Browsing by Author "Thomas, Carolyn L."

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    Development of a test system for screening toxic substances: a comparison using organic substances
    Thomas, Carolyn L. (Virginia Polytechnic Institute and State University, 1985)
    The purpose of this research was to develop a test system for screening toxic substances by predicting their aquatic ecosystem effects. The system studied was a static, one liter microcosm with a diverse species assemblage. Teh microcosm was composed of biotic inoculum, chemically defined medium and sediment. The biotic inoculum cotained primary producers, grazers, carnivores and decomposers. The chemical medium used was Taub #82 modified by adding sodium bicarbonate. Three different types of sediment were studied: sand, clay and clay plus sand. Four organic chemicals: phenol, triethylene glycol (TEG), quinoline and naphtoquinone were evaluated with this test system. The toxicities of TEG, quinoline and naphthoquinone were compared for each sediment type. Toxicity was evluated in terms of the chemicals' effects on primary productivity and heterotrophic activity though other effects are also noted. The toxicity of the chemicals in this study was compared to those from other toxicological evaluations based on threshhold toxicity values (EC20 and LC50). The screening test sytem evaluated in this study did not demonstrate significanly different threshhold toxicity values than the other screening systems to which it was compared. The ranking of the toxicants based on EC20 values was different for the two ecosystem properties, net production and heterotrophic activity. Naphthoquinone concentration exhibited no correlation between ecosystems property values and therefore, could not be ranked. Phenol exhibited the greatest toxicity to net production immediately after the toxicant addition. Quinoline was most toxic to net production over the longer time scale. TEG exhibited the least toxicity to net production, however, TEG exhibited higher toxicity to heterotrophic activity than either quinoline or phenol. Although the type of sediment used in the nicrocosms did not change the relative toxicities of the chemicals, the microcosms with clay sediment always were observed to exhibit lower net production and higher variability. Nonparametric statistical analyses are recommended for microcosm studies because of the lack of normally distributed data. Confidence limits of 80% are recommended because of the need for biologically conservative estimates of ecosystem toxicity.
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    The effects of boron supplementation on bone mineral density, blood and urinary calcium, magnesium, phosphorous and urinary boron in female athletes
    Darnton, Susan Meacham (Virginia Tech, 1991-09-20)
    The effects of boron supplementation on blood and urinary minerals were studied in 17 female college athletes and 11 sedentary college control subjects. The subjects were similar in age (19.8 ± 1.4 and 20.3 ± 1.1 years for athletes and sedentary groups, respectively) and weight (61.8 ± 9.1 and 59.6 ± 10.5 kgs for athletes and sedentary groups, respectively). The athletic subjects had lower percent body fat averages (20.6 ± 5.6 and 25.8 ± 6.5 %, respectively, (p < 0.05)) and higher aerobic capacities (2.9 ± 0.5 and 2.1 ± 0.4 L O₂*min₋₁, respectively, (p < 0.05) than sedentary controls. No differences in dietary intake were observed. Serum phosphorus levels were lower in boron supplemented subjects than in subjects receiving placebos (p < 0.05) and were lower during final analysis than during baseline analysis. A group-supplement interaction was noted with serum phosphorus also (p < 0.05). In the sedentary group, boron supplementation lowered serum phosphorus and placebo supplementation elevated serum phosphorus. In the athletic group, no changes in serum phosphorus were observed due to supplementation. Serum magnesium was greatest in the sedentary controls supplemented with boron and increased with time in all subjects (p < 0.05). Again, a group-supplement interaction was observed with serum magnesium; exercise in boron supplemented subjects lowered serum magnesium (p < 0.05). In all subjects, calcium excretion increased over time (p < 0.05) and in boron supplemented subjects boron excretion increased over time (p < 0.05). In conclusion, boron supplementation affected serum phosphorus and magnesium and the excretion of boron in the urine. The significance of these findings in relation to overall mineral status, bone mineral density, and exercise in college female athletes needs further investigation. It is possible that increasing the intake of foods high in boron may be found to be beneficial in the treatment and/or prevention of metabolic bone disorders such as those related to excessive exercise.