The womb is a factory. It is here that chemicals are assembled into a living machine of incredible complexity called a baby. Where do these chemicals come from? Mommy! She eats and she drinks. She processes the proteins, fats, carbs, minerals and vitamins she ingests to provide the building blocks needed by the growing embryo. But what if a monkey wrench gets thrown into the machinery at this point? What if chemicals not needed for healthy development find their way into the uterus? Can they gum up the works, possibly producing long term consequences? No doubt.
Agents that can disturb the development of the embryo or fetus are called teratogens. They may cause outright birth defects, as in the case of thalidomide, alcohol or the acne treatment isotretinoin. Or a teratogenic effect may not appear until years later. Diethylstilbesterol (DES) was used to treat recurrent miscarriage in the 1950s and 60s and was eventually found to cause a rare type of vaginal cancer in the daughters of women who had been treated in the first trimester of pregnancy. But more subtle effects are also possible. Lead and mercury exposure for example have been linked with problems in cognitive development. And there has also been suspicion that in-utero exposure to certain pesticides may impair intelligence later in life. That may not be as harebrained as it sounds.
A number of recent studies have explored the possibility of a such an effect by administering various intelligence tests to children whose mothers’ exposure to organophosphate pesticides during pregnancy had been determined by analysis of either umbilical cord blood or urine samples. Organophosphates are a common family of pesticides and function by inhibiting the action of an enzyme that breaks down the neurotransmitter acetylcholine. Essentially, these chemicals kill pests by over stimulating their nervous system. Since human nerves also use acetylcholine as a neurotransmitter, organophosphates can also affect us. Indeed, the classic chemical warfare agents such as Sarin are organophosphates and of course these can kill. Exposure of a developing embryo to tiny amounts of organophosphates is not going to be lethal, but what about subtle effects? Recent studies suggest a decided possibility.
In one study, urine from pregnant women in a farming community was collected and analyzed for organophosphate content. The same was done for their children at 6 months of age, as well as at 1, 2, 3.5 and 5 years. When the kids turned seven, intelligence tests were administered. The higher the pesticide level in the mother’s urine, the worse the offspring performed in terms of working memory, processing speed, verbal comprehension, perceptual reasoning and IQ! The differences were not huge, but statistically significant. Remarkably, there was no correlation of cognitive problems with pesticides in the childrens’ urine, suggesting that the critical period of exposure is in utero.
Another study examined the effects of chlorpyrifos, an organophosphate, on inner-city children whose mothers were exposed mostly through residential pesticide application. Levels of the chemical were measured in umbilical cord blood and again intelligence tests were performed at seven years of age. Again there were small declines in IQ and working memory with an increase in chlorpyrifos in umbilical blood. Yet a third study examined prenatal maternal blood for organophosphates as well as for the presence of paraoxonase, a key enzyme in the metabolism of organophosphates. In this case too, cognitive development was affected in parallel to increased blood levels of organophosphates, and furthermore, there was a genetic involvement. Children of mothers who carried a gene that imparts slow activity to the enzyme that helps break down organophosphate were more affected.
These are interesting studies, but there are a few items to note. Organophosphate use is declining and has been virtually eliminated from all but agricultural use. Chlorpyrifos is not allowed in products formulated for residential use. Also such studies can show an association but cannot prove cause and effect. Could other factors have been involved? Alcohol? Smoking? Nutritional differences? Mercury or lead exposure? Still, the fact that measures of intelligence were linked to levels of pesticides in maternal urine or umbilical blood in a proportional fashion is very suggestive of these chemicals being the culprits.
The take-home message here is that we have to be careful with the use of pesticides, particularly in terms of exposure during pregnancy. After all, let’s face it, pesticides are designed to do harm. What, though, can an individual do to reduce the risk? When pregnant, application of pesticides at home should be avoided. What about eating organic produce? Pesticide residues on conventional produce occur only in trace amounts, but there is some exposure. If an argument is to be made for buying organic, it is probably best made for doing so during pregnancy. There is some comfort to be had from these studies in that post natal exposure of children to pesticides was not linked to cognitive problems. Pregnancy is a special period indeed.
Obviously the best way to reduce pesticide exposure is to reduce pesticide use. One way to do this is through genetic modification. Implanting a gene from the Bacillus thuringensis bacterium that codes for the production of an insecticidal protein has been proven to be effective. This protein is harmless to humans but kills insects when they consume it. Implementation of Bt technology in China has already resulted in a 25% decrease in organophosphate use. Researchers around the world are working on safer pesticides, but as with all chemical issues, it comes down to a risk-benefit evaluation. And that evaluation is more critical during pregnancy. So if you are a developing fetus, and you sense mommy smoking or drinking, or chasing cockroaches with an insecticidal spray, give a good kick.