River biofilm plastic contamination and function from urban sites

Biofilms represent a nexus for the degradation of plastic materials in aquatic environments. The purpose of this study was to examine the influence of anthropogenic pollution on biofilm composition and function in a freshwater river (Saint-Lawrence River, Québec, Canada). Newly formed biofilms were collected on ceramic tiles at 2 combined sewers and street runoffs sites, one downstream of a large city (2 million inhabitants) and one site located 8 km downstream a municipal effluent dispersion plume. The data revealed that biofilms from the rainfall overflow sites were most contaminated with Nanoplastics while biofilms from the municipal effluent dispersion plume contained significantly more lipids. Biofilms from the overflow sites also exhibited increased esterase and biodegradation index compared to the other sites. However, no signs of oxidative stress were observed in biofilms suggesting that urban pollution was not deleterious to biofilm communities. In fact, 16S taxonomic analysis of biofilms revealed an increased presence of bacteria species usually associated with the plastisphere and known to degrade plastics in aquatic environments. In conclusion, biofilms could represent a sink to plastic pollution in urban environments.