Human health risk assessment for the occurrence of enteric viruses in drinking water from wells: Role of flood runoff injections

Wedemonstrated that floods can induce severemicrobiological contamination of drinkingwater fromwells and suggest strategies to better address water safety plans for groundwater drinking supplies. Since 2002, the Italian Water Research Institute (IRSA) has detected hepatitis A virus, adenovirus, rotavirus, norovirus, and enterovirus in water samples fromwells in the Salento peninsula, southern Italy. Perturbations in the ionic strength inwater flow can initiate strong virus detachments from terra rossa sediments in karst fractures. This study therefore explored the potential health impacts of prolonged runoff injections in Salento groundwater caused by severe flooding during October 2018. A mathematicalmodel for virus fate and transport in fractures was applied to determine the impact of floodwater injection on groundwater quality by incorporating mechanisms that affect virus attachment/detachment and survival in flowing water at microscale. This model predicted target concentrations of enteric viruses that can occur unexpectedly inwells at considerable distances (5-8 km) from the runoff injection site (sinkhole). Subsequently, the health impact of viruses in drinking water supplied from contaminated wells was estimated during the summer on the Salento coast. Specific unpublished doseresponse model coefficients were proposed to determine the infection probabilities for Echo-11 and Polio 1 enteroviruses through ingestion. Themedian (50%) risk of infectionwas estimated at 6.3 · 10-3with an uncertainty of 23%. The predicted burden of diseases was 4.89 disability adjusted life years per year, i.e., twice the maximum tolerable disease burden. The results highlight the requirement for additional water disinfection treatments in Salento prior to the distribution of drinking water. Moreover, monthly controls of enteric virus occurrence in water fromwells should be imposed by a newwater framework directive in semiarid regions because of the vulnerability of karst carbonate aquifers to prolonged floodwater injections and enteric virus contamination.