Organochlorine Pesticides Overview
Organochlorine pesticides, an older class of pesticides, are effective against a variety of insects. These chemicals were introduced in the 1940s, and many of their uses have been cancelled or restricted by the U.S. EPA because of their environmental persistence and potential adverse effects on wildlife and human health. Many organochlorines are no longer used widely in the U.S., but other countries continue to use them. Hexachlorobenzene has been used primarily as a fungicide or biocide.
Organochlorine pesticides can enter the environment after pesticide applications, disposal of contaminated wastes into landfills, and releases from manufacturing plants that produce these chemicals. Some organochlorines are volatile, and some can adhere to soil or particles in the air. In aquatic systems, sediments adsorb organochlorines, which can then bioaccumulate in fish and other aquatic mammals. These chemicals are fat soluble, so they are found at higher concentrations in fatty foods. In the general population, diet is the main source of exposure, primarily through the ingestion of fatty foods such as dairy products and fish. Usage restrictions have been associated with a general decrease in serum organochlorine levels in the U.S. population and other developed countries (Hagmar et al, 2006; Kutz et al., 1991). Contaminated drinking water and air are usually minor exposure sources. Infants can be exposed through breast milk, and the fetus can be exposed in utero via the placenta. Workers can be exposed to organochlorines in the manufacture, formulation, or application of these chemicals. The FDA, U.S. EPA, and OSHA have developed standards for allowable levels of certain organochlorines in foods, the environment, and the workplace, respectively. Attributing human health effects to specific organochlorine chemicals is difficult because exposure to multiple organochlorine chemicals occurs often, and these chemicals may have similar actions.
The table shows selected parent organochlorines and their metabolites that can be measured in serum or urine. Measurements of these chemicals can reflect either recent or cumulative exposures, or both. Some of the metabolites can be produced from more than one pesticide. The level of a metabolite in a person's blood or urine may indicate exposure to the parent pesticide as well as to the metabolite itself.
Organochlorine Pesticides and Metabolites
Measured in the National Biomonitoring Program
|Organochlorine pesticide (CAS number)||Serum pesticide or metabolite(s) (CAS number)||Urinary pesticide or metabolite(s) (CAS number)|
|Aldrin (309-00-02)||Aldrin (309-00-02)
|Chlordane (12789-03-6)||Oxychlordane (27304-13-8)
|Dieldrin (60-57-1)||Dieldrin (60-57-1)|
|Endrin (72-20-8)||Endrin (72-20-8)|
|Heptachlor (76-44-8)||Heptachlor epoxide (1024-57-3)|
|Hexachlorobenzene (118-74-1)||Hexachlorobenzene (118-74-1)||Pentachlorophenol (87-86-5)
|Mirex (2385-85-5)||Mirex (2385-85-5)|
CAS No. 67-72-1
Hexachloroethane is a solid that sublimates at room temperature. It is primarily used in combination with zinc or titanium oxides in military pyrotechnic or smoke generating devices, as an agent to degas or purify molten ores, as an ignition and explosive suppressant, and as a vulcanizing agent. Hexachloroethane is no longer produced in the U.S., and usage has declined since the 1970’s (ATSDR, 1997). In the past, hexachloroethane was used as an ingredient in some pesticides, in fire extinguisher fluids, and as a veterinary anti-helminthic (ATSDR, 1997). Hexachloroethane can enter the atmosphere from emissions during its production and use, or as a byproduct from the chlorination of other hydrocarbons. Hexachloroethane is relatively persistent in the environment and has been detected a low levels in ambient air and rarely in drinking water systems (USGS, 2006).
For the general population, hexachloroethane exposure is infrequent and occurs by inhaling contaminated air. A less common pathway is the ingestion of contaminated drinking water. Workers in metal and alloy refining or pyrotechnic and smoke device production may be exposed to larger amounts. Hexachloroethane is absorbed by inhalation, dermal and ingestion routes, and it is preferentially distributed to fat, kidney and liver. Metabolism in the liver results in formation of trichloroacetic acid and trichloroethanol, which are excreted in urine (ATSDR, 1997). A small portion of unmetabolized hexachloroethane is excreted in the feces.
Human health effects from hexachloroethane at low environmental doses or at biomonitored levels from low environmental exposures are unknown. Workers exposed to hexachloroethane reported irritation of the skin and mucous membranes, but no changes were noted in pulmonary function tests or in serum tests of renal, pancreatic, and liver function (Selden et al., 1994, Selden et al., 1997). Animals exposed to high air levels of hexachloroethane developed ataxia, facial twitching, tremors, and pneumonitis (Weeks et al., 1979). In feeding studies, animals developed dose-related abnormalities of the liver (enlargement, transaminase elevation, centrilobular necrosis) and kidney (tubular nephrosis and nephrocalcinosis) (ATSDR, 1997). Animal carcinogenicity studies show inconsistent evidence of hepatocellular carcinomas (NCI, 1978), an increased incidence of renal tumors in males (NTP, 1989), and no clear evidence of mutagenicity or genotoxicity. Hexachloroethane does not appear to be a reproductive or developmental
toxicant in animal studies (ATSDR, 1997).
Hexachloroethane is classified as a possible human carcinogen by IARC and is reasonably anticipated to be a human carcinogen by NTP. The U.S. EPA has established drinking water and other environmental regulations for hexachloroethane. Workplace standards and guidelines for hexachloroethane have been established by OSHA and ACGIH, respectively. Information about external exposure (ie., environmental levels) and health effects is available from ATSDR at https://www.atsdr.cdc.gov/toxprofiles/index.asp.
Levels of hexachloroethane in the blood reflect recent exposure. Blood levels were not detectable in the NHANES 2003-2004 or 2005-2006 subsamples as has been the case in several other general population studies (Ashley et al., 1994; Buckley et al., 1997; Foster, 1995; Selden et al., 1993).
Finding a measureable amount of hexachloroethane in blood does not imply that the level of hexachloroethane causes an adverse health effect. Biomonitoring studies of blood hexachloroethane can provide physicians and public health officials with reference values so that they can determine whether or not people have been exposed to higher levels of hexachloroethane than levels found in the general population. Biomonitoring data can also help scientists plan and conduct research on exposure and health effects.
Agency for Toxic Substances and Disease Registry (ATSDR). Toxicological profile for hexachloroethane. 1997 [online]. Available from URL: https://www.atsdr.cdc.gov/toxprofiles/tp.asp?id=870&tid=169 8/3/012
Ashley DL, Bonin MA, Cardinali FL, McCraw JM, Wooten JV. Blood concentrations of volatile organic compounds in a nonoccupationally exposed US population and in groups with suspected exposure. Clin Chem 1994;40(7 Pt 2):1401-1404.
Buckley TJ, Liddle J, Ashley DL, Paschal DC, Burse VW, Needham LL, Akland G. Environmental and biomarker measurements in nine homes in the lower Rio Grande Valley: multimedia results for pesticides, metals, PAHs, and VOCs. Environ Int 1997;23:705-32.
Foster WG. The reproductive toxicology of Great Lakes contaminants. Environ Health Perspect 1995;103 Suppl 9:63-9.
National Cancer Institute (NCI). Bioassay of hexachloroethane for possible carcinogenicity (CAS No. 67-72-1). NCI-CG-TR-68. Tech Report Ser No. 68. U.S. DHEW. Publ. No. (NIH) 78-1318. Bethesda MD. 1978. Available at URL: https://ntp.niehs.nih.gov/ntp/htdocs/LT_rpts/tr068.pdfpdf iconexternal icon. 8/3/12
National Toxicology Program (NTP). Toxicology and carcinogenesis studies of hexachloroethane (CAS No.67-72-1) in F344/N rats (gavage studies). Tech Report Ser No. 361. NIH Publication No. 89-2816. Research Triangle Part, NC: National Toxicology Program. Research Triangle Park NC, 1989 [online]. Available at URL: https://ntp.niehs.nih.gov/ntp/htdocs/lt_rpts/tr361.pdfpdf iconexternal icon. 8/3/12
Selden A, Kvamlof A, Bodin L, et al. Health effects of low level occupational exposure to hexachloroethane. J Occup Med Toxicol 1994;3(10):73-79.
Selden A, Nygren M, Kvarnlof A, Sundell K, Spangberg O. Biological monitoring of hexachloroethane. Int Arch Occup Environ Health 1993;65(1 Suppl):S111-S114.
Selden AI, Nygren Y, Westberg HB, Bodin LS. Hexachlorobenzene and octachlorostyrene in plasma of aluminium foundry workers using hexachloroethane for degassing. Occup Environ Med 1997;54(8):613-618.
United States Geological Survey (USGS). Volatile organic compounds in the nation’s ground water and drinking-water supply wells. Reston VA. 2006 [online]. Available at URL: https://pubs.usgs.gov/circ/circ1292/external icon. 8/3/012
Weeks MH, Angerhofer RA, Bishop R, Thomasino J, Pope CR. The toxicity of hexachloroethane in laboratory animals. Am Ind Hyg Assoc J 1979;40:187-199.