Sources, Transport Pathways, Entry and Impacts of Microplastics in Conventional Drinking Water Treatment Plants: A Critical Review

Abstract

Microplastics, usually defined as insoluble synthetic polymer particles under 5 mm, occur almost everywhere in the water cycle, from freshwater sources and raw intake water to treated drinking water and even the pipes that carry it to our taps. They enter these systems through a mix of primary and secondary routes: fragmenting plastic debris, shedding textile fibres, tyre and road wear, industrial losses, wastewater effluent, stormwater runoff, and atmospheric fallout. Conventional drinking-water treatment plants (DWTPs) built around coagulation, flocculation, sedimentation, granular-media filtration and disinfection form an important barrier against these particles, but how well they work depends heavily on particle size, shape, density, polymer type, surface weathering, water quality and how the plant is operated. Larger particles and fibres tend to get caught up in flocs and settle out or get filtered, while small microplastics and nanoplastics are much harder to pin down and remove with any consistency. It is also worth stressing that removing MPs from the water phase is not the same as destroying them; they typically end up concentrated in clarifier sludge, filter backwash water, and other residual streams. This creates its own set of downstream issues: interference with coagulation and filtration, buildup in treatment residuals, possible fragmentation during oxidative steps, and the risk that poorly managed backwash or sludge disposal sends retained particles right back into circulation. As for human health, the evidence so far does not point to a clear-cut risk from MP exposure through drinking water, though real uncertainty remains around small particles, the chemicals associated with plastics, and biofilm-related contaminants. This review takes a critical look at where these particles come from, how they travel, how they enter treatment systems, and what happens to them once they are there and it flags the analytical gaps and research priorities that matter most for keeping MPs out of the water we drink.Microplastics, usually defined as insoluble synthetic polymer particles under 5 mm, occur almost everywhere in the water cycle, from freshwater sources and raw intake water to treated drinking water and even the pipes that carry it to our taps. They enter these systems through a mix of primary and secondary routes: fragmenting plastic debris, shedding textile fibres, tyre and road wear, industrial losses, wastewater effluent, stormwater runoff, and atmospheric fallout. Conventional drinking-water treatment plants (DWTPs) built around coagulation, flocculation, sedimentation, granular-media filtration and disinfection form an important barrier against these particles, but how well they work depends heavily on particle size, shape, density, polymer type, surface weathering, water quality and how the plant is operated. Larger particles and fibres tend to get caught up in flocs and settle out or get filtered, while small microplastics and nanoplastics are much harder to pin down and remove with any consistency. It is also worth stressing that removing MPs from the water phase is not the same as destroying them; they typically end up concentrated in clarifier sludge, filter backwash water, and other residual streams. This creates its own set of downstream issues: interference with coagulation and filtration, buildup in treatment residuals, possible fragmentation during oxidative steps, and the risk that poorly managed backwash or sludge disposal sends retained particles right back into circulation. As for human health, the evidence so far does not point to a clear-cut risk from MP exposure through drinking water, though real uncertainty remains around small particles, the chemicals associated with plastics, and biofilm-related contaminants. This review takes a critical look at where these particles come from, how they travel, how they enter treatment systems, and what happens to them once they are there and it flags the analytical gaps and research priorities that matter most for keeping MPs out of the water we drink.