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

Estimating the Potential Toxicity of Chemicals Associated with Hydraulic Fracturing Operations Using Quantitative Structure-Activity Relationship Modeling

Yost, et al. Environmental Science & Technology. May 2016.


Researchers expanded upon a previous study that reported that chronic (lifetime) oral toxicity values are lacking for the majority of chemicals reported to be used in hydraulic fracturing fluids and/or found in flowback or produced waters from hydraulically fractured wells (1,026 of 1,173). To facilitate the evaluation of chemicals that lack chronic oral toxicity values, EPA utilized a quantitative structure activity relationship (QSAR) model to develop estimates of potential toxicity for the chemicals, in addition to presenting a framework for using the QSAR-based estimates for chemical ranking and prioritization. QSAR is a computer-based modeling technique where data on chemical structures and toxicity information for tested chemicals are used to estimate the toxicity of other, untested chemicals.

In total, high-confidence QSAR estimates were available for 389 of the 1,026 chemicals on EPA’s list that lack chronic oral toxicity values, including a subset of chemicals that are frequently used in hydraulic fracturing fluids. Results indicate that this QSAR model significantly increases the availability of toxicity data for the chemical list, and provides information that is useful to risk assessors for chemical ranking and prioritization.

Note: This study does not make any judgment about how, or the extent to which, people may be exposed to these chemicals or mixtures of these chemicals as a result of hydraulic fracturing activity.