I'm kicking around the idea of building a small passive sonar for an autonomous submarine. I've looked through the net for parts and finding a good transducer for converting the sound underwater into an electrical impulse. After looking at parts I got into the piezoelectric materials used for doing this such as barium titanate or Lead zirconate titanate. From what I've read on the web, some of these materials are toxic.
My question is, are there piezoelectric materials that one could to build a sensor from scratch that does not possess the toxic qualities? Something that could preferably thrown in a pool w/ my kids and not give them or me any defects.