Three different soils were spiked with 12 different concentrations of inorganic mercury (Hg). Sub-chronic Hg toxicity tests were carried out with Eisenia fetida in spiked soils by exposing the worms for 28 days following standard procedures. The toxicity studies revealed that Hg exerted less lethal effect on earthworms in acidic soil with higher organic carbon (S-3 soil) where water soluble Hg recovery was very low compared to the water soluble Hg fractions in soils with less organic carbon and higher pH (S-1 and S-2 soils). The concentrations of total Hg that caused 50 % lethality to E. fetida (LC50) after 28 days of exposure in S-1, S-2 and S-3 soils were 152, 294 and 367 mg kg-1, respectively. The average weight loss of E. fetida in three soils ranged from 5 to 65 %. The worms showed less weight loss in the organic carbon-rich soil (S-3) compared to less organic carbon containing soils (S-1 and S-2). The bioconcentration of Hg in E. fetida increased with increased Hg concentrations. The highest bioaccumulation took place in the acidic soil with higher organic carbon contents with estimated bioaccumulation factors ranging from 2 to 7.7. The findings of this study will be highly useful for deriving a more robust soil ecological guideline value for Hg.
Keywords: Accumulation; Earthworm; Eisena fetida; Mercury; Survival; Weight loss.