OBJECTIVETo describe trends of changes in blood lead levels in children aged 1 - 6 years during the time period before and after introducing lead free gasoline in Shanghai 1997 and 1999.

METHODSBlood lead levels of 1 969 children aged 1 - 6 years were determined by a sampling survey in five districts of Shanghai in August and September, 1997. Blood lead levels of the same population were re-determined by the same method from April to June in 1998 and from August to September in 1999. Filter paper blood lead test was carried out monthly using the filter paper blood lead proficiency testing program of Centers for Disease Control in the United States. The results from blood lead samples were under acceptable ranges during the study.

RESULTSThe geometric means of blood lead levels were 83 microgram/L in 1997, 80 microgram/L in 1998 and 76 microgram/L in 1999, respectively. The prevalence rates of childhood lead poisoning (blood lead level was equal or more than 100 microgram/L) were 37.8% in 1997, 25.7% in 1998 and 24.8% in 1999. The amounts of decrease on average blood lead levels in the five districts between 1997 and 1999 were 10 microgram/L, 11 microgram/L, 6 microgram/L, 4 microgram/L and 2 microgram/L, respectively.

CONCLUSIONLead poisoning is a preventable disease. The average levels of lead in young children in Shanghai decreased significantly after the introduction of lead free gasoline to Shanghai. Lead emissions from vehicles running on leaded gasoline was one of the important contributors to increase the children's blood lead levels in Shanghai. Lead poisoning is not evenly distributed among children in Shanghai, resulting in the different levels of decline.