Sorption behaviour of amine micropollutants on polyethylene microplastics - Impact of aging and interaction with green seaweed
Microplastics can be found ubiquitous in the environment. Due to a still rising global production, the emission of polymers into the environment and the abundance of microplastic increases accordingly. Due to the long mineralization processes of microplastic distribution in all compartments can be found. The hydrophobic surface of the particles can sorb chemical pollutants and therefore pose a potential pathway to organisms within the food web. However, little is known about how long-term aging and degradation processes of microplastics affect the sorption behaviour of organic pollutants on the particles. In this study, important industrial additives of emerging environmental concern such as hydrophobic aromatic amines were studied on their sorption behaviour on high-density polyethylene and low-density polyethylene microplastic. Diphenylamine (log POW (logarithmic octanol-water partition coefficient) = 3.5) showed a strong, carbamazepine (log POW = 2.5) a moderate and aniline (log POW = 0.9) no detectable sorption behaviour. Artificially aged particles exposed to photochemical aging and long-term mechanical treatment in water were compared to pristine microplastic. While mechanically aged microplastic promoted the sorption of aromatic amines, photochemically aged particles showed a decrease in sorption capacity due to changed surface chemistry. Importantly, the sorption capacity was increased with increasing salinity, leading to strong implications for ocean systems, resulting in an elevated uptake of pollutants under marine conditions. Moreover, our study demonstrates that the ecotoxicological effect of diphenylamine on the seaweed Ulva (sea lettuce, Chlorophyta) growth was reduced in the presence of microplastic. While the plastic particles withdrew enough contaminants from the solution, even toxic levels of diphenylamine (c = 10-4 M) became tolerable for the algae. However, the pollutants initially sorbed at the microplastic can be released again at a later point in the ageing process and thus have a delayed pollution potential.