~1H NMR-Based Metabolomics Approach To Study The Toxic Effects Of Lead On Earthworms

The non-biodegradable nature of lead is the prime reason for its prolonged persistence in soil. Lead can enter soil dwelling organisms and, via the food chain, enriched in humans, affecting various organ systems of the body like hematopoietic, immune, nervous and cardiovascular systems. Earthworms, accounting for a large part of the total animal biomass dwelling in soil, are considered to be excellent model organisms to monitor soil toxicity in ecotoxicological studies. In this study, a 1H NMR-based metabolomics approach combined with traditional methods was applied to investigate the toxic mode of action of lead on earthworms (Eisenia fetida) for the first time.According to the OECD guidelines, earthworms were exposed to sub-lethal lead concentrations in filter paper contact test and artificial soil test. After 48 h of filter paper contact test, lead was accumulated in earthworms, leading to severe impairments of tissues, and the imbalance of the antioxidative system and the occurring of neurotoxicity in earthworms. Orthogonal signal correction-partial least squares-discriminant analysis (OSC-PLS-DA) of NMR profiles disclosed that Pb produced a vast metabolic changes, which were associated with oxidative stress, disorders of energy and amino acid metabolism, imbalance of neurotransmitters and osmoregulators in earthworms. In artificial soil test, histopathological and biochemical inspection and NMR profiling revealed responses of earthworms after just 2 days of exposure even at very low concentrations, whereas they showed potential adaptation after 14 days of exposure. OSC-PLS-DA of NMR profiles disclosed metabolic changes involved in oxidative stress, osmotic equilibrium, amino acids metabolism as well as energy metabolism in Pb exposed earthworms. The metabolic response was observed to be more pronounced in the earthworms exposed to lead via contact filter paper tests in comparison to the earthworm response observed after the soil tests.This work highlights that 1H NMR-based metabolomics has great promise as a future tool in ecotoxicology to assess the environmental risks and underlying mechanisms of heavy metals.