Impact of polyethylene terephthalate microfibers on histopathological and molecular responses induced by cadmium in the polychaete Perinereis aibuhitensis

Heavy metals and microplastics have been found to co-exist in marine sediment environments. Nevertheless, the impact of microplastics on modifying the toxicity of heavy metals to marine benthic organisms remains poorly understood. Herein, we investigated the impact of polyethylene terephthalate microfibers (PET MFs, 100 μm in diameter, 500 items·kg·dw) on the toxicities and individual/subcellular bioaccumulation of cadmium (Cd, 1, 10 and 100 μg g·dw) in the benthic polychaete, Perinereis aibuhitensis, after 28 days of sediment exposure. Exposure to either Cd (10 and 100 μg g) or PET MFs alone induced the intestinal inflammation response including cell vacuolation, villi exfoliation, and cytolysis, and the presence of PET MFs significantly aggravated the inflammatory response at a Cd concentration of 1 μg g. PET MFs also had a significant impact on oxidative stress biomarkers including lipid peroxidation (LPO), protein carbonylation (PC) and glutathione S-transferase (GST) activity at 500 items·kg. In addition, compared to Cd exposure alone, co-exposure significantly reduced LPO and PC levels while enhancing GST enzyme activity at a Cd concentration of 100 μg g, suggesting a reduction in oxidative damage. Besides, co-exposure also significantly upregulated or downregulated the mRNA expression of selected genes involved in stress response (CAT, SOD, HSP70, HSP90), metabolism (CYP4) and detoxification (MPⅡ) as determined by real-time q-PCR. However, Cd bioaccumulation at individual or subcellular level was not affected by PET MFs, suggesting the key role of toxicity contribution of PET MFs themselves in the combined toxicity. The potential adverse effects of the co-existence of MFs and heavy metals in sediment environments under long-term exposure scenarios still require further validation.