CEHN Articles of the Month, February 2015 Issue
Preconception Maternal and Paternal Exposure to Persistent Organic Pollutants and Birth Size: The LIFE Study
Authors: Candace A. Robledo, Edwina Yeung, Pauline Mendola, Rajeshwari Sundaram, Jose Maisog, Anne M. Sweeny, Dana Boyd Barr, and Germaine M. Buck Louis
Persistent organic pollutants (POPs) are chemicals used for pest and disease control, crop production, and industry. There are a number of different classes of POPs including polychlorinated biphenyls (PCBs), which were once used for their non-flammability and chemical stability in things like transformers, insulation, and other electrical products; polybrominated diphenyl ethers (PBDEs), which are flame-retardants that are used in a variety of foam and plastic products, including flooring, furniture, and electronics; perfluorinated chemicals (PFCs), which make everyday products like cookware, mattresses, and carpets resistant to stains, grease, and water; polybrominated biphenyls (PBBs), which are non-flammable chemicals that were once used in things like televisions, computer monitors, and textiles; and organochlorine pesticides (OCPs), which are used for mosquito control and agriculture.
Many POPs do not degrade, or break down easily, and thus they persist for many years, even decades, in the environment. Thus, even POPs whose production has been banned pose continued threats to human health. POPs can easily travel long distances through the air before being deposited, and can thus be found all over the world. Human exposure is via direct contact with these chemicals in our living and working environments, through drinking water, and/or through consumption of contaminated foods, particularly dairy products, meats and seafood, and especially those animal products with high fat content, because POPs accumulate in fatty tissues. Accordingly, POPs build up in the fatty tissues of humans. Many are highly toxic and can cause a variety of health problems, including cancers, damage to body systems, and birth defects or child development issues.
The presence of POPs in maternal blood, umbilical cord blood, and breast milk has prompted studies examining the connection between the presence of POPs in maternal blood and the development of the fetus as measured by birth weight. Correlations between presence of POPs in maternal blood and a lower birth weight were found; however, these studies did not account for the presence of POPs before conception, nor did they account for possible effects of POPs in paternal blood.
The LIFE study aims to address the gaps in previous studies on POPs and fetal development by considering paternal POP blood levels in addition to maternal POP blood levels, and by measuring these levels before conception. The authors hypothesized that the presence of POPs in both maternal and paternal blood serum samples taken before conception is associated with low birth size measurements.
Between 2005 and 2009, couples living in Michigan and Texas who were planning a pregnancy and also likely to have significant exposure to environmental chemicals were identified. The couples were examined for basic health and fertility indicators as well as for the presence of 63 POPs from five major classes (OCPs, PBDEs, PFCs, PBBs, and PCBs) in their blood. In total, 501 healthy couples with confirmed POP exposure were recruited for the LIFE study. These couples were closely followed to determine the date of conception of an eventual 234 single-baby births. Mothers were instructed to record four birth size measurements--head circumference, length, weight, and ponderal index (a height-to-weight ratio)--on a birth announcement sheet to be returned to the study. When interpreting the birth size data, the babies were separated into female and male categories in order to eliminate sex as a confounder, and then various statistical methods were used to determine the relationship, if any, of POP concentration levels in parental blood before conception and the birth size measurements.
Concentrations of various POP compounds in both the mothers’ and fathers’ blood were mostly similar, however, some POP concentrations were higher in paternal blood. Several OCP, PBDE, and PCB compounds were found to be associated with lower birth size measurements. Some of these differences were statistically significant. PFCs and PBBs were not associated with any significant differences in birth size.
Overall, maternal and paternal POP levels as measured before conception resulted in decreases in birth weight between 85 and 195 grams. This is a similar range of decreased birth weight in comparison to studies that measured the birth weight of infants whose mothers smoked, were exposed to smoke, or lived in a polluted indoor environment during pregnancy (a decrease in birth weight between 33 and 189 grams). The LIFE study also revealed a possible difference in the effect of POPs on birth size outcomes depending on the sex of the fetus.
The 2001 international convention in Stockholm called for the immediate ban of 12 intentionally produced POPs, including PCBs and DDT. Other intentionally produced types of POPs continue to be added to this list for targeted ban. In addition to signing the Stockholm Treaty, the US has been an active supporter of efforts like the Commission for Environmental Cooperation between the US, Mexico, and Canada, and the Chemicals Information Exchange and Networking Project, which is part of the United Nations Environment Program.
However, despite global and domestic efforts, there still exists a large amount of unintentionally produced POPs from activities such as combustion. Moreover, the persistence of POPs in the environment, and their ability to be globally transported via the atmosphere, means that they still represent a hazard to human health, and particularly children’s health.
Exposure to POPs may be reduced through consumer education, public health programs, legislation, and environmental health infrastructure. The U.S. needs to adopt more proactive and preventive approach to chemical policy that includes adequate testing of chemicals using exposure models based on the most vulnerable subsets of the population. In 2003 the Institute of Medicine’s Food and Nutrition Board recommended that the U.S. government increase the availability of foods low in animal fats in government sponsored breakfast and lunch programs and in child-care food programs. Adequate support for efforts like this, and adequate funding for public health educational initiatives and preventive research are also important to help reduce exposures and protect children’s health.