Integrated Study of Polyethylene Microplastic Degradation and Its Interaction with the Insecticide Imidacloprid: Chronic Toxicity to Daphnia similis.

The presence of microplastics (MPs) in freshwater environments represents a growing environmental concern due to their persistence and ability to interact with contaminants such as pesticides. This study evaluated the influence of photodegradation on the toxicity of polyethylene microplastics (PE-MPs), alone and combined with the pesticide Imidacloprid (IMI), on the cladoceran Daphnia similis. Microparticles of polyethylene were aged under UV-C radiation for 94 days and subsequently characterized by Scanning Electron Microscopy (SEM) and Fourier-Transform Infrared Spectroscopy (FTIR). Surface analysis indicated polymer degradation through cracks and cavities, and increased surface roughness, while FTIR analyses showed polymer oxidation. Ecotoxicological results revealed that pristine MPs significantly reduced survival by 90% at 80 mg L-1, while photodegraded MPs caused more pronounced sublethal effects, particularly on reproduction, with a 69.8% reduction in neonates at 140 mg L-1. When associated with IMI, significant reductions in reproduction were observed, with a decrease of up to 75.7% in the number of neonates. However, the presence of IMI attenuated the toxicity of PE-MPs, evidencing an antagonistic interaction between the contaminants, particularly at concentrations of 80 and 140 mg L-1 of pristine PE-MPs. Taken together, these results demonstrate that the interactions between MPs and pesticides, as well as the state of particle degradation, significantly modulate ecotoxicological effects, posing a potential risk to the ecological integrity of aquatic ecosystems.