Changes in the forms of lead and manganese in soils by passage through the gut of the tropical endogeic earthworm (Pontoscolex corethrurus)

To investigate the effect of the soil passage through the gut of earthworms (Pontoscolex corethrurus) on the forms of Pb and Mn, casts and soil samples were analyzed by sequential extraction procedure. Soil samples were collected in an area under direct influence of mining and metallurgy of Pb in the Parana state, Brazil. The earthworms were incubated with the soils to collect castings. The Pb and Mn concentrations were determined in seven sequential phases: soluble; exchangeable; carbonate; organic matter; Fe and Mn oxides; Al oxides and aluminosilicates; residual. There was intense contamination with Pb in the area, mainly in the clayish soil surrounding the factory by the deposition of suspended material coming from the chimneys (maximum concentration 9716 mg kg−1). On the other hand, total concentration of soil Mn was little influenced by the mining and metallurgy activities in the area. The earthworms significantly reduced the amount of Pb in the soluble and exchangeable forms in the soil, considered environmentally more bioavailable. There was also a significant increase in Pb bound in Fe and Mn oxides in the casts (specific absorption), which is desirable for soil bioremediation.

► Earthworms used for the reclamation of contaminated areas with heavy metals.
► The clay fraction and typical earthworm of the tropical soils.
►  Adaptations on sequential Pb and Mn extraction methods to tropical soils.
► Reduction on soluble and exchangeable Pb, more bioavailable metal forms.
► Increase in Pb bound with typically tropical oxides (specific adsorption).