Water Quality Standards

Manganese is one of the more abundant metals in the earth´s crust and usually occurs together with iron. Dissolved manganese concentrations in ground and surface waters that are poor in oxygen can reach several milligrams per litre. On exposure to oxygen, manganese can form insoluble oxides that may result in undesirable deposits and colour problems in distribution systems. Daily intake of manganese from food by adults is between 2 and 9 mg.

Manganese is an essential trace element with an estimated daily nutritional requirement of 30–50 µg/kg of body weight. Its absorption rate can vary considerably according to actual intake, chemical form, and presence of other metals, such as iron and copper, in the diet. Very high absorption rates of manganese have been observed in infants and young animals.

Evidence of manganese neurotoxicity has been seen in miners following prolonged exposure to dusts containing manganese. There is no convincing evidence of toxicity in humans associated with the consumption of manganese in drinking-water, but only limited studies are available.

Intake of manganese can be as high as 20 mg/day without apparent ill effects. With an intake of 12 mg/day, a 60-kg adult would receive 0.2 mg/kg of body weight per day. Allocating 20% of the intake to drinking-water, and applying an uncertainty factor of 3 to allow for possible increased bioavailability of manganese from water, gives a value of 0.4 mg/litre.

Although no single study is suitable for use in calculating a guideline value, the weight of evidence from actual daily intake and studies in laboratory animals given manganese in drinking-water in which neurotoxic and other toxic effects were observed supports the view that a provisional health-based guideline value of 0.5 mg/litre should be adequate to protect public health.

It should be noted that manganese may be objectionable to consumers even at levels below the provisional guideline value (see Acceptability aspects).