title: Mercury, cadmium, and lead levels in human placenta: a systematic review.
abstract: BACKGROUND
  Placental tissue may furnish information on the exposure of both mother and fetus. Mercury (Hg), cadmium (Cd), and lead (Pb) are toxicants of interest in pregnancy because they are associated with alterations in child development.
  
  
  OBJECTIVE
  The aim of this study was to summarize the available information regarding total Hg, Cd, and Pb levels in human placenta and possible related factors.
  
  
  METHODS
  We performed a systematic search of PubMed/MEDLINE, EMBASE, Lilacs, OSH, and Web of Science for original papers on total Hg, Cd, or Pb levels in human placenta that were published in English or Spanish (1976-2011). Data on study design, population characteristics, collection and analysis of placenta specimens, and main results were extracted using a standardized form.
  
  
  RESULTS
  We found a total of 79 papers (73 different studies). Hg, Cd, and Pb levels were reported in 24, 46, and 46 studies, respectively. Most studies included small convenience samples of healthy pregnant women. Studies were heterogeneous regarding populations selected, processing of specimens, and presentation of results. Hg concentrations > 50 ng/g were found in China (Shanghai), Japan, and the Faroe Islands. Cd levels ranged from 1.2 ng/g to 53 ng/g and were highest in the United States, Japan, and Eastern Europe. Pb showed the greatest variability, with levels ranging from 1.18 ng/g in China (Shanghai) to 500 ng/g in a polluted area of Poland.
  
  
  CONCLUSIONS
  The use of the placenta as a biomarker to assess heavy metals exposure is not properly developed because of heterogeneity among the studies. International standardized protocols are needed to enhance comparability and increase the usefulness of this promising tissue in biomonitoring studies.
authors.affiliation: Subdirectorate for Health Promotion and Prevention, Madrid Regional Health Authority, Madrid, Spain.
authors.forename: María D
authors.initials: MD
authors.lastname: Esteban-Vasallo
authors.forename: Nuria
authors.initials: N
authors.lastname: Aragonés
authors.forename: Marina
authors.initials: M
authors.lastname: Pollan
authors.forename: Gonzalo
authors.initials: G
authors.lastname: López-Abente
authors.forename: Beatriz
authors.initials: B
authors.lastname: Perez-Gomez
mesh_terms: D015415:Biomarkers; D002104:Cadmium / Q000378:metabolism*; D004781:Environmental Exposure; D004784:Environmental Monitoring; D005260:Female; D006801:Humans; D007854:Lead / Q000378:metabolism*; D008628:Mercury / Q000378:metabolism*; D010920:Placenta / Q000737:chemistry*; D011247:Pregnancy
chemical_list: D015415:Biomarkers; D002104:Cadmium; D007854:Lead; D008628:Mercury