Prokaryotic metabolic response to water-soluble polymers enhances oxygen drawdown in freshwater systems: A polyethylene glycol case study

• Water-soluble polymers are emerging contaminants with widespread applications. • Incubation experiments were conducted to assess PEGs effect on river microbes. • PEG acts as a bioavailable carbon source, promoting microbial growth and deoxygenation. Water-soluble polymers (WSPs), such as polyethylene glycol (PEG), are emerging contaminants with widespread industrial and commercial applications. Despite their extensive use, the environmental fate and impact of WSPs in freshwater ecosystems remain largely unexamined. We hypothesize that PEG exposure will increase microbial oxygen consumption rates, thereby exacerbating deoxygenation. Short-term incubation experiments were conducted on water samples collected from the River Test, Romsey, UK, to assess PEG’s effect on microbial: oxygen consumption, leucine uptake and assimilation efficiency, to indicate rates of prokaryotic respiration and production, and eco-physiological status. A range of PEG molecular weights (100–1000 g/mol) and concentrations (50–1600 mg/L) were used. Our results demonstrate that PEG enhances microbial respiration, with an increase in oxygen consumption across all tested molecular weights and concentrations. Even at the lowest concentration (50 mg/L), PEG exposure resulted in a 40–80 % increase in oxygen consumption compared to controls. Leucine assimilation efficiency also increased, suggesting that PEG serves as a bioavailable carbon source, thereby promoting microbial growth and enhancing eco-physiological status. However, the relationship between PEG molecular weight, concentration, and oxygen consumption was non-linear, likely influenced by factors such as aggregation effects, microbial enzymatic selectivity, and threshold-driven metabolic responses. These findings suggest that WSPs may play an underappreciated role in altering oxygen dynamics in freshwater systems, with potential implications for eutrophication, aquatic ecosystem functioning and enhanced carbon dioxide production. Given the increasing global production and environmental presence of WSPs, further research is needed to assess their potential long-term environmental impacts to inform disposal strategies.