Human, swine waste pose dual threats to water quality after flooding
September 9, 2021
A study published in the journal ACS ES&T Water that monitored surface waters in the wake of 2018’s Hurricane Florence finds that waters were contaminated by fecal bacteria from both human and swine waste.
Dr. Angela Harris
Dr. Jill Stewart
Jill Stewart, PhD, the senior author of the study, is the Philip C. Singer Distinguished Professor in the Department of Environmental Sciences and Engineering at the UNC-Chapel Hill Gillings School of Global Public Health. Stewart she worked with corresponding author Angela Harris, PhD — an assistant professor of civil, construction and environmental engineering at North Carolina State University — and several other NCSU colleagues to evaluate microbial contaminants at sites across Eastern North Carolina after the hurricane passed through.
“We found that surface waters in eastern North Carolina were more likely to face dual contamination than to be contaminated by either human waste or swine waste by themselves,” Harris said. “This means people are dealing with multiple hazards. It also means there are two sources of fecal contamination that need to be addressed. It’s not just the swine industry, and it’s not just wastewater treatment plants or septic systems.”
For the study, researchers collected surface water samples at 40 sites across eastern N.C. Samples were collected one week after Hurricane Florence made landfall in September 2018, and again one month after landfall. These samples are referred to as Phase 1 and Phase 2, respectively.
The researchers tested the water samples for a variety of bacteria. Specifically, the samples were tested for: E. coli (an indicator species used to identify fecal contamination and the likelihood that there are pathogens present); pathogens such as Arcobacter butzleri and various Listeria species; and bacterial species associated specifically with either swine or humans, so that researchers could trace contamination back to its source.
“About 30% of the surface water sites we tested had levels of bacteria that would have made those waters unsafe for swimming,” Harris said.
The most commonly found pathogen was Arcobacter, but its presence wasn’t associated with human or swine fecal markers. In other words, it’s not clear where the pathogen is coming from.
Another mystery was that the levels of E. coli in Phase 2 samples taken from permanent water channels (as opposed to temporary floodplains) were actually higher than the levels of E. coli in the Phase 1 samples.
“We’re not sure why E. coli levels jumped in those Phase 2 samples,” said Harris. “It could be because water levels were decreasing, so there was less dilution. It could be due to temporary changes in regulatory requirements in the wake of the hurricane. It could be some other variable we haven’t identified. We need a lot more monitoring data to begin to tease that apart.”
“A lot of post-flooding work has been done in urban areas,” she added. “This is one of the few studies that looks at post-flooding water quality impacts in rural, agricultural areas. Our findings suggest that this merits a much closer look. This work is particularly important given concerns around antibiotic-resistant pathogens and the likelihood that we’ll be seeing more extreme wet weather events in the future.”
The study was conducted with support from the National Science Foundation, under grants 1901588 and 1901202; the North Carolina Policy Collaboratory; and the Institute for the Advancement of Food and Nutrition Sciences through an International Life Sciences Institute North America grant.
The original version of this story was published by Matt Shipman at NCSU.
Contact the UNC Gillings School of Global Public Health communications team at sphcomm@unc.edu.
