Commentary

Perspective on EWG Report on Chemicals Found
in Neonatal Cord Blood Samples

By Charles A. McKay, MD
University of Connecticut School of Medicine

The July 14, 2005, report by the Environmental Working Group (EWG) on environmental chemicals found in 10 neonatal cord blood samples possibly provides important data on the environmental exposures experienced in utero. If true, these results would be a cause for concern and action on the part of would-be parents, government and industry. Unfortunately, the results of this small study do not warrant the far-reaching recommendations or conclusions that are made.

As an example, the EWG report identifies a number of environmental chemicals that have been banned from use for decades. Although by definition this means the concentrations are lower than they have been in the past, the authors imply that these chemicals are responsible for the current increase of various health problems in the U.S. population. Attributing regional or global trends in disease incidence to what is, in essence, better analytical detection of a declining amount of an environmental chemical is disingenuous at best.

Proper interpretation of these results requires additional information that is not provided in the EWG report, reducing the usefulness of their report. To compare the maternal blood supply to the placenta as a "living lake that bathes the fetal capillaries" is a vivid and accurate picture. To state, as Dr. Greene does in a guest commentary, that: "(t)oday, this most primal of lakes has become polluted with industrial contaminants. And developing babies are nourished exclusively from this polluted pool" is misleading. The analytical capability highlighted in this report stands in stark contrast to the health effect relevance of these findings. While many of the cord blood samples had detectable amounts of a number of environmental chemicals, the concentrations of these were often in the parts per billion or parts per trillion range. This is equivalent to the detection of a single drop of a substance dispersed into a large lake. Furthermore, the extremely small amounts of the large number of substances detected are very prone to contamination during collection, storage, transport and analysis of the specimens. As these specimens were collected at different times and places, external contamination of the samples should have been addressed by appropriate sampling of the collection bags and anticoagulants used.

Epidemiological studies evaluating the effects of low-intensity exposure to environmental chemicals must deal with a difficult problem. The contrast between the very precise and accurate laboratory analysis for environmental chemicals on the one hand and the very coarse tools we have available for clinical evaluation of potential human health effects and adjustment for socioeconomic, educational, and other confounders makes conclusions regarding the causative meaning of an identified association very tenuous.

Recognizing the importance of possible environmental exposures to public health, the Centers for Disease Control and Prevention (CDC) has conducted surveys of the population for decades, looking at clinical status and laboratory findings. More recently, the analytical component has been extended by the National Centers for Environmental Health (NCEH) division of the CDC in the form of the National Report on Human Exposure to Environmental Chemicals. The 3rd National Report is due to be published this month and greatly extends the sampling, both in terms of populations and substances sampled. The results of neonatal sampling, as reported by the EWG, if demonstrated to be accurate, will add to this population sampling database, but should also be compared to it for accuracy.

Population measurements do help document the general amount of exposure to a variety of environmental chemicals, and allow us to both monitor population trends and particular populations at risk for higher exposures; they do not allow us to attribute an illness (or fear of illness) to the presence of the chemical alone. As the CDC report emphasizes: "just because people have an environmental chemical in their blood or urine does not mean that the chemical causes disease." All substances are chemicals; some are essential to life and some are harmful, but the concentration or accumulation of these is important in determining their effect on health.

An important outcome of biomonitoring studies, when properly performed and interpreted, will be a focus on those biopersistent or bioaccumulative environmental chemicals that are most likely to result in adverse health effects at concentrations experienced by vulnerable populations. The developing baby certainly represents such a population. Adding information about exposure concentrations with demonstrable clinical effects and differentiating animal experimental from human observational data will improve the utility of the data presented by the EWG study and allow appropriate focus on those environmental chemicals that present the smallest safety margins with current use.