ABSTRACT

Opperhuizen et al., 1985) Vapor pressure (mmHg): 6 x 10-3 at 20-30 °C (quoted, Mercer et al., 1990) Environmental fate: Biological. In activated sludge, <0.1% mineralized to carbon dioxide after 5 d (Freitag et al., 1985). The half-life of pentachlorobenzene in an anaerobic enrichment culture was 24 h (Beurskens et al., 1993). In an enrichment culture derived from a contaminated site in Bayou d’Inde, LA, pentachlorobenzene underwent reductive dechlorination to 1,2,4,5-and 1,2,3,5tetrachlorobenzene at relative molar yields of 9 and 91%, respectively. The maximum dechlorination rate, based on the recommended Michaelis-Menten model, was 131 nM/d (Pavlostathis and Prytula, 2000). Soil. An estimated degradation half-life of 270 d was reported for pentachlorobenzene in soil (Beck and Hansen, 1974). Photolytic. UV irradiation (λ = 2537 Å) of pentachlorobenzene in n-hexane solution for 3 h produced a 50% yield of 1,2,4,5-tetrachlorobenzene and a 13% yield of 1,2,3,5-tetrachlorobenzene (Crosby and Hamadmad, 1971). Irradiation (λ ≥285 nm) of pentachlorobenzene (1.1-1.2 mM/L) in an acetonitrile-water mixture containing acetone (0.553 mM/L) as a sensitizer gave the following products (% yield): 1,2,3,4-tetrachlorobenzene (6.6), 1,2,3,5-tetrachlorobenzene (52.8), 1,2,4,5-tetrachlorobenzene (15.1), 1,2,4-trichlorobenzene (1.9), 1,3,5-trichlorobenzene (5.3), 1,3-dichlorobenzene (0.9), 2,2′,3,3′,4,4′,5,6,6′-nonachlorobiphenyl (2.08), 2,2′,3,3′,4,4′,5,5′,6-nonachlorobiphenyl (0.34), 2,2′,3,3′,4,5,5′,6,6′-nonachlorobiphenyl (trace), one octachlorobiphenyl (0.53), and one heptachlorobiphenyl (0.49) (Choudhry and Hutzinger, 1984). Without acetone, the identified photolysis products (% yield) included 1,2,3,4-tetrachlorobenzene (3.7), 1,2,3,5-tetrachlorobenzene (13.5), 1,2,4,5-tetrachlorobenzene (2.8), 1,2,4-trichlorobenzene (12.7), 1,3,5-trichlorobenzene (1.0) and 1,4-dichlorobenzene (6.7) (Choudhry and Hutzinger, 1984). A carbon dioxide yield of 2.0% was achieved when pentachlorobenzene adsorbed on silica gel was irradiated with light (λ >290 nm) for 17 h (Freitag et al., 1985). The experimental first-order decay rate for pentachlorobenzene in an aqueous solution containing a nonionic surfactant micelle (Brij 58, a polyoxyethylene cetyl ether) and illuminated by a photoreactor equipped with 253.7-nm monochromatic UV lamp is 1.47 x 10-2/sec. The corresponding half-life is 47 sec. Photoproducts reported include all tetra-, tri-, and dichlorobenzenes, chlorobenzene, benzene, phenol, hydrogen, and chloride ions (Chu and Jafvert, 1994). Chemical/Physical. Emits toxic chlorinated acids and phosphene when incinerated (Sittig, 1985). Based on an assumed base-mediated 1% disappearance after 16 d at 85 °C and pH 9.70 (pH 11.26 at 25 °C), the hydrolysis half-life was estimated to be >900 yr (Ellington et al., 1988). Toxicity: EC50 (48-h) for Daphnia magna 122 µg/L (Hermens et al., 1984) and 150 µg/L (Marchini et al., 1999).