Chlorinated aliphatic compounds in the environment

Natural products and synthetic compounds

Chlorinated aliphatic compounds are abundant in nature. Among the more than 1500 natural product organohalides that have been identified (Gribble, 1992) are a significant number of chlorinated aliphatic compounds. Quantitatively, chloromethane is the most significant. It is estimated that 5 × 109kg are produced annually, principally by soil fungi (Rasmussen, Khalil & Dalluge, 1980). The biochemical reaction producing chloromethane has been investigated (Wuosman & Hager, 1990) and soil bacteria have been identified that grow on chloromethane as a sole carbon and energy source (Hartmans et al., 1986; Traunecker, Preub & Dieckert, 1991). Hence, chloromethane is one of the almost innumerable intermediates in the global carbon cycle.

Chlorinated aliphatic compounds of industrial origin are perhaps more widely known. They include chloroalkanes, chloroalkenes, and chlorinated cycloaliphatic compounds (Figure 9.1). The principal usages of these compounds are as solvents and synthetic intermediates. 1, 2-Dichloroethane is one of the most heavily used commodity chemicals, with 17.95 billion pounds produced in the United States in 1993 (Reisch, 1994). Industrial solvents such as dichloromethane, trichloroethylene (TCE), and tetrachloroethylene (PCE) have been valuable because of their relative chemical inertness, ease of evaporative transfer, and relatively low mammalian toxicity. Other prominent solvents are 1, 1, 1-trichloroethane, chloroform, and carbon tetrachloride. The latter two have seen greatly decreased usage due to demonstrated toxicity and carcinogenicity (Anders & Pohl, 1985). Chlorofluorocarbons used as refrigerants are predominantly C1 and C2 alkanes. Although they show excellent heat transfer and chemical inertness characteristics, their well-documented ozone-depleting effects are leading to drastic constraints on their use (Molina & Rowland, 1974).