Pesticide residues and earthworm reproduction in eighteen Brazilian soils

Agricultural intensification has been followed by the increasing use of pesticides, leading to the accumulation of a mixture of residues in the soil. These may have negative impacts on non-target animals like earthworms, but little is known regarding potential effects of contaminant mixtures on these animals in Brazilian soils. Hence, we evaluated the survival and reproduction of three species, two epigeics (Eisenia andrei, Perionyx excavatus) and one endogeic (Pontoscolex corethrurus), being the latter two more typical of tropical and subtropical regions. The bioassays followed standard ecotoxicological protocols in 18 soils from native vegetation and agricultural systems in both Cerrado and Atlantic Forest biomes. Tropical artificial soil (TAS) was used as a control. Soil texture and chemical analyses accompanied the determination of 48 pesticide residues. Residues of 29 pesticides were encountered, with 14 of them present in all 18 soils, and from 16–22 active ingredients detected in each soil. Most soils (83%) had high estimated risk quotients due to the residues, and these were negatively related to P. corethrurus and E. andrei adult biomass. Although residues of selected pesticides were positively (11 pesticides) or negatively (nine) related to earthworm reproduction, differences observed in biomass and reproduction in the soils and between species appeared to be more due to soil attributes associated with higher soil fertility such as higher micronutrient, CEC, clay, silt, N and C contents, rather than to pesticide contents. Survival of P. corethrurus was high in natural soils, but all individuals died in TAS, requiring attention in the choice of control soil for future assays. Survival was high for epigeic species in both TAS and natural soils and the high reproduction of P. excavatus confirms its potential use as an alternative species for ecotoxicological assays under tropical conditions. Furthermore, reduction in bioassay duration with P. excavatus should be explored, although more efficient ways of cocoon harvesting are necessary.