Applications of metabolomics to the environmental sciences

Metabolomics has become a versatile technique that is widely used by academia and industry in the medical, toxicological, nutritional, and other biological sciences. The purpose of focusing this journal issue on ‘‘Environmental Metabolomics’’ is to both recognize and highlight the growing number of metabolomics studies within the environmental sciences. Some may regard environmental metabolomics purely as the application of this technique to study organisms dwelling within the natural environment, with the goal to learn about the state or condition of the environment. However, the field is in fact considerably broader than this, including the application of metabolomics to areas such as ecophysiology—with a focus on understanding the underpinning biochemical responses of organisms to abiotic and biotic stressors in their environment; and to ecotoxicology and ecological risk assessment— which typically involves chemical toxicity testing within a controlled laboratory environment to inform upon the potential risks of chemicals to organisms in the natural environment. Ultimately all environmental metabolomics studies probe organism–environment interactions with the goal to characterise organism function at the molecular level and/or to inform upon environmental health. A review by Bundy et al. provides a comprehensive overview of environmental metabolomics studies to date, including a critical evaluation of the contribution that metabolomics has made to the environmental sciences. In addition, the authors discuss a number of recommendations to advance this field. As highlighted in this review, some of the pioneering work in environmental metabolomics included characterising the responses of organisms to toxic stress, with the potential of discovering novel biomarkers for subsequent environmental diagnostics. This is still a highly active field of study, evidenced by the six original articles in this special issue. Ekman et al. report the sex and time dependent metabolic responses of the fathead minnow (Pimephales promelas), a sentinel test species, to the synthetic estrogen 17-ethynylestradiol. The novel aspect of this research is the focus on the lipid metabolome, which has received minimal attention in environmental metabolomics. The ability of NMR metabolomics to differentiate responses to pesticides (atrazine and lindane) and natural environmental stressors (hypoxia and starvation), which is a prerequisite for its application in ecological monitoring, is highlighted by Greenwood et al. in studies of the marine mussel Mytilus edulis. Taylor and colleagues describe the first application of metabolomics to toxicity testing in Daphnia magna, a water flea that is used internationally for environmental risk assessment. They utilised direct infusion Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry to identify multiple metabolic responses to copper toxicity, and putatively identified more than a thousand low molecular weight polar metabolites in the tissue extracts. A time course study into the toxicity of the herbicide prometryn on a unicellular green alga (Scenedesmus vacuolatus) is reported by Kluender et al. The authors concluded that GC-MS studies of synchronous algal cultures represent a valuable new tool in ecotoxicology. Metabolomics studies of earthworms have been ongoing for more than a decade. Here three further studies are reported which serve to strengthen the growing literature on the applicability of earthworms for metabolomics-based environmental monitoring and chemical risk assessment. Using NMR spectroscopy, Guo and colleagues have confirmed that a diverse range of toxicants with unique modes M. R. Viant (&) School of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK e-mail: M.Viant@bham.ac.uk