“Environmental forensics” is defined as the systematic and scientific evaluation of physical,chemical and historical information for the purpose of developing defensible scientific and legal conclusions regarding the source or age of a contaminant release into the environment.Leaded gasoline had been regarded as one of the major source of human lead(Pb)exposure.Nowadays,the health impact from unleaded gasoline is still unclear.Pb has four stable isotopes: 204Pb(1.4%),206Pb(24.1%),207Pb(22.1%),and 208Pb(52.4%).Pb isotopic signatures have been demonstrated to be a robust proxy for distinguishing different sources of local and global lead pollutions.Techniques of high-precision gasoline Pb isotopic determinations by multi-collector inductively coupled plasma mass spectrometry(MC-ICP-MS)were developed.The characteristics of stable lead isotope ratios,including 208Pb/207Pb,208Pb/206Pb,207Pb/206Pb,and 206Pb/204Pb,of different brands and environmental material were measured.Samples included a set of 92 unleaded gasoline,95 unleaded gasoline,98 unleaded gasoline,and diesel fuel,from the Chinese Petroleum Corporation and Formosa Plastics Corporation.Pb concentration was determined on an inductively coupled plasma sector field mass spectrometer(ICP-SF-MS).Pb content of Gasoline ranges from 10 ng g-1 to 45 ng g-1.There is a significant difference of Pb isotope ratios in the gas products between the two brands.The estimated Pb isotope ratios from local vehicle exhaust are 208Pb/207Pb = 2.4269 and 207Pb/206Pb = 0.8710.The ratios are respectively close to the values of 2.4270 and 0.8720 in aerosol samples collected in Taipei area.This agreement suggests that aerosol Pb in Taipei area mainly results from local gasoline combustion.