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Adsorption behavior of triclosan by different microplastics and the impact of water chemistry
Summary
Researchers investigated how triclosan — an antimicrobial compound — adsorbs onto four types of microplastics under varying water chemistry conditions. They found hydrophobic partitioning was the dominant adsorption mechanism, with solution pH, ionic strength, and dissolved organic matter all influencing uptake capacity.
The mechanisms of triclosan (TCS) adsorption onto polyamide (PA), polystyrene (PS), polyvinylchloride (PVC) and low-density polyethylene (LDPE) microplastics (MPs) were investigated, along with the effects of solution pH, ionic strength, and dissolved organic matter (DOM). The Linear model better described TCS adsorption isotherms suggesting that hydrophobic partitioning was the primary mechanism for TCS adsorption, while the Freundlich and Langmuir model fittings showed that TCS adsorption onto MPs was favorable. Following normalization by the specific surface area (SSA) of MPs, adsorption distribution coefficient (K) values of 105.70, 0.56, 0.20, and 0.08 L/m were determined for PA, PS, PVC, and LDPE MPs, respectively. Hydrophobic interaction was the main adsorption mechanism, although other mechanisms, governed by the specific structure and functional groups of the MPs, also contributed. These included the formation of hydrogen bonds between the -OH on TCS (H-bond-donating) and the amide groups on PA (H-bond-accepting), and the π-π interactions between the benzene rings of PS and TCS, and hydrogen bonds between -OH on TCS and -COO/-COOH on PVC MPs. TCS adsorption by MPs was found to be pH-dependent, indicating that TCS was the main species involved in adsorption. The effects of ionic strength on TCS adsorption were not significant and therefore could be ignored. Humic acid (HA) impeded the adsorption of TCS by PA, PS, and LDPE MPs, potentially due to the hydrophobic interactions of HA with the three MPs, the hydrogen bonds with PA MPs, and the π-π interactions with PS MPs, all of which competed with TCS for adsorption sites. Fulvic acid (FA) inhibited TCS adsorption onto PS MPs, as FA could be sorbed by PS MPs through π-π interactions, competing with TCS for adsorption sites. These findings improve the accuracy of risk evaluations for organic pollutants such as TCS when co-occurring with MPs, furthering our understanding of the impacts of complex pollutant mixtures on both human and environmental health.