Sensitivity analysis of human health surface water quality criteria: a case study using perfluorooctane sulfonic acid

Human health surface water quality criteria (SWQC) for perfluorooctane sulfonic acid (PFOS) vary by up to five orders of magnitude between jurisdictions. The current study undertakes a probabilistic analysis to calculate a range of PFOS SWQC and rank input parameters based on their influence on criteria derivation. Probability distributions were used for exposure parameters (e.g., fish consumption rate, body weight, bioaccumulation factors), as well as the noncancer toxicity factor, which itself ranges over three orders of magnitude. Three distributions of the PFOS reference dose were evaluated: one based on animal data, one based on human data, and one based on both animal and human data. Using the three reference dose distributions, the 10th percentile SWQC range from 0.1 ng/L to 3 ng/L. Using the distribution based on human toxicity data only, approximately two thirds of the distribution of SWQC falls below typical analytical detection limits (around 1 ng/L). The sensitivity analysis identified fish consumption rate and PFOS toxicity factor as the most influential parameters, followed by bioaccumulation factors and relative source contribution. The application of probabilistic risk assessment as used in this study provides a useful tool for calculating a range of possible SWQC and understanding the relative importance of input parameters. The method of sensitivity analysis can be adapted to any chemical and target population.