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我国的耕地总面积位居世界前列,但人均耕地面积却远远落后于世界平均水平。为了确保粮食安全,农药被大量用来预防和减轻虫病草害,这些农药大部分流入环境并造成了较严重的污染问题[1]。有研究表明,有机磷农药的实际利用率仅为10%—20%,残留农药通过自然循环等途径流入土壤和水体中[2]。这些农药污染物随着时间不断富集,并借助农产品、饮用水等介质威胁着我们的食品安全和环境安全[3-4]。如Liu等[5]在我国的部分农产品和种植土壤样品中发现,36.4%的柿子样品和70.8%的枣样品中存在有机磷类、拟除虫菊酯类等多种农药化合物的残留成分。孙悦等[6]在51个不同产地的中药材三七样品中均检测出不同程度的农药残留,且有机磷类、有机氯类农药残留量对人体存在一定的健康风险。为了应对愈发严峻的农药残留对环境产生的污染问题,我国及日本等国已经将诸如甲胺磷、对硫磷、马拉硫磷、乙基对硫磷等具有急性神经毒性作用的农药列入禁用名单[7-8]。越来越多的研究表明,农药减量控害方面的研究对人类和环境健康具有愈发重要的意义[9]。
据统计,2019年全球农药市场中,除草剂和杀虫剂分别以40%和30%的占比位列前二[10]。在这两类典型的农药中,敌草快与氰草津是两种以化学结构分类具有代表性的除草剂,杀线威和敌百虫也因其药效好、用途多,在杀虫剂中使用范围广泛[11]。并且,上述4种农药都具有很高的水溶性,极易对水环境产生污染,因此有必要开展其对水生生物的毒性研究[12]。目前大部分学者对农药残留的毒性研究都停留在单一污染物层面[13-14],考虑到除草剂与杀虫剂在实际环境中常以混合污染物的形式存在,这些污染物对生物产生联合毒性作用时,其作用方式往往与单一污染物不同[15-16]。因此对除草剂与杀虫剂的混合物进行联合毒性方面的研究具有一定的现实意义[16]。
蛋白核小球藻(C. pyrenoidosa)是一种属于绿藻门的单细胞藻类。因其具有易培养、繁殖快以及呈游离分布与污染物接触充分等优点,是一种理想的污染物毒性实验的指示生物[17]。如王滔等[18]以C. pyrenoidosa为受试生物考察了三嗪类农药对水生生物的毒性作用,Li等[19]以C. pyrenoidosa为受试生物评估了矿区污染物对水生态系统初级生产者的环境风险。
本文选择环境中存在的两类典型农药(除草剂与杀虫剂)污染物为研究对象,以C. pyrenoidosa为受试生物,合理地设计这两类农药的二元混合物射线,应用时间依赖微板毒性分析法(time-dependent microplate toxicity analysis, t-MTA)测定农药及其混合物对C. pyrenoidosa的毒性结果,并应用经典加和模型浓度加和(concentration addition, CA)、绝对残差(deviation from CA, dCA)模型与拓展等效线图法分析不同混合物体系的联合毒性关系,为农药混合污染物的毒性评估和生态风险评估提供借鉴,同时也可以横向对比评估3种方法各自的优缺点,为混合物毒性的评估方法选择提供参考。
两种除草剂与两种杀虫剂对蛋白核小球藻的联合毒性作用评估
Evaluation of joint toxicity of two herbicides and two insecticides on Chlorella pyrenoidosa
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摘要: 为探讨两类典型农药(除草剂与杀虫剂)对水生生物的联合毒性效应,以两种除草剂:氰草津(cyanazine, CYA)、敌草快(diquat, DIQ)和两种杀虫剂:敌百虫(dipterex, DIP)、杀线威(oxamyl, OXA)为研究对象,采用直接均分射线法(direct equipartition ray, EquRay)设计4组二元除草剂-杀虫剂混合物体系,应用时间毒性微板分析法(Time-dependent microplate toxicity analysis, t-MTA)系统研究目标化合物及其二元混合物体系对蛋白核小球藻(Chlorella pyrenoidosa)在不同暴露时间(12、24、28、72、96 h)的毒性效应,分别应用浓度加和(concentration addition, CA)模型、绝对残差(deviation from CA, dCA)模型和拓展等效线图法分析除草剂和杀虫剂对C. pyrenoidosa的联合毒性作用。结果表明,4种农药的毒性由强到弱依次为CYA>DIQ>OXA>DIP,且两种除草剂在48—96 h的半数效应浓度(EC50)值均比两种杀虫剂的EC50值高出1—2个数量级;3种模型对混合物的毒性作用评估基本一致,除草剂与杀虫剂二元混合物OXA-CYA、OXA-DIQ、DIP-CYA的毒性作用整体上呈现由加和作用向拮抗作用转变,DIP-DIQ则呈现由加和作用向较弱的协同作用转变,且各混合物体系的毒性作用都具有时间依赖性和浓度比依赖性;3个模型各有优缺点, CA是最经典的模型,可以直观地描述所有混合物毒性作用的动态变化规律,dCA模型可以定量描述混合物毒性作用的强度,拓展等效线图可以直观的描述两元混合物各组分间相互作用的浓度比依赖关系。Abstract: In order to explore the joint toxic effects of two typical pesticides (herbicide and insecticide) on aquatic organisms, two herbicides: cyanazine (CYA), diquat (DIQ) and two insecticides: dipterex (DIP) and oxamyl (OXA) were used as research objects, and the direct equipartition ray (EquRay) was used to design four groups of binary herbicide-insecticide mixture systems. The time-dependent microplate toxicity analysis (t-MTA) was used to study the effects of target compounds and binary mixture systems on Chlorella pyrenoidosa (C. pyrenoidosa) at different exposure times (12, 24, 28, 72 and 96 h). Concentration addition (CA) model, deviation from CA (dCA) model and extended isobologram method were used to analyze the joint toxic effects of herbicides and insecticides on C. pyrenoidosa. The results showed that the order of toxicity of four pesticides was CYA>DIQ>OXA>DIP, and the median effect concentration (EC50) values of the two herbicides were 1—2 orders of magnitude higher than those of the two insecticides at 48—96 h. The toxicity interaction of mixtures evaluated by the three models was basically consistent. The combined toxicity of herbicide and pesticide binary mixtures OXA-CYA, OXA-DIQ and DIP-CYA showed a transformation from additive effect to antagonistic effect on the whole, while DIP-DIQ showed a transformation from additive effect to weak synergistic effect. The combined toxicity of each mixture system was time-dependent and concentration-ratio dependent. The three models have their own advantages and disadvantages. CA is the most classical model, which can intuitively describe the dynamic change rules of toxic effects of all mixtures, dCA model can quantitatively describe the toxicity interaction intensity of all mixtures, and the extended isobologram can more intuitively describe the concentration-ratio dependence of toxicity interaction between components of binary mixtures.
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Key words:
- pesticides /
- Chlorella pyrenoidosa /
- concentration addition /
- deviation from CA /
- extended isobologram /
- joint toxicity
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表 1 4种农药的化学结构式及基本理化性质
Table 1. Chemical structural formula and basic physical and chemical properties of four pesticides
农药
Pesticides简称Abbreviation 化学结构
Chemical structures分子式
Molecular formulaCAS 分子量/(g·mol−1)
Molecular weight纯度/%
Purity敌草快
DiquatDIQ C12H12Br2N2 2764-72-9 344.05 ≥97.0 氰草津
CyanazineCYA C9H13ClN6 21725-46-2 240.69 ≥97.0 敌百虫
DipterexDIP C4H8Cl3O4P 52-68-6 257.44 ≥99.0 杀线威
OxamylOXA C7H13N3O3S 23135-22-0 219.29 ≥99.0 表 2 农药二元混合物体系的组分构成及其浓度比(pi)
Table 2. The component and its concentration ratios (pi) for the binary mixture systems of pesticides
Ray pOXA pCYA Ray pOXA pDIQ R1 9.89×10−1 1.10×10−2 R1 9.65×10−1 3.52×10−2 R2 9.73×10−1 2.70×10−2 R2 9.16×10−1 8.36×10−2 R3 9.47×10−1 5.26×10−2 R3 8.46×10−1 1.54×10−1 R4 9.00×10−1 9.99×10−2 R4 7.33×10−1 2.67×10−1 R5 7.83×10−1 2.17×10−1 R5 5.23×10−1 4.77×10−1 Ray pDIP pCYA Ray pDIP pDIQ R1 9.99×10−1 1.04×10−3 R1 9.97×10−1 3.42×10−3 R2 9.97×10−1 2.61×10−3 R2 9.92×10−1 8.52×10−3 R3 9.95×10−1 5.20×10−3 R3 9.83×10−1 1.69×10−2 R4 9.90×10−1 1.04×10−2 R4 9.67×10−1 3.32×10−2 R5 9.75×10−1 2.55×10−2 R5 9.21×10−1 7.91×10−2 表 3 4种农药的Weibull函数拟合结果及其统计量
Table 3. Weibull function fitting results and statistics for the four pesticides
Name 时间/h
Timeα β RMSE R EC50/(mol·L−1) pEC50 OXA 12 1.84 0.82 0.055 0.8739 ∞ 0 24 1.17 0.62 0.063 0.8094 ∞ 0 48 3.65 0.99 0.107 0.9036 8.77×10−5 4.06 72 5.85 1.41 0.101 0.9506 3.90×10−5 4.41 96 10.14 2.35 0.080 0.9844 3.38×10−5 4.47 DIP 12 2.51 1.30 0.027 0.9641 ∞ 0 24 2.52 1.23 0.028 0.9710 ∞ 0 48 4.43 1.51 0.064 0.9660 6.66×10−4 3.18 72 6.50 2.04 0.083 0.9654 4.31×10−4 3.37 96 10.14 3.05 0.084 0.9780 3.59×10−4 3.45 DIQ 12 4.51 1.26 0.031 0.9665 ∞ 0 24 4.09 1.15 0.021 0.9823 ∞ 0 48 4.38 0.99 0.058 0.9630 1.61×10−5 4.80 72 5.28 1.11 0.064 0.9694 8.19×10−6 5.09 96 6.25 1.27 0.073 0.9690 6.17×10−6 5.21 CYA 12 2.53 0.68 0.045 0.9272 ∞ 0 24 2.63 0.71 0.052 0.9079 ∞ 0 48 3.92 0.79 0.081 0.9213 3.75×10−6 5.43 72 5.38 1.02 0.092 0.9377 2.32×10−6 5.63 96 6.62 1.22 0.092 0.9511 1.88×10−6 5.73 -
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