Distribution,Source And Risk Assessment Of Persistent Organic Pollutants In Topsoil Of Chongming Island

Persistent Organic Pollutants?POPs?have attracted much attention in recent years due to their teratogenic,carcinogenic and mutagenic toxicity characteristics.Because of its long-distance transport,POPs can be deposited in the soil for a long time through volatilization and deposition,and can contaminate other media through atmospheric deposition and surface runoff,and ultimately affect human health through biological enrichment.Therefore,the pollution of POPs in the soil is a problem that needs to be focused on and solved.In this paper,the pollution levels of PAHs and PBDEs in different land use types of soils on Chongming island were systematically investigated,the effects of total organic carbon on the occurrence of POPs in soil and the possible sources of POPs in soil were preliminarily analyzed,potential risks of POPs in soil were assessed using multiple evaluation criteria and models,it provides a basis for the construction of Chongming ecological island and soil restoration.The main conclusions are summarized as follows:The total concentration of PAHs in the surface soil of Chongming Island ranges from 47.97ng/g to 1674.52ng/g,with an average of 497.41 ng/g.The content of soil in different land use types showed some differences,average value of the content is characterized by road land>agricultural land>forest land.The 16 types of superior control PAHs specified by the USEPA have been detected.Among them,the middle?tetracyclic?component has the highest proportion,and the high?pentacyclic and hexacyclic?component has the second largest proportion.The lowest is the lower ring?second ring and third ring?.The total organic carbon in the soil in the study area was tested.The TOC content ranged from 0.51%to 10.3%,with an average content of 2.65%.The correlation between TOC and PAHs was analyzed,and the results showed no significant correlation.It shows that the distribution of TOC in the soil in the study area has no obvious effect on the occurrence of PAHs.A preliminary analysis of the source of PAHs in the soil of the study area was performed using the characteristic ratio method and factor/principal component analysis.The results show that the main source of PAHs in the soil is combustion sources,which are manifested by coal combustion,petroleum combustion,and fossil fuels.Incomplete combustion,part of the sample points indicate the source of oil,mainly oil leakage and automobile exhaust emissions.The biological toxicity evaluation method was used to analyze the effect of PAHs on the ecological environment.The results showed that the content of each monomer in the soil of Chongming Island did not exceed the ERL,indicating that the PAHs in Chongming Island soil had a low level of ecological risk to the environment;The results of the toxic equivalent evaluation method showed that the potential carcinogenic risk of surface soil in the study area was at a very low level;the use of a lifelong carcinogenic risk increase model to analyze the health risks of PAHs in the surface soil of the study area showed that children were exposed to different routes The carcinogenic risk of exposure to different types of soil is at a negligible level.Adults'exposure to agricultural land and road land through skin contact and oral intake is relatively high,indicating a potential carcinogenic risk to human health.In different land-use types of soil,the carcinogenic risk value is in order from agricultural land,road land and forest land.The contribution of different exposure routes to human health is from skin contact,oral intake and respiratory inhalation in order.The content of BDE209 in the surface soil of Chongming Island ranges from0.08 to 1.86 ng·g^-1,with an average value of 2.15 ng·g^-1.The total content of 18homologues(?₁₈PBDEs)except BDE209 ranges from 0.11 to 14.7 ng·g^-1,with an average value of 1.63ng·g^-1.The distribution pattern of agricultural land>road land>forest land appeared between different land use types.Nineteen polybrominated diphenyl ether homologues were detected in the study area,of which decabromobiphenyl ether accounted for the largest proportion,with its content accounting for 7.9%-79.4%,with an average of 44.2%.The use of commercial decabromo industrial products,followed by tetrabromodiphenyl ether,pentabromodiphenyl ether and nonabromodiphenyl ether,the content of which is0.5%⁶6.5%?average 13.5%?,0.7%³7.7%?Average 13.2%?and1.7%to 53.7%?average 14.2%?.Tetrabromodiphenyl ether and pentabromodiphenyl ether indicate the use of commercial pentabromo industrial products,and nonabromodiphenyl ether indicate the use of commercial octabromo industrial products.The correlation between TOC and PBDEs was analyzed,and the results showed that there was no significant correlation,indicating that the distribution of TOC in the soil of the study area had no obvious effect on the occurrence of PBDEs.The source of PBDEs in soil samples from the study area was preliminarily determined by using the factor/principal component analysis method.The results showed that the PBDEs in the soil of Chongming Island were mainly derived from the use of commercial decabromo industrial products,and there were commercial pentabromo Use of industrial and commercial octabromo industrial products.Using"Technical Guidelines for Risk Assessment of Contaminated Sites"to assess the carcinogenic risk of soil PBDEs to humans in the study area,the results show that oral intake is the most important contribution route,followed by skin contact routes,and finally soil particulate inhalation routes.The maximum value of the four types of PBDEs monomers ingested through the three routes is less than the standard value that can lead to human neurobehavioral requirements set by the US Environmental Protection Agency,indicating that the occurrence of PBDEs in the study area does not pose a carcinogenic risk to humans.