Microanalysis and image processing of stable and radioactive elements in ecotoxicology. Current developments using SIMS microscope and electron microprobe

Abstract

Ecotoxicological investigations were performed on two sets of biological models. The first one concerns marine pollution and was composed of invertebrates (molluscs and crustaceans) contaminated by stable or radioactive elements originating from wastes discharged into sea water. The second one concerns freshwater pollution and was composed of vertebrates (fish) contaminated by aluminium which was dissolved in rivers, as a consequence of an atmospheric pollution by acid rain. Mechanisms involved in the uptake, storage and elimination processes of these toxicants were studied, with a special emphasis on cellular and subcellular aspects of concentration sites. Two microanalytical methods were employed: secondary ion mass spectrometry (SIMS), using the ion microscope and the ion microprobe, and X-ray spectrometry using the electron microprobe (EMP). SIMS, which enables the visualization of trace elements, was associated with an image processing system using a highly sensitive television camera connected to an image computer. Polychromatic images were obtained, allowing to establish the cellular distribution of metal contaminants. In marine organisms, the target organs and tissues of Al, rare earth elements (Tm and La) and radionuclides (U, Pu, Am) were shown to be mainly digestive gland and exoskeleton. The target organelles were shown to be spherocrystals and lysosomes where the enzymatic lysosomal coprecipitation with phosphorus was observed. Amoebocytes, which are enzymatically equipped with lysosomal phosphatase, were involved in the phagocytic clearance of metal pollutants. In trout, two processes appeared to be involved in Al accumulation. The first one corresponds to the well known insolubilisation of Al phosphate, within lysosomes of organs devoted to uptake and excretion such as gill and kidney. The second one demonstrates that organs and tissues which cannot eliminate, such as bone, heart and brain, retain Al, exhibiting a high intracellular metal concentration; moreover, large Al deposits inducing nervous tissue destruction have been observed. Data have been discussed in connection with the relationship between man and his environment.