Effects of plastic contamination on water evaporation and desiccation cracking in soil

Environmental contamination of plastics is becoming an issue of concern globally. Detection of plastics, particularly microplastics, has been increasingly reported in both marine environments and inland waters. Recent work has indicated that soil in terrestrial environments has also been contaminated by plastics. Research has also shown that plastics can have adverse effects on soil biota. However, the impact of plastics on soil physical properties is still unclear. In this work, effects of plastic film of different sizes at environmental relevant concentrations on water evaporation and desiccation cracking in two clay soils were studied. The results showed that the presence of plastics in soil significantly increased the rate of soil water evaporation by creating channels for water movement. The effect was more pronounced in soils treated with 2 mm plastics than in soils treated with 5 and 10 mm plastics, and increased with increasing plastic content. Desiccation cracking was observed on the surface of soil treated with 5 and 10 mm plastics likely due to the destruction of soil structural integrity. While 2 mm plastics increased the rate of desiccation shrinkage, the shrinkage ratio was reduced at the residual stage. Results from this work suggest that plastic contamination can alter the water cycle in soils, which may exacerbate soil water shortages and affect the vertical transport of pollutants. Further work is required to study the effects of plastics of other shapes, and laboratory observations should be tested at field scale.