Synthesis Of ¹⁴C-Labled Lower Brominated Diphenyl Ether Congeners ?LBDEs? And The Fate Of LBDEs In Soil

Polybrominated diphenyl ethers?PBDEs?are additive flame retardants utilized in various materials including textiles,construction stuff,consumer electronics and other aera.The physical and chemical properties differed for the number of bromine atoms.Lower-brominated congeners of PBDEs?LBDEs,usually mono-to penta-congeners?with higher vapor pressure and water solubility are frequently detected in various environmental media including soil,sediments,wastewater treatment plant and air particles,as well as biota tissues including human milk and fish.LBDEs,together with the possible metabolites,were reported with endocrine toxicity,cytotoxicity and neurotoxicity including DNA damage and oxidative stress.LBDEs could originate from the commercial products,on the other hand could also be the metabolites from the debromination of higher-brominated congeners.Among the congeners,the detection of 4-bromodiphenyl ether?BDE3?,4,4'-dibromodiphenyl ether?BDE15?,and 2,2',4,4'-tetrabromodiphenyl ether?BDE47?were frequent in soil samples.When the LBDEs were disposed into soil,they could be biodegraded as well as binding with soil humic substances to the formation of non-extractable residues?NERs?.For the different patterns and forces between organic pollutants and soil humic substances,NERs could also be classified into different portion.However,the fate of LBDEs including mineralization and the formation of NERs in soil under oxic condition was not clear.Release of PBDEs together with heavy metals into the environment is caused by the recycling of e-wastes,especially in developing countries.The impacts of co-occurrence of heavy metals such as Cu on the fate of PBDEs in soil are unknown yet.Most studies on accumulation and toxicity of soil pollutants used epigeic earthworms,which live on soil surface,feed primarily on decaying organic matter,and accumulate soil pollutants via almost only skin sorption,while endogeic earthworms,which digest soil and are therefore exposed to soil pollutants in their gut.However,accumulation and transformation of lower-brominated congeners of PBDEs by geophagous earthworms are not evaluated yet.Radioactive ¹⁴C-labeled compounds allow the quantitative determination of mineralization,formation of NERs,and distribution of NERs in soil matrixes.However,the lack of commercially available ¹⁴C-labeled LBDEs has hampered the study on the fate of LBDEs and the nature of their residues in soil.Firstly,we synthesized three typical LBDE congeners with ¹⁴C-label,i.e.,¹⁴C-BDE47,¹⁴C-BDE15,and ¹⁴C-BDE3,starting from commercially available ¹⁴C-labelled phenol,which makes it possible for the study on the fate of LBDEs and the nature of their residues in soil.The results are as following:1.Starting from commercially ¹⁴C-labelled phenol,three congeners:¹⁴C-4- bromodiphenyl ether?BDE3?,¹⁴C-4,4'-dibromodiphenyl ether?BDE15?,and ¹⁴C- 2,2',4,4'-tetrabromodiphenyl ether?BDE47?were systhesized in two steps with high yields and high radiochemical purities.2.The major fate of the LBDE congeners in the soil was formation of NERs,followed by mineralization to CO₂,while no transformation product was detected in the soil after incubation for 105 days.The mineralization strongly decreased with increasing number of the bromine atom on the congener molecule,with trace amount of mineralization for BDE47?0.51±0.05%?,while mineralization rate constant was independent of the molecular structure,suggesting that solubility of LBDEs is the limit factor for their persistence in soil.The mineralization was positively linearly correlated with the formation of NERs,which was mainly located in humin fraction and formed already in sterilized soil,suggesting a binding of transformation intermediates to soil humic substances and a physico-chemical entrapment of LBDEs in soil.The results provide new insights into fate of LBDE congeners in soil,and suggest a need to elucidate nature of the NERs of LBDEs, especially the stability of NERs in the environment.3.Using a ¹⁴C-tracer,we studied mineralization,metabolism,and formation of non- extractable residues?NERs?of one PBDEs congener,i.e.,the 4-bromodiphenyl ether?BDE3?in oxic soil for 50 days,without and with amendment of Cu(400 mg kg^-1 soil dw).BDE3 rapidly dissipated with a half-life of 5.5 days and large amounts of CO₂?38.8±0.3%of initial applied amount at the end of incubation? and NERs?42.5±0.4%?were rapidly produced.One hydroxylated metabolite?4?- HO-BDE3?was formed?8.1±0.6%?at the beginning of the incubation,but then decreased to 2.2±0.4%.Only BDE3 occurred in physico-chemically entrapped NERs,amounting to 9.2±0.7%,while only 4?-HO-BDE3 in ester-linked NERs ?10.9±0.7%?.The addition of Cu strongly reduced the kinetics constants of the transformation?including dissipation,mineralization,and NER-formation?,the predicted maximal amounts of mineralization,as well as covalent binding of 4?- HO-BDE3 to soil.The results provide first quantitative insights into fate of lower- brominated congeners of PBDEs in soil and indicate that co-contamination by Cu may increase the environmental risks of biodegradable PBDEs in soil by increasing their persistence.4.Using radioactivity tracer,we incubated ¹⁴C-labelled BDE47 in soil for 21 days in the presence and absence of the geophagous earthworm Metaphire vulgaris. BDE47 accumulated in the earthworm predominantly via oral ingestion of soil, giving a biota-soil accumulation factor?BSAF?value of 1.3 for radioactivity at the end of incubation,and was mostly located in intestine,followed by clitellum ?organs region?and skin of earthworms.Accumulation was accompanied by significant decrease of BDE47 concentration in soil porewater and BDE47 mineralization in soil.BDE47 was transformed in the earthworm gut into two metabolites with higher polarities than BDE47.The results provide for the first-time insights into accumulation and transformation of lower-brominated congeners of PBDEs in geophagous earthworms,being helpful for environmental risk assessment of PBDEs.