At least 100,000 people who claim they suffered health problems because of exposure to the pesticide malathion are part of a lawsuit against the substance's manufacturer. The class action was filed in Tampa, Fla., against Cheminova Inc. of Wayne, N.J. The suit claims the company improperly handled and stored the chemical, which was sprayed in 1997 and 1998 in several Florida counties, including Hillsborough, Polk, Manatee and Sarasota. Malathion is used to eradicate the fruit-eating medfly. An estimated 1 million people lived and worked in the spray zone, and some complained of sinus congestion, headaches and respiratory problems.