Effects of microplastics on evaporation dynamics in porous media

Microplastics (MPs) pollution is an emerging threat to soil ecosystems. The present study aims to investigate the impacts of MPs on soil water evaporation dynamics and patterns. Two series of laboratory experiments were conducted using sand particles and clay mixed with different MPs to investigate how evaporation dynamics and patterns are influenced by the presence of MPs. Quartz sand including 0, 0.75, 1.5, and 4.5% of Polyethylene (PE) and Polyvinylchloride (PVC) were used to evaluate MPs effects on evaporation rates while bentonite mixed with sand and 0, 0.75, 1.5, 4.5, 6, 8, and 10% of PE and PVC were used to investigate evaporation-induced cracking patterns. The experiments were conducted under controlled laboratory conditions in a climate chamber at constant ambient temperature. Our results suggest that the addition of MPs led to more water evaporation compared to the samples without MPs. Microscopic imaging and analysis enabled us to evaluate the possible MPs effects on the modification of soil characteristics and pore structure affecting the evaporation behavior. Moreover, although increasing MPs concentrations appeared to induce only minor effects on the crack morphology formed as a result of evaporation from the mixture of sand and bentonite, the type of MPs (PE vs PVC) had more notable effects on the drying-induced cracking patterns. The reported experimental data and analysis extend our physical understanding of the parameters influencing soil water evaporation in the presence of MPs.