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<p>This study explores how EPS with varying molecular weights (MW) adsorb onto polystyrene nanoplastics coated with bare (PS-Bare), carboxylic (PS-COOH), or amine (PS-NH₂) functional groups. Experiments were performed in NaCl and CaCl<sub>2</sub> to characterize the formed eco-corona and their impacts on nanoplastics aggregation kinetics. The results show that while eco-corona shares similar chemical compositions, their thickness (ECT) correlates positively with both adsorbed EPS mass and MW. In NaCl, PS-Bare exhibited the narrowest ECT range (0.88–7.17&#xa0;nm), followed by PS-COOH (1.78–9.43&#xa0;nm), whereas PS-NH₂ displayed the broadest span (2.33–13.95&#xa0;nm). The ECT further increased in CaCl<sub>2</sub>. Enhanced ECT caused higher critical coagulation concentration (CCC). In NaCl, PS-Bare’s CCC rose from 343 mM to 466–1291 mM, and PS-COOH’s from 339 mM to 577–1373 mM. Under 5&#xa0;mg C L⁻¹ EPS, PS-NH₂ maintained a stable hydrodynamic diameter (D<sub>h</sub> ≈ 150&#xa0;nm) in both NaCl and CaCl<sub>2</sub>, indicating strengthened steric stabilization. In CaCl<sub>2</sub> with 5&#xa0;mg C L⁻¹ EPS, similar stabilization trends were observed. However, at 10&#xa0;mg C L⁻¹, high-MW EPS reduced CCC via bridging effects. For PS-NH<sub>2</sub>, low-MW EPS (5&#xa0;mg C L⁻¹) increased D<sub>h</sub> to 900–1200&#xa0;nm through charge neutralization and weak steric hindrance. The EPS <sub>&lt;3kDa</sub> further enlarged D<sub>h</sub> to 1400&#xa0;nm by patch-charge attraction. This study reveals that EPS molecular weight, by regulating eco-corona thickness and surface charge distribution, is a key factor influencing the colloidal stability of nanoplastics.</p>

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Molecular weight fractionated extracellular polymeric substances (EPS) impart different aggregation characteristics on polystyrene nanoplastics

  • 期刊论文

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  • 发表日期：

    2026年3月2日

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  • Feng-Yi Li,
  • Gui-Yun Song,
  • Qing-Xin Zhang,
  • Mi-Hong Hou

摘要

This study explores how EPS with varying molecular weights (MW) adsorb onto polystyrene nanoplastics coated with bare (PS-Bare), carboxylic (PS-COOH), or amine (PS-NH₂) functional groups. Experiments were performed in NaCl and CaCl2 to characterize the formed eco-corona and their impacts on nanoplastics aggregation kinetics. The results show that while eco-corona shares similar chemical compositions, their thickness (ECT) correlates positively with both adsorbed EPS mass and MW. In NaCl, PS-Bare exhibited the narrowest ECT range (0.88–7.17 nm), followed by PS-COOH (1.78–9.43 nm), whereas PS-NH₂ displayed the broadest span (2.33–13.95 nm). The ECT further increased in CaCl2. Enhanced ECT caused higher critical coagulation concentration (CCC). In NaCl, PS-Bare’s CCC rose from 343 mM to 466–1291 mM, and PS-COOH’s from 339 mM to 577–1373 mM. Under 5 mg C L⁻¹ EPS, PS-NH₂ maintained a stable hydrodynamic diameter (Dh ≈ 150 nm) in both NaCl and CaCl2, indicating strengthened steric stabilization. In CaCl2 with 5 mg C L⁻¹ EPS, similar stabilization trends were observed. However, at 10 mg C L⁻¹, high-MW EPS reduced CCC via bridging effects. For PS-NH2, low-MW EPS (5 mg C L⁻¹) increased Dh to 900–1200 nm through charge neutralization and weak steric hindrance. The EPS <3kDa further enlarged Dh to 1400 nm by patch-charge attraction. This study reveals that EPS molecular weight, by regulating eco-corona thickness and surface charge distribution, is a key factor influencing the colloidal stability of nanoplastics.