Study On Environmental Behavior Of Brominated Flame Retardant Hexabromocyclododecanes In Baiyangdian Lake Soil-plant System

Hexabromocyclododecanes（HBCDs）as a kind of hydrophobic cycloaliphatic brominated flame retardant,are widely used in the fields of electronics,chemicals and building materials.Baiyangdian Lake is the largest inland lake in Hebei Province,China.It is known as the"Pearl of North China".It is a very important water source and plays a vital role in the development of the Xiong’an New Area.With the development of the economy,the pollution problems of various persistent organic pollutants（POPs）in this area have become increasingly prominent in recent years.In the present thesis,the distribution and the selective behavior of diastereoisomers and enantiomers of HBCDs in farmland soil and plant systems from Baiyangdian Lake area was conducted for the first time,Main results acquired are as follows:1)The concentrations range ofΣHBCD in soil and maize samples collected in September 2018 were 1.52-53.75 ng·g^-1dw（dry weight）（soils）,0.39-2.65 ng·g^-1dw（roots）,0.11-0.61 ng·g^-1dw（stems）,0.69-3.23 ng·g^-1dw（leaves）,N.d.（lower than the detection limit）-0.75 ng·g^-1dw（kernels）.In most maize samples,the concentrations level of HBCDs followed the order of leaf>root>stem>kernel.2)In April 2019,20 farmland soil samples and 16 wheat samples were collected around Baiyangdian Lake.In September of the same year,another 20 farmland soil samples were collected from the same sampling points.The concentrations ofΣHBCD in soils（April and September）,wheat roots and wheat aboveground tissues ranged from0.57-7.88 ng·g^-1dw,0.38-4.52 ng·g^-1dw,0.14-5.55 ng·g^-1dw,and 0.05-1.14 ng·g^-1dw,respectively.Except for DSLZ and LGC,theΣHBCD levels in all wheat samples followed the order of root>aboveground tissue.3)It is noticeable that significant diastereomer-and enantio-selective enrichment behavior of HBCDs were found in soil and plant samples.In soils,maize roots,maize stems and wheat roots,γ-HBCD was the main diastereoisomer,but in maize leaves,kernels and wheat aboveground tissues,α-HBCD accounted for the largest proportion.In roots of maize and wheat,（-）-α-,（-）-β-and（+）-γ-HBCDs showed preferential enrichment,but（-）-α-,（-）-β-and（-）-γ-HBCDs showed preferential enrichment in the aboveground tissues of wheat.4)There were no significant correlation between the RCFs（Root concentration factors）and log K_owof the three diastereoisomers of HBCDs from the soil to the maize and wheat root system,which reflected the complexity of HBCDs transportation in the natural environment.There were a significant negative correlation between TFs（Translocation factors）and log K_owof the three diastereoisomers of HBCDs from the roots of maize and wheat to stems or aboveground tissues,which indicated that the translocation of HBCDs probably be passive and driven by water movement of transpiration stream.5)In this study for the first time estimated the inventories ofΣHBCD in farmland soil of Baiyangdian Lake area,and the inventory was 37.35kg.The health evaluation results showed that the hazard quotient<1（hazard quotient=estimated daily intakes/reference measurement value）,indicating that the intake of HBCDs by local residents through maize consumption would not cause health risks.In addition,the concentration levels ofΣHBCD and the three diastereoisomers in September 2019 showed a significant downward trend compared to April 2019.This result maight be mainly attributed to absorption during plant growth in summer,as well as active microbial activity and photolysis.