Ecotoxicity of cadmium in a soil collembolan-predatory mite food chain: Can we use the ¹⁵N labeled litter addition method to assess soil functional change?

Effects of cadmium (Cd) on predator-prey relationships and soil ecological function are poorly understood and there are few methods available to measure soil functional change. Thus, we structured a soil-dwelling food chain containing the predatory mite Hypoaspis aculeifer and its collembolan prey Folsomia candida to study the effects of Cd exposure for eight weeks in a spiked soil aged for five years. The ¹⁵N labeled litter was added as food to analyze the change in nitrogen (N) transfer content. H. aculeifer reproduction and growth and the survival and reproduction of F. candida were all negatively affected by Cd exposure, and H. aculeifer reproduction was the most sensitive parameter. The sensitivity responses of F. candida and H. aculeifer were different from those using the previous single species test. The results suggest that predator–prey interactions might influence the toxicity of Cd by predation and food restriction. Cadmium lethal body concentrations of adults and juveniles of F. candida and H. aculeifer juveniles were 500–600, 180–270 and 8–10 μg g⁻¹, respectively. The content of N transfer from litter to animals in the food chain decreased significantly with increasing soil Cd concentration between 100 and 400 mg kg⁻¹. The results suggest that the ¹⁵N labeled litter addition method is potentially useful for quantitative assessment of soil functional change for further risk assessment purposes. - Highlights: • Cd migrated and biomagnified through a collembolan-predatory mite food chain. • Predatory mites were more sensitive than collembolans to Cd in the food chain. • Soil Cd pollution reduced N incorporation in the animal tissues from litter. • The ¹⁵N labeled litter method can be used to assess soil functional change. - Predator-prey interactions in the food chain can increase the sensitivity of predatory mites at a higher trophic level to Cd pollution.