Plain polystyrene microplastics reduce the toxic effects of ZnO particles on marine microalgae Dunaliella salina

A critical literature survey on marine ecotoxicology reveals a lack of comprehensive studies to assess the impact of microplastics on the toxicity of engineered nanomaterials at environmentally relevant doses. Though ZnO and microplastics both are well known to be marine pollutants, the combined toxicity of ZnO particles with plain polystyrene (PS) microplastics are yet to be studied. Preliminary characterization of ZnO particles included examining particle size, morphology, and surface area. The amount of nominal and dissolved ions in the suspensions containing nano-sized ZnO particles was determined. The toxicity of bulk and nano-sized ZnO particles in combination with plain PS microplastics at low concentration (1 mg/ L) was assessed towards marine algae Dunaliella salina at three exposure concentrations 1.22, 12.28 and 122.88 mu M under UV-A and dark exposure conditions. As expected, a dose-dependent increment in the toxicity, ROS (extracellular & intracellular) generation and lipid peroxidation were noted for both bulk and nano-sized ZnO particles. The harmful effects of bulk and nano-sized ZnO particles were considerably reduced in the presence of plain PS microplastics. This study opens up new dimensions regarding the positive impact of microplastics at low concentration, where they lessen the toxic effects of co-pollutants in the marine ecosystem.