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ADVERSE HEALTH EFFECTS FROM ENVIRONMENTAL MANGANESE EXPOSURE.
Citation:
Hudnell, K. ADVERSE HEALTH EFFECTS FROM ENVIRONMENTAL MANGANESE EXPOSURE. Presented at International Neurotoxicology Association Meeting, Estoril, Portugal, June 17-22, 2001.
Description:
The ubiquitous element, manganese (Mn), is an essential nutrient, but toxic at excessive exposure levels. Therefore, the US EPA set guideline levels for Mn exposure through inhalation (reference concentration-RfC=0.05 ?g/m3) and ingestion (reference dose-RfD=0.14 mg/kg/day (10 mg/day for a 70 kg person)) with a modifying factor of 3 for water (0.047 mg/kg/day). The Mn drinking water equivalent level (DWEL) is 1.63 mg/L for adults (70 kg person consuming 2 L water/day). The Agency has not set a regulatory maximum contaminant level goal (MCLG) for Mn, which would be based on the DWEL for the most susceptible population and modified by consideration of the relative source contribution (e.g., 20% of ingested Mn intake through water). However, the Agency has established an advisory secondary maximum contaminant level (SMCL=50 ?g/L) based on aesthetic concerns. Recent evidence from environmental exposure studies is relevant to assessing the adequacy of these levels for protecting human health.
Derivation of the Mn RfC (0.05 ?g/m3) was based on observations of neurobehavioral deficits in workers with subchronic exposure to mean airborne Mn at 150 ?g/m3 and adjustments for continuous exposure and uncertainty factors. A recent population-based study observed subtle Parkinson-like alterations in adults with mean airborne-Mn exposure of 0.02 ?g/m3 (range=0.01-0.035) and a low mean drinking-water level of 4.4 ?g/L [1]. Residence in areas with higher airborne-Mn levels was associated with higher blood-Mn levels, which were associated with neurologic deficits, particularly in men > 50 years of age. A study where Mn drinking-water levels ranged from 4-15, 82-253, and 1,800-2,300 ?g/L across three areas, but air Mn levels were unreported, also observed Parkinson-like signs in men > 50 years of age [2]. A composite Parkinson's score increased with Mn drinking-water levels, as did hair Mn levels. Another study observed learning and neurobehavioral deficits and neurotransmitter alterations in school children where Mn drinking-water levels ranged from 241-346 ?g/L, relative to the control children's range of 30-40 ?g/L [3,4]. Hair Mn levels were elevated in the affected children, as were Mn levels in field-irrigation sewage water in the exposed town, but air levels were unreported. The Mergler study observed adverse health effects at airborne-Mn exposure levels below the RfC, but effects have not been reported at drinking water-Mn levels below the SMCL. Further research is needed to describe relationships between total Mn exposure, body burdens, and health outcomes in adults, children and susceptible populations. This abstract does not necessarily reflect the views of the Agency.