Mercury in Fly Ash - Hazardous in Concrete?

From Structural Engineer magazine:

For years structural engineers have incorporated fly ash into their concrete mix designs to produce high quality concrete, and its use as a cement replacement is increasing as engineers seek to reduce CO2 emissions. Questions have arisen recently over the appropriateness of incorporating fly ash into concrete due to concerns about the trace amounts of mercury found in the byproduct of coal combustion. Just as structural engineers were feeling that they were part of the solution to reduce CO2 emissions a monkey wrench was thrown into the works. This article hopes to answer some of the concerns regarding using fly ash in concrete.