Impact of nanoplastics on the algicide efficacy of CuSO4 against Microcystis aeruginosa and the release of microcystin: A physiological and metabolomic analysis

CuSO is frequently employed as a control measure for the emergency treatment of cyanobacterial harmful algal blooms. Concurrently, nano-plastics (NPs) have emerged as pervasive pollutants exacerbating the threat of eutrophication to aquatic ecosystem. However, there is little known regarding the influence of NPs on the efficacy of copper sulfate (CuSO) in controlling cyanobacterial harmful algal blooms (cyanoHABs). Here, we demonstrate that the co-existence of polystyrene nanoplastics (PS NPs) exacerbates the negative effects of CuSO to photosynthetic activity of Microcystis aeruginosa. This is caused via the differences in disrupting light energy absorption, inactivation of the reaction center, as well as disruptions in electron transport and metabolic pathways, which collectively induce oxidative stress and damage cell membrane. Treatment with either NPs or CuSO alone results in the downregulation of carbon-fixation, the tricarboxylic acid cycle, and pyruvate metabolism. Co-existence of NPs significantly influenced ABC transporters, carbon fixation, and the two-component system in M. aeruginosa. Notably, while single CuSO₄ treatment increased microcystin- leucine arginine (MC-LR) levels by 243.3 % relative to controls, combining CuSO₄ with NPs (PS, PS-NH₂, PS-COOH) significantly reduced MC-LR concentrations by 73.5 %, 90.2 %, and 70.7 %, respectively (p < 0.05). This study demonstrated that NPs exacerbated the oxidative stress induced by CuSO on M. aeruginosa cell, while concurrently reducing MCs release. Furthermore, the underlying molecular mechanisms were systematically investigated. These findings provided novel insights into the crucial importance of considering NPs impact prior to the application of CuSO for the management of (cyanoHABs).