Assessment of drinking water safety in the Netherlands using nationwide exposure and mortality data

Abstract

OPS 25: Drinking water contamination and adult health, Room 411, Floor 4, August 26, 2019, 10:30 AM - 12:00 PM Background: Drinking water in the Netherlands is generally accepted as safe. Although risk assessments for constituents point to large margins of safety between concentrations and health-based guideline values, public concern about health risks of long-term intake still exist. We explored associations between drinking water quality and causes-of-death using national databases. Methods: The cohort consisted of 6,998,623 persons who were at least 30 years old on January 1 2008 and lived at least five years on the same address. We evaluated mortality due to a natural cause, cardiovascular diseases, coronary heart disease, lung cancer or colon cancer. Home addresses in 1800 drinking water provision areas were linked to 233 production stations. The REWAB database with drinking water quality for parameters mentioned in the EU Drinking Water Directive was used to assess the average concentration of arsenic, nitrate, hardness, calcium and magnesium over 2000-2010 at the production stations. We applied age stratified Cox proportional hazards models with province as random effect. We adjusted for sex, marital status, country of origin, household income, socio-economic status, PM10 and NO2. Results: 453,035 persons died during the five year follow up period of a natural cause. For mortality due to cardiovascular diseases, a 100 mg/l increase in calcium was associated with a HR of 1.08 (95% CI: 1.03, 1.13) and an increase of 2.5 mmol/l of water hardness with a HR of 1.06 (95% CI: 1.01, 1.10). Magnesium was associated with a reduced risk for mortality due to coronary heart diseases: HR of 0.95 (95% CI: 0.90, 0.99) per 10 mg/l increase. For other combinations studied, no statistical significant associations were identified. Conclusions: The observed inverse relation for magnesium is in line with the literature. The results for calcium and hardness will be discussed in the light of the literature and of potential sources of bias.