Water Quality Standards

Concentrations of molybdenum in drinking-water are usually less than 0.01 mg/litre. However, in areas near mining sites, molybdenum concentrations as high as 200 µg/litre have been reported. Dietary intake of molybdenum is about 0.1 mg per day per person. Molybdenum is considered to be an essential element, with an estimated daily requirement of 0.1–0.3 mg for adults.

No data are available on the carcinogenicity of molybdenum by the oral route. In a 2-year study of humans exposed through their drinking-water, the NOAEL was found to be 0.2 mg/litre. There are some concerns about the quality of this study. An uncertainty factor of 10 would normally be applied to reflect intraspecies variation. However, as molybdenum is an essential element, a factor of 3 is considered to be adequate. This gives a guideline value of 0.07 mg/litre (rounded figure).

This value is within the range of that derived on the basis of results of toxicological studies in animal species and is consistent with the essential daily requirement.