Bug sprays may bug you, too - for a day.

People whose homes have been sprayed for bugs frequently complain of symptoms that resemble mild insecticide poisoning-headaches, burning eyes, runny noses, nausea, even tightness in the chest. However, such symptoms are less likely to stem from reactions to the pesticide than to the added solvents that make it sprayable, a new study concludes.

These emulsifiers and propellants account for up to 95 percent of sprayed material. Though manufacturers label them inert, this designation refers only to the fact that they are not part of the active pesticide, points out John A.

Bukowski, formerly of New Jersey's Pesticide Control Program in Trenton. In fact, he notes, many of these solvents, which tend to enter the air far more readily than the pesticides do, are quite irritating.

To see whether the solvents might reach concentrations likely to provoke symptoms, Bukowski's office teamed up with New Jersey's Environmental and Occupational Health Sciences Institute in Piscataway to study apartments treated with the insecticide chlorpyrifos.

Exterminators sprayed just the perimeter of two identical, unoccupied apartments, hitting baseboards and crevices along the edges of the floor. In another two, they sprayed a fine mist of the pesticide over the entire floor area, including carpets.

Computer models had indicated that solvent concentrations in such unventilated apartments would peak in 2 to 4 hours, suggesting that the dwellings should be ventilated for 3 to 6 hours. Though the concentrations peaked as predicted at about 22 milligrams per cubic meter of air, they didn't do so until 10 to 12 hours after treatment.

Even after 24 hours, solvents remained elevated in three of the apartments at more than twice their prespray concentrations, the researchers report in the August Environmental Science & Technology.

These solvents-some of which are found in paints or resemble volatile chemicals emitted by glues and fabric in new furniture and carpets-have been associated with sick building syndrome, notes Bukowski, now at the University of Prince Edward Island in Charlottetown. "What we're basically showing," he says, "is that you can get a sick building syndrome for a day or so from an insecticide application."

Robert Dyer, assistant director of the Environmental Protection Agency's National Health Effects and Environmental Research Laboratory (NHEERL) in Research Triangle Park, N.C., is not convinced. Bukowski's assertion that the elevated solvents could cause symptoms comes from comparing concentrations of the unidentified volatile organic chemicals (VOCs) emitted by chlorpyrifos to symptom-provoking concentrations of a well- defined mix of 22 VOCs studied at NHEERL. Unless the two groups of VOCs match, Bukowski's group may be "comparing apples and oranges," Dyer says.

The new study does "point to an issue that's very important," however-the need to improve labeling on when and how long to ventilate an area that has been treated, says Lynn R. Goldman, EPA's assistant administrator for prevention, pesticides, and toxic substances. Few pesticides developed for indoor use recommend vacating treated premises temporarily, Bukowski notes, or give airing-out instructions beyond "ventilate adequately."

Currently, EPA is reevaluating information and labeling for all pesticides registered before 1985. So far, Goldman told Science News, "in every case, we're finding a need to change how [pesticides] are used," which can include ventilation requirements. In the near future, she says, expect labeling with more explicit prescriptions on how long to air out treated areas, based on data for additives as well as active ingredients.