Occurrence, removal and potential threats associated with microplastics in drinking water sources

Microplastics (MPs) have gained increasing attention as an emerging contaminant in drinking water. However, there is no definitive conclusion on the deleterious effects of MPs on human health. Herein, we consider the potential threats of these anthropogenic particles that have been increasingly found in drinking water sources (DWSs) based on reviewing their occurrence and removal from a water treatment perspective. As revealed by 53 publications on MP presence in conventional DWSs, bulk sampling can better reflect the current knowledge on the pollution in DWSs; the median MP concentration in conventional water sources was 2.2 x 10(3) items m(-3) with the size of particles identified usually >50 mu m. Next, the removal efficiency of MPs across multiple barriers in drinking water treatment plants was also elaborated. Almost all MPs (>10 mu m) were removed after coagulation, sedimentation and filtration processes. For smaller MPs (>1 mu m), removal rates of >80 % were typically observed. Two size-dependent threats associated with MPs in DWSs were identified: 1) the increased probability of the accumulation of potential pathogenic bacteria and the transmission of antibiotic resistance genes where larger MPs in DWSs may serve as important carriers; 2) the release of nanoplastics and dissolved organic carbon from the photodegradation process of MPs. Additionally, MPs in alternative DWSs were given special attention due to their potential to accumulate MPs. The review provides new information for practitioners and scientists alike with respect to the potential threats posed by MPs in DWSs.