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(W/EH130) Toxicity effects of linear alkylbenzene sulfonate (LAS) in autotrophic ammonia-oxidizing bacteria from agricultural soil. Brandt, Kristian1, Nielsen, Klaus1, Hesselsøe, Martin1,2, Pedersen, Anders1, Henriksen, Kaj2, Sørensen, Jan1, 1 2 ABSTRACT- Autotrophic ammonia-oxidizing bacteria (AOB) comprise an ideal indicator group in microbial ecotoxicology. We present results on the effects of linear alkylbenzene sulfonates (LAS) to AOB in experimental soil systems. A newly developed microbial toxicity assay employing a recombinant bioluminescent strain of Nitrosomonas europaea was used in two soils to monitor the bioavailable fraction of LAS, which correlated well with the methanol extractable amount of LAS as measured by HPLC (R2 = 0.93; concentration range of 0-400 mg kg-1). The bioassay was subsequently used to monitor the presence of bioavailable LAS in different soil experiments. In soils amended with 250 mg LAS kg-1 at 4 water regimes (9, 32, 68 and 100 % of water holding capacity) potential ammonium oxidation activity was progressively inhibited over three weeks with a concomitant decimation of the viable population of AOB and a build-up of soil ammonia. Initial toxicity and subsequent recovery of AOB populations were positively correlated to soil moisture. As judged from both a laboratory and field experiment employing sewage sludge-soil interface systems, toxicity to soil AOB was greatly reduced when LAS was added with the sludge. Direct toxicity to AOB present in close proximity (0-5 or 0-10 mm) to the sludge compartment containing up to 20 or 50 g LAS kg-1 was hence observed only during the first few days. Although significant changes in the temporal and spatial patterns of microbiological activities in the surrounding soil subsequently occurred, our results suggest that LAS generally does not pose a significant risk to the soil microbial community in sludge-amended soil. Key words: ammonia-oxidizing bacteria, linear alkylbenzene sulfonate, sludge amended soil, toxicity |
