Development of a low-cost method for quantifying microplastics in soils and compost using near-infrared spectroscopy

Abstract

Near-infrared (NIR) spectroscopy is a promising candidate for low-cost, nondestructive, and high-throughput mass quantification of micro¬plastics in environmental samples. Widespread application of the technique is currently hampered mainly by the low sensitivity of NIR spectroscopy compared to thermoanalytical approaches commonly used for this type of analysis. This study shows how the application of NIR spectroscopy for mass quantification of microplastics can be extended to smaller analyte levels by combining it with a simple and rapid microplastic enrichment protocol. For this purpose, the widely used flotation of microplastics in a NaCl solution, accelerated by centrifugation, was chosen which allowed to remove up to 99 % of the matrix at recovery rates of 83–104 %. The spectroscopic measurements took place directly on the stainless-steel filters used to collect the extracted particles to reduce sample handling to a minimum. Partial least squares regression (PLSR) models were used to identify and quantify the extracted microplastics in the mass range of 1–10 mg. The simple and fast extraction procedure was systematically optimized to meet the requirements for the quantification of microplastics from common PE-, PP-, and PS-based packaging materials with a particle size < 1 mm found in compost or soils with high natural organic matter content (> 10 % determined by loss on ignition). Microplastics could be detected in model samples at a mass fraction of 1 mg g-1. The detectable microplastic mass fraction is about an order of magnitude lower compared to previous studies using NIR spectroscopy without additional enrichment. To emphasize the cost-effectiveness of the method, it was implemented using some of the cheapest and most compact NIR spectrometers available.

Application of Near-Infrared Spectroscopy for Monitoring and/or Control of Composting Processes

“…The potential for NIRS as a high throughput analytical method was also evaluated for the detection and quantification of microplastics in compost samples [81] and for the prediction of heavy metal content in compost [82]. Regarding the microplastic analysis in compost, the authors showed that partial least squares regression models (Figure 4), after applying a smooth first derivative of the raw data followed by normalization, could identify and quantify the extracted microplastics in a mass range of 1-10 mg.…”

High-resolution characterization technology for micro-/nano-plastics

“…In past few years, the development of handheld NIR spectrometers utilizing micro-electromechanical systems enhances the potential of NIR technology for on-site characterization of MPs in complex environmental conditions, allowing real-time monitoring and assessment of MP pollution [64]. Wander et al employed handheld NIR spectrometer to identify and quantify PP, PE, and PS with a particle size below 1 mm in compost or soils with substantial natural organic matter content, with a detection limit as low as 1 mg•g −1 [65].…”

Superabsorbent polymers in soil: The new microplastics?

“…Similarly, near-and mid-IR imaging may be applied. Both methods are common for rapid and low-cost microplastic analyses (Wander et al, 2022;Faltynkova and Wagner, 2023), but have not been adapted to SAPs yet.…”