Mechanistic Study and the Influence of Oxygen on the Photosensitized Transformations of Microcystins (Cyanotoxins)

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• 作者：Weihua Song ; Sabrina Bardowell ; Kevin E. O'Shea
• 刊名：Environmental Science & Technology
• 出版年：2007
• 出版时间：August 1, 2007
• 年：2007
• 卷：41
• 期：15
• 页码：5336 - 5341
• 全文大小：177K
• 年卷期：v.41,no.15(August 1, 2007)
• ISSN：1520-5851

文摘

Microcystins (MCs) produced by cyanobacteria arestrong hepatotoxins and classified as possible carcinogens.MCs pose a considerable threat to consumers of tainteddrinking and surface waters, but the photochemical fate ofdissolved MCs in the environment has received limitedattention. MCs are released into the environment upon celllysis along with photoactive pigments including phycocyaninand chlorophyll a. The concentrations of MCs andpigments are expected to be greatest during a bloomevent. These blooms occur in sunlit surface water andthus MCs can undergo a variety of solar initiated orphotosensitized transformations. We report herein therole of oxygen, sensitizer, and light on the photochemicalfate of MCs. The phycocyanin photosensitized transformation of MCs is elucidated, and photosensitized isomerizationplays an important role in the process. The UV-A portionof sunlight was simulated using 350 nm light and thephototransformations of three MC variants (-LR, -RR, -LF)were investigated. Singlet oxygen leads to photooxidation ofphycocyanin, the predominant pigment of cyanobacteria,hence, reducing the phototransformation rate of MCs. Thephototransformation rate of MC-LR increases as pHdecreases. The pH effect may be the result of MCsassociation with phycocyanin. Our results indicatephotosensitized processes may play a key role in thephotochemical transformation of MCs in the natural water.