In a few weeks a research report will appear in the prestigious journal Pediatrics on the effects of air pollution during fetal development on the IQ of New York City children at five years of age. In response to an early release of the report, the media have already started reporting on it. It's an important study, and maybe when the report finally appears in print in August it will be a wake-up call, a reminder that public health is not an abstraction, that it affects every one of us, including the fetus. The fetus, in fact, is estimated to be about 100 times more vulnerable to environmental toxic chemicals than children and adults. The mother's body acts as a filter to protect the fetus against the outside environment, but no filter is perfect, and for some toxic chemicals the mother is no filter at all.
This study involved polycyclic aromatic hydrocarbons (PAHs). These chemicals are released into the air during incomplete or complete burning of fossil fuel, tobacco, and other organic material. In this study, children of women living in New York City were monitored from in utero to five years of age, with determination of prenatal PAH exposure through personal air monitoring for the mothers during pregnancy. At five years of age, intelligence was assessed for 249 children using standard IQ tests.
The journal Pediatrics is the official journal of the American Academy of Pediatrics. The report is by a seven-member research team at Columbia University, the lead author Dr. Frederica Perera. This is apparently the first study in the medical literature to report an association between prenatal exposure to polycyclic aromatic hydrocarbons and IQ.
The authors of the study conclude: "These results provide evidence that environmental PAHs at levels encountered in New York City air can affect children's IQ adversely."
This is not the first study to associate prenatal exposure to environmental toxins with childhood IQ. There's much evidence already in the literature about lead, mercury, ethanol, arsenic, PCBs, and various pesticides and other chemicals. It's not clear that all "associations" involve cause-effect relations, but there's enough science now to make a great many people worried. And it's not only childhood IQ that may be involved, but also autism, ADHD, schizophrenia, and various physical illnesses -- all of it apparently related to chemical impacts on the fetus during development.
I'm using the term "environmental toxin" here to include any environmental toxic chemical -- not only chemicals derived from biological sources.
This is a vast subject that has many facets, scientific, social, political, and economic. Too many people avoid any reality that makes them uncomfortable until it's too late to fix a problem. If environmental toxins are harming children before they are even born, we need to know about it, and do something about it, and stop pretending that all environmental effects occur after birth and none before birth.
The idea of fetal vulnerability is certainly disturbing, but the reality is the fetus is extremely vulnerable. It's estimated that sixty percent of all conceptions never make it to full term, most embryos perishing during the first few days of pregnancy without the mother even knowing.
The fetus (or embryo, if it's the first 10 weeks of gestation) is extremely vulnerable to toxic chemicals for three primary reasons:
1) The early fetus (the embryo) is very small, only about two inches long at ten weeks, and of course much smaller earlier than that. The consequence is that any chemical that gets into the early embryonic environment rapidly spreads throughout the entire embryo by simple diffusion -- quickly getting into cells or getting to the surfaces of cells.
2) A "cascade" of events is a series of events in which one event acts as a trigger for the next event. Fetal development involves an enormous number of parallel biochemical cascades that result in cell differentiation and tissue organization. If any cascade is impacted by a toxic chemical at any particular point, the cascade may be seriously altered or even abolished -- with sharp effects on fetal development. The same paradigm applies to early progenitor cells -- an impact on an early progenitor cell can affect the entire lineage from that cell.
3) Everything in fetal development is happening at an extremely rapid pace. My favorite analogy is that fetal development is like turning a small lump of metal into the space shuttle. We start with a dot (the fertilized egg cell) about the size of the period at the end of this sentence, and we finish nine months later with an infant screaming at you to give it food and attention. If you want to know how fast human development occurs in the womb, consider that about halfway through the process the fetus is producing in its growing brain about 250,000 new nerve cells each minute. Any environmental chemical that changes the rate of any biochemical cascade in the developing fetal nervous system can have a serious impact on behavior and intelligence.
Fetal vulnerability is a reality. The presence of toxic chemicals in our environment is also a reality. It's estimated that 50,000 industrial toxic chemicals are already in our environment -- with only a hundred or so investigated for their fetal effects. It's our environment, our society, and the unborn children exposed to toxic chemicals are our children. With so much talk about "saving the unborn" it's a pity some of that social energy isn't applied to the problem of pollution of the fetal environment. It's a problem that needs public attention.