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 NOAA (National Oceanic and Atmospheric Administration), microplastics are very small (less than 5mm) plastic particles that can originate from a variety of everyday sources. Microplastics are thought to account for 99% of the plastics in the ocean and remain in the ocean indefinitely. Microplastics can eventually sink down into the ocean and be consumed by sea life. Microplastic pollution is a huge cause for concern as the surfaces may carry disease-causing organisms and act as a vector for diseases. Detecting microplastics is crucial as it poses many threats to aquatic life. If microplastic ingestion does not kill an animal, it can lead to damages to the internal organs and limit their ability to reproduce. The debris can continue to pass through the systems of each animal in a specific food chain. An average individual can greatly reduce the risk of microplastics in the ocean by incorporating recycling into their everyday life.
NIR (near infrared) reflectance spectroscopy is a fast, accurate and non-destructive solution to identify microplastics. Near and shortwave infrared regions of the electromagnetic spectrum provide distinct spectral features that allow researchers to quickly identify and characterize the type of microplastics found within the environment.
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. Reflectance measurements are one way to identify the unique spectral signatures of plastic polymers.
Spectral Evolution offers a range of field spectrometers/spectroradiometers that cover the full spectral range (350-2500 nm) in rugged, lightweight units with no moving optical components - ideal for in situ measurements. Our instruments have the performance required to identify microplastics with industry-leading resolution and sensitivity. Spectral Evolution’s NaturaSpec™ spectroradiometer offers the best spectral resolution and signal-to-noise performance in a field instrument on the market today. Paired with a 10mm reflectance contact probe, researchers can collect a full day of scans in the field. Our contact probe has a built-in 5 watt halogen light source with a scratch resistant window.
With the NaturaSpec™, plastic absorption regions were found and were identified to match characteristic plastic features. The spectra of microplastics show absorption features at 1210m, 1720nm, 2010nm, and 2052 nm. These absorption features were then compared to a pure HDPE plastic library spectrum. Our graphs show matches and are indicated by the green regions. Correlation scores closest to 1 are considered the best possible match. Due to the location of these absorption features on the electromagnetic spectrum, a full range spectrometer is needed.
Alongside Spectral Evolution’s NaturaSpec™, DARWin software is a full-featured, menu-driven program for easy data acquisition and analysis of multiple US-VIS-NIR spectra. Our add-on module, 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
Our application note has an in-depth analysis on our study.