An open-source shiny tool for the derivation of human health water quality criteria using probabilistic risk assessment

Under Section 304(a) of the Clean Water Act, the U.S. Environmental Protection Agency (EPA) is mandated to develop national recommended human health water quality criteria (HHWQC) which represent the concentration of specific chemicals, biologicals, and physical conditions in ambient water not expected to adversely affect human health. To date, EPA has set HHWQC using the deterministic approach for key exposure parameters for criteria development. However, these methods do not account for variability or uncertainty, and may substantially misestimate risk for the general population. Probabilistic approaches address these issues, but they have been hampered by several factors, including time and resource complexity, technical expertise requirements, lack of amenable open-source software, and lack of certainty regarding EPA approval. Here, we describe a new R Shiny tool, Surface Water Probabilistic Risk Online, developed for deriving HHWQC using either deterministic or probabilistic approaches to derive HHWQC for 105 chemicals for multiple risk management scenarios simultaneously. For the probabilistic approach, alternate distributions of body weight, fish consumption rate, and daily water intake can be parameterized using the tool's custom distribution module. The results of the tool can be aggregated and downloaded for record-keeping, reporting, and further analysis purposes. Given the flexibility and simplicity of the tool, development of probabilistic-based HHWQC may become more accessible for States' upcoming criteria reviews.