Of the ten known chlorophenols, five are produced as intermediates or end-products in the chemical industry (Table 9.4). Compared with chlorobenzenes, chlorophenols have a higher solubility in water and a lower Henry coefficient of nearly two orders of magnitude. Because of its high toxicity and its low biodegradability, pentachlorophenol (PCB) was used during the 1970s as an herbicide, fungicide and disinfectant worldwide in amounts of several 10 0001 a-1. As a result of stronger regulations, production decreased during the 1980s (BRD in 1983 produced 1800 t a-1, EU in 1989 produced 1000 t a-1; Rippen 1991).

Khandker (1992) studied the aerobic degradation of 4-MCP as the only source of carbon and energy by a culture with three strains of bacteria (YX/S = 0.63 MLSS (gMCP)-1, pmax = 3.6 d-1, KS = 21.1 mg L-1 MCP). The relatively high KS value points to a large region of substrate limitation.

The oxidation of 2-CP, 3-CP, 4-CP and 2,4-DCP by H2O2 was catalyzed by an immobilized peroxidase (Siddique et al. 1993). High oxidation rates were obtained, but high-molecular-weight polymerization products arose which precipitated as small solid particles.

Table 9.4 Some chlorophenols, their properties and use. For symbols used, see Table 9.1.

Compound c* H LD50 Uses EPA

2-Monochlorphenol 29.0 0.49 670

4-Monochlorophenol 27.0 (4-CP)

Pentachlorophenol 19 0.029 • 10-3 50

Intermediate in the production of phenols, phenol resins, dyes, bactericide, fungicide

Intermediate in the production of 2,4-DCP, TCP and TeCP solvent for mineral oil industry

Intermediate in the production of 2,4-dichlorophenoxy acetate herbicide, toxin for moths

Intermediate in the production of 2,4,5-trichlorophen-oxyacetate herbicide, fungicide, preservation aid

Herbicide, fungicide Wood preserver Disinfectant

204 | 9 Biodegradation of Special Organic Compounds 9.3

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