Olsman Helena, Hagberg Jessika, Kalbin Georgi, Julander Anneli, van Bavel Bert, Strid Ake, Tysklind Mats, Engwall Magnus
Man-Technology-Environment Research Centre (MTM), Department of Natural Science, Orebro University, Sweden.
Environ Sci Pollut Res Int. 2006 May;13(3):161-9. doi: 10.1065/espr2005.08.280.
GOAL, SCOPE AND BACKGROUND: The use of polybrominated diphenyl ethers (PBDEs) as flame retardants increases the risk for emissions of other brominated compounds, such as polybrominated dibenzodioxins (PBDDs) and dibenzofurans (PBDFs). The large homology in structure of PBDD/Fs and mechanism of toxic action, i.e. the capacity to activate the Ah receptor (AhR) pathway, compared to their well-studied chlorinated analogues, justifies a raised concern to study the environmental levels and fate of these compounds. Decabromodiphenyl ether (decaBDE) is the most widely used PBDE today. Studies on photolytic debromination of decaBDE in organic solvents have shown debromination of decaBDE, as well as formation of PBDFs. However, little is known about the transformation mechanisms and there are only scarce data on photoproducts and PBDE transformation in environmentally relevant matrices. In this study, mechanism-specific dioxin bioassays were used to study photolytic formation of AhR agonists in toluene solutions of decaBDE. In addition, the influence of irradiation time and UV-light wavelength on the formation was studied. PBDE congener patterns and presence of PBDD/Fs were analysed. Further, AhR agonists were analysed in agricultural soils contaminated with PBDEs. Soils were also exposed to UV-light to study changes in AhR agonist levels.
Toluene solutions of decaBDE were irradiated using three different spectra of UV-light, simulating UV-A (320-400 nm), UV-AB (280-400 nm), and UV-ABC (250-400 nm). Additionally, decaBDE solutions were exposed to narrow wavelength intervals (10 nm bandwidth) with the central wavelengths 280, 290, 300, 310, 320, 330, 340, 350, 360 nm. AhR agonists in decaBDE solutions were analysed with two different bioassays, the chick embryo liver-cell assay for dioxins (Celcad) and the dioxin responsive, chemically activated luciferase expression assay (DR-Calux). Also, the decaBDE solutions were analysed with LRGC-LRMS to obtain PBDE congener patterns for breakdown of decaBDE, and with HRGC-HRMS, for presence of PBDD/Fs. Four soils were exposed to UV-AB light, under both dry and moist conditions. Levels of AhR agonists in soil extract fractions, before and after UV-exposure, were analysed with the DR-Calux.
Significant levels of photoproducts able to activate the AhR pathway, up to 31 ng bio-TEQ/ml, were formed in UV-exposed decaBDE solutions. The transformation yield of decaBDE into AhR agonists was estimated to be at the 0.1%-level, on a molar basis. The net formation was highly dependent on wavelength, with the sample irradiated at 330 nm showing the highest level of dioxin-like activity. No activity was detected in controls. PBDE analysis confirmed decaBDE degradation and a clear time-dependent pattern for debromination of PBDE congeners. AhR agonist effect in the recalcitrant fractions of the soils corresponded to the levels of chemically derived TEQs, based only on chlorinated dioxin-like compounds in an earlier study. It was concluded that no significant levels of other AhR agonists, e.g. PBDFs, were accumulated in the soil. UV-light caused changes in AhR-mediated activity in the more polar and less persistent fractions of the soils, but it is not known which compounds are responsible for this.
The laboratory experiments in this study show that high levels of AhR agonists can be formed as photoproducts of decaBDE and it is important to elucidate if and under which conditions this might occur in nature. However, soil analysis indicates that photoproducts of PBDE do not contribute to the accumulated levels of persistent dioxin-like compounds in agricultural soil. Still, more data is needed to fully estimate the environmental importance of PBDE photolysis and occurrence of its photoproducts in other environmental compartments. Analysis with dioxin bioassays enabled us to gather information about photoproducts formed from decaBDE even though the exact identities of these compounds were not known.
Bioassays are valuable for studying environmental transformation processes like this, where chemical analysis and subsequent toxicological evaluation requires available standard compounds and information on toxicological potency. The use of bioassays allows a rapid evaluation of toxicological relevance.
目标、范围和背景：使用多溴二苯醚（PBDEs）作为阻燃剂会增加其他溴化化合物排放的风险，如多溴二苯并二恶英（PBDDs）和二苯并呋喃（PBDFs）。与研究充分的氯化类似物相比，PBDD/Fs的结构和毒作用机制具有高度同源性，即激活芳烃受体（AhR）途径的能力，这使得人们有理由更加关注研究这些化合物的环境水平和归宿。十溴二苯醚（decaBDE）是目前使用最广泛的PBDE。关于decaBDE在有机溶剂中的光解脱溴研究表明，decaBDE会发生脱溴反应，并生成PBDFs。然而，人们对其转化机制知之甚少，关于环境相关基质中光产物和PBDE转化的数据也很稀少。在本研究中，使用特定机制的二恶英生物测定法来研究decaBDE甲苯溶液中AhR激动剂的光解形成。此外，还研究了照射时间和紫外光波长对其形成的影响。分析了PBDE同系物模式以及PBDD/Fs的存在情况。此外，还对受PBDE污染的农业土壤中的AhR激动剂进行了分析。土壤也暴露在紫外光下，以研究AhR激动剂水平的变化。
使用三种不同光谱的紫外光照射decaBDE的甲苯溶液，分别模拟紫外-A（320 - 400 nm）、紫外-AB（280 - 400 nm）和紫外-ABC（250 - 400 nm）。此外，decaBDE溶液还暴露在中心波长为280、290、300、310、320、330、340、350、360 nm的窄波长区间（10 nm带宽）下。使用两种不同的生物测定法分析decaBDE溶液中的AhR激动剂，即用于二恶英的鸡胚肝细胞测定法（Celcad）和二恶英响应化学激活荧光素酶表达测定法（DR-Calux）。此外，使用低分辨气相色谱-低分辨质谱（LRGC-LRMS）分析decaBDE溶液，以获得PBDE同系物的降解模式，使用高分辨气相色谱-高分辨质谱（HRGC-HRMS）分析PBDD/Fs的存在情况。在干燥和潮湿条件下，将四种土壤暴露在紫外-AB光下。使用DR-Calux分析紫外照射前后土壤提取物组分中AhR激动剂的水平。
在暴露于紫外光的decaBDE溶液中形成了大量能够激活AhR途径的光产物，最高可达31 ng生物毒性当量/毫升。以摩尔为基础，decaBDE向AhR激动剂的转化产率估计在0.1%水平。净形成高度依赖于波长，在330 nm照射的样品显示出最高水平的二恶英样活性。对照组未检测到活性。PBDE分析证实了decaBDE的降解以及PBDE同系物脱溴的明显时间依赖性模式。根据早期一项研究中仅基于氯化二恶英样化合物的结果，土壤难降解组分中的AhR激动剂效应与化学衍生的毒性当量水平相对应。得出的结论是，土壤中没有积累显著水平 的其他AhR激动剂，例如PBDFs。紫外光导致土壤中极性更强、持久性更低的组分中AhR介导的活性发生变化，但尚不清楚是哪些化合物导致了这种变化。
本研究中的实验室实验表明，作为decaBDE的光产物可形成高水平的AhR激动剂，阐明其在自然界中是否以及在何种条件下可能发生非常重要。然而，土壤分析表明，PBDE的光产物对农业土壤中持久性二恶英样化合物的积累水平没有贡献。尽管如此，仍需要更多数据来全面评估PBDE光解及其光产物在其他环境介质中的环境重要性。即使这些化合物的确切身份未知，使用二恶英生物测定法分析也使我们能够收集有关decaBDE形成的光产物的信息。
生物测定法对于研究此类环境转化过程非常有价值，在这种情况下，化学分析和后续毒理学评估需要有可用的标准化合物和毒理学效力信息。使用生物测定法可以快速评估毒理学相关性。
