The influence of polyethylene microplastics on pesticide residue and degradation in the aquatic environment

Microplastics pollution has become a global concern in recent years. In this work, the potential influences of polyethylene (PE) microplastics on the residue, degradation and distribution behaviors of eight pesticides (epoxiconazole, tebuconazole, myclobutanil, azoxystrobin, simazine, terbuthylazine, atrazine and metolachlor) in the aquatic environment were investigated. The results showed that the presence of 2-50 g L-1 microplastics could decrease the pesticide residues in water. The adsorption isotherms were linear, indicating the process was dominated by partitioning into the bulk polymer. The desorption kinetics data implied the desorption process obeyed a pseudo-second-order kinetic model, with R2 above 0.99 in most cases. Aging treatment of microplastics had no significant effects on the interaction with the pesticides. The presence of PE microplastics could significantly prolong the degradation half-lives of pesticides in water, especially for those with moderate degradation half-lives and high log Kow values. Take terbuthylazine as an example, its half-life significantly increased from 31.8 days to 45.2 days in the presence of 10 g L-1 microplastics. Besides, PE microplastics had little impact on the behavior of the pesticides in the water-sediment system. The findings of this study indicated that PE could adsorb pesticides through partitioning, thus influencing the persistence of the pesticides in water.