1,2,4-Trichlorobenzene

1,2,4-Trichlorobenzene (1,2,4-TCB) is produced by the chlorination of benzene or dichlorobenzene, and was historically used as a high-boiling solvent in transformer oil and capacitor fluids, as a carrier solvent for pesticide production, and as an industrial degreaser [1]. It also forms as a byproduct in the production of 2,4,5-T and other chlorinated pesticides, and in the manufacture of some herbicides [2]. Transformer and dielectric fluid use has been a significant source of environmental contamination — old electrical equipment may contain trichlorobenzene-based insulating oils that leaked into soil over decades [1]. Like other chlorinated benzenes, it is persistent in the environment and is found in groundwater, sediment, and biota near contaminated sites [2].

Groundwater near electrical transformer facilities, former pesticide manufacturing plants, and industrial solvent disposal sites is the primary contamination source for private well users [1]. Food grown near contaminated soil can accumulate trichlorobenzene in fatty tissues [2]. Occupational inhalation occurs in facilities producing trichlorobenzene and in its industrial solvent applications [1].

1,2,4-TCB is metabolized by CYP enzymes to chlorinated phenol intermediates and catechol-type metabolites that generate reactive oxygen species [1]. It causes liver and kidney toxicity at occupational doses; thyroid effects have been observed in animal studies [2]. EPA classifies it as a possible (Group C) human carcinogen based on limited animal data. It is also a skin and mucous membrane irritant [1].

Private well users near contaminated industrial sites [1]. Industrial solvent and pesticide manufacturing workers [2].

1. Test well water near transformer facilities and former industrial sites [1]. 2. Activated carbon filtration for contaminated water [2]. 3. Occupational: local exhaust ventilation and respiratory protection [1].