I think it does - but just because it's green doesn't mean it's radioactive - in fact, most highly radioactive stuff is produced in such small quantities you wouldn't be able to see it anyway.
just have 2 textures for such an instance; one for the ground and dirt, and the other for grass which wouldn't be smokey, but rather.. 'patchy' with little grass streaks, and then also lower the amount of smoke that comes out when your on the grass down to a lower amount
I think if you actually see glowing radioactive material out in the open without any barrier between you and it, you're probably going to die real soon...
My father once told me he (or a relative of his) had a periodic table with little pieces of all (or most) the elements actually on it. One of these was Uranium.
And BTW, a small little piece of uranium will not hurt you unless it enters your body. It cannot get through your skin. You'd be at risk of skin cancer depending how long you are exposed, and how much.