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

Effects of cadmium on survival, growth and reproduction of the collembolan 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 K-f 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. K-f 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. K-f 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 mug Cd/g dry soil after 4 weeks, and slightly decreased after 6 weeks to 43.3-103 mug 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 EC(50)s. 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.