UV-B degradation affects nanoplastic toxicity and leads to release of small toxic substances†

Abstract

Fragmented micro- and nanoplastics are widespread pollutants with adverse effects on the environment. However, the breakdown process does not end with micro- and nanoplastics but is expected to continue until carbon dioxide has been formed. During this process the plastics will undergo chemical changes and small molecules may be released. We have broken down small amine-modified (∅53 nm) and carboxyl-modified (∅62 nm) polystyrene nanoparticles by UV-B irradiation during 100 days. We see a decreasing size and an oxidation of the nanoparticles over time. Simultaneously, the acute toxicity to zooplankton Daphnia magna decreases. UV-B irradiation releases small, dissolved molecules that are toxic to Daphnia magna. The dissolved molecules include aminated alkyls, styrene remnants and secondary circularization products. The study shows that UV-B radiation can change the original toxicity of nanoplastics and release new toxic substances.