In vitro and in vivo genotoxicity tests for studying contaminated aquatic environmental samples
This review deals with in vitro and in vivo genotoxicity bioassays carried out to evaluate the genotoxic potential of polluted environmental samples : continental and marine waters, domestic and industrial wastewaters, aquatic sediments and sludges of urban or industrial wastewater treatment plants. The end-points of the in vitro and in vivo assays are : genetic alterations, i.e. reverse and forward mutations, DNA adducts or chramosomic damages, i.e. chromosomic aberrations (AC), micronuclei (MN) and sister chromatid exchanges (SCE). The in vitro assays generally detect adverse effects on DNA only alter concentration or extraction of micropollutants. They constitute miniaturized tools, rapid and easy to use, thus well-suited for large screening studies. In vitro genotoxicity bioassays requiring only small volumes of samples are therefore systems of choice for testing concentrates or extracts from environmental contaminated samples. Among the in vitro assays reviewed, the Salmonella typhimurium gene mutation test is the most often used to assess the genotoxic potential of contaminated samples. However, genotoxicity tests performed on eukaryotic cell cultures are more relevant than those using bacteria for evaluating environmental pollution. The use of fish cell fines appears superior to the use of mammalian cells for assessing an aquatic impact. In vitro bioassays, whether performed on prokaryotic or eukaryotic cells, are limited for predicting the possible impact of genotoxic pollutants on the environment. It is clear that it is difficult to extrapolate in vitro bioassay results to higher organisms in which the response obtained integrates effects of complex metabolizing systems, hormonal regulation and immunological defenses. Therefore, genotoxicity studies performed with aquatic organisms such as molluscs (Mytilus sp.), fish (Umbra pygmaea, Notobranchius rachowi) or amphibians (Pleurodeles waltl) appear more representative of environmental conditions. The genotoxicity end-points of in vivo assays are mainly cytogenetic damage such as the SCE, AC or MN but also take into account DNA adducts. Direct testing of environmental samples without preconcentration is possible with in vivo assays. This means that factors such as bioavailability and metabolism will be integrated direcrly in the response of these assays. Hence, these in vivo assays are more sensitive titan in vitro genotoxicity tests. However, in vivo tests require important volumes of sample and it will be difficult or almost impossible to apply them for testing concentrates or sample extracts, generally only available in small quantities. An interesting area of application of in vivo assays is field studies and ecoepidemioiogy. In this respect, they would constitue an a posteriori control system of pollution effects, assuming that suitable control areas are available to eliminate the influence of confounding factors. As a general conclusion, if is important to emphasize the interest of using both in vitro and in vivo bioassays for evaluating the genotoxicity of contaminated environmental samples. This rationale is based on the fact that in vitro bioassays are well adapted for genotoxicity screening or concentrates and extracts testing, white in vivo tests are interesting because of their better representativity in terms of environmental conditions of exposure to pollutants.