Inhalation exposure assessments under REACH - Problems encountered using the approach recommended by the ECHA...

Consumers experience inhalation exposure events that are characterized by fluctuating substance air concentrations and typically exposure durations of less than 24 h. To assess the risk of such exposure events, a comparison with toxicological derived limits based on 24 h exposure duration per day is often necessary. Therefore, adjustments are needed to bridge the different time durations. One approach to handle this issue was recommended by the European Chemical Agency (ECHA) for consumer exposure. This approach is especially noteworthy, because it does not rely on the validity of Haber's law (which states that only total intake matters) but uses a modified Haber's law (with coefficient n = 3) as default. However, the proposed algorithm for its implementation can lead to the situation that increasing the exposure duration leads to lower predicted risk, which logically makes no sense. In this article, the correct way to implement the modified Haber's law is presented, which avoids logical fallacies. The presented algorithm has consequences for the sensitivity of the predicted risk regarding changes of exposure duration and ventilation rate, which are investigated in this article.