You are here:
A Multi-Laboratory Method Comparison for Quantifying Microplastics in Sediments: The Roles of Visual Microscopy and Spectroscopy
Citation:
Langknecht, T., W. Lao, C. Wong, D. El Khatib, S. Kotar, S. Robinson, R. Burgess, AND K. Ho. A Multi-Laboratory Method Comparison for Quantifying Microplastics in Sediments: The Roles of Visual Microscopy and Spectroscopy. SETAC North Atlantic Chapter, 28th Annual Meeting 2022, Groton, CT, June 27 - 28, 2022.
Impact/Purpose:
Microplastics, which are plastic pieces smaller than 5 mm, are abundant in aquatic ecosystems, particularly in marine sediments. Marine sediments are home to many organisms that play important roles in their ecosystesm. Quantification and identification of microplastics are increasingly important to understanding their impact on these ecosystems. However, methods for quantifying microplastics in sediments have not been standardized. This study aims to compare two microplastics extraction methods from extraction to identification of the polymer type to provide recommendations on how to improve and standardize microplastics methods. Two laboratories analyzed microplastics sediment samples using both methods and then identified the microplastics type using analytical instruments. We found that overall, microplastics recovery from sediments was quite low, indicating that there could be more microplastics in sediments than we thought. This study then provides recommendations for improving microplastics analyses so these methods can be used for long term monitoring. The intended audience of this research includes state, local, and federal agencies interested in conducting microplastic research, as well as academic and private research institutions.
Description:
Microplastics (MP) are globally distributed throughout marine ecosystems and settle into sediments where they may threaten benthic communities; however, methods for quantifying MP in sediments have yet to be standardized. This study compares two methods for quantifying MP in sediments, including isolation, extraction, and identification, and provides recommendations for improving MP analysis for effective monitoring of MP contamination in sediments. Two laboratories compared the performance of two methods, referred to as “core” and “augmentation”, for isolating and extracting MP in sediments, and identifying particles with visual microscopy and spectroscopy. Using visual microscopy, the augmentation method yielded mean particle recoveries (78%) significantly greater than the core method (47%) (p = 0.03), likely due to the use of separatory funnels. However, spectroscopic identification of recovered particles was much lower at 42 and 54% for the core and augmentation studies, respectively. We suspect the visual identification recoveries are over-estimations of MPs resulting from erroneous identification. This indicates that non-plastic materials persist post-extraction and visual identification alone is not an accurate method to identify MP particles, particularly in complex matrices like sediment. However, both Raman and FTIR spectroscopy proved highly accurate at identifying recovered MP, with 96.7% and 99.8% accuracy, respectively for both methods. Low spectroscopic % recovery of spiked particles indicates that MP recovery from sediments is lower than previously assumed and MP may be more abundant in sediments than current MP analyses suggest. To our knowledge, this is the first multi-laboratory study to quantify complete method performance (isolation, extraction, identification) for sediments, with regards to both capabilities and limitations. This is essential for real-world application as regulatory bodies, such as those identified in California’s recent MP legislation, move toward long-term environmental MP monitoring.
