It's not so much that we don't understand whether these compounds pose a risk to human health; the question is whether they're occurring in surface waters as a result of the fracking activity. That's the question, frankly, that we don't know.... There have been international studies. We've looked at the range of literature that has been published on this and, frankly, the results are mixed.
On May 12th, 2015. See this statement in context.