Triclosan (TCS) is a ubiquitous contaminant in municipal biosolids, which has also been detected in soils and earthworms sampled from agricultural fields amended with biosolids. The goal of this study was to evaluate the toxicity of TCS to earthworms using a metabolomics-based approach for an improved interpretation of toxicity. Toxicity of TCS was assessed using the OECD Method 207 filter paper contact test measuring the endpoints of weight loss, mortality, and ten metabolites determined by GC-MS. Eight earthworms were exposed as individual replicates to six concentrations of triclosan (0, 0.0001, 0.001, 0.01, 0.1, and 1 mg TCS cm(-2)) on filter paper, with mortality assessed after 6, 24 and 48 h. Mortalities were first observed at 24 h, with 100% mortality in the 1 and 0.1 mg cm(-2) treatments. Worms at 1 mg cm(-2) lost most of their coelomic fluid before they could be sampled. The 48 h LC50 for triclosan was estimated to be 0.006 and 0.008 mg cm(-2) by a linear and logistic model, respectively. Based on the LC50, triclosan is relatively more toxic to earthworms than a number of other emerging contaminants, but is less toxic than other chlorophenols and many pesticides. Alanine, valine, leucine, serine, phenylalanine, putrescine, spermidine, mannitol, and inositol were significantly different between treatments, although changes were most often associated with mortality rather than triclosan exposure. An increase in putrescine and decrease in amino acids, polyols, and spermidine were associated with mortality, suggesting decomposition had begun. Principal components analysis did not reveal evidence of metabolic impacts at sub-lethal concentrations. However, there were changes in the pattern of correlations between metabolite pairs in surviving worms at both 0.0001 and 0.001 mg cm(-2) exposure compared to the control. (C) 2016 Elsevier B.V. All rights reserved.