DeMarini D M, Abu-Shakra A, Felton C F, Patterson K S, Shelton M L
Environmental Carcinogenesis Division, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711, USA.
Environ Mol Mutagen. 1995;26(4):270-85. doi: 10.1002/em.2850260403.
Drinking water samples were prepared in a pilot-scale treatment plant by chlorination (Cl2), chloramination (NH2Cl), ozonation (O3), or O3 followed by Cl2 or NH2Cl; and the nonvolatile acidic organics of the raw and treated waters were extracted by XAD/ethyl acetate and evaluated for mutagenicity in Salmonella (-S9). The extracts were 2-8 times more mutagenic in TA100 than in TA98, and the mutagenic potencies of the water extracts ranked similarly in both strains: Cl2 > O3 + Cl2 > NH2Cl > O3 + NH2Cl > O3 > raw. 3-Chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX), which was estimated to account for approximately 20% of the mutagenic activity of the extracts, was shown to be the most potent compound tested thus far in a prophage-induction assay in Escherichia coli and a forward-mutation assay in Salmonella TM677. The mutations in approximately 2,000 revertants of TA98 and TA100 induced by MX and the water extracts were analyzed by colony probe hybridization and polymerase chain reaction/DNA sequence analysis. The water extracts and MX produced similar mutation spectra, which consisted in TA100 of predominantly of GC-->TA transversions in the second position of the CCC (or GGG) target of the hisG46 allele. This spectrum resembles that produced by large aromatic compounds and is distinct from that produced by alkylating agents and the semivolatile drinking water mutagen dichloroacetic acid. In TA98, MX and those water extracts resulting from the introduction of the chlorine atom produced 50-70% hotspot 2-base deletions and 30-50% complex frameshifts (frameshifts with an adjacent base substitution--mostly GC-->TA transversions as found in TA100). No other compound or mixture is known to induce such high frequencies of complex frameshifts. These results suggest that MX and "MX-like" compounds (possibly halogenated aromatics, such as halogenated polycyclic aromatic hydrocarbons) account for much of the mutagenic activity and specificity of the nonvolatile organics in drinking water and that these halogenated organics are especially capable of promoting misincorporation by the DNA replication complex. This study provides further evidence that the mutation spectrum of a complex mixture reflects the dominance of one or a few classes of chemical mutagens within the mixture.
在中试规模的处理厂中，通过氯化（Cl₂）、氯胺化（NH₂Cl）、臭氧化（O₃）或O₃后接Cl₂或NH₂Cl的方式制备饮用水样本；用XAD/乙酸乙酯萃取原水和处理后水中的非挥发性酸性有机物，并评估其对鼠伤寒沙门氏菌（-S9）的致突变性。提取物在TA100中的致突变性比在TA98中高2 - 8倍，且水提取物在两种菌株中的致突变效力排序相似：Cl₂ > O₃ + Cl₂ > NH₂Cl > O₃ + NH₂Cl > O₃ > 原水。3 - 氯 - 4 - （二氯甲基） - 5 - 羟基 - 2（5H） - 呋喃酮（MX）被估计约占提取物致突变活性的20%，在大肠杆菌的原噬菌体诱导试验和鼠伤寒沙门氏菌TM677的正向突变试验中，它是迄今为止测试的最具致突变性的化合物。通过菌落探针杂交和聚合酶链反应/DNA序列分析，对由MX和水提取物诱导的TA98和TA100的约2000个回复突变体中的突变进行了分析。水提取物和MX产生了相似的突变谱，在TA100中，主要是hisG46等位基因的CCC（或GGG）靶点第二位的GC→TA颠换。这种谱型类似于由大型芳香族化合物产生的谱型，与烷基化剂和半挥发性饮用水诱变剂二氯乙酸产生的谱型不同。在TA98中，MX和引入氯原子后得到的那些水提取物产生了50 - 70%的热点2碱基缺失和30 - 50%的复杂移码突变（带有相邻碱基取代的移码突变——大多是TA100中发现的GC→TA颠换）。已知没有其他化合物或混合物能诱导如此高频率的复杂移码突变。这些结果表明，MX和“类MX”化合物（可能是卤代芳烃，如卤代多环芳烃）在很大程度上解释了饮用水中非挥发性有机物的致突变活性和特异性，并且这些卤代有机物特别能够促进DNA复制复合体的错配掺入。这项研究进一步证明，复杂混合物的突变谱反映了混合物中一种或几类化学诱变剂的主导地位。
