THE TOXICOLOGY OF MANGANESE IN DRINKING WATER
Report No FR0313
Assessment of any risks posed to public health by the presence of manganese in drinking water at typical and elevated levels will help ensure that manganese will not become a future cause for public health or political concern.
To review the available data on human exposure to manganese and on its mammalian toxicity and bioavailability, in order to assess its significance to human health in relation to drinking water.
Manganese is routinely detected in UK drinking waters- Its presence in drinking water at levels above 20 µg l-1 leads to discoloration of the water, laundry and fixtures. The MAC of 50 µg l-1 in the drinking water regulations is based on these aesthetic properties, and levels in treated waters are generally below this value. However, due to encrustation of manganese in pipes and the presence of a manganese depositing biofilm, higher levels may be detected in distribution. The significance of manganese in drinking water with regard to consumers' health needs to be determined, as concern has been expressed about the neurotoxic effects of manganese.
Manganese is usually detected in UK drinking waters below 50 µg l-1 However, in some situations elevated manganese levels occur due to `pick up' from the encrustation of distribution pipes. Where the concentration is within `normal' limits, the major source of manganese exposure for the general public is through the diet and the contribution from water is minimal. However, where levels are substantially increased, the intake from water will contribute significantly to total daily intake. Furthermore, chemical forms of manganese, variations in diet and metal interactions have been shown to affect the bioavailability, and this raises questions regarding differences between manganese bioavailability from food and water. It appears that soluble manganese is one of the most readily bioavailable forms. However, it appears to be unlikely that humans will encounter the high levels of manganese that cause toxic effects in laboratory animals.
The major toxic effects are seen following long term occupational exposure to manganese ores and dusts. These toxic effects manifest as weakness, anorexia, muscle pain, apathy, slow speech, `masklike' facial expression and slow movement of the limbs. The levels of exposure which result in these effects are greatly in excess of those encountered in drinking water.
It has been suggested that the bioavailability of manganese is increased in water when compared to food. This should be examined in greater detail. There is also a need to determine the forms of manganese present when discoloration occurs and to determine their relative bioavailability. The US Environmental Protection Agency are currently devising methodologies for bioavailability studies of metals (including manganese) in water. These will be discussed in Autumn 1992, and the results of this working group should give a standard procedure for assessing metal bioavailability, including manganese.
The reliability of the published data on manganese toxicity via drinking water is questionable, including a recently published study which reported neurotoxic effects in people consuming tap water high in manganese. It is therefore recommended that any such studies are critically appraised in order that water suppliers are able to provide informed comment.
Published information on the bioavailability, metabolism and toxicity of manganese to humans and laboratory animals is reviewed and evaluated. This evaluation is considered along with information on the various sources of public exposure to manganese (including water), in order to determine whether its presence in drinking water poses a threat to public health.
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