Synthesis of earthworm trace metal uptake and bioaccumulation data: Role of soil concentration, earthworm ecophysiology, and experimental design

Abstract Trace metals can be essential for organo-metallic structures and oxidation-reduction in metabolic processes or may cause acute or chronic toxicity at elevated concentrations. The uptake of trace metals by earthworms can cause transfer from immobilized pools in the soil to predators within terrestrial food chains. We report a synthesis and evaluation of uptake and bioaccumulation empirical data across different metals, earthworm genera, ecophysiological groups, soil properties, and experimental conditions (metal source, uptake duration, soil extraction method). Peer-reviewed datasets were extracted from manuscripts published before June 2019. The 56 studies contained 3513 soil-earthworm trace metal concentration paired data sets across 11 trace metals (As, Cd, Cr, Cu, Hg, Mn, Ni, Pb, Sb, U, Zn). Across all field and laboratory experiments studied, the median concentrations of Hg, Pb, and Cd in earthworm tissues that were above concentrations known to be hazardous for consumption by small mammals and avian predators but not for Cu, Zn, Cr, Ni, and As. Power regressions show only Hg and Cd earthworm tissue concentrations were well-correlated with soil concentrations with R2 > 0.25. However, generalized linear mixed-effect models reveal that earthworm concentrations were significantly correlated with soil concentrations for log-transformed Hg, Cd, Cu, Zn, As, Sb (p