Toxicity of polystyrene microplastics on juvenile Oncorhynchus mykiss (rainbow trout) after individual and combined exposure with chlorpyrifos‎.

Microplastic (MP) sorption and transfer of chemical contaminants has been widely reported, yet few studies have investigated combined effects of contaminant-loaded MPs on organisms. This study examined effects of pristine or chlorpyrifos (CPF)-loaded polystyrene (PS)‎ fragments on histopathological and histomorphometrical biomarkers in rainbow trout (Onchorhynchus mykiss)‎. In laboratory, O. mykiss were exposed for 96 h to pristine PS-MPs concentrations (30 or 300 µg/L), concentrations of CPF ‎alone (2 or ‎‎6 µg/L), and the same concentrations of CPF in the presence of PS-MPs in aquaria‎. Results showed the highest histopathological alterations in both CPF concentrations and when combined with PS-MPs in fish gills. Alternatively, high histopathological lesions including massive necrosis, infiltration of inflammatory cells, and shed of villi tips were observed in fish gut in high CPF concentrations combined with high PS-MP concentrations of ‎(6 μg/L CPF+300 μg/L PS-‎MPs). Individual CPF and PS-MP concentrations or combined together showed significant changes in histomorphometrical biomarkers in fish gills, gut and skin. Findings highlight that pristine PS-MPs cause toxicity and increase adverse effects of CPF in O. mykiss, especially in gill tissue. We present evidence that pristine short-term exposure to even low concentrations of PS-MPs has a significant impact on biomarker responses in O. mykiss.