Importance of the nature of the dilution soils for the evaluation of toxicity of a polluted soil by a collembolan reproduction assay

The aim of this study was to compare the effect of two different dilution soils on the toxicity of an arsenic-contaminated mine soil by the collembolan reproduction assay. We diluted the contaminated soil either with an ISO soil or with a non-polluted soil having pedological and geological characteristics as similar as possible to those of the polluted site. The results were very different according to the dilution soil used: the lowest observed effect concentration (LOEC) was 1/256 with the ISO soil versus 1/4 with the natural dilution soil. The dilution soils influenced the bioavailability of xenobiotics and our results could be explained by the observed differences in arsenic and total organic carbon (TOC) concentrations in the pore water. Our results indicate that the physico-chemical characteristics of the dilution soil and their possible interactions with the polluted soil and its contaminants have to be taken into account in the interpretation of bioassays on polluted soils.