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Temporal dynamics of bacterial biofilms and their relationship with heavy metals on expanded polystyrene microplastics
Summary
A year-long field exposure study on expanded polystyrene microplastics at an aquaculture farm in the South China Sea found significant seasonal variation in attached bacterial communities dominated by Pseudomonas and Exiguobacterium, with high correlations between bacterial composition and co-occurring heavy metals. The findings demonstrate that EPS microplastics in aquaculture environments serve as dynamic carriers of both pathogenic bacteria and heavy metals, posing compounding contamination risks to farmed seafood and the humans who consume it.
Expanded polystyrene (EPS) is a common type of microplastics (MPs) often found in coastal areas especially aquaculture areas. It is considered as an important site for microbial colonization and biofilm formation, as well as a carrier of pollutants like heavy metals. However, the dynamic changes of bacterial communities attached to EPS and their interaction with heavy metals are still poorly unknown. In this study, a one-year field exposure experiment was conducted at an aquaculture farm near Donghai Island, in Leizhou Bay, Zhanjiang, Guangdong, in South China Sea. The bacterial communities attached to EPS MPs were examined by 16S rDNA high-throughput sequencing, and the relationships between bacterial biofilms and heavy metals were explored. The results show that there were notable seasonal variations in the bacterial diversity of EPS MPs. Species biodiversity was the highest in summer and the lowest in winter. The greatest number of bacterial species and lowest level of uniformity were observed in the spring. The bacterial community structure changed with exposure time, and the most significant difference in the 12-month group (P<0.05) was found. The dominant bacterial species attached to EPS MPs were mainly Proteobackteria and Firmicutes at the phylum level, and Pseudomonas and Exiguobacterium were dominant at the genus level. Furthermore, EPS MPs acted as transport carriers for potential pathogenic bacteria. High correlations were found between bacterial species and the total concentration of heavy metals on EPS MPs, as well as their speciation fractions. Different chemical speciation of heavy metals migrated and altered over seasons within biofilms, which would further exacerbate the ecological risks.