Abstract

The sources of pharmaceutical substances entering aquatic ecosystems are varied. Used in veterinary and animal medicine, these substances can be directly discharged by wastewater treatment plants that fail to eliminate them, or they may run off from fields amended with contaminated slurry into watercourses. Over the past few years, there has been a global contamination of rivers across the planet¹. This widespread exposure of aquatic organisms leads to the risk of ecotoxicological impacts.

Among the organisms likely to be impacted, biofilms are communities of microorganisms assembled within an extracellular matrix. These biofilms are found in all aquatic environments. In rivers, they develop in the sediment (sedimentary biofilms) or on the surface of submerged substrates (periphytic biofilms). The microbial communities that make up biofilms play a crucial role in ecosystems, contributing notably to the mineralization of organic matter, the production of primary and secondary matter that can be mobilized by higher trophic levels, sediment stabilization, or even the biodegradation of certain contaminants^2,3.

Exposure of biofilms to pharmaceutical substances may induce an impact on these communities. Studies suggest effects on their structure and diversity, as well as a disturbance of their intra- or extracellular activities ^4–8. According to the concept of tolerance induced by exposure to toxins (‘pollution-induced community tolerance’, PICT), this type of chemical exposure may also exert pressure that selects the most tolerant microorganisms, thereby increasing the overall tolerance of the community to the toxicity of these substances⁹. However, the links between biofilm exposure levels to pharmaceutical substances and the adaptive mechanisms of the resulting microbial communities remain largely unknown to this day.

As part of my PhD, I aim to better characterize these links, focusing specifically on the impact of different exposure levels to pharmaceutical substances on the structure, diversity, and activities of periphytic and sedimentary microbial communities, as well as on the evolution of their tolerance to these substances.

To do so, I rely, on one hand, on an in situ experiment conducted in a contaminated river (Tillet, Savoie) to study variations in the tolerance of periphytic communities to various pharmaceutical substances, depending on exposure level variations in a complex environmental context (Fig. 1).

I also base my research on laboratory channel experiments to control the concentrations and duration of exposure of sedimentary and periphytic communities to three model pharmaceutical substances, aiming to better understand the links between the tested exposure levels and the observed microbial responses (Fig. 2).

Funding

• Salary: 100% INRAE (AQUA department + DG)
• Operational Costs: ANSES PharmOneHealth project (ANSES-22-EST-066)

References

• ¹ Wilkinson, J. L. et al. Pharmaceutical pollution of the world’s rivers. Proc. Natl. Acad. Sci. U. S. A. 119, e2113947119 (2022).
• ² Besemer, K. Biodiversity, community structure and function of biofilms in stream ecosystems. Res. Microbiol. 166, 774–781 (2015).
• ³ Bonnineau, C. et al. Role of Biofilms in Contaminant Bioaccumulation and Trophic Transfer in Aquatic Ecosystems: Current State of Knowledge and Future Challenges. in Reviews of Environmental Contamination and Toxicology Volume 253 (ed. de Voogt, P.) 115–153 (Springer International Publishing, 2021). doi:10.1007/398_2019_39.
• ⁴ Carles, L. et al. Impact of wastewater on the microbial diversity of periphyton and its tolerance to micropollutants in an engineered flow-through channel system. Water Res. 203, 117486 (2021).
• ⁵ Corcoll, N. et al. Pollution-induced community tolerance to non-steroidal anti-inflammatory drugs (NSAIDs) in fluvial biofilm communities affected by WWTP effluents. Chemosphere 112, 185–193 (2014).
• ⁶ Kergoat, L. et al. Environmental Concentrations of Sulfonamides Can Alter Bacterial Structure and Induce Diatom Deformities in Freshwater Biofilm Communities. Front. Microbiol. 12, 643719 (2021).
• ⁷ Rosi-Marshall, E. J. et al. Pharmaceuticals suppress algal growth and microbial respiration and alter bacterial communities in stream biofilms. Ecol. Appl. Publ. Ecol. Soc. Am. 23, 583–593 (2013).
• ⁸ Desiante, W. L., Minas, N. S. & Fenner, K. Micropollutant biotransformation and bioaccumulation in natural stream biofilms. Water Res. 193, 116846 (2021).
• ⁹ Tlili, A. et al. Pollution-induced community tolerance (PICT): towards an ecologically relevant risk assessment of chemicals in aquatic systems. Freshw. Biol. 61, 2141–2151 (2016).