Résumé
The survival and cast production of the tropical endogeic earthworm Pontoscolex corethrurus and the changes in chemical and physical characteristics induced by gut passage were studied over an 80-day period in soils contaminated with different levels of Pb. The soils were from a Pb mining area in the state of Parana, SE Brazil, and ranged from clayey to sandy texture and total Pb contents from 52 to 9,716 mg kg(-1). In soils with the highest total Pb contents, earthworms showed lower survival rates, reduced biomass, high Pb uptake, and negligible cast production. In soils with low to intermediate total Pb (maximum 4,278 mg kg(-1)), earthworm survival and cast production were higher, biomass loss was lower, and gut passage increased pH, CEC, P, K+, and Mg2+ concentrations in the casts compared to the control soil. In the sandy soil (clay < 176 g kg(-1)), worms preferentially ingested finer soil particles, increasing organic C and silt contents in casts. However, this selective feeding also resulted in higher Pb accumulation in worm tissues. Gut passage also increased water-dispersible clay and reduced flocculation in the casts, increasing the susceptibility of the soil to erosion. Lead contamination and uptake into the tissues did not limit the ability of earthworms to select finer soil particles and to transform soil chemical and physical properties, although it affected cast production rates and survival (especially at high Pb concentrations).