Heavy metal uptake, accumulation patterns, and ecotoxicological responses in terrestrial isopods: a review

Soil heavy metal contamination poses persistent ecological risks to terrestrial ecosystems. Woodlice (Oniscidea), also known as terrestrial isopods, are important soil decomposers with strong capacities for heavy metal accumulation and detoxification. This review synthesizes current knowledge regarding heavy metal accumulation, distribution, physiological effects and ecological implications in woodlice. Heavy metals are predominantly accumulated in the hepatopancreas in woodlice, the principal organ for metal sequestration and detoxification. Copper generally exhibits higher bioconcentration factors (BCFs) than other metals because of its strong association with thiol-rich ligands in hepatopancreatic cells. Based on existing investigations, in contaminated areas, mean woodlouse Cd, Cu, Pb, and Zn concentrations were 42.7, 295, 150, and 472 mg kg^-1, respectively; woodlouse BCFs for soil Cd, Cu, Pb, and Zn were 4.72, 16.4, 2.39, and 2.38, respectively, while its BCFs for plant Cd, Cu, Pb, and Zn were 9.19, 14.1, 1.29, and 4.54, respectively. Heavy metal accumulation is influenced by metal type, concentration, and exposure duration, and body concentrations generally increase with exposure time until a steady-state equilibrium is reached. Elevated heavy metal exposure can impair feeding, reduce growth, induce hepatopancreatic histopathological damage, and increase mortality, potentially leading to reduced population density and simplified community structure under severe contamination. Although woodlice show potential as bioindicators of soil heavy metal contamination, nonlinear relationships between environmental and body metal concentrations limit their quantitative applicability. Current understanding of trophic transfer of heavy metals from woodlice to higher trophic levels remains limited and warrants further investigation.