Biomonitoring Summary

Carbamate Insecticides Overview

General Information

N-methyl carbamate insecticides (carbamates) have been widely used in the U.S. and throughout the world. In agricultural applications, the use of the carbamate insecticides has decreased, being replaced by pyrethroid and other insecticides. Carbamates have been used on residential lawns, ornamentals, in nurseries, and on golf courses. Carbamates do not persist in the environment and have a low potential for bioaccumulation. Some other chemical types of carbamates, thiocarbamates and dithiocarbamates, are used as herbicides and fungicides.

General population exposure to carbamates occurs during contact with residential uses and less commonly, from ingesting contaminated foods. Agricultural workers can be exposed when they re-enter areas recently treated. Exposures to workers also can occur during the manufacture, formulation, or application of these chemicals. Carbamates can be absorbed through the skin, via inhalation, or by ingestion. Criteria for allowable levels of specific carbamates in food, the environment, and the workplace have been developed by the U.S. FDA, U.S. EPA, and OSHA, respectively.

Carbamate insecticides act by inhibiting acetylcholinesterase enzymes, which leads to an increase of acetylcholine in the nervous system. At high doses, toxic symptoms include nausea, vomiting, cholinergic signs, weakness, paralysis, and seizures. The mechanism of toxicity of carbamate insecticides is similar to organophosphate pesticides; however, carbamate insecticides generally are reversible inhibitors of acetylcholinesterase activity, acting for a shorter time than organophosphate pesticides. Carbamate insecticides are rapidly eliminated from the body. In the National Biomonitoring Program, two carbamate metabolites that are measured relate to two (carbofuran and propoxur) of about nine carbamate insecticides still used in the U.S.

Propoxur

CAS No. 114-26-1

General Information

2-Isopropoxyphenol is a metabolite of propoxur, a carbamate used to control ants, roaches, hornets, and similar pests in residential areas and around commercial food-handling establishments. Propoxur has also been used in pest strips and pet flea collars. Like several other pesticides, propoxur has been used outside the U.S. as a replacement for DDT in malaria vector control. Propoxur may remain in the environment for weeks to several months, longer than most carbamates (U.S.EPA, 1997b). Despite its mobility in soil and potential for leaching into groundwater, propoxur has been rarely detected in U.S. surface or ground waters (Gilliom, 2007; USGS, 2007). Although propoxur is toxic to birds and aquatic life, ecologic exposures are unlikely due to current outdoor use restrictions.

General population exposure to propoxur through the diet is likely to be limited because of usage restrictions (U.S. EPA, 1997a). Estimated human intakes have been below recommended intake limits (U.S.EPA, 1997b). Pesticide applicators are likely to have the highest exposures. Propoxur can be absorbed through the skin, lungs, and gastrointestinal tract. Propoxur does not accumulate in blood or tissues and is eliminated rapidly from the body (Leenheers et al., 1992; WHO, 2003). In animal and human studies, 2-isopropoxyphenol was one of several urine metabolites (U.S.EPA, 1997b).

Human health effects from propoxur at low environmental doses or at biomonitored levels from low environmental exposures are unknown. In animal studies, propoxur has moderate acute toxicity consisting of anticholinesterase effects (U.S.EPA, 1997b). 2-Isopropoxyphenol does not inhibit acetylcholinesterase enzymes. Propoxur is not considered mutagenic, embryotoxic, or teratogenic (WHO, 2003). U.S. EPA considers propoxur to be a probable human carcinogen, based on bladder tumors in male rats (U.S. EPA, 1997b). The human carcinogenic potential of propoxur has not been evaluated by IARC or NTP. Additional information is available from U.S.EPA at: https://www.epa.gov/pesticides/.

Biomonitoring Information

Urinary 2-isopropoxyphenol levels reflect recent exposure. The level of this metabolite in urine may reflect exposure to propoxur or to 2-isopropoxyphenol as a degradation product in the environment or food (U.S.EPA, 1997b). In the U.S. representative subsamples from NHANES 1999-2000 and 2001-2002, most 2-isopropoxyphenol levels in urine were below the limit of detection (CDC, 2009). In a nonrandom subsample from NHANES III (1988-1994), the 95th percentile level of 2-isopropoxyphenol was 1.7 µg/L (Hill et al., 1995). Higher urinary levels of 2-isopropoxyphenol have been measured in a few pesticide applicators, ranging 45-306 µg/g creatinine (Hardt and Angerer, 1999).

Finding a measurable amount of 2-isopropoxyphenol in urine does not imply that the level of 2-isopropoxyphenol causes an adverse health effect. Biomonitoring studies on levels of 2-isopropoxyphenol provide physicians and public health officials with reference values so that they can determine whether people have been exposed to higher levels of propoxur than are found in the general population. Biomonitoring data can also help scientists plan and conduct research on exposure and health effects.

References

Centers for Disease Control and Prevention (CDC). Fourth National Report on Human Exposure to Environmental Chemicals. 2009. [online] Available at URL: https://www.cdc.gov/exposurereport/. 12/28/12

Gillion, R. Pesticides in U.S. streams and groundwater. Environ Sci Technol 2007;41:3409-3414. Available at URL: https://water.usgs.gov/nawqa/pnsp/pubs/files/051507.ESTfeature_gilliom.pdf. 12/28/12

Hardt J, Angerer J. Gas chromatographic method with mass-selective detection for the determination of 2-isopropoxyphenol in human urine. J Chromatogr B Biomed Sci Appl 1999;723(1-2):139-145.

Hill RH Jr, Head SL, Baker S, Gregg M, Shealy DB, Bailey SL, et al. Pesticide residues in urine of adults living in the United States: reference range concentrations. Environ Res 1995;71(2):99-108.

Leenheers LH, van Breugel DC, Ravensberg JC, Meuling WJ, Jongen MJ. Determination of 2-isopropoxyphenol in urine by capillary gas chromatography and mass-selective detection. J Chromatogr 1992;578(2):189-194.

U.S. Environmental Protection Agency (U.S.EPA). RED Facts. Propoxur. August 1997a. EPA 738 F-97-009. Available at URL: https://www.epa.gov/oppsrrd1/REDs/factsheets/2555fact.pdf. 12/28/12

U.S. Environmental Protection Agency (U.S.EPA). Reregistration Eligibility Decision (RED) Propoxur. August 1997b. EPA 738-R-97-009. Available at URL: https://www.epa.gov/pesticides/reregistration/REDs/2555red.pdf. 12/28/12

U.S. Geological Survey (USGS). The Quality of Our Nation's Waters Pesticides in the Nation's Streams and Ground Water, 1992-2001. Circular 1291. Supplemental Technical Information (available on-line only). March 2006, revised February 15, 2007. Available at URL: https://water.usgs.gov/nawqa/pnsp/pubs/circ1291/supporting_info.php. 12/28/12

World Health Organization (WHO). WHO Specifications and Evaluations for Public Health Pesticides. Propoxur. FAO/WHO Evaluation Report 80/2003. 2003. Available at URL:

http://www.who.int/whopes/quality/en/propoxur_eval_spec_WHO_October_2005.pdf. 12/28/12