A study comparing blood serum levels of the DDT metabolite, DDE, in 86 patients with Alzheimer's disease (average age 74) and 79 controls (average age 70), has found that levels of DDE were 3.8 times higher in 74 of the 86 Alzheimer’s patients (86%). Having the Alzheimer’s gene, APOe4, plus high levels of the pesticide, produced more severe cognitive impairment.

Brain cell studies found that DDE increased production of the amyloid precursor protein (APP).

DDT was banned in the U.S. in 1972, but is still used elsewhere. It also takes a long time to break down in the environment. DDE was found in 75-80% of blood samples collected from the Centers for Disease Control and Prevention for a national health and nutrition survey.

Organophosphate pesticides are the most widely used insecticides in the world; they are also (according to WHO), one of the most hazardous pesticides to vertebrate animals. While the toxic effects of high levels of organophosphates are well established, the effects of long-term low-level exposure are still controversial.

A meta-analysis involving 14 studies and more than 1,600 participants, reveals that the majority of well-designed studies undertaken over the last 20 years have found a significant association between low-level exposure to organophosphates and impaired cognitive function. Impairment was small to moderate, and mainly concerned psychomotor speed, executive function, visuospatial ability, working memory, and visual memory.

A study of 265 New York City minority children has found that those born with higher amounts of the insecticide chlorpyrifos had lower IQ scores at age 7. Those most exposed (top 25%) scored an average 5.3 points lower on the working memory part of the IQ test (WISC-IV), and 2.7 points lower on the full IQ test, compared to those in the lowest quartile.

The children were born prior to the 2001 ban on indoor residential use of the common household pesticide in the US. The babies' umbilical cord blood was used to measure exposure to the insecticide.

Previous research had found that, prior to the ban, chlorpyrifos was detected in all personal and indoor air samples in New York, and 70% of umbilical cord blood collected from babies. The amount of chlorpyrifos in babies' blood was associated with neurodevelopmental problems at age three. The new findings indicate that these problems persist.

While exposure to the organophosphate has measurably declined, agricultural use is still permitted in the U.S.

Similarly, another study, involving 329 7-year-old children in a farming community in California, has found that those with the highest prenatal exposure to the pesticide dialkyl phosphate (DAP) had an average IQ 7 points lower than children whose exposure was in the lowest quintile. Prenatal pesticide exposure was linked to poorer scores for working memory, processing speed, verbal comprehension, and perceptual reasoning, as well as overall IQ.

Prenatal exposure was measured by DAP concentration in the mother’s urine. Urine was also collected from the children at age 6 months and 1, 2, 3½ and 5 years. However, there was no consistent link between children’s postnatal exposure and cognition.

While this was a farming community where pesticide exposure would be expected to be high, the levels were within the range found in the general population.

It’s recommended that people wash fruit and vegetables thoroughly, and limit their use of pesticides at home.

A study involving 614 middle-aged vineyard workers has found that those who were exposed to pesticides were five times as likely to perform more poorly on cognitive tests compared to those not exposed, and twice as likely to show cognitive decline over a two-year period.

Participants were in their 40s and 50s and had worked for at least 20 years in the agricultural sector. One in five had never been exposed to pesticides as part of their job; over half had been directly exposed, and the remainder had been possibly or certainly indirectly exposed. Educational level, age, sex, alcohol consumption, smoking, psychotropic drug use and depressive symptoms were taken into account.

A study involving 725 black and Dominican pregnant women living in New York and, later, their 3-year-old children, has found that children who were more highly exposed to PBO in personal air samples taken during the third trimester of pregnancy scored 3.9 points lower on the Bayley Mental Developmental Index than those with lower exposures. This is a similar effect size to that of lead exposure.

PBO is a marker for the insecticide permethrin, which is one of the most common pyrethroid insecticides used in U.S. homes since the EPA phased out the widespread residential use of organophosphorus insecticides in 2000-2001 because of risks to child neurodevelopment.

PBO was detected in the majority of personal air samples (75%).

As this is the first study of these compounds, the results should be considered preliminary.

A study following over 300 Mexican-American children living in an agricultural community has found that their prenatal exposure to organophosphate pesticides (measured by metabolites in the mother’s urine during pregnancy) was significantly associated with attention problems at age 5. This association was stronger among boys, and stronger with age (at 3 ½ the association, although present, did not reach statistical significance — perhaps because attention disorders are much harder to recognize in toddlers). Based on maternal report, performance on attention tests, and a psychometrician’s report, 8.5% of 5-year-olds were classified as having ADHD symptoms. Each tenfold increase in prenatal pesticide metabolites was linked to having five times the odds of scoring high on the computerized tests at age 5. The child’s own level of phosphate metabolites was not linked with attention problems.

Organophosphate pesticides disrupt acetylcholine, which is important for attention and short-term memory. While the exposure of these children to pesticides is presumably higher and more chronic than that of the general U.S. population, food is a significant source of pesticide exposure among the general population.

Marks AR, Harley K, Bradman A, Kogut K, Barr DB, Johnson C, et al. 2010. Organophosphate Pesticide Exposure and Attention in Young Mexican-American Children. Environ Health Perspect :-. doi:10.1289/ehp.1002056
Full text available at

Older news items (pre-2010) brought over from the old website

Pre-term labor drug sensitizes brain to pesticide injury

A rat study has found that unborn rats exposed to terbutaline - a drug commonly prescribed to halt pre-term labor and stave off premature birth - suffered greater brain cell damage than those not given the drug upon secondary exposure to the common insecticide chlorpyrifos. This suggests that this drug might leave the brains of children susceptible to other chemicals ubiquitously present in the environment, and may help explain earlier suggestions that children whose mothers are administered terbutaline suffer cognitive deficits.

[2387] Rhodes MC, Seidler FJ, Qiao D, Tate CA, Cousins MM, Slotkin TA. Does pharmacotherapy for preterm labor sensitize the developing brain to environmental neurotoxicants? Cellular and synaptic effects of sequential exposure to terbutaline and chlorpyrifos in neonatal rats. Toxicology and Applied Pharmacology [Internet]. 2004 ;195(2):203 - 217. Available from: