Presistance Of Soil PAHs Background Value And Its Risk Screening Value In Guangzhou Urban Parks

With the increasing attention to the soil environmental quality,we has been working to improve the soil environmental policies,standard and management system in recent years.As one of the most important cities in China,Guangzhou,also actively responds to the national policy,formulating the risk screening value of the soil polycyclic aromatic hydrocarbons?PAHs?in Guangzhou,which is the basic for the investigation and management of the soil environment.The accumulation of PAHs in soil has the regional distribution characteristics in the soil.It is necessary to consider the content,structural characteristics and source of polycyclic aromatic hydrocarbons in the surface soil under the condition of no strong external pollution input.The assessment of human health risk of soil PAHs is the quantification of the influence of soil environment and human health,which provides the basis for the management of soil environmental quality and the protection of human health.In this paper,by sampling and analyzing the surface soil which is not disturbed by human activities in Guangzhou City Park,discussing the physical and chemical properties of soil,the background content of soil PAHs,and the contents and sources of the soil PAHs,to beaguidance for the quality management of soil PAHs environment.Secondly,the risk assessment models used in the United States,the United Kingdom,Holland and China are analyzed in detail,and the parameters of the model are studied.The models and parameters suitable for the study are put forward,and the local soil risk screening values in Guangzhou are calculated.Finally,the health risk assessment of soil PAHs in the study area is carried out.The main results of the paper are as follows:?1?Analysis soil samples from 19 parks in Guangzhou,which were built 30 years ago,Results show as:Soil organic matter content is 20.37g/kg,moisture content is 23%,soil bulk density is 1.48g/cm³,specific gravity is 2.69,soil pH is 5.33.The content and source of PAHs in soil showas:The content of total PAHs is ND⁴22.9ng/g,with a mean value of60.4 ng/g.In the structure,the middle and low?2³ ring,4 ring?ring accounted for more than69%,of which the 3 ring ratio is the highest;The proportion of the 5 and 6 rings in the central city is relatively high,accounting for 41%.The other regions are low ring components.The overall content trend is central urban area>suburban area>outer suburb area,and spatial distribution variability decreases sequentially.The preliminary source analysis showed that the base PAHs of Guangzhou urban park was mainly derived from the combustion of fossil fuels,followed by oil or petroleum input and biomass combustion,and the contribution rate was 60.6%,37.6%and 1.8%in turn.?2?In the formulation of screening values,the land use pattern is divided into three categories:Residential land,industrial/commercial land and parkandgreen land.In the selection of the parameters,the human exposure parameters were mainly taken from the Chinese population exposure manual,in which the average body weight?BW?,the average height?H?,the exposure frequency?EF?,and the daily breathing air?DAIR?were changed;The parameters of soil physical and chemical properties were the test result in this paper.The thickness of the surface layer of soil layer?d?the depth of the top buried depth?Ls?in the top of the lower layer of contaminated soil were all 0.5m and the thickness of the lower layer of contaminated soil(d_sub);In the air characteristic parameters,the atmospheric flow velocity(U_air)in the mixed area is 180 cm/s,and the inhalable particulate matter(PM₁₀)is analyzed by the Guangzhou meteorological report for the last 20 years;The building of characteristic parameters,the foundation area?A_b?is 9.7×10⁵ cm²,ground and wall fracture surface area accounted for 0.0005.Other parameters,including physical and chemical properties and toxic parameters,are selected according to the recommended values of the state.?3?This research complements the vacancies of some pollutants screening values both at home and abroad.Such as the screening values of Acy,Phe and BghiP in the United States and the United Kingdom;Ace,Flu,Ant,Chy,Acy and Fla in Canada;Acy,Ace,Flu,Phe,Fla,Ant,Pyr and BghiP in the Ministry of ecology and environment.The results showed that the PAHs value of residential land was the smallest.Under the way of industrial/commercial land use,the screening value of PAHs in middle bottom ring is larger than that in parks and greenbelts,and the high PAHs is relatively small.As a whole,the test results generally higher than those in Beijing,Shanghai,Zhejiang and Chongqing,and the screening values were lower than those in Australia and New Zealand;Slightly higher than the screening value of China's eco environment,which is slightly lower than Hongkong,but the difference is generally small.Compared with the United States,Guangzhou residential land and industrial/commercial land use,Ace,Flu,Fla and Pyr 4compounds screening value is far lower than the United States.?4?Using life cycle carcinogenesis increment model?ILCRs?model,we made human health risk assessment for PAHs of park's soil background.The results showed that the risk of cancer among adults and children in 7 parks in 19 parks is within acceptable safety limits,The cancer risk in Liuxihe Forest Park was the smallest,range from 6.01E-14 to1.81E-08,The cancer risk in the Dafushan Forest Park is the largest,ranging from 2.79E-10to 8.41E-05.In the three ways of exposure,skin contact is the most important way of exposure,followed by oral feeding,and the exposure risk of breathing inhalation pathway is far less than the first two,almost negligible.The cancer risk level of adult is greater than that of children,and the risk level decreases with the increase of distance from downtown.In conclusion,content of PAHs in the unpolluted soil of Guangzhou city park was low,but there was also a certain potentialcance risk of human body.Both the content and risk degree decrease with the decrease of urbanization.The formulation of soil risk screening value is very necessary,and the screening results obtained in this paper are in the normal range,which is of practical significance.