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ENVIRONMENTAL MANGANESE: GUIDELINE EXPOSURE LEVELS, EVIDENCE OF HEALTH EFFECTS AND RESEARCH NEEDS.
Otto, D A. AND H. K. Hudnell. ENVIRONMENTAL MANGANESE: GUIDELINE EXPOSURE LEVELS, EVIDENCE OF HEALTH EFFECTS AND RESEARCH NEEDS. Presented at 8th International Symposium on Neurobehavioral Methods and Effects in Occupational and Environmental Health, Brescia, Italy, 6/23-26/2002.
Introduction. The ubiquitous element, manganese (Mn), is an essential nutrient, but toxic at excessive exposure levels. The US EPA, therefore, 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 and determining research needs. Evidence. 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 chronic exposure to airborne-Mn at levels near the RfC in an area with 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 altered serum neurotransmitter levels 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. Other studies reported associations between violent behavior and elevated levels of Mn or Mn and Pb, but did not adequately identify exposure sources, environmental levels or body burdens. Conclusions. Effects from excessive Mn exposure may be qualitatively different across the life span. Parkinson-like alterations may occur in older adults chronically exposed to airborne Mn levels near the RfC or drinking water levels about 5 fold above the SMCL. Similar environmental exposures may impact learning and behavior in children and younger adults. Research Needs. Studies are needed which investigate interactions between age, total Mn exposure through air, water, and food, and adverse effects on learning, behavior, neuropsychiatric status, and health outcome. Special attention should be given to populations in areas where air and water Mn levels are near the RfC and SMCL, respectively. Research should address potential interactions between Mn exposure, concurrent exposures, pre-existing clinical conditions, and lifestyle factors. This is an abstract of a proposed presentation and does not necessarily reflect EPA policy.