| Contamination of Polycyclic aromatic hydrocarbons?PAHs?in atmospheric and soil was increasingly serious,which is mainly due to high level of emission of PAHs resulted from the predominating use of coal in energy consumption and continuous development of economy and society for years in China.There are potential threats to agricultural production in areas affected by coal combustion.However,the status of PAHs in winter wheat and the health risk of PAHs in winter wheat grains from the areas influenced by coal combustion was still not clear.During harvest season,the rhizosphere soils and winter wheat were collected from agricultural fields surrounding coal-fired power plants located in Shaanxi and Henan Provinces,respectively.In this study,accumulation and distribution status of PAHS in winter wheat various tissues of the plant,oral bioaccessibility of PAHs through intake wheat grains based on an in vitro digestion model,and the health risk assessment of PAHs in winter wheat of the exposed population by the values of incremental lifetime cancer risk?ILCR?were conducted.The present study showed that the mean concentrations of USEPA 15 priority PAHs?sum of the 3–6 ring PAHs?ranged from 486 to 1,117?g kg-1 in the rhizosphere soils,indicating serious PAHs contamination.Based on both the isomeric ratios of PAHs and a principal component analysis?PCA?,the main sources of PAHs in the agricultural soils were from combustion of biomass,coal and petroleum as well as petroleum.The mean concentrations of PAHs ranged from 69.58 to 557.0?g kg-1 and the 3-ring PAHs?acenaphthene,acenaphthylene,fluorene,phenanthrene and anthracene?were dominant in the wheat grains,accounting for approximately 70-81%of the total PAHs.The total PAHs were significantly?p<0.001?higher in the roots(287-432?g kg-1)than in the aerial tissues(221-310?g kg-1).The concentrations of 3-,4-,5-and 6-ring PAHs in the roots significantly?r=0.68-0.96,p<0.001?positive correlated with the corresponding concentrations of PAHs in the rhizosphere soils.There were a decreasing gradient of PAHs concentrations from roots,stems to leaves and from glumes to grains.Regardless of sampling sites,most PAHs detected in the roots and in the aerial tissues were 3-ring PAHs?acenaphthene,acenaphthylene,fluorene,phenanthrene and anthracene?and the percentages of 3-ring PAHs were much higher in the aerial tissues?72.5-82.7%?than in the roots?49.5-74.0%?and in the rhizosphere soils?36.3-65.7%?.In the winter wheat aerial tissues the concentrations of 3-4-ring PAHs significantly?r=0.32-0.64,p<0.001?positive and the 6-ring PAHs significantly?r=0.46-0.58,p<0.001?negative correlated with the concentrations of PAHs in the corresponding rhizosphere soils,respectively.But the 3-4-5-6-ring PAHs significantly?r=0.75-1.00,p<0.001?positive correlated in the adjacent tissues.These indicated that a proportion of 3-4-ring PAHs maybe come from soil-to-roots pathway and 5-6-ring PAHs come from the air-to-leaf pathway in winter wheat aerial tissues.The bioaccessibility of low molecular weight?2-3 ring?PAHs?51.1-52.8%?,high molecular weight?4-6 ring?PAHs?19.8-27.6%?and total PAHs?40.9-48.0%?in the intestinal condition was significantly?p<0.001?higher than that?37.4-38.6%;15.6-22.5%;30.7-35.5%?in the gastric condition,respectively.Based on total PAHs,the values of incremental lifetime cancer risk?ILCR?for children,adolescents,adults and seniors were all higher than the baseline value(10-6),although based on bioaccessibility PAHs the values of ILCR were reduced,but it's still above the baseline.The present study indicated that most grains from the areas affected by coal combustion possessed considerable health risk. |
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