Neuropsychological correlates of hair arsenic, manganese, and cadmium levels in school-age children residing near a hazardous waste site
Introduction
Many studies indicate that children exposed, at low levels, to metals such as lead (Pb) and mercury present signs of neurotoxicity, including reduced performance on neuropsychological tests and altered behavior (Bellinger and Adams, 2001). The extent to which low-level exposures to other metals, such as arsenic (As), manganese (Mn), and cadmium (Cd), are also neurotoxic is considerably less certain.
As has generally been considered to be a peripheral neurotoxicant, producing a clinical picture of severe polyneuropathy after acute poisoning. Recent mechanistic and neurobehavioral studies in animal models (Rao and Avani, 2004, Chaudhuri et al., 1999) and in humans (Calderon et al., 2001, Tsai et al., 2003, Wasserman et al., in press) suggest that this neurotoxicity includes the central nervous system as well. Mn, a transition metal, is both a nutrient and toxicant. Occupational exposures to Mn produce a clinical syndrome of memory loss, behavioral/mood changes and, in its final stages, a Parkinsonian-like motor dysfunction. Some studies suggest that Mn is a neurodevelopmental toxicant at environmental levels of exposure (Takser et al., 2003, He et al., 1994, Crinella et al., 1998). The central nervous system has generally not been considered to be an important target organ for Cd, although neurotoxicity has been reported in both adults and children (Bellinger et al., 2003).
In this cross-sectional pilot study, we evaluated the associations between the hair levels of As, Mn, and Cd and neurospsychological function and behavior in school-aged children. The study was conducted among children residing in Ottawa County, an area of northeast Oklahoma with a 100-year history of Pb and zinc (Zn) mining. Part of this region, called the Tar Creek Superfund site, was first listed on the U.S. Environmental Protection Agency's National Priorities List in 1983 and remains on the NPL (EPA site ID 0601269 (http://www.epa.gov/superfund/sites/npl/ok/htm). More than 75 million tonnes of mining waste (referred to as “chat”) was left on the surface in piles reaching as much as 200 ft in height. Chat contains metals other than Pb and Zn, including Cd and Mn. Mine tailings also contaminate more than 800 acres of flotation ponds in the Tar Creek region. Although As is not found in chat at levels above background environmental concentrations, Oklahoma is known to have high background levels of As. Due to community concerns about As, we included this metal in our study.
Section snippets
Study sample
In order to minimize a volunteer bias that might have resulted from community-wide requests for participants, the study sample was recruited from two science classes in the Miami, OK, school system. A letter describing the study was sent home with each child, along with a postcard for parents to return indicating interest in being contacted about participating. Positive responses were received from the parents of 32 of 80 children (40%), and appointments with the examiner (DCB) were scheduled.
Hair metal levels
Table 1 shows the hair metals levels of the 31 children. The correlations among the three metals measured were substantial (As and Mn: 0.65, p = 0.0001; As and Cd: 0.47; p = 0.008; Mn and Cd: 0.64; p = 0.0001). Arsenic levels were significantly lower in girls than boys (mean (S.D.) = 25.9 (4.0) parts per billion versus 11.0 (2.3) parts per billion, respectively; p = 0.002). Neither Mn nor Cd hair levels were related significantly to sex. Hair metals levels of American Indian and non-American Indian
Discussion
The major finding of this pilot study is that, in school-aged children, higher hair Mn and As levels, particularly, in combination, were associated with significantly lower scores on an IQ test, as well as on tests of verbal learning and memory.
Although the neurotoxicity of Pb is well established (Bellinger, 2004), relatively little is known about As and Mn neurotoxicity, particularly when exposure occurs during critical developmental periods. Oral administration of As trioxide increases
Acknowledgements
Supported by a Milton Fund grant from Harvard University to DCB (540-45496-624473-730001). ROW is supported by a grant from the National Institutes of Health, K23 ES00381. This work was also supported in part by a grant from the ATSDR Superfund Reconciliation & Reclamation Act, administered through the Association of Occupational and Environmental Clinics Association (AOEC), Washington D.C. The views expressed in this paper are solely those of the authors, and do not necessarily reflect the
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