Seasonal variation of lead uptake in the earthworm Lumbricus terrestris and the influence of soil liming and acidification

The influence of seasonal temperature variations and liming and acidification of the soil on lead uptake in juveniles and adults of the earthworm species Lumbricus terrestris L. was studied by enclosing specimens for up to five months in net bags provided with lead-contaminated, sandy soil. Lead concentrations were analyzed in the pharynx, gizzard, muscles, seminal vesicles and cerebral ganglion. Lead distribution in whole animals was assessed after an injection of ²⁰³Pb. The lead concentrations of the tissues were mostly linearly correlated with the soil concentrations, which ranged from <0.5 to 310 mg/kg, and the highest concentrations were generally found in the ganglion. The effects on lead concentrations in tissues of lowered soil pH from 5.6 to 5.1 or raised to 5.9 were insignificant, though more lead became allocated to muscles than to ganglion when pH was lowered. The lead uptake was strongly dependent on the ambient temperature, especially in the muscles, and the concentrations were reduced by 50% or more during the cold spell in the winter season, presumably as a consequence of a low feeding activity. Though juveniles seemed more prone to take up lead, the concentrations were not significantly higher than those in adults during the winter period. The observations are discussed in the light of the use of earthworms in standardized programs for environmental hazard assessment, especially with respect to species and tissue selection.