Appendix H Summary of Toxicity Studies For DMDS 

Birds

 The effect of DMDS on the Bobwhite quail (Colinus virginianus) is used to represent 

the effect for all birds, as well as reptiles and terrestrial-phase amphibians. Two acute 

avian studies were received, one for acute oral and one for acute inhalation. The 

Bobwhite (Colinus virginianus) acute oral LD50=314 mg/kg (250.2-403.0mg/kg) (MRID 

470528-13) was classified as acceptable. The acute oral study will not be used in the 

assessment because no dietary exposure is expected. 

 The acute oral toxicity of DMDS to 31-wk-old Northern Bobwhite quail (Colinus 

virginianus) was assessed over 21 days. DMDS was administered to the birds by 

lubricating an appropriately dosed gelatin capsule and orally inserting directly into the 

crop at nominal doses of 0 (negative control), 37, 62, 104, 172, 287, 496 and 798 mg 

ai/kg bw. The 21 day-acute oral LD50 was 314 mg ai/kg bw. The 21 day NOAEL of 

DMDS to the Northern Bobwhites (Colinus virginianus), based on a 17% reduction in 

mean male feed consumption was 104 mg ai/kg bw. According to the US EPA 

classification, DMDS would be classified as moderately toxic to Northern Bobwhites 

(Colinus virginianus) on an acute oral basis. 

 By test termination, mortality was 0% in the control and 0, 0, 0, 10, 40, 80 and 100% 

in the nominal 37, 62, 104, 172, 287, 496 and 798 mg ai/kg bw, respectively. There were 

treatment-related reductions in body weight change and mean feed consumption in the 

172-496 mg ai/kg bw treatment groups. The following symptoms of toxicity were noted: 

ruffled appearance, lesions, reduced reaction to external stimuli (sound and movement), 

wing droop, loss of coordination, lower limb weakness, loss of righting reflex, prostrate 

posture and anorexia. 

 Gross necropsy results revealed hemorrhaging of the lungs, discolored kidneys, lungs 

and spleens and a gelatinous film covering the surface of the crop, which appeared to be 

opaque. 

In an acute inhalation toxicity study, 16- to 17-week old northern bobwhite quail 

(five per sex; 181-220 g) were exposed by whole-body inhalation to DMDS (purity 

≥98.53%) for 4 hours at analytically-determined concentrations of 0 (control), 304, 402, 

504, 608, and 1512 ppm (equivalent to 0, 1.17, 1.55, 1.94, 2.34, and 5.82 mg ai/L, 

respectively). The animals were observed for up to 14 days post-exposure then subjected 

to gross pathological examination. 

At the control, 304, 402, 504, 608, and 1512 ppm levels, cumulative mortality 

was 0, 0, 1, 2, 4, and 5 for males, 0, 0, 1, 4, 5, and 5 for females, and 0, 0, 2, 6, 9, and 10 

for combined sexes, respectively. Except for a single male from the 608 ppm exposure 

level that was euthanized in extremis on day 5, all mortality occurred during the exposure 

period. The 4-hour LC50 (with 95% C.I.) was 512 (420-625) ppm for males, 449 (403-

501) ppm for females, and 478 (426-536) ppm for combined sexes. 
Clinical signs of toxicity were observed in birds from the ≥402 ppm levels during 

and immediately following exposure; effects included impaired equilibrium, prostration, 

gasping, hyperactivity, convulsions, twitching, labored respiration, and increased 

respiration. Surviving birds from the 402 ppm level completely recovered by day 2, but 

effects (impaired equilibrium, labored respiration, and/or white material on the anogenital 

or right leg areas) persisted in survivors from the 504 and 608 ppm levels through 14 

days. 

No treatment-related effects on body weight changes or food consumption were 

observed, and there were no remarkable findings at necropsy. 

Fish

 Fish are represented by a warm-water species and a cold-water species. An 

acceptable acute Zebra fish (Danio rerio) study resulted in an LC50=7.50mg/L (MRID 

470528-15). However, this was not the most sensitive reported endpoint. In a 96-h acute 

toxicity study, Zebrafish (Danio rerio) were exposed to DMDS at initial measured 

concentrations of <0.010 (<LOQ; control), 5.30, 10.6, 22.3, 40.2 and 89.1 mg ai/L under 

static-renewal conditions; nominal concentrations were 0 (negative control), 6.25, 12.5, 

25, 50 and 100 mg/L. The 96-h LC50 was 7.50 mg ai/L. The NOAEC value, based on 

mortality and sub-lethal effects, was 5.30 mg ai/L. Sub-lethal effects (i.e., lethargy, fish 

lying on the side, missing escape reflex, fish lying on abdomen and hyperventilation) 

were observed in the groups exposed to initial measured concentrations of 10.6, 22.3 and 

40.2 mg ai/L of DMDS. Based on the results of this study, DMDS would be classified 

as moderately toxic to Zebrafish (Danio rerio) in accordance with the classification 

system of the U.S. EPA. 

 An acceptable acute Rainbow trout (Oncorhynchus mykiss) study (MRID 470528-

14) resulted in an LC50=0.96 mg/L that will be used in this assessment. In a 96-h acute 

toxicity study, Rainbow Trout (Oncorhynchus mykiss) were exposed to DMDS at initial 

measured concentrations of <0.010 (<LOQ; control), 0.303, 0.563, 1.36, 3.44 and 7.55 

mg ai/L under static-renewal conditions; nominal concentrations were 0 (negative 

control), 0.625, 1.25, 2.5, 5 and 10 mg/L. The 96-h LC50 was 0.960 mg ai/L. The 

NOAEC value, based on mortality and sub-lethal effects, was 0.563 mg ai/L. Sub-lethal 

effects (i.e., lethargy, staggering, slow escape reflex, missing escape reflex, lying on the 

bottom of the test vessel and hyperventilation) were observed in the groups exposed to 

initial measured concentrations of 1.36, 3.44 and 7.55 mg ai/L. Based on the results of 

this study, DMDS would be classified as highly toxic to Rainbow Trout in accordance 

with the classification system of the U.S. EPA. 

Aquatic Invertebrates

 The 48-hour acute toxicity of DMDS to Daphnia magna was studied under staticrenewal conditions. Daphnids were exposed to nominal concentrations of 0 (negative 

control), 0.970, 2.13, 4.70, 10.3, 22.7, and 50 mg/L. Mortality and sub-lethal effects 

were observed daily. There was no control mortality over the 48h test period. The 48-
hour LC50/EC50 was 1.61 mg ai/L. The 48-hr NOAEC based on immobility was 0.621 mg 

ai/L. With the exception of immobility, no other biological effects were reported. 

Estuarine/marine fish

 In an acceptable 96-h acute toxicity study (MRID 473075-04), Sheepshead Minnow 

(Cyprinodon variegates) were exposed to DMDS at nominal concentrations of 0 

(negative control), 2.6, 4.3, 7.2, 12 and 20 mg a.i./L under static renewal conditions. The 

mean measured concentrations were <2.00 (<LOQ; negative control), 2.3, 4.0, 6.9, 10 

and 18 mg a.i./L . The 96-h LC50 (95% C.I.) was 5.6 (4.0-6.9) mg a.i/L. The NOAEC 

value was <2.3 mg a.i/L, based on sub-lethal effects observed at all levels; the EC50 was 

determined to be 3.7 (2.3-6.9) mg a.i./L, based on sub-lethal effects. 

 Cumulative mortality was 0% in the negative control, 2.3 and 4.0 mg a.i./L 

treatment groups. Cumulative mortality was 90% in the 6.9 mg a.i./L treatment group, 

and 100% in the 10 and 18 mg a.i./L treatment groups. Based on the results of this study, 

dimethyl disulfide would be classified as moderately toxic to Sheepshead Minnow 

(Cyprinodon variegatus) on an acute toxicity basis in accordance with the classification 

system of the U.S. EPA. 

 Signs of toxicity (lethargy, loss of equilibrium, lying on the bottom and surfacing) 

were observed during the test and were considered treatment related in all treatment 

groups. There were no sub-lethal effects observed in the control treatment group. Sublethal effects were noted in all subsequent treatment levels. Loss of equilibrium was 

observed in the 2.3 mg a.i./L treatment group at 72 hours. Loss of equilibrium was 

observed in the 4.0 mg a.i./L treatment group at 1.5, 24, 48, 72 and 96 hours. Surfacing 

and lying on the bottom was also observed in the 4.0 mg a.i./L treatment group at 72 

hours. Surfacing and lethargy was additionally noted in the 4.0 mg a.i./L treatment group 

at 96 hours. Loss of equilibrium was observed in the 6.9 mg a.i./L treatment group at 48 

and 72 hours. Lying on the bottom was also observed in the 6.9 mg a.i./L treatment group 

at 72 hours. Lethargy was additionally observed in the 6.9 mg a.i./L treatment group at 96 

hours. Surfacing was observed in the 10 mg a.i./L treatment group at 24 hours. Lying on 

the bottom was noted in the 10 mg a.i./L treatment group at 48 hours. 

Estuarine/marine invertebrates

 The effect of DMDS on marine invertebrates is represented by the mysid. An 

acceptable acute mysid toxicity test resulted in an LC50=4.9mg/L (3.9-6.1) (MRID 

473075-05). A NOEAC =2.5mg/L was also reported. Based on the LC50 in this study 

(4.9 mg ai/L), dimethyl disulfide would be categorized as moderately toxic to mysid 

shrimp on an acute toxicity basis. This value will be used in the assessment. 

A 96h static renewal test was conducted with juveniles <24h old. Nominal 

concentrations were 0 (negative control), 1.1, 2.3, 4.5, 9.0 and 18 mg ai/L. Mean 

measured concentrations were <0.5, 1.1, 2.5, 4.3, 10.0, and 19 mg a.i./L. Twenty 

organisms per treatment level were used. There was no control mortality. 
Terrestrial Plants

 The effect of DMDS on the vegetative vigor of monocot (corn, Zea mays; onion, 

Allium cepa; oat, Avena sativa; and ryegrass, Lolium perenne) and dicot (cabbage, 

Brassica oleracea; soybean, Glycine max; sugarbeet, Beta vulgaris; lettuce, Lactuca 

sativa; tomato, Lycopersicon esculentum; and radish, Rapahnus sativus) crops was 

studied at nominal concentrations of 18.8, 37.5, 75, 150, and 300 lbs a.i./A. 

 This study was conducted in a greenhouse. The controls and treatments were covered 

with plastic to retain the DMDS gas. After application, the plants were set outside to 

reduce cross contamination. The plastic was cut within 48h and the plants returned inside 

the greenhouse. On Day 21 the surviving plants per pot were recorded, cut, and dried for 

measuring the plant dry weight. Plant height was measured on days 7, 14, and 21 by 

measuring from the soil surface to the tip of the apical meristem or tip of the tallest leaf. 

No measured concentrations were made for this study. Therefore, nominal 

concentrations were used in the analysis. The highest application rate used in the study 

was 300lb/A. This is below the proposed application rate of 455lb/A. The most sensitive 

dicot for both height and weight was tomato. An acceptable study resulted in an EC25=82 

lbs/A for dry weight and an EC25=55 lbs/A for height. The tomato EC25 value for height 

will be used in this assessment. The NOAEC=37.5lb/A for tomato. 

The study authors used a standard phytotoxicity rating system. There were cases of 

necrosis, leaf curl, adventitious growth, mortality, and chlorosis across all species and 

most concentrations; there were generally less effects observed at the two lowest 

treatment levels. 

Terrestrial Invertebrates 

 The effect of DMDS on terrestrial invertebrates is represented by the Honey bee 

(Apis mellifera). The young adult worker bees were exposed for 48h. This acceptable 

study resulted in an LD50>100μg/bee (MRID 474712-03). This classifies DMDS as 

practically nontoxic to bees. This value will be used in the assessment. 

Aquatic Plants 

 The effect of DMDS on vascular plants is represented by toxicity results for 

Lemna. An acceptable study resulted in a Frond EC50 =28mg/L. In a 7-day acceptable 

toxicity study (MRID 474712-04), the freshwater floating aquatic vascular plants 

Duckweed (Lemna gibba) were exposed to dimethyl disulfide at nominal concentrations 

of 0 (negative control), 3.1, 6.3, 13, 25, 50, and 100 mg a.i./L under static renewal 

conditions. Time-weighted average concentrations were <2.00 (<LOQ, control), 3.2, 5.6, 

12, 24, 48, and 95 mg a.i./L. 
 The 7-Day NOAEC and EC50 values for frond density, the most sensitive endpoint, 

were 3.2 and 28 mg a.i./L, respectively. The % growth inhibition in frond density, in the 

treated algal culture as compared to the negative control, ranged from 2.6 to 86%. 

 Chlorosis was observed at all treatment levels and was more widespread in the 

highest two treatment levels. Necrosis was observed in all treatment levels except the 

lowest test concentration, and was more prevalent in the three highest treatment levels. 

Mortality was mostly observed at the highest treatment level. 

 There were also three freshwater nonvascular aquatic plant studies received. An 

acceptable study (MRID 474712-05) for the freshwater algae (Anabaena flos-aquae) 

resulted in a NOAEC <0.17mg/L and a 96h EC50=0.32mg/L (0.11-0.90 mg/L) for cell 

density. 

 In a 96-hour acute toxicity study, cultures of the freshwater blue-green algae 

Anabaena flos-aquae were exposed to Dimethyl Disulfide at nominal concentrations of 0 

(negative control), 0.15, 0.38, 0.96, 2.4, 6.0, and 15 mg a.i./L under static conditions. 

Mean-measured concentrations were <0.100 (<LOQ; control), 0.17, 0.34, 0.80, 1.9, 5.5, 

and 14 mg a.i./L. 

 The % growth inhibition in cell density, in the treated algal culture as compared to the 

negative control, ranged from 36 to 98%. The % growth inhibition in biomass, in the 

treated algal culture as compared to the negative control, ranged from 13 to 94%. The % 

growth inhibition in growth rate, in the treated algal culture as compared to the negative 

control, ranged from 9.5 to 72%. 

There was no adherence to cells to any of the test chambers and aggregations 

were not observed in any of the treatment groups. Enlarged cells were observed at the 

three highest test concentrations. 

 The other two freshwater nonvascular plant studies were for one freshwater diatom 

and one freshwater alga. An acceptable nonvascular aquatic plant study (MRID 474712-

06) for the freshwater diatom (Navicula pelliculosa) resulted in an EC50=22 mg/L (20-23 

mg/L) for biomass. In a 96-hour acute toxicity study, cultures of the freshwater diatom 

Navicula pelliculosa were exposed to Dimethyl Disulfide at nominal concentrations of 0 

(negative control), 2.3, 3.9, 6.5, 11, 18, and 30 mg a.i./L under static conditions. Initialmeasured concentrations were <1.00 (<LOQ; control), 2.76, 5.10, 7.05, 11.9, 18.8, and 

32.4 mg a.i./L. 

 The % growth inhibition in cell density, in the treated algal culture as compared to the 

negative control, ranged from -54 to -88% in the first five treatment levels, and was 94% 

at the highest treatment level. The % growth inhibition in biomass, in the treated algal 

culture as compared to the negative control, ranged from -28 to -32% in the first four 

treatment groups, and was 8.2 to 96% in the highest two treatment groups. The % growth 

inhibition in growth rate, in the treated algal culture as compared to the negative control, 

ranged from -10 to -14% in all but the highest treatment group, which was 63%. 
 A study (MRID 474712-07) received for the green algae (Pseudokirchneriella 

subcapitata) was classified as supplemental and will only be used as a Tier I study 

(MRID 470528-17). 

 In a 72-hour acute toxicity study, cultures of Pseudokirchneriella subcapitata were 

exposed to DMDS at serial dilution factors of 1:16, 1:8, 1:4, 1:2 and 1:1 of an initial 100 

mg/L stock solution under static conditions; a negative control was also included. The 

measured values at 0-hours were 5.73, 11.6, 21.9, 44.0 and 86.7 mg ai/L. The measured 

values at 72-hours were <LOQ, 7.2, 19.2, 39.8 and 78.9 mg ai/L. A mean measured 

concentration could not be determined for the 1:16 dilution factor and the mean measured 

concentrations for the serial dilutions of 1:8, 1:4, 1:2 and 1:1 were 9.40, 20.6, 41.9 and 

82.8 mg ai/L, respectively. The NOAEC and EC50/IC50 values based on cell density were 

5.73 and 17 mg ai/L, respectively. The % growth inhibition, based on cell densities at 72 

hours, in the treated algal culture as compared to the control ranged from -5 to 99%. 

Biomass was the most sensitive endpoint, with an EC50 of 15 mg ai/L; the NOAEC (and 

EC05) for biomass was lower than the lowest treatment level (i.e., 5.73 mg ai/L), which 

inhibited growth 10%, relative to the control. 

 Cells in the 44.0 and 86.7 mg ai/L treatment groups were observed to be enlarged. 

No major pH shifts were observed. 

In addition to the freshwater aquatic plant studies an estuarine/marine diatom 

study (MRID 474712-07) was classified as acceptable. This study with Skeletonema

costatum resulted in a biomass EC50=1.2 mg/L (0.55-2.6 mg/L). 

 

 In a 96-hour acute toxicity study, cultures of the marine diatom Skeletonema costatum

were exposed to Dimethyl Disulfide at nominal concentrations of 0 (negative control), 

0.58, 1.3, 2.8, 6.2, 14, and 30 mg a.i./L under static conditions. Mean-measured 

concentrations were <0.300 (<LOQ; control), 0.48, 0.95, 2.6, 5.7, 12, and 27 mg a.i./L. 

 The % growth inhibition in cell density, in the treated algal culture as compared to the 

negative control, ranged from 22 to 98%. The % growth inhibition in biomass, in the 

treated algal culture as compared to the negative control, ranged from 29 to 96%. The % 

growth inhibition in growth rate, in the treated algal culture as compared to the negative 

control, ranged from 5.8 to 94%. 

 The most sensitive endpoint was biomass, with NOAEC and EC50 values of <0.48 

and 1.2 mg a.i./L, respectively. 

There was no aggregation/flocculation of algae in the control or treatment groups. 

Adherence of cells to the test chambers was observed in the negative control and the first 

three test concentrations.