The effects of natural variation in background radioactivity on humans,animals and other organisms

Natural levels of radioactivity on the Earth vary by more than a thousand‐fold; this spatial heterogeneity may suffice to create heterogeneous effects on physiology, mutation and selection. We review the literature on the relationship between variation in natural levels of radioactivity and evolution. First, we consider the effects of natural levels of radiation on mutations, DNA repair and genetics. A total of 46 studies with 373 effect size estimates revealed a small, but highly significant mean effect that was independent of adjustment for publication bias. Second, we found different mean effect sizes when studies were based on broad categories like physiology, immunology and disease frequency; mean weighted effect sizes were larger for studies of plants than animals, and larger in studies conducted in areas with higher levels of radiation. Third, these negative effects of radiation on mutations, immunology and life history are inconsistent with a general role of hormetic positive effects of radiation on living organisms. Fourth, we reviewed studies of radiation resistance among taxa. These studies suggest that current levels of natural radioactivity may affect mutational input and thereby the genetic constitution and composition of natural populations. Susceptibility to radiation varied among taxa, and several studies provided evidence of differences in susceptibility among populations or strains. Crucially, however, these studies are few and scattered, suggesting that a concerted effort to address this lack of research should be made.     

Zooplankters as indicators of ecosystem health: past findings and future directions

Both acute (ingestion, respiration) and chronic bioassays (reproduction, survival) have been used to identify sources of pollutants. A mass-balance analysis suggests that acute tests be paired, using important indicator species asDaphnia, Ceriodaphnia and potentially others, to estimate the impact of contaminants upon the zooplankton community. Eventually groups of community bioassays may be combined to approximate an ecosystem bioassay. Hormesis or the stimulation of a physiological process by a compound which is toxic at high concentrations is characteristic of several bioassays; in this paper the ecotoxicology community is challenged to keep detailed records of the species, toxic compound, and physiological response involving hormesis in order to understand it; and ultimately to use it to simplify interpretation of bioassays. Life history characteristics of the cladoceran zooplankton, including early reproduction, high net reproductive rates, and the potential for many parthenogenetic generations with constant genotypes and low mutation rates make good choices for environmental bioassays. In contrast, high mutation rates of rotifers make them questionable choices. Five innovations, one or more of which may improve our ability to detect and identify pollutants, are suggested for ecotoxicologists using zooplankton. These include (a) the use of strains of known genotype; (b) determination of the genetic adaptation of clones to common toxins; (c) the use of common behaviors, including responses to light in detection of non-lethal chemicals at ambient levels; (d) record keeping on occurrence of cladoceran tumors; and (e) the determination of precise toxins responsible for the inhibition of zooplankton function and behavior.