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Extension Toxicology Network

A Pesticide Information Project of Cooperative Extension Offices of Cornell University, Michigan State University, Oregon State University, and University of California at Davis. Major support and funding was provided by the USDA/Extension Service/National Agricultural Pesticide Impact Assessment Program.


Publication Date: 9/93


Commercial names for the product include Thiodan, Endocide, Beosit, Cyclodan, Malix, Thimul and Thifor.


Endosulfan is a chlorinated hydrocarbon insecticide of the cyclodiene subgroup which acts as a contact poison in a wide variety of insects and mites. It can also be used as a wood preservative. It is used primarily on food crops like tea, fruits, vegetables and on grains.

The commercial product is made up of a mixture of two separate parts (isomers): the alpha and beta configurations. Endosulfan will be considered as a single (homogenous) product unless otherwise stated in this profile.



Endosulfan is a highly toxic substance and carries the signal word DANGER on the label. Toxicity is partly dependent on the manner with which the pesticide is administered (7). Undiluted endosulfan is slowly and incompletely absorbed into the body whereas absorption is more rapid in the presence of alcohols, oils and emulsifiers.

Stimulation of the Central Nervous System is the major characteristic of endosulfan poisoning (9). Symptoms of acute exposure are indistinguishable from symptoms from other cyclodienes (10). They include incoordination, even a loss of the ability to stand. Other signs of poisoning include gagging, vomiting, diarrhea, agitation, convulsions and loss of consciousness. Blindness has been documented for cows which grazed in a field sprayed with the compound. The animals completely recovered after a month following the exposure (10). In an accidental exposure, sheep and pigs grazing on a sprayed field suffered a lack of muscle coordination and blindness.

The oral LD50 in rats ranges from 18 - 220 mg/kg. Some other oral LD50 values are: mice 7.36 mg/kg, hamsters 118 mg/kg, cats 2 mg/kg, and dogs 76.7 mg/kg. The dermal LD50 for rats is 74 mg/kg while for rabbits figures from 200 to 359 mg/kg are recorded. As noted before, the solvents and emulsifiers used to dissolve endosulfan influence its toxicity. Rats have an inhalation LC50 of 8.0 mg/m3 for four hours. Dogs are less tolerant than rats to this compound and rats are nearly twice as susceptible to endosulfan when they have been deprived of protein.


Several chronic effects have been noted for animals exposed to endosulfan. The pesticide is most likely to affect kidneys, liver, blood chemistry and the parathyroid gland (9).

Reproductive Effects

Rats fed low doses of endosulfan (2.5 mg/kg/day) for three generations showed no ill effects. The same dose in dogs, however, produced vomiting, tremors, and convulsions. These are the symptoms of acute endosulfan poisoning. Higher doses of endosulfan (5.0 mg/kg/day) caused death in rat dams, increased resorption and caused skeletal deformities in the rat fetuses (10). Female mice fed the compound for 78 weeks (0.1mg/kg/day) had damage to their reproductive organs.

Teratogenic Effects

When moderate to high levels of endosulfan (5 or 10 mg/kg/day) were given orally to female rats on days 6 to 14 of pregnancy, no soft tissue defects were found in their offspring. Some delayed bone formation occurred, however. It is possible that chronic exposure to endosulfan may result in reproductive and/or developmental difficulties in humans. There is no direct evidence of this in humans though.

Mutagenic Effects

Endosulfan is mutagenic to bacterial cells and to yeast cells. The metabolites of endosulfan have also shown the ability to cause cellular changes (10). This compound has also caused mutagenic effects in two different mammalian species. It is possible that it would induce these changes in humans.

Carcinogenic Effects

In a National Cancer Institute study done with both mice and rats, the males of both groups experienced such a high mortality rate that no conclusions could be drawn (1). However, the females of both species failed to develop any carcinogenic conditions 78 weeks after being fed diets containing up to 445 ppm (about 23 mg/kg). There are no reports of cancer in humans exposed to endosulfan. The EPA has placed endosulfan in the "not classifiable" category due to the lack of data on its carcinogenicity.

Fate in Humans and Animals

Endosulfan is rapidly degraded and eliminated in mammals with very little absorption in the gastrointestinal tract. Cattle fed 0.15 mg/kg for 60 days had no residues in the fat. The metabolite, endosulfan sulfate, seems to show similar acute toxicity to the parent compound. The beta isomer is cleared from blood plasma more quickly than the alpha isomer (3). Most of the endosulfan seems to leave the body within a few days to a few weeks.

Mice fed endosulfan had both isomers plus two breakdown products in the feces. There were only traces of oxidized endosulfan in the kidney and muscle.


Birds in general are fairly sensitive to endosulfan poisoning. The oral LD50 is 33 mg/kg for young ducks (205-243 mg/kg for mature mallards). The oral LC50 is 805 mg/kg for bobwhite quail and 1,275 mg/kg for ring-necked pheasants. Male mallards from three to four-months-old exhibited wings crossed high over their back, tremors, falling, and other symptoms as soon as ten minutes after an acute, oral dose. The symptoms persisted for up to a month in a few animals (3).

Several fish species are quite susceptible to endosulfan. The 96- hour LC50 is 1.2 ppb for bluegill and 1.4 ppb for rainbow trout. In an accidental fish kill, the initial water level was 30.9 ppb which dropped to 0.01 - 6.5 ppb in four days. Endosulfan is also quite toxic to birds and to shellfish. It is moderately toxic to bees and is relatively non-toxic to beneficial insects such as parasitic wasps, lady bird beetles and some mites (8).


Endosulfan does not easily dissolve in water. It does stick to soil particles readily. Transport of this pesticide is most likely occur if endosulfan is attached to soil particles in surface runoff. Large amounts of endosulfan can be found in surface water near areas of application (9). It has also been found in surface water throughout the country at very low concentrations and has been detected in the air at minute levels. It is has been found, but not quantified, in well water in California (11). It is not expected to pose a threat to groundwater.

In raw river water at room temperature and exposed to light, both isomers disappeared in four weeks. A breakdown product first appeared within the first week. The breakdown in water is faster (five weeks) under neutral conditions than at more acidic conditions (five months). Under strongly alkaline conditions the half-life of the compound is one day.

The two isomers have different degradation times in soil. The half-life for the alpha isomer is 35 days and 150 days for the beta isomer under neutral conditions. These two isomers will persist longer under more acidic conditions. The compound is broken down in soil by fungi and by bacteria (2).

The breakdown product, endosulfan sulfate, has been observed in several field studies involving plants. The sulfate is more persistent than the parent compound, accounting for 90% of the residue in 11 weeks. Sulfate formation increases as temperatures increase (2). However, sunlight may play a role in the reaction, perhaps in starting the process. On most fruits and vegetables, 50% of the parent residue is lost within three to seven days.

Endosulfan and endosulfan residues have been found in numerous food products at very low concentrations. They have been detected in vegetables (0.0005 - 0.013 ppm), in tobacco, in various seafoods (0.2 ppt - 1.7 ppb), and in milk.

Exposure Guidelines:

NOEL (rat): 0.15 mg/kg/day
TLV-TWA: 0.1 mg/m3
TLV STEL: 0.3 mg/m3
ADI: 0.006 mg/kg/day (ppm) (WHO)
RfD: 0.00005 mg/kg/day (EPA); 0.0015 mg/kg/day (OPP)
LEL: 0.75 mg/kg/day (rat)

Physical Properties:

CAS #: 115-29-7
Chemical name: 6,7,8,10,10-hexachloro-1,5,51,6,9,9a-hexahydro-6,9-methano-2,4,3-benzadioxathiepin 3-oxide
Chemical class/use: chlorinated hydrocarbon insecticide
Solubility in water: alpha isomer: 0.32 mg/l; beta isomer: 0.33 mg/l
Solubility in other solvents: toluene 20 g/100 g; hexane 2.4 g/100 g;
Melting Point: alpha isomer: 109.2 degrees C; beta isomer: 213.3 degrees C; technical material 70-100 degrees C.
Vapor Pressure: 1.7 x 10 to the minus 7 power mm Hg


FMC Corporation
Agricultural Chemicals Group
2000 Market Street
Philadelphia, PA 19103
Telephone: 215/299-6000
Emergency: 800-331-3148

Review by Basic Manufacturer:

Comments solicited: October, 1992
Comments received:


  1. National Cancer Institute (1978). Bioassay of Endosulfan for Possible Carcinogenicity, U. S. Department of Health, Education and Welfare, Public Health Service, National Institutes of Health, Technical Report Series No. 62.
  2. National Research Council Canada (1975). Endosulfan: Its Effects on Environmental Quality. Subcommittee on Pesticides and Related Compounds, NRC Associate Committee on Scientific Criteria for Environ Quality, Report No. 11, Ottawa, Canada.
  3. National Library of Medicine (1987). Hazardous Substances Databank. TOX-NET, Medlars Management Section, Bethesda, MD.
  4. Chemical Information Systems, Inc. (1988). Oil and Hazardous Materials/Technical Assistance Data System, Baltimore, MD.
  5. Food and Agriculture Organization of the United Nations
  6. Pesticide Residues in Food - 1982. FAO Plant Production and Protection Paper 49.
  7. National Institute for Occupational Safety and Health (1985-86) Registry of Toxic Effects of Chemical Substances, U. S. Department of Health and Human Services, Centers for Disease Control.
  8. Maier - Bode, H. (1968). Properties, Effect, Residues, and Analytics of the Insecticide Endosulfan, Residue Reviews 22:10-44.
  9. Farm Chemicals Handbook. (1992). Meister Publishing Company. Willoughby, OH.
  10. US Department of Health and Human Services. 1990. Toxicological Profile for Endosulfan. Draft. Public Health Service, Agency for Toxic Substances and Disease Registry.
  11. Smith, Andrew G. (1991). Chlorinated Hydrocarbon Insecticides. in Handbook of Pesticide Toxicology, Volume 3, Classes of Pesticides. Wayland J. Hayes Jr. and Edward R. Laws, Jr. editors. Academic Press, Inc., NY.
  12. Howard, Philip H. 1991. Handbook of Environmental Fate and Exposure Data for Organic Chemicals. Volume III, Pesticides. Lewis Publishers, Chelsea, MI.