Some species of marine phytoplankton are believed to be more tolerant of high concentrations of trace metals than others, but no conclusive test of this hypothesis has been conducted. Eleven species of phytoplankton representing 5 classes were grown in Aquil medium containing Cd$ sp{2+}$ concentrations between 10$ sp{-9.85}$ and 10$ sp{-6.84}$ M. Growth rates and intracellular concentrations of Cd, C, N and S were measured. Cadmium quotas (mol Cd/litre-cell volume) were lower in members of Bacillariophyceae than in Chlorophyceae, Prymnesiophyceae, Dinophyceae and Cyanophyceae (ANOVA, p $<$ 0.001). Cellular C:S molar ratios decreased in phytoplankton grown at high (pCd 7.37-6.84) compared to low Cd (no added Cd), as S/litre-cell volume increased. Similar results were observed for C:N molar ratios. In two species that were examined, C:S ratios decreased as a linear function of increasing Cd concentration. Mean Cd$ sp{2+}$ concentration that reduced growth rate to 50% of maximum (pCd$ sp{50})$ was not significantly different among phytoplankton classes (ANOVA, p $<$ 0.05). When these experimental data were combined with pCd$ sp{50}$s calculated from published sources, Chlorophyceae were found to be the most resistant class (ANOVA, p $<$ 0.01). Cadmium and Cu resistance (pCd$ sp{50}$ and pCu$ sp{50})$ were correlated (r = 0.52, p $<$ 0.05), suggesting co-tolerance of phytoplankton to toxic levels of these metals. Chlorophyceae were most tolerant and Cyanophyceae the least tolerant of Cu (ANOVA, p $<$ 0.01). No significant differences were observed among Bacillariophyceae, Prymnesiophyceae, and Dinophyceae, which were of intermediate sensitivity to both metals. The results confirm the existence of a phylogenetic dependence of resistance to trace metal toxicity in phytoplankton.

Thesis (MSc (Paraclinical Sciences))--University of Pretoria, 2007. / Includes bibliographical references. Also available in print format.

The toxicity of ammonia has become an issue in recent years, especially in the Chesapeake Bay watershed. Currently, the EPA has set a chronic criterion of 0.035 mg/L (unionized ammonia). The chronic criterion is a four-day average concentration that cannot be exceeded more than once every three years. However, a lack of data exists on the toxicity of ammonia to saltwater organisms. Prior to this research, the chronic criterion was based on two saltwater and four freshwater organisms. This research was conducted to add additional data so more appropriate criteria may be set. Two saltwater fish, the Summer Flounder (Paralichthys dentatus), and the Atlantic Silverside (Menidia menidia) and one invertebrate, the Quahog Clam (Mercenaria mercenaria) were tested for acute toxicity to ammonia. The acute tests performed on the Summer Flounder (2 months old) were 48 and 96-hour tests performed in both synthetic seawater and natural seawater. Seven-day chronic tests were also performed on the Summer Flounder using synthetic seawater. Both 48 and 96-hour acute tests were performed on the Atlantic Silverside (10-14 days old.) using natural seawater. Both 48 and 96-hour acute tests were performed on the Quahog Clam (5mm shell height) using synthetic seawater. The 48-hour LC50s for the Summer Flounder in synthetic and natural seawater were 1.22 mg/L and 1.09 mg/L, respectively. The 96-hour LC50s for the Summer Flounder in synthetic and natural seawater were 1.07 mg/L and 0.889 mg/L, respectively. The 7-day chronic NOEC was 1.37 mg/L. The 48 and 96-hour LC50s for Atlantic Silverside in natural seawater were 1.52 mg/L and 1.18 mg/L, respectively. The 48 and 96-hour LC50s for Quahog Clam in synthetic seawater were 216 mg/L and 36.6 mg/L, respectively. The acute-chronic ratio for the Summer Flounder was 2.27. The refined chronic criterion was 0.081 mg/L based on this research and the research of others. Summer Flounder were more sensitive to ammonia in natural seawater than synthetic seawater. However, Atlantic Silverside showed no difference in sensitivity. / Master of Science

No description available.

No description available.

No description available.

The main aim of this project was to investigate the role of Fusarium solani in aqueous cutting fluid and increase understanding about the ecology of this organism in coolants. By adapting cell-line bioassay techniques to the direct testing of coolant emulsion, the role of Fusarium solani in cutting fluid toxicity was determined. The potential of fungal strains enhancing cutting fluid toxicity was investigated by fungal toxigenicity screening, to assess any potential for fungal species isolated to produce mycotoxins. 32 contaminated cutting fluid samples tested revealed 66 % fungal contamination and Fusarium solani was isolated from 81 % of these, highlighting the significance of this species in coolants. Using brine shrimp and cell-line bioassays, none of the fungi isolated were toxigenic, although Fusarium solani culture extracts were slightly toxic to cell-lines (min. cytotoxic dose 12.5-25 ug/ml). Using thin layer chromatography, it was revealed that the isolate Fusarium solani ISL-45 / IMI 360547 was not producing trichothecenes in culture, and that a maroon pigment normally produced at pH < 4 was responsible for slight cytotoxicity. It was revealed that pigment production was only stimulated in cultures less than pH 4 in the presence of excess phosphate. By assaying cutting fluid using cell-lines it was found that growth of Fusarium solani reduced cutting fluid toxicity twofold after 14 days growth and that fungal biodeterioration of vegetable oil and ethylene glycol was responsible for the toxicity decrease. Cutting fluid not supplemented with yeast extract or other nitrogenous material was unable to support growth of Fusarium solani demonstrating that there was an obligate requirement for an external assimilable nitrogen source in addition to nitrogenous cutting fluid constituents. Fusarium solani biomass yields were highest in cutting fluid experiments supplemented with iron / aluminium swarf and inert beads. Biomass yields were poor in cutting fluid containing no swarf or inert material suggesting that surfaces promote fungal adhesion and accumulation of mycelium. Although swarf metal was stimulatory to growth, cutting fluid treated with dissolved swarf materials was inhibitory to growth. II In metal ion tests; Ca2+, Mg2+ and Mn2+ had little effect on fungal physiology whereas A13+, Cu2+, Fe3+, Ni2+ and Ti3+ were very toxic (min. inhibitory dose M.I.D. < 2mM) and C~+, Co2+, Fe2+, Pb2+ and Zn2+ were moderately toxic (M.I.D. 2-10 mM). 0.5 mM Pb2+ and Zn2+ were associated with increased production of maroon pigment, by Fusarium solani, in media containing glucose. Water hardness was found to have little or no effect on fungal physiology although coolant emulsion stability was reduced with Ca2+ concentrations exceeding 5 mM.

No description available.

No description available.

No description available.