Metabolic Responses of Eisenia Fetida to Individual Pb and Cd Contamination in Two Types of Soils

To characterize the potential toxicity of low Pb-and Cd-contaminated arable soils, earthworms were exposed to Pb contaminated ferrosol, cambosol or Cd contaminated ferrosol for two weeks. Polar metabolites of earthworms were detected by nuclear magnetic resonance. Data were then analyzed with principal component analysis followed by orthogonal signal correction-partial least squares-discriminant analysis and univariate analysis to determine possible mechanisms for the changes in metabolites. The survival rates, metal concentrations and bioaccumulation factor (BAF) of the earthworms were also measured and calculated as auxiliary data. The results showed that the metabolite profiles were highly similar in Pb-contaminated ferrosol and cambosol (R-2 = 0.76, p < 0.0001), which can be attributed to similar response mechanisms. However, there was a more intense response in ferrosol likely due to higher Pb concentrations in earthworms. Metabolic pathways and BAFs exhibited apparent distinctions between Pb-and Cd-contaminated ferrosol, likely because they bind to different bio-ligands. The affected metabolic pathways were involved in alanine-aspartate-glutamate, purine, glutathione, valine-leucine-isoleucine biosynthesis and degradation and nicotinate and nicotinamide metabolism. Regarding the bioavailability in earthworms, Pb availability was higher for ferrosol than for cambosol. We confirmed that the potential toxicity of low Pb/Cd-contaminated soils can be characterized using earthworm metabolomics.