Hmmm, I am suspicious. So a one breath diver happens to be filming on one breath and a dog end appears?
In addition the fish dont eat it but bounce around it as fish do. Unlikely to be toxic.
However that detracts from the real problem of rubbish in the sea and how it is stopped a problem I really cant see an answer to. Even if the West, who can afford it, manage to deal with their waste effectively poorer nations cant and wont. And as for dog ends can you imagine telling all those poor people around the world they must take their fag ends back home with them after being out on the water?