| Summary: | Linear alkylbenzene (LAB) is a light non-aqueous phase liquid used as insulating oil in buried electricity transmission cables, from where it may enter soil and groundwater in the event of damage to the cable casing or joints. LAB is also found in the aquatic environment due to its use as a precursor in the manufacture of linear alkylbenzene sulphonate (LAS) detergents, in which it remains as a trace contaminant. LAB is readily biodegraded under aerobic conditions, but because of its use in buried cables, it may be release into anoxic environments where it can persist for some time. Most previous work has focused on the effects of LAB in freshwater and estuarine sediments, with little published data on terrestrial ecotoxicity and fate. LAB has been found to be acutely toxic to the free-living soil nematode. Caenorhabditis elegans, with a 24h LC50 of 5.2 g kg-1 dry weight soil. Aqueous enrichment cultures of organisms from cable oil-contaminated soil show that LAB can be degraded under nitrate-reducing conditions, and that isomeric analysis of the remaining LAB is a good indicator of the degree of degradation. However, soil column experiments and anaerobic respirometry of soil slurries using 14C-labelling LAB do not show appreciable degradation even after 5-6 months. Degradation under iron-reducing, sulphate-reducing and methanogenic conditions has not been demonstrated. Lately, preliminary work using denaturing gradient gel electrophoresis (DGGE) of eubacterial rDNA polymerase chain reaction (PCR) product has provided an indication that changes in microbial diversity do occur in soil following contamination. Furthermore, anaerobic contaminated soils showed rapid LAB degradation upon exposure to aerobic conditions, suggesting that a community of facultative anaerobes capable of degrading the oil had developed.
|
|---|
