Comparison of cadmium kinetics in four soil arthropod species

Soil organisms may play an important role in the transfer of metals through the ecosystem in metal-polluted environments. To evaluate this role, four representative species were compared through modelling their toxico-kinetics when exposed to cadmium in chronic laboratory experiments. Considerable differences in consumption and assimilation of food and cadmium were found between the species. Cadmium assimilation correlated with food assimilation. Cadmium excretion and equilibrium concentrations also differed considerably between the species. The differences in equilibrium concentrations were comparable to the differences between these species in the field. Cadmium assimilation efficiencies were high in the predatorsNotiophilus biguttatus andNeobisium muscorum, and were lower in the saprotrophsOrchesella cincta andPlatynothrus peltifer. Excretion constants were high in the insectsN. biguttatus andO. cincta and low in the arachnidsN. muscorum andP. peltifer. There was no direct relationship between assimilation efficiency and excretion ability. The differences in cadmium assimilation efficiencies reflect differences in trophic level and most probably differences in nutrient demand, which may be determined taxonomically. The influence of excretion ability on the equilibrium concentration is larger than that of assimilation efficiency. Species with a high equilibrium concentration combine low excretion ability with either low or high assimilation. Together with compartment modelling, the study of uptake and excretion of cadmium by individual species provides a suitable tool for predicting the amount in the different soil invertebrates and for calculating pollutant fluxes.