Identifying Microplastics with an NIR Spectrometer

Plastics are implemented for many uses across almost every industry in society. When plastics are exposed to natural forces like sunlight and wave action, they will degrade into microplastics. According to the National Oceanic and Atmospheric Administration (NOAA), microplastics are plastic particles that are less than 5mm in size and originate from a variety of everyday sources. Microplastics are thought to account for 99% of the plastics polluting the ocean. Microplastics can accumulate in the food web threatening the health of aquatic life and birds. This is a cause for concern as the surfaces of microplastics may carry disease-causing organisms and even enter the food industry. Recycling can help keep plastics out of the ocean, as well as reducing our consumption of single-use plastics, however research is needed to further identify and quantify the presence of microplastics. Most methods studying the identification of microplastics involve lab preparation of a sample. Reflectance spectroscopy offers a fast, accurate, and non-destructive solution to identifying microplastics with an NIR Spectrometer in the field and in the lab.

Different types of plastic polymers have unique spectral signatures defined by reflectance or absorption features as a function of wavelength. Reflectance measurements show distinct spectral features, which allows researchers to quickly identify and characterize the type of microplastic found in the environment. This can identify the types of plastics found and help to identify origin and potential causes of the accumulation.

In the fall of 2022, researchers at Boston University were conducting a study on microplastic detection in Massachusetts’ coastal waters. Samples were collected by researchers, Gabe Calistro and Sal Genovese, from the mouth of the Nepsonet River in Milton, MA and the inner region of the river in Quincy, MA. These samples were a mixture of gravel, sand, and mud. Each sample was prepared by separating the organic matter and artificial
microplastic material. Once samples were prepared, reflectance measurements were taken using Spectral Evolution’s NaturaSpec™ spectroradiometer. These reflectance measurements identify the unique spectral signatures of the plastic polymers within.

Collected Samples:
SAMPLE 22-1: Microplastics taken from the mouth of Neponset River in Milton, Massachusetts, USA.
SAMPLE 232-1: Microplastics taken from the inner region of Neponset River in Allston, Massachusetts, USA

For accurate analysis, EZ-ID™ spectral matching software instantly compares your target spectral data against reference spectral libraries. A spectral library of plastics can be used to compare an unknown sample for quick identification without needing to send samples to a lab for characterization. Utilizing Spectral Evolution’s NaturaSpec™ paired with our EZ-ID™ software, the samples were compared to a pure HPDE plastic library spectrum. The figures below show a high correlation with plastics from the library showing successful identification.

It is important to note that absorption features of plastics are far in the NIR, therefore instruments with high sensitivity in these regions are needed. Spectral Evolution’s instruments offer the high spectral resolution and sensitivity required to identify microplastics. EZ-ID™, will allow you to build your own spectral library as well as compare data to reference libraries for instant identification and classification. Our software and spectrometers are the essential instruments to identify microplastics in situ.

(Figure 5) Correlation score in EZ-ID showing absorption match regions of plastics in Sample #22-1

(Figure 6) Correlation score in EZ-ID showing absorption match regions of plastics in Sample #232-1