Toxicity and bioavailability of antimony to the earthworm (Eisenia fetida) in different agricultural soils

Laboratory experiments in which earthworms were exposed to four different Sb spiked agricultural soils (acidic, neutral, alkaline and calcareous alkaline soil) were conducted in a climate-controlled room. The study surveyed the toxicity of Sb to the Eisenia fetida at the individual (mortality, growth inhibition, Sb accumulation), physiological (enzymatic activities), subcellular and tissue levels (histological damage), and for the induction of an avoidance response of Sb. The results showed that earthworms clearly avoided Sb spiked soil, and the avoidance response tended to be correlated to the exposure dose. The EC50 values of the net avoidance response in the four soils were as followed: S1 (acidic soil, 135 ± 37 mg kg-1) < S3 (alkaline soil, 430 ± 114 mg kg-1) < S4 (calcareous alkaline soil, 455 ± 29 mg kg-1) < S2 (neutral soil, 946 ± 151 mg kg-1). Different toxic effects of Sb to earthworms cultivated in the four types of soils were observed. Antimony was more toxic in a sandy alkaline soil than that in the other three soils tested. The LC50 of the 28 d mortality ranged as follows: S3 (22.2 ± 0.1 mg kg-1) < S2 (372 ± 177 mg kg-1) < S4 (491 ± 140 mg kg-1) < S1 (497 ± 29 mg kg-1). Changes in oxidative stress and the subcellular distribution of Sb in earthworms induced by Sb exposure differed between soil types. Additionally, histological damage in earthworm's epidermis and intestine were observed under Sb stress. Mortality, growth inhibition and Sb accumulation in the earthworms tended to increase with Sb exposure regardless of soil type and were all significantly correlated with the exposure dose. The growth inhibition and Sb concentration in tissues of earthworms were sensitive indicators of Sb bioavailability. The relatively comprehensive toxicological data provided herein can contribute to the toxicity threshold and assessment of bioavailability of Sb contaminated agricultural soil, and then to the ecological risk assessments.