PAthways of Chemicals Into Freshwaters and their ecological ImpaCts (PACIFIC)

Manufactured chemicals are essential for the maintenance of public health, food production, and quality of life, including a diverse range of pharmaceuticals, pesticides, and personal care products. The use of these compounds throughout society has led to increasing concentrations and chemodiversity in the environment. Whilst there has been a focus on understanding the impacts of chemicals on a subset of freshwater biodiversity (particularly invertebrates and fish), we understand less about how chemical pollution impacts freshwater microbes. These microbial communities (the 'microbiome') number in the millions to billions of cells per milliliter of water or gram of sediment and form the most biodiverse and functionally important component of freshwater ecosystems. The biogeochemical and ecological functions delivered by freshwater microbes are essential to wider freshwater ecosystem health.

The PAthways of Chemicals Into Freshwaters and their ecological ImpaCts (PACIFIC) project will focus on understanding the link between sources of anthropogenic chemicals and their pathways, fate and ecological impacts in freshwater ecosystems, with an emphasis on freshwater microbial ecosystems and the functions they perform. We will investigate the relationship between predicted diffuse and point source chemical pathways and measured chemical concentrations in water and sediments at locations across the Thames and Bristol Avon catchments, chosen to represent gradients of diffuse pollution sources. These locations will be chosen to coincide with Wastewater Treatment Works (WwTWs) to understand how sewage effluent contributes to chemical burden across these gradients. Liquid chromatography coupled with (high resolution) tandem mass spectrometry and QTOF (quadrupole Time-of-Flight) mass spectrometry will be used to perform targeted and untargeted profiling of chemical groups proven and suspected to impact freshwater ecology. A range of microbial community ecosystem endpoints will also be measured at each location to identify the impact of chemical exposure, including bacterial and fungal community composition via DNA sequencing, the expression of nutrient cycling and chemical stress and resistance genes, the production of extracellular enzymes involved with biogeochemical cycling, and the functional gene repertoire of whole microbial communities.

We will perform experimental microcosm exposures on freshwater microbial communities, with increasing complexity and realism, deploying high-throughput screening to identify novel chemical groups (and their structural features) with the capacity to restructure these communities. Exemplar microbial community modifying chemicals will be investigated in more detail by applying cutting-edge molecular techniques to determine ecological exposure thresholds that represent different taxonomic and functional aspects of freshwater microbial ecosystems. Novel field-based mesocosms will be used to explore wastewater exposures in more realistic, but controlled settings, allowing us to explore how chemical pollution may interact with other ecological drivers such as nutrients and temperature, and how microbial responses scale up to higher trophic levels and alter ecosystem functioning.

Spatially and temporally up-scaled models of diffuse and point source chemical pollution pathways will be combined with novel thresholds developed from the lab and field exposures, to determine chemical threats to freshwater microbes, supporting the development of tools for the better management of the risks of chemical pollution to freshwater ecosystem health. These will be combined with future hydrological, climate, and socio-economic scenarios, informed by responses in our experiments and co-developed with project collaborators, the Environment Agency, to explore future threats to microbial freshwater ecosystems and wider ecosystem health.