In 1939, Gerhard Schrader, a German chemist, was searching for better methods to control insects when he chanced upon a substance, chemically an organophosphate, that had greater insecticidal activity than anything he had ever seen. He named the new compound "Tabun" and envisioned a breakthrough for agriculture. Hitler, however, had something else in mind for the newly developed substance. If it could kill pests, it could also kill people. A terrible new weapon was born. Tabun was actually a colorless, odorless, relatively volatile liquid. Exposure to a few milligrams was enough to cause death. It penetrated through intact skin without any irritating effect so that a fatal dose could be absorbed with no warning.
The term "nerve gas" was used to describe the substance because of its mechanism of action. The chemical interferes with the way information is transmitted from one nerve cell to another. Such transmission involves the release of chemicals called neurotransmitters from a nerve ending followed by the migration of this substance across the tiny gap separating nerve cells, known as the synapse. The neurotransmitter then stimulates an adjacent cell by fitting into a "receptor site" on its surface, very much as a key fits into a lock. This cell then releases a neurotransmitter which stimulates the next cell, and thus the message is propagated. The specific neurotransmitter involved in the nerve gas story is acetylcholine.
Once acetylcholine has carried out its job of triggering a reaction in an adjacent cell, it is decomposed by an enzyme present in the synapse. Overstimulation is therefore prevented. It is this enzyme, acetylcholinesterase, that is inactivated by nerve gases. The result is overstimulation of the nervous system, eventually leading to convulsions, paralysis and respiratory failure. The Germans never managed to use organophosphates in warfare but Schrader’s vision of these compounds as effective insecticides proved to be correct. As DDT and other organochlorides fell into disfavor in the 1960s because of concerns over their persistence in the environment, the organophosphates, which break down much more readily, gained popularity to the extent that today roughly 70% of all pesticides used belong to this family.
It goes without saying that organophosphates are toxic compounds, that of course is what makes them effective pesticides. It also goes without saying that our extensive reliance on organophosphates to protect our homes and food supply from insects means that we can’t escape exposure to these compounds. Urine analysis confirms that most of us have organophosphate breakdown products cruising through our bodies. The amounts are way too little to cause acute effects but there is the lingering worry about what exposure to traces of organophosphates may do in the long run. And now a study by researchers at the University of Montreal, published in the journal Pediatrics, suggests that organophosphates may be linked with attention deficit hyperactivity disorder (ADHD).
The study involved analyzing single urine samples from 1139 children aged 8 to 15 for organophosphate metabolites. Some of these children, 148 to be exact, met the criteria for a diagnosis of ADHD, and interestingly they were more likely to have higher urinary levels of organophosphate breakdown products. Such an association cannot prove cause and effect; it may be possible, for example, that children who have ADHD metabolize toxins differently or that their liquid intake may be different, altering the concentration of chemicals in the urine. But it is also possible that organophosphates really can be a causal factor in ADHD. After all, it is clear that these compounds have an effect on the nervous system and ADHD is likely a nervous system disorder. Still, it must be remembered that this study was based on analyzing a single urine sample and there was no indication about the extent of exposure to household pesticides. It is therefore premature to blame pesticide residues on food for an increase in ADHD, but we can’t absolve them of blame either. Eating organic produce reduces exposure, and is a good option as long as the extra expense doesn’t lead to consuming fewer fruits and vegetables. More important is to be very careful about using pesticides around the home and to resort to organophosphates only if absolutely necessary. Finally, ADHD is a complex condition with many possible causes ranging from genetic factors and consuming certain food additives to early exposure to lead, nicotine or alcohol.