Phototransformation and toxicity enhancement of silver chloride nanoparticles by polystyrene microplastics under sunlit

Silver chloride nanoparticles and microplastics are polluting in surface waters, yet their interactions, associated toxicity and environmental risks are poorly known. Here we hypothesized that polystyrene microplastics could enhance the phototransformation of silver chloride nanoparticles and modify their toxicity. We conducted phototransformation of silver chloride nanoparticles with polystyrene microplastics under light irradiation. The photo-dissolution of silver chloride nanoparticles and photo-reduction of silver ions were determined in both double-distilled-water and environmental waters. We found that polystyrene microplastics highly enhanced the phototransformation of silver chloride nanoparticles by hydroxyl radicals, singlet oxygen, and triplet state microplastics, leading to the release of silver ions and chloride ions. Subsequently, the silver ions were reduced to silver nanoparticles by superoxide radicals. Consequently, the silver species transformation increased the toxicity of silver chloride nanoparticles even at environmental concentration, as evidenced by survival rate of zebrafish larvae reduced from 100% to 23.3%. This is the first study to show that polystyrene microplastics can enhance the phototransformation of silver chloride nanoparticles to silver nanoparticles, thereby increasing the environmental risks of silver chloride nanoparticles in environmental waters.