Sediment metabolomics indicates chemical spill-induced damage to a phytoplankton population

When chemical spills occur in aquatic systems, they cause not only visible damage to macroscopic organisms but also invisible harm to microorganisms such as phytoplankton. However, the magnitude of the damage is generally assessed through the visible indicators. Phytoplankton communities form the base of the aquatic food web; thus, developing methods to assess their damage is crucial. In this study, we simulated chemical spill conditions using field water and sediment collected from a river stream. Subsequently, the metabolome of the sediment containing dead phytoplankton was profiled, as it is expected to provide insights into population-level damage and the timing of death. Nontargeted mass spectrometry-based metabolomics was applied. The results revealed distinct differences in metabolite abundances depending on the extent of phytoplankton population-level damage, as measured by algal growth rate inhibition. Furthermore, a total of 120 potential biomarker candidates were found, including 117 tentatively annotated metabolites and 3 putatively annotated metabolites, which may indicate phytoplankton population-level damage or the timing of death. Fatty acids, alkaloids, terpenoids, and other plant- or organism-derived secondary metabolites and natural products were recognized as major biomarker candidates. A comparison with previous studies indicates that these metabolites are likely derived from dead algal cells or microorganisms present within the sediment. Consequently, this study supports the potential application of metabolomics as a new methodology for assessing phytoplankton damage that results from a chemical spill.