1. Charge Question 5-1 Comment Summary for HHCB Peer Review Panel Meeting January 9, 2014

2. Issue 5. Environmental Risk Characterization. Environmental risk for HHCB is calculated by comparing the measured environmental concentrations of HHCB to the ecological concentrations of concern from toxicity studies for each risk scenario. The range of environmental concentrations is incorporated in the analysis by calculating risk for both mean and upper limit concentrations. Question 5-1: Please comment on the calculation of risk derived from the different datasets and how they account for environmental variability. Please provide specific recommendations as needed for improving the risk characterization and references to support any recommendations. Response Themes 1.Calculation of risk; level of conservatism 2.How variability is accounted for 3.Recommendations for improving risk characterization Question 5-1

3. Calculation of Risk Hazard assessment, not risk assessment (PC) – Evaluating possibility, not probability of risk – HQs rather than RQs? – Be sure HQ/RQ exceedances only indicate potential for risk Consider a Margin of Exposure (MOE) assessment (ACC) – Basically, inverse of RQ ratio (COC/Env. Conc.) – Suggested MOE threshold = 30 Same as RQ threshold of 0.33…seems more conservative than EPA?

4. Calculation of Risk Consider probabilistic and/or mode of action- based approaches (DS) – Probabilistic (or species sensitivity distribution?) approach, e.g., PNEC (HC 05 ?) – Adverse Outcome Pathways (Ankley et al. 2010) Explores linkage between molecular initiating event, and the adverse outcome at ecological level of organization (e.g., survival, growth, reproduction) – See also BG comment #6; pg. 38 Question: Ultimately, what RC approach meets EPA’s program objectives for this analysis?

5. Level of Conservatism Very conservative assessment (ACC, others) Level of conservatism not very transparent (BG) – Why particular UFs selected? – ECxx methods preferred over NOEC/LOEC methods Provides more transparent effect level, not as dependent on experimental design Ultimately, does level of conservatism meet specific EPA program objectives? (BG)

6. Variability Accounted For? Range likely representative, at least based on water/effluent based on exposure data (BG) – Concerned over limited soil/biosolids data; may not represent full range of variability Range of RQs likely OK, but can we evaluate exposure (and, hence, RQ) ranges using Monte- Carlo analysis? (LW) Toxicity data limited, so may not represent full range of sensitivities, and represents additional uncertainty (PC)

7. RC Improvement Suggestions Uncertainty analysis (PC) – Additional discussion, more explicit assumptions – Limited N for toxicity tests – Lack of half-lives for anaerobic conditions More information on data quality? (DH) – Do the data types and quality meet EPA program objectives? Evaluate future HHCB use scenarios (BD) – Are increasing use patterns accounted for?

8. RC Improvement Suggestions Calculate RQs for USGS maximum concentrations – Improve clarity and transparency around limited RQ exceedances in sediments; only 95 th percentile RQ in Table 3-8 Consider calculating RQs for effluent data (BG) – More representative of effluent-dominated systems. May lead to: RQ (max) = 2.48 RQ (highest mean) = 1.01