Microplastics as a vector for micropollutants in aquatic environments.

Souza Moura, Diana

Abstract

Poor water quality has been of increasing environmental concern, particularly related to man-made contaminants. It is becoming evident that microplastics can interact with micropollutants when co-existing in the environment. The aim of this thesis was to elucidate the potential role of microplastics as a vector for cyanotoxins (microcystins) and anthropogenic contaminants (pharmaceuticals) in freshwater. To this end, polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET), polyamide (PA), polystyrene (PS), and polyvinyl chloride (PVC) microparticles were acquired commercially in two sizes (described in this thesis as small, D50 < 35 μm, and large, D50 95-157 μm). The virgin microplastics were also artificially aged to achieve more environmentally relevant particles for experimentation. The virgin and artificially aged particles were fully characterised. The characterisation of the material received from the supplier led to a publication that highlights the importance of a detailed characterisation of commercially acquired microplastics for reliable interpretation of data. The analytical findings uncovered inconsistencies in the supplier stated purity and size of the commercial microplastics. Furthermore, eight microcystin analogues (MC-RR, -YR, -LR, -WR, -LA, -LY, -LW, and -LF), and five pharmaceuticals (ibuprofen, carbamazepine, venlafaxine, fluoxetine, and ofloxacin) were selected to evaluate their interaction with microplastics. The selected micropollutants were placed in contact with microplastics in a range of pollutant combinations (in mixtures and individually). Later, fluoxetine was selected to evaluate the adsorption and desorption mechanisms onto/from virgin and artificially aged, small PP, PA, and PVC. Finally, Daphnia magna neonates were exposed to the virgin and aged particles of fluoxetine-loaded small PP, PA, and PVC. Results demonstrated that the microplastic type, weathering of the microplastics, the size of the particles, and the properties of the compound were all key factors affecting the adsorption onto microplastics. Among the microplastic types evaluated, small PP stood out with the greatest adsorption of microcystins (80-100%) and pharmaceuticals (16-97%). More worrying if available to aquatic life, the more toxic compounds (MC-LW, -LF, and fluoxetine) adsorbed in greater amounts onto the microplastics. For the microcystin analogues, results demonstrated the more toxic and more hydrophobic microcystin analogues (MC-LW and -LF) competed with the more hydrophilic analogues (MC-RR and -LR) for the binding sites on the microplastics. Furthermore, the aging of the microplastics for 72 h increased up to 30-fold the adsorption of pharmaceuticals onto microplastics, while decreasing the adsorption of microcystin onto small PP, PE, and PS. The bioavailability of the fluoxetine loaded onto microplastics also varied according to the microplastic type. Despite the significant adsorption, almost no desorption was observed from small PP. On the other hand, up to 20% of the adsorbed fluoxetine desorbed from the small PA and PVC particles under freshwater environment conditions (pH 7, 25 °C). D. magna was demonstrated to ingest PP, PA, and PVC particles when exposed to microplastics for 48 h. More importantly, all three microplastic types investigated either unloaded or when loaded with fluoxetine had a negative impact on the D. magna neonate's survival in a short period of exposure (48 h). This thesis has demonstrated that the ingestion of microplastics loaded with micropollutants can be a route for micropollutants into the food web with potentially hazardous effects to wildlife.

Citation

SOUZA MOURA, D. 2023. Microplastics as a vector for micropollutants in aquatic environments. Robert Gordon University, PhD thesis. Hosted on OpenAIR [online]. Available from: https://doi.org/10.48526/rgu-wt-2271475

• Thesis Type: Thesis
• Deposit Date: Mar 14, 2024
• Publicly Available Date: Mar 14, 2024
• DOI: https://doi.org/10.48526/rgu-wt-2271475
• Keywords: Water pollution; Cyanobacteria; Pharmaceutical waste; Microplastics; Adsorption
• Public URL: https://rgu-repository.worktribe.com/output/2271475
• Award Date: Sep 30, 2023