Unfortunately, I don't have anything readily available. I went through an engineering school that, at the time, won an award for concrete research. This question did come up because the fly ash contains mercury.
There is a lot of research on this because of how often concrete is used for everything. There is some leaching but it is extremely slow and extremely low levels. This is why it is allowed to be used for drinking water tanks and pipes.
Keep in mind this is also only with fly ash concrete (and maybe blast furnace slag concrete). The fly ash is usually only like 5% of the total mix and most of it is also non-toxic. Normal concrete is non-toxic.
Fly ash is not an inert filler in concrete. It chemically reacts with cement and water to form minerals (just like cement does) and this helps lock up many of the metals in it.
If you google it you can find a lot of articles. If you go to google scholar, you will also find a lot but most of it they will want you to pay for. Here is one that I found while searching.
http://infohouse.p2ric.org/ref/45/44766.pdf
