Date of Award

2017

Document Type

Open Access Thesis

Department

Art

Sub-Department

Earth and Environmental Resources Management

First Advisor

Sarah Rothenberg

Abstract

Objectives. Microbial pathogens and their threat to human health have been the primary concern of sanitary sewer overflows (SSO); however, SSOs may also be a source of metals, including methylmercury, to local waterways. We hypothesized that SSOs had elevated concentrations of metals compared to nearby reference creeks.

Methods. Unfiltered and filtered (0.2 μm) surface water samples were collected monthly between November 2015 and March 2016 from three sewage-impacted creeks in Columbia, South Carolina. During this period, three sewage events were captured including an active SSO, a ruptured force main sewer pipe, and one site downstream from SSOs. In October 2016 and January 2017, three additional SSOs were sampled during two heavy rainfall events. Total mercury and methylmercury concentrations were quantified in unfiltered and filtered surface water samples (n=56), and 34 other metals were determined in filtered samples (n=51). Dissolved organic carbon concentrations (DOC) (n=41) were measured, and we investigated whether the stable carbon isotopic composition of DOC differed for sewage events and creek reference sites.

Results. Compared to creek reference sites, unfiltered methylmercury concentrations were enriched by factors of 1.7 to 3.3 during three of the six sewage events while during all six events, total mercury was enriched by factors of 2.0 to 9.8 compared to the reference sites. In addition, several metal concentrations had elevated concentrations in the sewage events above the average reference sites concentrations. DOC concentrations were elevated in the sewage events, and the δ13C values of DOC were more positive for the SSO and ruptured sewer main compared to the creek reference sites, suggesting that the DOC source between the sewage events and the creek reference sites differed.

Conclusions. Results indicate that SSOs are a potential source of metals, including methylmercury, that in combination with DOC may have an impact on receiving waterbodies. With thousands of SSOs occurring annually in the United States, it is important to further investigate how these events may influence the biogeochemical cycling and bioavailability of metals in aquatic environments.

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