Exploring The Enrichment And Metabolic Transformation Mechanism Of Typical Novel Brominated Flame Retardants In The Aquatic Environment

Brominated flame retardants(BFRs)are widely used due to the advantages of high flame retardant efficiency and economic applicability.In recent years,the existence of BFRs has been detected in countries around the world and even in the Arctic,and the environmental problems caused by this have attracted attention.At present,most studies are based on field sampling to analyze the pollution level,but there are few studies about the biological conversion behavior of BFRs.In this paper,five kinds of bromine flame retardants:Decabromodiphenyl ether(BDE209),Decabromodiphenyl ethane(DBDPE),hexabromobenzene(HBB),1,2-bis(2,4,6-Tribromophenoxy)ethane(BTBPE)and Pentabromotoluene(PBT)were mentioned as target pollutants.Compounds of 0.2,1.0,5.0,25.0 and 50.0 mg/kg were prepared contaminated sediments;mudsnail(Bellamya aeruginosa)and zebrafish were used as test organisms to build an aquatic microcosm unit in the laboratory.A 35-day enrichment experiment and a 14-day removal experiment were performed to explore the bioconcentration level,removal ability and metabolic transformation mechanism of BFRs.These data can provide scientific basis for aquatic ecological risk assessment.The main results are as follows:(1)The amount of enrichment in vivo is positively correlated with exposure time and dose.There is no significant difference in the concentration of BFRs between male and female mudsnails(P>0.05).The content of BFRs in the pleopod was lower than that in the viscera organs.BTBPE was accounted for 25.3%-58.1%of the pleopod,DBDPE and BDE209 in the viscera were accounted for more than half of the total BFRs.The bio-sediment accumulation factor(BSAF)value of mudsnail viscera for each substance was DBDPE>BDE209>BTBPE>PBT>HBB,the R-square of linear fitting between BSAF and logKow was greater than 0.9.BFRs can be transmitted from parent generation to child generation and accumulated in the offspring.The first-order kinetic model calculated the average elimination half-lives of PBT,HBB and BTBPE for mudsnail pleopod were 2.2,4.2 and 13.0 days,and the corresponding elimination half-lives of viscera were 8.9,4.9 and 19.6 days.The clearance half-life of DBDPE and BDE209 in each concentration group was greater than 7 days.(2)The concentration of each pollutant in the water samples during the enrichment period did not exceed 186.88 ng/L,the BFRs content in the zebrafish was higher than that in the water but lower than that in the mudsnail.The largest enrichment rank in the 6 types of tissues is liver(7504.54 ng/g)>intestine(6936.99 ng/g)>gill(3532.97 ng/g)>brain(1531.93 ng/g)>roe(1277.87 ng/g)>muscle(605.80 ng/g).Principal component analysis(PCA)shows that PBT and HBB mainly accumulated in zebrafish liver and roe,BDE209 and DBDPE are more concentrated in gill and muscle,and BTBPE has a higher proportion in the intestine.The average elimination half-lives of PBT,HBB,BTBPE,DBDPE and BDE209 in zebrafish were 4.01,4.09,2.90,3.72 and 3.75 days,respectively.(3)In the single BFR exposed system at 50.0 mg/kg,the surface of the mudsnail liver was significantly damaged under the scanning electron microscope(SEM)compared with the control group,including shrinkage,perforation,cracks,tissue proliferation and separation.All substances have experienced metabolic transformation in the tested organism.Combined with the detection results of GC-ECNI-MS and GC-EI-MS,it has been identified that 2,4,6-tribromotoluene was the metabolite of PBT;the main products of HBB were 1,2,4,5-tetrabromobenzene and 1,2,4-tribromobenzene;one of the metabolites of BTBPE was 2,4,6-tribromophenol;DBDPE experienced a reduction debromination process in the organism;BDE209 was converted into low bromine homologues including pentabromo to nonabromo.