Aquatic toxicity of UV-irradiated commercial polypropylene plastic particles and associated chemicals

Plastics often contain non-polar chemical additives, such as antioxidants, flame retardants, plasticizers, and UV stabilizers, which improve performance but have poorly understood environmental risks. This study assessed the aquatic toxicity of polypropylene (PP) containing the antioxidant Irgafos 168 (IRG) to the crustacean Daphnia magna and the green alga Raphidocelis subcapitata. Commercial PP containing IRG (PPc) and additive- and oligomer-free PP (PPd) were irradiated at 254 nm using germicidal light, both with and without H₂O₂. The tested particles included microplastics (MPs, 1-50 μm and 50-500 μm) and nanoplastics (NPs, < 1 μm). The results showed that the toxicity was influenced by particle size, concentration, and the presence of the antioxidant additive. Smaller particles, along with the presence of IRG and its degradation products, tris(2,4-di-tert-butylphenyl) phosphate, bis(2,4-di-tert-butylphenyl) phosphate, and 2,4-di-tert-butylphenol, contributed to higher toxicity in both D. magna and R. subcapitata. The highest toxicity was observed for NPs containing IRG (PPc), which resulted in an EC₂₀ for D. magna immobilization of 7.2 ± 0.1 mg/L, compared to the less toxic NPs free of IRG (EC₂₀ 28.7 ± 4.2 mg/L). The growth rate of R. subcapitata was also more affected by NPs generated from PPc (EC₂₀ 0.2 ± 1.2 mg/L) than by the corresponding NPs free of IRG (LOEC 3 mg/L). Our findings showed that the main toxicity was driver was an increase of intracellular reactive oxygen species, lipid peroxidation (LPO), damage to cell membrane integrity and impairment of esterase activity. The results demonstrated that irradiated plastic particles act as carriers for toxic non-polar compounds, enhancing negative effects on aquatic organisms, with particle size being a key factor. This study highlights the complex toxicological impacts of micro- and nano-plastics containing additives on aquatic biota.