The placenta forms in eutherian mammals, and is responsible for the nutrition of the developing fetus. However, maternal exposure to environmental pollutants both before and during pregnancy may result in the passage of toxins through the placental barrier and into fetal tissues. The placenta is the only organ derived from both maternal and fetal tissues, and establishes a link between the fetus and the environmental exposures of the mother. The analysis of placentae for the presence of environmental pollutants offers the possibility of exposure measurements in both the mother and the developing fetus. Specifically, trace element determination in human placentae may reveal fetal nutritional requirements, as well as identify potential indicators of negative health effects in both the mother and fetus.;The principal goal of this project is to analyze approximately 160 archived human term placental tissues (placenta body, placenta membrane, and umbilical cord) for essential trace elements, such as copper, zinc, and selenium, nonessential trace elements, including mercury, lead, and cadmium, and the rare earth elements of the lanthanide series. Sample preparation procedures focus on trace element homogeneity within the placenta, and contamination prevention. Analytical methodologies based on inductively coupled plasma mass spectrometry (ICP-MS) and electrothermal atomic absorption spectrometry (ETAAS) are developed and validated for all analytes of interest, using a variety of quality control materials. Subsequently, total element concentrations in each tissue component are measured and compared. Possible inter-element correlations within each tissue component are identified, as well as potential associations between analytical measurements and selected demographic and obstetric variables collected from the population studied.;Results indicate that the placenta largely accumulates cadmium, an element strongly correlated with maternal smoking behavior. Lead and mercury are easily transported into fetal tissues. Placental concentrations of rare earth elements followed the typical abundance pattern of these elements in Earth's crust, suggesting natural sources of exposure. Inter-element correlations were found for rubidium and cesium, as well as for aluminum and other bone-seeking elements, such as lead, lanthanum, uranium, barium, and strontium. Manganese in the placenta was positively correlated with infant growth variables, including birth weight, length, and head and chest circumference.