The one I take Fibroboost from Nutricology is "FibroBoost is manufactured in accordance with FDA approved current Good Manufacturing Practices (“cGMP”)."

As the stuff is processed, it is also filtered and then tested for impurities.

The Klamath Lake blue-green algae in Oregon was what sounded the whistle on Seaweed being a sponge for metals and such. Sure problems can be anywhere, but it is all in how it is tested and filtered. Nobody wants a lawsuit on their hands, so it would behove any manufacturer not to cut corners on testing. And the one I use doesn't.