It might have a slight effect, however garlic, eggs, and other better sulfur sources probably work much better. I realize cocoa tastes better than raw garlic. MSM is more controversial though.
The issue isn't just detoxifying from mercury, but also from candida toxins and other toxins. Acetylaldehyde is a toxin present in many fragrances, cigarrette smoke, diesel fumes, and is what drinking alcohol is metabolized into.