Microplastics in sandy soils: alterations in thermal conductivity, surface albedo, and temperature

Rapid growth in plastic production has exacerbated disposal of plastic wastes in terrestrial ecosystems. Unfortunately, soils represent large reservoirs for disposal of microplastics (MPs). MPs infiltrate into the soil through various pathways and alter its intrinsic properties. Despite advances in understanding the impact of MPs on soil physical, biological, and hydrological processes, their influence on surface energy balance and soil temperature remains understudied. Such information is more necessary than ever, considering the ongoing changes to soil systems caused by climate variations and extremes. We conducted laboratory experiments on sandy soils to investigate how MPs with different characteristics impact soil temperature dynamics. The changes in the soil thermal conductivity and surface albedo, in the presence of polyethylene (PE) and polyvinylchloride (PVC) particles at various concentrations were measured. The results demonstrate that MPs, and particularly PVC, with amorphous characteristics may decrease effective thermal conductivity of sand by 38%. Moreover, the deposition of MPs at the surface of samples may increase surface albedo by 28% and 77% with addition of 5% PVC and 5% PE, respectively. Such effects are pronounced at higher soil moisture contents, facilitating migration and deposition of MPs on the surface. We ultimately examined the impact of changes in soil thermal and radiative properties on soil temperature dynamics by monitoring the thermal regime in drying sand columns. Our findings indicate that MPs significantly alter evaporative flux and subsurface temperature profile, hence providing insights into understanding the changes in soil energy balance due to the presence of MPs.