The influence of soil characteristics on cadmium toxicity for Folsomia candida (Collembola: Isotomidae).

Effects of cadmium on survival, growth and reproduction of the collembotan Folsomia candida was determined in four soils differing in organic matter (3.0-10.9%) and clay content (1.4-5.2%) but all having a pH of approx. 6.0. Total, 0.01 M CaCl2-exchangeable, water-soluble and porewater cadmium concentrations were measured in all soils, and so were internal cadmium concentrations in the surviving animals. Freundlich Kf values for cadmium desorption from soil, based on porewater or water-soluble concentrations, differed by a factor of 2 between the four soils tested, and increased only slightly during the 6-week test period. Kf values based on porewater concentrations were a factor of 10 lower than the ones for water-soluble concentrations, which can mainly, but not completely, be explained from the dilution achieved when preparing water-soluble fractions. Kf values based on CaCl2-exchangeable concentrations did not differ between the test soils. Toxicity of cadmium for the Collembola, expressed on a total soil concentration basis, differed by a factor of 1.8-6.4, with largest difference being observed after 4 weeks of exposure; at other time intervals difference was less than a factor of 3.2. EC50 values for the effect on reproduction ranged between 53.7 and 193 μg Cd/g dry soil after 4 weeks, and slightly decreased after 6 weeks to 43.3-103 μg Cd/g dry soil. Differences in toxicity between the four soils were not reduced by using CaCl2-exchangeable, water-soluble, porewater or internal concentrations instead of total cadmium concentrations as a basis for calculating EC50s. The absence of a consistent relationship between cadmium toxicity and soil properties suggests that differences of less that a factor of 3-4 in organic matter and clay content, in soils with the same pH, do not lead to significant differences in cadmium toxicity to Collembola