The 'Trojan Horse Effect' of nanoplastics with various aquatic contaminants
Creators: Robinson, Abigail SR
Publisher: name: University of Alberta Library
Year: 2023

<p>As of 2016, the global annual production of plastic was 330 million metric tonnes (Plastics Europe, 2017).  This staggering number is expected to double over the next 20 years as consumption increases (Plastics Europe, 2017; Lebreton et al., 2019). Less than half of the plastic produced reaches a landfill or recycling depot, leaving the remainder to litter the terrestrial, aquatic and marine environments (Rochman et al., 2013). These plastics break down over time via weathering and degradation to eventually produce micro or nanoplastics (NPs) (Mattsson et al., 2018). The definition of NPs has varied over time, but today is defined as a synthetic organic polymer that has at least one dimension between 1 and 1000 nm (Mattsson et al., 2018). These small dimensions increase the threat posed to aquatic environments because surface area increases exponentially as diameter decreases which leads to strong sorption affinities for contaminants (Velzeboer et al. 2014). The adsorption of contaminants to the NPs is concerning as studies have shown that NPs (and potentially the adsorbed co-contaminant) bioaccumulate and can pass through lipid-membranes (Bergmann et al., 2015).<br>
Co-contaminant uptake is also known as the “trojan horse effect”. This occurs when NPs increase the uptake of the contaminant by adsorption and subsequent transportation through the organism, leading to increased toxicity or accumulation compared to the contaminant presented in the absence of the plastics (Trevisan et al., 2020). Previous research in our lab indicated that NPs can increase the uptake of the hydrophobic organic pollutant phenanthrene in zebrafish embryos, verifying the Trojan Horse effect for that contaminant in the presence of NPs (Zhang et al., 2020).<br>
The overall aim of my research is to contribute to a co-contaminant uptake model that, contributes substantially to the field of NPs toxicology through the provision of a “read across” for risk assessors that will eliminate the need to examine every plastic/contaminant combination. <br>
The first aim of this thesis was to determine the co-contaminant uptake and depuration rate of 14C-Phenanthrene when sorbed to various sized (20 nm and 500 nm) NPs. The model organism Daphnia magna was used throughout the uptake and depuration experiments. 14C-Phenanthrene accumulation was lower at multiple time points when sorbed to 500nm NPs when compared to 14C-Phenanthrene alone or 14C-Phenanthrene sorbed to 20 nm NPs. Depuration rates were similar amongst all 14C-Phenanthrene groups.<br>
The second aim of this thesis was to determine the effects of chemical properties such as Kow on the co-contaminant uptake rates when various aquatic contaminants are sorbed to NPs (20 and 500 nm). The model organism Daphnia magna was used throughout the 14C-Fluoxetine and 14C-Glyphosate experiments as well. The percentage of 14C-Fluoxetine uptake was only significantly different between groups at one timepoint (2h), where the 500 nm sorbed group had significantly higher uptake compared to both the 20 nm sorbed group and the chemical control. The percentage of 14C-Glyphosate uptake was relatively low amongst all treatment groups, and therefore depuration experiments were not completed. However, at one timepoint (4h) the 500 nm sorbed group had significantly higher uptake than the 20 nm sorbed group and the chemical control. Determination of the uptake-rate using various aquatic contaminants that have differing chemical properties will aid in the development of a model, overall leading to a “read-across” that will provide efficiency in risk assessment.<br>
Overall, this thesis aims to generate empirical data necessary for a co-contaminant uptake-kinetic model to be further developed. This research will impact the field of risk assessment significantly by allowing prediction of toxicity when plastics and contaminants are co-incidentally present.</p>