Illustrative case using the RISK21 roadmap and matrix: prioritization for evaluation of chemicals found in drinking water

Abstract

The HESI-led RISK21 effort has developed a framework supporting the use of twenty-first century technology in obtaining and using information for chemical risk assessment. This framework represents a problem formulation-based, exposure-driven, tiered data acquisition approach that leads to an informed decision on human health safety to be made when sufficient evidence is available. It provides a transparent and consistent approach to evaluate information in order to maximize the ability of assessments to inform decisions and to optimize the use of resources. To demonstrate the application of the framework's roadmap and matrix, this case study evaluates a large number of chemicals that could be present in drinking water. The focus is to prioritize which of these should be considered for human health risk as individual contaminants. The example evaluates 20 potential drinking water contaminants, using the tiered RISK21 approach in combination with graphical representation of information at each step, using the RISK21 matrix. Utilizing the framework, 11 of the 20 chemicals were assigned low priority based on available exposure data alone, which demonstrated that exposure was extremely low. The remaining nine chemicals were further evaluated, using refined estimates of toxicity based on readily available data, with three deemed high priority for further evaluation. In the present case study, it was determined that the greatest value of additional information would be from improved exposure models and not from additional hazard characterization.

Keywords: Drinking water; RISK21; integrated evaluation strategy; prioritization; risk assessment; tiered approach.

Figure 1.

General conceptual framework of the RISK21 approach (Embry et al. 2014).

Figure 2.

Overview of the case study evaluation steps.

Figure 3.

First evaluation. RISK21 matrix plot illustrating the use of the TTC approach. The 13 chemicals belonging to Cramer Class III (of 20 in total) are plotted to demonstrate exposure (calculated based on solubility) relative to the Cramer Class III threshold of 1.5E-3 and which chemicals (toxaphene & HCB) fall below this value of 3 μg/kg/day. (This illustrates the flexibility of the RISK21 matrix approach.).

Figure 4.

Third evaluation. Matrix plot of the nine remaining chemicals (point estimates for both exposure and toxicity). Those circled are the three designated high priority for further evaluation based on proximity to the yellow zone.