Gosh I feel sorry for you. i am not convinced 2 4 d drift caused this. First off, 2 4 is a broad leaf chemical so when u say ur brome was already smoked, that's not from 2 4 d. Brome is a grass n not killed by 2 4 d unless possibly sprayed by a very heavy dose. If they sprayed only a day ago there is little chance a decrease in oxygen could occur as plants don't decay a day after being sprayed. Something else is going on. Be interesting to see what you find out. Hope you get an answer.
