Zinc has been evaluated by JECFA in 1966 and 1982. The PMTDI is established to 0.3-1 mg/kg bw, based on clinical studies in which up to 600 mg of zinc sulfate (equivalent to 200 mg elemental zinc) has been administered daily in divided doses for a period of several months, without any reported adverse effects, including effects on blood counts and serum biochemistry. There is a wide margin between nutritionally required amounts of zinc and toxic levels.
WHO proposed in 2003 that, taking into account recent studies on humans, the derivation of a guideline value was not required at the time. It was stated however, that drinking-water containing zinc at levels above 3 mg/litre may not be acceptable to consumers based on taste considerations.