Here is what I read from a mercury toxic book written by a bio chemist "Andy Cutler" on NAC.

"Patients who have imparied metabolic conversion of cysteine to taurine and sulfate may respond negatively to NAC, though much less so than to cysteine itself. NAC is also much more effective in elevating liver glutathione than either cysteine or glutathione.

Those who have low glutathione or glutathione conjugation on the liver detox test are likely to benefit from NAC (600 - 4,000 mg/day).

People who are sensitive to paint fumes, exhaust fumes, etc are likely to benefit from NAC".

It helps the liver by increasing glutathione and therefore aids with the elmination of toxic metals, but is no replacement for proper chelation. I hope this helps.