, 郑小燕华侨大学化工学院环境科学与工程系, 厦门 361021
收稿日期: 2017-06-30; 修回日期: 2017-08-13; 录用日期: 2017-08-13
基金项目: 国家自然科学基金（No.41203077）；泉州市科技计划项目（No.2012Z85）
作者简介: 韩文亮(1980—), 男, E-mail: wl_han@163.com
通讯作者（责任作者）: 韩文亮, 男, 博士, 讲师, 硕士生导师, 从事持久性有机污染物的环境化学研究. E-mail: wl_han@163.com
摘要: 十溴二苯醚（BDE-209）是我国环境中主要的多溴二苯醚（PBDEs）同系物.为研究BDE-209及其降解产物对水环境的影响，以初级消费者浮游动物大型蚤（Daphnia magna）和初级生产者浮游植物水华微囊藻（Microcystis flos-aquae）为染毒对象，研究BDE-209及其降解不同阶段产物对浮游生物的毒性.结果表明，大型蚤方面，繁殖毒性大于生长毒性，48 h半数致死浓度（48h-LC50）大小为：还原降解中间产物（0.80 mg·L-1，高毒）> BDE-209（8.74 mg·L-1，中毒） > 还原降解终产物（15.27 mg·L-1，低毒），还原-氧化降解终产物的死亡率与溶剂空白一致，表明其基本无毒.水华微囊藻方面，染毒物质的毒性大小顺序与大型蚤一致，1 mg·L-1的BDE-209、还原中间产物、还原终产物及还原-氧化终产物对水华微囊藻的抑制率分别为15.7%、93.7%、6.6%和1.3%.BDE-209降解过程中易生成毒性较大的中间产物，彻底还原脱溴可降低其毒性，后续辅以氧化降解，可消除其环境毒性.
关键词:十溴二苯醚降解毒性浮游生物大型蚤水华微囊藻
Toxicity of decabromodiphenyl ether and its degradation products to plankton
HAN Wenliang
, ZHENG Xiaoyan Department of Environmental Science and Engineering, College of Chemical Engineering, Huaqiao University, Xiamen 361021
Received 30 June 2017; received in revised from 13 August 2017; accepted 13 August 2017
Supported by the National Natural Science Foundation of China (No.41203077) and the Science and Technology Project of Quanzhou, China (No.2012Z85)
Biography: HAN Wenliang (1980—), male, E-mail: wl_han@163.com
*Corresponding author: HAN Wenliang, E-mail: wl_han@163.com
Abstract: Decabromodiphenyl ether(BDE-209) is the primary congener of polybrominated diphenyl ethers(PBDEs) in the environment in China. In order to investigate the effects of BDE-209 and its degradation products on the aquatic environment, the zooplankton Daphnia magna(a primary consumer), and the phytoplankton Microcystis flos-aquae(a primary producer) were used to study the toxicities of BDE-209 and its degradation products of different stages. In Daphnia magna, the propagation toxicities were higher than that of growth. 48h-LC50 of pollutants followed the order of intermediate reductive products(0.80 mg·L-1, high toxicity) > BDE-209(8.74 mg·L-1, moderate toxicity) > reductive final products(15.27 mg·L-1, low toxicity). The motality of the final reductive-oxidative products was comparable with that caused by the solvent, indicating that it was largely nontoxic. In Microcystis flos-aquae, the toxicity of pollutants followed the same order as in Daphnia magna, under the condition of 1 mg·L-1 of BDE-209, intermediate products, the final reductive products, or the final reductive-oxidative products, the inhibition rate for Microcystis flos-aquae were 15.7%, 93.7%, 6.6% and 1.3%, respectively. During the BDE-209 degradation process, greater toxic intermediate products were generated. However, their environmental toxicity would be reduced if the reductive debromination process could be completely conducted, and moreover, their environmental toxicity would even be eliminated if the reductive process was followed up by subsequent oxidative degradation process.
Key words: decabromodiphenyl ether(BDE-209)degradationtoxicityplanktonDaphnia magnaMicrocystis flos-aquae
1 引言(Introduction)多溴二苯醚(Polybrominated Diphenyl Ethers, PBDEs)是一类全球用量较大的添加型溴代阻燃剂(BFRs), 也是一类持久性有机污染物(POPs), 在各类环境介质中广泛存在(Han et al., 2016; 韩文亮等, 2016a; 2016b;周鹏等, 2016; 聂志情等, 2016), 对浮游生物(Sormo et al., 2009; Davies et al., 2012; Ju et al., 2016; Cristale et al., 2013a; Scanlan et al., 2015)、鱼类(Cruz et al., 2015)、哺乳动物及人类(Li et al., 2014)等有潜在的毒害作用.十溴二苯醚(Decabromodiphenyl Ether, BDE-209)是我国环境中主要的PBDEs同系物(Han et al., 2016; 韩文亮等, 2016b), 其全球生产使用量(1970—2005年约为110×104~125×104 t)和环境赋存量较大(Abbasi et al., 2015; Zhou et al., 2012), 且其在不少淡水湖泊中的含量仍在增加(Yang et al., 2016; Iqbal et al., 2017; Venier et al., 2014).BDE-209在天然水体中主要通过光化学作用、微生物还原或生物代谢等作用, 逐级还原脱溴生成一系列低溴BDEs等二次污染物, 对水环境构成更大的威胁(Waaijers et al., 2016; Iqbal et al., 2017; 韩文亮等, 2017).
水体沉积物既是PBDEs的“汇”也是“源”, 在风、底栖生物扰动、流动紊流和洪水事件等特定环境条件下, 含有PBDEs的沉积物再悬浮就成为水体中PBDEs的污染源(Liu et al., 2017).虽然理论上BDE-209因其亲脂疏水性应主要存在于固相中, 但Cristale等(2013b)对英国亚耳河的研究发现, BDE-209在大多数河水样品中被检出, 且含量较高(17~295 ng·L-1).Venier等对美国五大湖的研究也表明, 湖水中PBDEs主要为BDE-47(20%±2%)、BDE-99(20%±3%)和BDE-209(18%±3%), 这表明水中有大量的BDE-209存在, 原因在于有相当部分的BDE-209以胶体态存在于水中, 且PBDEs在胶体中的分配比例会随溴代数增加而提高(Venier et al., 2014; Guan et al., 2009).
研究发现, 浮游动物体内PBDEs尤其是低溴BDEs的含量高于底栖生物(Sormo et al., 2009), 而浮游植物对水体中PBDEs的富集和迁移有重要作用(Ju et al., 2016).因此, 研究BDE-209及其降解不同阶段产物对浮游生物的毒性有重要的理论和现实意义.大型蚤(Daphnia magna)属浮游动物, 是浮游植物的主要摄食者之一(Bessa Da Silva et al., 2016; Sikora et al., 2016), 是水体中重要的初级消费者(Bundschuh et al., 2016; Bessa Da Silva et al., 2016), 以其生活周期短、繁殖快、对毒物敏感及易于培养等优势成为公认的标准试验生物.水华微囊藻(Microcystis flos-aquae)属浮游植物, 浮游植物是水体中重要的初级生产者(Taipale et al., 2016; Brand et al., 2016), 是整个水生生态系统物质能量循环的基础, 其生长代谢会直接受到外源性毒物的影响, 从而影响初级和高级消费者的生长代谢.同时, 水华微囊藻也是引起淡水水体富营养化的优势藻种之一(Harke et al., 2016).
本文以大型蚤和水华微囊藻这两种不同营养级的浮游生物为染毒对象, 通过测定大型蚤的首胎产蚤时间、产蚤总数、母蚤体长和死亡率等亚急性毒性指标, 以及水华微囊藻的藻密度和生长抑制率等, 研究BDE-209及其降解不同阶段产物的毒性及变化, 以期为研究BDE-209降解产物的毒性及其对水环境的影响积累有益经验.
2 材料与方法(Materials and methods)2.1 材料大型蚤(Daphnia magna, 62D.M)购自中国预防医学科学院环境和卫生工程研究所, 水华微囊藻(Microcystis flos-aquae, FACHB-1028)购自中国科学院武汉水生生物所淡水藻种库.二甲亚砜(DMSO)、四氢呋喃(THF)、曲拉通(Triton X-100)、正己烷、丙酮等试剂为分析纯或更优(上海国药)；BDE-209(纯度98%, Sigma-Aldrich)母液用含0.1%曲拉通(Berton et al., 2016; Fontana et al., 2009; Oleszczuk et al., 2015)的DMSO(Li et al., 2014; Zhao et al., 2011; Su et al., 2016)配制；还原中间产物及还原终产物, 由纳米Ni-Fe/蒙脱石还原降解50 mg·L-1的BDE-209, 分别反应10 min和12 h得来.还原终产物加H2O2进行类Fenton氧化0.5 h得到还原-氧化终产物.还原中间产物主要化合物为逐级还原脱溴得到的一系列溴代数相对较低的BDEs, 主要为2~9 Br的PBDEs同系物(Tan et al., 2017; Xie et al., 2014; Luo et al., 2012; Davies et al., 2012).还原终产物主要为完全脱溴产物二苯醚(Diphenyl Ether, DE), 以及部分1~2 Br的PBDEs同系物(Luo et al., 2012; 2011;Xie et al., 2014).还原-氧化终产物方面, 还原终产物在类Fenton氧化体系中发生了羟基化和2个芳环结构的断裂开环, 进而降解为草酸等低分子有机物, 随后彻底矿化产物为CO2和H2O(Luo et al., 2011; 韩文亮等, 2017).各降解产物用丙酮/正己烷(1: 1)液液萃取, 有机相用无水Na2SO4除水, 旋转蒸发浓缩, 加入5 mL含0.1%曲拉通的DMSO, 继续旋蒸置换出其他溶剂, 得到降解产物母液.
2.2 实验方法2.2.1 浮游生物的培养大型蚤使用OECD规定的M4培养基(OECD, 2012; 2004), 培养3代以上开始实验.大型蚤置于人工气候箱(PYX-250Q-B, 杭州科力仪器)内培养, 温度25 ℃, 湿度60%, 光照黑暗比为16 h: 8 h, 选取同一母代所生小蚤作为母蚤留种进行试验, 以斜生栅藻(Scenedesmus obliquus)喂食, 每隔2 d更换培养液, 并定期分离出小蚤.
水华微囊藻使用OECD规定的BG11培养基(Wan et al., 2015), 置于人工气候箱内培养, 温湿度设置同大型蚤, 光照黑暗比为12 h: 12 h, 每天摇动3次.初始接种密度约106 cells·L-1.每次实验前, 藻种均经2~3周期活化, 以保证其处于最佳生长状态.采用血球计数板显微镜计数, 结合紫外可见光光度计(UV-2800AH, 尤尼克仪器)测定吸光度(波长680 nm)的方法研究水华微囊藻的生长情况.
PBDEs难溶于水, THF(Pan et al., 2016; Su et al., 2016)和DMSO(Li et al., 2014; Zhao et al., 2011; Su et al., 2016)是常用的助溶剂, 首先比较了两者的水溶液毒性.0.5%的THF对大型蚤毒性较大, 第2 d时开始出现死亡, 第5 d死亡率达66.7%, 且在第10 d全部死亡, 所有母蚤不繁殖小蚤；与之相比, 0.5%的DMSO组在第13 d时死亡率仅为8.3%, 且第7 d开始繁殖小蚤, 后续有大量小蚤出生, 表明THF对大型蚤的毒性远大于DMSO.DMSO为0.1%~0.5%时死亡率均＜10%, 且首胎产蚤时间、产蚤总数和母蚤体长差别较小.但当DMSO增加到1%时, 各指标与空白组相比均有极显著差异(One-Way ANOVA, LSD), 其中, 产蚤总数锐减至2.5只·只-1, 死亡率达50%.与大型蚤一致, 0.5%的THF对水华微囊藻的生长抑制明显(＞50%), 而0.5%的DMSO则影响很小.1%和2%的DMSO对水华微囊藻的生长抑制率比较大, 第12 d时抑制率分别达45%和52%左右；而0.2%的DMSO则有微弱的促进作用.当DMSO浓度为0.5%时, 生长情况和空白组最接近.综合考虑溶剂毒性和PBDEs的疏水性, 选择0.5%的DMSO作为溶剂进行后续实验.
在亚急性毒性实验初期, 通过参考相关文献(Scanlan et al., 2015; Davies et al., 2012; Mhadhbi et al., 2012; 彭颖等, 2012; 胡恒等, 2015)和受试降解产物主要化合物的性质, 以较大的浓度梯度间隔染毒进行预实验, 并根据实验结果调整细化浓度范围, 在此基础上, 确定正式实验中降解产物的设定浓度.
2.2.2 大型蚤毒性实验将出生6~24 h、大小均等的大型蚤暴露于浓度为0、0.5、1、1.0、1.5、3 mg·L-1的重铬酸钾溶液中进行24 h急性毒性试验.24 h后记录死亡数, 以反复转动试验容器, 15 s内失去活动能力为标准(ISO, 2012).采用水质-物质对蚤类(大型蚤)急性毒性测定方法(GB/T 13266-91)、化学农药环境安全评价试验准则第13部分：溞类急性活动抑制试验(GB/T 31270.13-2014)和ISO 6341:2012(ISO, 2012)等推荐的概率单位图解法算出重铬酸钾对大型蚤的24 h半数致死浓度(24h-LC50)为1.18 mg·L-1, 95%置信区间(95% Confidence Interval, 95% CI)为1.06~1.32 mg·L-1, 符合ISO 6341:2012等标准的要求(0.6~2.1 mg·L-1)(OECD, 2004; ISO, 2012).因此, 本研究培养的大型蚤能作为标准试验生物进行毒理试验, 并评价毒物的毒性大小.
用50 mL小烧杯盛25 mL BDE-209或各降解产物, 分别加入出生6~24 h、大小均等的小蚤, 每隔2 d换一次培养液, 以斜生栅藻喂食, 培养13 d.每天观察大型蚤的生长情况, 记录大型蚤首胎产蚤时间、产蚤总数、母蚤体长和死亡数.
2.2.3 水华微囊藻毒性实验母藻活化后培养至藻密度为106 cells·L-1, 分装100 mL藻液至250 mL三角瓶, 调节污染物浓度, 所有操作在无菌超净工作台完成, 定时测定藻液吸光度.血球计数板显微计数法得出的藻细胞密度(Y)与分光光度法测定的吸光度(X)之间呈线性关系, 因此, 可通过测定吸光度来反映藻的生长情况.水华微囊藻密度(105 cells·mL-1)与OD680的线性方程为：Y=213.52X-2.12(R2=0.9996)；抑制率R的计算公式为：R=(1-C/C0)×100%, 其中, C和C0为染毒组和对照组的藻细胞密度.
2.3 数据统计方法数据统计分析使用SPSS 16.0完成(α=0.05), 所有统计推断数据经检验均符合正态分布(Kolmogorov-Smirnov Test)且方差无显著差异(Levene' Test).
3 结果(Results)3.1 大型蚤毒性由表 1可知, 随BDE-209浓度增加, 在大型蚤生长方面, 体长略有减小, 死亡率逐渐增大；在繁殖方面, 首胎产蚤时间逐渐延迟, 直至不产蚤；在产蚤总数上, BDE-209毒性最明显, BDE-209浓度≥2 mg·L-1时, 产蚤总数与对照组均有极显著差异(p≤0.004)；BDE-209浓度为5 mg·L-1时, 产蚤总数仅3.8只·只-1, 远低于对照组；BDE-209浓度为10 mg·L-1时, 母蚤不产蚤, 且第9 d全部死亡.可见, BDE-209对大型蚤的毒性随浓度增加而增大, 且繁殖毒性大于生长毒性(Sancho et al., 2016).
表 1(Table 1)
| 表 1 BDE-209及其降解产物对大型蚤的毒性(13 d) Table 1 Toxicities of BDE-209 and its degradation products to the growth of Daphnia magna(13 d) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
表 1 BDE-209及其降解产物对大型蚤的毒性(13 d) Table 1 Toxicities of BDE-209 and its degradation products to the growth of Daphnia magna(13 d)
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随还原中间产物浓度增加, 大型蚤各指标受到的抑制作用迅速加大.在生长方面, 体长显著减小, 死亡率迅速增长, 与对照组有显著或极显著差异.还原中间产物浓度为0.2和0.5 mg·L-1时, 大型蚤第13 d的死亡率分别为41.7%和83.3%；还原中间产物浓度为1 mg·L-1时, 第2 d母蚤已死亡2/3, 且第3 d全部死亡.在繁殖方面, 还原中间产物浓度为0.2 mg·L-1时, 大型蚤有少量繁殖(＜1/3), 极显著小于对照组, 且首胎产蚤时间比对照组晚了3 d左右, 有极显著的推迟(p=0.000)；还原中间产物浓度≥0.5 mg·L-1时, 大型蚤已不能繁殖.表明还原中间产物对大型蚤的毒性随浓度增加而增大, 且毒性远大于BDE-209, 繁殖参数较生长参数更敏感.
还原终产物浓度为0.5 mg·L-1时, 各指标均优于对照组, 其中, 产蚤总数显著高于对照组(p=0.0104), 而浓度为1 mg·L-1时则与对照组无显著差异；浓度为2 mg·L-1, 产蚤总数仅为对照组的2/3, 显著小于对照组(p=0.034), 死亡率增加；浓度为5 mg·L-1时, 除体长外, 其他3个指标均与对照组有极显著差异(p≤0.008), 其中, 产蚤总数锐减至6.0只·只-1, 死亡率升至33%；浓度为10 mg·L-1时, 大型蚤不再繁殖, 死亡率(75%)和体长均与对照组有极显著差异, 但仍有25%的大型蚤能继续存活.综上, 还原终产物对大型蚤的毒性较小, 且具有低浓度促进、高浓度抑制(低促高抑)的特点, 繁殖毒性大于生长毒性.
还原-氧化终产物对大型蚤的致死率与对照组一致, 仅在首胎产蚤时间、产蚤总数、体长3个指标上略有差异.其中, 还原-氧化终产物浓度为1和5 mg·L-1时略优于溶剂对照, 而浓度为10 mg·L-1时, 首胎产蚤时间延迟, 产蚤总数、体长与溶剂对照接近.可见, 还原-氧化终产物对大型蚤的毒性很小, 且也有低促高抑作用, 繁殖毒性大于生长毒性.
3.2 水华微囊藻毒性不同浓度BDE-209对水华微囊藻抑制率的变化趋势相似(图 1a)且显著相关(r=0.78~0.97, p＜0.02).BDE-209浓度为1 mg·L-1时第8 d抑制率达到最大(23.8%), 浓度为2、5、10 mg·L-1时则在第10 d达到最大(31.0%、34.4%和44.1%)；第16 d时, 1、2、5、10 mg·L-1浓度组的抑制率则分别降至15.7%、18.5、28.0%和35.4%.可见, BDE-209对水华微囊藻的抑制率随时间先增加, 后略有下降, 且浓度越高, 抑制率越大.
图 1(Fig. 1)
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| 图 1 BDE-209及其降解产物对水华微囊藻生长的抑制率 (a. BDE-209, b.还原中间产物, c.还原终产物, d.还原-氧化终产物) Fig. 1Inhibition ratios of BDE-209 and its degradation products on the growth of Microcystis flos-aquae |
由图 1b可知, 还原中间产物浓度为0.5和1 mg·L-1时对水华微囊藻的生长影响很大, 抑制率最高分别达92.1%(第8 d)和94.6%(第12 d), 但后期随培养时间的增加, 较低浓度(0.1和0.5 mg·L-1)组的抑制作用略有减小, 藻又有明显的生长趋势.因此, 还原中间产物对水华微囊藻的毒性大, 有强烈的抑制作用, 且浓度越高, 抑制作用越大.
还原终产物对水华微囊藻的生长抑制作用较小, 且先增大后减小, 第10 d时达到最大, 浓度为1、5、10 mg·L-1组的抑制率分别为11.9%、18.6%和29.4%, 第16 d则分别降至6.6%、10.4%和15.6%(图 1c).可见, 还原终产物对水华微囊藻的毒性较小.
还原-氧化终产物对水华微囊藻的毒性则更小(图 1d), 在第16 d时, 1、5、10 mg·L-1组对水华微囊藻的生长抑制率分别为1.3%、3.6%、6.9%, 远小于BDE-209及其还原中间产物和还原终产物.
综合大型蚤与水华微囊藻的研究结果可知, BDE-209还原过程中生成了高毒性的中间产物, 而还原终产物的毒性则较小, 最终在类Fenton氧化下, 生成了基本无毒的还原-氧化终产物.
4 讨论(Discussion)4.1 大型蚤毒性GB/T 31270.13-2014基于毒物对大型蚤的48 h毒性, 将毒物分级为：低毒(＞10 mg·L-1)、中毒(1~10 mg·L-1)、高毒(0.1~1 mg·L-1)、剧毒(≤0.1 mg·L-1).根据各浓度BDE-209及其降解产物48 h大型蚤的死亡率, 采用概率单位图解法(ISO, 2012)算出其对大型蚤48 h半数致死浓度(48h-LC50)排序为：还原中间产物(0.80 mg·L-1, 95% CI：0.67~0.94 mg·L-1, 高毒)>BDE-209(8.74 mg·L-1, 95% CI：6.46~11.83 mg·L-1, 中毒)>还原终产物(15.27 mg·L-1, 95% CI：10.99~21.20 mg·L-1, 低毒).还原-氧化终产物的致死率与对照组相近, 表明其基本无毒.研究表明, BDE-209的生物毒性较小(Davies et al., 2012), 而还原中间产物主要是毒性较大的低溴BDEs(Tan et al., 2017; Davies et al., 2012; Mhadhbi et al., 2012), 且溴代数相对较低的Penta-BDE毒性高于Octa-BDE, 如Scanlan等(2015)发现, Penta-BDE对大型蚤的毒性(48h-LC50 0.058 mg·L-1)远大于Octa-BDE(3.96 mg·L-1).彭颖等(2012)得出BDE-47对大型蚤的48h-LC50为1.04 mg·L-1(高毒), 与本研究还原中间产物毒性相近.还原终产物主要是毒性很小的完全脱溴产物二苯醚(Luo et al., 2012; Luo et al., 2011).还原-氧化终产物则大都开环矿化, 毒性基本消除(Tan et al., 2017; Luo et al., 2011).综上, BDE-209彻底还原降解可降低其毒性, 后续辅以氧化降解则可基本消除其环境毒性.
此外, 多种毒物对大型蚤等浮游动物的繁殖毒性大于其生长毒性.如Sancho等(2016)研究发现, 杀菌剂戊唑醇对大型蚤体长变化的影响小于首胎产蚤时间或产蚤总数, 本研究与之一致.Chen等(2014)研究发现, 有机磷农药对卜氏晶囊轮虫的运动速度有低促高抑作用.Stanley等(2013)研究发现, 三硝基甲苯(TNT)对大型蚤生长和繁殖有低促高抑效应, 低促的原因在于TNT影响了类脂和脂肪酸的代谢.本研究还原终产物及还原-氧化终产物对大型蚤也有低促高抑现象.低剂量的污染物可以诱发细胞活性, 产生毒物兴奋效应(hormesis)；但在高剂量毒物下, 活性氧自由基大量积累, 机体抗性来不及反应, 细胞结构和功能遭到破坏(彭颖等, 2012; Chen et al., 2014; Prosnier et al., 2015; Bour et al., 2016).也有研究表明, 低浓度污染物对大型蚤的生长繁殖无促进作用, 而是浓度越大, 抑制作用越强(Sancho et al., 2016), 本研究BDE-209及还原中间产物对大型蚤的毒性效应也是如此.BDE-209及其降解不同阶段产物的毒性作用变化不一致, 其原因可能在于各污染物因性质不同, 致毒模式和途径亦不同, 也可能与污染物浓度设置不够低(Sancho et al., 2016; Esterhuizen-Londt et al., 2015)或溶剂的影响有关(Li et al., 2014; Zhao et al., 2011; ISO, 2012).
4.2 水华微囊藻毒性1 mg·L-1的BDE-209、还原中间产物、还原终产物和还原-氧化终产物在第16 d对水华微囊藻的抑制率分别为15.7%、93.7%、6.6%和1.3%.其中, 水华微囊藻对还原中间产物的浓度变化最敏感, 16 d时, 0.1 mg·L-1组的抑制率仅为14.1%, 而0.5和1 mg·L-1组则大部分死亡(83.2%和93.7%).可见, BDE-209及其降解产物对水华微囊藻有不同程度的抑制作用, 中间产物毒性最大, 还原-氧化终产物毒性最小, 原因可能在于不同物质对藻类的毒性机制不同(Magdaleno et al., 2015).BDE-209的疏水性比中间产物(低溴BDEs混合物)大, 较难进入藻细胞内, 短时间难以致毒(胡恒等, 2015)；而终产物主要是完全脱溴产物二苯醚, 虽然水溶性更大, 但致毒的溴原子已被脱除, 毒性较小, 但较高浓度的还原终产物对水华微囊藻仍有一定的抑制作用.
BDE-209及其降解产物对水华微囊藻的抑制率随培养天数的增加先增加后减小, 如中间产物浓度为0.5 mg·L-1, 4~8 d时水华微囊藻大部分死亡, 但从第10 d起其抑制率开始下降.这是因为生物具有一定的耐受性, 在其承受范围内能根据环境变化调整自身机制, 但当污染物浓度超过其阈值时, 生物的这种机能就会被破坏(Stanley et al., 2013; Wan et al., 2015).
BDE-209及其降解产物对大型蚤和水华微囊藻的毒性大小均为：还原中间产物＞BDE-209＞还原终产物＞还原-氧化终产物, 表明BDE-209还原降解中生成了高毒中间产物.由于自然条件下BDE-209的降解很不彻底(Kim et al., 2014; Su et al., 2014), 主要生成了一系列毒性相对更大的低溴BDEs(Waaijers et al., 2016; Chang et al., 2016; Su et al., 2016), 且在某些条件下可能进一步生成PBDD/Fs等剧毒二次污染物(Kim et al., 2014; 孙文文等, 2016; Su et al., 2016), 可影响生物基因的正确表达(Su et al., 2014; Su et al., 2016), 构成潜在的环境和健康威胁.因此, 将BDE-209彻底还原脱溴, 后续辅以氧化降解, 可基本消除其环境毒性.
5 结论(Conclusions)1) BDE-209及其降解产物对大型蚤的繁殖毒性大于其生长毒性.BDE-209及其降解产物(1 mg·L-1)对大型蚤和水华微囊藻的致死/抑制率大小为：还原中间产物(100%/93.7%)＞BDE-209(16.7%/15.7%)＞还原终产物(8.3%/6.6%)＞还原-氧化终产物(8.3%/1.3%).
2) BDE-209降解过程中易生成高毒中间产物, 彻底还原脱溴可降低其毒性, 后续辅以氧化降解, 可基本消除其环境毒性.
致谢:(Acknowledgements):感谢周树锋教授对本文英文摘要的精心修改!
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