A Review of the Origins of Microplastics arriving at Wastewater Treatment Plants

Concerns regarding the impacts of microplastics in the global environment have brought into focus the need to understand better their origins, transport, and fate. Wastewaters (WW) are important in this regard: discharges from households, commercial and industrial premises, and surface run-off deliver microplastics to wastewater treatment plants (WWTPs) via sewerage systems, through which they are removed along with sewage sludge or destined for release into the environment in treated effluent. This review provides a contemporary and critical analysis of factors influencing the quantities and composition of microplastics (MPs) reaching wastewater treatment plants, including both primary and secondary sources. Three specific areas of concern were highlighted. First, current legislation, where present, needs to address regulation of microplastics in personal care and cosmetic products that cross international borders. Secondly, accurate estimation of microplastics arising from some sources and activities (e.g., mis-managed waste and hand washing of textiles) is challenging and estimated contributions of associated microplastics remain unsatisfactory as a basis for management decisions. Thirdly, information relating to microplastics in personal care and cosmetic products used by male consumers is lacking and contributions of such products to wastewater remain uncertain. We recommend that (1) voluntary practices and programmes should be replaced with formal regulation to achieve compliance, and (2) the role of consumers’ behaviour in generating microplastics that are destined for wastewater treatment plants remains largely unknown and that more research in this domain is needed.