In a pioneering study examining the exposure of urban and suburban children to household pesticides, all but one of 96 Seattle-area preschool children were found to have trace levels of pesticide in their urine, according to researchers at the University of Washington. The study found that "children whose families reported pesticide use in their gardens had significantly higher [chemical] concentrations than whose who had gardens but did not use any pesticides." All the concentrations were relatively tiny and therefore unlikely to cause immediate health problems. But scientists don’t yet know whether long-term exposure to pesticides at low levels can eventually lead to serious problems.