I did use 4 of them in a fishless pond over the summer. I had set it up as part of an outside basking area for a box turtle. The turtle spent maybe a total of 10 hours out there, in and out of the water. That is probably not enough "exposure" to give any serious indication of possible problems (and no, I did not intend to use the turtle as an indicator of possible problems with the bricks...I just did not consider the potential issues when I set up the pond). The pond itself seems remarkably healthy, some unknown plantlife started up by itself, some algea, water is clear (has a filter on it) and smells good.
Does any of this hint that the bricks might be ok? I could use just the 4 that have been in the pond for three months.
Edit: I should add that it is a fairly small volume of water, maybe 20 gallons max. And I never changed the water, just added for evaporation. Rainwater took care of most of that, really.
Bricks might affect pH? I do add crushed coral to my filter, otherwise my pH drifts down. With the coral, it stays a steady 7.2-7.6.