Ecological risks of an old wood impregnation mill: application of the Triad approach

Although many studies deal with the distribution and mobility of chromated copper arsenate (CCA) metals in soil, the ecotoxicity of CCA-contaminated soils is rarely studied. The Triad approach was applied to determine the ecological risks posed by a CCA mixture at a decommissioned wood impregnation mill in southern Finland. A combination of (1) chemical analyses; (2) toxicity tests with plants (aquatic: Lemna minor; terrestrial: Lactuca sativa), earthworms (Lumbricus rubellus), and enchytraeids (Enchytraeus albidus) conducted on contaminated soils, their aqueous extracts, and well water collected from the site; and (3) determination of the abundance of enchytraeids and nematodes and the bioaccumulation of metals in plants (horsetail) collected from the field were used to assess the actual risk. Although metal concentrations were low, L. minor growth appeared to be reduced by As contamination of the well water. In soil, metals were heterogeneously distributed with total concentrations of 14.8 to 4360 mg As/kg, 15.2 to 1740 mg Cr/kg, and 4.83 to 790 mg Cu/kg. In several samples, concentrations were above Finnish regulatory guideline values and exceeded the half maximal effective concentration (EC50) or 50% lethal concentration (LC50) values for the toxicity of the individual metals to earthworms and enchytraeids, indicating hazards to the ecosystem. (Bio)availability of metals was high, as indicated by weak electrolyte extractions and body residues in L. rubellus and E. albidus exposed in bioassays. Earthworm survival correlated significantly with body metal concentrations, but not with soil total metal concentrations. Enchytraeid responses in the soil bioassays were less sensitive to CCA metal exposure. Plant growth was affected by CCA pollution, with L. sativa root elongation correlating significantly with total and available As concentrations and L. minor development being significantly reduced in H2O extracts of the most contaminated soil sample. Abundance of enchytraeids and nematodes in the field was much lower than in nonpolluted Finnish soils but did not significantly correlate with CCA contamination. Arsenic accumulation in horsetail did not correlate with As concentrations in soil. Overall, the results of the 3 lines of evidence of the Triad approach indicate possible increased risks to the ecosystem at the most contaminated sites of the CCA treatment area.