An official website of the United States government.

We've made some changes to If the information you are looking for is not here, you may be able to find it on the EPA Web Archive or the January 19, 2017 Web Snapshot.

EPA's Study of Hydraulic Fracturing and Its Potential Impact on Drinking Water Resources

Overview of Chronic Oral Toxicity Values for Chemicals Present in Hydraulic Fracturing Fluids, Flowback and Produced Waters

Yost, et al. Environmental Science and Technology. April 2016.


EPA evaluated the availability of chronic (lifetime) oral toxicity values for chemicals reported to be used in hydraulic fracturing fluids and/or found in flowback or produced waters from hydraulically fractured wells. Chronic oral toxicity values for cancer identify an estimate of the increased cancer risk from a lifetime of oral exposure to a substance.  For effects other than cancer, the value represents the amount of a substance that one can ingest every day for a lifetime that is not anticipated to cause harmful health effects. EPA has identified a list of 1,173 chemicals associated with hydraulic fracturing activities nationwide. Overall, chronic oral toxicity values were available for 147 of the chemicals identified. The study found that chronic oral toxicity values were lacking for 1,026 of the chemicals and that a significant data gap exists. This lack of toxicity values is not unique to the hydraulic fracturing industry; in fact, there are estimated to be tens of thousands of chemicals in industrial use that have not undergone significant toxicological evaluation. This suggests that risk assessors and researchers will have to turn towards alternative data sources in order to identify potentially hazardous chemicals, and prioritize chemicals for further research. This work was done as part of EPA’s Study of the Potential Impacts of Hydraulic Fracturing for Oil and Gas on Drinking Water Resources.

Note: EPA is in the process of securing access to the submitted manuscript.