Evaluation of an SOS-Chromotest-based approach for the isolation and detection of sediment-associated genotoxins

A series of experiments was conducted to evaluate an approach advanced by t he St. lawrence Centre (SLC) of Environment Canada for assessing the genoto xic potential of sediments. The SLC method entails the extraction, isolatio n and solvent exchange of the organic constituents in sediment, and the tes ting of these solubilized extracts with the SOS Chromotest (Escherichia col i PQ37). A total of five sediments, three variously contaminated by organic compounds and two reference materials certified for persistent organic che micals were Soxhlet-extracted. Each of the five extracts was then split, wi th a portion remaining in crude form and another portion fractionated into two molecular-weight classes of organic contaminants, thus yielding a total of 15 extract samples. The ability of the SOS Chromotest to detect, genoto xins in the various organic extracts was evaluated and compared with that o f the Ames Fluctuation Assay (Salmonella typhimurium, strain TA100). The in tra-laboratory variance associated with the SOS Chromotest was also assesse d. Procedural details are presented and results are discussed. The SOS Chro motest results were in good agreement with those of the Ames Fluctuation As say, especially after metabolic activation. However, the E. coli PQ37 syste m was slightly more sensitive than the Salmonella assay for detecting genot oxins in the sediment extracts. The SOS Chromotest was also the most discri minating of the two assays, generating SOS-induction factors that were cons istent with the organic contamination gradient reported in the sediment sam ples. The removal of macromolecules from the dichloromethane extracts by si ze-exclusion chromatography prior to testing enhanced the sensitivity of bo th test systems. The intra-laboratory variance of the SOS Chromotest ranged from 0.24% to 23.82%, depending on the extract sample. As applied in this study, the SOS Chromotest can serve as a sensitive test for screening the g enotoxic potential of uncharacterized sediment extracts. A more sensitive a ssay would be appropriate, however, as a confirmation for definitive invest igations, especially for the detection of direct-acting genotoxins. (C) 200 1 Elsevier Science Ltd. All rights reserved