Biological endpoints in earthworms (Amynthas gracilis) as tools for the ecotoxicity assessment of soils from livestock production systems

Due to the intensification and modernization of livestock farming practices, large amounts of trace metals, veterinary pharmaceuticals and pesticide residues are released to the soil along with animal feces. Hence, there is an increasing concern about the effects of pollutants derived from livestock activities on soil organisms. The objective of this study is to assess the ecotoxicity of soils from livestock production systems using a set of validated tissue and cellular biomarkers of non-native earthworms (Amynthas gracilis) exposed ex situ to real contaminated livestock soils. Overall, the results showed that livestock pollutants present clear environmental risks, since the exposure during 14 days to soils from livestock systems triggered significant sub-lethal effects in A. gracilis, revealed by the increase of acetylcholinesterase activity in earthworms’ tissues (from 34.15 ± 0.79 to 62.74 ± 2.10 nmol of acetylthiocholine hydrolyzed min ⁻¹ mg ⁻¹ of protein), the decrease of antioxidant defense associated enzymes (superoxide dismutase activity, from 2.76 ± 0.11 to 1.90 ± 0.04 U mg ⁻¹ of protein) and of lysosomal integrity (neutral red uptake, from 113.00 ± 4.81 to 83.73 ± 2.25%). Moreover, coelomocytes of earthworms exposed to the livestock soil displayed significantly higher DNA damage values (comet assay, from 126.67 ± 8.67 to 199.67 ± 23.15 GDI). This study validates the applicability of the tested biomarkers as early warning tools to assess sub-lethal toxicity to organisms inhabiting soil impacted by livestock pollutants. This study also highlights the relevance of A. gracilis as a suitable sentinel species to provide an integrative and more ecologically relevant response of soil ecosystem health in livestock production systems.