Scientists reaffirm that airplane fuel used for small aircraft continues to pose a risk to the public.By Claire BarberFor years health officials have held that there is no safe level of lead exposure for humans. Even low levels can cause irreversible cognitive decline in children. Yet despite the risk, leaded aviation fuel—whose particulates travel in the air and are inhaled or can settle in soil or other substrates—continues to be used in small airplanes and helicopters around the country.