Lysosomal membrane response of earthworm, Eisenia fetida, to arsenic contamination in soils

Abstract

Earthworm (Eisenia fetida) were exposed to sandy soils contaminated with arsenate (0.01-0.3 micromol g(-1)) for 28 days. Lysosomal membrane stability was used as a biomarker to determine the applicability of neutral-red retention times (NRRTs) for arsenic (As) toxicity to earthworm in soils. Total As and As speciation were analyzed to evaluate dose-response relationship between As accumulation and NRRTs and to observe the role of As metabolism in earthworms on a subcellular level toxicity. Significant decrease of NRRTs was found with the increasing As concentration in soils (ANOVA, P < 0.05). Adverse effects on earthworm survival and growth did not occur when exposed to 0.1 and 0.05 micromol g(-1) at 14 and 28 days, respectively, whereas NRRTs showed significant reduction from the control, as was readily bioconcentrated in the reduced form of As(III) in earthworms and clear dose-response relationships were found for As body burden and NRRTs. Therefore, it is possible to conclude that As has an adverse effect on lysosomal membrane of coelomocytes, and NRRT assay is a potentially applicable method to assess As toxicity as an early warning tool. Also, sequestered As in the form of As(III)-thiol complex can be expected to cause an adverse effect on lysosomal membrane stability.