Chlorpyrifos Toxicology Information

Chlorpyrifos is an organophosphate class insecticide which inhibits the production of cholinesterase, an enzyme (click for more info) which regulates the firing of nerves. It binds irreversibly to the active site of an enzyme essential for normal nerve impulse transmission, acetylcholine esterase (AchE), inactivating the enzyme. A common diagnostic for poisoning is to assay for blood AchE depression. Repeated or prolonged exposure to organophosphates may result in the same effects as acute exposure, including delayed symptoms. Some of the other chemicals in this class of chemicals are notorious warfare agents such as Sarin, a material used in chemical weapons. An example of what these type chemicals can do was in 1995 when Japanese terrorists used Sarin in subways.

Chlorpyrifos Increases the Risk of Parkinson's Disease

New studies now show that chlorpyrifos consumption in well water increases the risk by 70 to 90% of developing Parkinson's Disease. Here are two links to these new studies:

Parkinsons Association with Pesticide Exposure Gains Strength Mar 28 2008

Well-water consumption and Parkinson's disease in rural

Rural Well Water Linked to Parkinson's Disease

It is important to note that the above studies assume that the well water user was drinking chlorpyrifos not the much more toxic chlorpyrifos oxon. Chlorpyrifos oxon was created when Dow required anyone with a known well contamination to use the "Dow Decontamination Procedure for Wells Contaminated with Chlorpyrifos".

The well decontamination procedure was not the only hazard Dow was hiding about Chlorpyrifos -

Here's a fact that Dow has known about internally for over twenty-five years but has intentionally hidden.  Dow also suppressed outside researchers from revealing the information when they first discovered it.

• Chlorpyrifos is a semi-volatile compound; it volatilizes after application and will be re-deposited on surfaces in treated rooms for weeks/months/years after the initial application.

As a result, it may adhere to objects such as children's toys that are brought into the room hours or days after the pesticide is applied. Young children with high frequency mouthing behavior would therefore be at risk of acute exposure to chlorpyrifos residues. In the mid 90's Dow added a statement to some Dursban product labels warning that the occupants should stay out of the dwelling until the spray had dried. While this did allow the application surfaces to dry and the spray particles in the air to possibly settle, Dow hid their knowledge that chlorpyrifos was a volatile chemical. Dow knew this volatility would cause the occupants to be repeatedly exposed to airborne chlorpyrifos. They additionally knew that the airborne chlorpyrifos would be deposited on surfaces which the occupants would consider safe from exposure because the spray had dried. Dow hid this information which is now believed to be the primary reason for restrictions on chlorpyrifos use by the EPA, specifically the Dursban products removal from the market. Dow prospered while it was on the market and while they hid this information. 

Research indicates that apparently non-toxic childhood exposure to pesticides, which can go undetected because of the lack of overt symptoms, may have long-term impacts on behavior, and the studies emphasize the necessity to conduct long-term evaluations to identify later-emerging behaviors.³

Work by Fenske et al. found that air levels 24 hours after a proper application were as high as 30µg/ m3 in the infant breathing zone, 60 times the EPA's limit. Furthermore, Fenske calculated that infant exposure through inhalation and skin absorption might be more than five times the human threshold for acute effects or what is called the "No Observable Effect Level". The researchers state that, "Exposures to cholinesterase inhibiting compounds following properly conducted broadcast applications could result in doses at or above the threshold of toxicological response in humans."

"A 1996 study of children exposed to chlorpyrifos in utero found that extensive and unusual patterns of birth defects, including brain, nervous system, eyes, ears, palate, teeth, heart, feet, nipples, and genitalia. Published literature and EPA documents contain reports that identify similarities in defects found in test animals and children exposed to chlorpyrifos".⁵

The authors of this new study reported:

"That children with high exposure, defined as a Dursban level of more than 6.17 pg/g plasma, on average scored 6.5 points lower on the Bayley Psychomotor Development Index (P=0.03) and 3.3 points lower on the Bayley Mental Development Index at age three (P=0.06), compared with children with lower exposure levels.

They also found that "the developmental trajectories for psychomotor development index and mental development index scores confirmed that adverse cognitive and psychomotor effects increased over time, and these effects were present in both Dominican and black subjects, which supported the main conclusion of the study."

In addition, children with high levels of prenatal exposure to the pesticide were significantly more likely than children with low exposure to score in the clinical range on test for attention problems, attention deficit hyperactivity disorder, and pervasive developmental."

According to Dr. Philip Landrigan of the Department of Community and Preventative Medicine at Mount Sinai Medical Center in New York City, "Excellent studies conducted by independent scientists have clearly shown that chlorpyrifos, the active ingredient in Dursban, is toxic to the human brain and nervous system and is especially dangerous to the developing brain of infants".

What is being learned from research outside of Dow is that chlorpyrifos and its highly toxic metabolite - chlorpyrifos oxon - can even cross the placenta barrier. Recent studies have found that if pregnant women are exposed to this pesticide, at even very low levels, it can affect their unborn children by lowering the birth weight and interfering with the fetus's brain development. Crossing the placenta barrier is something that Dow scientists had adamantly said in the past would not occur but science is proving them to be wrong again. Of course these effects would not be so obvious that one would notice the problem immediately in an individual and it would be even harder at a later time to know that chlorpyrifos was the cause so they probably felt they'd never be caught.

There continues to be connections being discovered between chlorpyrifos and long-term nerve damage. The symptoms are similar to those seen in "Gulf War Syndrome". It is well known that chlorpyrifos was used extensively in the Gulf War for pest control in the command areas and the soldiers' camp areas. A Duke University study years ago discovered compounded effects of nerve damage when a combination of chlorpyrifos, insect repellents, and another insecticide was used. Chlorpyrifos, Deet, and permethrin were all used in the Gulf War and soldiers were exposed to all three in many situations. The symptoms of Gulf War Syndrome are similar to OPIDN or OrganoPhosphate Induced Delayed Neuropathy. "Delayed neurotoxic effects of OP have been described as degeneration of long axons in the peripheral nervous system and selected tracts of the central nervous system, concomitant ataxia and paralysis; which can be irreversible. The onset of symptoms is delayed and about 2 weeks after a single exposure to some OP may occur. This OP induced delayed neuropathy (OPIDN) is totally independent of anticholinesterase activity and can be the consequence of mild exposure to OP (used industrially and in the war) that do not inhibit cholinesterase." ⁴  

Dow states that chlorpyrifos has nothing to do with Gulf War Syndrome but studies keep coming back to a possible organophosphate cause and Dursban was used extensively during the Gulf War. As you will see in compiling all the facts to see the big picture, the Dow researchers who say chlorpyrifos is not part of the problem are some of the same individuals caught by the EPA falsifying reports. How credible are their assurances of safety? Those same researchers have knowingly and intentionally allowed entire families including infants to drink chlorpyrifos oxon so do you think they'd care about the people who put their life on the line to protect our country?

After reviewing the information compiled on this website we believe you also will have serious doubts about the ethics and integrity of the people at Dow and in trusting anything they may say.

EPA's Phase Out of Chlorpyrifos Use

Many news reports erroneously state that chlorpyrifos has been banned by the EPA. This is not true. One of the initial steps that was taken by the EPA to reduce the use of chlorpyrifos during the last five years was to limit it's availability by removing it's ability to be purchased by homeowner-type consumers who purchase through retail trade. Sales of most chlorpyrifos products are now only available as a Restricted Use category pesticide that requires a certified pesticide applicators license. Purchasing and use requires application training and detailed records of the applications of these restricted products. From the most recent EPA usage data, the phase out has had little impact on the pounds of chlorpyrifos used in the U.S. EPA data shows an estimated 8-10 million pounds used in the year 2001, while 9-13 million pounds were used in 1997. Not much of a usage decline change in an attempt to phase out a pesticide. Dow has tried to stop the EPA's phase out for certain usages such as termite control in treatments for new building construction. A use which would continue to put chlorpyrifos around millions of homes in the U.S.. Chlorpyrifos is still widely used today throughout the world.

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