Dense Nonaqueous Phase Liquids (DNAPLs)

1,2,4-Trichlorobenzene

Human Health Toxicity

1,2,4-Trichlorobenzene (1,2,4-TCB) has use as an industrial solvent, a feedstock for the synthesis of other chemicals, a component of dielectric fluids, and an herbicide for the control of aquatic weeds. The general population can be exposed to the chemical via inhalation of contaminated ambient air and by the ingestion of contaminated foodstuffs, such as fish. Nursing infants might be exposed to 1,2,4-TCB, as this compound has been found in breast milk.

1,2,4-TCB appears to be well absorbed by all routes of administration; however, absorption is inferred from observing the systemic effects of the compound in dermal and inhalational toxicity studies. Animal studies show that once absorbed, the initial distribution of the compound is to the liver, kidney and adrenals, with subsequent accumulation in abdominal fat and liver. The products of 1,2,4-TCB metabolism are excreted in urine and to a lesser extent in feces.

Few studies report the effects of 1,2,4-TCB on humans. Laboratory rodent studies show the compound to be acutely toxic to rats and mice, capable of producing liver damage and an increase in weight of the adrenal glands. A chronic toxicity study using mice suggests that 1,2,4-TCB is carcinogenic in these animals, as the test subjects developed liver cancer after dietary exposure.

A multi-generational rat study of the reproductive toxicity of 1,2,4-TCB identified no treatment-related effects on fertility, neonatal weight, maternal weight litter size, post-weaning growth, blood chemistry, or locomotor activity. Other laboratory rat studies were negative for the teratogenicity of the compound.

1,2,4-TCB has given both positive and negative results in standard genotoxicity assays

References

Public Health Goal for 1,2,4-Trichlorobenzene in Drinking Water
Polakoff, J.
California Environmental Protection Agency, Office of Environmental Health Hazard Assessment, 27 pp, 1999

Chlorobenzenes other than Hexachlorobenzene: Environmental Aspects
Malcolm, H.M., P.D. Howe, and S. Dobson.
World Health Organization, Geneva. Concise International Chemical Assessment Document 60, 2004

Ecological Toxicity

The Pesticide Action Network Database gives summary data for the acute toxicity of 1,2,4-TCB to nine groups of aquatic organisms in addition to data for the effects of the compound for other ecological receptors. The range of 1,2,4-TCB toxicity has been summarized as "moderate to high toxicity" for zooplankton, annelids, and fish, "moderate toxicity" to nematodes, flatworms, echinoderms, and cnideria, and "slight to very high toxicity" to crustaceans. 1,2,4-TCB toxicity data for aquatic species are also presented in Rowe et al. (1997) and Malcolm et al. (2004). No terrestrial ecological studies were found for this compound, but a toxicity reference value is given in DOE (1999).

References

1,2,4-Trichlorobenzene: Identification, Toxicity, Use, Water Pollution Potential, Ecological Toxicity, and Regulatory Information
Kegley, S.E., B.R. Hill, S. Orme, and A.H. Choi.
PAN Pesticide Database. Pesticide Action Network, San Francisco, CA, 2010

Chlorobenzenes other than Hexachlorobenzene: Environmental Aspects
Malcolm, H.M., P.D. Howe, and S. Dobson.
World Health Organization, Geneva. Concise International Chemical Assessment Document 60, 2004

Summary of Published Aquatic Toxicity Information and Water Quality Criteria for Selected Volatile Organic Compounds
Rowe, B.L., S.J. Landrigan, and T.J. Lopes.
U.S. Geological Survey Open-File Report 97-563, 66 pp, 1997

Terrestrial Toxicity Reference Values
U.S. DOE
Manual ERD-AG-003 Revision 0 (TRVs), 1999

This 13-page Department of Energy manual provides toxicity reference values for earthworms, various mammals, and various bird species.