The Experts below are selected from a list of 225 Experts worldwide ranked by ideXlab platform
B L Mcgee - One of the best experts on this subject based on the ideXlab platform.
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a field based population model for the sediment toxicity Test Organism leptocheirus plumulosus i model development
Marine Environmental Research, 2001Co-Authors: M Spencer, B L McgeeAbstract:We describe the development of a stage-structured population matrix model for the estuarine amphipod Leptocheirus plumulosus, a sediment toxicity Test Organism, based on regular sampling of a natural population for approximately 2 years. Annual population dynamics were characterized by abundance peaks in the spring and fall, and low densities in the summer and winter. We use a sequence of seasonal projection matrices to capture these qualitative patterns in population dynamics. We compare two methods for estimating transition probabilities: multiple regression and truncated singular value decomposition (SVD). Overall, SVD gave more realistic parameter estimates than regression, although fecundity estimation was problematic. There were predictable trends in growth, survival and fecundity within years. The SVD-derived model provides a framework for assessing the population-level effects of contaminants on Leptocheirus.
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a field based population model for the sediment toxicity Test Organism leptocheirus plumulosus ii model application
Marine Environmental Research, 2001Co-Authors: B L Mcgee, M SpencerAbstract:A stage-structured population model has been developed for the estuarine amphipod Leptocheirus plumulosus to provide interpretive guidance for sediment toxicity Tests with this species. This time-varying, field-based model includes several matrices to reflect seasonal changes in demographics. In this paper, we conduct sensitivity analysis of the model to identify which life history parameters have the greaTest potential impact on population growth rate (λ). Results indicate seasonal variability in the relative demographic importance of vital rates. Over winter, annual population growth is most sensitive to the persistence of juveniles and adults and growth from the juvenile to the adult stage. In spring and fall, changes in fecundity are likely to have large effects on population dynamics. In addition, we demonstrate the applicability of the model by using it to interpret toxicological data from an assessment of sediment contamination in Baltimore Harbor, MD. The model was parameterized with survival data from acute toxicity Tests with L. plumulosus to project effects on population growth rate (λ). Results of these model simulations indicate that relatively small changes in survival can result in large changes in λ, indicating high risk to benthic populations. Furthermore, population projections mirror observed abundances of L. plumulosus at the Test sites. These analyses provide a first indication of the usefulness of the Leptocheirus population model as a tool for exploring ecological effects of sediment contamination.
M Spencer - One of the best experts on this subject based on the ideXlab platform.
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a field based population model for the sediment toxicity Test Organism leptocheirus plumulosus i model development
Marine Environmental Research, 2001Co-Authors: M Spencer, B L McgeeAbstract:We describe the development of a stage-structured population matrix model for the estuarine amphipod Leptocheirus plumulosus, a sediment toxicity Test Organism, based on regular sampling of a natural population for approximately 2 years. Annual population dynamics were characterized by abundance peaks in the spring and fall, and low densities in the summer and winter. We use a sequence of seasonal projection matrices to capture these qualitative patterns in population dynamics. We compare two methods for estimating transition probabilities: multiple regression and truncated singular value decomposition (SVD). Overall, SVD gave more realistic parameter estimates than regression, although fecundity estimation was problematic. There were predictable trends in growth, survival and fecundity within years. The SVD-derived model provides a framework for assessing the population-level effects of contaminants on Leptocheirus.
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a field based population model for the sediment toxicity Test Organism leptocheirus plumulosus ii model application
Marine Environmental Research, 2001Co-Authors: B L Mcgee, M SpencerAbstract:A stage-structured population model has been developed for the estuarine amphipod Leptocheirus plumulosus to provide interpretive guidance for sediment toxicity Tests with this species. This time-varying, field-based model includes several matrices to reflect seasonal changes in demographics. In this paper, we conduct sensitivity analysis of the model to identify which life history parameters have the greaTest potential impact on population growth rate (λ). Results indicate seasonal variability in the relative demographic importance of vital rates. Over winter, annual population growth is most sensitive to the persistence of juveniles and adults and growth from the juvenile to the adult stage. In spring and fall, changes in fecundity are likely to have large effects on population dynamics. In addition, we demonstrate the applicability of the model by using it to interpret toxicological data from an assessment of sediment contamination in Baltimore Harbor, MD. The model was parameterized with survival data from acute toxicity Tests with L. plumulosus to project effects on population growth rate (λ). Results of these model simulations indicate that relatively small changes in survival can result in large changes in λ, indicating high risk to benthic populations. Furthermore, population projections mirror observed abundances of L. plumulosus at the Test sites. These analyses provide a first indication of the usefulness of the Leptocheirus population model as a tool for exploring ecological effects of sediment contamination.
J.h. Lange - One of the best experts on this subject based on the ideXlab platform.
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a mixture toxicity study employing binary combinations of dinitrobenzene and trinitrobenzene using the bioluminescent marine bacterium vibrio harveyi as the Test Organism
International Journal of Environmental Studies, 2003Co-Authors: Kenneth W. Thomulka, J.h. LangeAbstract:A combination mixture study was conducted with two organic compounds, dinitrobenzene and trinitrobenzene, using the marine bioluminescent bacterium Vibrio harveyi . This assay employs the photogenic properties of this Organism for determination of toxicity in a direct procedure. Evaluation of toxicity was performed using an additive index methodology, mixture toxicity index and graphic representations. Graphic representations employed were isobole plot and isobologram, both isopleths. The additive index procedure employed both chemicals at their estimated median effective concentration (EC 50 ) for determination of a toxicity value. Isopleths employed combinations of both chemicals, using an equitoxic concentration, at 20% intervals of their EC 50 . An additive index value for this mixture was statistically antagonistic. Mixture toxicity index suggests that these chemical in various combinations are antagonistic. Combinations for both isopleths were similar and exhibited additivity for three mixture value...
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mixture toxicity of nitrobenzene and trinitrobenzene using the marine bacterium vibrio harveyi as the Test Organism
Ecotoxicology and Environmental Safety, 1997Co-Authors: Kenneth W. Thomulka, J.h. LangeAbstract:Abstract Vibrio harveyi,a bioluminescent marine bacterium, was used to evaluate combined or mixture toxicity of two organic compounds, nitrobenzene and trinitrobenzene. An estimated median effective concentration (EC50) and confidence interval were determined for each chemical. These chemicals at their EC50were evaluated in combination and an additive index method was used to determine a numerical toxicology value. Combinations at 20% intervals of the EC50were performed using isopleths. The isopleths employed were the isobole plot and the isobologram. Bioluminescent change was also determined and graphed for evaluation of toxicity. Statistical evaluation of isopleths and the additive index method were employed by incorporating confidence intervals. Bioluminescent change and isopleths suggest that mixtures of nitrobenzene and trinitrobenzene are additive, while the additive index method is suggestive of synergism. Statistical evaluation between mixtures and single values, using thezTest, was in some cases different at the 5% level. These data suggest that interaction of combinations should be evaluated and described by multiple methodologies. Evaluation of these data suggests, in part, that one mixture is statistically different for antagonism. This study supports the use of bioluminescent microbial toxicity Tests with various evaluative methodologies for the determination of mixture interactions.
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A Mixture Toxicity Study Employing Combinations of Tributyltin Chloride, Dibutyltin Dichloride, and Tin Chloride Using the Marine BacteriumVibrio harveyias the Test Organism
Ecotoxicology and Environmental Safety, 1996Co-Authors: Kenneth W. Thomulka, J.h. LangeAbstract:Abstract Mixture toxicity studies in dual combinations for three metals, tributyltin chloride, dibutyltin dichloride, and tin chloride, and one experiment using all chemicals were performed using the bioluminescent marine bacteriumVibrio harveyias the Test Organism in a direct toxicity Test procedure. Combination toxicity was evaluated using an additive index equation method and two isopleth procedures, isobole plot and isobologram. Additive index values were determined at both estimated effective median concentration (EC50) and one-third EC50values for each dual combination and all three chemicals for one-third EC50values. Isopleths employed chemical combinations at 20% intervals of the EC50concentrations. Additive index values for various mixtures were either additive or antagonistic (less than additive). Isobolograms for all mixtures were descriptively additive or synergistic (greater than additive). Isobole plots were also descriptively additive or synergistic, although a few measurements were statistically different for synergism. Statistical evaluation between mixtures and single values, using thezTest, were in some cases different at the 5% level. Bioluminescent counts were determined to be normally distributed using a statistical Test for small sample numbers at the 1% level. Evaluation for outliers, using the Dixon Test, was also performed and found one mixture to have an outlier. This single outlier had no influence on the combined toxicity results. The use of low-cost and rapid bioluminescent microbial toxicity Tests for mixture studies is discussed.
Kenneth W. Thomulka - One of the best experts on this subject based on the ideXlab platform.
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a mixture toxicity study employing binary combinations of dinitrobenzene and trinitrobenzene using the bioluminescent marine bacterium vibrio harveyi as the Test Organism
International Journal of Environmental Studies, 2003Co-Authors: Kenneth W. Thomulka, J.h. LangeAbstract:A combination mixture study was conducted with two organic compounds, dinitrobenzene and trinitrobenzene, using the marine bioluminescent bacterium Vibrio harveyi . This assay employs the photogenic properties of this Organism for determination of toxicity in a direct procedure. Evaluation of toxicity was performed using an additive index methodology, mixture toxicity index and graphic representations. Graphic representations employed were isobole plot and isobologram, both isopleths. The additive index procedure employed both chemicals at their estimated median effective concentration (EC 50 ) for determination of a toxicity value. Isopleths employed combinations of both chemicals, using an equitoxic concentration, at 20% intervals of their EC 50 . An additive index value for this mixture was statistically antagonistic. Mixture toxicity index suggests that these chemical in various combinations are antagonistic. Combinations for both isopleths were similar and exhibited additivity for three mixture value...
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mixture toxicity of nitrobenzene and trinitrobenzene using the marine bacterium vibrio harveyi as the Test Organism
Ecotoxicology and Environmental Safety, 1997Co-Authors: Kenneth W. Thomulka, J.h. LangeAbstract:Abstract Vibrio harveyi,a bioluminescent marine bacterium, was used to evaluate combined or mixture toxicity of two organic compounds, nitrobenzene and trinitrobenzene. An estimated median effective concentration (EC50) and confidence interval were determined for each chemical. These chemicals at their EC50were evaluated in combination and an additive index method was used to determine a numerical toxicology value. Combinations at 20% intervals of the EC50were performed using isopleths. The isopleths employed were the isobole plot and the isobologram. Bioluminescent change was also determined and graphed for evaluation of toxicity. Statistical evaluation of isopleths and the additive index method were employed by incorporating confidence intervals. Bioluminescent change and isopleths suggest that mixtures of nitrobenzene and trinitrobenzene are additive, while the additive index method is suggestive of synergism. Statistical evaluation between mixtures and single values, using thezTest, was in some cases different at the 5% level. These data suggest that interaction of combinations should be evaluated and described by multiple methodologies. Evaluation of these data suggests, in part, that one mixture is statistically different for antagonism. This study supports the use of bioluminescent microbial toxicity Tests with various evaluative methodologies for the determination of mixture interactions.
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A Mixture Toxicity Study Employing Combinations of Tributyltin Chloride, Dibutyltin Dichloride, and Tin Chloride Using the Marine BacteriumVibrio harveyias the Test Organism
Ecotoxicology and Environmental Safety, 1996Co-Authors: Kenneth W. Thomulka, J.h. LangeAbstract:Abstract Mixture toxicity studies in dual combinations for three metals, tributyltin chloride, dibutyltin dichloride, and tin chloride, and one experiment using all chemicals were performed using the bioluminescent marine bacteriumVibrio harveyias the Test Organism in a direct toxicity Test procedure. Combination toxicity was evaluated using an additive index equation method and two isopleth procedures, isobole plot and isobologram. Additive index values were determined at both estimated effective median concentration (EC50) and one-third EC50values for each dual combination and all three chemicals for one-third EC50values. Isopleths employed chemical combinations at 20% intervals of the EC50concentrations. Additive index values for various mixtures were either additive or antagonistic (less than additive). Isobolograms for all mixtures were descriptively additive or synergistic (greater than additive). Isobole plots were also descriptively additive or synergistic, although a few measurements were statistically different for synergism. Statistical evaluation between mixtures and single values, using thezTest, were in some cases different at the 5% level. Bioluminescent counts were determined to be normally distributed using a statistical Test for small sample numbers at the 1% level. Evaluation for outliers, using the Dixon Test, was also performed and found one mixture to have an outlier. This single outlier had no influence on the combined toxicity results. The use of low-cost and rapid bioluminescent microbial toxicity Tests for mixture studies is discussed.
Maria Teresa Rayarodriguez - One of the best experts on this subject based on the ideXlab platform.
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assessment of the freshwater annual fish cynopoecilus melanotaenia as a toxicity Test Organism using three reference substances
Environmental Toxicology and Chemistry, 2003Co-Authors: Alexandre Arenzon, Regis Fontana Pinto, Patrick Colombo, Maria Teresa RayarodriguezAbstract:This study presents a preliminary evaluation of the use of the Brazilian fish Cynopoecilus melanotaenia as a Test Organism in toxicity Tests. The cryptobiotic stage presented by the eggs of fish C. melanotaenia can overcome the difficulty of continuously keeping cultures and recruiting healthy animals in sufficient numbers to be used in toxicity Tests. In order to determine the applicability of this species as a Test Organism, three different reference substances were evaluated in 96-h acute toxicity Tests: Copper sulfate (CuSO4·5H2O), sodium dodecil sulfate (C12H25NaO4S), and sodium chloride (NaCl). Sensitivity ranged as follows: copper sulfate (0.05-0.13 mg/L), sodium dodecil sulfate (10.7-19.0 mg/L), and sodium chloride (1.44-1.96 g/L). We conclude that C. melanotaenia shows potential as a Test Organism in toxicity Tests; however, further research should be conducted with other substances and should be compared with the research on other species before we can reach more conclusive results.
