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Single and combined effects of microplastics and lead on the freshwater algae Microcystis aeruginosa
Summary
Researchers tested the individual and combined effects of microplastics and lead (Pb) on the growth, photosynthetic pigments, and antioxidant responses of the freshwater cyanobacterium Microcystis aeruginosa. They found that microplastics alone inhibited growth while low-dose Pb promoted it, but their combination altered toxicity outcomes in complex ways depending on concentration, indicating that co-exposure risks in freshwater cannot be predicted from single-contaminant studies.
Recently, the pollution of microplastics (MPs) in the global freshwater environment has become increasingly problematic, but there are few studies on the freshwater environment risks of MPs. The present study, therefore, has investigated the single and combined effects of MPs and lead (Pb) on the freshwater algal Microcystis aeruginosa. Results showed that Pb-only (>0.05 mg·L) promoted the growth of algal cells, while MPs-only (1 mg L) resulted in growth inhibition. However, compared with the corresponding concentration of Pb-only groups, the growth of algal cells was promoted in MPs + Pb treatments. MPs-only and Pb-only (0.5 mg L) both reduced the content of photosynthetic pigments and affected algal photosynthesis. The MPs-only treatment and MPs + Pb (no pretreatment, 0.5 mg L Pb) treatments showed significant cell aggregation. At the same time, MPs-only caused a significant increase in bound extracellular polysaccharides (bEPS), while 0.5 mg L Pb reduced bEPS. Furthermore, under high Pb stress (0.5 mg L), the effects of combined MPs and Pb on chlorophyll content, antioxidant enzyme activity (peroxidase (POD), catalase (CAT)), and damage to algal cells were less compared to individual effects, and the combination of MPs and Pb had a synergistic effect on promoting aggregations of M. aeruginosa. These results demonstrate that single and combined effects of MPs and Pb can induce differential responses in the freshwater algal M. aeruginosa, which can have a significant impact on aquatic ecosystems.