I got a package today with the "dead tree & fish" label on it & a
13-page safety data sheet inside. It turns out that desoldering braid
is so labelled because copper is "aquatic acute 1, H400" and "aquatic
chronic 1, H410". (The other component, rosin, is marked as "skin
sens. 1, H317".)

I'm a bit surprised that copper is apparently safe to contain & carry
drinking water but a hazard if dropped in water outside. What am I
missing here?