UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION

September 11, 2015

MEMORANDUM

SUBJECT: PC Code: 900177; Dimethyl Sulfoxide; Human Health Risk Assessment 

and Ecological Effects Assessment to Support Proposed Exemption from 

the Requirement of a Tolerance When Used as Inert Ingredients in 

Pesticide Formulations.

All PC Code: 900177 DP Barcode: N/A 

Decision No.: N/A Regulatory Action: Inert 

Tolerance Exemption; 40 

CFR 180.920.

Petition No: IN-10713 All CAS Reg. No: 67-68-

5

Inert Tracking No: N/A

FROM: Lisa Austin, Ph.D., Toxicologist

Chemistry, Inerts and Toxicology Assessment Branch (CITAB)

Registration Division (7505P)

THROUGH: Kerry Leifer, Team Leader

Chemistry, Inerts and Toxicology Assessment Branch (CITAB)
2

Registration Division (7505P)

TO: PV Shah, Ph.D., Branch Chief

Chemistry, Inerts and Toxicology Assessment Branch (CITAB)

Registration Division (7505P)

EXECUTIVE SUMMARY

EPA received a petition (PP#IN-10713) from ISK BioSciences (7470 Auburn Rd., Suite A, 

Concorde, OH 44077), requesting that 40 CFR 180.920 be amended by modifying the exemption 

from the requirement of a tolerance for residues of dimethyl sulfoxide (here in referred to 

DMSO, CAS Reg. No. 67-68-5) in cyclaniliprole formulations for pre-harvest applications 

including post-emergence use. DMSO will be used as a diluent in cyclaniliprole formulations 

(60.02% (w/w) with upper and lower limits of 61.82% and 58.22%, respectively) under 40 CFR 

part 180.920. DMSO has an existing tolerance exemption for use as a pesticidal inert under 40 

CFR 180.920 as a solvent or co-solvent for formulations used before crop emerges from soil or 

prior to formation of edible parts of food plants (EPA, 2006). EPA published the notice of filing 

(NOF) for this petition in the Federal Register on March 4, 2015 (80 FR 11611). No comments 

were received in response to this notice.

The following documents are available on DMSO: the IUCLID summary (2003) and the 

OECD SIDS document (2000). The Agency reassessed DMSO in 2006. As no new data were

submitted the agency relied primarily on and reproduced data from these documents and 

previous assessment. Below is a summary of the critical studies that comprise the toxicity

profile of DMSO. For more details on all available toxicity studies please refer to the 

aforementioned documents included in MRID 49388701.

DMSO has low acute toxicity via the oral and dermal routes in rats and mice and the 

inhalation route in rats. The acute oral LD50 > 7,920 mg/kg in rats and mice. The acute dermal 

LD50 > 40,000 mg/kg in rats and mice. The acute inhalation LC50 > 1600 mg/m3(equivalent to

277 mg/kg) in rats. It is a dermal, eye and gastric irritant in rats and rabbits. It is a sensitizer in 

guinea pigs. 
3

Overall systemic toxicity with regard to DMSO is low. The target organ of toxicity is the 

eye. Changes in the lens of the eyes such as refractile changes in the lens and lens composition 

is seen in various animals at doses above the limit dose (1000 mg/kg/day).

Subchronic and chronic toxicity studies were available in the rat, rabbit and dog. In 

subchronic studies in dogs and rabbits, eye effects were observed at > 2,500 mg/kg/day

following up to 24 weeks of DMSO treatment. In chronic oral toxicity studies in the dog, and 

rabbit, toxicity was manifested as decreased body-weight gain and/or changes in the refractive 

index of the nuclear region in the eye at doses > 1 mL/kg/day (1100 mg/kg/day). 

Reproduction/developmental toxicity studies were available for review. In the rat, neither 

maternal nor fetal effects were observed up to 1000 mg/kg/day, the limit dose. Maternal 

(decreased bodyweight gain and food consumption) and fetal (decreased fetal body weight and 

delayed rib ossification) effects were observed at 5000 mg/kg/day (5 times the limit dose). 

Reproduction was also not effected up to 1000 mg/kg/day. In rabbits, maternal toxicity was 

manifested as reduced food consumption and body weight gain at 1000 mg/kg/day. The no 

observable adverse effect level (NOAEL) was 300 mg/kg/day. Developmental toxicity was not 

observed up to 1000 mg/kg/day.

Classical carcinogenicity studies with DMSO were not available. However, cancer 

initiation/promotion studies are available and were used to ascertain the cancer potential of 

DMSO. In a study in rats, DMSO (50 ppm, equivalent to 5 mg/kg/day) in the drinking water did 

not affect the latency or frequency of tumors induced by 7,12-dimethylbenz[a] anthracene 

(DMBA), a known carcinogen. In an initiation-promotion study in mice, DMSO (0.1 mL) didn’t 

induce skin tumors following a single dermal application of DMBA. Also, tumors were not 

observed in rats when DMSO (0.02 mL) was applied dermally. 

There are mixed results in mutagenicity studies available with DMSO, but the weight of 

evidence showed no genotoxic risk from exposure to DMSO. 

Dermal toxicity studies were available in the rabbit and dog. In subchronic and chronic 

toxicity studies with rabbits and dogs, lenticular changes were observed at doses 1.1 g/kg/day

(1100 mg/kg/day). 

In toxicity studies with rats via the inhalation route of exposure, systemic toxicity was not 

observed at doses up to 0.964 mg/L (equivalent to 250 mg/kg/day). The lowest observed adverse 

concentration (LOAEC) was 2.783 mg/1 (equivalent to 722 mg/kg/day) based on respiratory

tract irritation. 
4

Neurotoxicity studies were not available for review, however, evidence of potential 

neurotoxicity was not observed in the submitted studies. In addition, functional observation 

battery parameters were not affected following inhalation exposure in rats for 13 weeks.

An immunotoxicity study with DMSO was available for review. DMSO administered via the 

inhalation route of exposure caused an increase in the number of antibody secreting cells in male 

rats at concentrations > 0.310 mg/L (equivalent to 80 mg/kg/day). However, this effect is not 

considered adverse. In mice, 5% DMSO (equivalent to 27,000-52,000 mg/kg/day) administered 

in the drinking water for 6 weeks caused did not cause immunotoxicity. 

In the rat and monkey, DMSO administered via the oral and/or dermal route was rapidly

absorbed, metabolized and excreted. Excretion was primarily via urine, feces was a minor route

in the rat only. The major metabolite was dimethyl sulfone. Dimethyl sulfide, another 

metabolite, is eliminated through the breath. There was no bioaccumulation. 

EPA has determined that reliable data show the safety of infants and children would be 

adequately protected if the FQPA SF were reduced to 1X.

Available toxicity data on DMSO demonstrated no adverse effects at doses less than 1,100 

mg/kg/day. Therefore, since there are no endpoints of concern for DMSO a qualitative dietary

exposure risk assessment is appropriate.

DMSO is used as an inert ingredient in pesticide products that could result in residential 

exposure. However, based on the lack of toxicity, a quantitative exposure assessment from 

“residential exposures” was not performed.

The Agency believes that establishing the tolerance exemption to include 40 CFR § 180.920 

in a cyclaniliprole formulations will not significantly/measurably increase occupational 

exposure. The change in use pattern would be expanded to include post-emergence use in 

pesticide products on all pre-harvest food commodities. Based on the regulatory history of 

DMSO and no new toxicological information to indicate otherwise, it is not necessary to 

quantitatively assess occupational exposure.
5

DMSO has low toxicity to aquatic organisms. Also, it is not expected to be toxic to 

mammals. It is not expected to persist in the environment and does not bioaccumulate. It is 

biodegradable.

Potential areas of environmental justice concerns, to the extent possible, were considered in 

this human health risk assessment, in accordance with U.S. Executive Order 12898, "Federal 

Actions to Address Environmental Justice in Minority Populations and Low-Income 

Populations," http://www.eh.doe.gov/oepa/guidance/justice/eo12898.pdf. 

Taking into consideration all available information on DMSO (CAS Reg. No. 67-68-5), EPA 

concludes that there is a reasonable certainty that no harm will result to the general population or 

to infants and children from aggregate exposure to DMSO. Therefore, the establishment of an 

exemption from tolerance under 40 CFR 180.920 for residues of DMSO for use as an inert 

ingredient (diluent) at a level not to exceed 62% in pesticide formulations used before crop 

emerges from soil or prior to formation of edible parts of food plants; for pesticide formulations 

used after crop emerges but before harvest, provided that the potential for increased residues of 

the formulation’s active ingredient(s) in or on food commodities has been assessed, can be 

considered safe under section 408 of the FFDCA.

2. BACKGROUND

On May 14, 2014 ISK BioSciences (7470 Auburn Rd., Suite A, Concorde, OH 44077), 

submitted a petition (IN-10713) requesting that 40 CFR 180.920 be amended by modifying the 

exemption from the requirement of a tolerance for residues of DMSO (CAS Reg. No. 67-68-5) in 

cyclaniliprole formulations for pre-harvest applications including post-emergence use. DMSO 

will be used as a diluent in cyclaniliprole formulations (60.02% (w/w) with upper and lower 

limits of 61.82% and 58.22%, respectively) under 40 CFR part 180.920. EPA published the 

notice of filing (NOF) for this petition in the Federal Register on March 4, 2015 (80 FR 11611). 

No comments were received in response to this notice. 

Currently, DMSO has an existing tolerance exemption for use as a pesticidal inert under 40 

CFR 180.920 as a solvent or co-solvent for formulations used before crop emerges from soil or 

prior to formation of edible parts of food plants (EPA, 2006).
6

This document provides an assessment of the risk to human health and the environment for 

DMSO when used as an inert ingredient in pesticide formulations applied pre-harvest to 

agricultural commodities.

3. PHYSICAL AND CHEMICAL PROPERTIES

DMSO was previously reassessed in 2006 by the agency. The following physical and 

chemical properties were reproduced from the reassessment document.

Table 1. Physical and Chemical Properties of DMSO

Parameter Value Source

Structure

EPA Inert Reassessment: One 

Exemption from the Requirement 

of a Tolerance for Dimethyl 

sulfoxide (CAS Reg. No. 67-98-5)

(2006)(MRID 49388701)

Chemical Name Dimethyl Sulfoxide

CAS # 67-68-5

Molecular Weight (g/mol) 78.13

Common Names

Delton, Demasorb, Dimexide, Domoso,

Methyl sulfoxide, Methyl sulfinylmethane

Physical State Practically colorless liquid or crystals

Melting Point (°C) 18.5

Boiling Point (°C) 189

Vapor Pressure (mm Hg @ 25 

°C)

0.61

Partition Coefficient ( Log Kow) -1.35

Water Solubility (mg/L at 25C) 1.0x106

;Miscible

Henry's Law Constant (atm

m

3

/mol at 25 C) 1.51 x10-9
7

4. Hazard Assessment

The Agency reassessed DMSO in 2006. The following toxicity data are reproduced from 

that document (MRID 49388701). Toxicity data are also reproduced from the IUCLID summary

and OECD SIDS (MRID 49388701).

Acute Toxicity Studies

Table 2. Acute Toxicity Profile of DMSO

Study Type Results

Acute Oral – Rat LD50 = 14.5-28.3 g/kg

(14,000-28,300 mg/kg)

Acute Oral – Mouse LD50 = 16.5-21. 4 g/kg

(16,500-21,400 mg/kg)

Acute Oral – Rat LD50 >20 mL/kg

Acute Oral – Mouse LD50 =20 mL/kg

Acute Oral – Rat LD50 >15 mg/kg (50% DMSO)

Acute Oral – Mouse LD50 >14 mg/kg (50% DMSO)

Acute Oral – Mouse LD50 = 21400 mg/kg

Acute Oral – Mouse LD50 = 7920 mg/kg

Acute Dermal – Rat 40-50 g/kg

(40,000-50,000 mg/kg)

Acute Dermal – Mouse 40 g/kg

(40,000 mg/kg)
8

Study Type Results

Acute Inhalation - Rat Mild pulmonary irritation (edema)

1600 mg/m3 (equivalent to 277 mg/kg) (4 hr)

2900 mg/m3 (equivalent to 3008 mg/kg) (24 hr)

2000 mg/m3 (equivalent to 3458 mg/kg) (40 hr)

Eye Irritation-Rabbit Slight conjunctivitis at 24-hour

observation period; cleared by 48 hours

Eye Irritation-Rabbit Undiluted; no effects

Eye Irritation-Rabbit Slight erythema

Sensitization-Guinea pig Not a sensitizer 

Acute Oral Toxicity

DMSO administered orally is of low acute toxicity to rats and mice. After massive single 

doses, experimental animals exhibited rapid breathing, restlessness, and coma, leading to 

hypothermia and death within a few hours (Gosselin, e tal., 1984 as cited in MRID 49388701). 

Administration of pure DMSO (100%) resulted in serious and rapid modification of the red 

blood cells, along with "certain coagulation defects" (Caujolle, et al., 1967 as cited in MRID 

49388701). Lethal oral doses caused ataxia, myasthenia, decreased motor activity, and 

bradypnea shortly after administration (Wilson, et al., 1965 as cited in MRID 49388701). Nonlethal oral doses produced only decreased motor activity, although polydipsia and polyuria were 

noted in rats following doses of 20 g/kg (equivalent to 20,000 mg/kg). Hyperemia and 

inflammation in the eyes of Sprague-Dawley rats were observed following single oral doses of 

>13 g/kg (equivalent to 13,000 mg/kg) DMSO (MRID 49388701).

Acute Dermal Toxicity

DMSO is of low acute toxicity by the dermal route. Studies have demonstrated that DMSO 

is a skin irritant when used in sufficiently high or multiple doses, but it is not a serious eye 

irritant. (Fishman, 1969as cited in MRID 49388701).
9

Acute Inhalation Toxicity

In a study conducted by Fishman et. al., Sprague-Dawley rats were exposed to DMSO at 

concentrations of approximately2900 mg/m3(equivalent to 3008 mg/kg) for 24 hours, 2000 

mg/m3(equivalent to 3458 mg/kg) for 40 hours, or 1600 mg/m3 (equivalent to 277 mg/kg) for 4 

hours. Others were exposed to 200 mg/m37 hours a day, 5 days a week for a total of 30 

exposures. Mild pulmonary irritation was observed at >1600 mg/m3. The LC50 > 1600 mg/m3

(Fishman, 1969 as cited in MRID 49388701).

Sensitization

DMSO did not induce skin sensitization in guinea pigs using the Buehler test (Marzulli and

Maguire, 1982), the Magnusson and Kligman maximization method (Marzulli and Maguire, 

1982; Nakamura et al., 1994) and the Draize test, the Cyclophophamide/CFA assay and the Split 

adjuvant test (Marzulli and Maguire, 1982)(As cited in MRID 49388701).

Repeated Dose Studies

Subchronic Toxicity- Oral

Dog:

Young adult beagle dogs (6/sex/group) received daily oral doses of 0, 2.5, 5, 10, 20, or 40 

g/kg/day (0, 2,500; 5,000; 10,000; 20,000; 40,000 mg/kg/day) DMSO, 5 days/week for up to 23 

weeks (Rubin and Barnett, 1967). Dose levels of 20 and 40 g/kg/day were not tolerated well and 

were reduced. After 9 weeks of administration, changes in the lens of the eye were observed in 

dogs receiving 5 g/kg/day, and by the 18th week, all dogs at the lowest dose level were affected 

similarly. After 23 weeks, treatment was stopped and the dogs were observed for 31 weeks. Eye 

changes persisted after withdrawal of DMSO but became less pronounced. The lowest 

observable adverse effect level (LOAEL) was 2.5 g/kg/day (2,500 mg/kg/day). The NOAEL 
10

was not established. Although, a NOAEL was not established it was noted that effects were seen 

above the limit dose, improved after treatment cessation and eye opacity was not observed.

Rabbit:

New Zealand rabbits were treated orally (drinking water) with 0.5 g/kg/day or 10 g/kg/day

(500 or 10,000 mg/kg/day) of DMSO for 24 weeks (Wood and Wirth, 1969). The 10 g/kg 

rabbits exhibited progressive changes in the optical lenses when examined with the 

biomicroscope at 2, 6, 12, and 24 weeks. The effect was characterized by refractile changes, and 

there were alterations in the composition of lens proteins. The no adverse effect level (NOAEL) 

was observed in the rabbits dosed at 0.5 g/kg/day (500 mg/kg/day). The LOAEL was 10 

g/kg/day (10,000 mg/kg/day) based on progressive changes in the optical lenses.

Chronic Toxicity

Rat:

In a chronic oral toxicity study, 50 Sprague-Dawley rats/sex/group were administered DMSO 

[a 50% aqueous solution containing DMSO doses of 0, 1, 3, or 9 mL/kg/day (1100, 3300, or 

9900 mg/kg/day)] via gavage 5 days/week for 18 months. Clinical signs, body weight, and food 

consumption were monitored, and periodic assessments of hematological, clinical chemistry and

urinary parameters, ophthalmoscopic examination, and gross and histopathological examinations 

were performed.

There was a dose-related depression of weight gain in both sexes, with the exception of 

males receiving 1 mL/kg (in males, ca. -20% at the top dose and ca. -10% at the mid dose and in 

females, ca. -20% at the top dose and ca -10% at the mid and low doses). There was no 

accompanying reduction of food intake. A slight reduction of hemoglobin and packed-cell 

volume (PCV) in male rats receiving 9 mL/kg (9900 mg/kg/day) was observed.

Examination of the eye revealed no changes in the retina or vitreous humor. No peripheral

(equatorial) opacities were seen and there was no difference in incidence of polar opacities 

between the test and control animals. Prominent nuclear annuli were seen in a small number of 
11

animals towards the end of the study, but there was no dose-relationship to suggest any 

treatment-related effects. The only relevant finding was some degree of change in the refractive 

index of the nuclear region in 3 rats receiving 9 mL/kg (9900 mg/kg/day).

The LOAEL = 9 mL/kg (9900 mg/kg/day) based on decreased weight gain in both sexes and 

the change in the refractive index of the nuclear region in the eye. The NOAEL = 3 mL/kg/day

(3300 mg/kg/day) (Noel et al, 1975 as cited in MRID 49388701). 

Dog:

In a chronic oral toxicity study, groups of 5 pure-bred Pembrokeshire Corgi dogs/sex/group 

were administered DMSO [a 50% aqueous solution containing DMSO doses of 0, 1, 3, or 9 

mL/kg/day (1100, 3300, or 9900 mg/kg/day)] via gavage 5 days/week for 18 months or 24 

months. Clinical signs, body weight, and food consumption were monitored, and periodic 

assessments of hematological, clinical chemistry and urinary parameters, ophthalmoscopic 

examination, and gross and histopathological examinations were performed.

No treatment-related effects were observed on body weight. At the mid- and high-dose 

levels, persistent diuresis but no renal damage was observed. Increased PCV and hemoglobin 

levels were observed at the high dose, although the erythrocytes had normal hemoglobin 

concentrations and were of normal size. Lenticular changes (alterations in the refractive index of 

the central portion of the lens, lens opacity, opalescence in the central region of the lens, and/or 

changes in vitreous humor) and biochemical changes in the lens (an increase in insoluble protein

and reductions in soluble protein, glutathione, and water) were observed. Ocular changes were 

evident before 10 weeks at the high dose, with obvious progression with continued dosing. The 

sequence of changes occurred at the 3 mL/kg/day dose level, although the onset of changes was 

delayed. At the low dose, nuclear refractive changes were observed after 6 months, but none of 

these dogs had opalescence.

There were no marked clinical signs and only one accidental death occurred. Occasional 

isolated bouts of vomiting were seen at 9 mL/kg/day and transitory "head shaking" was 

temporarily observed during weeks 11 and 12 at this and the 3 mL/kg/day level.

No adverse effects on bodyweight and food intake were recorded. Electrocardiogram (ECG)

records were normal throughout except for a transient, minimal slowing of the heart rate in 

recordings made after 4 weeks. Terminal radiology of excised bone showed no evidence of 
12

osteoporosis. Laboratory investigations confirmed the persistence of diuresis in dogs receiving 3 

mL/kg and above but no renal damage resulted.

Persistently increased PCV, hemoglobin levels, and total red cell count were observed at 9 

mL/kg. The red cells had normal hemoglobin concentrations (MCHC) and were of normal size 

(MCV). Bone marrow examination prior to termination revealed no evidence of toxic changes. 

It seemed possible that the constant diuresis had resulted in a balance with a slightly higher 

degree of hemoconcentration than is normally found.

Ocular effects were observed after 5-10 weeks dosing in the dogs receiving 9 mL/kg 

including central (nuclear) lenticular changes with alteration of the refractive index (myopia) and 

by the fifth month, transitory equatorial opacities, central (nuclear) opalescence, and changes in 

the vitreous humor. Similar effects were observed in dogs receiving 3 and 1 mL/kg but they

occurred more slowly, respectively after 16 and 31 weeks of treatment.

No abnormalities, other than those in the eye, were detected during macroscopic or 

microscopic examination of organs.

Dogs withdrawn from the study at 18 weeks showed partial (high-dose) to complete (middose) recovery by two years. No other histopathological abnormalities were observed. The 

LOAEL is 1100 mg/kg/day, based on ophthalmologic changes, and thus, no NOAEL could be 

determined for this study (Noel et al, 1975 as cited in MRID 49388701). Although, a NOAEL 

was not established it was noted that the eye effects observed at 1100 mg/kg/day were less 

severe, occurred after 16 weeks of treatment, were reversible and eye opacity was not observed.

Reproduction/Developmental Toxicity Screening Test

Rat:

In a study performed according to the OECD Guideline # 421 and GLP, four groups of 12 

male and 12 female Sprague-Dawley rats received DMSO (purity 99.977%), daily, by oral 

(gavage) administration, before mating and through mating and, for the females, through 
13

gestation until day 21 post-partum, at dose-levels of 0, 100, 300 or 1,000 mg/kg/day (dosing 

volume: 5 mL/kg in purified water).

Clinical signs and mortality were checked daily. Body weight and food consumption were 

recorded weekly until mating and then at designated intervals throughout gestation and lactation. 

The animals were paired for mating and the dams were allowed to litter and rear their progeny 

until day 22 postpartum. The total litter sizes and numbers of pups of each sex were recorded 

after birth, pup clinical signs were recorded daily and pup body weights were recorded on days 1 

and 4 post-partum and then weekly until day 21 post-partum. The males were sacrificed after 

completion of the mating period. The body weight and selected organs weights were recorded 

and a macroscopic postmortem examination of the principal thoracic and abdominal organs was 

performed, with particular attention paid to the reproductive organs. A microscopic examination 

was performed on selected organs for all males in the control and high-dose group. The dams 

were sacrificed on day 22 postpartum (or on day 25 post-coitum for females which did not 

deliver or 24 days after the end of the pairing period for unmated females) and a macroscopic 

examination of the principal thoracic and abdominal organs was performed, with particular 

attention paid to the reproductive organs. In females that were apparently non-pregnant, the 

presence of implantation scars on the uterus was checked using ammonium sulfide staining 

technique. A microscopic examination was performed on selected organs of females in the 

control and high-dose group. The litters were culled on day 4 postpartum to four males and four 

females whenever possible and non-selected pups were sacrificed and retained. Selected pups 

sacrificed on day 22 post-partum and pups prematurely sacrificed or found dead were carefully

examined for gross external abnormalities and a macroscopic post-mortem examination was 

performed.

There were no unscheduled deaths and no treatment-related clinical signs during the study in 

males or females. There were no effects of treatment with DMSO on male body weight gains or 

food consumption. All DMSO treated female groups had slightly, but not statistically

significant, lower body weight gains than the controls during the pre-pairing period (-11, -26 and 

-22% at 100, 300 and 1,000 mg/kg/day, respectively). However, on day 15, the body weight 

differences between the treated females and the controls were less than 3% (control 268g, treated 

264, 262 and 261 g at 100, 300 and 1,000 mg/kg/day, respectively). No effect was observed on 

the body weight gains during gestation or lactation periods, as well as on food consumption. No 

DMSO related effects were noted on mating and fertility parameters. There were no effects on 

estrus stages, on the mean number of days taken to mate and no effect on the mean duration of 

gestation. There were no effects of treatment with the test item on pup mortality and survival, 

mean pup body weight, body weight gain or sex ratio. Pup necropsy finding was limited to a 

slightly increased incidence of dilated renal pelvis in the group treated at 1,000 mg/kg/day. 

However, this effect was not statistically significant, in the range of the historical values and 

there was no dose-relationship between the groups treated at 100 or 300 mg/kg/day.
14

Marginally higher absolute (+10%) and relative (+8%) liver weights were noted in the FO 

males given 1,000 mg/kg/day. There were no treatment-related macroscopic findings. The 

treatment with DMSO at the highest dose-level did not affect the incidences of microscopic 

findings in testes, epididymides and ovaries.

The NOAEL for parental toxicity was considered to be 1000 mg/kg/day, the highest dose 

tested. The NOAEL for reproductive performance (mating and fertility) was considered to be 

1,000 mg/kg/day and the NOAEL for toxic effects on the progeny was 1,000 mg/kg/day

(Arkema, 2007 as cited in MRID 49388701).

Rabbit:

In a study to evaluate the potential toxic effects of DMSO on embryonic and fetal 

development, DMSO was administered daily by oral gavage at 100, 300 or 1,000 mg/kg/day to 

pregnant New Zealand white rabbits during the period of organogenesis (day 7 to day 28 postcoitum). This study was conducted according OECD guidelines #414 and GLP.

No signs of maternal toxicity were observed at 100 mg/kg/day. At 300 mg/kg/day, the signs 

of maternotoxicity were confined to a slightly lower food consumption compared to the control 

group (-18%) during the first two days of treatment but was not thereafter statistically different 

from the control group. At 1,000 mg/kg/day, the signs of maternotoxicity compared to the 

control group were: a slightly lower food consumption during the first part of the study (days 7 

to 15: -17%) with a more marked effect during the first two days of treatment (days 7 to 9: -32%) 

and slightly lower body weight gain during the first part of the study (days 7 to 15: -37%) with a 

more marked effect during the first two days of treatment, where a slight body weight loss was 

recorded.

There was no abortion at any dose-level. There was no effect, at any dose-level, on the 

number of corpora lutea, implantation sites, post-implantation loss, number of live fetuses, fetal 

body weight and sex-ratio. The embryofetal development was not affected and there were no 

teratogenic effects at any dose-level.

The NOAEL for maternal toxicity was 300 mg/kg/day and the LOAEL was 1000 mg/kg/day

based on reduced food consumption and body weight gain. The NOAEL for embryofetal
15

development was 1,000 mg/kg/day, the highest dose tested (Atofma, 2002b as cited in MRID 

49388701).

Carcinogencity

Initiation/Promotion Studies:

Rat:

The effects of DMSO on the tumorigenic activity of 7, 12-dimethylbenz[a] anthracene 

(DMBA) was investigated in rats. Three groups of 50 male Sprague-Dawley rats were given 20 

mg DMBA by gavage. In the two first groups, DMBA treatment was followed by 50 ppm 

DMSO in their drinking water 3 days before or 3 days after DMBA administration, respectively. 

The third group received no DMSO and served as untreated controls. The animals were treated 

or observed for up to 18 months, DMSO had no effect on the latency or frequency of tumors 

induced by DMBA. Rats receiving DMSO weighed more and had fewer tumors than did the 

controls at the end of the 18-month study period. This was suggestive that DMSO decreased the 

total number of tumors, although the difference between treated and control rats did not reach 

statistical significance (OECD SIDS, MRID 49388701).

Two groups of 40 Sprague-Dawley rats were treated dermally, 3 times a week, for at least 26 

weeks, with 0.02 mL of a 1% solution of 9, 10-dimethylbenzanthracene (DMBA) dissolved 

either in DMSO or acetone. A third group (40 animals) received only DMSO (0.02 mL). The 

animals were observed weekly and the number of tumors counted. Specimens were taken from 

all tumors for histological examination at the end of the experiment. In the rats treated with 

DMBA dissolved in acetone, the time of appearance of the first tumor was shorter (26 weeks) 

compared to DMBA in DMSO (34 weeks) and the number of papillomas was greater (141 versus 

32). No skin tumor was observed in the rats treated with DMSO alone (OECD SIDS, MRID 

49388701).

Mouse:
16

In 20 ICR/Ha Swiss mice, dermal application of 0.1 mL DMSO, 3 times weekly over a 

period of 400 days, after a primary treatment with DMBA (applied once only, 20ug in 0.1 mL

acetone), induced no skin tumors (OECD SIDS, MRID 49388701).

Dermal Toxicity

Rabbits:

Groups of male and female New Zealand white rabbits received daily applications of 50% or 

90% aqueous solution of DMSO to normal and abraded skin at volumes equivalent to 0, 1.5, 2,7, 

4.5 or 8.1 mL undiluted DMSO per kg (0, 1,650; 2,970; 4,950 and 8,910 mg/kg/day, 

respectively). Treatments continued for 6 months; animals were kept under observation for an 

additional 12 weeks after treatment was terminated. Each rabbit was observed daily, weighed 

weekly and its water consumption was recorded during week 26. Ophthalmoscopic examination 

was performed on all animals before dosing commenced and then after 5, 8, 14, 20, 22, 28 and 

33 weeks. Hematological investigations comprising PCV, hemoglobin, total and differential 

white cell count, and erythrocyte sedimentation rate, were performed initially and at 4, 12, 26 

and 32 weeks. At termination, each animal was subjected to a post mortem examination, with 

subsequent organ weight analysis and histopathology. Rabbits received dermal applications of 

DMSO to normal and abraded skin for a period of 23 weeks, when ocular changes were 

observed. Treatment was withheld from animals showing ocular changes; the remaining animals 

continued to receive DMSO applications for the scheduled 26 weeks (6 months).

Macroscopic and hematological examinations, organ weight analysis, and histopathology did 

not reveal any adverse effects. There were no changes in dermal morphology except for random

occurrences of inflammatory reaction. After 23 weeks of treatment, adverse ocular (lenticular)

effects were observed at all dose levels (1, 5, 3 and 8 rabbits with a normal skin and 3, 7, 4 and 

11 rabbits with an abraded skin, respectively at 1.5, 2.7, 4.5, and 8.1 mL/kg). These were 

restricted to the lens, and consisted of nuclear refractive changes. There was no effect on the 

peripheral lens, vitreous humor, or retina. The systemic NOAEL was not established. The 

systemic LOAEL was 1.5 mL/kg (1650 mg/kg/day) based on lenticular changes (OECD SIDS, in 

MRID 49388701).

In another study, medical grade DMSO was applied daily to the shaved backs of groups of 10 

rabbits for 30 days at the dose of 0, 1 and 5 g/kg (1000 and 5000 mg/kg/day). Blood was drawn 

by cardiac puncture from each rabbit 1 and 7 days prior to treatment, and on treatment days 1, 7, 
17

and 30. Serum chemistry, serum enzyme levels and liver alcohol dehydrogenase levels were 

evaluated. Eye lenses of each rabbit were examined with a biomicroscope before and during 

treatment. At the end of the study, all rabbits were autopsied and examined for gross pathology.

There was no mortality. At both 1 and 5 g/kg/day (1000 and 5000 mg/kg/day) of DMSO 

administration resulted in elevated values for serum lactic dehydrogenase. Transient elevations 

of the serum hemoglobin values were observed at 1 g/kg, as well as serum hemoglobin, total 

bilirubin and glucose at 5 g/kg. There were no gross lesions in DMSO or control animals 

examined at the end of the study. None of the animals treated with 1 g/kg/day displayed 

lenticular changes. All of the rabbits treated with 5 g/kg/day displayed microscopic ocular 

changes, which were first detected after 10-15 days treatment. The LOAEL was 5 g/kg/day

(5000 mg/kg/day) based on ocular changes. The NOAEL was 1 g/kg/day (1000 mg/kg/day)

(OECD SIDS, MRID 49388701).

Inhalation Toxicity

Rat:

In 2 range-finding studies, three groups of 5 males and female Crl:CD®BR rats were 

exposed, by inhalation (snout only), to an atmosphere of droplets and/or vapor generated from 

DMSO for 6 hours each day, over a period of 14 or 28 days. The rats were killed on the day

following the last exposure. The achieved study mean analyzed respirable concentrations of 

DMSO in air were 0, 0.520 (vapor), 1.390 (> 64% of droplets < 7 um) and 5.360 mg/1 (> 64% of 

droplets < 7 um) for the 14-day study and 0, 0.132 (vapor), 0.507 (vapor) and 1.886 (75% of 

droplets < 7um) mg/1 for the 28-day study. In both studies, clinical signs both during exposures 

and at rest were monitored and recorded. Body weight was recorded twice weekly and food and 

water consumption were recorded daily. In the 28-day study, body rectal temperature was 

recorded on one occasion during the week prior the start of exposure and immediately after the 

6-hour exposure on week 1 and 4 for the control and high dose animals. In the 14-day study, 

laboratory investigations comprising analysis of hematological and blood chemistry parameters 

were conducted at the end of the treatment period. In both studies, following sacrifice of the 

animals rats were subjected to detailed macroscopic examinations followed by preservation of 

tissues. Adrenals, kidneys, liver, lungs, spleen and testes were weighed and, the larynx, lungs, 

nasal passages, trachea, and any gross lesions were subject to histopathological examination with 

in addition, eyes, kidneys and liver, in the 14-day study.
18

There were no unscheduled deaths during these studies. There were no clinical signs 

attributable to the administration of DMSO. There were no treatment-related effects on body

temperature. In the 14-day study, the mean body weight gain of high and intermediate dose rats 

(both sexes) and low dose female rats was lower than control values. The mean cumulative food 

consumption of high and intermediate dose rats (both sexes) and low dose female rats was lower 

than the concurrent controls. The mean cumulative water consumption of high dose female rats 

was higher than that of controls. None of these effects on the body weight gain and the food and 

water consumption were observed in the 28-day study. In the 14-day study, there were no 

findings considered to be of toxicological importance in hematology and blood biochemistry

parameters investigated prior to sacrifice. There were no treatment-related macroscopic findings 

at necropsy and mean organ weights of all test groups were similar to control values in both 

studies. Aggregations of macrophages in the lungs, epithelial hyperplasia in the larynx and 

eosinophilic inclusions in the olfactory epithelium of the nose were detected at the high dose 

level in the 14-day study but not in the 28-day study.

Based on the 28-day study, the NOAEC for systemic toxicity and local effects on the 

respiratory tract is estimated to be >1.886 mg/1(489 mg/kg/day) (OECD SIDS, MRID 

49388701).

In a study compliant with the OECD guideline #413 and GLP, three groups of rats (each of 

10 males and 10 females) of the Crl:CD®BR strain were exposed to DMSO, 6 hours a day, 7 

days a week, for 13 weeks using a snout-only exposure system. A fourth group, acting as 

control, was exposed to air only. An additional 10 male and 10 female rats concurrently exposed 

at the control and high dose levels were retained following the final exposure for a further 4 

weeks to assess the reversibility of any adverse findings. The study was designed to comply 

with OECD, US EPA OPPTS guidelines and GLP. The mean analyzed chamber concentrations 

of DMSO were 0.310 mg/1, 0.964 mg/1 and 2.783 mg/1 (equivalent to 80, 250, and 722 

mg/kg/day) for groups 2 (low dose), 3 (intermediate dose) and 4 (high dose) respectively.

Throughout the study, the animals were checked twice a day for mortality and clinical signs. 

Body weight and food consumption were recorded weekly. Water consumption was recorded 

daily. The eyes of all main and recovery group rats were examined once before the start of 

dosing using a Keeler indirect ophthalmoscope. Similarly, all main and recovery group rats in 

groups 1 and 4 were examined during week 13. Functional observations were conducted on 10 

male and 10 female rats from each group, pre-treatment, on week 12 and at the end of the 

recovery period. Vaginal smears were prepared daily from all female rats during weeks 8 and 9 

of the study for assessment of the oestrus cycle. Blood and urine samples for hematology, 

biochemistry and urinalysis were collected from all main group rats during week 13 of dosing. 

All main group animals were killed following 13 weeks of dosing and subject to a detail 
19

macroscopic examination. Sperm samples from rats from all groups were assessed for motility, 

sperm morphology and number. Histopathological examinations were performed on all 

scheduled tissues. A high dose group male was sacrificed on humane grounds in week 13 due to 

the condition of the upper incisors and subsequent weight loss. Treatment-related clinical signs 

consisted of red staining around the nose of rats exposed to 0.964 and 2.783 mg/1. Rats exposed 

to 2.783 mg/1 gained less weight over the exposure period compared with the controls. The 

trend was reversed during the recovery phase. However, the differences were small (-17% in 

males and -16% in females compared to controls) and in the absence of any other indications of 

systemic toxicity probably reflected a loss of appetite caused by the mildly irritant nature of 

DMSO.

Differences between control and treated groups for food and water consumption were 

minimal and of no toxicological importance. Ophthalmic examination, functional observation 

battery, oestrus cycle, sperm analysis, hematology, biochemistry, urinalysis, macroscopic 

pathology and organ weights were unremarkable. Treatment-related microscopic changes were 

found in the nasal passages and pharynx of high dose males and females after treatment for 90 

days, but not in rats from the low and intermediate dose groups. The pathology in the nasal 

passages comprised of lesions in the inferior ventral medial meatus and an increased degree of 

eosinophilic inclusions in the olfactory epithelium. In the pharynx, prominent goblet cells were 

present in the majority of high dose rats. In rats killed after the recovery period, changes were 

still evident in the nasal passages of high dose male and females and also in the pharynx of the 

females. According to these results, the no adverse effects concentrations (NOAEC) could be 

established at 0.964 mg/1 for respiratory tract irritation and 2,783 mg/1 (equivalent to 722 

mg/kg/day) for systemic toxicity (OECD SIDS, MRID 49388701).

Neurotoxicity

Neurotoxicity studies were not available for review, however, evidence of potential 

neurotoxicity was not observed in the submitted studies. In addition, functional observation 

battery parameters were not affected following inhalation exposure in rats for 13 weeks (OECD 

SIDS, MRID 49388701).

Mutagenicity

In vitro:
20

DMSO was negative for mutagenicity in the reverse mutation assays in strains TA97, TA98, 

TA100, TA102, TA 1535, TA1537, and TA1538 at concentrations up to 300,000 ug/plate 

(WHO, 2000). DMSO was mutagenic in Salmonella typhimurium strains TA1537 and TA2637 

at concentrations of 0.1-0.4 mL/plate and in E. coli WP2uvrA at concentrations of 0.2-0.4 

mL/plate, with and without metabolic activation (Hakura, et a/., 1993); however, the 

concentrations were relatively high with some being cytotoxic. Additionally, DMSO was 

mutagenic in the umu test with Salmonella typhimurium strains TA1535/pSK1002 carrying the 

umuC-lacZ fusion gene (Nakamura, et al., 1990). The umu gene expression was detected only at

high-dose levels (5%-15%). The level of p-galactosidase activity, which reflects umu expression

was increased in a concentration-related pattern (121-313 units compared to 90 units in control). 

There was a dose-related increase in gene conversions at certain loci of log phase cells of the D4 

strain of Saccharomyces cerevisiae following exposure to dose levels up to 1.4 M for 4 hours at 

37°C. The gene conversions were attributed to the metabolic conversion of DMSO to a 

genetically active compound by cytochrome P-450 mixed function oxidation reactions.

In a study performed with a method comparable to the OECD Guide-line no. 471, DMSO 

was tested in two separate laboratories in the gene mutations assay in bacteria. Concentrations of 

DMSO (100, 333, 1000, 3333, and 10,000 ug) were added to overnight cultures of Salmonella 

typhimurium strains TA97, TA98, TA100, TA1535, TA1537, and S-9 mix or buffer were 

incubated without shaking for 20 minutes. The top agar was added and the contents of the tubes 

were mixed and poured onto the surfaces of petri dishes. His+ (histidine dependent) colonies 

arising on plates were machine-counted after two days incubation. Initial testing was without 

metabolic activation, with 10% rat liver S-9, or with 10% hamster liver S-9. After a negative 

result was obtained, DMSO was retested without S-9 and with 30% S-9 from rat and hamster. 

Positive controls were sodium azide (TA 1535 and TA100), 9-aminoacridine or ICR-191 (TA 97 

and TA1537) and 4-nitro-o-phenylenediamine (TA98) without S9 and 2-aminoanthracene (all 

strains) with S9: The positive control chemicals induced a significant increase of the revertant 

frequency in all tester strains, either with or without metabolic activation. DMSO was negative, 

in the presence and absence of metabolic activation, in all tester strains (OECD SIDS, MRID 

49388701).

In addition DMSO was not mutagenic in the Salmonella typhimurium mutagenicity assay

using the standard plate incorporation protocol, both in the presence and absence of metabolic 

activation (OECD SIDS, MRID 49388701).

DMSO did not induce dominant lethality in male rats injected intraperitoneally at a dose 

level of 1 mL/kg/day for 10 weeks (Sheu and Green, 1979 as cited in MRID 49388701), or in 
21

Swiss mice injected with doses up to 10 g/kg twice at intervals of about 20 hours 

(Aravindakshan, et al., 1975 as cited in MRID 49388701). 

In vivo:

In a study performed with a method comparable to the OECD Guide-line no. 473, DMSO 

was tested with Chinese hamster ovary (CHO) cells in culture at concentrations of 0, 499, 1,500 

and 4,990 ug/mL, in the presence and absence of liver microsomal fraction (S9) from Aroclor 

1254-induced male Sprague-Dawley rats, to determine its in vitro cytogenetic potential. Medium 

control was used with each assay with or without S9. Mitomycin C was used in the experiments 

without metabolic activation, and cyclophosphamide was used in the experiments with activation 

as positive controls. The positive control chemicals induced a significant increase of the 

frequency of the chromosomal aberrations. DMSO did not induce cell toxicity or cell cycle 

delay, and did not induce an increase in the incidence of chromosomal aberrations (OECD SIDS, 

MRID 49388701).

In an in vivo micronucleus assay performed according to the OECD guideline no. 474 and 

GLP, groups of 6 male and 6 female Han Wistar rats received 5 daily i.p. injections at the dose 

levels of 0, 200, 1,000 and 5,000 mg DMSO/kg bw/day. The animals were sacrificed 24 hours 

after the last dosing and bone marrow collected and evaluated for the presence of micronucleated 

polychromatic erythrocytes. The negative and positive controls in the study were purified water 

and cyclophosphamide, respectively. There was no increase in the incidence of micronuclei in 

the polychromatic erythrocytes of the bone marrow of male and female Han Wistar treated with 

DMSO as compared to concurrent controls (OECD SIDS, MRID 49388701).

Immunotoxicity

As part of a 13-week inhalation toxicity study, four satellite groups of Sprague-Dawley rats 

(5/sex/group) were exposed snout-only, 6 hours/day, 7 days/week, for 28 days to mean analyzed 

chamber concentrations of 0, 0.310, 0.964 and 2.783 mg /1 (equivalent to 0, 80, 250 and 722 

mg/kg/day) DMSO. To act as a positive control, a further group of satellite animals were 

injected i.p. with cyclophosphamide at a dose of 50 mg/kg 2 days prior to termination. The study

was designed to comply with OECD/US EPA OPPTS guidelines and GLP regulations. Sheep 

Red Blood Cell (SRBC)-specific antibody secreting cells (ASCs) were enumerated using a 

modification of the Jerne Plaque Forming Cell (PFC) assay.
22

Inhalation exposure to DMSO led to an apparent increase in the number of antibody secreting 

cells in male rats, compared with controls. Changes in the total number of antibody secreting 

cells in the spleen (PFC/spleen) and also changes in the relative numbers of antibody secreting 

cells, associated with changes in other spleen cell populations (PFC/106 cells) were measured.

Since DMSO increased both PFC/106 cells and PFC/spleen in male rats, the effect is likely to be 

a genuine enhancement, not simply a broad spectrum increase in spleen cell numbers. It is worth 

noting that there was a high degree of inter-animal variation in the PFC response. This is almost 

certainly linked to the genetic background of the Sprague-Dawley rats, which are an outbred 

population. The adaptive immune response is known to have strong genetic linkage and work 

from other sources has shown that while outbred species are popular models in toxicology they

have an inherent variability in immune responses. Based in the high variability observed in male 

rats, the lack of effects in female rats and the lack of effect on the other end-points relevant for 

immunotoxicity (spleen and thymus weights, lymphocyte count) reported in the 13-week study, 

these data are of doubtful toxicological significance. The NOAEL was 2.783 mg /1 (equivalent 

to 722 mg/kg/day), the highest dose tested (OECD SIDS, MRID 49388701).

Metabolism 

Rat:

35S-DMSO (0.55 g/kg (equivalent to 550 mg/kg), approximately 0.5 uCi) was administered 

to male Sprague-Dawley rats orally or dermally, the animals were killed at various times and the 

tissues were assayed for total radioactivity.

After an oral dose the concentration of radioactivity in plasma was maximal (equivalent to

600 ug equivalent DMSO/mL) between 0.5 and 4 hours, then declined to equivalent to 70 ug eq. 

DMSO/mL at 24 hours, 0.5 hours after administration. Kidney, spleen, lung, heart and testes 

appeared to have somewhat higher levels (equivalent to 60 to 70% of the plasma concentration) 

than liver, fat, small intestine, brain, skeletal muscle and red cells (equivalent to 50%). 

Concentrations in the testes, brain, skeletal muscle and heart increased (60 to 85% of the plasma 

concentration) at 4hours, but remained virtually constant in other tissues. Levels had declined to 

minimal values in plasma and all tissues after 24 hours. The ratio of DMSO2 to DMSO in rats 4 

hours after oral administration of 35S-DMSO was found to be virtually constant in liver, testes,

kidney, spleen, small intestine, heart and plasma, averaging about 6.5% (range of 4.1-10.6% for
23

tissues of 2 rats). Thus, the major part, at least, of radioactivity present in tissues seems to be

represented by DMSO.

After dermal administration, tissue concentrations of radioactivity were also appreciable after 

0.5 h (equivalent to 300 ug eq. DMSO/mL), but were somewhat lower than after an oral dose. 

The concentration of radioactivity in plasma was maximal (equivalent to 600 ug eq. DMSO/mL) 

2 hours after the administration, and then declined to equivalent to 70 ug eq. DMSO/mL at 24 

hours. At 0.5 hours, levels in the spleen, liver and lungs were higher (equivalent to 70% of the 

plasma concentration) than the other tissues (40 to 60%). Concentrations in the liver, testes, 

kidney, spleen, brain, lungs, skeletal muscle, heart, plasma and red cells increased after 4 hours

to values comparable to those after an oral dose. Levels in the fat and small intestine remained 

virtually constant. All tissue concentrations had declined to minimal values after 24 hours 

(OECD SIDS, MRID 49388701).

Monkey:

The pharmacokinetics of DMSO in rhesus monkeys was studied during and after a 14-day

oral administration of a dose level of 3 g/kg as a 50% solution in water. DMSO and DMSO2

were measured in serum, urine and feces by gas-liquid chromatography. The absorption of 

DMSO was rapid. After the first administration, an average peak serum concentration of 2.3 

mg/mL was observed after about 4 hours, which declined relatively rapidly to about 0.95 mg/mL

after 24 hours. DMSO half-life was 16 hour and its elimination rate constant was about 4% per 

hour. DMSO2 became detectable in serum after about 2 hours, rose slowly and reached about 

0.18 mg/mL at 24 hours.

With continued daily oral administration, serum DMSO rose slightly from 0.95 to 1.1 mg/mL

on day 2. DMSO and DMSO2 reached a steady state concentration of about 0.9 mg/mL and 0.34 

mg/mL after 4 days, respectively. After the last DMSO dose, serum DMSO declined rapidly and 

was not detected after 72 hours. The mean DMSO2 serum concentration declined slowly over the 

next 96 hours and trace amounts were detected at 120 hours. DMSO2 half-life was calculated to 

be about 38 hours and its elimination rate constant about 2% per hour.

About 60% of an orally administered dose was excreted in the urine as DMSO and about 

16% as DMSO2. Neither DMSO nor DMSO2 could be detected in feces. The pulmonary

elimination of DMSO was not quantified in this study but was detectable as a sweet smell in the 

exhaled air (OECD SIDS, MRID 49388701).
24

Table 3. Toxicology Profile for DMSO

Study Type Doses Results

23-week-Oral Toxicity 

Study- Dog-diet

0, 2.5, 5,10, 20, or 40 

g/kg/day (0, 2,500; 5,000; 

10,000; 20,000; 40,000 

mg/kg/day)

NOAEL was not established.

LOAEL: 2,500 mg/kg/day based on changes in the lens of 

the eye.

24-week-Oral Toxicity 

Study- Rabbit-drinking 

water

0, 0.5 or 10 g/kg/day

(0, 500 or 10,000 

mg/kg/day)

NOAEL = 0.5 g/kg/day (500 mg/kg/day).

LOAEL = 10 g/kg/day (10,000 mg/kg/day) based on 

changes in the optical lenses. 

18-Month-Oral Toxicity 

Study- Rat-Gavage-(5 

days/week)

0,1, 3, or 9 mL/kg/day 

(1100, 3300, or 9900 

mg/kg/day)

NOAEL = 3 mL/kg/day (3300 mg/kg/day).

LOAEL = 9 mL/kg/day (9900 mg/kg/day) based on 

decreased body weight gain and the change in the refractive 

index of the nuclear region in the eye. 

18 and 24-Months-Oral 

Toxicity Study- DogGavage-(5 days/week)

0,1, 3, or 9 mL/kg/day 

(1100, 3300, or 9900 

mg/kg/day)

NOAEL was not established.

LOAEL = 1 mL/kg/day (1100 mg/kg/day) based on 

ophthalmologic changes.

Reproduction/Development

al Toxicity Screening-RatGavage

0, 100, 300 and 1000 

mg/kg/day

Maternal NOAEL = 1000 mg/kg/day.

Maternal LOAEL was not established.

Reproduction NOAEL = 1000 mg/kg/day.

Reproduction LOAEL was not established. 

Developmental NOAEL = 1000 mg/kg/day.

Developmental LOAEL was not established.

Developmental ToxicityRabbit-Gavage

0, 100, 300 and 1000 

mg/kg/day) 

Maternal NOAEL = 300 mg/kg/day.

Maternal LOAEL = 1000 mg/kg/day based on reduced body 

weight and food consumption.

Developmental NOAEL = 1000 mg/kg/day.

Developmental LOAEL was not established.

Cancer 

Initiation/Promotion-Rat

20 mg DMBA-gavage

50 ppm DMSO-drinking 

water

3 days before or 3 days after 

for 18 months

No increased tumorigenesis.
25

Study Type Doses Results

Cancer 

Initiation/Promotion-RatsDermal-3 times/week-34 

weeks

DMSO (0.02 mL) Tumors were not observed.

Cancer 

Initiation/Promotion-MiceDermal-3 times/week-400 

days

DMBA (applied once only, 

20ug in 0.1 mL acetone)

DMSO -0.1 mL

(3 times/week-400 days)

No increased tumorigenesis.

6 Month -Dermal Toxicity 

Study-Rabbit

0,1.5, 2.7, 4.5, or 8.1 

mL/kg/day

0, 1,650; 2,970; 4,950 or

8,910 mg/kg/day)

Systemic NOAEL was not established.

Systemic LOAEL = 1.5 mL/kg (1650 mg/kg/day) based on 

lenticular changes.

30 days -Dermal Toxicity 

Study-Rabbit

0, 1 and 5 g/kg (1000 and 

5000 mg/kg/day)

Systemic NOAEL = 1 g/kg (1000 mg/kg/day).

Systemic LOAEL = 5 g/kg (5000 mg/kg/day) based on 

ocular changes.

14 Days Inhalation 

Toxicity-Rat-(rangefinding study)

0, 0.52, 1.39 and 5.36 

mg/1(equivalent to 135, 

360, and 1390 mg/kg/day)

Systemic NOAEC was not established.

Systemic LOAEC = 0.52 mg/1 (equivalent to 135

mg/kg/day) based on decreased mean body weight gain.

14/28 Days Inhalation 

Toxicity-Rat-(rangefinding study)

0, 0.132, 0.507 and 1.886 

mg/1(equivalent to 34, 131, 

and 489 mg/kg/day).

Systemic NOAEC = 1.886 mg/1 (equivalent to 489 

mg/kg/day).

Systemic LOAEC was not established.

90 Days Inhalation 

Toxicity-Rat

0, 0.3, 10, 0.964 and 2.783 

mg/1 (equivalent to 80, 250, 

and 722 mg/kg/day)

Systemic NOAEC = 2.783 mg/1 (equivalent to 722 

mg/kg/day).

Systemic LOAEC was not established.

Ames Test 100-300 mg/plate Negative.

Dominant lethal assay in 

Rodents-intraperitoneal 

injection.

1 mL/kg/day for 10 

weeks(rats) 

10 g/kg twice at intervals of 

about 20 hours (mice)

Not clastogenic
26

Study Type Doses Results

Sister chromatid exchange 

assay in CHO cells

up to 4,999 ug/mL

+/-S9

Not clastogenic.

Micronucleus assay in rat 

bone marrow

0,200, 1,000 and 5,000

mg/kg/day

Not clastogenic

Plaque-Forming Cell Assay 

-Mice-Inhalation

0, 0.310, 0.964 and 2.783

mg/1(equivalent to 0, 80, 

250 and 722 mg/kg/day)

NOAEL 2.783 mg /1 (equivalent to 722 mg/kg/day).

LOAEL was not established.

Metabolism-Rat-Oral and 

Dermal

0.55 g/kg (equivalent to 550 

mg/kg)

DMSO is rapidly absorbed, metabolized and excreted.

Excretion was primarily via urine, feces was a minor route. 

The major metabolite was dimethyl sulfone. Dimethyl 

sulfide, another metabolite, is eliminated through the breath. 

It did not bioaccumulate.

14-Day MetabolismRhesus Monkey

3 g/kg/day (equivalent to

3000 mg/kg/day)

DMSO is rapidly absorbed, metabolized and excreted.

Excretion was primarily via feces. The major metabolite 

was dimethyl sulfone. Dimethyl sulfide, another 

metabolite, is eliminated through the breath. It did not 

bioaccumulate.

5. Toxicity Endpoint Selection

The available toxicity studies indicate that DMSO has low toxicity. These data demonstrated 

effects at 1100 mg/kg/day (above the limit dose) and no toxicity at doses up to 500 mg/kg/day. 

Although, the lowest NOAEL in the database is 300 mg/kg/day in a developmental study in 

rabbits, it was not selected because of the dose spread, as effects were not observed in rabbits 

treated with 500 mg/kg/day in the 24 week oral toxicity study. Therefore, since no endpoint of 

concern was identified for DMSO, a qualitative risk assessment is appropriate.

6. Special Considerations for Infants and Children

Section 408 of the FFDCA provides that EPA shall apply an additional margin of safety for 

infants and children in the case of threshold effects to account for prenatal and post natal toxicity
27

and the completeness of the database on toxicity and exposure unless EPA determines that a 

different margin of safety will be safe for infants and children. EPA concludes that the FQPA 

safety factor could be reduced to 1X for DMSO for the following reasons:

i. The database is considered complete for FQPA assessment based on the toxicity

information on DMSO. The following acceptable studies are available:

Subchronic (rat, dog, rabbit, monkey)

Chronic (rat, dog, monkey)

Reproduction (rat)

Developmental toxicity study (rat, rabbit)

ii. Fetal susceptibility was not observed in any of the reproduction/developmental toxicity

studies with rats or rabbits administered DMSO. 

iii. Neurotoxicity studies were not available for review. However, signs of potential 

neurotoxicity were not observed in any of the submitted studies with DMSO. EPA 

concluded that neither a neurotoxicity nor a developmental neurotoxicity study is 

required at this time. 

iv. An immunotoxicity study was available for review. In a Jerne Plaque Forming Cell 

(PFC) assay, the total number of antibody secreting cells in the spleen and the relative 

numbers of antibody secreting cells were increased. However, this effect is not 

considered adverse. Therefore, EPA concluded that the immunotoxicity study is not 

required at this time.

Taking into consideration the available information, EPA concludes the additional 10X 

FQPA safety factor can be reduced to 1X.

7. Exposure Assessment
28

In evaluating dietary exposure to DMSO, EPA considered exposure under the petitioned for 

exemptions from the requirement of a tolerance. EPA assessed dietary exposures from DMSO in 

food as follows:

Dietary Exposure

Dietary exposure can occur from eating foods containing residues of DMSO. Because no 

hazard endpoint of concern was identified for the acute and chronic dietary assessment (food and 

drinking water), a quantitative dietary exposure risk assessment was not conducted.

Residential Exposure (non-dietary exposure)

The term “residential exposure” is used in this document to refer to non-occupational, nondietary exposure (e.g., textiles (clothing and diapers), carpets, swimming pools, and hard surface 

disinfection on walls, floors, tables). DMSO is used as an inert ingredient in pesticide products 

that could result in short- and intermediate-term residential exposure. However, based on the 

lack of toxicity, a quantitative exposure assessment from residential exposures was not 

performed.

8. Aggregate Risk

Based on the lack of any endpoints of concern, EPA concludes that there is a reasonable 

certainty that no harm will result to the general population or to infants and children from 

aggregate exposure DMSO residues.

9. Occupational Exposure/Risk Pathway

The Agency believes that establishing the tolerance exemption to include 40 CFR § 180.920 

in a proprietary product will not significantly/measurably increase occupational exposure. The 

change in use pattern would be expanded to include post-emergence use in pesticide products on 

all pre-harvest food commodities. Based on the regulatory history of DMSO and no new 

toxicological information to indicate otherwise, it is not necessary to quantitatively assess 

occupational exposure.
29

10. Cumulative Exposure:

Section 408(b)(2)(D)(v) of FFDCA requires that, when considering whether to establish, 

modify, or revoke a tolerance, the EPA consider "available information" concerning the 

cumulative effects of a particular pesticide's residues and "other substances that have a common 

mechanism of toxicity." Unlike other pesticides for which EPA has followed a cumulative risk 

approach based on a common mechanism of toxicity, EPA has not found DMSO to share a 

common mechanism of toxicity with any other substances and DMSO does not appear to 

produce a toxic metabolite produced by other substances. An endpoint of concern was not 

identified for DMSO in various dietary and non-dietary exposure scenarios. Additionally, the 

risk to aggregate exposure of DMSO was below the Agency’s concern. For information 

regarding EPA's efforts to determine which chemicals have a common mechanism of toxicity

and to evaluate the cumulative effects of such chemicals, see the policy statements released by

EPA's Office of Pesticide Programs concerning common mechanism determinations and 

procedures for cumulating effects from substances found to have a common mechanism on 

EPA's website at http://www.epa.gov/pesticides/cumulative/.

11. Environmental Fate 

Detailed information regarding environmental fate can be found in the OECD SIDS 

Dimethyl Sulfoxide document found in MRID 49388701. Below is a summary of environmental 

fate reproduced from that document.

DMSO is mainly found in water and soil. In the atmosphere DMSO concentrations are low 

and associated with aqueous phase. Stability and behavior are strongly related to the physicochemical characteristics of the compartment considered but DMSO can be considered as mobile 

in soil and relatively stable in water.

Ecotoxicity

Detailed information regarding ecotoxicity can be found in the OECD SIDS Dimethyl 

Sulfoxide document found in MRID 49388701. Below is a summary of ecotoxicity reproduced 

from that document.
30

Acute toxicity studies, carried out for some of them according to guidelines similar to OECD 

guidelines, reveal 48-hour EC50's ranging from 24,600 to 58,200 mg/L for daphnid (Daphnia 

magna) and 96-hour LC50's ranging from 32,300 to 43,000 mg/L for fish according to the 

species considered (eg. Ictalurus punctatus, Lepomis cyanellus). Modeling calculation for algae 

indicates 96-hour EC50 value of about 400 mg/L. On this basis DMSO can be considered nontoxic for aquatic compartment.

12. Environmental Justice

Potential areas of environmental justice concerns, to the extent possible, were considered in 

this human health risk assessment, in accordance with U.S. Executive Order 12898, "Federal 

Actions to Address Environmental Justice in Minority Populations and Low-Income 

Populations," http://www.eh.doe.gov/oepa/guidance/justice/eo12898.pdf).

As a part of every pesticide risk assessment, OPP considers a large variety of consumer 

subgroups according to well-established procedures. In line with OPP policy, HED estimates 

risks to population subgroups from pesticide exposures that are based on patterns of that 

subgroup’s food and water consumption, and activities in and around the home that involve 

pesticide use in a residential setting. Extensive data on food consumption patterns are compiled 

by the USDA under the Continuing Survey of Food Intake by Individuals (CSFII) and are used 

in pesticide risk assessments for all registered food uses of a pesticide. These data are analyzed 

and categorized by subgroups based on age, season of the year, ethnic group, and region of the 

country. Additionally, OPP is able to assess dietary exposure to smaller, specialized subgroups 

and exposure assessments are performed when conditions or circumstances warrant. Whenever 

appropriate, non-dietary exposures based on home use of pesticide products and associated risks 

for adult applicators and for toddlers, youths, and adults entering or playing on treated areas 

post-application are evaluated. Further considerations are currently in development as OPP has 

committed resources and expertise to the development of specialized software and models that 

consider exposure to bystanders and farm workers as well as lifestyle and traditional dietary

patterns among specific subgroups.

13. Human Studies

This assessment relies in part on data from studies in which adult human subjects were 

intentionally exposed to a pesticide. These studies, listed below, have received the appropriate 

ethical review for use in risk assessment.
31

The PHED Task Force, 1998. The Pesticide Handler Exposure Database (PHED), Version 

1.1. Task Force members: Health Canada, U.S. Environmental Protection Agency, the 

California Department of Pesticide regulation, and the American Crop Protection Association; 

released August 1998.

14. Risk Characterization

EPA received a petition (PP#IN-10713) from ISK BioSciences (7470 Auburn Rd., Suite A, 

Concorde, OH 44077), requesting an exemption from the requirement of a tolerance for dimethyl 

sulfoxide (here in referred to DMSO, CAS Reg. No. 67-68-5) in cyclaniliprole formulations for 

pre-harvest applications including post-emergence use. DMSO will be used as a diluent in 

cyclaniliprole formulations (60.02% (w/w) with upper and lower limits of 61.82% and 58.22%, 

respectively) under 40 CFR part 180.920. DMSO has an existing tolerance exemption for use as 

a pesticidal inert under 40 CFR 180.920 as a solvent or co-solvent for formulations used before 

crop emerges from soil or prior to formation of edible parts of food plants (EPA, 2006). 

DMSO has low acute toxicity via the oral and dermal in rats and mice and inhalation route in 

rats. The acute oral LD50 > 7,920 mg/kg in rats and mice. The acute dermal LD50 > 40,000 

mg/kg in rats and mice. The acute inhalation LC50 > 1600 mg/m3(~277 mg/kg) in rats. It is a 

dermal, eye and gastric irritant in rats and rabbits. It is a sensitizer in guinea pigs. 

Overall systemic toxicity with regard oral and dermal exposure to DMSO is low also. The 

target organ of toxicity is the eye. Changes in the eyes, such as refractile changes in the lens and 

lens composition are seen in various animals at doses above the limit dose (1000 mg/kg/day).

Systemic toxicity is not observed following exposure to DMSO up to 1000 mg/kg/day, the 

limit dose, in the subchronic, chronic or reproduction/developmental toxicity studies via oral, 

dermal or inhalation exposures in rats, dogs and rabbits. DMSO is not expected to be 

carcinogenic based on the lack of mutagenicity and the lack of tumor formation in cancer 

initiation/promotion studies. It is not neurotoxic nor immunotoxic.

Toxicity via the inhalation route of exposure is limited to portal of entry effects at 2.783 

mg/1 (equivalent to 722 mg/kg/day). 

In the rat and monkey, DMSO administered via the oral and/or dermal route is rapidly

absorbed, metabolized and excreted. Excretion is primarily via urine, feces was a minor route in 
32

the rat only. The major metabolite was dimethyl sulfone. Dimethyl sulfide, another metabolite, 

is eliminated through the breath. There is no bioaccumulation. 

The FQPA SF was reduced to 1X. Available toxicity data on DMSO demonstrated no 

adverse effects at doses up to 1,100 mg/kg/day. Therefore, since there are no endpoints of 

concern for DMSO a qualitative dietary, non-dietary and occupational exposure risk assessments

were appropriate.

DMSO has low toxicity to aquatic organisms. Also, it is not expected to be toxic to 

mammals. It is not expected to persist in the environment and does not bioaccumulate. It is 

biodegradable.

Potential areas of environmental justice concerns, to the extent possible, were considered in 

this human health risk assessment, in accordance with U.S. Executive Order 12898, "Federal 

Actions to Address Environmental Justice in Minority Populations and Low-Income 

Populations," http://www.eh.doe.gov/oepa/guidance/justice/eo12898.pdf. 

Taking into consideration all available information on DMSO (CAS Reg. No. 67-68-5), EPA 

concludes that there is a reasonable certainty that no harm will result to the general population or 

to infants and children from aggregate exposure to DMSO. Therefore, the establishment of an 

exemption from tolerance under 40 CFR 180.920 for residues of DMSO for use as an inert 

ingredient (diluent) at a level not to exceed 62% in pesticide formulations used before crop 

emerges from soil or prior to formation of edible parts of food plants; for pesticide formulations 

used after crop emerges but before harvest, provided that the potential for increased residues of 

the formulation’s active ingredient(s) in or on food commodities has been assessed, can be 

considered safe under section 408 of the FFDCA.
33

REFERENCES

MRID 49388701 Freeman, E. (2014) Compilation of References for the Petition for Dimethyl 

Sulfoxide (DMSO) (CAS RN 67-68-5) as a Pesticide Inert Ingredient in Non-Food Use 

Formulations and For Exemptions from the Requirement of a Tolerance in Accordance with 40 

CFR §180.920 for Post-Emergence Pre- Harvest use in the Cyclaniliprole Formulations.