Department of Civil and Environmental Engineering, Stanford University , 473 Via Ortega, Stanford, California 94305, United States.
Aquatic Ecology and Ecosystem Studies, School of Civil, Environmental and Mining Engineering, The University of Western Australia , 35, Stirling Highway M015, Crawley, Western Australia 6009, Australia.
Environ Sci Technol. 2016 Aug 16;50(16):8505-13. doi: 10.1021/acs.est.6b01801. Epub 2016 Aug 5.
The transport of microcystin, a hepatotoxin produced by cyanobacteria (e.g., Microcystis aeruginosa), to estuaries can adversely affect estuarine and coastal ecosystems. We evaluated whether halogen radicals (i.e., reactive halogen species (RHS)) could significantly contribute to microcystin photodegradation during transport within estuaries. Experiments in synthetic and natural water samples demonstrated that the presence of seawater halides increased quantum yields for microcystin indirect photodegradation by factors of 3-6. Additional experiments indicated that photoproduced RHS were responsible for this effect. Despite the fact that dissolved organic matter (DOM) concentrations decreased in more saline waters, the calculated photochemical half-life of microcystin decreased 6-fold with increasing salinity along a freshwater-estuarine transect due to the halide-associated increase in quantum yield. Modeling of microcystin photodegradation along this transect indicated that the time scale for RHS-mediated microcystin photodegradation is comparable to the time scale of transport. Microcystin concentrations decline by ∼98% along the transect when considering photodegradation by RHS, but only by ∼54% if this pathway were ignored. These results suggest the importance of considering RHS-mediated photodegradation in future models of microcystin fate in freshwater-estuarine systems.
微囊藻毒素是由蓝藻（如铜绿微囊藻）产生的一种肝毒素，它向河口的迁移会对河口和沿海生态系统产生不利影响。我们评估了卤原子（即反应性卤族物质（RHS））是否可以在河口内迁移过程中对微囊藻毒素的光降解产生重大影响。在合成水和天然水样中的实验表明，海水中卤化物的存在将微囊藻毒素间接光降解的量子产率提高了 3-6 倍。进一步的实验表明，光产生的 RHS 是造成这种影响的原因。尽管在盐分更高的水中溶解有机物质（DOM）浓度降低，但由于与卤化物相关的量子产率增加，在沿淡水-河口的一条剖面上，微囊藻毒素的光化学半衰期计算值随盐度的增加而减少了 6 倍。沿该剖面的微囊藻毒素光降解模型表明，RHS 介导的微囊藻毒素光降解的时间尺度与迁移的时间尺度相当。如果考虑到 RHS 介导的光降解，微囊藻毒素的浓度沿剖面下降了约 98%，但如果忽略这条途径，浓度仅下降约 54%。这些结果表明，在未来淡水-河口系统中微囊藻毒素命运的模型中，考虑 RHS 介导的光降解非常重要。
