By: Richard Cassidy
Obesity has long been accepted as a risk factor for diabetes. The results of four recently published studies, however, have revealed that the real risk factor may be the insecticides present in that fat. The initial investigations showed that the expected association between obesity and diabetes/insulin resistance was absent in people who had low levels of organochlorine insecticides in their blood (1, 2). However, the expected association between obesity and diabetes/insulin resistance increased with levels of these insecticides. In the last year, two additional studies have linked these insecticides with diabetes (3, 4).
In all four studies, the insecticides that consistently had the greatest association with diabetes were compounds of the chlordane family (oxychlordane, trans-chlordane, trans-nanochlor, and heptachlor), all of which are found in technical chlordane. (See Audios, Reviews, and Scientific Reports)
Technical chlordane was used to treat termite infestation in approximately 30 million homes from the 1950s until it was banned in 1988. Chlordane compounds are highly persistent in soil and vaporize at a slow rate. Chlordane vapors migrate out of soil and into the air of homes through opening around pipes and cracks in concrete floors. Once inhaled, chlordane compounds accumulate in the fat tissues.
The level of chlordane compounds in the air of treated homes depends on where it was applied. Today, the highest levels of chlordane in air of homes is from application below basement floors, followed by application to the soil under homes with concrete slab floors, which was a common construction practice in the South. Lower levels are found in air from homes in which chlordane was applied to the soil of ventilated crawl spaces or the soil outside the foundation.
Still here 30 years later
Chlordane levels in the air of homes are known to remain high 30-plus years after application. In a study in Massachusetts, chlordane, heptachlor, and/or dieldrin were found in the air of 50 to 60 percent of the homes tested, with levels four to 40 times the U.S. Environmental Protection Agency (USEPA) guidelines (5). Because termite infestation and treatment increase in warmer climates, these numbers should increase in homes located farther south.
Recently, the Centers for Disease Control mapped the incidence of diabetes by state. There is a striking correlation between the incidence of diabetes and the use of chlordane for termite control in these states. (see the compare maps here). Southern states with the highest temperatures and humidity have not only the highest rates of termite infestations and chlordane use, but also the highest rate of diabetes. States from the midsection of the United States, with moderate temperatures and humidity and lower chlordane applications, have lower rates of diabetes. In northern states such as Minnesota, where chlordane was rarely used, the incidence of diabetes is less than 50 percent that of southern states.
For persons living in homes built prior to 1988 and located in the southern three-quarters of the United States, the main route of exposure is breathing chlordane in the air of their homes. According to the United States Environmental Protection Agency, occupants of treated homes can have exposures up to 25 times those found in the average American diet. (6).
For persons not living in chlordane-treated homes, the diet is the source of chlordane exposure. From the 1950s until it was banned in 1975, millions of pounds of technical chlordane were applied to agricultural soil, mainly for crops such as corn, soybeans, and vegetables. Chlordane compounds are still found in food, especially in meat and dairy fats and, to a lesser extent, in grains and vegetables grown in treated soils.
The persistence of chlordane in the soil and the uptake of chlordane by plants were demonstrated by a study conducted in 1998, in which vegetables grown in soils treated with technical chlordane in 1960 had high levels, especially zucchini and the peels of potatoes and carrots (7). Although body burdens of other organochlorine insecticides, such as DDT and DDE, have diminished markedly over the last 20-plus years, levels of chlordane compounds in the U.S. populace have not declined to the same extent. Levels of chlordane compounds in body fat increase with age in the United States.
Exchanging one problem for another
All of these insecticides are in the same class of organochlorines, called cyclodienes, which were first made in the 1940s. Their development was by chance, during a search for possible uses of a byproduct of synthetic rubber manufacturing. By chlorinating this byproduct, persistent and potent insecticides were easily and cheaply produced. The chlorines, seven in the case of heptachlor and eight in trans-chlordane, oxychlordane, aldrin, and dieldrin, surround and stabilize the cyclodiene ring (the carbon skeleton).
Chlordane compounds are stable endocrine disruptors that have been shown by this author (8) and others to bind to estrogen receptors found in and on many cell types, including insulin-producing cells of the pancreas. The binding of chlordane compounds to these receptors causes increases in oxidants and phosphorylation of regulator proteins. Oxidants can directly damage insulin-producing cells in the pancreas and perpheral cells, limiting the production of insulin and the uptake of glucose (9). Released oxidants can further induce the release of inflammatory mediators in various cells, initiating localized chronic inflammation.
Besides diabetes and insulin resistance, exposure to chlordane compounds has been linked to a variety of symptoms (headache, lethargy, and upper respiratory infections), human cancers (prostate, breast, and testicular cancers, leukemia, and lymphoma), and chronic diseases (allergies, anxiety, depression, Parkinson’s, and Crohn’s disease). These symptoms and diseases could, at least in part, be caused by local chronic inflammation.
There is no safe level of exposure to chlordane compounds. However, two federal agencies have published minimal risk values. The Agency for Toxic Substances and Disease Registry has established 10 ng/M3 as the Minimal Effect Level for non-cancer effects. The U.S. Environmental Protection Agency, however, reports that the same concentration of chlordane compounds in air increases lifetime cancer rates by 1 one in 1 one million exposed persons.
Over the last 14 years, this author has sampled and analyzed the air of hundreds of homes in the United States. There appears to be a relationship between the level of exposure of occupants to chlordane compounds and the severity of their symptoms. High levels, greater than 300 nanograms of chlordane compounds per cubic meter of air (300 ng/M3), are usually associated with neurological problems, especially depression. Scientific studies have now established links between diabetes and depression in patients (10).
What to do
Persons who have been diagnosed with diabetes and/or insulin resistance and would like to reduce their exposures to chlordane compounds should consider taking the following actions in the following order.
- If you live in a house built before 1988 that is located in the southern three-quarters of the United States, test the air in your home for chlordane compounds.
- Reduce your consumption of meat and dairy fat.
- Consider peeling vegetables like potatoes and carrots grown in soils of unknown chlordane history.
If chlordane is found in your home air, consider installing a heat-exchange ventilation system. Most major heating/air conditioning manufacturers offer these systems, which have been shown to markedly reduce chlordane levels and can be easily interfaced to current ducting systems.
If you have questions about chlordane compounds in the air of your home and their health risks, email Dr. Cassidy at firstname.lastname@example.org or call 888.836.4489. Additional information about chlordane, testing for chlordane in home air, links to other websites, and Dr. Cassidy’s publications and bio can be found at www.toxfree.net.
Dr. Cassidy received a Doctorate of Toxicology from the University of Cincinnati Medical School, a Master of Science in Toxicology from University of Kentucky, and a Bachelor of Science in Biology from University of Evansville.
- D. Lee, et al. (2006). A strong dose-response relationship between serum concentrations of persistent organic pollutants and diabetes. Diabetes Care. 29:1638-1644.
- D. Lee, et al. (2007). Association between serum concentrations of persistent organic pollutants and insulin resistance among nondiabetic adults. Diabetic Care. 30:622-628.
- S. Cox, et al. (2007). Prevalence of self-reported diabetes and exposure to organochlorine pesticides among Mexican Americans: Hispanic health and nutritional examination survey, 1982-1984. Environmental Health Perspectives. 115:1747-1752.
- M. P. Montgomery, et al. (2008). Incident diabetes and pesticide exposure among licensed pesticide applicators: Agricultural health study, 1993-2003. American Journal of Epidemiology Advance Access published March 14 2008. http://aje.oxfordjournals.org/cgi/content/abstract/kwn028v1.
- R.A. Ruthann, et al. (2003). Phthalates, Alkylphenols, Pesticides, Polybrominated Diphenyl Ethers, and other Endocrine-Disrupting Compounds in Indoor Air and Dust. Environmental Science & Technology. 37:4543-53.
- U.S. Environmental Protection Agency. (1990). Nonoccupational pesticide exposure study (NOPES) EPA 600/3-90-003. NTIS no. PB90-152224.
- M. J. Mattina, et al. (2000). Chlordane Uptake and Its Translocation in Food Crops. Journal of Agriculture and Food Chemistry. 48:1909-1915.
- R. A. Cassidy, et al. (2005). The link between the insecticide heptachlor epoxide, estradiol, and breast cancer. Breast Cancer Research and Treatment. 90:55-64.
- N. Houstis, et al. (2006). Reactive oxygen species have a causal role in multiple forms of insulin resistance. Nature. 440:944-948.
- S. H. Golden, et al. (2008). Depressive Symptoms and Diabetes. JAMA. 300:2116.