Blackwell Publishing Journal Backfiles 1879-2005
Abstract Several soil and subsoil samples from a soil accumulation and from the aquifer of a site of a former pesticide production factory, which were contaminated with chlorinated benzenes (CB), chlorinated phenols (CP) and hexachlorocyclohexanes (HCH) were investigated chemically for their content of individual pollutants, and microbiologically for the presence and the activity of different microorganisms. The samples of the soil accumulation (until 2 m depth) showed a higher content of chlorinated organic compounds (〉 1000 mg extractable halogenated organic substances (EOX) kg−1 soil; ratio CB:HCH:CP = 88:10:2), than the samples from the aquifer (〈 150 mg EOX kg− soil; ratio CB:HCH:CP = 88:6:6). All isomers of CB and CP, and the five important isomers of HCH could be detected in the samples. In samples of the accumulation, 1,2,3,4,-tetrachlorobenzene and pentachlorobenzene were the dominant CB in the upper layers, and 1,2,4-trichlorobenzene in the lower layers. In almost all samples α-HCH was predominant (〉 50%) among the HCH. The major pollutant of samples from the aquifer was 1,2,4-tricholorobenzene (〉 50% of CB). Among the HCH, δ-HCH was predominant, with only three exceptions. Degradation experiments with mixed bacterial cultures showed the aerobic degradation of monochlorobenzene, 1,3- and 1,4-dichlorobenzene, 1,2,4-trichlorobenzene, 1,2,3,4- and 1,2,4,5-tetrachlorobenzene 1,2,3-tricholorobenzene only in combination with 1,2,4-trichlorobenzene, and α-HCH, whereas 1,2-dichlorobenzene, 1,3,5-trichlorobenzene, β-HCH, 4-chlorophenol, and 2,4,5-trichlorophenol were not significantly transformed. It should be stressed that the compounds which were biodegraded in the laboratory were present in relatively high concentrations in situ, indicating limiting factors in their in situ degradation. Soil and subsoil microorganisms were present in numbers up to 105 colony forming units (CFU) g−1 soil. In soil samples, Gram-positive bacteria (coryneforms and Bacillus spp.) were dominant, mainly in the upper layers, but in the subsoil samples of the aquifer the majority of isolates were Gram-negative and could be identified as Pseudomonas stutzeri, Ps. fluorescens, Aeromonas sp. and Acinetobacter sp. The degradation potential observed under laboratory conditions should be studied further under in situ conditions to assess the success of a bioremediation.
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