Adsorption Characteristics of Cd and Pb on Microplastic Films Generated in Agricultural Environment

Objectives:Plastics are widely used in daily life and in various industrial fields due to their convenience and thermal insulation, and the use of plastics is continuing to increase. In agricultural environments, plastics are largely used for vinyl houses and mulching vinyl. Used plastics are degraded into small fragments through physical, chemical, and biological processes. Among these, plastics with a particle size of 5 mm or less are defined as microplastics. Since microplastics have a relatively large surface area, various pollutants including heavy metals can potentially be adsorbed and affect the agricultural ecosystem. The purpose of this study is to evaluate the Pb and Cd adsorption characteristics on microplastic films frequently generated in agricultural environments.Methods:The Pb and Cd adsorption characteristics on microplastic films were studied with 3 different plastic films. Microplastic samples were prepared by cutting PVC (polyvinyl chloride) and PE (polyethylene) films to have the sizes of < 5 mm×5 mm. The prepared microplastic samples were placed in Pb or Cd solutions having a range of concentrations and shaken for 72 h for sorption tests. The experimental results were fitted to the Langmuir, Freundlich, and Temkin isothermal adsorption models.Results and Discussion:The isothermal adsorption test results obtained fitted well to the Langmuir and Freundlich models (R<sup>2</sup>>0.9), but not the Temkin model. Regardless of the plastic type, the values of Langmuir constant (KL) and Temkin constant (AT) for Pb were larger than those for Cd, and the Freundlich constant (nF) showed a tendency of Pb>Cd>1, indicating the greater Pb sorption strength or affinity than Cd on PVC and PE.Conclusions:This study shows that the microplastics in soil adsorb heavy metals like Cd and Pb affecting the heavy metal fate in the soil environment. With an increasing attention on the environmental problems due to plastic wastes, this study provides the basis for the need of management of soil environment. Therefore, further research on microplastics in soil environment is required.