Sorption Behavior of Trace Organic Chemicals on Nanoplastics and their Implications on Co-contaminant Transport
Creators: Nurain, Afrida
Publisher: name: University of Alberta Library
Year: 2023

<p>Nanoplastics are plastic fragments less than 1000 nm and are a growing concern within the plastic pollution crisis. They have distinct properties that differ from bulk plastics because of their size, large surface area-to-volume ratio, and their potential to disrupt biological processes once ingested. These particles can be further transported at larger distances and can be carriers for other pollutants via the “Trojan Horse” mechanism. This co-contaminant transport and uptake raise a concern as pollutants bound to nanoplastics can have a larger effect than they would on their own. Hence, understanding the role of nanoplastics as vectors for organic contaminants is crucial for formulating effective strategies to mitigate their adverse effects on aquatic organisms and human health.<br>
This thesis evaluated the adsorption of two different-sized polystyrene nanoplastics (PSNPs) (500 and 20 nm) with various trace organic substances in four types of water matrices. The sorption of plant protection products (glyphosate, methyl parathion), an antidepressant (fluoxetine), a ubiquitous industrial chemical (perfluorooctanoic acid [PFOA]) and a polycyclic aromatic hydrocarbon (phenanthrene) to commercially available polystyrene PSNPs was measured via radiolabeled techniques. The impacts of pH changes, low and high amounts of natural organic matter (NOM), and tertiary-treated wastewater effluent (pre- and post-UV treatment) on sorption were further evaluated.<br>
Based on the calculated sorption coefficients (Kd in L/kg), the sequence of chemicals displaying the highest to lowest sorption affinity towards 20 and 500 nm PSNPs is – fluoxetine &gt; phenanthrene &gt; methyl parathion &gt; PFOA &gt; glyphosate. The sorption of compounds onto PSNPs was impacted by the interactions between the plastics and target chemicals, with cationic (e.g., fluoxetine) and hydrophobic (e.g., phenanthrene) compounds more amenable to sorption. Substances that are negatively charged (i.e., glyphosate) showed poor sorption onto PSNPs due to the electrostatic repulsion between the plastics and the chemical. Although PFOA has a log Kow &gt; 4, it was found to sorb poorly likely because of its negative charge brought by the ionization of its carboxylic functional group. Overall, 20 nm PSNPs sorb more amounts of chemicals than 500 nm PSNPs suggesting that the ingestion of smaller-sized NPs may be more concerning with regards to the Trojan Horse effect.<br>
The extent of sorption varied based on chemicals and was affected by pH, NOM, and other substances present in treated wastewater effluent (cations, anions). Increasing the pH resulted in more adsorption of fluoxetine and glyphosate in 500 nm PSNPs, while the opposite was observed for PFOA. There were no significant pH-related effects detected in relation to phenanthrene as it was not ionizable. The decrease in sorption was additionally noted in water containing high levels of NOM and in treated wastewater effluent (pre- and post-UV). Although it may be perceived as a positive influence on reducing the availability of chemicals from aqueous environments, the mobility of nanoplastics allows them to cover larger distances and potentially spread contamination to different regions. Their small size also makes them easily digested by a variety of organisms and can subsequently release the contaminants that were initially sorbed.<br>
This thesis has contributed to an enhanced understanding of the sorption mechanisms involving representative organic chemicals on nanoplastics. It also yielded quantitative information (Kd, sorption at various pH conditions) that can hold potential for the development of predictive models to simulate the fate and transport of nanoplastics and their sorbed contaminants across diverse environmental settings. By examining the potentially complex interactions between nanoplastics and pollutants in aquatic environments, researchers can better understand the multipart mechanisms that play to effectively assess their implications for aquatic ecosystem health.</p>