Background

Cyanobacteria and their toxins occur in high concentrations during the so-called bloom events in surface waters. To be able to assess the risks associated with cyanobacterial blooms, we need to understand the persistence and fate processes of these toxins and other bioactive metabolites. In this study, we investigated the photochemical fate of 54 cyanopeptides extracted from two strains of Microcystis aeruginosa (PCC7806 and UV006), Planktothrix rubescens, and Dolichospermum flos aquae. We determined half-lives during sunlight exposure in lake water and inspected the effect of pH on transformation kinetics for 27 microcystins, 8 anabaenopeptins, 14 cyanopeptolins, 2 cyclamides, and 3 aeruginosins.

Results

For cyanopeptides from D. flos aquae and P. rubescens, we observed the highest removal of 28 and 26%, respectively, after 3-h sunlight exposure. Most cyanopeptides produced by the two M. aeruginosa strains were rather persistent with only up to 3% removal. The more reactive cyanopeptides contained amino acids known to undergo phototransformation, including methionine and tyrosine moieties or their derivatives. Photochemical half-lives of 14 tyrosine-containing cyanopeptides decreased by one order of magnitude from nearly persistent conditions at pH 7 (half-life > 70 h) to shorter half-lives at pH 10 (< 10 h).

Conclusions

More work is needed to distinguish the contribution of different photochemical reaction pathways including the contributions to the pH effect. To the best of our knowledge, this is the first assessment of transformation kinetics of such a wide range of cyanopeptides. The abundant and persistent cyanopeptides that have not been studied in detail yet should be prioritized for the evaluation of their ecosystem and human health risks and for their abatement during drinking water treatment.

中文翻译：

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地表水中蓝细菌毒素和次级代谢产物的光转化动力学

背景

蓝藻及其毒素在地表水中所谓的水华事件期间以高浓度存在。为了能够评估与蓝藻绽放有关的风险，我们需要了解这些毒素和其他生物活性代谢物的持久性和命运过程。在这项研究中，我们调查的54个cyanopeptides由两种菌株中提取光化学命运铜绿微囊藻（PCC7806和UV006），Planktothrix冬凌草，并Dolichospermum FLOS藻。我们测定了阳光在湖水中的暴露期间的半衰期，并检查了pH对27种微囊藻毒素，8种Anabaenopeptins，14种cyanepteptolins，2种环酰胺和3种铜绿素的转化动力学的影响。

结果

对于D. flos aquae和P. rubescens的氰肽，我们在阳光下暴露3小时后观察到最高去除率分别为28％和26％。由两个铜绿假单胞菌菌株产生的大多数氰基肽相当持久，去除率最高可达3％。反应性更高的氰肽包含已知会进行光转化的氨基酸，包括蛋氨酸和酪氨酸部分或其衍生物。14种含酪氨酸的氰肽的光化学半衰期从pH值7的近乎持久的条件（半衰期> 70 h）到pH 10的半衰期（<10 h）降低了一个数量级。

结论

需要更多的工作来区分不同光化学反应途径的贡献，包括对pH效应的贡献。据我们所知，这是对如此广泛的氰肽的转化动力学的首次评估。尚未对其进行详细研究的丰富而持久的氰基肽，应该优先用于评估其生态系统和人类健康风险以及在饮用水处理过程中的消除效果。