[3H]-NA converted into [3H]-H2O???

[XZHENG at GAMMA.IS.TCU.EDU]

I am a graduate student working on 3H-NA uptake by synaptosomes. I was told
that 3H on the phenyl ring of NA can be converted into 3H-water so the 
counting may not reflect the total NA taken up by synaptosomes. Any reference
on this issue? Or should I use [14C]-NA instead?
Alan Zheng