We were in the Caribbean this time last year, and saw TBT antifouling in the local swindleries. And on top of the basic toxic stuff, if you want to keep your boat in a seriously weedy environment, you can buy extra Tri Butyl Tin powder to up the potency of your antifouling even more. HWMBO was well impressed. Wanted to buy some to bring home.
To be fair, it is very potent, and because our boats spend more time stationary than moving, the concentrations immediately local to out moorings can get very high. Sufficient to knock out shell fish, and corals in the Caribbean.