MICROBIOLOGICAL AND CHEMICAL EVALUATION OF A SITE CONTAMINATED WITH CHLORINATED AROMATIC-COMPOUNDS AND HEXACHLOROCYCLOHEXANES

Several soil and subsoil samples from a soil accumulation and from the aquifer of a site of a former pesticide production factory, which wer e contaminated with chlorinated benzenes (CB), chlorinated phenols (CP ) and hexachlorocyclohexanes (HCH) were investigated chemically for th eir content of individual pollutants, and microbiologically for the pr esence and the activity of different microorganisms. The samples of th e soil accumulation (until 2 m depth) showed a higher content of chlor inated organic compounds (> 1000 mg extractable halogenated organic su bstances (EOX) kg(-1) soil; ratio CB:HCH:CP = 88:10:2), than the sampl es from the aquifer (< 150 mg EOX kg-l soil; ratio CB:HCH:CP = 88:6:6) . All isomers of CB and CP, and the five important isomers of HCH coul d 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 almos t all samples alpha-HCH was predominant (> 50%) among the HCH. The maj or pollutant of samples from the aquifer was 1,2,4-trichlorobenzene (> 50% of CB). Among the HCH, delta-HCH was predominant, with only three exceptions. Degradation experiments with mixed bacterial cultures sho wed the aerobic degradation of monochlorobenzene, 1,3- and 1,4-dichlor obenzene 1,2,4-trichlorobenzene, 1,2,3,4- and 1,2,4,5-tetrachlorobenze ne, 1,2,3-trichlorobenzene only in combination with 1,2,4-trichloroben zene, and alpha-HCH, whereas 1,2-dichlorobenzene, 1,3,5-trichlorobenze ne, beta-HCH, 4-chlorophenol, and 2,4,5-trichloropheno1 were not signi ficantly transformed. It should be stressed that the compounds which w ere biodegraded in the laboratory were present in relatively high conc entrations in situ, indicating limiting factors in their in situ degra dation. Soil and subsoil microorganisms were present in numbers up to 10(5) colony forming units (CFU) g(-1) soil. In soil samples, Gram-pos itive bacteria (coryneforms and Bacillus spp.) were dominant, mainly i n the upper layers, but in the subsoil samples of the aquifer the majo rity of isolates were Gram-negative and could be identified as Pseudom onas stutzeri, Ps. fluorescens, Aeromonas sp. and Acinetobacter sp. Th e degradation potential observed under laboratory conditions should be studied further under in situ conditions to assess the success of a b ioremediation.