Impact of polystyrene nanoplastics on the biodegradation of a polyhydroxyalkanoate and its associated biofilm

Biodegradable polymers such as polyhydroxyalkanoates (PHAs) have been proposed as sustainable alternatives to conventional plastics. Their environmental biodegradation is influenced by complex microbial interactions, particularly within biofilms. The presence of nanoplastics in marine environments has unknown impacts on biodegradation processes. This study investigated the effect of polystyrene nanoplastics (PS NPs) on the biodegradation extent of PHA, biofilm spatial organization, and microbial community composition over 35 days using a natural seawater inoculum from the Wadden Sea off the coast of the Netherlands. The results indicated that PS NPs do not significantly impact the biodegradation extent of PHA at the concentrations tested. The spatial organization of the biofilm revealed the presence of large PS NP aggregates, indicating that microbial biofilms may serve as a temporary 'sink' for NPs in the water column. Biofilms exposed to the lowest NP concentration exhibited greater microbial diversity than those at the highest concentration at 21 days. However, by the end of the experiment, no significant differences in relative microbial abundances were detected across treatments, though differences in absolute cell counts within the biofilm were observed. These findings provide new insights into how PS NPs interact with marine biofilms and influence biofilm dynamics and functionality.