Environmental metabolomics is an emerging field referred to the application of metabolomics to characterize the interactions of living organisms with their environment. In this sense, the importance of monitoring the effects of toxic metals on living organisms has increased as a consequence of natural changes and anthropogenic activities that have led to an increase of toxic metal levels in terrestrial and aquatic ecosystems. For this purpose, the use of metabolomics based on MS to study metal toxicity is gaining importance in recent years. Environmental metabolomics can be used to: discover the mode of action (MOA) of toxic metals through controlled laboratory experiments; evaluate toxicity (biological adverse response to a substance), that may be useful in risk assessment; and develop new biomarkers (based in metabolome shifts discovered through controlled laboratory experiments) that may be applied in environmental biomonitoring (environmental realistic scenario). In this review, it is discussed how metabolomics based on MS can be applied to study metal toxicity, considering the most important hallmarks related to metabolomic experiments.