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A portable toilet manufacturer in northwest Indiana (USA) released polyethylene microplastic (MP) pollution into a protected wetland for at least three years. To assess the loads, movement, and fate of the MPs in the wetland from this point source, water and sediment samples were collected in the fall and spring of 2021–2023. Additional samples, including sediment cores and atmospheric particulates, were collected during the summer of 2023 from select areas of the wetland. The MPs were isolated from the field samples using density separation, filtration, and chemical oxidation. Infrared and Raman spectroscopy analyses identified the MPs as polyethylene, which were quantified visually using a stereomicroscope. The numbers of MPs in 100 mL of the marsh water closest to the source ranged from several hundred to over 400,000, while the open water samples contained few microplastics. Marsh surface sediments were highly contaminated with MPs, up to 18,800 per 30.0 g dry mass (dm), compared to core samples in the lower depths (>15 cm) that contained only smaller MPs (<200 µm), numbering 0–480 per 30.0 g (dm). The wide variations in loads of MP contaminants indicate the influence of numerous factors, such as proximity to the point source pollution, weather conditions, natural matter, and pollution sinks, namely sediment deposition. As proof of concept, we demonstrated a novel remediation method using these real-world samples to effectively agglomerate and remove MPs from contaminated waters.
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Optimizing density separation methods for microplastics extraction from marine sediments Session: GC068: Microplastics and the biosphere
Many different techniques are used to extract microplastics (MPs) from sediment samples of variable composition and grain size. The lack of uniform methodology makes it challenging to compare results across studies and to select methods appropriate to local sedimentary conditions. This study (a) evaluates the separation efficiency, yield, and contamination (blank) of settling compared centrifugation density separation, and (b) examines the distribution of MP across successive separation phases (interstitial water, organic matter, sediment). Two different density-separation dependent extraction methods were tested with tropical marine sediments from the US Virgin Islands with variable grain size and composition: (1) suspension within a settling column, and (2): centrifugation. The samples were processed under a laminar flow hood using published best practices to minimize contamination. The two separation techniques produced similar MP yields (85-100%), which were calculated by tracing polyethylene microspheres. However, processing in the settling column sometimes produced incomplete settling of fine organic matter and took a significantly longer time (week vs. minutes) than did separation via centrifugation. Analytical blanks (contamination) were also slightly greater using a settling column (avg: 5.3±1.1) vs the centrifuge (avg: 3.6±0.9). However, the most important reason why the centrifugation is preferable is that it allows for the complete removal of separatory solutions via compaction of the sediment. This allows phased separation of MPs through sequential interstitial water removal, hydrogen peroxide treatment and removal (to target organic matter bound MP), and density separation phases. Our experiments showed that a significant portion of the total MP in the samples were potentially located in the interstitial water phase (16±12%) and the following hydrogen peroxide phase (25±20%). In the literature, intermediate treatment solutions are often discarded, resulting in an underestimation of total MP in the sediments. In summary, we found that the most effective method of MP extraction from organic rich or fine-grained sediments is a phased centrifugation process which includes counting MP from all phases.
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- Award ID(s):
- 1700920
- PAR ID:
- 10487695
- Editor(s):
- no editor
- Publisher / Repository:
- American Geophysical Union
- Date Published:
- Journal Name:
- Transactions American Geophysical Union
- Edition / Version:
- 1
- Volume:
- 1
- Issue:
- 1
- ISSN:
- 2379-6723
- Page Range / eLocation ID:
- 1
- Subject(s) / Keyword(s):
- microplastics, sediments
- Format(s):
- Medium: X Size: 1 Other: 1
- Size(s):
- 1
- Location:
- San Francisco
- Sponsoring Org:
- National Science Foundation
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