Bioaccumulation of Total and Methyl Mercury in Three Earthworm Species (Drawida sp., Allolobophora sp., and Limnodrilus sp.)

We determined total and methyl mercury contents in soil, three earthworm species and their vomitus to study the species-specific differences of mercury bioconcentration in Huludao City, a heavily polluted region by chlor-alkali and nonferrous metal smelting industry in Liaoning Province, northeast China. Total and methyl mercury contents were 7.20 mg/kg and 6.94 ng/g in soil, 1.43 mg/kg and 43.03 ng/g in Drawida sp., 2.80 mg/kg and 336.52 ng/g in Alolobophora sp., respectively. Total mercury contents were 0.966 mg/kg in Drawida sp. vomitus and 4.979 mg/kg in Alolobophora sp. vomitus, respectively. Total mercury contents in earthworms and their vomitus were significantly species-specific different and were both in decreasing with earthworms body lengths, which might due to the growth dilution. Among the soil, earthworms and their vomitus, total mercury contents were in the order of soil > earthworms > earthworm vomitus. Methyl mercury was about 3.01% of total mercury in Drawida sp., 12.02% of total mercury in Alolobophora sp., respectively. It suggested that mercury was mostly in inorganic forms in earthworms. Bioaccumulation factors of methyl mercury from soil to earthworms were much higher than those of total mercury, which suggested that methyl mercury might be more easily absorbed by and accumulated in earthworms because of its lipid solubility.