Study On Organochlorine Pesticides(OCPs) And Halogenated Flame Retardants(HFRs) In The Atmosphere Of The Pearl River Delta

Persistent organic pollutants（POPs）have the characteristics of high toxicity,persistence,bioaccumulation and long-range atmospheric transport（LART）,which could cause damage to the environment and human health.The Stockholm Convention,which aims to prohibit and restrict the production and use of POPs on a global scale,was signed in 2001 and implemented in phases in 2004.On the one hand,reassessment of the regional status of POPs in the environment can not only test the implementation effect of Stockholm Convention,but also provide a basis for China to formulate further POPs emission reduction strategies and action plans.On the other hand,some substitutes of POPs,which are called"regretful substitutions",often have similar properties with POPs,such as persistence,LART,bioaccumulation,and may pose threats to human health and the environment.Therefore,it is sensitive and urgent to study on the characteristics and use status of POPs and their substitutes.The Pearl River Delta（PRD）,located in the subtropical region of southern China,has experienced rapid industrialization and urbanization.It is not only the most widely used area of pesticides,but also the main area of electronic manufacturing,plastic production and electronic waste disposal in China.An air sampling campaign was carried out during 2017-2018 in nine cities of the PRD using high volume active sampler.Organochlorine Pesticides（OCPs）and Halogenated Flame Retardants（HFRs）were analyzed to i)understand the pollution characteristics of OCPs and HFRs in the atmosphere of the PRD,ii)explore the source,historical use and spatial distribution of OCPs,iii)investigate the relationship between HFRs and PM_2.5,and iv)evaluate environmental health risks of atmospheric OCPs and HFRs.The results of this research on OCPs in the atmosphere of the PRD indicate that OCPs have different levels（winter:chlordane>Hexachlorobenzene（HCB）>Dichlorodiphenyltrichloroethane,DDTs）>Hexachlorocyclohexane（HCHs）>Endosulfan;Summer:Chlordane>DDTs>Endosulfan>HCB>HCHs)and seasonal characteristics.DDTs,endosulfan and HCHs have higher concentrations in summer than winter.Chlordane showed minor seasonal variation,while HCB prevailed in winter.Technical DDTs compositions still dominated,signaling a still existing illegal usage of DDTs in antifouling paints for fishing ships during the suspension period in summer,while the dicofol-type DDTs was almost excluded.Chlordane may emit into the air by kinetically-limited release from historic building foundations and dams,rather than by temperature-controlled evaporation from surface soil.HCB was unintentionally-produced by combustion transported from the north in winter.The unique coupling of summer monsoon with paint DDT usage,winter monsoon with combustion HCB emission,as well as the historical“sealed”chlordane jointly presented a dynamic picture of these OCP compounds in the air of the PRD.The environmental health risk assessment showed that the cancer risk in the atmosphere of PRD exceeded the acceptable carcinogenic risk level(10^-6)recommended by the United States Environmental Protection Agency（US EPA）,and the highest cancer risk level was found in Guangzhou.For HFRs in the atmosphere of the PRD,our study confirmed that Decabromodiphenyl Ethane（DBDPE,median:59.9 pg/m³）was the most abundant compound in the ambient air of PRD.∑₇PBDEs,Decabromodiphenyl Ether（BDE-209）and∑₅NBFRs（median 9.89,8.37 and 8.81 pg/m³,respectively）obtained a similar atmospheric level,whilst the concentrations of Dechlorane Plus（DPs,median 1.74pg/m³）was at the lowest range.Compared with previous studies,the concentration of PBDEs,including BDE-209,has decreased significantly,reflecting the effectiveness of restrictions and prohibitions for PBDEs and e-waste control in the PRD region.Meanwhile,the concentration of DBDPE was relatively stable.In the particulate phase(PM_2.5),no correlation between BDE-209,Pentabromoethylbenzene（PBEB）,1,2-Bis（2,4,6-Tribromophenoxy）Ethane（TBE）,DBDPE and PM_2.5 was observed,the reason of which may be that the secondary components of newly formed aerosol in PM_2.5 are less adsorbed or absorbed Flames Retardant（FRs）with low volatility and stable matrix.On the contrary,BDE-28,BDE-47,BDE-99,BDE-100,BDE-153,BDE-154,BDE-183,Hexabromobenzene（HBB）,2-Ethylhexyl Tetrabromobenzoate（TBB）,Bis（2-Ethylhexyl）Tetrabromophthalate（TBPH）showed a significant correlation with PM_2.5,which may be due to the adsorptional distribution of FRs with high volatility,unstable matrix and good water solubility in the gas phase and particle phase.It may also be due to their common combustion source.Therefore,the correlation between brominated flame retardants and PM_2.5 may be affected by the physicochemical properties of brominated flame retardants,the matrix stability of industrial products,and their emission pathways to the atmosphere.It is worthwhile to study further.In addition,the daily atmospheric exposure to HFRs in the PRD was below the EPA recommended reference dose（2×10⁶pg/（kg·d））.