JK, selenium probably binds tighter to mercury than DMSA does, and it forms an insoluble salt that doesn't get excreted.
Studies on DMSA and Zinc showed DMSA did not raise zinc excretion in the urine to any significant amount (though it did very slightly), so it most likely does not have the same effect on chelation that selenium does. I would guess mercury would still bind tighter with the DMSA than the Zinc would so it shouldn't be a problem.
As for vitamin C, here is a study that showed 1g of ascorbic acid daily reduced naturally produced anti-oxidants, and signficantly reduced endurance during exercise. This study was done on both humans and rats with the same results
I never trusted, nor tried mega-dosing of vitamin C. I know animals naturally produce there own vitamin C, and that humans don't have that ability anymore, but I'm pretty sure we have evolved some other mechanism to make up for that loss.
