Dissertação apresentada para a obtenção do grau de doutor em Bioquímica pela Universidade Nova de Lisboa, Faculdade de Ciências e TecnologiaArsenic is a metalloid that occurs naturally in soils and is toxic to living organisms at high concentrations. The arsenic poisoning can occur indirectly (food chain) or directly through drinking water. In humans the chronic exposure to arsenic is linked to cancer, vascular diseases and skin lesions. In countries like Bangladesh the problems related to arsenic poisoning are very dramatic and has become a public health problem.
Selenium is an essential micro-nutrient to humans and it is known for its anti-cancer and anti-oxidant properties. This element is present in nature at small amounts and enters the food chain through the plants that uptake it from the soils. Although there are some references to diseases related with selenium poisoning, they are rarely documented and for this reason the effects of selenium toxicity in humans remains unknown.
Throughout its evolution, many organisms have developed strategies and mechanisms to excrete heavy metals preventing their adverse effects. In the late 90’s a study with small mammals showed that an enriched diet in selenium had decreased the arsenic toxic effects on mammals exposed to high concentrations of this metalloid. Afterwards the bio-formation of a metabolite that contained in its composition arsenic and selenium was identified. This metabolite was easily excreted by the organism which suggesting the presence of a biological mechanism for the detoxication of metals in mammals.
The present work studies the possibility to use selenium as an ecological solution to avoid/diminish the toxicity of arsenic in drinking waters, using food supplements as a selenium source. Techniques were developed with the goal of determining the total amount and speciation of selenium in biological samples and food supplements by HPLC and ET-AAS. For solid-liquid selenium extraction it was used an enzymatic digestion accelerated with ultrasonic energy. This methodology, that has reduced the extraction time from hours to minutes, was firstly reported in 2004 in the Analytical Chemistry journal and since then it has been extensively used by the scientific community. A bibliographic review has been developed in order to establish the state of the art and to enhance the divulgation of this methodology between the scientific community. To study the antagonistic effects of selenium and arsenic in biological systems, freshwater clams (C. fluminea) were exposed during 21 days to different concentrations of these elements. The determination of arsenic and selenium on the clam’s soft tissue (digestive gland and remains body) was performed by ET-AAS. For the identification of proteins by peptide mass fingerprint, a new and fast ultrasonication assisted enzymatic digestion with immobilized trypsin (on magnetic particles and glass beads) method was developedFundação para a Ciência e Tecnologia,financial suppor
