Abstract
Microplastics (<5 mm) have been documented in environmental samples on a global scale. While these pollutants may enter aquatic environments via wastewater treatment facilities, the abundance of microplastics in these matrices has not been investigated. Although efficient methods for the analysis of microplastics in sediment samples and marine organisms have been published, no methods have been developed for detecting these pollutants within organic-rich wastewater samples. In addition, there is no standardized method for analyzing microplastics isolated from environmental samples. In many cases, part of the identification protocol relies on visual selection before analysis, which is open to bias. In order to address this, a new method for the analysis of microplastics in wastewater was developed. A pretreatment step using 30% hydrogen peroxide (H2O2) was employed to remove biogenic material, and focal plane array (FPA)-based reflectance micro-Fourier-transform (FT-IR) imaging was shown to successfully image and identify different microplastic types (polyethylene, polypropylene, nylon-6, polyvinyl chloride, polystyrene). Microplastic-spiked wastewater samples were used to validate the methodology, resulting in a robust protocol which was nonselective and reproducible (the overall success identification rate was 98.33%). The use of FPA-based micro-FT-IR spectroscopy also provides a considerable reduction in analysis time compared with previous methods, since samples that could take several days to be mapped using a single-element detector can now be imaged in less than 9 h (circular filter with a diameter of 47 mm). This method for identifying and quantifying microplastics in wastewater is likely to provide an essential tool for further research into the pathways by which microplastics enter the environment.
Highlights
Microplastic pollution is a topic of increasing concern to society.[1]
We evaluate the effectiveness of a 30% H2O2 preparation step to remove the organic matter from wastewater, including the efficiency of this method at aiding sample filtration, and the effects of H2O2 on the Fourier-transform infrared (FT-IR) spectra of 5 plastic types commonly recorded in microplastic studies.[30]
The main rationale for applying a H2O2 pretreatment step was to facilitate filtration and to improve the micro-FT-IR imaging of microplastics within wastewater samples by removing organic matter that would otherwise accumulate on the membrane filter surface
Summary
Microplastic pollution is a topic of increasing concern to society.[1]. The term “microplastics” was introduced approximately a decade ago to describe small synthetic plastic particles with an upper size limit of 5 mm.[2]. We present a novel method for the analysis of microplastics in wastewater samples using FPA-based reflectance micro-FT-IR imaging and H2O2 pretreatment.
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