Iodine and bromine have been known to occur in sponges since the early part of the nineteenth century. Since then a large number of analyses, primarily of the bath sponge but also of other sponges, have been reported. Both iodine and bromine have been found in most cases, although in greatly varying amounts....
Low, Eva M.. 1949. "Iodine and bromine in sponges." Journal of Marine Research 8, (1). https://elischolar.library.yale.edu/journal_of_marine_research/707