Effects of Iran Light Crude Oil and Corexit EC9500A on the UV-Induced Formation, Colloidal Stability, and Bacterial Toxicity of Gold Nanoparticles in Simulated Seawater.

Oil-derived organic matter and dispersant components can generate reactive oxygen species under irradiation, but their role in mediating Au(III) reduction and gold nanoparticle formation remains unclear. Here, laboratory-prepared WAO, WAD, and DWAO systems in simulated seawater were used as model matrices for Au(III) photoreduction. EPR analysis revealed the generation of O2•-, •OH, and 1O2 during nanoparticle formation. Scavenger experiments suggested that O2•- was a major contributor to Au(III) reduction, while •OH and 1O2 appeared to influence the process indirectly. Stability assessments showed that DWAO-AuNPs exhibited the highest colloidal stability, as evidenced by the highest critical coagulation concentration (CCC) values in NaCl, Na2SO4, and CaCl2 solutions. DLVO and E-DLVO analyses suggested that the enhanced stability of DWAO-AuNPs was associated mainly with larger hydrodynamic diameters and stronger repulsive interaction energy. Toxicological assays against Escherichia coli and Staphylococcus aureus revealed that WAO-AuNPs showed comparatively stronger bactericidal effects, primarily due to cell membrane damage and greater intracellular internalization, without the release of Au(III) ions. Conversely, DWAO-AuNPs showed lower antibacterial activity under the tested conditions, possibly due to their larger particle size and reduced cellular uptake and the surface coating-mediated "stealth" effect.