Date of Award

8-26-2026

Document Type

Thesis

Degree Name

Master of Science in Coastal Marine and Wetland Studies

Department

Coastal and Marine Systems Science

College

College of Science

First Advisor

Angelos Hannides

Second Advisor

Kaijun Lu

Third Advisor

Ryan Rezek

Abstract

The growing reliance and widespread use of herbicides on a global scale is negatively affecting non-targeted biota and, consequently, their ecosystems. Herbicide levels and their impacts have been extensively researched around the world in riverine and lacustrine ecosystems. However, studies of the levels and effects of herbicides on coastal intertidal benthic communities have been lacking. This study focused on testing spectrophotometric methodologies for herbicides (atrazine and glyphosate) and documenting their presence and levels in sediment, water, and biotic tissue of intertidal coastal beaches and marshes of Waties Island and Singleton Swash, Horry County, South Carolina. A laboratory microcosm was employed to determine the toxicological response of microphytobenthos to these herbicides. Results indicate that atrazine is potentially present in the coastal environment, but the methodology cannot reliably distinguish it from background levels. Atrazine concentrations in water and sediment averaged 0.045 (±0.065) μg/L and 0.009 (±0.018) μg/kg, indicating no sorption to the sediments. No difference was observed between marsh and beach sites. Eastern oysters (Crassostrea virginica) were observed to bioaccumulate atrazine ×2.83 (1.88-3.78), but no risk is posed to humans at these concentrations (<0.3 μg/kg). Exposure experiments indicated a negative effect from herbicide exposure after 72 h (10-30 μg/L for atrazine and 1000 μg/L for glyphosate). The effect of low atrazine treatment (1 μg/L) was not significant but still negative. In contrast, the effect of low glyphosate treatments (<100 μg/L) was positive after 72 hours. The positive response could be due to the release of nitrogen and phosphorus from the degradation of glyphosate that overcompensates for any negative effects. These findings indicate that herbicides can have a negative effect on intertidal microphytobenthic communities, but not at the low concentrations of atrazine measured at the study locations.

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