The presence, bioavailability, and impact of antibiotics in rural and urban streams of North Carolina

UNCG Author/Contributor (non-UNCG co-authors, if there are any, appear on document)
Austin Douglas Gray (Creator)
The University of North Carolina at Greensboro (UNCG )
Web Site:
Anne Hershey

Abstract: Antibiotic pollution in stream ecosystems in the United States remains a research area that has received little attention. The presence of antibiotics in streams presents a vehicle for these contaminants to be transferred from inland areas to coastal waters. Antibiotics can enter streams via runoff, wastewater effluent, and sewage leaks. The presence of antibiotic residues in bivalves presents one pathway that antibiotics can enter the food web. Due to antibiotics’ inhibitory nature, their presence in sediment can alter or inhibit microbial communities that facilitate biogeochemical processes. There remains very little research on antibiotic pollution’s implications on critical processes such as nitrification, denitrification, and methanogenesis. My research aims were to: 1) assess the occurrence and distribution of antibiotics in rural groundwater, rural streams, and urban streams in the Piedmont of North Carolina; 2) measure antibiotic concentrations from Asian clams exposed to three antibiotics in single and mixture exposures; and 3) investigate how antibiotics in single and mixture exposures at an environmentally relevant concentration can impact sediment biogeochemical processes. Using non-target screening, I detected 15 predicted antibiotics based on their respective ion masses in rural groundwater and streams. The four most commonly predicted antibiotics detected from non-target screening were then confirmed through target analysis (sulfamethoxazole, sulfamerazine, erythromycin, and danofloxacin) and quantified. Maximum concentrations in surface water, groundwater, and stream sediment were 1.2 ?g/L, 1.8 ?g/L, and 400 ?g/kg, respectively (Chapter II). The concentration of antibiotics detected in rural groundwater from private wells did not pose any risk to residents based on risk assessment calculations (Chapter II). Following rural stream and groundwater assessment, I detected ten predicted antibiotics in urban streams. The four antibiotics targeted in the rural study were all below the level of quantification in urban streams (Chapter III). Laboratory assays exposing Asian clams to sulfamethoxazole, ciprofloxacin, and erythromycin showed that antibiotic concentrations did not differ depending on single versus mixture exposures. Concentrations of erythromycin were lower than ciprofloxacin and erythromycin. Asian clams may be a suitable bioindicator for antibiotic pollution. However, due to not dissecting the clam, not rinsing the clam’s external body, or allowing for a proper depuration period, concentrations measured include those assimilated into tissues, present in the digestive tract, and/or adsorbed to the external body of the clam (Chapter IV). Due to antibiotic occurrence in sediments, their impact on nitrification, denitrification, and methanogenesis was of interest. The assay consisted of single and mixture antibiotic treatments (sulfamethoxazole, danofloxacin, and erythromycin) at a relevant concentration (10 ?g/L each) and a control treatment (no antibiotic addition). The study was conducted over seven days with an initial 24-hour oxic period (oxygen levels = 5.5%; samples collected at 0, 6, 12, and 24 hours), with only NH4+ and NO3- consumption rates measured. Following the oxic period, there was a hypoxic or anoxic period following (samples collected on days 2, 4, and 7) to determine the influence of antibiotics on N2, N2O, CH4, and CO2 concentrations. During this period, microcosm oxygen levels were = 5.5% (based on a preliminary oxygen demand study that concluded at 24 hours). NO3- consumption rates did not differ amongst antibiotic and control treatments. By day 7, concentrations of N2O, N2, CH4, and CO2 did not differ among antibiotic and control treatments. In my assessment of NH4+ consumption, the control, danofloxacin, and erythromycin treatments exhibited a decline in NH4+ concentration. However, the SMX treatment exhibited no change in NH4+ concentration over the study’s 24-hour oxic period. The mixture treatment experienced an increase in NH4+ concentration over the oxic period (Chapter V). Results from my dissertation illustrate that antibiotic pollution in the Piedmont of North Carolina is widespread. Antibiotics can be detected in Asian clams. The antibiotic sulfamethoxazole alone inhibited nitrification. When mixed with danofloxacin and erythromycin, nitrification can be reduced, and mineralization is enhanced. [This abstract has been edited to remove characters that will not display in this system. Please see the PDF for the full abstract.]

Additional Information

Language: English
Date: 2020
Antibiotics, Biogeochemical, Mass Spectrometry, Mixtures, Streams
Antibiotics $x Environmental aspects
Water quality $z North Carolina
Rivers $z North Carolina

Email this document to