Nematode-based risk assessment of mixture toxicity in a moderately polluted river floodplain in The Netherlands

Heavymetal polluted soils usually containmixtures of different metals,whereas legislation is derived fromconcentrations of individualmetals. The mixture toxicity of the Dutch floodplain Afferdensche and Deestsche Waarden was estimated to be high (msPAF ranged from67–94%). Analyses of nematode community based bioindicators (Maturity Index, taxonomic diversity, trophic groups, multivariate analysis, DoFT-sentinels) were used to determine the ecological effects of the mixture toxicity in the floodplain soil. None of the indices indicated direct effects of heavymetals on the nematode community. This can be explained by the high adsorption of heavy metals on organic matter and clay particles resulting in a low bioavailability, and questions the estimation of the toxicity based on total concentrations of heavy metals in such environments. The nematode fauna showed great seasonal variation, which most probably was related to the temporal inundation of the floodplain.