Date of Award
Chemistry and Biochemistry
This research centers on the determination of metals (Cd, Pb, V, Cr, Mn, Fe, Co, Ni, Cu) and microplastics (MPs) in marine sediment from oyster reefs in the Mississippi Sound Estuary. Oysters (Crassostrea virginica) are a vital part of the Gulf Coast economy, but their population has dramatically declined in recent years due to multiple stressors, including oil spills and fluctuations in salinity from flooding. Increasingly frequent flooding events also introduce high loads of MPs and sediments containing heavy metals from the Mississippi River. These pollutants can have deleterious effects on oyster biology; however, they have not been adequately studied at oyster reefs along the Gulf Coast. As filter-feeders, oysters are especially vulnerable to MPs and heavy metals. Moreover, MPs absorb certain contaminants, including heavy metals and hormone disruptors, exacerbating the situation by exposing the organisms to additional toxins.
Metals were leached from the sediment using microwave-assisted nitric acid digestion and determined using inductively coupled plasma mass spectrometry (ICP-MS). Concentrations ranged from 0.021 µg/g for Cd to 1024 µg/g for Fe. Concentration of the metals were compared between sites and with literature values. No metal concentrations exceeded the sediment quality guideline probable effect level, although Pb was close at a few sites, suggesting that heavy metal contamination at the site is not a major concern.
Putative MPs in the sediment were isolated using a ZnCl2 separation followed by filtration and characterized using a stereomicroscope. Total MP counts in 20 g sediment samples ranged from 162 to 379. We observed between 22 and 31 fibers and fragments at sites 1 and 4, however, site 6 had 52 fibers and 56 fragments. Beads ranged from 6 to 319, with higher numbers in the 45-125 µm size fraction compared to the >125 µm size fraction.
Overall, this study is one of the first to assess both heavy metals and MPs at oyster reefs in the Mississippi Sound. While metal concentrations do not appear to be a risk based on current guidelines, MPs were prevalent in the sediment and may be resuspended during storm events, exposing oysters and other biota to the plastic pollution.
Goza, Shelby, "Determination of Metals and Microplastics in Sediment from Oyster Reefs in the Mississippi Sound" (2021). Honors Theses. 1677.
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