QMRA of intestinal nematode infection via multimedia exposure pathways

The human health risks associated with multimedia exposure pathways of Ascaris lumbricoides (A. lumbricoides) are poorly understood including use of surface water contaminated with untreated wastewater in agriculture, consumption of uncooked raw vegetables irrigated with polluted stream-water, and incidental ingestion of fecally contaminated water by recreators. We analyzed a total of 65 water samples for the presence of helminthes collected from 5 monitoring locations in Salta City over a 13-month period on the Arias-Arenales river in the northwestern region of Salta province in Argentina. The average density of A. lumbricoides in the surface water was 5 eggs/liter. A. lumbricoides was detected in 35 of the 65 samples with a maximum concentration of 28 (1.31 × 10^-4) compared to the adults (6.47 × 10^-5) and secondary recreators (6.50 × 10^-6) whereas the annual probability of mean infection risk from incidental consumption of surface water in children was 2.62% followed by 1.33% in adults, and least in secondary recreators i.e. 0.13%. Consumers of wild water-cress (assumed mean single exposure raw consumption of 100 grams/person) collected from Arenales river had the highest single exposure mean infection risk compared to consumers of other in β-binomial D-R) from accidental ingestion of irrigation water by growers, assuming 75 days of active irrigation exposure, was higher using β-binomial D-R than the recommended annual tolerable risk level of 1.2 × 10^-3 per person per year for wastewater use in agriculture. This research also showed the impact of using different D-R models in human health risk assessment. Application of conditional D-R models led to higher risk estimates resulting in higher estimates of extreme risks. The concentration of the infectious nematode in the surface water and the rates of accidental ingestion of contaminated water were the key drivers in the risk estimates and had the greatest effect on the total uncertainty of the estimated risks in all of the scenarios.