Pesticides Disrupt 
Brain Development & Reproduction  
UPdate Spring 2003

During last spring's Parliamentary hearings into the proposed new Pest Control Products Act, many experts testified to the serious and long term health impacts of pesticides, and argued that the final law needed to be stronger and more effective. None of the changes they proposed were incorporated into the new law.  The testimony of Dr. Margaret Sanborn, reprinted in part below, looks at the effect of pesticides on neurodevelopment (the brain) and reproduction.

Pesticides are designed to kill something. The mechanisms for doing this involve disruption of processes inside the cell. The ability of the chemical to do this means that it can also disrupt human cell processes. I will focus on two of these: neuro- developmental effects, and reproductive effects.

Neurodevelopmental Effects
The human brain has 100 billion neurons, and an exponentially larger number of synapses, or connecting links between neurons. From birth to 2 years of age, the child's brain goes through unique growth and change. These growth processes include synaptogenesis, or formation of the connecting links between the nerve cells, and maturation and differentiation of specialized nerve cells. This process is mostly completed by age two, and then forms the "hard wiring" of the brain for the rest of life. Examples of brain functions which are sensitive to the quality of brain development during this period include gross motor skills, coordination of movement, ability to process multiple simultaneous inputs, and adjusting to a new

The effect of pesticides on brain formation, or neurodevelopment, is an area of great concern. Animal studies have shown that pesticide-exposed rats and mice have fewer brain cells, permanent changes in the levels of neurotransmitters (messenger chemicals) in the brain, defective cell-to-cell signaling, and hyperactive behaviour which persists into adult life. These changes occur at exposure levels which do not cause acute toxicity. They also occur from pesticides in current household use, such as chlorpyrifos and pyrethroids - substances previously thought to be much
safer than the old organochlorine insecticides.

It is clear that the brains of children are more susceptible to pesticide effects. For example, in pesticide poisonings, 25% of children present with seizures as a symptom; in adults only 2-3% present with seizures.  In children, we are concerned about sharp increases in the rates of autism and attention deficit disorders (previously called hyperactivity). Health Canada has stated recently that 28% of Canadian children under the age of 12 have an identified learning or behaviour problem. Apart from these known clinical disorders, there is a spectrum of less severe problems which involve memory and attention, and affect learning ability and skills to socialize and form relationships. Given the animal data, it is a concern that some of the increase in these problems may be pesticide-related. It is instructive to note that the recent quiet withdrawal of DEET formulations over 30% was done because of neurodevelopmental toxicity.

I would like to draw attention to the dramatic population effects caused by small reductions in brain function. A reduction of only 5 IQ points across the whole population causes a 57% increase in those classified as "mentally challenged", and a corresponding 57% decrease in those classified as "intellectually gifted". The economic and social costs of such a shift, both in increased health and social costs at the lower end, and reduced capacity for innovation and knowledge-based economic output at the upper end, are enormous. I believe these concepts deserve serious consideration when cost-benefit , or "health risk-value" analyses of pesticides are conducted.

Reproductive Effects
"The developing fetus has a critical period between 3-8 weeks gestation when major organs are being formed. This is the period when pesticides appear to have their strongest effect; it is also a time when women may be unaware they are pregnant. A study done in California showed that maternal pesticide exposure from 3-8 weeks was associated with an increase in miscarriages due to major birth defects. The Ontario Farm Family Health Study documented a 40-50% increase in early spontaneous abortions in farm women exposed to 2,4-D or atrazine type herbicides before conception.  Research done in Montreal has shown that fetuses exposed to pesticides by maternal home and garden use during pregnancy have a 2-5X risk of
developing acute lymphocytic leukemia by age 9.  The risk of leukemia is highest if the child has one of two genetic subtypes which cause an inability to break down pesticides. This genetic subtype is not a rare occurrence; in the Montreal study it was present in 35.5% of children. In other words, about one-third of Canadian children are born with a specific inability to detoxify commonly used pesticides, and a corresponding increased vulnerability to adverse health effects including cancer. Cancer in Canadian children under age 15 has doubled over the past 25 years.


Dr. Margaret Sanborn is a rural family physician, Assistant Clinical Professor of Family Medicine at McMaster University, and a member of the Ontario College of Family Physicians Environmental Health Committee.