Exposure assessment of genotoxic compounds

Apart from studying the incidence of neoplasia, many other markers have been applied in order to assess the exposure to genotoxins in wildlife species, such as DNA adducts, chromosomal aberrations, micronuclei, c-K-rav oncogenes, etc. Correlations between contaminant exposure and mutations in oncogenes have been examined in molluscs (Van Beneden, 1994). Pink salmon (Oncorhynchus gorbuscha) embryos exposed to crude oil were shown to have high frequencies of mutations in the K-ras oncogene (Roy et al., 1999). 

Not all fish species seem equally well suited to study DNA adduct formation. Van der Oost (1997) summarized that about 50% of the species studied under field conditions can be considered as responders by showing significant increases of DNA adduct levels in liver in a polluted environment. In general, in order to obtain meaningful results, the choice of appropriate reference sites is of crucial importance in studies on aquatic organisms. Furthermore, fish from different 

A comparison of DNA adducts in the blood and liver from different Mugil species collected in a PAH-polluted harbour suggests that DNA adducts in the blood reflect recent exposure as a result of the more rapid turnover of blood cells compared with liver cells (Telli-Krakoc et al., 2001). The level of DNA adducts in the liver has been shown to correlate well with development and the pattern of prevalence of liver tumours in flounders (Vethaak and Wester, 1996). 

Other species have been used as environmental sentinels. The frequency of chromosomal aberrations in the gill tissue of Mytilus edulis transplanted to field sites contaminated to different extents increased with increasing exposure to contaminants (Al-Sabti and Kurelec, 1985). Pavlica et al. (2001) measured a significant increase of the tail length of comets in haemocytes of zebra mussels (.Dreissena polymorpha) after experimental exposure to polychlorophenol. Reichert et al. (1999) showed aromatic DNA adducts in the liver of Phoca vitulina richardsi (harbour seals) exposed to petroleum after the Exxon Valdez oil spill. 

As for the soil compartment, the comet assay on coelomocytes of earthworms (Eisenia foetida) kept in PAH-contaminated soil samples had higher DNA damage than in control samples (Verschaeve, 2002). However no dose-effect relationship was observed. Also, the levels of PAH-DNA adducts in Lumbricus terrestris, another earthworm species, kept on industrially contaminated soils increased with exposure time (Van Schooten et al., 1995). Few surveys have been performed on terrestrial plant species, but trifluralin was shown to induce a significant increase in tail length in the comet assay applied on the leaves of Viciafaba (Bierkens et al., 1998). 

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