

incorporates atmospheric stability along with vertical gradients of temperature, concentration, 

and wind speed using monitored profiled data at four or five height levels at the center of the 

treated field. 

In general, flux rates determined using the aerodynamic method showed a similar temporal trend 

compared to the indirect method. . The trends between the aerodynamic method and indirect 

method were similar except the absolute maximum occurred 8 hours later during Hours 4 - 8 in 

Day 1, reaching a level of 38.44 μg/m2

s. 

Since 608 lbs. a.i./acre was applied and based on the indirect and aerodynamic flux calculations, 

the calculated flux accounts for 8.1 percent of the applied residue while tarped.
Tifton, GA Loamy Sand (Field 1), Loamy Sand (Field 2), and Sand – Pre-Bedded 

Shank Injection to Raised Beds with HDPE Tarp (Field 1) and LDPE Tarp (Field 2 and 3)

A three-way mixture of containing a co-formulated product (containing 79% DMDS and 21% 

chloropicrin) and the Vapam formulation of Metam Sodium (containing 42% a.i.) was applied to 

three fields. An equivalent of 546.7 lbs. of DMDS was applied to field 1, 538.8 lbs. of DMDS 

was applied to field 2, and 568.9 lbs. DMDS was applied to field 3. The mixture was applied to 

around ~1 acre fields, with 32 - 35 raised beds, with height of 8 inches, followed by immediate 

tarping with Virtually Impermeable Film and on field 1, and Low Density Polyethylene (LDPE) 

tarp on fields 2 and 3. Application times were unknown, but were all expected to occur during 

the afternoon on February 7. The tarp was cut and removed 270 hours post-application. 

The field air samples were fortified with 1.0, 10.0, and 100 μg of dimethyl disulfide. 

Posttreatment samples were collected were collected every five hours through hours 0 – 5, every 

6 hours from hours 5 – 47, every 9 hours from hours 47 – 56, every 12 hours from hours 56 – 

272, every 6 hours from hour 272 – 284, and every 12 hours from hour 284 – 320 hours 

posttreatment for Field 1. Posttreatment samples were collected were collected every five hours 

through hours 0 – 4, every 5 hours from hours 4 – 9, every 6 hours from hours 9 – 45, every 9 

hours from hours 45 – 54, every 12 hours from hours 55 – 270, every 6 hours from hours 270 – 

282, and every 12 hours from hour 282 – 318 hours posttreatment for Field 2. Posttreatment 

samples were collected were collected every two hours through hours 0 – 2, every 4 hours from 

hours 2 – 6, every 6 hours from hours 6 – 42, every 9 hours from hours 42 – 51, every 12 hours 

from hours 51 – 267, every 6 hours from hour 267 – 279, and every 12 hours from hours 279 – 

315 hours posttreatment for Field 3. The average field spike recoveries for all fortifications 

ranged between 58.02 – 176.5 percent with an overall average recovery of 104.8 percent. 

Flux of dimethyl disulfide was back-calculated using monitored off-field concentrations and the 

meteorological data using the ISCST3 model for the first sampling period for Fields 1 and 2 and 

the first two sampling period for Field 3. Flux profiles were developed from the comparison of 

monitored concentrations to modeled concentrations from a unit flux rate of 0.001 g/m2

s. The 

relationship between monitored versus modeled concentrations used in the determination of the 

flux was statistically significant for the first 18 sampling periods with the exception of the Day 0, 

Hours 16 – 24 and Day 1, Hours 1 - 4 samples. 

Flux of dimethyl disulfide was also calculated using the integrated horizontal flux method for the 

remaining sampling periods. This method incorporates measurements of wind speed, 

concentration, and fetch (dependent on wind direction) at four or five height levels. The wind 

speed and concentrations are fit to log-linear regression following the expected Log Law profile 

over the treated field. The flux is solved using the following equation, which integrates the 

components of flux from the surface roughness length height (z0) to the top of the plume height 

(zp): 

= ∑ + +

ZP

Z

i i dzDzLnCBzLnA

x

P

0

))(*(*))(*( 1

16 
where A is the slope of the wind speed regression line from monitoring data by ln(z), B is the 

intercept of the wind speed regression line from monitoring data by ln(z), C is the slope of the 

concentration regression from monitoring data by ln(z), D is the intercept of the concentration 

regression from monitoring data by ln(z), z is the height above ground level. Zp can be 

determined from the following equation: 

 Equation 3 ( )

⎥

⎦

⎤ ⎢

⎣

⎡ − = C

D Z P

1.0

exp

In general, flux rates on Field 1 with VIF tarps applied varied between 3.16 – 54.37 μg/m2

s and 

accounted for 35.2 percent of the amount applied on the field of 546.7 lbs. a.i./A. For Field 2 

with LDPE tarp applied, flux rates were higher and varied between 1.46 – 298.19 μg/m2

s and 

accounted for 68.27 percent of the amount applied. For Field 3 with LDPE tarp applied, flux 

rates were higher than Field 1 but lower than Field 2 and varied between 0.72 – 153.34 μg/m2

s 

and accounted for 37.92 percent of the amount applied.

835.8100 Field Volatility (MRID No. 47377801)

Nominally 98 percent dimethyl disulfide was applied at rates of 378.4 kg a.i./ha, 400.8 kg a.i./ha, 

377.6 kg a.i./ha, and 417.7 kg a.i./ha in Lagosanto, Italy loamy sand soil, Agrofresas, Spain 

sand soil, San Giuseppe, Italy loamy sand soil, and Aldhams Farm sandy silt loam soil, 

respectively over 1 – 1.557 ha fields. In the Lagosanto, Italy study, dimethyl disulfide was 

applied via broadcast shank injection to a depth of 25 to 30 cm. In the Spain study, dimethyl 

disulfide was applied via shank injection to a depth of 25 cm over raised beds. In the San 

Giuseppe, Italy study, dimethyl disulfide was applied via broadcast shank injection to a depth of 

20 cm. In the United Kingdom study, dimethyl disulfide was applied via shank injection to a 

depth of 15 to 20 cm over raised beds. In all fields, tarps classified as Virtually Impermeable 

Film (VIF) by the study author were applied immediately after treatment. 

At all sites, a total of 20 air samplers were symmetrically distributed about radial distances of 25, 

50, and 75 meters completely surrounding the center of the treated field at 1.5 meters above 

ground-level. Meteorological data consisted of air temperature, rainfall, wind speed, and wind 

direction (heights above ground level unspecified). All air and meteorological monitoring data 

was collected up to 10 days posttreatment. Tarps were cut and removed 8 days posttreatment. 

This study is classified as Supplemental. The necessary meteorological data of solar radiation 

was not provided. Given the study design using off-field air monitors, solar radiation is 

necessary to determine the Pasquill-Gifford Stability Class turbulence parameterization in order 

to back-calculate dimethyl disulfide emissions over time using the ISCST3 dispersion model. In 

addition, the application rates were lower than the maximum labeled application rate in all of the 

studies. 

835.1710, 850.1730, 850.1850 Aquatic Organisms – Bioavailability, Biomagnification, and 

17 
18 

Toxicity 

WSKOW version 1.4 calculates log Kow of dimethyl disulfide to be 1.77. Furthermore, Hansch, 

C. et al., 1995 experimentally determined that dimethyl disulfide possesses a log Kow of 1.87. 

Partitioning of dimethyl disulfide residues to tissue is not a concern with these properties. 

Therefore, this study is waived.

835.6100 Terrestrial Field Dissipation 

This study is waived since the all proposed labels require immediate tarping after application. 

The traditional terrestrial field study guideline requires residues of the test substance to be 

extracted immediately following its application. This study procedure will not be representative 

of real-world conditions as the tarp will have to be punctured in order to collect and extract the 

samples. 

Volatility of Dimethyl Disulfide in Aqueous Media (MRID #47307501) 

In this non-guideline study, 1,000 ppm of diemthyl disulfide was applied in duplicate to samples 

of fresh water (tap water) and salt water, prepared by dissolving 33 g of Crystal Sea Marinemix 

in 1 liter of MilliQ water. Dimethyl disulfide samples were then extracted directly and analyzed 

by HPLC at 0, 15, 30, 60, 120, 240, and 1,200 minutes posttapplication. In all samples, dimethyl 

disulfide was undetected by 20 hours posttapplication. The study author states accordingly that 

the residues of dimethyl disulfide remained unstable overtime. 

Several factors indicating the fate of dimethyl disulfide in water are inconclusive from this study. 

The dissipation and degradation routes of dimethyl disulfide in this study are unclear. Due to the 

volatile nature of dimethyl disulfide, volatile trapping solutions (not mentioned in the study 

report) may account for a portion of the material balance. In addition, it was not stated whether 

the study was conducted in darkness. As indicated by, “Dimethyl disulfide photolysis in the 

environment”, (MRID No. 47052818), aqueous photolysis along with volatilization can both be 

significant pathways contributing to the unstable trend in dimethyl disulfide observed in this 

study. Furthermore, the lack of sterility by the usage of tap water and possibly the sea water 

(sterility not verified) suggests that additives in the water samples may lead to chemical reactions 

and subsequent formation of degradates (detections also not attempted in the determination of 

the overall material balance) which may not occur in the natural environment. 

Exposure Assessment of Dimethyldisulfide Movement to Ground Water and Surface Water 

Associated with Shank Injection and Drip Irrigation on Agricultural Crops (MRID# 

47307502)
19 

The registrant conducted an independent assessment on aquatic exposure using the EXPRESS 

shell (version1.00.00.00 – January 2005) to execute PRZM and EXAMS. The study report 

shows estimates of dimethyl disulfide residue concentrations in surface water (Georgia Farm 

Pond). Dimethyl disulfide residue loadings are compartmentalized by erosion, runoff, leaching, 

degradation, soil storage, and volatilization elements. The exposure modeling was conducted at 

application rates of 100, 200, 375, and 600 kg/ha for drip irrigation (soil incorporation depth of 5 

cm) and shank injection (soil incorporation depth of 20 cm) management practices. The study 

author conducted the exposure assessment with the California onion, California tomato, Florida 

strawberry, Florida tomato, North Carolina sweet potato, and North Carolina tobacco PRZM 

crop scenarios. 

This study was not considered in this risk assessment for the following reasons: 

• The current approved version of EXPRESS is 1.03.02 (July 2007). The earlier version of 

EXPRESS possessed known errors in the way data from the PRZM and EXAMS 

environment were imported. Therefore, the results from utilizing the version of 

EXPRESS presented in the study author’s assessment may not be consistent with actual 

PRZM/EXAMS modeling results. 

• The versions of PRZM and EXAMS for which simulations are conducted are not stated 

by the study author. Revisions to numerous algorithms have been incorporated into the 

current approved version of PRZM (Version 3.12.3 – June 2006) and EXAMS (Version 

2.98.04.06 – April 2005). 

• Numerous additional crop scenarios are available to be considered in the current version 

of PRZM based on the proposed label uses.