Biomonitoring Summary

Organochlorine Pesticides Overview


CAS No. 95-95-4


CAS No. 88-06-2
Metabolites of Organochlorine Pesticides and Other Environmental Chemicals

General Information

The chlorophenols, 2,4,5-trichlorophenol (2,4,5-TCP) and 2,4,6-trichlorophenol (2,4,6-TCP), are metabolites of several organochlorine chemicals, including hexachlorobenzene and hexachlorocyclohexanes. Historically, 2,4,5-TCP and 2,4,6-TCP were used as intermediates in the production of certain pesticides; 2,4,6-TCP was also used as a wood preservative and may still be used in production of some fungicides (ATSDR, 1999). Trichlorophenols are no longer manufactured commercially, but they may be produced as by-products during manufacturing of other chlorinated aromatic compounds. Formation of 2,3,7,8-tetrachlorodibenzo-p-dioxin occurs during the synthesis of 2,4,5-trichlorophenol. Small amounts of trichlorophenols also can be produced during combustion of natural materials and the chlorination of drinking water or waste water that contains phenols. Environmental sources of these compounds include industrial discharges or run off from pesticide facilities or disposal sites. Both chemicals have been detected in air, surface water, soils, and sediments; however, recent sampling of U.S. public drinking water systems did not detect 2,4,6-TCP in any of the samples (U.S. EPA, 2006). Trichlorophenols have been detected in fish taken from waters near waste water treatment and industrial discharges (ATSDR, 1999).

General population exposure may occur by ingesting contaminated food or water and by inhaling contaminated air. Exposure to trichlorophenols also may result from metabolism of lindane, hexachlorobenzene, other organochlorines, and polychlorinated benzenes (Kohil et al., 1976). Occupational exposures, usually at herbicide production or waste incineration facilities, may occur by inhalation or dermal routes. Such workers would probably be exposed to mixtures of chlorophenols, in addition to dioxins, furans, and other chlorinated compounds. However, recent small studies have not demonstrated increased exposure to trichlorophenols in workers who dredged contaminated soils or incinerated waste materials (Agramunt et al., 2003; Radon et al., 2004).

Human health effects from 2,4,5-TCP or 2,4,6-TCP at low environmental doses or at biomonitored levels from low environmental exposures are unknown. Laboratory animals chronically fed high doses of 2,4,6-TCP had increased rates of hepatic tumors, leukemias, and lymphomas. At lower doses, animals showed hepatocellular abnormalities. Neither 2,4,5-TCP nor 2,4,6-TCP were developmental or reproductive toxicants in animals (ATSDR 1999). IARC classifies combined exposures to polychlorophenols, which includes trichlorophenols, as being possibly carcinogenic to humans. IARC considers the experimental evidence for animal carcinogenicity inadequate for 2,4,5-TCP and limited for 2,4,6-TCP. NTP classifies 2,4,6-TCP as reasonably anticipated to be a human carcinogen. More information about external exposure (i.e., environmental levels) and health effects is available from ATSDR at

Biomonitoring Information

In the NHANES 2003-2004, 2005-2006, 2007-2008, and 2009-2010 subsamples, adult urinary 2,4,6-TCP levels at the 95thpercentile (1.1-1.3 µg/L) were about half the value 3.3 µg/L in a nonrandom adult subsample from NHANES III (Hill et al., 1995) and similar to the 95thpercentile value of 1.3 µg/L reported in German adults aged 18-69 years (Becker et al., 2003; CDC, 2012). Among 6-11 year old children in NHANES 2003-2004, the 95th percentile urinary 2,4,6-TCP level was approximately one half the value in the corresponding percentile for a small group of2-6 year old children living near an herbicide manufacturing facility: 1.9 versus 4 µg/L, respectively (CDC, 2012; Hill et al., 1989). In the same 2-6 year old children, the 95th percentile urinary 2,4,5-TCP, 7.0 µg/L, was more than 20 times greater than the corresponding percentile for 6-11 year old children in NHANES 2003-2004 (0.30 µg/L) (CDC, 2012; Hill et al., 1989). The 95th percentiles for urinary 2,4,5-TCP among adults in NHANES 2003-2004 were slightly higher than values reported in German adults aged 18-69 years: 0.4 and 0.9 µg/L (Becker et al., 2003; CDC, 2012). A small study of adults who ate Great Lakes sport fish reported a mean urine 2,4,5-TCP level of 0.7 µg/L, which is about two times greater than the 95%tile in NHANES 2003-2004 (Anderson et al., 1998; CDC, 2012). Urinary 2,4,5-TCP and 2,4,6-TCP were monitored in a group of hazardous waste incinerator workers from 1999-2002. Mean values of2,4,5-TCP (0.2-0.6 g/g creatinine) and 2,4,6-TCP (0.7-3.5 g/g creatinine) were similar or slightly lower than the higher percentiles (75th -95th) for males in NHANES 2003-2004 (Agramunt et al., 2003; CDC, 2012). In harbor workers exposed to chlorophenol-contaminated river silt, the 75th percentile urinary 2,4,6-TCP level, 0.36 g/g creatinine, was similar to the corresponding percentile in adult males in NHANES 2003-2004 (CDC, 2012; Radon et al., 2004). Sawmill workers exposed to chlorophenol wood preservatives had mean urinary 2,4,6-TCP levels ranging from 278 to 992 µg/L, more than 750 times greater than the 95th percentile level for adult males in the NHANES 2003-2004 subsample (CDC, 2012; Pekari et al., 1991).

Finding a measurable amount of 2,4,5-TCP or 2,4,6-TCP in urine does not imply that the level of2,4,5-TCP or 2,4,6-TCP causes an adverse health effect. Biomonitoring studies on levels of2,4,5-TCP and 2,4,6-TCP provide physicians and public health officials with reference values so that they can determine whether people have been exposed to higher levels of 2,4,5-TCP or 2,4,6-TCP than are found in the general population. Biomonitoring data will also help scientists plan and conduct research about 2,4,5-TCP or 2,4,6-TCP exposure and health effects.


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