The potential of microplastics to act as a vector for micropollutants of natural or anthropogenic origin is of rising concern. Cyanobacterial toxins, including microcystins, are harmful to humans and wildlife. In this study, we demonstrate for the first time the potential of microplastics to act as vectors for two different microcystin analogues. A concentration of up to 28 times from water to plastic was observed for the combination of polystyrene and microcystin-LF achieving toxin concentrations on the plastic of 142 ± 7 μg g-1. Based on the experimental results, and assuming a worst-case scenario, potential toxin doses for daphnids are calculated based on published microplastic ingestion data. Progressing up through trophic levels, theoretically, the concentration of microcystins in organisms is discussed. The experimental results indicate that adsorption of microcystins onto microplastics is a multifactorial process, depending on the particle size, the variable amino acid composition of the microcystins, the type of plastic, and pH. Furthermore, the results of the current study stressed the limitations of exclusively investigating microcystin-LR (the most commonly studied microcystin congener) as a model compound representing a group of around 250 reported microcystin congeners.
Keywords: cyanobacteria; cyanotoxins; freshwater; microcystins; microplastics; trophic accumulation.