APPENDIX I-K: Dibrom Idaho 06.


Spray used in West Nile mosquito control a potential health hazard?

OK, got your attention. Much of Boise, Idaho will undergo aerial application of Dibrom, a pesticide, beginning tomorrow night (Monday, 8-21). Idaho has the dubious distinction of having the largest number of human cases of West Nile, prompting our temp governor Jim Risch to declare a disaster. About 50,000 acres of Ada County will be sprayed with Dibrom, applied by Vector Disease Control, a southeast company. Brian Wilbur, director of Ada County's pest control district, says the chemical is not harmful to humans, pets, birds or fish.

Is that really the case?


Naled (trade name Dibrom) is an organophosphate with many of the same characteristics and concerns as malathion. Naled can cause cholinesterase inhibition in humans: that is, it can over stimulate the nervous system causing nausea, dizziness, confusion, and at high exposures, can cause respiratory paralysis and death. One of the byproducts of degradation of Naled is dichlorvos, another registered organophosphate. This compound is of toxicological concern.

Researchers at the Cornell University Program on Breast Cancer and Environmental Risk Factors in New York State review several studies on dichlorvos. In one study, female mice that were fed high doses of dichlorvos over a long period of time had a higher frequency of stomach cancers than untreated mice. High doses of dichlorvos fed over two years caused an increase in the number of male rats that had pancreatic tumors and leukemia. A higher number of leukemia cases were reported in one study among male farmers who used dichlorvos for more than ten days per year, compared to those who had not used dichlorvos. A higher number of childhood brain cancer cases were reported among families that used dichlorvos than among families that did not.18

The pesticide trichlorfon is a common ingredient in the mosquito pesticide dibrom (naled). In one study, trichlorfon was found to cause a "severe reduction" in brain weight (and shape) in test animals exposed. The timing of exposure to the developing offspring appeared to be the key factor in determining neurological damage (known as the "critical brain growth period"). It occurred when the chemical was administered between 40-50 days gestation for the guinea pig, which scientists say, correlates with the brain growth spurt period for the animal.

Russian scientists studied the growth rates of fish called Bream (Abramis brama) after exposure to the dibrom/naled contaminant dichlorvos. The first major effect detected was a significant reduction in the growth rates of the fish. Researchers believe it may be due to the subtle neurotoxin actions of the pesticide and its effects upon the areas of the brain involved in feeding or food search mechanisms.

Naled is characterized as very highly toxic to bees and aquatic invertebrates. It is moderately to highly toxic to fish and slightly toxic to upland game birds and waterfowl. There is potential for chronic risk from Naled to estuarine invertebrates.

And, toxicity to humans aside, is the use of such pesticides even the best way to control mosquito populations and the spread of West Nile?

- OVERKILL: Why Pesticide Spraying for West Nile Virus May Cause More Harm Than Good

Executive Summary

"The current policies by state and municipal officials in the Commonwealth that allow and encourage the spraying of toxic pesticides to combat the West Nile virus (WNv) are both dangerous and ineffective.

Spraying toxic pesticides to combat WNv, may cause more harm than good, exposing the population to a new public health threat through exposure to toxic chemicals. In fact, spraying may even have the paradoxical effect of increasing the mosquito population by affecting its predators."