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Table 3 Overview and discussion of major sources of data uncertainty

From: Estimation of incidence and social cost of colon cancer due to nitrate in drinking water in the EU: a tentative cost-benefit assessment

Source of uncertainty Evaluation
Exposure-response function Epidemiological evidence is suggestive but far from conclusive.
Differences in water supply and life style factors for colon cancer incidence between Iowa and Europe. Meat intake is an important risk factor for cancers. Total meat consumption in Europe and the US are comparable, but beef consumption in Iowa is higher.
The assumption that exceedance of 25 mg/L NO3 in groundwater samples at 5-20 m depth is equivalent to exposure in all drinking water from small public supply and private wells. No data were available about extraction depth and water treatment for this type of supply. Local data on nitrate in groundwater and actual use for drinking water were not available.
Focus on groundwater that is affected by agricultural nitrogen loading. Relatively unpolluted aquifers overlain by forest or semi-natural vegetation are underrepresented. Therefore exposure probably is overestimated.
Not considering surface water based drinking. Considering non-compliance in surface water based public drinking water increases health cost by about 15%. Although about 40% of EU surface waters exceed 25 mg/L NO3[41], we assume that private use of surface water for drinking water is negligible compared to groundwater.
Not considering consumption of bottled water. In EU27, the consumption of bottled drinking water, that is very low in nitrate, increased from around 12% of total intake in 2001 to 15% in 2007 and consideration would slightly lower exposure estimates. In fact total beverage consumption is relevant; fruit juices can be high in nitrate and beers high in nitrosamines [42].
The assumption that percentage of drinking water samples from large public facilities not complying with standards for nitrate (50 mg/L) or nitrite (0.5 mg/L NO2) is equivalent to exposure, and identical for groundwater and surface water sources Non-compliance may be incidental and assumption may overestimate exposure. Estimates of exposure to exceedance of 25 mg/L NO3 will be more robust.