Abstract
Microplastics in the environment has been of increasing concern the last decade. Its abundance in the environment has greatly increased, posing as hazard to wildlife. Microplastic fibres are a common type of microplastics found in environmental sampling. These fibres are mainly derived from textiles, such as clothing, and are released to the environment through washing of clothes. Little to none research has been done on the impact of microplastic fibres in the environment and their interaction with organic pollutants. In this study, the sorptive behaviour between the polycyclic aromatic hydrocarbons (PAHs) phenanthrene, 1-metylphenanthrene 1-, fluoranthene and 9-phenanthrol with the synthetic fibres polyester, polyamide and polyacrylonitrile and the natural fibre wool were studied. Sorption of phenanthrene on microplastics fibres and wool was investigated in seawater at three different temperatures (4 °C, 10 °C and 20 °C) and in freshwater at 20 °C, to determine the influence of temperature and salinity on degree of sorption. Additionally, the sorption of 1-methylphenanthrene, fluoranthene and 9-phenanthrol to microplastic fibres and wool was investigated in seawater at 20 °C to determine effect of different microplastics fibres physicochemical properties on organic contaminant sorption.
No significant sorption of any of the PAHs was observed for polyacrylonitrile microplastics fibres. It was found that phenanthrene,1-methylphenanthrene and fluoranthene have high degree of sorption onto polyamide microplastics fibres. When compared to polyamide, less degree of sorption of phenanthrene, 1-methylphenanthrene and fluoranthene onto both polyester and wool fibres was observed.
Sorption equilibrium between PAHs and microplastic fibres was achieved within 10 days in all cases and was influenced by several of the studied parameters. Importantly, wool achieved equilibrium with PAHs faster (within few days) than any of the synthetic fibres. In general, it was observed that the degree of sorption increased with increasing temperature and decreasing salinity.
Adsorption isotherms fitted to the experimental data showed that the Redlich-Peterson model (RP) and the Sips model gave best fit in most cases. The Dubinin-Astakov model (DA) also gave good fit with much of the experimental data, especially with wool. The results indicate that adsorption on PES and PA mainly occurs as layer-by-layer sorption on heterogenous surface as indicated by the RP and Sips model. For wool, both layer-by-layer and pore filling sorption mechanisms was predicted due to good fit with both the Sips model and the DA model. Other isotherm models such as the Langmuir model, Freundlich model and Dubinin-Raduskevich model was also tested.
Sorption of toxic compounds, such as PAHs, to particles, such as microplastic fibres, present in aqueous environments, may affect the ultimate fate and bioavailability of such compounds. As evidenced by the current thesis, both MPF properties and environmental parameters will play a role and must be taken into consideration when researching and discussing implications of combined effects chemical and particulate pollutants. Importantly, naturally occurring particles may be as important as synthetic as a potential transport vector for pollutants.