By Usman Khan and Jim A. Nicell
Pharmaceutically active compounds (PhACs) have been widely used for more than half a century, but it is only relatively recently that their environmental release has been viewed with significant concern. The question that needs to be answered is whether such concerns are justified and, if so, which compounds are the most likely to be problematic.
PhACs that result from human sources are primarily released to the environment through the discharge of untreated and treated wastewater. Some PhACs released to the environment are sufficiently persistent in the environment such that they are not only detected in intakes of downstream drinking water treatment plants but, in certain instances, also the associated treated drinking water. In Canada, for example, as many as 20 PhACs have been detected in samples of treated drinking water. The reported presence of PhACs in drinking water supplies typically raises significant concerns since, due to their very nature, PhACs are expected to be pharmacologically active upon human exposure. These concerns are further heightened by the fact that drinking water standards have been developed for only a handful of PhACs and, thus, they are not being regularly monitored in drinking water nor are their human health impacts widely understood by most water utilities, health professionals, regulators, the news media, and the general public.
Our recently published AAPS Journal article Human Health Relevance of Pharmaceutically Active Compounds in Drinking Water aims to develop a better understanding of the sources through which PhACs are released to the environment and the evaluation of their human health relevance with respect to their potential presence in drinking water supplies. Through the application of a set of selection criteria established as part of this study, over 300 PhACs were selected for evaluation, making it one of the largest studies of its kind. Predicted and measured exposure concentrations were used to estimate the exposure to each PhAC in the evaluation set and safe levels for human ingestion for each PhAC were estimated by considering various human-health endpoints.
Our evaluation suggested that up to seven distinct sources can lead to the aquatic release of a given PhAC, with the importance of a given source term varying significantly from one case to another. When the human-health relevance with respect to the potential presence of the more than 300 PhACs in drinking water was evaluated, it was concluded that the vast majority of them are expected to pose a negligible risk to human health. However, the analysis indicated that 14 of the compounds should be prioritized for further investigation—both in terms of taking steps to confirm their presence in actual drinking water supplies and to evaluate their potential health impacts in greater detail. Surprisingly, this study also demonstrated that most of the PhACs that are likely to be of importance in terms of potential impact have yet to be monitored in the environment, which in turn indicates that the existing monitoring data available for the presence of PhACs in surface and drinking water—particularly those most likely to be problematic—is insufficient.
Overall, our study suggests that most PhACs, when considered individually, are unlikely to pose human-health impacts due to their potential presence in drinking water supplies. The study also demonstrates the utility of modeling as a tool to help prioritize investigations into the potential impacts of individual compounds on human health.