Earthworm (Eisenia fetida) behavioral and respiration responses to sublethal mercury concentrations in an artificial soil substrate

Mercury (Hg) is a highly toxic metal that has multiple natural and anthropogenic sources. Many studies have explored the effects of Hg on various physiological and biochemical processes in soil animals. However, the effects of Hg on earthworm behavior and respiration are unknown. In this study, earthworms (Eisenia fetida) were exposed to Hg-spiked artificial soils prepared to OECD specification. An avoidance test was performed using soils with 0, 1, 2, 4, 8, 16, 32, 64, and 128 mg Hg2+ kg−1 dry soil,. The avoidance concentration of Hg to earthworms was 128 mg kg−1, as determined according to ISO guidelines. Soils with 0, 2, 8, 32, and 128 mg Hg2+ kg−1 dry soil were prepared to investigate the effects of Hg on the burrowing activity and respiration rate of earthworms. The cumulative burrow lengths of earthworms in 2D terraria were significantly shorter in soil containing Hg at concentrations of 8 mg kg−1 or higher, compared with those in the control (no Hg). However, the maximum burrowing depth was significantly decreased only in soil containing the highest concentration of Hg (128 mg kg−1). The respiration rates of earthworms were lower in all Hg treatments than in the control after 2 days and 7 days of exposure. This is the first report on the toxic effects of Hg on earthworm behavior and respiration. These results provide useful information for environmental monitoring and for assessment of Hg contamination in soils.