I have some zinc bolts in mine, and some stainless also. I have cooked on it for over a year and a half, and I am still around along with my family. You would have to get it awfully hot to get enough bad fumes to hurt anything.
If it's only bolts there isn't enough area of the zinc to matter anyway. Now if you were using a zinc coated grill, you might have a problem. That is my opinion, but wait for the "zinc police" to chime in. Good luck! Welcome to the DRUM CORPS.
UDS, cheap o grill, rusted chimney, yeller wannabe thermo pen, Maverick ET 732, 1950 model wife.