Caged amphibian tadpoles and in situ genotoxicity monitoring of aquatic environments with the alkaline single cell gel electrophoresis (comet) assay

In previous studies we demonstrated that indigenous amphibian tadpoles are suitable organisms for monitoring small bodies of water (e.g., creeks, ponds, and drainage ditches) using the alkaline single cell gel electrophoresis (SCG) or `comet' assay. This approach involves detection, under alkaline conditions, of cell DNA fragments which on electrophoresis migrate from the nuclear core, resulting in a `comet with tail' formation. However, although often plentiful, tadpoles are not present in all aquatic environments. Both larger bodies of water (e.g., lakes and rivers) and those impacted upon heavily by man (e.g., bodies of water near industrial sites, on landfills, and in urban areas) often do not support amphibian tadpole populations. An alternative approach to the collection of indigenous tadpoles is to place caged tadpoles at these sites for short term exposures to environmental contaminants. To determine the feasibility of such an approach, Rana clamitans (green frog) and Bufo americanus (American toad) tadpoles were housed in cages at 11 sites in southwestern Ontario (Canada). In a preliminary experiment, we found that tadpoles caged at a polluted reference site (Tallgrass Prairie Heritage Park in Windsor, Ontario) for either 7 or 14 days showed significant ( P