Wastewater contaminants in a fractured bedrock aquifer and their potential use as enteric virus indicators

Domestic wastewater is a source of persistent organic pollutants and pathogens to the aquatic environment, including groundwater aquifers. Wastewater contaminants include a variety of personal care products, pharmaceuticals, endocrine disrupters, bacteria, and viruses. Groundwater from 22 wells completed in a semi-confined to confined, fractured Silurian dolostone aquifer in southern Wellington County, Ontario, Canada, was analyzed for 14 organic wastewater contaminants (4 artificial sweeteners, 10 pharmaceuticals) as well as E. coli, total coliforms, and 6 human enteric viruses. Enteric viruses were detected in 8.6% of 116 samples, and at least one organic wastewater contaminant was detected in 82% of the wells (in order of decreasing detection frequency: acesulfame, ibuprofen, sulfamethoxazole, triclosan, carbamazepine, and saccharin). Virus indicator metrics [positive and negative predictive values (PPV, NPV), sensitivity, specificity] were calculated at the sample and well level for the organic wastewater compounds, E. coli, and total coliforms. Fecal bacteria were not good predictors of virus presence (PPV = 0%-8%). Of the potential chemical indicators, triclosan performed the best at the sample level (PPV = 50%, NPV = 100%), and ibuprofen performed the best at the well level (PPV = 60%, NPV = 67%); however, no samples had triclosan or ibuprofen concentrations above their practical quantification limits. Therefore, none of the compounds performed sufficiently well to be considered reliable for assessing the potential threat of enteric viruses in wastewater-impacted groundwater in this bedrock aquifer. Future studies need to evaluate the indicator potential of persistent organic wastewater contaminants in different types of aquifers, especially in fractured rock where heterogeneity is strong.IMPORTANCEAssessing the potential risk that human enteric viruses pose in groundwater aquifers used for potable water supply is complicated by several factors, including: (i) labor-intensive methods for the isolation and quantification of viruses in groundwater, (ii) the temporal variability of these viruses in domestic wastewater, and (iii) their potentially rapid transport in the subsurface, especially in fractured rock aquifers. Therefore, aquifer risk assessment would benefit from the identification of suitable proxy indicators of enteric viruses that are easier to analyze and less variable in wastewater sources. Traditional fecal indicators (e.g., E. coli and coliforms) are generally poor indicators of enteric viruses in groundwater. While many studies have examined the use of pharmaceutical and personal care products as tracers of domestic wastewater and fecal pollution in the environment, there is a paucity of data on the potential use of these chemical tracers as enteric virus indicators, especially in groundwater.