Single and combined effects of phenanthrene and polystyrene microplastics on oxidative stress of the clam (Mactra veneriformis)

Toxicity of single organic pollutants or microplastics on organisms have been reported widely, however, their combined toxicity on bivalves was rarely investigated. In this paper, single and combined effects of phenanthrene (Phe, 20 μg·L and 50 μg·L) and polystyrene (PS, 17 μm and 150 μm with 1 mg·L) microplastics on oxidative stress of the clam Mactra veneriformis were assayed under laboratory conditions with biomarkers including superoxide dismutase (SOD), glutathione-S-transferase (GST) and malondialdehyde (MDA). We found that Phe or PS single stress source could induce oxidative stress to clams. Besides, exposed to Phe 50 μg·L or PS 150 μm caused the reduced expression of SOD and GST activities, leading to potential oxidative injury in clams. At each Phe concentration level, the order of single and combined toxicity on clams was Phe + PS 150 μm > Phe ≈ Phe + PS 17 μm. Phe exhibited a stronger toxic effect on clams than PS. Under joint exposure stress, the toxicity influence of Phe is still dominant. Furthermore, MDA and GST could be considered the most sensitive oxidative stress biomarkers in clams under Phe or PS single and combined exposures, respectively.