Are Ni-Cd toxicity models derived from simple bioassay applicable to natural soils? A bioassay-MSMs coupling approach

Abstract

The application of terrestrial toxicity models to real soil environments is a challenge due to the heterogeneity of soil. We presented here a novel bioassay-geochem-model coupling approach to predict the bioaccumulation and toxicity of a metal mixture in different soils. Equations describing dose-accumulation and dose-toxicity relationships of Cd-Ni mixtures to wheat root elongation were generated using a standard sand culture bioassay. A geochemical multi-surface speciation model (MSM) with default parameters was employed to predicted the dissolved metal contents Cdis of three soils collected in China with different properties. Several toxicity models (TU/CAM + FIAM/BLM/GCSM) were screened to identify the one yielding the most accurate predictions. The results showed that metal bioaccumulation was better predicted by the MSM-Cdis integrated with the dose-accumulation equation (RMSE < 0.58) than by the detection of metal contents in soil porewater (RMSE < 0.74). The MSM predicted metal ion activities combined with the BLM+CAM model successfully predicted Cd-Ni toxicity in all three soils (RMSE = 20.7%), but the deviation was slightly larger than that obtained in measurements of metals in soil porewater (RMSE =17.2%). Our study demonstrates that the MSM coupled with the dose-accumulation and dose-toxicity equations derived from sand bioassays offers a promising approach in risk assessments of mixed metals in actual soils while avoiding tedious soil bioassays, which will greatly improve the practical application value of terrestrial toxic models.