Strong sorption of two fungicides onto biodegradable microplastics with emphasis on the negligible role of environmental factors

Microplastics have attracted much attention in recent years because they are able to interact with other pollutants including pesticides, with implications for the potential risks to biota. However, the sorption behavior of pesticides on microplastics, especially on biodegradable microplastics which are promising alternatives to conventional polymers, has been insufficiently studied. In this study, triadimefon and difenoconazole were selected as model triazole fungicides, and their sorption behavior on a typical biodegradable microplastics (PBS: polybutylene succinate) and two conventional polyethylene (PE) and polyvinyl chloride (PVC) microplastics was investigated with batch experiments in an aqueous solution. PBS presented the highest sorption capacity for triadimefon (104.2 ± 4.8 μg g⁻¹) and difenoconazole (192.8 ± 2.3 μg g⁻¹), which was 1.8- and 1.3-fold that on PE and 4.4- and 7.4-fold that of PVC, respectively. The results of sorption kinetic and isotherm modeling were better fit by a pseudo-second order model and linear model, respectively. More importantly, the effects of environmental factors (pH, salinity and dissolved organic matter) on the sorption behavior were investigated. Fungicide sorption on PBS was generally not affected by salinity, pH or dissolved organic matter. However, in contrast, salinity and dissolved organic matter both significantly decreased sorption on PE and PVC. The results showed that not only the sorption capacities of biodegradable microplastics but also their responses to environmental factors are quite different from those of conventional microplastics. This finding highlights the importance of the role played by biodegradable microplastics in the accumulation and transportation of organic pollutants.