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Aggregation of positively charged polystyrene nanoplastics in soil–root systems
Summary
Researchers showed that positively charged polystyrene nanoplastics aggregate in the presence of plant root exudates and soil leachate while negatively charged nanoplastics remain stable and mobile, driven by organic acid adsorption onto nanoparticle surfaces. Understanding nanoplastic charge-dependent behavior in soil-root systems is crucial for assessing how nanoplastics are taken up by crops and may enter the human food supply.
The occurrence of nanoplastics in agricultural land is a potential threat to human health and food security, yet the fate of nanoplastics is soil–root systems is poorly known. Here we investigated the aggregation behavior of polystyrene nanoplastics bearing different charges in cucumber root exudates and soil leachate, and in the presence of common environmental Ca2+ ions. Results show an increase in the aggregation size of positively charged amino-modified polystyrene nanoplastics, whereas negatively charged nanoplastics did not aggregate and showed no significant changes in particle size. This is possibly due to the adsorption of organic acids from soil leachates and root exudates onto the surfaces of nanoparticles. We observed that the critical condensation concentrations of Ca2+ for negatively charged nanoplastics increased by more than 1.4 times in root exudates and soil leachates compared with that in deionized water. Our findings suggest that root exudates and soil leachates can reduce the aggregation of negatively charged nanoplastics in Ca2+ solutions.