The extensive use of 2,4-dichlorophenoxiacetic acid (2,4-D) in agriculture is an important source of pollution to water and soil. Toxicity of commonly used herbicides to non-target, planktonic photosynthetic organisms has not been described completely yet. Therefore, we determined the effect of subinhibitory 2,4-D concentrations on the Chlorophycean alga Ankistrodesmus falcatus and on a toxigenic strain of the cyanobacterium Microcystis aeruginosa. Population growth, photosynthetic pigments, macromolecular biomarkers (carbohydrates, lipids, and protein), and antioxidant enzymes (catalase [CAT], glutathione peroxidase [GPx], and superoxide dismutase [SOD]) were quantified, and the integrated biomarker response (IBR) was calculated. Scanning electron microscope (SEM) and transmission electron microscope (TEM) observations were also performed. The 96-h median inhibitory concentration (IC₅₀) for 2,4-D was 1353.80 and 71.20 mg L^− 1 for the alga and the cyanobacterium, respectively. Under 2,4-D stress, both organisms increased pigments and macromolecules concentration, modified the activity of all the evaluated enzymes, and exhibited ultrastructural alterations. M. aeruginosa also increased microcystins production, and A. falcatus showed external morphological alterations. The green alga was tolerant to high concentrations of the herbicide, whereas the cyanobacterium exhibited sensitivity comparable to other phytoplankters. Both organisms were tolerant to comparatively high concentrations of the herbicide; however, negative effects on the assessed biomarkers and cell morphology were significant. Moreover, stimulation of the production of cyanotoxins under chemical stress could increase the risk for the biota in aquatic environments, related to herbicides pollution in eutrophic freshwater ecosystems.

2，4-二氯苯氧乙酸（2,4-D）在农业中的广泛使用是对水和土壤污染的重要来源。尚未完全描述常用除草剂对非目标浮游光合生物的毒性。因此，我们测定亚抑菌2,4-d浓度对绿藻藻类效果Ankistrodesmus falcatus和对蓝藻的产毒的菌株铜绿微囊藻。人口增长，光合色素，大分子生物标志物（碳水化合物，脂质和蛋白质）和抗氧化酶（过氧化氢酶[CAT]，谷胱甘肽过氧化物酶[GPx]和超氧化物歧化酶[SOD]）被定量，综合生物标志物响应（IBR）被计算了。还进行了扫描电子显微镜（SEM）和透射电子显微镜（TEM）观察。96小时中值抑制浓度（IC ₅₀为2,4-d）为1353.80和71.20 毫克 大号^{-  1}为藻类和蓝细菌，分别。在2，4-D胁迫下，两种生物都增加了色素和大分子的浓度，改变了所有评估酶的活性，并表现出超微结构的改变。中号。绿脓杆菌也增加了微囊藻毒素的生产，和一个。恶性猫表现出外部形态学改变。绿藻可耐受高浓度的除草剂，而蓝藻则显示出与其他浮游植物相当的敏感性。两种生物都耐受较高浓度的除草剂。然而，对评估的生物标志物和细胞形态的负面影响是显着的。此外，在化学胁迫下刺激氰毒素的生产可能会增加水生环境中生物群的风险，这与富营养化淡水生态系统中的除草剂污染有关。