Ishaque Ali B, Johnson Linda, Gerald Tonya, Boucaud Dwayne, Okoh Joseph, Tchounwou Paul B
Department of Natural Sciences, University of Maryland Eastern Shore, Princess Anne, Maryland 21853, USA.
Int J Environ Res Public Health. 2006 Mar;3(1):118-20. doi: 10.3390/ijerph2006030014.
Although most researches with non-essential metals (NEMs) have been done with single or individual metals, in reality, organisms are often exposed to multiple contaminants at the same time through the air, food and water. In this study, we tested the toxicity of four NEMs, As, Cd, Pb, and Hg, individually and as a composite mixture using the microtox bioassay. This assay uses the reduction of bioluminescence of the bacterium Vibrio fischeri as a measure of toxicity. The concentrations of each chemical in the mixture were based on multiples of their maximum contaminant levels (MCLs) set by the U.S. EPA. The highest concentration of exposure was 20 times the MCL, which translated into 200, 100, 40 and 300 ppb for As, Cd, Hg and Pb, respectively. The ratio for the mixture from these concentrations was 10:5:2:15 for As, Cd, Hg and Pb, respectively. Among the individual metals tested, the ranking of toxicity was Hg>Pb>Cd>As based on the EC50 values of 109, 455, 508 and 768 ppb for Hg, Pb, Cd and As, respectively. The EC50 for the composite mixture was 495% MCL which translated into nominal concentrations of 49, 25, 10 and 74 ppb for As, Cd, Hg, and Pb, respectively. Overall, the EC50 value of each NEM within the mixture was lower than the EC50 of the individual chemical; an evidence of synergism for the mixture. The individual toxic units (TU) were 0.06, 0.05, 0.09, and 0.16 for As, Cd Hg, and Pb, respectively and the summed toxic unit (TU) was 0.37 (less than 1). This study provides needed scientific data necessary for carrying out complete risk assessment of As, Cd, Hg, and Pb mixtures of some priority compounds.
尽管大多数关于非必需金属（NEMs）的研究都是针对单一金属进行的，但实际上，生物体常常通过空气、食物和水同时接触多种污染物。在本研究中，我们使用微毒性生物测定法分别测试了四种非必需金属——砷（As）、镉（Cd）、铅（Pb）和汞（Hg）及其复合混合物的毒性。该测定法利用费氏弧菌生物发光的减弱作为毒性的衡量指标。混合物中每种化学物质的浓度基于美国环境保护局（EPA）设定的最大污染物水平（MCLs）的倍数。最高暴露浓度为MCL的20倍，分别对应砷、镉、汞和铅的浓度为200、100、40和300 ppb。这些浓度下混合物中砷、镉、汞和铅的比例分别为10:5:2:15。在所测试的单一金属中，根据汞、铅、镉和砷的半数有效浓度（EC50）值分别为109、455、508和768 ppb，毒性排名为汞>铅>镉>砷。复合混合物的EC50为495% MCL，分别对应砷、镉、汞和铅的名义浓度为49、25、10和74 ppb。总体而言，混合物中每种非必需金属的EC50值均低于单一化学物质的EC50值；这是混合物具有协同作用的证据。砷、镉、汞和铅的个体毒性单位（TU）分别为0.06、0.05、0.09和0.16，总毒性单位（TU）为0.37（小于1）。本研究为对某些优先化合物的砷、镉、汞和铅混合物进行全面风险评估提供了所需的科学数据。
