Effects of arsenic on the transport and attachment of microplastics in porous media

Understanding the impact of arsenic (As(III), inorganic pollutant widely present in natural environments) on microplastics (MPs, one type of emerging contaminants) mobility is essential to predict MPs fate and distribution in soil-groundwater systems, yet relevant research is lacking. This study explored the effects of As(III) copresent in suspensions (0.05, 0.5, and 5 mg/L) on MPs transport/attachment behaviors in porous media containing varied water contents (θ = 100 %, 90 %, and 60 %) under different ionic strengths (5, 10, and 50 mM NaCl) and flow rates (2, 4, and 8 m/day). Despite solution ionic strengths, flow rates, porous media water contents, sizes, and surface charges of MPs, with coexisting humic acid, and in actual water samples, As(III) of three concentrations increased MPs transport in quartz sand and natural sandy soil. The increased electrostatic repulsion between MPs and sand caused by the altered MPs surface charge via the adsorption of As(III) together with steric repulsion from As(III) in solution contributed to the promoted MPs mobility in porous media. The occupying attachment sites by As(III) partially contributed to the increased mobility of MPs with negative surface charge in porous media. Clearly, As(III) coexisting in suspensions would enhance MPs transport in porous media, increasing MPs environment risks.