Bromide ion is in fact essential to animal (including human) life. It's necessary in trace amounts for the production of a weird S=N double bond in collagen IV

Bromide ion is in fact essential to animal (including human) life. It's necessary in trace amounts for the production of a weird S=N double bond in collagen IV, in a process where it is briefly converted to the BrO- ion (the +1 oxidation state). This was only discovered fairly recently; getting a fruit fly diet sufficiently depleted in bromide for the deficiency to show up was difficult. Sea salt should have a fair amount of bromide in it. Bromine can be produced commercially by bubbling chlorine gas through sea water.