Microbiological and chemical evaluation of a site contaminated with chlorinated aromatic compounds and hexachlorocyclohexanes

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.

Biological responses of maize (Zea mays) plants exposed to chlorobenzenes. Case study of monochloro-, 1,4-dichloro- and 1,2,4-trichloro-benzenes

“…Analysis of subsoil from a former pesticide factory in Germany has shown that TCB are more dominant (60%) and total CBs concentrations range from 1.5 to 18,400 mg kg -1 (Feidieker et al 1994(Feidieker et al , 1995. The soil sorption coefficients for CBs range from 466 to 58,700 and generally increase with increasing chlorination degree (Malcolm et al 2004).…”

Biodegradation of hexachlorocyclohexane (HCH) by microorganisms

“…despite an increase in total bacterial counts (Bollen et al 1954). Feidieker et al (1994) reported reduced microbial diversity in soil containing HCHs (up to 11,055 mg kg )1 ) and other chlorinated aromatic compounds (up to 18,500 mg kg )1 CB and 132 mg kg )1 CP), using selective culture techniques, metabolic testing on microtitre plates and fatty acid analyses. In a 70-day study, Rodriguez & Toranzos (2003) used Biolog, 16S rDNA and denaturing gradient gel electrophoresis (DGGE) analyses to monitor the diversity of bacteria in a tropical soil with a history of HCH contamination and spiked with 100 mg kg )1 c-HCH.…”

Microbial degradation of chlorinated benzenes

“…Brahushi et al (2002) observed that volatilization of 14 C-CB from aerated laboratory soil microcosms amended with different substrates was the main loss mechanism whereas mineralization was of minor importance However, other studies provide careful aerobic biodegradation measurements of chlorinated benzenes in contaminated soil incubated in enclosed vessels or microcosms (Marinucci and Bartha 1979;Schroll et al 2004). Based on chloride release and increase in optical density (due to cell growth), it was determined that CB, 1,3-DCB, 1,4-DCB, 1,2,4-TCB, 1,2,3,4-TeCB, and 1,2,4,5-TeCB were biodegradable when incubated in soil slurries (Feidieker et al 1994). In moist pristine soil, 1,2,3-TCB and 1,2,4-TCB were biologically mineralized at a rate of 0.012 and 0.052 nmol CO 2 g -1 soil dry weight day -1 , respectively (Marinucci and Bartha 1979).…”