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Researchers from Northwestern University's School of Medicine have determined that the use of certain pesticides over a lifetime produces a shortening of chromosome telomeres.
The researchers tested 1,234 men as part of a study of 57,310 licensed pesticide contractors – from the Agricultural Health Study, orchestrated by the National Cancer Institute, the National Institute of Environmental Health Sciences, and the U.S. Environmental Protection Agency. This particular study was conducted in partnership with the Robert H. Lurie Comprehensive Cancer Center.
The researchers had the subjects – adult males involved with pesticide application on farms or other environments – fill out extensive questionnaires on their pesticide use over their lifetimes. Some 48 pesticides were used and included in the study.
The researchers also collected from each subject buccal cells – taken from cheek swabs. Using what is called "Real-time polymerase chain reaction" testing, the researchers analyzed those cells for telomere length.
The researchers found that those males who applied pesticides in their work more during their lifetimes had significantly reduced telomere length. And the more pesticides used over their lifetimes, the shorter their telomeres were.
The researchers also matched up and quantified telomere length together with specific pesticides, and determined that certain pesticides produced significant telomere shortening. These included:
• alachlor (2-Chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide; herbicide, brand names Alanex, Bronco, Cannon, Crop Star, Intrro, Lariat, Lasso, Micro-Tech, and Partner)
• metolachlor ((RS)-2-Chloro-N-(2-ethyl-6-methyl-phenyl)-N-(1-methoxypropan-2-yl)acetamide; herbicide, brand names Bicep, Dual, Pennant, CGA-24705 and Pimagram)
• trifluralin (a,a,a-Trifluoro-2,6-dinitro-N,N-dipropyl-p- toluidine, brand names Treflan, Elancolan, Trefanocide)
• permethrin (3-Phenoxybenzyl (1RS)-cis,trans-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropanecarboxylate; insecticide, included in many formulations including Elimite, Nix, Acticin, and many others)
• toxaphene (2,2,5-endo,6-exo-8,9,10-Heptachloro-bornane; brand names include Chlorinated camphene, Octachlorocamphene, Camphochlor, Agricide Maggot Killer, Alltex, Allotox, Crestoxo, Compound 3956, Estonox, Fasco-Terpene, Geniphene, Hercules 3956, M5055, Melipax, Motox, Penphene, Phenacide, Phenatox, Strobane-T, Toxadust, Toxakil, Vertac 90%, Toxon 63, Attac, Anatox, Royal Brand Bean Tox 82, Cotton Tox MP82, Security Tox-Sol-6, Security Tox-MP cotton spray, Security Motox 63 cotton spray, Agro-Chem Brand Torbidan 28, and Dr Roger's toxene).
• DDT (dichloro-diphenylchloroethane)
For DDT, the researchers found that the more high-intensity days someone used DDT, the shorter their telomere length was.
Telomeres are repeated DNA sequences at the end of chromosomes. Research has found that telomeres help protect the chromosomes and provide for continuous replication of cells. Telomere lengths typically shorten as our number of potential cell replications dwindle – but also occur in DNA abnormalities such as cancer. A shortening of telomere length has also been linked with aging.
The researchers found that the seven pesticides/herbicides producing the most telomere shortening were also ones that have been linked with cancer. They stated:
Seven pesticides previously associated with cancer risk in the epidemiologic literature were inversely associated with reduced telomere length in buccal cell DNA among cancer-free pesticide applicators."
Other research has linked pesticide/herbicide use with higher rates of cancers. A 2006 study found metolachlor application was linked with higher risks of lung cancer. A 2009 study found that butylate was linked with prostate cancer and non-Hodgkin lymphoma. A 2012 review from Health Canada found that 12 pesticides were linked with increased cancer rates and six pesticides – including several noted above that shorten telomere length – also had laboratory evidence of cancer association.
The Health Canada research found that chlorpyrifos, diazinon, dieldrin, metolachlor and pendimethalin were linked with higher rates of lung cancer among those who applied these chemicals more frequently.
They found that EPTC (s-ethyl dipropylthiocarbamate – Chemolimpex, Eptam) and pendimethalin (3,4-Dimethyl-2,6-dinitro-N-pentan-3-yl-aniline - Prowl, PRE-M, Stomp, Stealth, Halts, Pendulum) were linked with higher rates of pancreatic cancer.
They determined that aldicarb, dicamba, EPTC and imazethapyr were linked with higher rates of colorectal cancers.
They found that alachlor was linked with higher rates of lymphatic-type cancers.
Imazethapyr was linked with greater incidence of bladder cancer.
Prostate cancer incidence was linked with fonofos use.
Brain cancer was linked with chlorpyrifos application.
Carbaryl and toxaphene were both linked with greater melanoma incidence.
The Health Canada research also found that children on Iowa farm families that applied higher levels of pesticides/herbicides had greater incidence of overall cancer, and greater lymphoma rates.
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Hou L, Andreotti G, Baccarelli AA, Savage S, Hoppin JA, Sandler DP, Barker J, Zhu ZZ, Hoxha M, Dioni L, Zhang X, Koutros S, Beane Freeman LE, Alavanja MC. Lifetime Pesticide Use and Telomere Shortening among Male Pesticide Applicators in the Agricultural Health Study. Environ Health Perspect. 2013 Jun 7.
Rusiecki JA, Hou L, Lee WJ, Blair A, Dosemeci M, Lubin JH, Bonner M, Samanic C, Hoppin JA, Sandler DP, Alavanja MC. Cancer incidence among pesticide applicators exposed to metolachlor in the Agricultural Health Study. Int J Cancer. 2006 Jun 15;118(12):3118-23.
Lynch SM, Mahajan R, Beane Freeman LE, Hoppin JA, Alavanja MC. Cancer incidence among pesticide applicators exposed to butylate in the Agricultural Health Study (AHS). Environ Res. 2009 Oct;109(7):860-8.
Weichenthal S, Moase C, Chan P. A review of pesticide exposure and cancer incidence in the agricultural health study cohort. Cien Saude Colet. 2012 Jan;17(1):255-70.