New developments in paleo-ecotoxicology: Emerging approaches in applying lake sediment archives to assess impacts from aquatic pollution

Many aquatic ecosystems have experienced a history of impacts from exposure to environmental contaminants, with aquatic biota often exhibiting population and/or community changes following toxicant exposure. However, identifying aquatic effects can be challenging due to a paucity of monitoring data and gaps in monitoring records. The study of lake sediments as natural environmental archives (paleolimnology) provides an opportunity to assess the long-term impacts of pollution on aquatic organisms and ecosystems. Cores collected from polluted systems can preserve both a record of the toxicant(s) in question, and also an archive of biotic changes at multiple scales of organization, from molecular levels to communities to ecosystem processes (paleo-ecotoxicology). Here, we review recent examples of the application of the paleo-ecotoxicological approach based on ‘classical’ paleolimnological indicators of contamination (e.g. metals, organic contaminants) and ecotoxicological response variables (e.g. pigments and subfossil morphological indicators). We also outline emerging environmental contaminants (e.g. microplastics, pharmaceuticals) that are increasingly being detected and documented in sediment records, highlighting evolving sources and intensities of toxicological stressors that are fruitful areas for future paleo-ecotoxicological inquiry. In addition, the ability to characterize aquatic community changes using emerging sedimentary DNA approaches has rapidly expanded, providing a powerful opportunity to build on the ecological information obtained from traditional indicators to better understand ecosystem responses to contamination. Finally, we argue for the importance of methodological approaches that specifically examine the ecotoxicological impacts of contamination in the future application of the paleo-ecotoxicological approach by exploring several recent examples.