Combined effects of organic matter and pH on acute toxicity of cadmium to Paronychiurus kimi (Collembola): Development of response surface model

A second-order central composite design was employed to investigate the effect of organic matter (OM) content and soil acidity (pH) on the cadmium toxicity to Paronychiurus kimi (Lee), a collembolan species native to Korea. Two independent variables, OM and pH, were adjusted from 0 to 10% (in total dry wt) and 4.5 to 7.0, respectively. Cadmium concentrations tested were 10, 20, 40, 80, and 160mg/kg dry soil. The toxic effects that cadmium exerted on P. kimi (28-day median lethal concentration (LC₅₀s)) varied significantly with different combinations of OM content and pH. The second-order response surface model was appropriate for describing combined effects of OM and pH on the cadmium toxicity to P. kimi. Linear effects (OM and pH) were predominant contributors accounting for ≈70% of the total variance of cadmium toxicity to P. kimi. No significant quadratic (pHpH) and interaction (OMpH) effects were observed; therefore, the final second-order response surface model could be reduced as follows: 28-day LC₅₀ of cadmium (mg/kg)≤94.87+26. 69×OM+16.64pH 1.82OM². Validation of the developed response surface model using 4 soil media with different OM content and pH resulted in a significant correlation coefficient (R²≤0.97) between predicted and observed 28-day LC₅₀. Based on physico-chemical properties of the test media, developed models can be used to explain the variation of cadmium toxicities at various environmental conditions and may improve current environmental risk assessment procedures of metals.