200-2 Microplastics in an agriculturally dominated watershed in SW Ohio: A case study in the Acton Lake watershed, Butler County, Ohio

Session: Microplastics in the Environment

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Microplastics are particles smaller than 5 mm in diameter, thought to be nearly ubiquitous, especially in aquatic environments, and may be broadly linked to negative environmental health impacts. Rivers and streams near human activities tend to be extensively polluted due to a high input of plastics and a smaller reservoir for the plastics to disperse compared to that of larger marine settings. Acton Lake, an artificial recreational lake, presents a prime study location to investigate the extent of microplastic pollution and the geological setting of this contaminant. This study quantifies and characterizes microplastics in sediment at eight sites including the three main tributaries, the lake outflow, and four sites along the lake transect. Three separation techniques were used to compare efficiency: zinc chloride, sodium chloride, and oil based. Plastics were initially observed and counted under a dissecting microscope with selected subsets observed under fluorescent microscopy, scanning electron microscopy (SEM), and a bifocal compound microscope. Sodium chloride (density of 1.2 g/cm³) has a lower separation efficiency than that of zinc chloride (density of 1.5 g/cm³). Despite this difference in efficiency, performing both techniques allows for a density fractionation that better characterizes the pollution. Depending on the site along the watershed, the microplastic pollution was as low as 63 particles per kg dry weight (p/kg dw) and as high as 687 p/kg dw. Fluorescent microscopy using Nile red staining was used in tandem with a quality check of a second microscopist to ensure microplastic counts were as accurate as possible. Nile red estimates resulted on average 16% higher concentration estimates given the same separation conditions due to higher detection of non-fibrous plastics. Given the limitations of the methodologies, the microplastics observed were all larger than 20 micrometers in diameter and were less dense than 1.52 g/cm³. The geological background of each site was investigated through trace element analysis using high resolution inductively coupled plasma mass spectroscopy (HR-ICP-MS) and clay mineralogy using X-ray diffraction (XRD). The resulting pollution level of Acton Lake is relatively low compared to other streams but similar to other artificial lakes in rural areas. Results provide a benchmark for long term monitoring and comparison in the region. 

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

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