Chaoqi Chen, William Vesely, Weichao Su, Erin Ling , Brian Benham, Asa Spiller, Kang Xia 

Occurrence of emerging contaminants (ECs) including parent compounds, their metabolites, and antibiotic resistance genes (ARGs) and their relationships to common chemical and microbial indicators have rarely been investigated for private wells. In this study, occurrence of 109 parent compounds (ECs), 29 EC metabolites, and 15 ARGs were screened in private well water samples from 57 Southwest Virginia households and in municipal drinking water samples from similar areas. In the U.S., private well water is not regulated under the Safe Drinking Water Act like municipal water systems. Although well construction regulations exist in Virginia, there is no requirement for water testing, treatment, or system maintenance beyond the initial construction of the well. We found that 58 ECs, 18 EC metabolites, and 10 ARGs were detectable in at least one of the well water samples. Homeowner-reported household point of entry water treatment devices reduced the occurrence of ECs and EC metabolites, but some were not effective in eliminating the presence of ARGs. Oxcarbazepine, methylparaben, gabapentin, and triclosan were the most frequently detected in the well water in 68.4%, 66.7%, 61.4%, and 61.4% percent of samples, respectively. Ten ARGs were detectable in at least one well water sample, with strA (52.6%), sul2 (50.9%), and tetW (50.9%) being the most frequently detected. The overall number of detectable ECs, EC metabolites, and ARGs as well as levels of caffeine, tylosin, and triclosan in the well water were similar to municipal water samples. The occurrence of ECs, EC metabolites, and ARGs was not significantly different between the well water samples from the two counties, nor were they correlated with the homeowner-reported well depth, age, or distance from an onsite septic system. Occurrence of ECs and EC metabolites in the well water samples was positively correlated with some chemical water quality constituents (e.g., nitrite, sodium, and heavy metals), but not with total dissolved solids (TDS) or microbial-indicators (e.g. total coliform bacteria, E.coli bacteria). However, microbial indicators were positively associated with the occurrence of ARGs. This study provides evidence of widespread occurrence of emerging contaminants in private well water samples and suggests the possibility of further ARG transfer among microbial constituents.