Abstract:

Microplastics (plastic particles ≤ 5mm) are recognized as widespread environmental contaminants, and wastewater treatment plant outfalls are a source of them to aquatic ecosystems. Once present in water bodies, microplastics may be retained in basal resources such as sediment or biofilms, making them potentially available to be ingested by aquatic organisms, including insects. Emergent insects, having both aquatic and terrestrial life stages, may ingest and transport microplastics out of aquatic ecosystems, and into near-shore food webs. Our study examined microplastics sourced from eight wastewater treatment facilities in the Grand River watershed, ON, using a multi-trophic approach by assessing microplastics in wastewater effluent, sediment, biofilm, larval aquatic insects, emerged adult insects and riparian spiders. Microplastics were extracted from sediment with CaCl2 density separations, and from biofilm, insects and spiders using H2O2. Microplastics counts varied between sites, with some downstream locations having elevated levels when compared to upstream of the wastewater treatment facility (p<0.05). Fibres were the most common microplastic found across all sample types, and microplastic abundance varied based on month sampled in all sample types except in larval insects and spiders. Overall, spiders were found to contain low amounts of microplastics, suggesting potential transfer of microplastics from aquatic to riparian ecosystems. The risk posed by microplastics may not only remain in aquatic ecosystems, therefore this research addresses a key gap in our understanding by providing novel and much-needed information on the presence, transfer, and fate of microplastics in the environment.