I'm very surprised. I've spent many hours analyzing incoming raw material ( often times clays) usually for heavy metals. Clays are often the source of heavy metals when medical issues come up.

interesting! I've seen people using clay to filter water in Nicaragua, but I don't have an understanding of how that worked.

Hmm. This is surprising to me too. Iron-rich clay can readily adsorb arsenic under oxygen-rich conditions (this is actually the root of Bangladesh, and most of SE Asia's, arsenic contamination -- when the electrochemical conditions change, iron becomes soluble and releases the sorbed arsenic into the water), so I see how the clay could be useful. It doesn't make sense to me how this would sorb lead... My guess is just that it blocks suspended solids, which contain lead, rather than the clay or bamboo actually sorbing lead. In any case, this is interesting. I'd like to look for the journal papers published on this method, which would hopefully discuss the chemistry and provide data about its effectiveness.

For a project I was looking at toxins in water and read about sunflower stalks being used for this purpose. There was even a startup in NJ, but not sure they still exist. Here's one report on the topic. https://pdfs.semanticscholar.org/c095/24ae9b4640fee57e3bc21b4e7316e9a61722.pdf