Estimation of health risks caused by exposure to enteroviruses from agricultural application of wastewater effluents.

Agricultural reuse of wastewater is a common practice worldwide, especially in arid and semiarid area due to the freshwater scarcity. Wastewater irrigation in the Middle East, one of the most water-stressed regions in the world, could be a key factor for socio-economic development, but the microbial contamination of untreated or partially treated wastewater is a serious public health concern. Potential transmission of enteric viral infections through wastewater reuse in agricultural activities represents a true health risk for exposed individuals. Accordingly, it is important to assess the health risks associated with wastewater reuse. A quantitative microbial risk assessment (QMRA) with Monte-Carlo simulation was used to estimate the annual risk of enterovirus (EV) infection and disease burden for farmers and consumers of wastewater-irrigated lettuce in Iran, a semiarid country in the Middle East region. Risk analysis was performed based on the measured concentrations of EV in effluent of two activated sludge wastewater treatment plants (WWTP). Wastewater effluent sampling was carried out over a nine-month period, and the presence of total and fecal coliforms and EV was determined. Fecal coliform bacteria were found at a high level exceeded the guideline limit for wastewater reuse in agriculture. EVs were detected in 40% of samples with the highest frequency in summer with a mean of 12 and 16 pfu/ml for WWTP-A and B, respectively. Statistical analysis showed no correlation between the concentration of fecal coliforms and EV. The estimated infection risk for EVs was 8.8 × 10-1 and 8.2 × 10-1 per person per year (pppy) for farmers of WWTP-A and -B, respectively which was about 2 log higher than the tolerable infection risk of 2 × 10-3 pppy. The estimated risk for lettuce consumers exhibited a lower level of infection and disease burden but higher than the guideline limits. The median disease burden for consumption of lettuce irrigated with activated sludge effluents was about 10-3 Disability Adjusted Life Years (DALY) pppy which exceeded the WHO guideline threshold of 10-4 DALY pppy. The results of study indicated that the activated sludge effluents require an additional reduction of EVs to achieve the acceptable level of risk for agricultural reuse of wastewater.