If you use the media too much it can build up a concentration of lead. I met a guy once at a match in VT who had developed lead poisoning from breathing the dust from his tumbler. Best to use it 8 to 10 times max and dump it (I use the stuff to absorb oil, etc. in my garage) before the lead becomes a problem. If you follow this method, you will cosume a lot of corn cob, but it is cheap health insurance. I use about 50 lb a year.