摘要:【目的】明確鄰甲酚對(duì)斑馬魚成魚的急性毒性及其對(duì)肌肉、鰓和肝臟組織顯微結(jié)構(gòu)的影響,為鄰甲酚對(duì)斑馬魚毒性效應(yīng)的分子機(jī)理研究與環(huán)境安全評(píng)價(jià)和生態(tài)風(fēng)險(xiǎn)評(píng)估提供理論依據(jù)。【方法】采用靜水式方法,將斑馬魚成魚分為6組,暴露于0(對(duì)照)、15.00、19.74、25.98、34.19和45.00mg/L鄰甲酚溶液中,記錄染毒24、48、72和96h的各組斑馬魚中毒癥狀和死亡尾數(shù),計(jì)算死亡率、半致死濃度(LC,)和安全濃度(SC),并進(jìn)行安全性評(píng)價(jià),采用組織病理學(xué)技術(shù)分析不同濃度鄰甲酚對(duì)斑馬魚肌肉、鰓和肝臟組織顯微結(jié)構(gòu)的影響?!窘Y(jié)果】與對(duì)照組相比,45.00mg/L(最高濃度)組斑馬魚急性中毒癥狀表現(xiàn)為呼吸困難、狂游、抽搐、輕微側(cè)翻且對(duì)外周刺激反應(yīng)遲鈍,逐漸失去平衡而靜臥水底,24h內(nèi)全部死亡。鄰甲酚對(duì)斑馬魚成魚24、48、72和96h的LC?分別為34.721、30.079、27.123和27.092mg/L,SC為6.612mg/L,毒性等級(jí)為低毒。組織病理學(xué)分析表明,15.00和19.74mg/L組斑馬魚染毒96h后,肌肉、鰓和肝臟組織顯微結(jié)構(gòu)無(wú)明顯變化。鄰甲酚濃度達(dá)34.19和45.00mg/L時(shí),斑馬魚肌肉組織的肌纖維逐漸斷裂、腫脹和壞死;鰓組織中鰓小片末端腫大出血,上皮細(xì)胞腫脹、脫落和損傷,紅細(xì)胞數(shù)量明顯增多,細(xì)胞排列混亂;肝臟出現(xiàn)大面積細(xì)胞空泡化,肝細(xì)胞核萎縮變形、溶解或偏移,導(dǎo)致肝細(xì)胞呈壞死狀態(tài)?!窘Y(jié)論】鄰甲酚對(duì)斑馬魚成魚的毒性效應(yīng)隨著暴露濃度升高、時(shí)間延長(zhǎng)而增強(qiáng),屬于低毒性酚類污染物。高濃度鄰甲酚暴露可導(dǎo)致斑馬魚成魚肌肉、鰓和肝臟組織顯微結(jié)嚴(yán)重?fù)p傷。
關(guān)鍵詞:斑馬魚;鄰甲酚;急性毒性;半致死濃度;顯微結(jié)構(gòu)
中圖分類號(hào):S917.4文獻(xiàn)標(biāo)志碼:A文章編號(hào):2095-1191(2024)01-0290-09
Effects of o-cresol on acute toxic and histological microstructure of adult zebrafish(Danio rerio)
SONG Xing-chao,JIANG Qian-qian,GAN Zhen-bo,LIANG Zheng-qi, MEI Jie,BA Jia-wen*
(Collegeof Agroforesry Engineering and Planning,Tongren University/Guizhou Provincial Key Laboratory for Biodiver-sity Conservation and Utilization in the Fanjing Mountain Region,Tongren,Guizhou554300,China)
Abstract:[Objective]Inorder to investigate the acute toxicity and histological microstructure of o-cresol on muscle,gill,and liver tssues of adult zebrafish,and provide theoretical basis for the molecular mechanism of the toxic effect of o-cresol on zebrafish,environmental safety assessment and ecological risk assessment.[Method]Adult zebrafish were di vided into6groups and exposed to0(control),15.00,19.74,25.98,34.19and45.00mg/L o-cresol solution for96h using the static water method,respectively.The symptoms and numbers of death ofpoisoning of zebrafish in each group at24,48,72and96h were recorded.The mortality,median lethal concentration(LCso)and the safe concentration(SC)were calculated,and the safety level was evaluated.The effects of different concentrations of o-cresol on the histological structure of muscle,gill and liver tissues of adult zebrafish were further analyzed based on histopathological techniques.【Result]Compared with the control group,the acute poisoning symptoms of zebrafish in the45.00mg/L(thehighest con-centration)group were characterized by difficulty breathing,wild swimming,convulsions,slight rolling,slow response to peripheral stimulation,and gradually losing balanceand lyingat the bottom of the water,all of which died within24h The LCo of o-cresol on adult zebrafish at24,48,72and96h were34.721,30.079,27.123and27.092mg/L,respec-tively,and the safe concentration of o-cresol was6.612mg/L,which belonged to low toxicity compound.Histopathologi-cal analysis showed that the microstructure of muscle,gill and liver of zebrafish did not change significantly after96h of exposure at concentrations of15.00and19.74mg/L.However,when the concentration of o-cresol was34.19and45.00mg/L,muscle fibers gradually broke,and swelling and necrosis appeared.In gill issue,the end of the secondary lamellae was swollen and bleeding,the epithelial cells were swollen,shed and damaged,the number of red blood cells increased greatly,andthe arrangement of various cells was disorderly.Large area vacuolation occurred in hepatocytes,hepatic nu-clei atrophied,deformed,dissolved or migrated,and hepatocytes showed necrosis.【Conclusion]The toxic effect of o-cresol on adult zebrafish is enhanced with increasing exposure concentration and prolonged time,and which belongs to low toxicity phenolic pollutant.Exposuretohigh concentrations of o-cresol can cause severe damage to the microstructure of muscle,gill and liver tissues in adult zebrafish.
Keywords:zebrafish;o-cresol;acute toxicity;median lethal concentration;microstructure
Foundation items:National Natural Science Foundation of China(32060274);Guizhou High-level Innovative Ta-lent(Thousand Level)Project[2024-(2022)-048];Guizhou Science and Technology Support Project(QKHZC〔2023〕Yiban081);Innovation and Entrepreneurship Training Project for College Students in Guizhou(202210665056)
0引言
【研究意義】鄰甲酚(O-cresol)屬于烷基酚類化合物,作為一種重要的精細(xì)化工原料被廣泛應(yīng)用于農(nóng)藥、醫(yī)藥消毒劑和香料等工農(nóng)業(yè)產(chǎn)品加工制造領(lǐng)域(劉俊逸等,2018)。研究表明,烷基酚類化合物是細(xì)胞原漿毒物,從皮膚和黏膜滲透進(jìn)入血液循環(huán)后,不僅會(huì)破壞細(xì)胞結(jié)構(gòu),還能與細(xì)胞原生質(zhì)中的蛋白結(jié)合,導(dǎo)致生物體內(nèi)蛋白質(zhì)變性,并使細(xì)胞失去活性,對(duì)生物具有致癌、致畸和致突變等潛在危害(殷偉等,2020),長(zhǎng)期染毒會(huì)造成心臟、肝臟、腎臟和中樞神經(jīng)系統(tǒng)等形態(tài)損傷,是一類毒性較強(qiáng)的化學(xué)污染物(Duan et al.,2018)。在實(shí)際生產(chǎn)中,未經(jīng)處理的鄰甲酚可通過多種途徑進(jìn)入水環(huán)境且較難降解,嚴(yán)重威脅水生生物的生存和繁衍,進(jìn)而影響水生態(tài)環(huán)境平衡(K?ktürk et al.,2021)。因此,研究鄰甲酚對(duì)水生生物的急性毒性,對(duì)突發(fā)鄰甲酚污染水體的安全評(píng)估具有重要的理論意義與實(shí)際應(yīng)用價(jià)值。【前人研究進(jìn)展】在鄰甲酚毒性效應(yīng)方面,Parkhurst等(1979)研究發(fā)現(xiàn),大型水蚤對(duì)鄰甲酚較敏感,其48h半致死濃度(LCs?)為5.00mg/L。大西洋鱈魚(Gadus morhua)鄰甲酚96h半數(shù)效應(yīng)濃度(ECs)為12.00mg/L,10.00mg/L鄰甲酚可抑制魚受精卵發(fā)育過程中色素的沉積(Falk-Petersen et al.,1985)。鄰甲酚對(duì)中肋骨條藻(Skeletonema costatum)和三角褐指藻(Phaeodactylum tricornutum)96h的EC??分別為7.99和13.28mg/L,為中度和輕度毒性,較高濃度的鄰甲酚能刺激藻類細(xì)胞中總蛋白、總脂質(zhì)和碳水化合物等合成以防御外源污染物刺激(Feng et al.,2023)。然而,鄰甲酚對(duì)淡水魚類,特別是模式生物斑馬魚的毒性效應(yīng)機(jī)理尚不明確。斑馬魚(Danio rerio)為輻鰭魚綱(Actinopterygii)鯉形目(Cyprini-formes)鯉科(Cyprinidae)短擔(dān)尼魚屬(Danio)小型淡水魚類,因其對(duì)水環(huán)境變化較敏感且具有體型小、成本低、易飼養(yǎng)等特點(diǎn),成為藥物篩選和化學(xué)品急、慢性毒性研究的重要?jiǎng)游锬P停↙in et al.,2016;王成等,2019;de Abreu et al.,2019)。目前,斑馬魚藥物毒性研究主要關(guān)注胚胎發(fā)育(陳玉翠和陳錦云,2016;Cooman et al.,2022)及心血管、神經(jīng)(Correia et al.,2019)和肝臟(Li et al.,2022)等組織器官。在烷基酚類化合物對(duì)斑馬魚的毒性方面,Puy-Azurmendi等(2014)研究表明,壬基酚通過抑制孵化酶活性導(dǎo)致斑馬魚胚胎孵化時(shí)間延遲,影響胚胎正常孵化。張慧等(2017)研究表明,4-壬基酚暴露不僅顯著增加斑馬魚胚胎畸形率,同時(shí)對(duì)仔魚具有致畸和致死效應(yīng)。Liu等(2023)將斑馬魚胚胎暴露于不同濃度的四氯雙酚A中,結(jié)果發(fā)現(xiàn)斑馬魚早期生活階段出現(xiàn)畸形、甲狀腺受損、腦血管缺失和異常游泳行為,表明四氯雙酚A具有神經(jīng)和心血管毒性。在鄰甲酚對(duì)斑馬魚的毒性方面,僅見張正勇(2008)報(bào)道為中等毒性,但其采用的毒性等級(jí)劃分標(biāo)準(zhǔn)與現(xiàn)行國(guó)家標(biāo)準(zhǔn)不一致;房妮等(2011)研究了鄰甲酚與對(duì)甲酚對(duì)斑馬魚的聯(lián)合毒性,但側(cè)重于分析胚胎發(fā)育變化?!颈狙芯壳腥朦c(diǎn)】鄰甲酚對(duì)斑馬魚成魚的急性毒性相關(guān)報(bào)道較少,缺乏與組織病理的聯(lián)合分析,其毒性機(jī)理尚不明確?!緮M解決的關(guān)鍵問題】明確鄰甲酚對(duì)斑馬魚成魚的急性毒性及其對(duì)肌肉、鰓和肝臟組織顯微結(jié)構(gòu)的影響,為鄰甲酚對(duì)斑馬魚毒性效應(yīng)的分子機(jī)理研究與環(huán)境安全評(píng)價(jià)和生態(tài)風(fēng)險(xiǎn)評(píng)估提供理論依據(jù)。采用靜水式方法,將斑馬魚成魚分別暴露于不同濃度鄰甲酚溶液中,記錄染毒24、48、72和96h的各組斑馬魚中毒癥狀和死亡尾數(shù),計(jì)算死亡率、LCs?和安全濃度(SC),并進(jìn)行安全性評(píng)價(jià),采用組織病理學(xué)技術(shù)分析不同濃度鄰甲酚對(duì)斑馬魚肌肉、鰓和肝臟組織顯微結(jié)構(gòu)的影響。
1材料與方法
1.1試驗(yàn)材料
鄰甲酚(純度≥98%)購(gòu)自上海麥克林生化科技股份有限公司,丙酮購(gòu)自貴州科益創(chuàng)生物科技有限公司,甲醛、無(wú)水乙醇、二甲苯、冰醋酸、氨水、蘇木精、伊紅、石蠟和中性樹膠均購(gòu)自南昌雨露實(shí)驗(yàn)器材有限公司,斑馬魚膨化配合飼料購(gòu)自成都通威集團(tuán)有限公司。斑馬魚成魚購(gòu)自中國(guó)科學(xué)院水生生物研究所國(guó)家斑馬魚資源中心,體長(zhǎng)34.47±2.21mm,經(jīng)5%食鹽水消毒后置于圓形蓄養(yǎng)槽(直徑820mm、高700mm)馴養(yǎng)7d,養(yǎng)殖用水為人工曝氣72h以上的自來(lái)水,水溫(26.35±1.98)℃,溶解氧gt;6.5mg/L,pH7.35±0.10。馴養(yǎng)期間每天7:00和18:00各投喂1次膨化配合飼料,投喂量為斑馬魚體質(zhì)量1%~3%;每天換水1/3~1/2,并清除糞便和食物殘?jiān)?d死亡率不超過5%視為合格,選取健康、大小一致且無(wú)疾病的斑馬魚作為試驗(yàn)材料。動(dòng)物試驗(yàn)由銅仁學(xué)院動(dòng)物倫理委員會(huì)批準(zhǔn),批準(zhǔn)號(hào):EAE-TRU-2022-018。
1.2急性毒性試驗(yàn)
正式試驗(yàn)前,于2022年9月8—22日參照孔志明(2017)的方法進(jìn)行預(yù)試驗(yàn),確定鄰甲酚對(duì)斑馬魚96h最高耐受濃度(LC?)和24h最低全致死濃度(LC1o0)。在二者間按等對(duì)數(shù)間距設(shè)5個(gè)鄰甲酚濃度梯度,分別為15.00、19.74、25.98、34.19和45.00mg/L試驗(yàn)組,以不添加鄰甲酚(0mg/L)為對(duì)照組,每組設(shè)4個(gè)平行,每平行15尾魚,其中3個(gè)平行用于數(shù)據(jù)統(tǒng)計(jì),1個(gè)平行用于解剖觀察。于2022年9月23—30日進(jìn)行正式試驗(yàn),采用靜水式方法,將斑馬魚暴露于相應(yīng)濃度鄰甲酚溶液中,每天更換1/2相應(yīng)濃度鄰甲酚溶液,測(cè)定并記錄溶液溫度、pH和溶解氧,及時(shí)清理死魚,試驗(yàn)期間不投喂飼料。試驗(yàn)開始后連續(xù)觀察8h,記錄染毒24、48、72和96h的各組斑馬魚中毒癥狀和死亡尾數(shù),對(duì)照組死亡率不超過2%視為試驗(yàn)有效,按公式(1)計(jì)算死亡率。
死亡率(%)=死亡尾數(shù)/總尾數(shù)×100(1)
1.3組織病理觀察
分別于斑馬魚染毒24、48、72和96h時(shí),隨機(jī)選取3尾魚進(jìn)行解剖觀察,收集染毒96h的斑馬魚肌肉、鰓和肝臟組織,用4%甲醛進(jìn)行固定。參照李培倫等(2022)的魚類組織器官石蠟切片制作方法并略加改動(dòng),將固定好的斑馬魚肌肉、鰓和肝臟組織經(jīng)梯度酒精脫水后,進(jìn)行石蠟包埋、切片(厚度5μm)、蘇木精—伊紅染色(HE染色)和中性樹膠封片,使用光學(xué)顯微鏡觀察分析并拍照記錄各組織主要病變部位。
1.4統(tǒng)計(jì)分析
采用SPSS27.0對(duì)試驗(yàn)數(shù)據(jù)進(jìn)行整理,以平均值±標(biāo)準(zhǔn)差表示。利用加權(quán)回歸法計(jì)算不同染毒時(shí)間的LC。和95%置信區(qū)間。
根據(jù)特倫堡(Turubell)公式,計(jì)算鄰甲酚對(duì)斑馬魚成魚的安全濃度(SC)。
SC=48h-LC50×0.3/(24h-LC50/48h-LC50)2(5)
式中,24h-LC,為24h的半致死濃度(mg/L),48h-LC50為48h的半致死濃度(mg/L)。
毒性等級(jí)劃分參照現(xiàn)行國(guó)家標(biāo)準(zhǔn)GB/T31270.12—2014《化學(xué)農(nóng)藥環(huán)境安全評(píng)價(jià)試驗(yàn)準(zhǔn)則第12部分:魚類急性毒性試驗(yàn)》,根據(jù)96h的LCs將鄰甲酚對(duì)斑馬魚急性毒性的等級(jí)劃分為劇毒(96h-LC50≤0.10mg/L)、高毒(0.10mg/Llt;96h-LC50≤1.00mg/L)、中毒(1.00mg/Llt;96h-LC50≤10.00mg/L)和低毒(96h-LC50gt;10.00mg/L)。
2結(jié)果與分析
2.1不同濃度鄰甲酚對(duì)斑馬魚行為的影響
隨著鄰甲酚濃度的升高和染毒時(shí)間的延長(zhǎng),斑馬魚中毒癥狀呈加重趨勢(shì)。對(duì)照組斑馬魚行為正常。19.74mg/L組多數(shù)斑馬魚表現(xiàn)較正常,但存在部分死亡個(gè)體。34.19mg/L組斑馬魚在96h內(nèi)表現(xiàn)為前期異常興奮,中期游動(dòng)緩慢且嚴(yán)重側(cè)翻,后期靜臥水底并逐漸死亡,魚體表明顯受損,解剖后發(fā)現(xiàn)內(nèi)臟器官均嚴(yán)重?fù)p傷。45.00mg/L(最高濃度)組斑馬魚染毒即出現(xiàn)強(qiáng)烈應(yīng)激反應(yīng),急性中毒癥狀表現(xiàn)為呼吸困難、狂游、抽搐、輕微側(cè)翻、對(duì)外周刺激反應(yīng)遲鈍,10~15min后嚴(yán)重側(cè)翻,2~3h后失去平衡而靜臥水底,24h內(nèi)全部死亡;肉眼觀察可見該組斑馬魚肌肉、泄殖孔和鰭基部嚴(yán)重紅腫出血,解剖后發(fā)現(xiàn)鰓絲出血,腹腔內(nèi)存在黃色積液,肝胰臟和膽囊腫脹,少量個(gè)體出現(xiàn)肌肉、鰓絲和肝臟腐爛。
2.2不同濃度鄰甲酚對(duì)斑馬魚的急性毒性
如表1所示,對(duì)照組斑馬魚在96h急性毒性試驗(yàn)中均未死亡。15.00mg/L組斑馬魚染毒96h時(shí)無(wú)明顯中毒癥狀,15.00mg/L為96h最高耐受濃度(LC?),持續(xù)染毒7d后仍有斑馬魚存活,表明該濃度鄰甲酚對(duì)斑馬魚的毒性較低。染毒48h時(shí),19.74、25.98和34.19mg/L組死亡率較24h時(shí)升高,45.00mg/L組斑馬魚全部沉至水底死亡。染毒72h時(shí),25.98和34.19mg/L組死亡率較48h時(shí)升高,19.74mg/L組無(wú)明顯變化。染毒96h時(shí),34.19mg/L組死亡率較72h時(shí)升高,其余組無(wú)明顯變化。45.00mg/L組染毒24h時(shí)死亡率達(dá)100%,45.00mg/L為24h最低全致死濃度(LC100)。
2.3鄰甲酚對(duì)斑馬魚的LC?及安全性評(píng)價(jià)
如表2所示,鄰甲酚對(duì)斑馬魚成魚24、48、72和96h的LC50分別為34.721、30.079、27.123和27.092mg/L,SC為6.612mg/L。參照毒性等級(jí)劃分標(biāo)準(zhǔn),96h-LC50gt;10.00mg/L,毒性等級(jí)為低毒。
2.4不同濃度鄰甲酚對(duì)斑馬魚肌肉組織顯微結(jié)構(gòu)的影響
由圖1可知,對(duì)照組斑馬魚肌纖維完整,呈長(zhǎng)圓柱形,不分支,肌纖維邊緣、肌膜下方分布具有明顯核仁的橢圓形細(xì)胞核(圖1-A)。15.00和19.74mg/L組斑馬魚染毒96h后,肌纖維無(wú)明顯變化(圖1-B和圖1-C);25.98mg/L組斑馬魚染毒96h后,肌纖維出現(xiàn)輕微斷裂(圖1-D);隨著鄰甲酚濃度的增加,34.19mg/L組斑馬魚染毒96h后,肌纖維出現(xiàn)斷裂和溶解,腫脹、壞死(圖1-E);45.00mg/L組斑馬魚染毒96h后,肌纖維嚴(yán)重?cái)嗔押腿芙?,腫脹和壞死程度明顯加重(圖1-F)。
2.5不同濃度鄰甲酚對(duì)斑馬魚鰓組織顯微結(jié)構(gòu)的影響
由圖2可知,對(duì)照組斑馬魚鰓小片呈扁平囊狀,清晰完整,兩側(cè)排列整齊,上皮層由泌氯細(xì)胞、扁平細(xì)胞等構(gòu)成,細(xì)胞排列規(guī)則,緊貼鰓小片表面(圖2-A)。15.00和19.74mg/L組斑馬魚染毒96h后,鰓組織無(wú)明顯變化(圖2-B和2-C)。25.98mg/L組斑馬魚染毒96h后,鰓小片頂端輕微腫大、上皮隆起、上皮細(xì)胞腫脹(圖2-D)。34.19mg/L組斑馬魚染毒96h后,鰓小片末端明顯腫脹,上皮細(xì)胞出現(xiàn)損傷和脫落,紅細(xì)胞數(shù)量增多(圖2-E)。45.00mg/L組斑馬魚染毒96h后,鰓上皮細(xì)胞損傷、脫落加重,鰓小片末端明顯腫脹,紅細(xì)胞數(shù)量增多,導(dǎo)致細(xì)胞輪廓模糊、排列雜亂,并伴隨細(xì)胞溶解(圖2-F)。
2.6不同濃度鄰甲酚對(duì)斑馬魚肝臟組織顯微結(jié)構(gòu)的影響
由圖3可知,對(duì)照組斑馬魚肝臟由大量肝板構(gòu)成,肝細(xì)胞排列組成2層板狀結(jié)構(gòu),肝板間為互相連接的無(wú)規(guī)則排列網(wǎng)狀血竇;肝細(xì)胞呈不規(guī)則橢圓狀,大小勻稱且排列整齊,圓形細(xì)胞核位于細(xì)胞中央,肝血竇大小及形態(tài)正常(圖3-A)。15.00和19.74mg/L組斑馬魚染毒96h后,肝臟顯微結(jié)構(gòu)無(wú)顯變化,肝細(xì)胞以中央靜脈為中心呈樹狀分布,中央靜脈中分布紅細(xì)胞(圖3-B和圖3-C)。25.98和34.19mg/L組斑馬魚染毒96h后,肝臟出現(xiàn)大面積細(xì)胞空泡化,細(xì)胞溶解明顯,肝細(xì)胞核萎縮變形、溶解或偏移,血竇擴(kuò)張(圖3-D和圖3-E)。45.00mg/L組斑馬魚染毒96h后,肝細(xì)胞輪廓模糊,空泡數(shù)量明顯增加、范圍擴(kuò)大,細(xì)胞溶解程度加重,肝細(xì)胞核萎縮變形、溶解程度加深,血竇中紅細(xì)胞破裂,肝細(xì)胞呈壞死狀態(tài)(圖3-F)。
3討論
3.1鄰甲酚對(duì)斑馬魚成魚的急性毒性
鄰甲酚是環(huán)境激素類化合物中的一種,本研究中,斑馬魚成魚的中毒癥狀表現(xiàn)為前期異常興奮,中期游動(dòng)緩慢且嚴(yán)重側(cè)翻,后期靜臥水底并逐漸死亡,該癥狀與房妮等(2011)研究4種烷基酚類化合物對(duì)斑馬魚毒性效應(yīng)結(jié)果基本吻合。鄰甲酚對(duì)斑馬魚成魚24、48、72和96h的LC50分別為34.721、30.079、27.123和27.092mg/L,SC為6.612mg/L,毒性等級(jí)為低毒,而房妮等(2011)報(bào)道鄰甲酚對(duì)斑馬魚為中等毒性,可能是由于參照的毒性等級(jí)劃分標(biāo)準(zhǔn)不同,但48、72和96h的LC?與前人研究結(jié)果相近,而24h的LC??相對(duì)較低,可能與斑馬魚品系不同和外界環(huán)境因素等有關(guān),尚需進(jìn)一步驗(yàn)證。相同染毒時(shí)間下,隨著鄰甲酚濃度的升高,斑馬魚成魚死亡率呈上升趨勢(shì),表明在一定濃度范圍內(nèi),鄰甲酚對(duì)斑馬魚成魚具有急性毒性;相同鄰甲酚濃度下,隨著染毒時(shí)間的延長(zhǎng),斑馬魚成魚死亡率也呈上升趨勢(shì),表明鄰甲酚在斑馬魚成魚體內(nèi)存在累積效應(yīng),與戚珍珠等(2016)研究得出壬基酚對(duì)1月齡泥鰍(Misgurnus anguilli-caudatus)急性毒性具有累積效應(yīng)的結(jié)果一致。相關(guān)研究表明,含酚類化合物的工業(yè)、農(nóng)業(yè)廢水排放危害魚類及其他水生生物的正常生命活動(dòng)(Wang et al.,2022;Arifin et al.,2023),在水產(chǎn)養(yǎng)殖中應(yīng)及時(shí)關(guān)注水環(huán)境變化。本研究中,斑馬魚成魚鄰甲酚安全濃度是由單一鄰甲酚暴露所致,但在實(shí)際養(yǎng)殖生產(chǎn)中,水環(huán)境中其他酚類化合物的種類和濃度可能增強(qiáng)或降低鄰甲酚毒性,且毒物間存在拮抗、相加或協(xié)同效應(yīng),尚需開展鄰甲酚與其他酚類化合物的聯(lián)合毒性研究或結(jié)合養(yǎng)殖實(shí)際環(huán)境進(jìn)行綜合分析。
3.2鄰甲酚對(duì)斑馬魚肌肉組織顯微結(jié)構(gòu)的影響
魚類等水生動(dòng)物的肌肉組織是其與外界水環(huán)境距離較近的部位,作為水生動(dòng)物機(jī)體運(yùn)動(dòng)功能的效應(yīng)器官,也是其能量代謝的關(guān)鍵部位,當(dāng)水體受化學(xué)藥物污染、溶解氧不足或水溫波動(dòng)時(shí),可能導(dǎo)致肌肉組織發(fā)生形態(tài)損傷和病理變化,影響機(jī)體的運(yùn)動(dòng)功能(Wu et al.,2012)。張紀(jì)亮等(2012)研究三苯基錫對(duì)鯽(Carassius auratus)稚魚肌肉組織結(jié)構(gòu)的影響,發(fā)現(xiàn)10ng/L三苯基錫暴露可造成部分肌絲斷裂,100ng/L三苯基錫暴露可使肌纖維間隙增大,導(dǎo)致肌纖維明顯斷裂。吳楠等(2015)研究表明,不同濃度的溴氰菊酯均可損傷克氏原螯蝦(Procambarus clarkii)肌纖維超微結(jié)構(gòu),導(dǎo)致肌原纖維斷裂、肌漿網(wǎng)溶解。本研究中,鄰甲酚濃度為15.00和19.74mg/L時(shí),斑馬魚肌肉組織顯微結(jié)構(gòu)無(wú)明顯變化,推測(cè)此時(shí)毒性較低,尚未導(dǎo)致肌肉組織病理?yè)p傷,鄰甲酚濃度達(dá)34.19和45.00mg/L時(shí),斑馬魚肌纖維嚴(yán)重?cái)嗔押腿芙?,并伴隨腫脹和壞死癥狀,與張紀(jì)亮等(2012)、吳楠等(2015)的研究結(jié)果一致,表明酚類化合物可通過血液循環(huán)進(jìn)入肌肉組織,造成肌肉蛋白變性及脂類溶解,導(dǎo)致肌無(wú)力,與本研究中高濃度鄰甲酚暴露后,斑馬魚成魚游動(dòng)緩慢且嚴(yán)重側(cè)翻等行為吻合,可能是鄰甲酚抗氧化作用導(dǎo)致了斑馬魚應(yīng)激反應(yīng),其毒理學(xué)機(jī)制尚需通過掃描電鏡或透射電鏡分析肌肉組織超微結(jié)構(gòu)及測(cè)定相關(guān)應(yīng)激抗氧化酶活性等進(jìn)一步研究。
3.3鄰甲酚對(duì)斑馬魚鰓組織顯微結(jié)構(gòu)的影響
鰓組織作為魚類重要的呼吸器官直接暴露于水環(huán)境中,是機(jī)體直接與外界進(jìn)行氣體交換的媒介,可為魚類機(jī)體的新陳代謝活動(dòng)提供充足氧氣,在參與滲透壓調(diào)節(jié)、維持離子穩(wěn)態(tài)及含氮類廢物排泄等方面發(fā)揮關(guān)鍵作用(Ni et al.,2019)。鰓組織主要由鰓弓、鰓耙、鰓絲和鰓小片構(gòu)成,對(duì)水環(huán)境變化較敏感,水體受烷基酚類化合物污染時(shí)可在短時(shí)間內(nèi)導(dǎo)致鰓組織形態(tài)結(jié)構(gòu)遭受破壞,影響魚類的正常生理呼吸和滲透壓調(diào)節(jié)功能,進(jìn)而阻礙其生長(zhǎng)發(fā)育和生存繁衍。同時(shí),鰓是多種有害物質(zhì)的靶器官,其組織顯微結(jié)構(gòu)變化反映了化學(xué)污染物對(duì)魚類的毒性效應(yīng),有助于獲取水環(huán)境污染信息(Paravani et al.,2019)。環(huán)境中的有毒化合物主要通過2種方式損害鰓組織顯微結(jié)構(gòu):一種是刺激鰓組織的防御系統(tǒng),通過應(yīng)激反應(yīng)引起間接損傷,表現(xiàn)為上皮細(xì)胞腫大且部分增生、細(xì)胞水樣變性或毛細(xì)血管充血等;另一種是有毒化合物以鰓組織為靶器官引起直接損傷,導(dǎo)致上皮細(xì)胞損傷、壞死或脫落等(Fanta et al.,2003)。Zod-row等(2004)研究表明,斑馬魚腹腔注射70ng/g(魚體質(zhì)量)2,3,7,8-四氯二苯并-對(duì)-二噁英5d后,鰓絲上皮細(xì)胞腫大,鰓小片出現(xiàn)融合。Velmurugan等(2007)報(bào)道高效氯氟氰菊酯可導(dǎo)致麥瑞加拉鯪(Cirrhimus mrigala)鰓上皮細(xì)胞壞死和脫落。Gao等(2021)研究發(fā)現(xiàn),0.70mg/L馬杜拉霉素暴露可導(dǎo)致克氏原螯蝦鰓上皮細(xì)胞斷裂、脫落,細(xì)胞核凝結(jié),微血管腔受損。本研究結(jié)果與上述研究結(jié)果一致,鄰甲酚濃度為15.00和19.74mg/L時(shí),斑馬魚鰓組織顯微結(jié)構(gòu)無(wú)明顯變化,隨著鄰甲酚濃度的升高,斑馬魚鰓組織顯微結(jié)構(gòu)損傷程度呈加重趨勢(shì),45.00mg/L(最高濃度)鄰甲酚暴露96h后,斑馬魚鰓小片末端腫大出血、上皮細(xì)胞脫落并溶解,使血液與水環(huán)境的氧氣交換受阻,導(dǎo)致具有運(yùn)輸氧氣功能的紅細(xì)胞數(shù)量增多,與直接損傷表現(xiàn)一致,推測(cè)斑馬魚鰓組織可能是鄰甲酚毒性侵害的關(guān)鍵靶器官之一。
3.4鄰甲酚對(duì)斑馬魚肝臟組織顯微結(jié)構(gòu)的影響
肝臟是不僅是魚類的代謝中心,而且是各種外源有毒化合物解毒的重要器官,具有抵御外來(lái)藥物和毒物侵害的作用(Ratn etal.,2018)。由于肝臟自身功能、位置和血液運(yùn)輸?shù)奶匦?,其也是許多水體污染物聚集的主要器官,當(dāng)水體受污染后,肝臟組織的顯微結(jié)構(gòu)呈細(xì)胞空泡化(van der Oost et al.,2003;Pesce et al.,2008),其機(jī)制是毒性化合物侵入魚類體內(nèi)后,造成肝細(xì)胞線粒體腫大,使活性氧自由基增加,引起脂質(zhì)過氧化,從而導(dǎo)致細(xì)胞膜系統(tǒng)的結(jié)構(gòu)和功能遭受破壞。本研究中,斑馬魚暴露于15.00和19.74mg/L鄰甲酚96h后,肝臟組織顯微結(jié)構(gòu)無(wú)明顯變化,鄰甲酚濃度達(dá)34.19mg/L時(shí),肝臟組織細(xì)胞溶解明顯,肝細(xì)胞核萎縮變形、溶解或偏移,表明此時(shí)鄰甲酚誘導(dǎo)肝臟產(chǎn)生了氧化應(yīng)激。斑馬魚暴露于45.00mg/L鄰甲酚96h后,肝細(xì)胞輪廓模糊,空泡數(shù)量明顯增加,細(xì)胞溶解程度加重,肝細(xì)胞核萎縮變形、溶解程度加深,導(dǎo)致肝細(xì)胞呈壞死狀態(tài)。水生動(dòng)物受外源有毒污染物入侵后,其肝臟細(xì)胞膜系統(tǒng)受侵害,肝細(xì)胞變形、細(xì)胞空泡化和細(xì)胞溶解均預(yù)示細(xì)胞壞死,細(xì)胞壞死情況加重會(huì)引起肝臟功能受損,從而導(dǎo)致非正常死亡(Tullio et al.,2024)。張武肖等(2015)研究表明,25.00mg/L氨氮脅迫后,團(tuán)頭魴(Megalobrama amblycephala)幼魚肝組織纖維結(jié)構(gòu)表現(xiàn)為肝細(xì)胞腫大、細(xì)胞核溶解、細(xì)胞空泡化和血竇擴(kuò)張等。本研究結(jié)果與張武肖等(2015)的研究結(jié)果一致,鄰甲酚毒性效應(yīng)的分子機(jī)制有待深入研究。
4結(jié)論
鄰甲酚對(duì)斑馬魚成魚的毒性效應(yīng)隨著暴露濃度升高、時(shí)間延長(zhǎng)而增強(qiáng),屬于低毒性酚類污染物。高濃度鄰甲酚暴露可導(dǎo)致斑馬魚成魚肌肉、鰓和肝臟組織顯微結(jié)構(gòu)嚴(yán)重?fù)p傷。
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