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The present study reports a profile of potential bio-accessible heavy metal fractions(Ba,Cd,Cu,Mn,Ni,Pb and Zn)in urban atmosphere of Pakistan.For this purpose,an in-vitro physiologically based extraction test has been applied for extraction of bio-accessible metal fractions in airborne particulate matter(APM)samples collected from urban sites in Pakistan using different widely employed leaching agents for risk assessment studies(H2O,ammonium acetate,ammonium citrate,synthetic gastric juice and artificial lung fluids).Obtained extracts were then measured using an ETV-ICP-OES procedure which allowed highly sensitive measurement of dissolved analytes even in the presence of leaching agents as well as complex sample matrix.Derived results indicated that the urban atmosphere of Karachi,Pakistan is highly contaminated with bio-accessible heavy metal fractions.The concentrations of bio-accessible metal fractions varied from 0.5 ng m-3(Cd)to 753 ng m-3(Zn)for PM10 samples collected from Karachi.Furthermore,it was found that investigated leaching agents extract different amounts of potentail bio-accessible metals.In general,leaching agents with organic nature yielded comparatively greater extractable and thus bio-accessible trace metal fractions to that of simple solvents like H2O.With water,only 25.4±3.8%of Cd was found to be bio-accessible whereas 87.4±22.6%of Cd was obtained as bio-accessible fraction with the use of synthetic gastric juice.Further outcome of present study was that the leaching agents which mimic conditions of body fluid give more realistic data about potential bio-accessible trace metals.