Adsorption of hydroxamate siderophores and EDTA on goethite in the presence of the surfactant sodium dodecyl sulfate

Siderophore-promoted iron acquisition by microorganisms usually occurs in the presence of other organic molecules, including biosurfactants. We have investigated the influence of the anionic surfactant sodium dodecyl sulfate (SDS) on the adsorption of the siderophores DFOB (cationic) and DFOD (neutral) and the ligand EDTA (anionic) onto goethite (α-FeOOH) at pH 6. We also studied the adsorption of the corresponding 1:1 Fe(III)-ligand complexes, which are products of the dissolution process. Adsorption of the two free siderophores increased in a similar fashion with increasing SDS concentration, despite their difference in molecule charge. In contrast, SDS had little effect on the adsorption of EDTA. Adsorption of the Fe-DFOB and Fe-DFOD complexes also increased with increasing SDS concentrations, while adsorption of Fe-EDTA decreased. Our results suggest that hydrophobic interactions between adsorbed surfactants and siderophores are more important than electrostatic interactions. However, for strongly hydrophilic molecules, such as EDTA and its iron complex, the influence of SDS on their adsorption seems to depend on their tendency to form inner-sphere or outer-sphere surface complexes. Our results demonstrate that surfactants have a strong influence on the adsorption of siderophores to Fe oxides, which has important implications for siderophore-promoted dissolution of iron oxides and biological iron acquisition

Adsorption of Contaminants of Emerging Concern (CECs) with Varying Hydrophobicity on Macro- and Microplastic Polyvinyl Chloride, Polyethylene, and Polystyrene: Kinetics and Potential Mechanisms

Microplastic particles are of concern to aquatic environments because their size enables them to be easily ingested by animals and they may become vectors of potentially harmful chemicals. This study focused on understanding the impact of plastic size and plastic types on adsorption and adsorption kinetics of commonly found contaminants of emerging concern (CECs). We exposed macro- and micro-sized polyethylene (PE), polystyrene (PS), and polyvinyl chloride (PVC) to six CECs: diclofenac (DCF), atenolol (ATN), ibuprofen (IBU), 4-acetamidophenol (ACE), bisphenol A (BPA), and 2-mercaptobenzothiazole (MBT). Our results showed that the pseudo-first order model described the adsorption kinetics better than the pseudo-second order model. The rate of adsorption ACE onto macro-PS was the fastest rate of adsorption for all CECs and microplastics evaluated. Generally, the mass fraction of CECs sorbed at equilibrium did not depend on the size of the plastic and chemical hydrophobicity. With a relatively low K-ow among the CECs studied here, ACE had the most mass fraction sorbed onto all the plastics in this study. DCF was also consistently sorbed onto all the plastics. The mechanism van der Waals interaction may have dominated in all the adsorptions in this study, but pi-pi interaction could also be a major mechanism in the adsorption of DCF, IBP, and ACE. Fast adsorption of ATN, IBP, and ACE may occur during wastewater treatment, but slow adsorption may still continue in the wastewater effluent. Our study highlights an ecotoxicological concern for plastics being a vector of commonly found CECs that are not highly hydrophobic