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Title: Predicting relative toxicity and interactions of divalent metal ions: Microtox{reg_sign} bioluminescence assay

Abstract

Both relative toxicity and interactions between paired metal ions were predicted with least-squares linear regression and various ion characteristics. Microtox{reg_sign} 15 min EC50s (expressed as free ion) for Ca(II), Cd(II), Cu(II), Hg(II), Mg(II), Mn(II), Ni(II), Pb(II), and Zn(II) were most effectively modeled with the constant for the first hydrolysis (K{sub H} for M{sup n+} + H{sub 2}O {yields} MOH{sup a{minus}1} + H{sup +}) although other ion characteristics were also significant in regression models. The {vert_bar}log K{sub H}{vert_bar} is correlated with metal ion affinity to intermediate ligands such as many biochemical functional groups with O donor atoms. Further, ordination of metals according to ion characteristics, e.g., {vert_bar}log K{sub H}{vert_bar} facilitated prediction of paired metal interactions. Pairing metals with strong tendencies to complex with intermediate or soft ligands such as those with O or S donor atoms resulted in strong interactions.

Authors:
;  [1]
  1. Savannah River Ecology Lab., Aiken, SC (United States)
Publication Date:
Sponsoring Org.:
USDOE
OSTI Identifier:
215598
Resource Type:
Journal Article
Resource Relation:
Journal Name: Environmental Toxicology and Chemistry; Journal Volume: 15; Journal Issue: 3; Other Information: PBD: Mar 1996
Country of Publication:
United States
Language:
English
Subject:
56 BIOLOGY AND MEDICINE, APPLIED STUDIES; CALCIUM; BIOASSAY; CADMIUM; COPPER; MERCURY; MAGNESIUM; MANGANESE; NICKEL; LEAD; ZINC; PHOTOSYNTHETIC BACTERIA; SENSITIVITY; FORECASTING; MATHEMATICAL MODELS

Citation Formats

Newman, M.C., and McCloskey, J.T. Predicting relative toxicity and interactions of divalent metal ions: Microtox{reg_sign} bioluminescence assay. United States: N. p., 1996. Web. doi:10.1002/etc.5620150308.
Newman, M.C., & McCloskey, J.T. Predicting relative toxicity and interactions of divalent metal ions: Microtox{reg_sign} bioluminescence assay. United States. doi:10.1002/etc.5620150308.
Newman, M.C., and McCloskey, J.T. 1996. "Predicting relative toxicity and interactions of divalent metal ions: Microtox{reg_sign} bioluminescence assay". United States. doi:10.1002/etc.5620150308.
@article{osti_215598,
title = {Predicting relative toxicity and interactions of divalent metal ions: Microtox{reg_sign} bioluminescence assay},
author = {Newman, M.C. and McCloskey, J.T.},
abstractNote = {Both relative toxicity and interactions between paired metal ions were predicted with least-squares linear regression and various ion characteristics. Microtox{reg_sign} 15 min EC50s (expressed as free ion) for Ca(II), Cd(II), Cu(II), Hg(II), Mg(II), Mn(II), Ni(II), Pb(II), and Zn(II) were most effectively modeled with the constant for the first hydrolysis (K{sub H} for M{sup n+} + H{sub 2}O {yields} MOH{sup a{minus}1} + H{sup +}) although other ion characteristics were also significant in regression models. The {vert_bar}log K{sub H}{vert_bar} is correlated with metal ion affinity to intermediate ligands such as many biochemical functional groups with O donor atoms. Further, ordination of metals according to ion characteristics, e.g., {vert_bar}log K{sub H}{vert_bar} facilitated prediction of paired metal interactions. Pairing metals with strong tendencies to complex with intermediate or soft ligands such as those with O or S donor atoms resulted in strong interactions.},
doi = {10.1002/etc.5620150308},
journal = {Environmental Toxicology and Chemistry},
number = 3,
volume = 15,
place = {United States},
year = 1996,
month = 3
}
  • Quantitative structure-activity relationships have been used to predict the relative toxicity of organic compounds. Although not as common, ion characteristics have also proven useful for predicting the relative toxicity of metal ions. The purpose of this study was to determine if the relative toxicity of metal ions using the Microtox{reg_sign} bioassay was predictable using ion characteristics. Median effect concentrations (EC50s) were determined for 20 metals in a NaNO{sub 3} medium, which reflected freshwater speciation conditions, using the Microtox bacterial assay. The log of EC50 values was modeled using several ion characteristics, and Akaike`s Information Criterion was calculated to determine whichmore » ion characteristics provided the best fit. Whether modeling total ion or free ion EC50 values, the one variable which best modeled EC50s was the softness index, while a combination of {chi}{sub m}{sup 2}r ({chi}{sub m} = electronegativity, r = Pauling ionic radius) and {vert_bar}log K{sub OH}{vert_bar} was the best two-variable model. Other variables, including {Delta}E{sub 0} and {chi}{sub m}{sup 2}r (one-variable models) and (AN/{Delta}IP, {Delta}E{sub 0}) and ({chi}{sub m}{sup 2}r, Z{sup 2}/r) (two-variable models), also gave adequate fits. Modeling with speciated (free ion) versus unspeciated (total ion) EC50 values did not improve fits. Modeling mono-, di-, and trivalent metal ions separately improved the models. The authors conclude that ion characteristics can be used to predict the relative toxicity of metal ions whether in freshwater (NaNO{sub 3} medium) or saltwater (NaCl medium) speciation conditions and that this approach can be applied to metal ions varying widely in both valence and binding tendencies.« less
  • The use of predictive effects models with metals has received little attention in toxicology. The purpose of this study was to predict the relative toxicity of individual metal ions and metal mixtures using ion characteristics. The concentration of metal resulting in a 50% reduction in light output (EC50) in marine bacteria (Vibrio fischeri) was determined for several metals using the Microtox{reg_sign} Toxicity Analyzer. Trends in metal toxicity were predicted by combining metal speciation calculations with empirical models based on metal ion characteristics. These trends were consistent for nine divalent metals (Ca{prime} Cd, Cu, Hg, Mg, Mn, Ni, Pb and Zn)more » whether the media mimicked salt water (NaC, medium) or freshwater (NaNO{sub 3} medium). When expanding the study to include an additional 14 mono-, di-, and trivalent metal ions, ion characteristics were still useful for predicting the relative toxicity of metal ions to bacteria. The prediction of nonadditive toxic effects using metal mixtures was also possible based on ion characteristics. Overall, models based on ion characteristics show much promise for predicting the relative toxicity of metal ions using the Microtox{reg_sign} assay.« less
  • Recent literature indicates that the elemental sulfur occurring in organic extracts of sediment samples can be toxic to the bacterium Vibrio fischeri, used in standard Microtox{reg_sign} bioassays. This observation was tested by means of the solvent extraction of 14 freshwater sediment samples from rivers tributary to Lake Geneva (Switzerland-France), measuring both Microtox toxicity and the elemental sulfur concentration of the extracts. Aliquots of these sediment extracts were further treated to remove the sulfur by adding acid-activated copper to the crude extracts; for 18 h in one case, and for 116 h in another. The results were a significant amount ofmore » the observed acute toxicity in the Microtox assay of 81% of sample extracts was due to elemental sulfur, and despite a median decrease of 99.1% of elemental sulfur in the extracts subject to a 116-h cleanup, sulfur toxicity was not completely excluded for 57% (8/14) of the samples. Clearly, the Microtox methodology needs to be amended to more accurately assess the potential impact of organic pollutants in sediments when solvent extracts are used. This will help to cut down on costly and unnecessary remedial actions.« less
  • This project examined the influence of different extraction methods on the measured toxicity of contaminated soils collected from manufactured gas plant (MGP) sites differing in soil composition and contaminant concentration. Aged soils from a number of MGP sites were extracted using a saline solution, supercritical fluid extraction (SFE), and Soxhlet extraction. Toxicity was assessed using two forms of Microtox tests: acute aqueous tests on saline and SFE soil extracts and solid-phase tests (SPTs) on soil particles. Microtox SPTs were performed on soils before and after SFE to determine resulting toxicity reduction. Three hypotheses were tested: (1) Toxicity of soil extractsmore » is related to contaminant concentrations of the extracts, (2) measured toxicity significantly decreases with less vigorous methods of extraction, and (3) supercritical fluid extractability correlates with measured toxicity. The EC50s for SPTs performed before and after SFE were not different for some soils but were significantly greater after extraction for other soils tested. The most significant toxicity reductions were observed for soils exhibiting the highest toxicity in both preextraction SPTs and acute aqueous tests. Acute Microtox tests performed on SFE extracts showed significantly lower EC50s than those reported from saline-based extraction procedures. Toxicity of the soils measured by Microtox SPTs was strongly correlated with both SFE efficiency and measures of contaminant aging. Data from this project provide evidence of sequestration and reduced availability of polycyclic aromatic hydrocarbons (PAHs) from soils extracted via physiologically based procedures compared to vigorous physical extraction protocols.« less
  • Qualitative and quantitative analysis of the components of wastewaters is a necessary step towards determining the nature of aqueous effluents. However, toxicity levels of the effluents and receiving waters should also be determined to obtain a more comprehensive understanding of the effects the discharges may have on aquatic environments. The Microtox{reg_sign} test was successfully used to measure EC50 values of nonionic polyethoxylate surfactants. However, toxicity measurements of real samples that contain surfactants above a particular concentration, termed the critical toxicity concentration (CTC) are not valid. These samples require dilution before the test is performed, and because the relationship between toxicitymore » and concentration is not linear above the CTC, the EC50 cannot be extrapolated back to give the toxicity of the original concentrated sample and a true estimation of toxicity is therefore not possible. This phenomenon may be related to the minimum surface tension requirement of the bacteria or other physical properties of the surfactant such as the tendency to assemble at interfaces and surfaces and the tendency to form micelles.« less