Presentations 2016

Exploring the origin and migration of antibiotics in aquifers to evaluate their impact on groundwater resources quality

Catalan Institute for Water Research & University of Girona

https://www.youtube.com/watch?v=BCZ3OciIN-c&list=PLZC-5vj9_JAZyX_rSnsMiIz7z62iJEf3D&index=3

Emergent organic contaminants (EOCs), especially veterinary antibiotics related to farming activities, are of great concern on groundwater quality. They presence affect microbial communities inhabiting aquifers, shaping their composition and stimulating the spread of antibiotic resistance among community members.This study focuses on the behavior of antibiotics in groundwater in an agricultural area. Nevertheless, aquifer interaction with stream recharge, fertilization and infiltration of treated wastewater creates a mixture of both domestic and veterinary antibiotics. As reactive compounds, their migration is controlled by soil processes, mainly adsorption. Their origin and fate in the subsurface are key factors for designing mitigation and prevention strategies; not only in terms of water quality, but also in relation to the spread of antibiotic resistance in groundwater microbiota.A field study is being conducted in a fluvio-deltaic aquifer (Fluvià River, NE Catalonia). Samples collected during spring 2015 consist of 47 groundwater, 7 surface water, and 2 wastewater treatment plant effluents. We measured their hydrochemistry, including isotopic data for water and nitrate molecules. Antibiotics were pre-concentrated by solid phase extraction and quantified using an optimized protocol based on liquid chromatography tandem mass spectrometry (UHPLC–QqLIT). The phylogenetic composition of groundwater bacterial communities was analyzed by high throughput sequencing. Concentration of antibiotic resistance genes (ARGs) were determined using qPCR and specific primers for target genes (qnrS, ermB, tetW, sul-I and blaTEM). Also, copy numbers of the Class I integron integrase gene (intl1) was analyzed as a proxy for anthropogenic pollution. Copy numbers of bacterial 16S rRNA gene were also determined to estimate bacterial abundance and to normalize ARG data. Seasonal campaigns are being conducted in 8 representative wells.Average nitrate concentration in groundwater and surface water was 42.4 mg/L and 7.3 mg/L. Up to 21% of the groundwater samples had nitrate concentrations above 50 mg/L. Antibiotics found in groundwater were fluoroquinolones (Ciprofloxacin, Danofloxacin, Enrofloxacin, Norfloxacin, Ofloxacin, and Orbifloxacin), macrolides (Azithromycin), quinolones (Flumequine, Oxolinic Acid, and Pipemidic Acid) and sulfonamides (Sulfamethoxazole). Sulfamethoxazole was detected in 80% of the samples with a mean concentration of 6.1 ng/L, with a highest concentration of 28.6 ng/L. Ciprofloxacin was measured in 45% of the samples, with mean concentration of 77.2 ng/L and highest concentration of 298.3 ng/L. In turn, only fluoroquinolones (Ciprofloxacin, Enrofloxacin, Norfloxacin and Orbifloxacin) and sulfonamides (Sulfamethoxazole) were detected in surface water samples. Most detected antibiotics were Sulfamethoxazole and Ciprofloxacin (mean concentrations of 8.5 and 211.8 ng/L; highest concentrations of 211.8 and 287.7 ng/L, respectively), similarly to the results obtained for groundwater. Enrofloxacin was also quantified in 2 samples with relatively high concentration (290 ng/L). Results showed presence of all analyzed ARGs, and allowed to distinguish the origin of the antibiotics, whether veterinary or clinical. In particular, sul-I and intI1 were the most abundant ARGs in all samples (averages of 1.10x105 and 1.63x104, respectively). In summary, despite the widespread occurrence of veterinary antibiotics detected in the Baix Fluvià aquifer, the stream influence may also contribute to the groundwater antibiotic load with antibiotics used in human health. Despite the diffuse origin of most veterinary, no continuous spatial concentration trend has been observed in the aquifer. This suggests that soil adsorption and dilution may locally alter the antibiotic composition of groundwater. Some wells showed a high relative abundance of several ARGs highlighting that antibiotic pollution maintain a reservoir of resistance in groundwater that may eventually pose a risk for human health. This field study points out the multifaceted aspects of antibiotic pollution that finally control the impact on groundwater quality and its management.Acknowledgements: This study is part of the PERSIST project funded by the EU Water JPI (JPIW2013-118).