title: Relation of Prenatal Methylmercury Exposure from Environmental Sources to Childhood IQ.
abstract: BACKGROUND
  Although prenatal methylmercury exposure has been linked to poorer intellectual function in several studies, data from two major prospective, longitudinal studies yielded contradictory results. Associations with cognitive deficits were reported in a Faroe Islands cohort, but few were found in a study in the Seychelles Islands. It has been suggested that co-exposure to another contaminant, polychlorinated biphenyls (PCBs), may be responsible for the positive findings in the former study and that co-exposure to nutrients in methylmercury-contaminated fish may have obscured and/or protected against adverse effects in the latter.
  
  
  OBJECTIVE
  We aimed to determine the degree to which co-exposure to PCBs may account for the adverse effects of methylmercury and the degree to which co-exposure to docosahexaenoic acid (DHA) may obscure these effects in a sample of Inuit children in Arctic Québec.
  
  
  METHODS
  IQ was estimated in 282 school-age children from whom umbilical cord blood samples had been obtained and analyzed for mercury and other environmental exposures.
  
  
  RESULTS
  Prenatal mercury exposure was related to poorer estimated IQ after adjustment for potential confounding variables. The entry of DHA into the model significantly strengthened the association with mercury, supporting the hypothesis that beneficial effects from DHA intake can obscure adverse effects of mercury exposure. Children with cord mercury ≥ 7.5 μg/L were four times as likely to have an IQ score < 80, the clinical cut-off for borderline intellectual disability. Co-exposure to PCBs did not alter the association of mercury with IQ.
  
  
  CONCLUSIONS
  To our knowledge, this is the first study to document an association of prenatal mercury exposure with poorer performance on a school-age assessment of IQ, a measure whose relevance for occupational success in adulthood is well established. This association was seen at levels in the range within which many U.S. children of Asian-American background are exposed.
authors.affiliation: Department of Psychiatry and Behavioral Neurosciences, Wayne State University School of Medicine, Detroit, Michigan, USA.
authors.forename: Joseph L
authors.initials: JL
authors.lastname: Jacobson
authors.forename: Gina
authors.initials: G
authors.lastname: Muckle
authors.forename: Pierre
authors.initials: P
authors.lastname: Ayotte
authors.forename: Éric
authors.initials: É
authors.lastname: Dewailly
authors.forename: Sandra W
authors.initials: SW
authors.lastname: Jacobson
mesh_terms: D000293:Adolescent; D001110:Arctic Regions; D002648:Child; D015331:Cohort Studies; D004281:Docosahexaenoic Acids / Q000633:toxicity*; D004781:Environmental Exposure; D004785:Environmental Pollutants / Q000633:toxicity*; D005260:Female; D006801:Humans; D007360:Intelligence / Q000187:drug effects*; D008297:Male; D008767:Methylmercury Compounds / Q000633:toxicity*; D011078:Polychlorinated Biphenyls / Q000633:toxicity*; D011247:Pregnancy; D011297:Prenatal Exposure Delayed Effects / Q000139:chemically induced / Q000453:epidemiology*; D011792:Quebec / Q000453:epidemiology
chemical_list: D004785:Environmental Pollutants; D008767:Methylmercury Compounds; D004281:Docosahexaenoic Acids; D011078:Polychlorinated Biphenyls