JOURNAL OF PESTICIDE REFORM/ FALL 2002 • VOL. 22, NO. 3 ● INSECTICIDE FACTSHEET NALED (DIBROM) Naled is an insecticide in the organophosphate pesticide family used primarily for mosquito control. Dibrom is a common brand name for naled products. About one million pounds are used annually in the U.S. Like all organophosphates, naled is toxic to the nervous system. Symptoms of exposure include headaches, nausea, and diarrhea. Naled is more toxic when exposure occurs by breathing contaminated air than through other kinds of exposure. In laboratory tests, naled exposure caused increased aggressiveness and a deterioration of memory and learning. Naled’s breakdown product dichlorvos (another organophosphate insecticide) interferes with prenatal brain development. In laboratory animals, exposure for just 3 days during pregnancy when the brain is growing quickly reduced brain size 15 percent. Dichlorvos also causes cancer, according to the International Agency for Research on Carcinogens. In laboratory tests, it caused leukemia and pancreatic cancer. Two independent studies have shown that children exposed to household “no-pest” strips containing dichlorvos have a higher incidence of brain cancer than unexposed children. Aerial applications of naled can drift up to one-half mile. According to the U.S. Environmental Protection Agency, naled is moderately to highly toxic to birds and fish. It also reduced egg production and hatching success in tests with birds and reduced growth in tests with juvenile fish. BY CAROLINE COX convulsions, paralysis, and death.3 Figure 1 Naled Breakdown Products Naled (see Figure 1) is an in- O Naled breaks down into dichlorvos, secticide in the organophosphate pes- Br another organophosphate insecticide, ticide family that is commonly used to in animals and soil.4,5 (See Figure 2.) P Cl kill adult (flying) mosquitoes. Naled H3CO O Inert Ingredients has been registered for use in the U.S. Cl since 1959 and is sold under the brand OCH3 Br Like most pesticides, commercial name Dibrom. AMVAC Chemical Cor- naled-containing insecticides contain poration has been the major manufac- 1,2-dibromo-2,2-dichloroethyl dimethyl ingredients other than naled. Many of turer of naled since 1998.1 phosphate these ingredients, according to U.S. pesticide law, are called “inert.” Ex- Use cept for tests of acute effects, toxicol- About one million pounds of Figure 2 ogy tests required for the registration naled are used every year in the U.S. Dichlorvos of a pesticide are not conducted with Approximately 70 percent of this is the combination of ingredients found used for mosquito control; almost O in commercial products.6 all of this is applied aerially. The re- Cl Most inert ingredients are not identi- maining 30 percent is used in agricul- P fied on product labels, and little infor- ture. Major agricultural uses are on H3CO O mation about them is publicly available. Cl cotton in California and Louisiana, on OCH3 For information about the inert in- alfalfa in Idaho and Oregon, and on gredients in Dibrom products, see grapes in California.2 “Inerts in Dibrom Products,” p. 17. naled kills insects by inhibiting acetyl- Mode of Action cholinesterase (AChE), an enzyme in- Symptoms of Exposure Like all organophosphate insecticides, volved in the transmission of nerve im- Symptoms of exposure to naled and pulses from one nerve cell to another. all organophosphate insecticides This causes a “jam” in the transmission include headaches, muscle twitching, Caroline Cox is NCAP’s staff scientist. system, resulting in restlessness, nausea, diarrhea, difficult breathing, NORTHWEST COALITION FOR ALTERNATIVES TO PESTICIDES/NCAP 16 P. O. BOX 1393, EUGENE, OREGON 97440 / (541)344-5044 JOURNAL OF PESTICIDE REFORM/ FALL 2002 • VOL. 22, NO. 3 depression, seizures, and loss of con- exposure was less than 1/6 of the low- sciousness.7 est oral dose causing the same effect.11 Figure 3 An additional study by the Uni- Acute Toxicity of Naled Toxicity to the Nervous versity of California researchers men- 200 System tioned above found that small drop- A symptom of exposure to naled lets of naled (the size produced by that occurs at low doses (whether by ultra low volume sprayers often used breathing, through the skin, or orally) in mosquito spraying) were about 150 is inhibition of acetylcholinesterase four times more acutely toxic than (AChE). In studies conducted by naled larger droplets.12 manufacturers, exposure of rats to Effects on Behavior naled in air at a dose of 0.3 milli- 100 grams per kilogram of body weight Exposure to naled has multiple (mg/kg) per day for three weeks, skin effects on behavior. In a study con- exposures of 20 mg/kg per day for 4 ducted by naled’s manufacturer, naled weeks, and oral exposure of 10 mg/ caused reduced muscle strength, slow 95% confidence intervals 50 kg per day for 4 weeks caused inhibi- responses to stimulation, and reduced with tion of AChE. activity in rats. These behavioral (Smaller lethal dose = higher toxicity) Long-term exposure also caused changes occurred at all but the lowest AChE inhibition; reduced AChE activ- dose level tested in males and all dose 0 ity occurred in dogs exposed orally to levels tested in females,13 suggesting Median lethal dose to rats in milligrams per kilogram Breathing Oral 2 mg/kg per day for 1 year and in rats that females are more sensitive than Type of exposure exposed orally to the same dose for 2 males to naled poisoning. Source: Berteau, P.A. and W.A. Dean. 1978. 8 A comparison of oral and inhalation toxicities years. Exposure to naled’s breakdown of four insecticides to mice and rats. Bull. In addition, the long-term study with product dichlorvos causes increased Environ. Contam. Toxicol. 19: 113-120. dogs found that doses of 2 mg/kg per aggression and impaired memory. The day also caused mineralization of the Indian biochemists mentioned above Naled is more acutely toxic from exposure via spinal cord.8 found that fighting was about 5 times breathing than from oral exposure. Naled’s breakdown product dichlo- rvos inhibits the activity in rats of a nervous system enzyme called neur- opathy target esterase. In experiments NERTS IN IBROM RODUCTS conducted by biochemists at the Post- “I ” D P graduate Institute of Medical Educa- Dibrom Concentrate (EPA Regis- Anemia in newborns can be caused tion and Research (India), doses of 6 tration No. 5481-480) contains the by exposure during pregnancy.6 mg/kg per day reduced the enzyme’s inert ingredient aromatic hydrocar- 1,2,4-trimethylbenzene is activity by about 40 percent. Inhibi- bon solvent (Chemical Abstract Ser- irritating to eyes and skin. It can tion of this enzyme causes partial pa- vices number 64742-94-5), also depress the central nervous system ralysis of the hind legs followed by called solvent naphtha.1 This sol- and cause headache, fatigue, nau- incoordination.9 vent contains two aromatic hydro- sea, and anxiety. It has also caused carbons, naphthalene and 1,2,4- asthmatic bronchitis.7 Toxicity Caused by Breathing trimethylbenzene.2 Naled 1. U.S. EPA. Office of Prevention, Pesticides Dibrom 8 Emulsive (EPA Regis- and Toxic Substances. Office of Pesticide Naled is more potent when expo- tration No. 5481-479) contains Programs. 2002. Letter from L.V. Moos, In- 3 formation Resources and Services Division sure occurs through breathing than naphthalene. acting director, to NCAP, July 25. when exposure occurs through eating Dibrom 8 Miscible (EPA Regis- 2. Shell Chemical Company. 2002. Material contaminated food or drinking con- tration No. 34704-351) contains sol- safety data sheet: Shellsol® A150. 4 www.euapps.shell.com/MSDS/GotoMsds. taminated water. Toxicologists at the vents whose ingredients can in- 3. Amvac Chemical Corp. 2002. Material safe- University of California found that in- clude naphthalene and trimethyl- ty data sheet: Dibrom® 8 Emulsive. halation was 20 times more toxic to benzene.5 www.cdms.net. 4. Platte Chemical Co. 2001. Material safety rats than oral dosing (dosing through Naphthalene has been classified data sheet: Dibrom 8 Miscible. the mouth) of naled.10 (See Figure 3.) by EPA as a possible human car- www.cdms.net. 5. Shell Chemical Company. 2002. Material The U.S. Environmental Protection cinogen because it caused lung tu- safety data sheet: Shellsol A100. Agency (EPA) came to a similar con- mors in mice following inhalation. www.euapps.shell.com/MSDS. clusion based on tests submitted to Naphthalene exposure also causes 6. Hazardous Substance Data Bank. 2002. Naphthalene. http://toxnet.nlm.nih.gov. the agency by naled’s manufacturer: headaches, restlessness, lethargy, 7. Hazardous Substance Data Bank. 2002. the dose required to cause cholinest- nausea, diarrhea, and anemia. 1,2,4-trimethylbenzene. http://toxnet.nlm.nih.gov. erase inhibition through inhalation NORTHWEST COALITION FOR ALTERNATIVES TO PESTICIDES/NCAP P. O. BOX 1393, EUGENE, OREGON 97440 / (541)344-5044 17 JOURNAL OF PESTICIDE REFORM/ FALL 2002 • VOL. 22, NO. 3 entists found that injections of Figure 4 dichlorvos at weekly intervals in Exposure to Naled’s Breakdown Product Increases mice caused a 3-fold increase in the Aggressiveness and Disrupts Learning number of mutations in liver cells.26 A team of geneticists from the National 20 Fighting 8 Learning an Research Centre (Egypt) found that Avoidance Behavior oral doses of dichlorvos given to mice, or feeding mice diclorvos-treated 15 6 beans, increased the incidence of chro- mosome abnormalities in both spleen 10 4 and sperm cells.27 Ability to Cause Cancer 2 5 (Carcinogenicity) (with standard deviations) Number of trials required to EPA classifies naled as a “Group E” learn an avoidance behavior Number of fighting episodes 0 0 chemical. Group E chemicals have (per minute, with standard deviations) Unexposed Exposed Unexposed Exposed demonstrated “evidence of noncar- cinogenicity” in laboratory tests.28 Source: Sarin, S.