Identification and Quantification of Microplastics in Wastewater Using Focal Plane Array-Based Reflectance Micro-FT-IR Imaging

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.

Nile Red Staining as a Subsidiary Method for Microplastic Quantifica-tion: A Comparison of Three Solvents and Factors Influencing Application Reliability

“…We hypothesize that this is due to the specific surface and density properties of the expanded material. Compared to spectroscopic analysis methods such as (micro-)FTIR 13,15,16 or Raman-(micro)spectroscopy 6,17 the proposed approach is less time consuming and costly, but also less accurate and lacks information on the chemical composition of the sample. Nevertheless, staining polymer particles with Nile Red is less time-consuming and less cost intensive than (micro-)FTIR or Raman-(micro)spectroscopy.…”

“…3,[10][11][12] The identification of microplastics as synthetic polymers poses a major challenge due to interference issues associated 35 with organic particles. 13,14 Currently, the assessment of the polymer composition via (micro-)Fourier transform infrared (FTIR) spectroscopy, 13,15,16 (micro-)Ramanspectroscopy 6,17 and Pyrolysis-gaschromatography with mass spectrometry [18][19][20] are approaches commonly applied allowing consistent predictions on the abundance and composition of microplastics within a sample. 21,22 However, these methods rely on expensive equipment and include time-consuming procedures.…”

Micro- and Nanoplastic Pollution of Freshwater and Wastewater Treatment Systems

“…Micro-and nanoplastic research is still a developing field, with as yet no standardised procedures for their study, and method advancement is still in its early stages [24,89]. The different size class distinctions and methods used may reduce comparability of results across studies, highlighting the need to unify size class definition and develop simple, low-cost and precise methods for their detection and monitoring [24,39].…”

“…Further, MNP surfaces can provide habitats for microbial colonisation and biofilm formation, allowing for migration of opportunistic pathogens and invasive species [64,98]. The latter may be relevant for WWTP as it could affect the functioning of the treatment processes, as well as increase the transport of WWT bacteria from these facilities to receiving waters [89,98].…”

“…Sample processing usually involves a combination of approaches including visual pre-selection, size fraction sieving, flotation and density separation, filtration and organic matter (OM) digestion [17,47,78,89]. Sieve analysis is useful for separation of particles into different size ranges.…”