Can expired C2 and C2A1 filters (m40 and MCU 2/p gas masks)protect against most biological attacks and teargas?

All i really want is protection against tear gas and most biological pathogens, but i have also read that because the C2 style filters use radioactive chromium as part of the filtering agent and using it would be more dangerous than going without a mask (due to the chromium's decomposition and or expiration), is it worth getting these older filters or splurging on the expensive ones (in which case i would have to hope for a an N.B.C attack as an excuse to use them)