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Photoaging of polyethylene microplastic and its effect on the chlorpyrifos adsorption
Summary
This study examined how UV-B radiation ages polyethylene microplastics over time and how that aging changes their ability to adsorb the pesticide chlorpyrifos. Photoaging modified the surface chemistry and structure of the plastic, altering its interaction with the pesticide, suggesting that weathered microplastics in aquatic environments may carry different — and potentially higher — loads of toxic chemicals than fresh particles. This "Trojan horse" effect is important for understanding how microplastics contribute to broader chemical contamination of waterways.
The presence of microplastics in the aquatic environment is a growing concern, since several aquatic species can ingest these materials, potentially accumulating in the trophic chain. Another concern is to assess the ability of microplastics to cause contamination in the aquatic environment by transporting organic components. In this sense, the present study seeks to investigate the effect of photoaging of microplastic (PM) polyethylene (PE) under ultraviolet (UV) radiation, at different exposure times, on the physical-chemical properties of the material and its interaction with the pesticide chlorpyrifos, evaluating the potential of this polymer to concentrate and transport organic contaminants in the aquatic environment. PE samples were photoaged in a chamber containing ultraviolet lamps type B (UV-B) at different exposure times (1, 4, 6 and 8h) and the morphological, chemical and structural characteristics of the materials obtained were monitored by microscopy techniques scanning (SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TG), zero charge potential (pHpcz) and X-ray diffraction (XRD). The aged materials were used in the adsorption tests and the capacities to adsorb the pesticide chlorpyrifos were obtained. The FTIR results indicated structural changes in polyethylene after exposure to UV-B, due to the increase in oxygen-containing groups, referring to the carbonyl group, which was proportional to the exposure time. SEM analyzes showed an increase in roughness and the appearance of pores in the aged polymer. The carbonyl index values were higher for microplastics submitted to longer exposure to irradiation, as well as a reduction in the crystallinity index. Adsorption tests revealed that aged PE PMs had their adsorption capacity (mg g-1) increased at times of 1h (10.51± 2.03); 4h (10.89 ± 0.81); 6h (10.25 ± 0.2) and 8h (11.4 ± 0.05) when compared with PE in natura (7.97 ± 0.53). From the data, it is concluded that plastics aged in the environment have an increased adsorption capacity, that the effect of photodegradation positively affects their capacity to retain pesticides and other organic pollutants, by means of hydrophobic and electrostatic interactions, indicating that these Mps can have their toxic effects potentiated when exposed to environmental weather.
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