Impact of earthworms on trace element solubility in contaminated mine soils amended

16 The common practice of remediating metal contaminated mine soils with compost can reduce 17 metal mobility and promote re-vegetation, but the effect of introduced or colonising 18 earthworms on metal solubility is largely unknown. We amended soils from an As/Cu (1150 19 mgAs kg and 362 mgCu kg) and Pb/Zn mine (4550 mgPb kg and 908 mgZn kg) with 0, 20 5, 10, 15 and 20 % compost and then introduced Lumbricus terrestris. Porewater was 21 sampled and soil extracted with water to determine trace element solubility, pH and soluble 22 organic carbon. Compost reduced Cu, Pb and Zn, but increased As solubility. Earthworms 23 decreased water soluble Cu and As but increased Pb and Zn in porewater. The effect of the 24 earthworms decreased with increasing compost amendment. The impact of the compost and 25 the earthworms on metal solubility is explained by their effect on pH and soluble organic 26 carbon and the environmental chemistry of each element. 27 28