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Combined effects of microplastics and excess boron on Microcystis aeruginosa
Summary
Researchers studied the combined effects of microplastics and excess boron on a common freshwater cyanobacterium (Microcystis aeruginosa). They found that amino-modified polystyrene microplastics were the most harmful, inhibiting growth and worsening boron toxicity, while other surface-modified types actually stimulated growth. The study reveals that the surface chemistry of microplastics plays a key role in how they interact with other pollutants to affect aquatic microorganisms.
Both microplastics (MPs) and excess boron (B) have adverse effects on microalgae. However, the combined toxic effects of MPs and excess B on microalgae have not been studied. The aim of this study was to investigate the combined effects of excess B and three types of surface-modified microplastics, including plain polystyrene (PS-Plain), amino-modified polystyrene (PS-NH), and carboxyl-modified polystyrene (PS-COOH), on chlorophyll a content, oxidative damage, photosynthetic activity and microcystin (MC) production in Microcystis aeruginosa. The results showed that PS-NH inhibited the growth of M. aeruginosa, with the maximum inhibition rate of 18.84 %, while PS-COOH and PS-Plain showed stimulatory effects with the maximum inhibition rates of -2.56 % and - 8.03 % respectively. PS-NH aggravated the inhibition effects of B, while PS-COOH and PS-Plain alleviated the inhibition effects. Furthermore, the combined exposure of PS-NH and excess B had a much greater effect on oxidative damage, cell structure, and production of MCs in algal cells than the combined effects of PS-COOH and PS-Plain. The charges on microplastics affected both B adsorption on microplastics and the aggregation of microplastics with algal cells, indicating that the charge on microplastics is a dominant factor influencing the combined effects of microplastics and excess B on microalgae. Our findings can provide direct evidence for the combined effects of microplastics and B on freshwater algae and improve the understanding of the potential risks of microplastics in aquatic ecosystems.