Effects of polystyrene microplastics on the distribution behaviors and mechanisms of metalloid As(III) and As(V) on pipe scales in drinking water distribution systems

Pipe scales have long been considered the primary adsorption medium for trace heavy metals in drinking water distribution systems (DWDSs). Microplastics (MPs) potentially affect the distribution of metalloid arsenic (As) pollutants in DWDSs. Herein, the accumulation behaviors of As(Ⅲ) and As(V) on pipe scales and polystyrene microplastics (PSMPs) under different water conditions were studied. Additionally, As(Ⅲ) and As(V) accumulation behaviors on pipe scales coexisting with PSMPs were investigated. Results showed that pipe scales played a key role in the accumulation of As (pipe scales = 1.08-4.80 mg/g > PSMPs = 0.02-3.38 mg/g). The adsorption amount of As(Ⅲ) on PSMPs was higher than that of As(V). The addition of PSMPs promoted the accumulation of As(Ⅲ) on pipe scales at pH = 3-8 while inhibiting the accumulation of As(V) on pipe scales at pH = 3-10 due to the competitive adsorption. The oxidation of As(III) and the reduction of As(V) occurred during the accumulation of As(Ⅲ) and As(V) on pipe scales. Notably, PSMPs accumulated on pipe scales were beneficial to the oxidation of As(Ⅲ), potentially reducing the As-related risks. Overall, our results provide new insights into the hazards posed by MPs in DWDSs.