Coexposure of Micro and Nano-Plastics with Pesticides: Cytotoxicity and Bioaccumulation Effects on a Fish Intestinal Cell Line

Micro- and nanoplastics (MNPs) occur in aquatic environments and accumulate in fish. MNPs can also adsorb other contaminants present in aquatic environments, and there is limited information on exposure scenarios involving MNP and pesticide mixtures. Ultraviolet (UV) radiation and chemical oxidation of MNPs can affect the sorption properties of MNPs and chemicals, thus altering the exposure and effects on fish. Our study investigated the toxicity and bioaccumulation of a lindane and dichlorodiphenyldichloroethylene (DDE) mixture adsorbed onto pristine and weathered polyethylene (PE) MNPs. Three different PE MNP types were used: microplastics (2-10 μm), oxidized microplastics (10-15 μm), and a MNP mixture (0.2-9.9 μm), and additionally each type was UV-aged for comparisons. RTgutGC cells, derived from rainbow trout (Oncorhynchus mykiss) intestine, were used to evaluate the role of the particle type on pesticides bioaccumulation and toxicity. Results showed that UV aging did not affect the agglomeration in solution but decreased the MNP's capacity to adsorb the pesticides (i.e., non-aged adsorbed 35% and 69% and UV-aged adsorbed 9.7% and 63% of lindane and DDE, respectively) likely due to a shift in MNPs hydrophobicity and consequently reduced the cytotoxicity of the pesticide MNPs mixture. Nanoplastics induced approximately 20% more lysosomal damage than microplastics, suggesting a distinct toxicity mechanism. Fluorescently labeled MNPs accumulated in intestinal cells which confirmed the internalization. Finally, bioaccumulation of DDE decreased approximately 2 to 8-fold in cells coexposed with all particle types, although lindane was not detected in the cells. Overall, our study indicated that MP and NPs reduce bioavailability of pesticides, but UV aging and particle fragmentation to nano size increased their bioaccumulation and toxicity in fish intestinal cells.