【期刊】中国科大盛国平：污染物化学形态影响其植物毒性和吸收特性
图文摘要 | Graphical abstract
导读 | Introduction
环丙沙星（CIP）是使用最广泛的氟喹诺酮类抗生素之一，常被用于治疗人类的细菌感染性疾病，并被列入世界卫生组织基本药物标准清单。然而，环丙沙星不能被人体完全代谢转化也无法在城镇污水处理系统中得到有效去除，导致其不可避免地被释放到环境中，并可能在作物中发生吸收积累，引起潜在的健康风险和生态威胁。植物吸收环丙沙星等抗生素是非常复杂的过程，会受到诸如植物类型、生长条件和抗生素的理化性质等因素的影响。哌嗪基团和羧基的存在使环丙沙星成为一种两性离子型化合物，其化学形态随外界环境的变化而变化。因此，本研究以水稻为模式植物，解析外界环境变化驱动的环丙沙星化学形态的改变，将如何影响其植物毒性和吸收特性？
Ciprofloxacin (CIP) is one of the most broadly used fluoroquinolones antibiotics, which widely used for the treatment of bacterial infections in human diseases, and incorporated into the World Health Organization (WHO) model list of essential medicines for a basic health-care system. Owing to the partial metabolism in human beings and wastewater treatment systems, CIP is widely detected in various aquatic matrices, soils or sediments. The extensive distribution of CIP in environments may induce the occurrence of antibiotic resistance, or directly result in negative impacts on terrestrial and aquatic organisms. Furthermore, CIP can be taken up and then accumulated in different crop plants, which is certain to be an intricate process and may be affected by plenty of factors, such as plant species and genotypes, and own physicochemical properties of CIP. Therefore, considering the pH-dependent speciation of CIP with zwitterionic groups of a piperazine moiety and a carboxyl group, we selected rice (Oryza sativa L.) as the model plant to investigate the effects of CIP chemical speciation on its phytotoxicity and uptake by plants.
一、植物根系对环丙沙星的吸附
Adsorption behavior of CIP on rice roots
水稻根系对环丙沙星的吸附动力学和吸附等温线分别符合伪一级动力学模型和朗格缪尔吸附模型（图1），且当环丙沙星的化学形态由正离子转变为两性离子再转变为负离子时，其吸附速率和容量均呈现降低的趋势。结果表明，环丙沙星的化学形态会影响其在植物根系的吸附行为，正离子型环丙沙星更易于被带负电的植物根系吸附。
The adsorption kinetics and isotherms of CIP with different chemical speciation onto rice roots were all well depicted by the pseudo-first order model and Langmuir adsorption model (Fig. 1). Moreover, the adsorption kinetic constant and adsorption capacity both decreased with the change of CIP chemical speciation from cation to zwitterion to anion. The findings indicate that chemical speciation of CIP could affect its adsorption on rice roots, and cationic CIP tended to be adsorbed by negatively charged plant roots.
图1 植物根系对环丙沙星的吸附（pH 5.5:正离子；pH 7.5:两性离子；pH 8.5:负离子）
Fig. 1 Adsorption of CIP by rice roots (pH 5.5: cation; pH 7.5: zwitterion; pH 8.5: anion)
二、植物对环丙沙星的吸收和代谢
Uptake and metabolism of CIP by rice plants
环丙沙星化学形态由正离子转变为两性离子再转变为负离子时，其在溶液中的消减率和其在植物中的含量均逐渐降低（图2），这可能归因于环丙沙星在质外体（pH=4-6）中主要以正离子形式存在，更易于与带负电的细胞壁发生静电结合而难以向上迁移，因此其主要积累于根部。此外，在植物中共检出6种可能的代谢产物，并据此提出了2条可能的代谢路径：羟基/氟取代和哌嗪开环的代谢转化。
The CIP dissipation percentages from solutions and concentrations in rice tissues decreased with CIP speciation changing from cation to anion (Fig.2). CIP majorly presented as cation due to the pH of apoplast ranging from 4 to 6, which led to be trapped in apoplast of roots and hardly transferred to the aboveground tissues owing to the ion exchange interaction with negatively charged plant cell walls. Besides, a total of 6 intermediates were detected in rice plants, and two possible transformation pathways were proposed, including hydroxyl/fluorine substitution and piperazine ring cleavage and further transformation.
图2 环丙沙星在溶液中的消散和在植物组织中的迁移积累
Fig. 2 CIP dissipation from solutions and accumulation in plant tissues
三、环丙沙星的植物毒性
Phytotoxicity of CIP on rice plants
当环丙沙星外部投加浓度增加或化学形态由正离子转变为两性离子再转变为负离子时，植株鲜重和光合色素含量均逐渐降低（图3），这些生长抑制效应可能是由于环丙沙星干扰光合电子传递链，触发植物体内产生大量活性氧，从而诱导氧化损伤所导致的。
The inhibitory effects of CIP on biomass growth and pigments contents gradually aggravated with the increase in CIP dosages and the changes of CIP speciation from cation to zwitterion to anion (Fig. 3). All these negative effects may occur due to the destruction of photosynthetic electron transport by CIP and the following oxidative damage caused by the formed reactive oxygen species.
图3 环丙沙星对水稻生物量和光合色素含量的影响
Fig. 3 Biomass and photosynthetic pigments contents of rice plants under different treatments
总结 | Conclusions
抗生素环丙沙星的化学形态会影响其植物毒性和吸收特性，培养液高pH驱动的环丙沙星化学形态的改变会明显加重其植物毒性，正离子型环丙沙星更易被水稻根系吸附和吸收，也更易于积累在植物根部而难以向茎叶部迁移。本研究加深了我们对植物吸收两性离子型有机污染物的理解和认识。
The chemical speciation of ciprofloxacin, a zwitterionic antibiotic, could affect its phytotoxicity and uptake by plants. High solution pH-driven changes of CIP chemical speciation aggravated plant growth inhibition and decreased photosynthetic pigments contents. Besides, the adsorption and uptake of CIP by rice roots and plants decreased with CIP changing from cation to zwitterion to anion. Therefore, considering the changed uptake and toxicity behaviors of CIP in different chemical species, more comprehensive investigations for pollutant-plant interactions should be conducted in the future.
扫二维码 | 查看原文
/https://www.sciencedirect.com/science/article/abs/pii/S0048969720383200本文内容来自ELSEVIER旗舰期刊Sci Total Environ第711卷发表的论文：
Yi Hu, Nuzahat Habibul, Yan-Yun Hu, Fan-Li Meng, Guo-Ping Sheng, 2021. Chemical speciation of ciprofloxacin in aqueous solution regulates its phytotoxicity and uptake by rice (Oryza sativa L.). Sci Total Environ 771, 144787.
DOI: https://doi.org/10.1016/j.scitotenv.2020.144787
第一作者：胡怡 博士
中国科学技术大学 环境科学与工程系
在中国科学技术大学获得博士学位，现为中国科学技术大学环境科学与工程系博士后研究员。主要研究方向为环境污染的植物修复及其强化技术。以第一作者或共同作者在Science of the Total Environment、Environmental Science & Technology、Water Research等国际期刊发表论文5篇。
通讯作者：盛国平 教授
中国科学技术大学 环境科学与工程系
中国科学技术大学教授、博士生导师，教育部青年长江学者、基金委杰出青年基金获得者；获全国优秀博士论文奖，获2014年国家自然科学二等奖，获2015年安徽省科技进步一等奖等奖项；目前担任Environment International副主编，Journal of Hazardous Materials Advances共同主编；主要研究方向为废水处理及回用、污染控制材料、环境污染分析等。
资料收集：高天聪
排版编辑：赵虹雯
责任编辑：李菊英 史薇
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