Efficiency of bio-indicators for low-level radiation under field conditions

Relatively little is known about biological consequences of natural variation in background radiation, and variation in exposure due to nuclear accidents, or even the long term consequences to human health stemming from the over-use of nuclear medicine and imaging technologies (i.e. CAT scans). This realization emphasizes the need for assessment and quantification of biological effects of radiation on living organisms. Here we report the results of an environmental analysis based on extensive censuses of abundance of nine animal taxa (spiders, dragonflies, grasshoppers, bumblebees, butterflies, amphibians, reptiles, birds, mammals) around Chernobyl in Ukraine and Belarus during 2006–2009. Background levels of radiation explained 1.5–26.5% of the variance in abundance of these nine taxa, birds and mammals having the strongest effects, accounting for a difference of a factor 18 among taxa. These effects were retained in analyses that accounted for potentially confounding effects. Effect size estimated as the amount of variance in abundance explained by background level of radiation was highly consistent among years, with weaker effects in years with low density. Effect sizes were greater in taxa with longer natal dispersal distances and in taxa with higher population density. These results are consistent with the hypotheses that costs of dispersal (i.e. survival) were accentuated under conditions of radioactive contamination, or that high density allowed detection of radiation effects. This suggests that standard breeding bird censuses can be used as an informative bio-indicator for the effects of radiation on abundance of animals.