Comparisons of Mercury and Methylmercury Bioaccumulation in Earthworms (Bimastos parvus) Native to Landfill-leachate-contaminated Forest Soil

<p>To explore total mercury (THg) and methylmercury (MeHg) bioaccumulation in the Bimastus parvus species earthworm (B. parvus), native to the leachate-contaminated forest soils around a Hg polluted traditional landfill, Japan. General soil properties, concentrations of THg and MeHg in forest soils and in B. parvus were determined. The results indicated that the average THg concentrations in B. parvus and forest soils in the leachate-contaminated sites were 10.21 and 14.90 times higher than the control sites, respectively, whereas similar average MeHg concentrations were observed in forest soils (< 0.01 kg^-1) and B. parvus (0.100 - 0.114 mg kg^-1) across all sampled sites. The average bioaccumulation factors of B. parvus in forest soil THg (BAF_THg) were similar between the leachate-contaminated sites and the control sites. Cluster and regression analyses demonstrated that the B. parvus Hg (THg / MeHg) and soil THg were positively correlated with each other and with soil organic matter (SOM) and clays, but negatively correlated with sand and hardly correlated with silts and pH in leachate-contaminated forest soils. From these results, it is proposed that Hg exposure to food chains is possible through B. parvus, because B. parvus shows a high ability to accumulate THg and MeHg in both leachate contaminated and control forest soils. Together these findings indicated that the role of B. parvus in MeHg production is not clear, and it is possible that the MeHg in B. parvus was firstly formed within forest soils and then accumulated in their tissues. </p>