"Sponges with notable accumulations of bromine and iodine compounds in the fibers of the skeleton were charred and used, in ancient times, for fumigation. In Microciona prolifera the iodine content can be 0.3 percent of the total dry weight."
Microciona is also known as the Redbeard sponge, it occurs in the Gulf of Mexico among other places. It has long been used in studies of cell dissociation and reaggregation. (You can push it through a strainer and it will crawl back to reassociate itself like the Terminator). It lives of of sponges and grows/reproduces very quickly when fed with the bacteria of human feces, such as E. coli. I believe it has a silicon skeleton.
So, as thought, this seems to be a dead end, unless you are willing to create a sponge farm (which you could feed with your own shit) or import from some place you can obtain them cheaply.
Information from "Living Invertebrates" by Pearse and Buchsbaum
Wow, just noticed that I got my first utfse. Shouldn't take tfse for granted never would have guessed that this was discussed. My bad, won't happen again.
