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What's in the spray, anyway?

As efforts to resume aerial mosquito spraying Wednesday night were once again dashed by the winds, the Sacramento region continued slogging through a crash course on the chemicals being sent aloft to attack West Nile virus.

If this stuff kills mosquitoes so well, some people are asking, what the heck is it doing to humans?

Probably very little, largely because the exposure is so brief, according to doctors and scientists familiar with pesticide research.

Last week, the Sacramento-Yolo Mosquito and Vector Control District began spraying a fine mist of EverGreen Crop Protection EC 60-6 over more than 50,000 acres north of the American River.

Although a plane took off at 8:12 p.m. Wednesday on a mission to spread pesticide over as much as 66,000 acres south of the river, winds were so troublesome that it turned back without spraying, said Allen Loe, president of Vector Disease Control, the mosquito district's contractor. All efforts to spray Wednesday night were called off by 10 p.m.

About 10 protesters gathered on the Capitol steps Wednesday evening to protest the spraying, arguing there wasn't enough warning for all residents and saying they feared the health impacts on children.

The ongoing pesticide applications have sent Sacramentans scurrying to Web sites, product labels, advocacy groups and anyone else who can tell them more about the makeup and effects of EverGreen 60-6.

Some have found alarming snippets. There is at least one case of a woman dying from an allergic reaction to a flea shampoo with similar ingredients. One study in farmers found a statistical link between one of the ingredients and leukemia. Some animal studies have prompted the U.S. Environmental Protection Agency to classify one ingredient as a possible carcinogen.

What's often missing from such summaries is a fundamental of toxicology.

"It all depends on the dose. Everything is a poison if you get the doses high enough, and that includes pure water," said Dr. Stephen McCurdy, a UC Davis professor whose interests include pesticides and farmworker hazards.

Given what a tiny dose could be delivered during three days of spraying in any one area, and given that people can cut their dose basically to zero by staying indoors, the aerial treatments should hurt no one - and could help prevent a sometimes-fatal disease, he said.

Sacramento County leads the state in human West Nile activity.

McCurdy calculated that so little pesticide is being used aerially that someone would have to work very hard to get as much exposure from the spraying as they'd get from a single treatment with a common de-lousing shampoo.

Ray Chavira, an environmental scientist in the pesticides office of the U.S. EPA's regional office in San Francisco, gave similar assurances, saying that EverGreen's home uses against fleas, lice, ticks and more make it one of the least toxic products out there.

Even so, Chavira noted that all pesticides by nature are toxic. "We don't label things as safe," he said. "The standard of safety is 'no unreasonable adverse effect.' "

Because pesticides are undeniably meant to kill, some spraying critics worry that we may not know all the ways the spraying could affect people or interact with the sea of other man-made chemicals in the environment, and doctors do not dispute that. They just consider its likelihood to be remote.

The EverGreen product being used in Sacramento skies is a chemical cocktail with a one-two punch.

Its two active ingredients are pyrethrins and piperonyl butoxide, pronounced PIP-er-nil bew-TOX-ide and often shortened to PBO.

Pyrethrins, which are derived from chrysanthemums, attack the nervous system. Stricken mosquitoes first speed up and fly erratically before falling to the ground, legs twitching. Sometimes the tremors are so intense the legs twitch off, said Dan Markowski, one of the district's pest control contractors.

Mosquitoes' own defenses can fight back, and some might survive pyrethrins alone. PBO is a "synergist" that disables those defenses, stopping or slowing the insect's ability to break down pyrethrins so that the pesticide will be more deadly.

Pyrethrins don't last long in insects, people or the environment, breaking down quickly in sunlight and moisture, and are considered a relatively benign choice among pesticides.

"This is a whole lot less toxic than a whole lot of other mosquito and vector districts are using," said Steve Zien, a Citrus Heights pesticide applicator specializing in organic landscapes who opposes the aerial spraying but still applauds the district for its choice of pesticides.

EverGreen 60-6 contains about 6 percent pyrethrins, 60 percent PBO and 34 percent of unspecified ingredients.

PBO also moves quickly through the body, said Dr. Christian Sandrock, a UC Davis professor of medicine with expertise in infectious diseases and pulmonary medicine. There is no evidence it significantly affects the way the human body processes pyrethrins or other pesticides, and it would be unlikely to do so since it stays in the system for such a short time, he said.

In humans, massive overdoses of the pyrethrins-PBO combo can cause nausea, vomiting, tremors and, in extreme cases, seizures or death, Sandrock said. At minute levels, though, it is simply broken down in the liver and excreted through urine, he added.

Chavira, the EPA environmental scientist, said that even if PBO is a carcinogen - and that's not certain - a short exposure to a low concentration of the chemical is not cause for worry.

A review in 2003 by the U.S. Centers for Disease Control and Prevention of nine states that sprayed insecticides aerially to control mosquitoes carrying West Nile virus found few serious human health problems potentially related to the spraying. Reported problems most often involved four pesticides considered more toxic than EverGreen 60-6.

Two of those were malathion and naled, both in a class of pesticides known as organophosphates that attack the nervous system and can cause systemic poisoning in people. Malathion was the pesticide used to kill the Medfly farm pest in a highly controversial aerial spraying campaign in California in the 1980s.

The other two mosquito pesticides most frequently associated with problems were sumithrin and resmethrin. Both are pyrethroids, a synthetic version of pyrethrins. Pyrethroids are designed to last in the environment longer than and generally have been found to be more toxic than their natural cousins.

Dr. Walter Alarcon, who works in the division of surveillance, health evaluation and field studies of CDC's National Institute for Occupation Safety and Health, said the main health problem in people associated with exposure to pyrethrins is an allergic reaction.

"It can produce contact dermatitis and be a respiratory allergen," Alarcon said.

West Nile at a glance

To report a dead bird, call (877) 968-2473 (WNV-BIRD)

Sacramento and Yolo County residents can request mosquitofish, report untreated pools of standing water, get aerial spraying information and sign up for e-mail notification of local insecticide treatments by calling the Sacramento-Yolo Mosquito and Vector Control District at (800) 429-1022 or (916) 685-1022, or at

Placer County residents can get West Nile information and obtain mosquitofish by calling the Placer Mosquito Abatement District at (916) 435-2140. For other information, contact the Placer County West Nile virus line at (530) 889-4001 or go to or

Butte County residents can go to, or call (800) 339-2941.

Anyone with concerns about the health effects of spraying can call the California Poison Control number at (800) 876-4766.

Other helpful Web sites:

Centers for Disease Control and Prevention,;

California Department of Health Services,

Prevention tips

To reduce the risk of catching West Nile, the Sacramento-Yolo Mosquito and Vector Control District recommends:

Use an effective mosquito repellent containing ingredients such as DEET, Picaridin or oil of lemon eucalyptus.

Repair tears in door and window screens.

Drain standing water.

Wear long pants and long sleeves outdoors when practical.

Avoid being outside at dawn and dusk, when mosquitoes are most active.

About the writer:

  • The Bee's Carrie Peyton Dahlberg can be reached at (916) 321-1086 or Bee medical writer Dorsey Griffith contributed to this report.