Metabolomics reveals increased toxicity in earthworms (Eisenia fetida) of the transformation product methyl-triclosan

The effects of the antimicrobial triclosan (TCS) and its transformation product methyl-triclosan (MTCS) on the earthworm Eisenia fetida were investigated using GC-MS metabolomics. TCS is ubiquitous in sewage sludge, but a large proportion is transformed into MTCS during wastewater treatment and in soil when sewage sludge is applied to land. Our objective was to determine if earthworms exposed to ng/g to μg/g concentrations of TCS or MTCS exhibit toxic effects, and to identify the toxic mode of action of each compound. Ten individual earthworm replicates in 10 g worm bedding were exposed to 0, 0.25, 1, 4, 16, or 64 μg/g of either TCS or MTCS (120 experimental units) for 14 days. No mortalities were observed. All MTCS exposed worms had an instantaneous growth rate (IGR) over two times higher than the control during the study, but there was no effect of increasing concentration. Succinic acid was elevated relative to the control at concentrations ≥ 0.25 μg/g and glucose was elevated at 1 μg/g. There was separation from the control at all concentrations except 4 μg/g using Principal Components Analysis. Glucose, palmitic acid, and IGR contributed most strongly to the separation. Discriminant analysis with succinic acid, glucose, and IGR as variables showed a clear separation at all concentrations from the control along Canonical 1. Disruption of energy metabolism was hypothesized as a possible mode of action for MTCS.