1H NMR-based metabolomic observation of a two-phased toxic mode of action in Eisenia fetida after sub-lethal phenanthrene exposure

H-1 NMR-based metabolomics was used to examine the response of the earthworm Eisenia fetida to sublethal phenanthrene exposure. E. fetida were exposed via contact tests to six sub-lethal (below the measured LC50 of 1.6 mg cm(-2)) concentrations of phenanthrene (0.8-0.025 mg cm(-2)) for 48 h. Multivariate statistical analysis of the H-1 NMR spectra of earthworm tissue extracts revealed a two-phased mode of action (MOA). At exposures below 1/16th of the LC50, the MOA was characterised by a linear correlation between the metabolic response and exposure concentration. At exposures >= 1/16th of the LC50, the metabolic response to phenanthrene appeared to plateau, indicating a distinct change in the MOA. Further data analysis suggested that alanine, lysine, arginine, isoleucine, maltose, ATP and betaine may be potential indicators for sub-lethal phenanthrene exposure. Metabolite variation was also found to be proportional to the exposure concentration suggesting that NMR-based earthworm metabolomics is capable of elucidating concentration-dependent relationships in addition to elucidating the MOA of sub-lethal contaminant-exposure.