Population consequences of cadmium toxicity in soil microarthropods

Chronic toxicity experiments were performed using the collembolan Orchesella cincta (L.) and the oribatid mite Platynothrus peltifer (Koch), which were exposed to various levels of cadmium in the food (green algae). Experimental results were combined with life-history information to obtain realistic estimates of the intrinsic rate of population increase and its sensitivity to Cd stress. Chronic LC50 values for dietary exposure to Cd were estimated as 1.60 mumol/g for O. cincta and 3.18 mumol/g for P. peltifer. No-observed-effect concentrations (NOECs) for growth and reproduction were 0.042 mumol/g for O. cincta and 0.026 mumol/g for P. peltifer. The main effects of Cd were, however, different in each species. In O. cincta, Cd affected primarily female growth, without a direct effect on reproduction; in P. peltifer, the effect was primarily on reproduction. Uptake of Cd was higher in P. peltifer than in O. cincta, and caused a loss of zinc in the former species. As a consequence of their differing physiological responses to Cd, mites and collembolans also reacted differently in their population growth rates. The capacity for population increase of mites appeared to be rather sensitive to Cd, while collembolans were able, to some extent, to maintain their capacity for increase, in spite of toxic effects at the individual level. These results may contribute to developing ecotoxicological theory for the population consequences of toxic action in species with diverging life histories. Soil microarthropods may be suitable test organisms for evaluating the risk of chemicals to the soil ecosystem.