Widespread occurrence and potential for biodegradation of bioactive contaminants in Congaree National Park, South Carolina

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Organic contaminants with designed molecular bioactivity, such as pesticides and pharmaceuticals, originate from human and agricultural sources, occur frequently in surface waters, and threaten the structure and function of aquatic and terrestrial ecosystems. Congaree National Park in South Carolina (USA) is a vulnerable park unit due to its location downstream of multiple urban and agricultural contaminant sources and its hydrologic setting, being composed almost entirely of floodplain and aquatic environments.

Project Chief: Paul M. Bradley
Program: Toxic Substances Hydrology Program, USGS-NPS Water Quality Partnership Program
Project Timeline: 2010-Present
Cooperator(s): U.S. National Park Service, U.S. Environmental Protection Agency

A study led by the U.S. Geological Survey in cooperation with the National Park Service found dozens of contaminants within the protected areas of Congaree National Park in South Carolina.

The study examined whether contaminants are commonly found within protected areas, and if so, their sources. These insights have implications for managing these, and other, protected lands in the United States.

Map of Congaree National Park, SC, showing sampling locations
Map of Congaree National Park showing sampling locations and median cumulative (sum of all compounds) detections and concentrations (ng/L) of pharmaceutical contaminants detected in surface‐water samples during 2013 to 2015.(Public domain.)

The contaminants found were detected at levels below any considered to pose a risk to the health of park visitors who might drink or come in contact with waters in the backcountry. Additional research would need to take place to determine if the present levels or mixture of contaminants could cause adverse health impacts to aquatic organisms.

“Congaree National Park, like other parks around the country, is positioned in a landscape where surrounding land uses, municipal wastewater discharges and on-site visitation can potentially introduce contaminants into the protected areas,” said Paul Bradley, USGS Research Ecologist/Hydrologist and lead author of the study. “Our main goal with this study, which was requested by the National Park Service, was to provide key information to help park managers understand the potential sources of a variety of water contaminants detected in protected areas.”

The researchers collected 72 water and sediment samples from 16 river and lake sites around the park and found 49 pharmaceuticals and 47 other contaminants, including pesticides and chemicals associated with wastewater.

“While there was a large variety of contaminants found during the study, many were detected in locations that could be explained by agriculture or wastewater treatment plants on rivers upstream and outside of the park,” Bradley said. “However, some of the contaminants were found in lakes far away from the rivers flowing into the park, leading us to believe the source of these was likely people within the park.”

Pharmaceuticals were found in water samples from across the park, with higher occurrences and concentrations near the Congaree and Wateree Rivers and in Horseshoe Lake, which are all locations downstream of municipal wastewater discharges from Columbia, South Carolina and Charlotte, North Carolina.

Metformin, a drug used to treat diabetes and one often found when wastewater discharges into rivers or streams, was the most frequently detected pharmaceutical. It was found in 61 percent of the samples, and was the only pharmaceutical observed in either water or sediments at all 16 sites. 

Some of the contaminants found, like antibiotics and antibacterials, have been shown in studies elsewhere to negatively affect microbes, which form the base of aquatic food webs. Other pharmaceuticals detected in the park have been shown elsewhere to alter fish behavior and health.

The insect repellant DEET, or N, N-diethyl-m-toluamide, was one of the most commonly found contaminants in the park, being detected in 71 percent of all water samples. It was found at least once in every surface water body within the park, including those deep in the park unaffected by wastewater discharges.

In order to protect aquatic life and minimize human exposure to contaminants, all municipal wastewater is treated to add oxygen, disinfect water, and in some cases remove nutrients before it is released back into rivers and streams. However, wastewater treatment plants are not required to remove pesticides, pharmaceuticals, and other organic compounds commonly found at low levels in wastewater effluents.

The researchers also examined the likelihood that sediment-bound contaminants could naturally biodegrade in the park. They determined the park’s marsh-like floodplains are characterized by low oxygen conditions that are not conducive to biodegradation.      

“Most of the detected contaminants are not going to disappear very quickly,” Bradley said.

This study is one of several examining the source of contaminants entering protected areas.

“The National Parks are protected areas, but contaminants that may be of health concern to aquatic life have the potential of entering the park from both inside and outside sources,” Bradley said. “Understanding if contaminants are present and, if so, what their likely sources are is key to helping park leadership manage the risk of exposure to people and wildlife.”

To read the entire study, titled “Widespread Occurrence and Potential for Biodegradation of Bioactive Contaminants in Congaree National Park, USA,” click here.

The USGS Toxic Substances Hydrology Program and the USGS National Water Quality Program, NPS Water Quality Partnership supported this research.

Click here to read an associated Science Feature “Sources of Commonly Used Chemicals in National Parks—USGS and National Park Service Working Together.”