Measurement of lead concentration in biological tissues by atomic spectroscopy techniques

Dissertation for the degree of Doctor of Philosophy in Physics

Lead is a toxic element that has no biological role. To increase the knowledge of the mean lead concentrations accumulated and excreted by the organism, a study was developed to measure lead concentrations, using different atomic spectrometry techniques, in several tissues and excretions of Wistar rats. These rats were divided in two groups: one exposed to lead since foetal period, by lead acetate in drinking water, and a control group, not exposed to lead. By collecting samples of rats with different ages it was also studied the influence of age in lead concentrations. The studied organs and excretions were: iliac bone, tibia-fibula, femur, skull, liver, kidney, urine and faeces. When conducting a study like this, the analytical techniques used the knowhow and the ability to understand the physical processes occurring are also of major relevance. In this work it was used the Energy Dispersive X-ray Fluorescence (EDXRF) technique to analyze the solid samples and the Electro Thermal Atomic Absorption Spectrometry (ETAAS) technique to analyze the urine. To carry on with the urine analysis it was developed an Ultrasound Solid-Liquid Extraction (USLE) procedure. This procedure was also applied to analyse brain samples. The Total Reflection X-ray Fluorescence (TXRF) technique was also used to study urine samples and to assess some of the results obtained with ETAAS. In this work, several correlations between the different tissues were found. A possible evidence of pre-natal exposure was verified because the samples belonging to rats with 1 month old presented much higher mean lead concentrations than the concentrations, measured in works of other authors, of rats exposed to lead but not from foetal period. Furthermore, this study seems to corroborate that lead ingestion decreases with age, once it was measured a decrease of lead excretion by faeces with age. It was observed that lead concentration in tissues depends on the type of tissue. Mean lead concentrations measured were higher in bones (iliac, femur, tibia-fibula>skull) - hundreds of ppm, then in kidney - dozens of ppm and finally in liver on the order of ppm. The urine samples had the lowest mean lead concentrations on the order of hundreds/thousands of ppb, and faeces the highest mean lead concentrations, with values of dozens of thousands of ppm. One of the main contributions of this work was to show that lead accumulation and excretion decreases with age by plateaus in all tissues except in the kidneys.

Fundação para a Ciência e Tecnologia - PhD Grant (SFRH/BD/38788/2007); European Community Fund FEDER through the COMPETE - Project No. PEstOE/FIS/UI0303/2011