Effects Of Particle Size And Carbon Composition On Inhalation Bioaccessibility Of Particle-Bound Pahs As Evaluated With An In Vitro Method

There are increasing concern on the human health risks of inhalation exposure to particle-bound organic contaminants in atmosphere.Gradually,the bioaccessible concentrations of particle-bound organic contaminants,instead of total concentration,have been used for conservatively and accurately assessing the exposure health risk.However,the concentrations of particle-bound organic contaminants are usually size-dependent.In addition,the sorption capability of organic contaminants are related with the contents of organic carbon in particles.To date,there are few references on the effects of particle size and organic contents on the inhalation bioaccessibile fractions（IBAFs）of particle-bound organic contaminants,even the assessment of health risk.Therefore,typical organic contaminants,i.e.,polycyclic aromatic hydrocarbons（PAHs）,were taken as the target compounds in the present study.Two simulation scenarios of particle emission sources,barbecue and smoking,were constructed for obtaining the size-fractionated particles（from 0.056 to>18μm）with high concentrations of PAHs.The objects of the present study were（1）determine size-dependent IBAFs of PAHs in charcoal and cigarette burning PM using an in vitro method;（2）examine the effects of particle size and OC/EC contents on IBAF of PAHs;（3）explore the changes in contributions of individual PAHs to inhalation exposure risk with involving of their size-dependent bioaccessibilities.Results showed that the emission factors（EFs）of particle-bound∑₂₈PAH emitted from burning cigarette,smoke-type charcoal and smokeless-type charcoal were 3482,537 and 4.6μg g^-1,respectively.2-and 3-ring PAHs were the dominant compounds with the 32?63%contribution of total concentration.A unimode distribution of particle-bound PAHs was observed for three emission scenarios,with a peak at 0.56?1.0μm.The total concentrations of particle-bound PAHs from three emission scenarios were 1049,1034 and 12.3μg g^-1,satisfying the determinations of inhalation bioaccessibility of PAHs in size-fractionated particles.The IBAFs of particle-bound PAHs emitted from burning cigarette,smoke-type charcoal and smokeless-type charcoal were 65%,54%and 74%in ALF,and 68%,62%and 35%in MGS,respectively.The IBAFs of∑₂₈PAH decreased from first and then increased.The IBAFs of some2-and 3-ring PAHs in all fractionated particles were close to 100%,and the variation trend with particle size was not obvious.In particular,the size distributions of IBAFs of 3 and 5-ring PAHs were opposite with their concentration distribution,suggesting the significant effects of particle size on the IBAFs of particle-bound PAHs.The contents of OC and EC in size-fractionated particles varied with the particle emission sources.Generally,lower IBAFs of PAHs were found in the particles with higher contents of OC and EC.Correlation analysis showed that results showed that OC and EC were correlated with the IBAFs of particle-bound PAHs than particle size.On the other hand,the hydrophobicity of PAHs exerted some effects on their IBAFs.The size-dependent IBAF of particle-bound individual PAH deriving from three sources of combustion were 1?99%.The IBAFs of PAHs decreased with their increasing hydrophobicity.The IBAF of PAHs decreased with increasing hydrophobicity(or higher log K_OWvalues)following a sigmoidal distribution.These results suggested that the diffusive transport of chemicals in the lungs maybe explained by the two-way resistance model.The assessment of human health risk showed that the exposure health risk(10^-6)of particle-bound PAHs based on the total concentration of PAHs（Risk _O）,the deposition efficiency of PAHs(Risk _DE)and the bioaccessibility of PAHs and its deposition efficiency(Risk _DE+BA)were0.4?3.2,0.21?1.5 and 0.14?0.87 respectively in ALF,and in MGS,the exposure health risk(10^-6)were 1.8?8.2,0.92?3.9 and 0.37?2.8,respectively.The exposure health risk of particle-bound PAHs based on deposition efficiency declined with approximately 50%from those based on the total concentration of PAHs.The exposure health risk of particle-bound PAHs based on the bioaccessibility of PAHs and its deposition efficiency declined with approximately 70%from those based on the total concentration of PAHs.In particular,3-and 4-ring PAHs were the largest contributor to the exposure health risk,suggesting their potential human exposure risk through inhalation could not be ignored.