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Exploring the influence of key extracellular polymeric substances components on nanoplastic mobility in seawater-saturated porous media during biofilm formation
Summary
Researchers tracked how biofilm age and extracellular polymer composition on sand grains affect nanoplastic mobility through seawater-saturated sediment columns, finding that the loosely bound fraction of extracellular polymers — particularly its humic substances — enhances nanoplastic transport, while proteins in those polymers reduce it.
Although the influence of biofilm formation on marine porous media and the associated secretion of extracellular polymeric substances (EPS) on nanoplastic (NP) transport has been well studied, the roles of specific EPS subcomponents, such as loosely bound (LB-EPS) and tightly bound (TB-EPS) fractions, produced by bacteria at different growth stages remain poorly understood. Also unclear are the functions and mechanisms of certain chemical constituents within EPS, including proteins, polysaccharides, and humic substances. This study examines how biofilms and their EPS affect the transport of NPs through seawater-saturated sand columns. Our results show that biofilm age significantly affects the effluent recovery rate of NPs (M). The highest recovery rates were observed in biofilms aged 24 h (68.18 %) and 144 h (68.45 %), compared to only 53.96 % in the uncolonized sand control. Similarly, the presence of EPS coatings on sand grains also enhanced NP mobility, with recovery rates of 64.67 % at 24 h and 61.51 % at 144 h. Further analysis separating EPS into LB-EPS and TB-EPS revealed that LB-EPS influences NP recovery in a manner similar to that of intact biofilms, and its effect is more pronounced than that of TB-EPS. Component analysis indicated a significant negative correlation between protein content and M (P < 0.05, r = -0.9842), and a significant positive correlation with humic substances (P < 0.05, r = 0.9823). The protein-to-polysaccharide ratio, an indicator of sand surface hydrophobicity, was negatively correlated with M (P < 0.05, r = -0.9869). Finally, proteins and humic substances within LB-EPS were identified as key factors regulating NP transport, showing strong correlations at P < 0.001 (r = -0.9994) and P < 0.01 (r = 0.9920), respectively.