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Use of a nanoplastic carrier for assessing the aquatic toxicity of an organo-phosphite polymer additive
Summary
Researchers produced polypropylene nanoplastics free of additives and oligomers, then reloaded them with specific chemicals to test the aquatic toxicity of the polymer additive Irgafos 168. This controlled approach allowed them to distinguish the toxicity of the additive from that of the plastic particle itself. The study demonstrates that chemical additives leaching from nanoplastics can pose distinct environmental risks beyond those caused by the plastic particles alone.
This work reports the production of nanoplastics (NPs) from polypropylene (PP) free of the antioxidant Irgafos® 168 (IRG) and alkane oligomers (ALK). PP pellets were milled into a powder with particle sizes in the 100-500 μm range. Additives and oligomers were removed using dichloromethane, and the powder exposed to UV irradiation, followed by filtration through 1 μm filters. PP suspensions, free of antioxidant and oligomers, were reloaded with IRG and ALK to their original commercial concentrations. This approach allowed testing the aquatic toxicity of IRG at concentrations compromised by water solubility limits. Toxicity assays using the cladoceran Daphnia magna with 24-48 h immobilization of neonates as endpoint showed toxicity for NPs containing IRG, with EC (48 h) in the 1.8-3.5 mg/L range, that corresponded to IRG exposure <1.2 μg/L. Suspensions of PP containing ALK, but not IRG, exhibited low toxicity (EC > 20 mg/L). The results allowed estimating the toxicity of IRG with a EC value of 3.3 ± 1.1 μg/L. Assays with different proportions of IRG and its oxidized form showed no differences. This work demonstrated the aquatic toxicity of IRG, for which there were no previous data, and developed a method for testing the toxicity of non-polar additives without being limited by their solubility.