Chlorinated benzenes in the environment.

Chlorinated benzenes are composed of twelve chemical species: one mono-, three di-, three tri-, three tetra-, one penta-, and one hexachlorobenzene. Most of these are not only important intermediates for various kinds of chemicals but are also extensively employed for various applications singly or in combination. For example, 1,4-dichlorobenzene is used chiefly against termites in soil; trichlorobenzenes are used as solvents for pesticides and also as heat transfer agents with PCBs; the mixture of trichlorobenzene and tetrachlorobenzene is applied in controlling shellfish predators; and hexachlorobenzene is applied to wheat as a fungicide in some countries and as an additive to rubber products. The annual production (1973) of monochlorobenzene, 1,2-dichlorobenzene, and 1,4-dichlorobenzene in Japan was about 23,000, 9000, and 20,000, tons, respectively. Production volumes of other chlorinated benzenes are not well known but are assumed to be smaller than those of the above three compounds. The total annual production of chlorinated benzenes far surpasses the peak production of PCBs (7000 tons/year) which are known as a ubiquitous pollutant in this country. Since chlorinated benzenes have a chemical structure and properties similar to those of PCBs and PCTs, it seemed necessary to direct our attention to environmental contamination by these materials. The present paper describes only the occurrence and the fate of these materials. Toxicity and biological impact are not referred to here.