Szlag David C, Spies Brian, Szlag Regina G, Westrick Judy A
Department of Chemistry, Oakland University, Rochester, MI 48309, USA.
Department of Chemistry, Wayne State University, Detroit, MI 48202, USA.
J Toxicol. 2019 May 28;2019:3231473. doi: 10.1155/2019/3231473. eCollection 2019.
Permanganate pretreatment of drinking water is effective in transforming dissolved, noxious contaminants and in reducing halogenated by-products. Permanganate targets specific compounds such as taste and odor compounds, disinfection precursors, manganese, and natural organic contaminants that are not removed readily by conventional treatment alone. Cyanobacterial blooms (cHABs) can increase disinfection by-product precursors as well as the cyanotoxin, microcystin (MC), a potent liver toxin. MC toxicity is conferred by a unique, conserved amino acid, Adda, that inhibits protein phosphatase 1 and 2A. Although over 150 MC congeners have been reported, thousands of MCs are statistically possible. Over the last ten years, one congener, MC-LA, has been reported with increasing frequency, making it one of the most common cyanotoxins identified in North American freshwater systems; yet its oxidation has not been widely studied. Frequently, Adda specific enzyme-linked immunosorbent assay (ELISA) and protein phosphatase inhibition assay (PPIA) are used to quantitate total MCs to evaluate treatment efficiency and exposure. Anecdotal reports suggest that MC degradation products can cause interference with the Adda-ELISA. MC-LA was used as the model MC compound in this study. PPIA quantitation of MC-LA in water agreed with liquid chromatography high resolution mass spectrometry (LC/HRMS), whereas the ELISA quantitation did not agree with LC/HRMS quantitation. We determined the second order rate constant for MC-LA as 118 ± 9 M s, the activation energy to be 21.2 kJ mol, and the rate to be independent of pH between pH 6 and 9. Ten oxidation products (OPs) were observed by LC/HRMS and three primary reaction pathways are proposed. The reaction pathways were used to explain differences in the quantification by Adda-ELISA, HRMS, and PPIA. The oxohydroxylation of MC-LA produced two major OPs, CHNO [M+H] = 942.4819 and CHNO [M+H] =960.4925. Major OPs may contain an unmodified Adda and are the likely cause of interference with the Adda-ELISA. Several governmental agencies recommend the use of the Adda-ELISA to determine the MC quantitation for treatment efficiency and customer exposure; yet our results suggest that these or other OPs interfere with the Adda-ELISA causing artificially high values for total MCs.
饮用水的高锰酸盐预处理在转化溶解的有害污染物和减少卤代副产物方面是有效的。高锰酸盐针对特定的化合物，如味觉和气味化合物、消毒前体、锰以及仅通过常规处理难以去除的天然有机污染物。蓝藻水华（cHABs）会增加消毒副产物前体以及蓝藻毒素微囊藻毒素（MC），一种强效的肝毒素。MC的毒性由一种独特的、保守的氨基酸Adda赋予，它会抑制蛋白磷酸酶1和2A。尽管已报道了150多种MC同系物，但从统计学角度来看，可能存在数千种MC。在过去十年中，一种同系物MC-LA的报道频率不断增加，使其成为北美淡水系统中最常见的蓝藻毒素之一；然而其氧化情况尚未得到广泛研究。通常，使用针对Adda的酶联免疫吸附测定（ELISA）和蛋白磷酸酶抑制测定（PPIA）来定量总MC，以评估处理效率和暴露情况。轶事报告表明，MC降解产物可能会干扰Adda-ELISA。本研究中使用MC-LA作为模型MC化合物。水中MC-LA的PPIA定量结果与液相色谱高分辨率质谱（LC/HRMS）一致，而ELISA定量结果与LC/HRMS定量结果不一致。我们确定MC-LA的二级反应速率常数为118±9 M⁻¹s⁻¹，活化能为21.2 kJ/mol，且该反应速率在pH值为6至9之间与pH无关。通过LC/HRMS观察到了十种氧化产物（OPs），并提出了三条主要反应途径。这些反应途径被用于解释Adda-ELISA、HRMS和PPIA定量结果之间的差异。MC-LA的氧羟基化产生了两种主要的OPs，CHNO [M+H]⁺ = 942.4819和CHNO [M+H]⁺ = 960.4925。主要的OPs可能含有未修饰的Adda，这可能是干扰Adda-ELISA的原因。一些政府机构建议使用Adda-ELISA来确定MC的定量，以评估处理效率和客户暴露情况；然而我们的结果表明，这些或其他OPs会干扰Adda-ELISA，导致总MC的人为高值。
