Effects of microplastics on 3,5-dichloroaniline adsorption, degradation, bioaccumulation and phytotoxicity in soil-chive systems.

Microplastics (MPs) and pesticides are two pollutants of concern in agricultural soils. 3,5-dichloroaniline (3,5-DCA), a highly toxic metabolite of dicarboximide fungicides, commonly co-exists with MPs and poses a risk to the environment and food safety. Batch adsorption and soil incubation experiments were employed to investigate the effects of polyethylene (PE) and polylactic acid (PLA) MPs on the environmental behavior of 3,5-DCA in soil. Chive (Allium ascalonicum) was used as the experimental plant, a pot experiment was conducted to examine the effects of individual or combined exposure to MPs and 3,5-DCA on plant 3,5-DCA bioaccumulation, growth characteristics, and phytotoxicity. The results showed that PE- and PLA-MPs increased the adsorption capacity of soil to 3,5-DCA and prolonged the degradation half-life of 3,5-DCA by 6.24 and 16.07 d, respectively. Two MPs partially alleviated the negative effects of 3,5-DCA on the root length and fresh weight of chives, while PE-MPs had a positive and dose-dependent impact on the contents of photosynthetic pigment in chive leaves. Co-exposure to 3,5-DCA and MPs increased residues of 3,5-DCA in soil and chive roots but had no significant effect on 3,5-DCA residues in chive stems or leaves. Moreover, 3,5-DCA residues in PLA-MP soil were consistently higher than those in PE-MP soil. Conclusively, MPs altered the 3,5-DCA adsorption and degradation behavior in soil, as well as its bioaccumulation in chives. Co-exposure to MPs and 3,5-DCA had dose-dependent and MP-specific effects on chive plant development and phytotoxicity.