An international team of researchers lead by an epidemiologist from Columbia University’s School of Public Health has uncovered some very disturbing evidence that DDT, a pesticide taken out of use in the United States 1972, may be linked to autism. 1Brown
The scientists reviewed cases from the Finnish Prenatal Study of Autism, a study that had collected blood serum samples from more than a million women who gave birth between 1987 and 2005 (serum is a clear liquid that can be separated from clotted blood).2 Medicine.Net Almost 800 cases of childhood autism were matched with almost 800 normal control subjects. Serum samples taken from both groups of mothers early in the pregnancy were analyzed for a byproduct of DDT—a biomarker called p,p′-DDE which would be present only if women were exposed to DDT.
The researchers found that children born to mothers with a high level of DDT biomarkers (those in the top quartile for having p,p′-DDE) were 32% more likely to develop autism with intellectual impairment than children born to women with a lower level of DDT biomarkers.3Rearson
The study concluded, “These findings provide the first biomarker-based evidence that maternal exposure to insecticides is associated with autism among offspring.” 1Brown
In considering why prenatal exposure to DDT could trigger autism, the research team observed that Maternal DDE “is associated with low birthweight, a well-replicated risk factor for autism4Longnecker… Second, they point to androgen receptor binding, a process key to neurodevelopment. A study in rats found DDE inhibits androgen receptor binding, an outcome also seen in a rat model of autism.”5Kelce, 6ScienceDaily
It is a familiar story to many that Rachel Carson brought the dangers of DDT to the public in her groundbreaking book, Silent Spring in 1962.7Carson
Among the issues that came to light was a decline in bald eagle populations caused by DDT. It would take another ten years for the use of DDT to be discontinued in the U.S. By 2004, the Stockholm Convention on Persistent Organic Pollutants severely restricted the production and use of DDT worldwide.8Stockholm
According to the National Pesticide Action Center, DDT (dichlorodiphenyltrichloroethane) was a very commonly used pesticide in the U.S. before it was banned. The following are some of its characteristics:9NPAC
- DDT is highly persistent in the environment.
- The half-life of DDT in an aquatic environment is about 150 years
- DDT tends to accumulate in the fatty tissues of insects, wildlife, and people
- DDT is metabolized into various breakdown products in the body including DDE
- When fat stores are used during periods of starvation the breakdown products of DDT are released into the blood where they may be toxic to the liver and the nervous system
- Breast milk is often used to measure a population’s exposure to DDT
- Because of DDT’s chemical properties, it has the tendency to accumulate in animals. As animals lower on the food chain are eaten by other animals higher up, DDT becomes concentrated in the fatty tissues of predators
According to information from the Pesticide Action Network, long-lasting effects of DDT we are experiencing include:10PAN
- Food supplies: USDA found DDT breakdown products in 60% of heavy cream samples, 42% of kale greens, 28% of carrots and lower percentages of many other foods.
- Body burden: DDT breakdown products were found in the blood of 99% of the people tested by CDC.
- Health impacts: Girls exposed to DDT before puberty are 5 times more likely to develop breast cancer in middle age, according to the President’s Cancer Panel.
How Are We Exposed to DDT?
According to the U.S. Agency for Toxic Substances and Disease Registry, people in the United States are exposed to DDT, DDE, and DDD mainly by eating foods containing small amounts of these compounds.
“DDT, DDE, and DDD last in the soil for a very long time, potentially for hundreds of years. Most DDT breaks down slowly into DDE and DDD, generally by the action of microorganisms.
These chemicals may also evaporate into the air and be deposited in other places. They stick strongly to soil, and therefore generally remain in the surface layers of soil. Some soil particles with attached DDT, DDE, or DDD may get into rivers and lakes in runoff.”11ATSDR
“In surface water, DDT will bind to particles in the water, settle, and be deposited in the sediment. DDT is taken up by small organisms and fish in the water. It accumulates to high levels in fish and marine mammals (such as seals and whales), reaching levels many thousands of times higher than in water. In these animals, the highest levels of DDT are found in their adipose tissue. DDT in soil can also be absorbed by some plants and by the animals or people who eat those crops.” 11ATSDR
How Can We Reduce Risk?
Here is the U.S. government advice: “At this time, most people are exposed to DDT and its breakdown products as a result of eating foods or drinking liquids that may be contaminated with small amounts of DDT. Studies have shown that cooking will reduce the amount of DDT in fish.
Many other countries still use DDT; therefore, food brought into the United States from these countries may contain DDT. DDT has been found in both root and leafy vegetables. DDT attaches to the roots of plants, but it does not easily move to other parts of the plants. DDT in the air can be deposited on to the surfaces of plants. Washing fruits and vegetables before eating them is a healthful practice.” 11ATSDR
1Brown AS. et al. Association of maternal insecticide levels with autism in offspring from a national birth cohort. American Journal of Psychiatry 2018; 175(11):1094-1101. https://ajp.psychiatryonline.org/doi/10.1176/appi.ajp.2018.17101129
2MedicineNet.com. Medical definition of serum. https://www.medicinenet.com/script/main/art.asp?articlekey=5470
3Reardon S. Autism and DDT: What one million pregnancies can — and can’t — reveal. Nature News, 16 August 2018. https://www.nature.com/articles/d41586-018-05994-1
4Longnecker MP, et al. Association between maternal serum concentration of the DDT metabolite DDE and preterm and small-for-gestational-age babies at birth. Lancet. 2001 Jul 14;358(9276):110-4. https://www.ncbi.nlm.nih.gov/pubmed/11463412?dopt=Abstract
5Kelce WR, et al. Persistent DDT metabolite p,p’-DDE is a potent androgen receptor antagonist. Nature. 1995 Jun 15;375(6532):581-5. https://www.ncbi.nlm.nih.gov/pubmed/7791873?dopt=Abstract
6Science Daily. Columbia University’s Mailman School of Public Health. “First biomarker evidence of DDT-autism link: National birth cohort study finds DDT metabolites in the blood of pregnant women are associated with elevated odds of autism in offspring.” ScienceDaily. 16 August 2018. www.sciencedaily.com/releases/2018/08/180816081500.htm
7Carson R. Silent Spring. New York: Houghton Mifflin Company, 1962. http://www.rachelcarson.org/SilentSpring.aspx
8Secretariat of the Stockholm Convention. History of the negotiations of the Stockholm Convention. http://chm.pops.int/TheConvention/Overview/History/Overview/tabid/3549/Default.aspx
9National Pesticide Action Center. DDT General Fact Sheet. http://npic.orst.edu/factsheets/ddtgen.pdf
10Pesticide Action Network. The DDT Story. http://www.panna.org/resources/ddt-story
11Agency for Toxic Substances and Disease Registry. Public Health Statement for DDT, DDE, and DDD. https://www.atsdr.cdc.gov/phs/phs.asp?id=79&tid=20
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