中国环境科学 2021,41(5)：2434~2440 China Environmental Science 全氟辛烷磺酰胺在小麦和蚯蚓中的富集与转化吴思寒,吴雨濛,王双杰,陈萌,刘青,祝凌燕*(南开大学环境科学与工程学院,环境污染过程与基准教育部重点实验室,天津城市生态环境修复与污染防治重点实验室,天津 300350)摘要：研究了不同培养介质和培养方式下全氟辛烷磺酰胺(PFOSA)在小麦、蚯蚓体内的生物富集和转化.结果表明:小麦根系可以从培养介质中吸收PFOSA并向上转运至茎叶.土壤中PFOSA生物有效性受总有机碳(TOC)的影响显著,高TOC含量土壤中PFOSA的生物有效性降低,导致其在小麦和蚯蚓中的生物富集因子分别由(61.24 ± 8.42)和(21347.91 ± 208.86)降至(5.61 ± 0.23)和(1404.92 ± 108.21).PFOSA在小麦的根和茎叶以及蚯蚓中都可以转化为PFOS,但在蚯蚓中的转化率((3.87 ± 1.71)%)显著低于小麦((26.39 ± 3.02)%).小麦根中PFOS的支链异构体(br-PFOS)比例在低、高TOC含量时分别为(14.8 ± 2.0)%、(66.1 ± 26.2)%,低于茎叶(分别为(63.0 ± 21.3)%、(85.2 ± 2.4)%)),可能是由于根部转化生成的br-PFOS更容易向茎叶转运.小麦特别是小麦茎叶中的br-PFOS比例((85.2 ± 2.4)%)显著高于蚯蚓((16.5 ± 4.0)%).小麦的存在可以提高土壤中PFOSA的生物有效性,从而促进蚯蚓对PFOSA 的富集,但对其转化影响不大.本文为小麦和蚯蚓中PFOSA的富集和转化提供了证据,有助于探索环境中PFOS的间接来源.关键词：全氟辛烷磺酰胺(PFOSA)；小麦；蚯蚓；生物富集；生物转化中图分类号：X131 文献标识码：A 文章编号：1000-6923(2021)05-2434-07Bioaccumulation and biotransformation of perfluorooctane sulfonamide in wheat and earthworms. WU Si-han, WU Yu-meng, WANG Shuang-jie, CHEN Meng, LIU Qing, ZHU Ling-yan* (Key Laboratory of Pollution Processes and Environmental Criteria of Ministry of Education, Tianjin Key Laboratory of Environmental Remediation and P ollution Control, College of Environmental Science and Engineering, Nankai University, Tianjin 300350, China). China Environmental Science, 2021,41(5)：2434~2440 Abstract：The bioaccumulation and biotransformation of perfluorooctane sulfonamide (P FOSA) in wheat and earthworms was investigated in different culture media by different culture methods. The results indicated that PFOSA was effectively absorbed by wheat roots from the culture media and translocated from roots to shoots. The bioavailability of PFOSA in soil was significantly affected by the soil total organic carbon (TOC) content. The bioavailability of P FOSA in the soil with higher TOC content was reduced, resulting in the bioaccumulation factors in wheat and earthworms decreased from (61.24 ± 8.42) and (21347.91 ± 208.86) to (5.61 ± 0.23) and (1404.92 ± 108.21), respectively. PFOSA could be transformed into PFOS in the earthworms as well as in the roots and shoots of wheat, but the transformation rate of PFOSA in the earthworms ((3.87 ± 1.71)%) was significantly lower than that in the wheat ((26.39 ± 3.02)%). The ratio of branched P FOS isomers (br-P FOS) in the wheat roots was (14.8 ± 2.0)% and (66.1 ±26.2)% at low and high TOC content, respectively, lower than those in the shoots ((63.0 ± 21.3)% and (85.2 ± 2.4)%), respectively), which might be because it was easier to translocate br-PFOS formed in roots to shoots. The ratio of br-PFOS in wheat, especially in wheat shoots ((85.2 ± 2.4)%), was significantly higher than that in earthworms ((16.5 ± 4.0)%). The presence of wheat enhanced the bioavailability of P FOSA in the soil, thereby promoted the accumulation of P FOSA in earthworms, but had little effect on the transformation of P FOSA. The results provided evidence for the bioaccumulation and biotransformation of P FOSA in wheat and earthworms, and were helpful to explore the indirect sources of PFOS in the environment.Key words：PFOSA；wheat；earthworm；bioaccumulation；biotransformation全氟和多氟化合物(PFASs)因其优异性质已在日常生活中被广泛使用,如食品包装材料、消防泡沫、表面活性剂、纺织品等[1].PFASs结构中的C-F 键是最强的共价单键,因此PFASs极为稳定,难以发生生物和非生物降解(如水解、光解),可在环境中长期存在,并发生生物富集、生物放大效应[2-3].全氟辛烷磺酸(PFOS)是研究最多、环境中最常见的一种PFASs[4],已在环境介质和人体中[5-10]广泛检出,并对生殖、免疫、内分泌和神经系统以及肝脏均具有毒害作用[11-12],因此于2009年列入斯德哥尔摩公约,被逐步禁用[13].除直接排放外,环境中PFOS的另一主要来源是环境中前体物(PreFOS)的转化[14].据报道,1970~2002年间,PreFOS的最大历史排放量(6800 ~45250t)要远高于PFOS(450 ~ 2700t)[15].全氟辛烷收稿日期：2020-10-08基金项目：国家重点研发计划(2018YFC1801003,2019YFC1804203),国家自然科学基金资助项目(41991313,21737003)* 责任作者, 教授,****************.cn5期吴思寒等：全氟辛烷磺酰胺在小麦和蚯蚓中的富集与转化 2435磺酰胺(PFOSA)是一种在环境中广泛检出的典型PreFOS[16-19].它是许多其他大分子PreFOS转化为PFOS的中间物质,且是限速步骤[20-26].工业生产的PFOSA中,支链异构体(br-PFOSA)比例为24.7%[27]. PFOSA的转化存在异构体选择性,其异构体转化特征会对环境中PFOS的异构体分布特征产生影响,有助于追溯环境中PFOS的来源[28].但目前关于PFOSA在陆生动植物中的特异性转化研究较少,因此对其进行研究十分必要.土壤是PFASs在环境中的重要归属地之一[6], PFASs能通过点源污染、大气沉降、地面径流等进入土壤系统[29].例如,在美国空军设施附近的土壤中PFOSA最高浓度甚至已达到20000ng/g[6].土壤中PFASs可以通过植物或动物进入食物链,经食物链的富集产生生物放大效应,对人体健康产生危害.小麦(Triticum aestivum L.)是一种世界各地都广泛种植的禾本科农作物,是人类食物的重要来源之一[12].蚯蚓(Eisenia fetida)是土壤中生物量最大的无脊椎动物,其生命活动会直接或间接地对有机污染物在土壤中的迁移和转化产生影响[30].土壤的性质、生物种类等都会影响PFOSA的生物富集和生物转化,因此本文以小麦、蚯蚓为受试生物,PFOSA为目标污染物,研究不同培养介质和培养方式下PFOSA在小麦、蚯蚓体内的生物富集和转化,为探索环境中PFOS的间接来源、评价PFOSA的人类健康和生态风险以及环境修复提供理论参考.1材料与方法1.1实验材料实验所用试剂如下:全氟辛烷磺酰胺工业品(PFOSA,>90%,北京百灵威科技有限公司),全氟辛烷磺酸标准品及其内标(PFOS和13C-PFOS,>99%)、全氟辛烷磺酰胺标准品及其内标(PFOSA和13C-PFOSA, >99%)购自加拿大惠灵顿实验室.甲醇(色谱纯)、过氧化氢30%(H2O2,质量分数,分析纯)均购自天津市化学试剂供销公司,甲基叔丁基醚(分析纯,天津市康科德科技有限公司),氢氧化钠(NaOH,优级纯)、四丁基硫酸氢铵(TBAHS,分析纯)、无水碳酸钠(Na2CO3,优级纯)均购自天津市津科精细化工研究所.甲酸(色谱纯,上海安谱实验科技股份有限公司)、氨水(色谱纯,阿拉丁)、甲醇(HPLC级)和乙腈(HPLC级)购自美国Fisher公司.实验所用小麦种子(Triticum aestivum L.)购自天津农科院,所用赤子爱胜蚓(Eisenia fetida)购于天津当地养殖场.1.2暴露实验1.2.1小麦在土壤和石英砂介质中的暴露实验首先将小麦种子于3% H2O2(质量分数)中浸泡30min消毒,用Milli-Q水冲洗5次后,用Milli-Q水浸泡一夜,之后在铺有湿滤纸的底部未全封闭的透气托盘架上均匀铺开,使之于22 ~ 27℃下发芽,托盘架上部铺一层铝箔以保证含水率,防止水分蒸发过快.为了研究土壤中TOC对PFOSA生物有效性的影响,实验采用2种培养介质种植小麦,分别为土壤和石英砂,设立4组实验:有毒有植物、无毒有植物、有毒无植物和无毒无植物,染毒浓度为200ng/g,每组设置3个平行.将发芽3d、大小均一的小麦幼苗移植到1L塑料花盆中,每盆装有650g培养介质,种植7株小麦.将花盆放置于采光较好的天台处培养,每天随机更换盆的位置以保证小麦受阳光照射条件良好,每天浇水使土壤含水率保持在30%左右,14d后收获小麦.收获时用蒸馏水冲洗小麦根部,之后用滤纸擦干,将小麦根和茎叶分离,弃去根茎连接处,于-20℃冰箱中储存.1.2.2蚯蚓在不同TOC含量土壤中的暴露实验将蚯蚓于未染毒土壤中避光驯养14d.实验采用土壤和土壤/石英砂(8:2,质量比)两种培养介质,染毒浓度为0, 200ng/g,设置3个平行.将驯养好的蚯蚓放入250mL烧杯,每杯装有100g培养介质,放入10条蚯蚓.将烧杯用铝箔包裹,避光培养,每天加水保持土壤湿度在30%左右,分别培养7和14d后收获蚯蚓.收获时从土壤中取出蚯蚓并用水清洗,在装有潮湿脱脂棉的玻璃杯中放置24h清肠后用水冲洗,再用滤纸吸去水分,于-20℃冰箱中储存.1.2.3蚯蚓-小麦联合暴露实验小麦种子的培育见1.2.1,蚯蚓驯养见1.2.2.将赤子爱胜蚓与小麦联合培养,采用土壤和土壤/石英砂(8:2)两种培养介质,染毒浓度为0, 200ng/g,设置3个平行.将发芽3d的小麦和驯养完成的蚯蚓放入1L塑料花盆中,每盆装有650g培养介质,加入7株小麦和10条蚯蚓.用铝箔包裹花盆边缘并高出边缘3cm,以防蚯蚓在实验期间爬出.每天加水保持土壤湿度在30%左右,14d后收2436 中国环境科学 41卷获小麦和蚯蚓.小麦和蚯蚓的取样方式同1.2.1和1.2.2.1.3样品前处理生物样前处理采用Chen等[31]的方法并稍作改进.将生物样置于冷冻干燥机中-50℃下干燥48h,剪碎.称取一定质量干重样品(根取0.01g,茎叶取0.05g,蚯蚓取0.1g)于10mL PP 离心管中,加入2ng内标(包括M4-PFOS和M8-PFOSA),涡旋振荡,使其充分混匀,平衡至少2h.依次加入1mL 0.5mol/L的TBAHS 溶液(pH值用氢氧化钠溶液调至10)和2mL 0.25mol/L的Na2CO3缓冲液,充分混匀后,加入4mL 甲基叔丁基醚,混合液于250r/min下震荡20min,然后在4℃、6000r/min下离心10min使有机相与水相分离,将上层有机相转移至新10mL离心管中.萃取过程重复2次,萃取液氮吹至干.用2mL甲醇复溶,加入50mg Carb填料以去除色素等杂质,混匀后在4℃,11000r/min下离心15min.取上清液至新离心管中氮吹干.用1mL甲醇复溶,过0.22µm尼龙滤膜后转移到进样小瓶中,放在冻存盒中于-20℃冰箱中保存,以待分析.培养介质前处理采用Zhao等[30]的方法并稍作改进.将培养介质置于冷冻干燥机中-50℃下干燥48h,将1g干燥的介质置于10mL PP离心管中,加入2ng内标(包括M4-PFOS和M8-PFOSA),涡旋振荡,使其充分混匀,平衡至少2h.加入5mL甲醇,然后于250r/min下震荡10min.将离心管于40℃超声10min.将该混合物在3000r/min下离心10min.重复提取3遍,并将上清液合并到另一个新的离心管中.萃取液氮吹至2mL.加入50mg Carb填料以去除色素等杂质,混匀后在4℃,11000r/min下离心15min.取上清液至新离心管中氮吹干.用1mL甲醇复溶,过0.22µm 尼龙滤膜后转移到进样小瓶中,放在冻存盒中于-20℃冰箱中保存,以待分析.1.4仪器分析在负电喷雾电离模式下,使用Waters超高效液相色谱-质谱联用仪(ACQUITY-UPLC/XEVO-TQS)分析样品中各物质含量.色谱柱采用FluoroSep-RP Octyl柱(150mm×2.1mm,3µm粒径; ES Industries, West Berlin,NJ).柱温为38℃,进样体积为10µL,流动相流速为0.15mL/min.对于PFOSA异构体,流动相A、B分别为3mmol/L甲酸的水溶液(pH值用氨水调至4.15)和乙腈溶液.流动相初始比例为60%A、40%B,保持1min,在3min变为74%B,在35min变为80%B,在35.1min变为100%B并保持至40min,在45min回到初始比例.对于PFOS异构体,流动相A、B分别为3mmol/L甲酸的水溶液(pH值用氨水调至4.15)和甲醇溶液.流动相初始比例为60%A、40%B,保持0.3min,在1.9min变为64%B,在5.9min变为66%B,在7.9min变为70%B,在26min变为74%B,在30min变为100%B并保持至33min,在35min回到初始比例并保持至40min.质谱条件为:毛细管电压2700V;离子源温度150℃;去溶剂温度350℃;锥孔气流速150L/Hr;去溶剂气流速800L/Hr;雾化气流速7bar.目标化合物的定量离子、锥孔电压及碰撞能参数如表1所示.表1目标化合物的定量离子、锥孔电压、碰撞能Table 1 Instrumental information of target compounds目标化合物定量离子锥孔电压(V) 碰撞能(eV)n-PFOSA 498 > 78 10 30iso-PFOSA 498 > 169 10 301m-PFOSA 498 > 419 10 152m-PFOSA 498 > 164 10 153m-PFOSA 498 > 259 10 254m-PFOSA 498 > 269 10 255m-PFOSA 498 > 219 10 35M8-PFOSA 506 > 78 10 30n-PFOS 499 > 80 45 40iso-PFOS 499 > 169 45 501m-PFOS 499 > 419 45 252m-PFOS 499 > 230 45 253+5m-PFOS a499 > 130 45 554m-PFOS 499 > 330 45 35M4-PFOS 503 > 80 45 40注:a3m-和5m-PFOS异构体无法进行基线分离,因此被合并为3+5m-PFOS.1.5质量保证与质量控制回收率实验通过向空白基质中加入标准品进行.在样品前处理过程中添加过程空白以校正背景污染.根据样品峰面积与内标峰面积之比对物质浓度进行定量.方法检出限(MDL)定义为信噪比为3:1时物质浓度.各物质的回收率和检出限如表2所示.本实验中,各基质中PFOSA和PFOS的回收率均在80%~100%范围内,因此不使用回收率对测得的各物质浓度进行校正.在暴露实验开始前,小麦中就检测到一定浓度5期 吴思寒等：全氟辛烷磺酰胺在小麦和蚯蚓中的富集与转化 2437的PFOSA(根(11.71 ± 0.93) ng/g,茎叶(2.64 ± 0.44) ng/g)和PFOS(根(16.89 ± 4.25) ng/g,茎叶(4.20 ± 2.56) ng/g).在暴露14d 后,空白小麦中检测到相似水平的PFOSA(根(9.53 ± 1.74) ~ (10.38 ± 1.60) ng/g,茎叶(2.56 ± 0.59) ~ (3.34 ± 1.64) ng/g )和PFOS(根(15.31 ± 1.31) ~ (16.24 ± 1.96) ng/g,茎叶(1.64 ± 0.54) ~ (1.71 ± 0.47) ng/g).空白蚯蚓体内PFOSA 和PFOS 的浓度远低于实验组蚯蚓(相差103 ~ 105个数量级).由此判断,空白组小麦和蚯蚓中PFOSA 和PFOS 来源于背景污染.本文所用暴露组浓度均扣除了空白组浓度.表2 目标化合物的回收率和方法检出限(MDL) Table 2 Recoveries and MDLs of target compoundsP F OSA P F OS 基质回收率(%) MDL(ng/g)回收率(%) MDL(ng/g)根 95.80 ± 1.98 0.0502 89.59 ± 2.84 0.1318 茎叶 98.47 ± 2.71 0.0404 93.53 ± 2.98 0.0533 蚯蚓 89.51 ± 0.33 0.0316 87.86 ± 2.85 0.3445 石英砂 90.82 ± 1.45 0.0372 89.91 ± 3.31 0.0483 土壤 88.64 ± 1.940.044989.83 ± 0.350.04651.6 数据分析对小麦的根富集因子(RCF)、蚯蚓的生物富集因子(BSAF)和转化率(TR)进行计算,公式如下: root m RCF /C C = (1)e m BSAF /C C = (2)PFOS PFOS PFOSA TR /()C C C =+ (3) 式中: C m 为培养介质中PFOSA 的浓度, ng/g;C root 为小麦根中PFOSA 浓度, ng/g dw;C e 为蚯蚓中PFOSA 浓度, ng/g dw;C PFOS 为小麦或蚯蚓中PFOS 浓度, ng/g dw;C PFOSA 为小麦或蚯蚓中PFOSA 浓度, ng/g dw.使用IBM SPSS Statistics 22进行数据分析.使用配对t 检验评估各组间RCF 、TR 和br -PFOS 比例的差异,当P < 0.05时认为存在显著性差异,当P < 0.01时认为差异极显著. 2 结果与讨论2.1 小麦和蚯蚓的生理状况在整个实验周期内,小麦和蚯蚓生理状况良好,没有不良反应、死亡等现象,空白对照组和实验组小麦和蚯蚓生物量无显著性差异(P > 0.05). 2.2 小麦对PFOSA 的富集和转化通过公式(1)计算小麦的RCF,发现PFOSA 在石英砂培养小麦中的RCF((61.24±8.42))远大于土壤中培养的小麦((5.61±0.23)),存在显著性差异(P <0.01),说明培养基质中的总有机碳含量(TOC)会显著影响其生物有效性.Liu 等[32]研究表明土壤TOC 含量与所吸附的PFOS 量之间存在显著的线性关系(P < 0.01).土壤中TOC 含量高于石英砂,对PFOSA 具有较强的吸附能力,使得土壤中可生物利用的PFOSA 减少,导致在土壤中生长的小麦的RCF 较低.在小麦的根和茎叶中均测得转化产物PFOS.通过公式(3)计算了小麦中PFOSA 的转化率,发现茎叶中转化率远高于根中(P <0.01,图1).有实验表明,当辛醇-水分配系数(log K ow )>4时,疏水性有机化合物会强烈吸附于根的上表皮,难以转运到茎叶[33].Zhao等[34]研究也表明当有机化合物log K ow >4时,该物质从根到茎叶转运因子(TF)随log K ow 的增加而指数递减.PFOSA 的log K ow (5.62)小于PFOS(log K ow = 6.43)[35],表明PFOS 较PFOSA 更难从根转运至茎叶,因此茎叶中较高的转化率表明叶中PFOS 不仅来源于根部转运,还来源于茎叶的生物转化.此外还发现PFOSA 在土壤培养的小麦根(P <0.05)和茎叶(P < 0.01)的转化率均大于石英砂中小麦(图1).这可能是由于PFOSA 被土壤中微生物转化为PFOS [36],生成的PFOS 被小麦富集.土壤中有机碳可以为微生物的生长提供充足的碳源,从而提高微生物数量和活性[37].Bizkarguenaga 等[38]也观察到在高TOC 的土壤中生菜对PFOSA 降解更强.根茎叶51015202530354045转化率(%)图1 生长在不同培养基质中的小麦对PFOSA 的转化率 Fig.1 TR of PFOSA in wheat grown in different culturemedia**、*分别表示差异极显著(P <0.01)和显著(P <0.05)2438 中 国 环 境 科 学 41卷除石英砂培养的小麦根外((14.8±2.0)%),小麦中br -PFOS 比例均显著高于24.7%(土壤中小麦根:(66.1±26.2)%,土壤中小麦叶:(85.2±2.4)%,石英砂中小麦叶:(63.0±21.3)%,图2),说明小麦中br -PFOSA 比n -PFOSA 优先发生转化.小麦中br -PFOS 比例呈现以下趋势:根中br -PFOS 比例小于茎叶,石英砂培养的小麦中br -PFOS 比例小于土壤.小麦根中br - PFOS 比例要小于茎叶,这是因为直链异构体比相应的支链异构体具有更高的疏水性[18],导致br -PFOS 比n -PFOS 更易从根转运至茎叶.石英砂介质培养的小麦根中br -PFOS 比例低于24.7%,可能也是由于根中生成的br -PFOS 部分转运至茎叶.已有研究表明,PFOSA 是N -EtFOSE 生物转化过程的中间产物[21,39].Liu 等[25]在好氧土壤中观察到N -EtFOSE 的异构体特异性生物转化并检测到br -PFOS 的生成.Chen 等[31]表明,br -PFOSA 在生物体内会优先转化为br -PFOS.因此可以推测,土壤中微生物对br -PFOSA 进行优先转化,生成更多的br -PFOS 并被小麦吸收,从而导致土壤中培养的小麦中br -PFOS 比例高于石英砂中培养的小麦.根 茎叶20 40 60 80 100 b r -P F O S (%)图2 小麦根和茎叶中br -PFOS 比例 Fig.2 Ratio of br -PFOS in wheat roots and shoots2.3 蚯蚓对PFOSA 的富集和转化通过计算蚯蚓对PFOSA 的生物富集因子(BSAF),发现随培养时间增加,PFOSA 在蚯蚓体内的BSAF 增加(图3).培养14d 后,土壤/石英砂(8:2)介质中PFOSA 在蚯蚓体内的BSAF 值(21347.91±208.86)远高于土壤中(1404.92±108.21),是土壤中的15.20倍(图3),该趋势与PFOSA 在小麦体内富集的结果相同,进一步说明土壤中TOC 对PFOSA 具有较强的吸附能力,降低了土壤中PFOSA 的生物有效性.714500010000150002000025000B S A F时间(d)图3 不同培养时间和培养介质下蚯蚓中PFOSA 的BSAF Fig.3 BSAF of PFOSA in earthworms treated with differentculture time and culture media在蚯蚓中同样检测到PFOSA 转化产物PFOS 的生成,但其TR 相对较低.在土壤中培养了14d 的蚯蚓中PFOSA 的TR((3.87 ± 1.71)%)显著低于小麦中((26.39 ± 3.02)%),表明不同生物对PFOSA 的转化能力存在很大差异[40].7145101520253035b r -P F O S (%)时间(d)图4 不同培养时间和培养介质下蚯蚓中br -PFOS 比例 Fig.4 Ratio of br -PFOS in earthworms treated with differentculture time and culture media不同培养介质对蚯蚓中br -PFOS 比例会产生影响,土壤/石英砂(8:2)介质中,br -PFOS 比例更高(图4, P <0.05).这可能是由于土壤/石英砂(8:2)介质加入了石英砂,土壤黏性降低,孔隙度高,通气透水性强,更适宜蚯蚓生存,其中蚯蚓的活性更高.在生物体内br -PFOSA 异构体会优先代谢[31,41],生成br -PFOS.5期 吴思寒等：全氟辛烷磺酰胺在小麦和蚯蚓中的富集与转化 2439土壤/石英砂(8:2)介质仅加入20%的石英砂,TOC 含量与土壤差距不大,所以推测其微生物数量和活性差异较小,对PFOSA 转化的影响也差别不大.因此土壤/石英砂(8:2)介质中蚯蚓体内br -PFOS 比例高.与小麦特别是茎叶中较高的br -PFOS 比例不同,在土壤中培养了14d 的蚯蚓中br -PFOS 比例为(16.5± 4.0)%,小于24.7%.这可能是由于蚯蚓通过大量排出粪便向外排出污染,而br -PFOS 比n -PFOS 更易从体内排出[31].2.4 小麦共同生长对蚯蚓中PFOSA 的富集和转化的影响蚯蚓和小麦联合培养时,土壤/石英砂(8:2)介质中PFOSA 在蚯蚓体内的BSAF(32176.65±844.49)高于土壤中(26743.14±11311.21)(图5),进一步说明土壤TOC 会显著影响其中PFOSA 的生物有效性.由图5可知,联合培养时PFOSA 在蚯蚓体内的BSAF 显著高于蚯蚓单独培养时的结果(P <0.05).Kelsey 等[42]、Zhao 等[34]也发现南瓜和小麦会促进蚯蚓对p,p'-DDE 和PFASs 的富集.这主要是由于植物根系分泌物会提高PFOSA 从土壤中的解吸,提高其生物有效性.小麦存在时,蚯蚓中PFOSA 转化率与单独培养时无显著性差异(P >0.05),表明小麦的存在对蚯蚓中PFOSA 转化率无影响.E E+W5000 1000015000 2000025000 3000035000 40000 B S A F实验组图5 不同培养方式和培养介质下蚯蚓中PFOSA 的BSAF Fig.5 BSAF of PFOSA in earthworms treated with different culture methods and culture mediaE:蚯蚓单独培养; E+W:蚯蚓和小麦联合培养3 结论 3.1 小麦根能从土壤溶液中吸收PFOSA 并转运至茎叶.土壤TOC 含量显著影响其中PFOSA 的生物有效性,TOC 含量高,其生物有效性降低.PFOSA 在小麦的根和茎叶中都可以转化为PFOS,且土壤培养的小麦中PFOSA 的转化率更高.小麦中br -PFOS 比例关系为根<茎叶,石英砂<土壤.3.2 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