Denmark: Nitrate in drinking water increases the number of colorectal cancers
December 1, 2023:
127 colorectal cancer cases can be avoided each year in Denmark and the Danish society can save $302 million each year if the limit of nitrate in drinking water is reduced to 3.87 mg/L, according to a study published in the journal Science of the Total Environment.
Nitrate in drinking water is a contaminant which can affect human health and has been associated with an increased risk of, amongst other diseases, colorectal cancer.
Based on epidemiologic data from Denmark the study analyzed the association between drinking water nitrate and colorectal cancer, the health and economic consequences of lowering the standard of nitrate in drinking water from 50 mg/L to 9.25 mg/L and 3.87 mg/L.
The drinking water nitrate attributable number of cases was estimated using the risk in the exposed and unexposed population based on current nationwide exposure distributions in Denmark.
Groundwater is used for drinking water
All drinking water in Denmark is produced from groundwater. Danish groundwater normally undergoes no or simple treatment (oxidation and filtration) at the waterworks with no significant changes in nitrate concentrations.
Nitrate levels in the Danish ground- and drinking water are regularly monitored. Generally, the nitrate concentration levels in oxic groundwater correlate to the nitrogen surplus in Danish agriculture. Nitrate polluted groundwater is especially found in areas where the groundwater reservoirs are vulnerable due to poor geologic protection from thin overlying clay layers, and often also because the impact from nitrogen losses from intensive agriculture is high.
Fewer cases of colorectal cancer
The analysis in the study shows that a lower limit of 9.25 mg/L would decrease the annual number of colorectal cancer cases by 72 and by an additional 55 for a stricter limit of 3.87 mg/L. This means that with a level of nitrate of 3.87 mg/L the total amount of Danish colorectal cancer cases that can be avoided each year is 127.
Saved health costs by reducing nitrate in drinking water
The study found that the resulting avoided health-related costs are $179 million per year for the 9.25 mg/L nitrate limit and another $138 million per year for a further reduction to 3.87 mg/L nitrate. This means that the direct and indirect health costs linked to colorectal cancer that can be saved in Denmark are annually is $317 million with a limit of nitrate of 3.87 mg/L.
Costs of reducing nitrate in drinking water
To reduce the levels of nitrate in the drinking water will incur costs linked to either changes in land use management (reducing the level of leaching of agricultural fertilizer nitrates), well reallocation and/or use of treatment technologies (biological denitrification, ion exchange or reverse osmosis). Reducing nitrate levels in the drinking water from public and private wells using these measures in Denmark would cost around $15 million annually.
The Danish economic health benefits are higher than the costs for both limits with net gains of $170 million (9.25 mg/L) and additionally $132 million (3.87 mg/L) a year. With these figures the study finds that there is an annual net Danish national benefit of $302 million with a new standard of 3.87 mg/L nitrate in the Danish drinking water.
"Health-economic valuation of lowering nitrate standards in drinking water related to colorectal cancer in Denmark", Science of the Total Environment; doi.org/10.1016/j.scitotenv.2023.167368
Among the coauthors are MARCHES participant Jörg Schullehner from the Department of Public Health, Aarhus University.