The study I saw implied that most of the metals were on the surface as dust, so you could rinse about 60% off. I would expect the bran, containing a lot of the protein and minerals, would have more in it, and also make it more difficult to remove surface contamination.

Incidentally there are also some studies challenging the heavy metals in broadleaf plants link. The newer studies suggest surface contamination is a much bigger factor. That's also another 'pro' in the column for cleaning your vegetables with white vinegar instead of soap. Acids are pretty good at dissolving metal dust, especially from residual contamination near roads from leaded gas. My yard tested high.