Validation of a Method for Extracting Microplastics from Complex, Organic-Rich, Environmental Matrices

Abstract

Complex and organic-rich solid substrates such as sludge and soil have been shown to be contaminated by microplastics; however, methods for extracting plastic particles have not yet been systemically tested or standardized. This study investigated four main protocols for the removal of organic material during analysis of microplastics from complex solid matrices: oxidation using HO, Fenton's reagent, and alkaline digestion with NaOH and KOH. Eight common polymer types were used to assess the influence of reagent exposure on particle integrity. Organic matter removal efficiencies were established for test sludge and soil samples. Fenton's reagent was identified as the optimum protocol. All other methods showed signs of particle degradation or resulted in an insufficient reduction in organic matter content. A further validation procedure revealed high microplastic extraction efficiencies for particles with different morphologies. This confirmed the suitability of Fenton's reagent for use in conjunction with density separation for extracting microplastics. This approach affords greater comparability with existing studies that utilize a density-based technique. Recommendations for further method optimization were also identified to improve the recovery of microplastic from complex, organic-rich environmental samples.

A Global Perspective on Microplastics

“…Analysis should be automated where feasible to reduce costs and accelerate sample throughput. To date, researchers in the field have utilized different techniques for extraction from environmental matrices (Fuller & Gautam, ; Hurley, Lusher, et al, ; Hurley, Woodward, et al, ; Wagner et al, ) and for polymer identification (Fries et al, ; Käppler et al, ; Mintenig et al, ). Differences in method effectiveness make comparison of data between studies more difficult.…”

Microplastic Contamination in Freshwater Environments: A Review, Focusing on Interactions with Sediments and Benthic Organisms

“…Another option for digestion is the utilization of alkali (e.g., NaOH or KOH). NaOH has an high efficiency of organic matter digestion, but can also degrade several polymers (e.g., PC, cellulose acetate, PVC, and PET) [166]. KOH, in contrast, is less aggressive.…”

“…With the setting of a standard method, data will be comparable, permitting a comparison of the status of different freshwater systems in order to manage the impacts of MPs on ecosystems. Therefore, studies aiming to compare different treatments and analysis techniques are strongly encouraged (e.g., [166,174]), in order to reach a clear understanding of the best techniques for different environmental matrices.…”

Microplastics in a Stormwater Pond

“…It cannot be ruled out that the 100 µm PS beads have a different recovery compared to some naturally occurring MPs, as the beads were spherical and had not undergone ageing prior to use. It is quite possible that different materials and particle shapes were recovered at different rates, and that the recovery of naturally occurring MPs was better for larger particles and poorer for smaller particles, further contributing to the uncertainties of quantification [38]. Due to these issues, it was not feasible to correct the data (Table 1) for recovery.…”