Microplastics and microfibres in the municipal water systems and agricultural lands of the Niagara Region, Ontario

Abstract

Microplastics are ubiquitous in freshwater and terrestrial environments across the globe. Undoubtedly, plastics are entering Niagara (Ontario) water systems as well; entering as microplastics and microfibres derived from household products and materials. These microplastics are known to enter wastewater treatment plants with untreated municipal influent and exit with the treated effluent (up to 99%), making their way into water bodies where they may be taken up by aquatic organisms. Furthermore, wastewater biosolids are applied to agricultural fields as fertilizer throughout southern Ontario. Thus, microplastics may be making their way into agricultural soils where runoff can further transport these particles to downstream environments. To investigate the microplastic pathways facilitated by the wastewater treatment system to the environment, monthly effluent sampling was conducted on a local wastewater treatment plant, and monthly tap water sampling at three sites in the Niagara Region. Surface waters upstream and downstream of effluent discharge were also sampled. Wastewater effluent had an average concentration of 1.22±1.59 microplastics per litre, dominantly polyester fibres. In surface waters, greater microplastic concentrations were found downstream than upstream (3.17±2.37 and 0.35±0.33 microplastics per m3, respectively), dominantly polyethylene. In tap water, an average of 0.89 microplastics per litre was recovered (dominantly polyester). One year of monthly effluent sampling showed significant seasonal differences in microplastic concentrations, suggesting that longer studies are necessary to account for seasonal change. This study also highlights the influence of combined sewer overflows on microplastic concentrations in surface waters, which has not been thoroughly discussed in previous studies. To investigate microplastic accumulation in agricultural soils in Niagara, two receiving biosolid application and one control site were investigated. An average concentration of 4.4±4.8 and 4.3±2.4 microplastics per gram was found in soils and biosolids, respectively. Controlled-release plastic fertilizer coatings were found to be a dominant source of microplastics to agricultural soils. This study is the first to our knowledge to highlight the accumulation of polymeric fertilizer coatings in agricultural soils.