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草甘膦(Glyphosate),是目前世界范围内使用最广泛的除草剂[1]。文献[2]认为,草甘膦能够在土壤中因吸附和降解而迅速失活,因此被认为是环境中相对安全的化合物。文献[3-4]统计,2014年时全球范围内草甘膦的使用量达到了826 000 t。20世纪70年代末到2016年,世界范围内的草甘膦使用总量增加了100倍,未来仍有可能进一步增加[5]。由于不正确的应用实践和过量的施用,草甘膦广泛存在于水生和陆地环境中[6]。PESCE et al[7]的研究发现,草甘膦能够改变藻类群落的组成;WONG[8]的研究表明低浓度的草甘膦可以刺激四线藻的生长;还有研究称,草甘膦能够对水体中微藻造成不良影响[9],并有可能造成微生物群落的变化[10]。
塑料在机械作用、生物降解、光降解及光氧化降解作用下,能够被降解为微塑料(microplastics;< 5 mm)以及纳塑料 (nanoplastics;<0.1 µm)[11-12]。目前的城市污水处理技术,无法彻底清除微塑料[13],因此,这种塑料微珠最后常常进入当地的水流、河流和大型贮水池中[14],由于微塑料的持久性强,淡水中的微塑料能够随水体进入海洋并在全球范围内分散,甚至南极洲附近的海域中能探测出微塑料的存在[15]。微塑料自身,因其粒径小,易于被生物摄取,进入生物体的微塑料能够随着食物链进行传递和富集,并可能最终影响整个生态系统[16]。另外,微塑料尺寸小,比表面积大,疏水性强,因此容易吸附及富集多种有机污染物 [17]。此外,带正电荷的氨基修饰的钠聚苯乙烯塑料的毒性高于带负电荷的羧基修饰的钠聚苯乙烯微塑料[18]。当不同粒径的Nano-PS-NH2表面吸附其他有机污染物(菲)后,测试它们对蚤类生物的毒性,结果表明,粒径较小的Nano-PS-NH2(50 nm)显示出最高的毒性和生理损伤[19]。
我国的大多数湖泊及河流等都发生过水华现象,如洪泽湖、太湖和巢湖等[20]。微囊藻是造成蓝藻水华的重要种群之一,而铜绿微囊藻作为一种模式生物,在蓝藻水华中分布最为广泛[21]。对于单细胞藻类而言,光合作用是其生长代谢最重要的过程。光合作用的相关基因如负责编码PSII反应中心蛋白psb各亚基基因、负责编码PSI反应中心蛋白psa各亚基基因、负责编码CO2固定Rubisco酶的基因rbcS和rbcL,它们是控制光反应和暗反应过程的关键基因[22]。
目前对微塑料特别是Nano-PS-NH2与有机污染物的联合毒性的研究还相对匮乏。本研究选择铜绿微囊藻为研究对象,通过批次培养试验研究Nano-PS-NH2与草甘膦在单独暴露及复合条件下对铜绿微囊藻生长、产藻毒素和多种生理功能的调控效应,并选择rbcL、psaB和psbD3个光合作用相关基因,从基因水平上阐述其对铜绿微囊藻的毒理机制。
纳塑料与草甘膦对铜绿微囊藻的复合毒性机制
Mechanism of the joint toxicity of nanoplastics and glyphosate on Microcystis aeruginosa
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摘要: 文章以铜绿微囊藻为研究对象,探究草甘膦(Glyphosate)和氨基修饰的纳塑料(Nano-PS-NH2)联合暴露对铜绿微囊藻急性(48 h)毒性影响。分别探究了单一与复合污染物对铜绿微囊藻的毒性效应。结果表明,污染物单独暴露或者联合暴露下,铜绿微囊藻叶绿素a的含量均显著下降,细胞膜通透性、超氧化物歧化酶含量和藻毒素(MCs)释放量均显著增加;草甘膦单独暴露下,光合系统核心蛋白编码基因psaB、psbD和催化固定CO2的相关基因rbcL的表达量有所下调,在Nano-PS-NH2单独暴露下,psaB、psbD的表达量都有所下降,rbcL的表达量略微上调;在联合暴露作用下,psaB、psbD和rbcL的表达量均显著上调。该研究对于认识有机污染物与微塑料复合对铜绿微囊藻的作用及控制铜绿微囊藻水华有一定的参考价值。Abstract: The Microcystis aerugniosa was selected as the research object in this paper. The 48 h acute toxicity of the Nano-PS-NH2 and the glyphosatethe to M. aerugniosa was investigated. The toxicity effect of the single and combined pollutants was also studied. The results showed that the content of chlorophyll a in M. aeruginosa decreased significantly, the membrane permeability and the superoxide dismutase levels as well as the release of MCs significantly increased with the single exposure and combined exposure. The expression level of psaB, psbD (encoding the photosynthetic system core protein) and rbcL (fixing CO2) decreased under the single exposure of glyphosate. The expression levels of psaB and psbD decreased, and the expression of rbcL slightly increased under the exposure of nanoplastics. However, the expression levels of psaB, psbD and rbcL increased significantly when M. aeruginosa was treated with the combined exposure of glyphosate and Nano-PS-NH2. This study provides a certain reference for understanding the effect of organic pollutants and microplastics on M. aeruginosa and controlling the bloom of M. aeruginosa.
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Key words:
- nanoplastics /
- glyphosate /
- Microcystis aeruginosa /
- joint toxicity /
- gene expression
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表 1 实时PCR扩增反应引物对序列
基因 正反引物 16S rDNA Forward 5’-GCCGCRAGGTGAAAMCTAA-3’ Reverse 5’-AATCCAAARACCTTCCTCCC-3’ rbcL Forward 5’-CGTTTCCCCGTCGCTTT-3’ Reverse 5’-CCGAGTTTGGGTTTGATGGT-3’ psaB Forward 5’-CGGTGACTGGGGTGTGTATG-3’ Reverse 5’-ACTCGGTTTGGGGATGGA-3’ psbD Forward 5’-TCTTCGGCATCGCTTTCTC-3’ Reverse 5’-CACCCACAGCACTCATCCA-3’ -
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