Heavy metal accumulation in earthworms exposed to spatially variable soil contamination

Ecotoxicity of contaminated soil is commonly tested in standard laboratory tests. Extrapolation of these data to the field scale is complicated due to considerable differences between conditions in laboratory tests and conditions in situ in contaminated soils. In this thesis, heavy metal accumulation in earthworms was studied under various laboratory conditions to identify and obtain knowledge that is needed to predict accumulation in earthworms exposed to in situ soil contamination. Both Cu accumulation-rate and Cu excretion-rate appeared large, which implies that Cu tissue concentrations in earthworms change rapidly in spatially variable contaminated soils. Soil moisture content did not influence the heavy metal accumulation. Soil PH did not influence the Cu availability for uptake, but significantly affected the toxicity of Cu contaminated soil. This indicates that there are two different exposure routes. Earthworms were also exposed to soil containing a mixture of Cd and Cu. A considerable tissue Cd accumulation, which could result in an increase in Cu binding capacity of earthworms, did not affect tissue Cu accumulation in these group of earthworms. Also the addition of Pb to Cu contaminated soil, which could result in an increase in Cu availability, did not affect tissue Cu accumulation. The results of the laboratory experiments imply that of factors studied only the total extractable soil Cu content controls tissue Cu accumulation, whereas mortality is controlled by Cu concentrations in soil solution. Predictions of tissue Cu accumulation in earthworms that were introduced in a heavy metal (Cu, Pb, Zn) contaminated site were based on these assumptions. Measurements of tissue Cu concentration appeared in excellent agreement with the observations in laboratory studies. Hence, laboratory studies with earthworms are very useful for estimation of the effects of soil contamination in situ on earthworms, provided that laboratory conditions are realistic with regard to field conditions.