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Effect of salinity and humic acid on the aggregation and toxicity of polystyrene nanoplastics with different functional groups and charges
Summary
Researchers showed that surface charge governs nanoplastic behavior in water — higher salinity caused negatively charged nanoplastics to aggregate while positively charged particles remained stable — and that humic acid (dissolved organic matter) alleviated toxicity to Daphnia, increasing survival from 15% to nearly 100% in some cases.
Studies regarding the effect of environmental factors on the environmental behaviour and potential toxicity of nanoplastics (NPs) are limited but important. In this study, four polystyrene NPs with different functional groups and charges (PS, PS-COOH, n-PSNH, p-PSNH) were selected to investigate the effect of humic acid (HA) and salinity on their aggregation behaviour and toxicity. The results showed that salinity significantly accelerated the aggregation of the four NPs, while HA mainly exerted a stabilizing effect on the three negatively charged NPs. In contrast, the positively charged p-PSNH aggregated significantly at first but remained stable as HA concentration further increased. The joint effect mainly depended on their concentration ratio. The aggregation phenomena can be explained by the Derjaguin - Landau - Verwey - Overbeek (DLVO) theory. Also, the acute toxicity of NPs on Daphnia magna was affected by the surface charge of NPs, and the positively charged p-PSNH showed the lowest toxicity among the selected NPs. Furthermore, the presence of HA effectively alleviated the toxicity of PS and p-PSNH, as the survival rates increased from 15% to 45%-95% and 100% respectively. Our results demonstrate that the surface properties of NPs significantly influence their aggregation and toxicity.
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