Probabilistic environmental risk assessment of zinc in Dutch surface waters

In the framework of the European Union (EU) New and Existing Chemicals Policy, a regional risk assessment for Zn according to the current technical guidance documents and a probabilistic approach, by mathematically integrating both best-fitting exposure concentrations and species-sensitivity distributions into a probabilistic risk quotient distribution using Monte Carlo analysis, was explored for The Netherlands. Zinc is an essential element, and the current probability distributions may not adequately deal with this property. The threshold Pareto distribution provided the best fit to the chronic Zn toxicity data, resulting in a predicted-no-effect concentration (PNECadd) for dissolved Zn of 34.2 microg/L, whereas use of the conventional normal distribution resulted in a PNECadd for dissolved Zn of 14.6 microg/L. The extracted exposure data resulted in a regional predicted environmental concentration (PEC) for dissolved Zn in the Dutch surface waters of 20.1 microg/L and in PECadd values for dissolved Zn of between 15.5 and 17.3 microg/L, depending on the background correction used. The conventional deterministic risk characterization identified a regional risk for Zn in the Dutch surface waters. The more comprehensive probabilistic approach used in the present study, however, identified only very limited potential risks for the Dutch region. A probabilistic median risk, that the environmental concentration is greater than the no-observed-effect concentration of a species in Dutch surface waters (0.5-0.6%), depending on the inclusion of background correction, was obtained from the best-fitting distributions. Because probabilistic approaches provide a quantifiable and improved assessment of risk and quantification of the uncertainty associated with that assessment, these techniques may be considered as a way to improve the EU risk assessment procedures for data-rich substances.