Toxicity of microcystin-LR adsorbed onto microplastics: Impacts on Daphnia magna

Microplastics are ubiquitous in aquatic ecosystems, posing significant environmental concerns due to their impacts on organisms and potential risks to human health. Recent studies have shown that microplastics can interact with coexisting contaminants, such as microcystins–hepatotoxins produced by Microcystis aeruginosa during cyanobacterial blooms. These toxins persist in freshwater environments and adsorb onto microplastic surfaces, facilitating their transport across ecosystems. Despite extensive research on toxicological effects of microplastics and microcystins individually or in co-exposure scenarios, the toxicity of microcystins adsorbed onto microplastics remains poorly understood. This study investigated the role of microplastics as carriers of microcystins and evaluated their ecotoxicological effects using Daphnia magna (D. magna) as a model organism. Microcystin-LR (MC-LR), a potent hepatotoxin, and 220 nm polystyrene (PS) microplastics were selected as test materials. Experimental groups included PS microplastics and MC-LR individually as controls, and MC-LR adsorbed onto PS microplastics (with an adsorption capacity of approximately 307.30 µg per gram of PS) to assess combined toxicity. Toxicity assessments were conducted by analyzing behavioral (e.g., swimming patterns), physiological (e.g., heart rate and reproduction), biochemical (e.g., enzyme activity), and molecular (e.g., gene expression) parameters in D. magna. This study enhances our understanding of microplastics’ role as environmental contaminants and carriers of MC-LR, emphasizing their ecological risks and broader implications for aquatic ecosystems.