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Behavioral changes and control strategies of downstream microplastics under the influence of wastewater treatment plants: A review
Summary
Wastewater treatment plants catch most microplastics before releasing cleaned water back into rivers and streams, but this review of existing research shows that the microplastics that do slip through aren't harmless—they can carry toxic chemicals, travel long distances, and affect fish and other wildlife downstream. Since these waterways often connect to the water and food supplies we rely on, the authors call for better treatment technology and monitoring to keep tabs on this often-overlooked pollution source.
MP pollution is one of the critical environmental challenges. WWTPs act as critical sinks for MPs. Although most MPs are intercepted during treatment, the steady discharge of treated effluent may still impact downstream habitats. Therefore, effectively mitigating MP contamination discharged from WWTPs (hereafter referred to as effluent MPs) is crucial for environmental protection. Based on this, this study reviews the distribution, transport mechanisms, impacts, and control strategies of effluent MPs in downstream environments. It has been shown that the relative abundance of MPs upstream and downstream of the discharge point has no apparent correlation with the relative distance from the outlet to the upstream and downstream areas. However, methodological differences across studies may lead to distorted conclusions. Therefore, we have proposed relevant recommendations regarding the current sampling and analysis framework. In addition, the pollution source, the level and method of treatment, and the proportion of discharge can initially influence downstream MPs. Subsequently, local geography and hydrology alter their transport. WWTP processes also modify MP properties, which may affect fish predation and indirectly influence the MP migration. However, effluent MPs can not only produce toxic substances but also carry other pollutants from WWTPs. Furthermore, they may rapidly release some pollutants and transport others over long distances, thus impacting the downstream biosphere and atmosphere. To mitigate pollution, enhancing prevention, developing new treatment technologies, and advancing downstream resource recovery technologies are essential. In summary, special attention should be paid to effluent MPs, which may possess stronger environmental effects.