POPs blood levels down in a sample of pregnant US women.

Jun 23, 2009

Wang, RY, RB Jain, AF Wolkin, CH Rubin and LL Needham. 2009. Serum concentrations of selected persistent organic pollutants in a sample of pregnant females and changes in their concentrations during gestation. Environmental Health Perspectives doi: 10.1289/ehp.0800105.


First time expectant mothers in the US have much lower blood levels of selected persistent organic pollutants than women did before the chemicals' ban and restrictions on use and emissions.

Blood levels of some of the most dangerous compounds are decreasing in people since they were regulated some 40 years ago, finds a study comparing first time pregnant women from two different generations.

The results are consistent with prior studies and with what would be expected since the chemicals were banned or limited in the 1970s in the United States. Researchers compared levels of persistent organic pollutants (POPs) in the blood of women sampled between 1959-1966 and women from 2001-2002.

Encouraging is the finding that levels of a PCB indicator fell drastically, from 140 nanograms per gram in women sampled between 1959-1966 to about 8 nanograms per gram in women from the more recent sample. Still, a metabolite of the insectide DDT, which has not been used in the US for 30 odd years, was detected in all of the women's blood.

Levels of the compounds sampled varied throughout the pregnancy. In general, levels remained steady between first and second trimesters but increased during the third. The increases – statistically significant for PBDDs and PCBs – are likely due to the pollutants being released from body fat that is used to produce breast milk.

Chemicals categorized as persistent organic pollutants – POPs – pollute the environment and are found in people and wildlife. The long-lived compounds can travel long distances, tend to accumulate in fat and cause a variety of health effects.

The 2001 Stockholm Convention named 12 of the most harmful POPs, including polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) and selected organochlorine pesticides such as dichlorodiphenyltrichloroethane (DDT). Even though the US banned and limited the chemicals' emissions in the mid- to late 1970s, people are still exposed to low levels, mainly through food and diet.

POPs are of interest to researchers because exposure can result in disturbance of the endocrine, reproductive, and immune systems; neurobehavioral outcomes and possibly cancer.

During pregnancy, these chemicals can be released from fat where they are stored and move around the body, exposing the mother and her fetus. First time mothers are a good group to study and compare, because they have not had prior pregnancies or breastfed, both of which can reduce POPs levels.

The authors reviewed chemicals and chemical metabolites of first-time pregnant females living in the United States who participated in the National Health and Nutrition Examination Survey (NHANES) during 1999-2002. NHANES is large study designed to assess the health and nutritional status of adults and children in the United States. They evaluated PCDDs, PCDFs, some types of PCBs, organochlorine pesticides and selected insecticide metabolites.

The findings in this study are limited by the cross-sectional design, use of self-reported data for reproductive history and small sample size.