Toxicity of metals in biological systems

This thesis incorporates reports of research on the development and application of innovative chemical and biochemical techniques to the study of mechanisms of metal toxicity m simple single-celled organisms and more complex multicellular organisms including humans. The thesis is based on research undertaken over the last 10 years and published m 26 refereed scientific papers Single-celled algae are the foundation of most aquatic food chains and account for much of the productivity of aquatic ecosystems Marine and freshwater algae are particularly sensitive to a wide range of metals and organic compounds, and their viability can be used as an indicator of environmental change. Chrome toxicity tests, based on algal growth and enzyme inhibition, have been developed and applied to assessments of the bioavailability and toxicity of metals in aquatic systems Specific applications of the algal bioassays for assessing mine-derived contaminants in natural systems has been described Knowledge of modes of action of different metal species at a sub-cellular level is essential to understanding and predicting the bioavailability and toxicity of metals in natural waters. Research on the mechanisms of toxicity of copper and zinc to microalgae has been described, with particular emphasis on the link between chemical speciation and toxicity Research on the mechanisms of toxicity of metals was extended from the study of simple unicellular organisms to investigating metal toxicity in humans. Novel methods for analysing metals in human sweat, urine and hair were developed, with particular emphasis on lead and manganese These techniques were used to study skin absorption of lead in occupationally-exposed workers and in the study of manganese toxicity in Australian aborigines from Groote Eylandt, Northern Territory Skin absorption was identified as a new route of exposure to inorganic lead in humans The ability of lead salts to enter the body through the skin without significantly raising blood lead levels has important implications for occupational health control because measurement of lead in blood is the main criterion which has previously been used to assess exposure Additional biological monitoring techniques that can detect skin-absorbed lead are now required by occupational health and safety authorities. The research described in this thesis has shown that the mechanisms of toxicity of metals is largely dependant on the chemical form of the metal. By taking into account the speciation of the metal and its mode of action within the cell, it is now possible to predict the toxicity of metals and to identify those factors which ameliorate toxicity in natural waters and biological systems, thus facilitating timely and cost-effective remediation.