I've started looking up everything that I never thought to in the past on the database-coco coir, sphagnum, ewc, etc. It's really interesting, and it's easy to see how these metals build up to harmful levels in a grow. I'm determined to come up with a mix that has as close to zero heavy metals as possible, but I keep running into problems. The latest "eye opener" is earthworm castings. The best deal for EWC on Amazon is the 30 lb bags of "Red Wiggler" castings-I've bought at least 6 bags of this stuff in the past. Well, these castings have 5 ppm Arsenic, and a whopping 16 ppm LEAD. Most of the castings I looked up were similar, and my thinking is that since we feed the worms a lot of these same rock dusts, they are concentrating the heavy metals in their castings. Even things like perlite and pumice can have heavy metal contamination-the regulations here are meant to protect corporate profits not the consumer, so don't assume that simply because something is for sale, it's not going to hurt you. I've been able to find untainted product replacements for almost all of these inputs however, with the exception of the rock dusts (which are pretty bad), insect frass (another surprise), and a few others. Crustacean shell is usually high in arsenic and cadmium, but many shrimp meals are "not detectable." I know this is a tough pill to swallow for a lot of people who have invested a lot of time, money, and energy into their living soils, but the entire goal is better health for you and the environment, right?