Although Benjamin and Ryan Barrus would rather play outside each evening, Kaylene Barrus keeps her 7- and 8-year-old sons inside their Mesa home, protected from mosquitoes that might be carrying the West Nile virus.
But Barrus isn’t sure what she is more afraid of — mosquito bites or the clouds of pesticide released from fogging trucks nightly throughout Maricopa County.
"It concerns me both ways," Barrus said. "The thing that bothers me is it doesn’t seem to matter what we think (about mosquito fogging). They’re just going to do it."
Barrus’ conflict reflects the public health dilemma county and state officials say they’re facing as they fight West Nile virus: Either spray pesticides in communities or risk more human infections.
As the number of people infected with the virus grows, the Maricopa County Board of Supervisor’s decision Aug. 5 to ramp up ground-level fogging efforts using the pesticide Sumithrin was clear, said John Townsend, vector control manager for the county Environmental Services Department.
"We have to look at it from a public health standpoint," he said. "I don’t know of anyone dying from (exposure to Sumithrin). I know of three people who have died of West Nile."
But it is unclear exactly how safe Sumithrin is.
• The U.S. Environmental Protection Agency and the Centers for Disease Control and Prevention have found low health risks to humans from exposure to Sumithrin, but their findings are based on animal research. Few studies have been done on humans exposed to the pesticide.
• The EPA is in the process of reassessing all pesticides registered before 1984, using updated scientific research. Sumithrin, which was registered in 1975, is not scheduled for its reassessment until September 2008.
• Sumithrin contains Piperonyl Butoxide, which the EPA classifies as a possible human carcinogen.
• Public health authorities in Arizona and other states using Sumithrin have advised people to stay inside their homes during pesticide applications. On its Web site, the EPA also suggests turning off air conditioners to prevent the chemical from entering the home.
• State and county Web sites and educational materials released to the public during this West Nile season have provided little information about Sumithrin.
"Safety is a relative term," said Paul Baker, a pesticide coordinator at the University of Arizona. "It’s always a balancing act between minimizing and keeping the West Nile problem under control (protecting) the health safety of the general public."
Environmental and public health authorities insist that Sumithrin, which belongs the chemical family of syn thetic pyrethroids, is the best pesticide that Arizona could use on mosquitoes.
An increasingly common substance used by states fight ing West Nile, pyrethroids a synthetic version of the natural insecticide in chrysanthemums, degrading within hours of being applied. The EPA CDC have approved the use
synthetic pyrethroids, which exist in common household products such as insect spray and lice shampoo.
And Sumithrin is applied low doses — less than one third ounce for every acre.
"It’s not without its risks," Brown told the Board of Supervisors August 5. "There are studies here and there of health effects, but this one still stacks up as the safest one out there."
But while synthetic pyrethroids mimic a naturally occurring insecticide, they were developed in the laboratory to work better and faster than their botanical counterpart, according to pesticide authorities. Sumithrin is a neurotoxin, causing mosquitoes to seize to death.
Piperonyl Butoxide is added to make the pyrethroid more lethal to insects, cutting off their ability to detoxify the chemical.
Laboratory tests on animals found that high doses of synthetic pyrethroids caused liver damage, low birth weights in pups born from pregnant rats, rapid breathing, tremors, tw itching, aggression, benign skin lesions and benign tumors in the ovaries, liver and the thyroid, according to the National Pesticide Information Center, a cooperative effort of Oregon State University and the EPA.
In animals fed high doses of Piperonyl Butoxide, some studies have found liver damage and liver cancer, as well as impaired motor skills in male mice and lowered weight in pregnant rats and fetuses.
But people are not likely to suffer such adverse outcomes if they are exposed to Sumithrin, public health authorities said, because the dose would be much lower.
"The bottom line here is the dose makes the poison," Baker said.
While animal studies of synthetic pyrethroids and Piperonyl Butoxide are abundant, data on humans is almost nonexistent.
For both substances, the center reports no human data on accidental poisonings, work-related exposures or other human studies that could determine human risks for cancer, reproductive problems or birth defects.
"Why would human beings subject themselves to a study of known toxins?" said Eric Hampton, a naturopathic physician in Mesa who treats chemically sensitive people. "Nobody is going to do that, and that’s why there haven’t been studies."
But without data on humans, public health officials cannot be sure of the public health risks of spraying pesticides, said Sheldon Krimsky, a professor in the department of urban and environmental policy and planning at Tufts University, Boston.
Krimsky researched synthetic pyrethroids in his fight agai nst fogging in Massachusetts.
Studies are needed on lowdose exposure in humans, on risks to children when they touch toys or playground equipment hit by synthetic pyrethroids, and other real-life consequences to pesticide application, he said.
Such data would be especially important to pregnant women and those with compromised immune systems, chemical sensitivities and asthma.
"The logic I used was that if the government were planning to develop a vaccine to treat West Nile, they would have to prove it was safe and efficacious," Krimsky said.
"It seems to me they should have to demonstrate the same thing with pesticides," Krimsky said.
What’s needed are systematic epidemiological surveys on people exposed to synthetic pyrethroids, Krimsky said.
From 1999 to 2002, nine states, including Arizona, reported surveillance data to the CDC on people with illnesses associated with exposures to synthetic pyrethroids and other insecticides.
Out of a combined population of about 118 million in 2000, the CDC identified 133 cases of acute insecticiderelated illness.
The CDC concluded that certain pesticides "posed a low risk for acute, temporary health affects among persons in areas that were sprayed."
But the CDC also found that surveillance results probably underestimated the magnitude of illnesses associated with mosquito-control efforts.
The surveys could not account for people who did not seek medical care for pesticide exposure, were not properly diagnosed or did not have their case reported.
This year, the Valley doesn’t have an integrated system in place to report exposures related to mosquito fogging, said Doug Hauth, spokesman for the county’s Department of Public Health.
Having one would be too costly, he said.
People can have their pesticide exposures recorded by the county, but they must be seen by a physician first to ensure that a medical condition exists, Hauth said.
Meanwhile, the county officials said they are fogging up to 16,500 acres a night and achieving the 75 percent mosquito kill rate expected by Sumithrin’s manufacturer.
"I don’t think we’ve jumped the gun (by using Sumithrin) because it’s the only gun we have," said Townsend of the county Environmental Services Department. "Our only option is to fog, and this is the safest way."
West Nile in Arizona: There have been 281 reported West Nile virus infections statewide as of Aug. 12. Three of those cases reulted in death. If you have questions:
• For information about areas Maricopa County will fog for mosquitoes, call (602) 372-3000 or visit www.maricopa.gov/wnv
• For public information on the West Nile virus, call (602) 747-7500 or visit www.maricopa.gov/wnv
• To register as a chemically sensitive person for alerts from the county when there is mosquito fogging in your area, call (602) 506-0700.