Metallobiochemistry of heavy metal pollution: nuclear and radiochemical techniques for long term--low level exposure (LLE) experiments.

The chronic exposure of man to increasing amounts of heavy metals as a consequence of environmental pollution, requires accurate knowledge of how much the homeostatic control of trace elements can stand increased exposure to abnormal amounts of metal pollutants without alteration of the biochemical functions. This topic includes the study of the accumulation of metal pollutants in the body with the identification of metal biocomplexes under long term-low level exposure (LLE) conditions. Extremely sensitive analytical techniques are required for experimentation at the heavy metal levels which are typical of a polluted environment in order to assess the limits of physiological homeostatic controls. The possiblity of applying nuclear and radiochemical techniques, such as neutron activation analysis, multiple tracing, high resolution gamma-ray spectrometry and Cerenkov counting, coupled with biochemical techniques, such as gel filtration, ion-exchange chromatography, polyacrylamide gel electrophoresis and differential centrifugation, has been demonstrated in various typical applications in metallobiochemistry. The subject of the first part of this paper is the development and improvement of the techniques, dealing with potential metal binding components, such as metalloenzymes and nucleic acids chosen as models. The developments refer to: preparation of labelled metal pollutants with very high specific activity to label in vivo nanogram or subnanogram amounts of pollutant metals; neutron activation analysis of enzymes and nucleic acids with the aim of analyzing concentrations of many metal pollutants in the identified metal binding components of the microsamples; radiochemical methods including radiobiochemical techniques for multielement tracer experiments and for studying the interaction of heavy metas and metal binding components; development of complementary counting techniques. The in vivo applications are centered on biochemical studies on cadmium, in particular on the long term-low exposure experiment, which is under investigation at present, with the identification of both critical organs of accumulation and of the cadmium binding components. Results are given for biochemical mechanisms involving cadmium such as the stimulation of the "de novo" biosynthesis of rat liver and intestine cadmium binding proteins (CdBP) and on the systematic study of the interaction of metal pollutants and rat liver cadmium binding proteins itself. Preliminary data are also given for short term experiments dealing with the identification of cellular metal binding components for V, Se, Cd and Pb.