Association of Potential Human Pathogens with Microplastics in Freshwater Systems

Abstract

Microplastics (MPs) have gradually become a global environmental pollution concern and are readily colonised by environmental microorganisms. MPs persist in the environment and serve as potential vectors for spreading bacterial pathogens of humans, due to their low biodegradability, high surface area to volume ratio and hydrophobicity. In the pelagic and benthic environments, surfaces are always colonised by microorganisms, forming biofilms. As a consequence, microorganisms absorbed onto MPs can be transferred towards other marine species along the trophic web. Despite recent findings on microorganisms associated with MPs in marine environments, there is a lack of information on microbial colonisation of microplastics in freshwater ecosystems. Due to their small size, MPs in rivers provide a solid surface on which dense biofilms can form. Therefore, we employed a 14-day experiment to investigate bacterial colonisation on polyethylene (PE) MPs within the River Barrow, Carlow, Ireland. MP beads were placed in-situ in the river as well as in river water samples in the laboratory and left for 14 days. High throughput 16S ribosomal DNA (rDNA) gene sequencing was used to profile bacterial communities on the surfaces of microplastic particles. Different bacterial communities and lower microbial diversity were observed in the laboratory samples compared to the in-situ river water samples. Results revealed the presence of potentially pathogenic species, such as Enterobacter spp, Helicobacter spp, Arcobacter spp, Clostridium perfringens and Escherichia coli. This suggests that MP do have the capacity to support and transport potential harmful bacteria.