Soil compaction as a stressor, and its effect on cadmium toxicity to Paronychiurus kimi (Collembola)

The effects of soil compaction alone or in combination with cadmium treatment on Paronychiurus kimi were investigated in OECD artificial soil in order to quantify how changes in compaction affect the behavior and reproduction of P. kimi. Four series of compaction levels including an uncompacted control were examined (0, 15.7, 28.0, and 73.7g/cm²). The cadmium concentration used in these experiments was 28.3mg/kg (28-d EC₅₀-reproduction). Movement of P. kimi adults between soil surface and subsoil, which was expressed as the difference in the number found on the surface to those in the subsurface of the soil divided by the total (STS), was used as the behavioral endpoint. In the compaction only experiment, STS increased and reproduction decreased significantly in a compaction level dependent manner, indicating that compaction is an important stressor affecting the performance of P. kimi. In cadmium treated soils, the STS patterns was similar to those in the compaction only experiment, but the decrease in reproduction in the cadmium treated compacted soil was different. The most notable finding was that the change in the cadmium bioaccumulation factor was closely related to the relative reduction in reproduction (r²=0.81), implying soil compaction affected the uptake and toxicity of cadmium in P. kimi by influencing the magnitude of exposure to cadmium through dermal contact. The present study clearly demonstrated that soil compaction is an important factor affecting the performance (behavior and reproduction) of P. kimi as well as the toxicity and bioavailability of cadmium to P. kimi. Therefore, soil compaction should be included in soil ecotoxicity tests and ecological risk assessments.