Close encounters on a micro scale: Microplastic sorption of polycyclic aromatic hydrocarbons and their potential effects on associated biofilm communities
Within systems as dynamic as the aquatic environment, it is paramount to address the impacts of an ever growing network of emerging pollutants at their intersection. With previous research having demonstrated the capacity of microplastics (MP) to sorb persistent organic pollutants, we ask in our study how different plastic polymers that are found throughout aquatic systems interact with polycyclic aromatic hydrocarbons (PAHs) and how this convergence of pollutants might impact the bacterial communities that form on MP surfaces. Through an in situ incubation experiment conducted at different sites along the Baltic Sea coast, we found the PAH sorption patterns of polyethylene (PE), polystyrene (PS), and aquaria stone to be dictated predominantly by substrate type and secondly by incubation site. While PE showed a general positive trend of sorption, stone rather leached PAHs into the environment, whereas the PAH levels of PS remained relatively unchanged following incubation. These sorption patterns correlated significantly with the composition of biofilm communities observed on all three substrate types after a 6-week incubation period. Elevated levels of specific 3- and 4-ring PAHs on PE and PS coincided with higher proportions of specific taxa reportedly capable of hydrocarbon utilisation as well as a reduced diversity among biofilm communities. The findings in our study highlight the importance of investigating the effects and extent of these complex pollutant interactions to fully understand how MP impact surrounding ecological systems as it traverses the different compartments of the aquatic ecosystem.