A Review on Adsorption and Transport of Microplastics in Soil and the Effect of Ageing on Environmental Behavior of Pollutants

Microplastics, defined as the plastic material with a size of < 5mm, have been widely attracting attention due to the high mobility and strong affinity toward pollutants. Microplastics concentrate in soil through plastic film breakage, landfill and atmospheric deposition. Microplastics can migrate downward in soil, and adsorb co-existing pollutants. The ageing of microplastics due to surface geochemical processes, would result in a great threat to the environment.

To comprehensively understand the environmental behavior of microplastics and their potential environmental risks.

The key factors controlling vertical transport of microplastics in soil were summarized, including microplastics properties such as the size, shape and functional groups, and soil properties such as the porosity, organic matter and soil minerals. The adsorption of organic pollutants and heavy metals on microplastics and the effect of ageing were analyzed.

The results obtained from recent studies showed that: (1) The transportation of microplastics can be affected by their inherent properties and the soil environments. (2) Microplastics can adsorb heavy metals and organic pollutants, and co-transport in soil, which would change the environmental fate and bioavailability of pollutants. (3) The ageing process can impact the microplastics mobility, adsorption capacity, and the release of the associated contaminants derived from the microplastics. The release of endogenous organics phthalate esters from aged microplastics could reach 50.3-6660ng/g, and that of heavy metal Pb²⁺ reach 5.1-81.4μg/g.

In view of the current research and existing problems, this review gives guidance on microplastics transport, adsorption and ageing effect for future studies. (1) The interaction mechanisms between microplastics and pollutants should be elucidated under multi-factor coupling conditions in soil, especially for the influence of different soil types and environmental factors on the adsorption/desorption/migration of pollutants on the microplastics. (2) The effects of different ageing processes on the properties and environmental behavior of the microplastics should be studied by experimental simulation. (3) In order to uncover the effects of aging on the release behavior of endogenous pollutants, the study on the release of endogenous pollutants from microplastics in different ageing environment should be strengthened.