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Assessment of Individual and Combined Toxicities of Four Non-Essential Metals (As, Cd, Hg and Pb) in the Microtox Assay
Department of Natural Sciences, University of Maryland Eastern Shore, Princess Anne, Maryland 21853, USA
Molecular Toxicology Research Laboratory, NIH-Center for Environmental Health, College of Science, Engineering and Technology, Jackson State University, Jackson, MS 39217, USA
* Author to whom correspondence should be addressed.
Received: 31 October 2005; Accepted: 15 March 2006 / Published: 31 March 2006
Abstract: 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.
Keywords: Combined toxicities; Non-essential metals; Microtox assay
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Ishaque, A.B.; Johnson, L.; Gerald, T.; Boucaud, D.; Okoh, J.; Tchounwou, P.B. Assessment of Individual and Combined Toxicities of Four Non-Essential Metals (As, Cd, Hg and Pb) in the Microtox Assay. Int. J. Environ. Res. Public Health 2006, 3, 118-120.
Ishaque AB, Johnson L, Gerald T, Boucaud D, Okoh J, Tchounwou PB. Assessment of Individual and Combined Toxicities of Four Non-Essential Metals (As, Cd, Hg and Pb) in the Microtox Assay. International Journal of Environmental Research and Public Health. 2006; 3(1):118-120.
Ishaque, Ali B.; Johnson, Linda; Gerald, Tonya; Boucaud, Dwayne; Okoh, Joseph; Tchounwou, Paul B. 2006. "Assessment of Individual and Combined Toxicities of Four Non-Essential Metals (As, Cd, Hg and Pb) in the Microtox Assay." Int. J. Environ. Res. Public Health 3, no. 1: 118-120.