Biomonitoring of the genotoxic potential of aqueous extracts of soils and bottom ash resulting from municipal solid waste incineration, using the comet and micronucleus tests on amphibian (Xenopus laevis) larvae and bacterial assays (Mutatox and Ames tests).

The management of contaminated soils and wastes is a matter of considerable human concern. The present study evaluates the genotoxic potential of aqueous extracts of two soils (leachates) and of bottom ash resulting from municipal solid waste incineration (MSWIBA percolate), using amphibian larvae (Xenopus laevis). Soil A was contaminated by residues of solvents and metals and Soil B by polycyclic aromatic hydrocarbons and metals. MSWIBA was predominantly contaminated by metals. Two genotoxic endpoints were analysed in circulating erythrocytes taken from larvae: clastogenic and/or aneugenic effects (micronucleus induction) after 12 days of exposure and DNA-strand-breaking potency (comet assay) after 1 and 12 days of exposure. In addition, in vitro bacterial assays (Mutatox and Ames tests) were carried out and the results were compared with those of the amphibian test. Physicochemical analyses were also taken into account. Results obtained with the amphibians established the genotoxicity of the aqueous extracts and the comet assay revealed that they were genotoxic from the first day of exposure. The latter test could thus be considered as a genotoxicity-screening tool. Although genotoxicity persisted after 12 days' exposure, DNA damage decreased overall between days 1 and 12 in the MSWIBA percolate, in contrast to the soil leachates. Bacterial tests detected genotoxicity only for the leachate of soil A (Mutatox). The results confirm the ecotoxicological relevance of the amphibian model and underscore the importance of bioassays, as a complement to physico-chemical data, for risk evaluation.

Biomonitoring of the genotoxic potential of draining water from dredged sediments, using the comet and micronucleus tests on amphibian (Xenopus laevis) larvae and bacterial assays (Mutatox and Ames tests).

Management of contaminated dredged sediments is a matter of great human concern. The present investigation evaluates the genotoxic potential of aqueous extracts of five sediments from French channels (draining water from dredged sediments), using larvae of the frog Xenopus laevis. Two genotoxic endpoints were analyzed in larvae: clastogenic and/or aneugenic effects (micronucleus induction after 12 d of exposure) and DNA-strand breaking potency (comet assay after 1 and 12 d of exposure) in the circulating blood. Additionally, in vitro bacterial assays (Microtox and Ames tests) were carried out and the results were compared with those obtained with larvae. Physicochemical analyses were also taken into account. Analytical analyses highlighted in the five draining waters a heavy load of contaminants such as metals and hydrocarbons. The results obtained with the micronucleus test established the genotoxicity of three draining waters. The comet assay showed that all 5 draining waters were genotoxic after 1 d of exposure. Although 3 of them were still genotoxic after 12 d of exposure, DNA damage globally decreased between d 1 and 12. The comet assay can be considered as a genotoxicity-screening tool. Data indicate that both tests should be used in conjunction in Xenopus. Bacterial tests (Ames) revealed genotoxicity for only one draining water. The results confirm the relevance of the amphibian model and the need to resort to bioassays in vivo such as the Xenopus micronucleus and comet assays for evaluation of the ecotoxicological impact, an essential complement to the physicochemical data.

Evaluation of toxic and genotoxic potential of stabilized industrial waste and contaminated soils.

Artificial aqueous samples (eluates, percolates, immersion waters) were obtained from contaminated soils and stabilized industrial wastes. The toxicity and genotoxicity of these aqueous fractions have been evaluated in vivo in the aquatic larvae of the amphibian Xenopus laevis. Four biotests have been applied: a test of subchronic toxicity and three biomakers: (1) measurement of the activity of ethoxyresorufine-o-dealkylase in the liver, (2) detection of DNA adducts in the liver and the blood, and (3) measurement of the rate of micronuclei in the erythrocytes. Biological datas were completed through a chemical analysis. The main conclusions of this study are: The importance of integrating different toxicity criterias into a biological battery (phenotypic and genotypic criterias). Some aqueous extracts did not seem to be very toxic, whereas their genotoxic effects were rather significant [e.g. the stabilized Municipal Solid Waste (MSW) ashes]. The importance of coupling together chemical and biological approaches to refine the impact. Actually, some eluates (lixiviation or percolation) coming from polluted soils appeared to be very poorly loaded with pollutants, whereas the toxic and genotoxic impact of these complex matrices were rather noticeable. In addition, when applying the leaching standardized procedure, the hazardous potential of the two analysed soils may be underestimated if the results on percolates and on eluates have been compared. This study highligths the importance of coupling the tools of characterization and preparation of samples to be analysed according to the objectives to be reached.