Human health risk assessment of the mixture of pharmaceuticals in Dutch drinking water and its sources based on frequent monitoring data.

The presence of pharmaceuticals in drinking water is a topic of concern. Previous risk assessments indicate that their low concentrations are very unlikely to pose risks to human health, however often conclusions had to be based on small datasets and mixture effects were not included. The objectives of this study were to a) investigate if pharmaceuticals in surface and polder water penetrate in drinking water, b) assess the lifelong exposure of consumers to pharmaceuticals via drinking water and c) assess the possible individual and mixture health risks associated with this exposure. To fulfill these aims, a 2-year set of 4-weekly monitoring data of pharmaceuticals was used from three drinking water production plants. The 42 pharmaceuticals that were monitored were selected according to their consumption volume, earlier detection, toxicity and representation of the most relevant therapeutic classes. Lifelong exposures were calculated from concentrations and compared with therapeutic doses. Health risks were assessed by benchmarking concentrations with provisional guideline values. Combined risks of mixtures of pharmaceuticals were estimated using the concept of Concentration Addition. The lifelong exposure to pharmaceuticals via drinking water was calculated to be extremely low, i.e. a few mg, in total corresponding to <10% of the dose a patient is administered on one day. The risk of adverse health effects appeared to be negligibly low. Application of Concentration Addition confirmed this for the mixture of pharmaceuticals simultaneously present. The investigated treatment plants appeared to reduce the (already negligible) risk up to 80%. The large available monitoring dataset enabled the performance of a realistic risk assessment. It showed that working with maximum instead of average concentrations may overestimate the risk considerably.