In several European countries, TSE (Transmissible Spongiform Encephalopathies) epidemic in cattle is a major economic problem for the sustainability of breeding activities. Moreover, concern is growing for public health with the transmission of TSE to human beings by consumption of contaminated meat (new variant of the disease). The soil can be contaminated and become a potential reservoir of TSE infectivity as a result of
a) accidental dispersion from storage plants of meat and bone meal;
b) incorporation of meat and bone meal in fertilizers;
c) spreading of effluents of slaughter-houses, rendering plants and gelatin industry;
d) possible natural contamination of pasture soils by grazing herds and
e) burial of carcasses of contaminated animals.
In order to assess the risks mentioned above, a fundamental knowledge of the mechanisms involved in TSE infectivity dispersion and remanence in soil is needed. The interaction of the prion with both mineral and organic soil constituents, and its susceptibility to hydrolytic events mediated by soil microorganisms (free or associated with soil invertebrates), need to be studied, since very few information is presently available.
The ISE Institute, Section of Firenze, is involved in an UE project: "Biotic and Abiotic mechanisms of TSE infectivity Retention and Dissemination in soil". The Institute, within the Project, is the leaders in chemical and physical studies on organo and organo-mineral complexes in soils and will be in charge of study about prion entrapment in those particular soil components, highly affected by agricultural practices and biogeochemical context. In particular the main tasks are the better understanding of:
a) the mechanisms of adsorption of prions on soil mineral surfaces in order to know the most important factors affecting retention of prions in soils and possible modifications of conformation that may affect TSE infectivity. Expected achievements are a complete characterisation of the pH and ionic strength dependence of adsorption on clay minerals, with a complete study of the adsorbed protein by FTIR and NMR spectroscopies and atomic force microscopy;
b) the mechanisms of interaction and entrapment of prions with soil organic matter as organic matter is also an important constituent of soil with properties markedly different from mineral constituents. Expected achievements are a characterisation of the differences in adsorption between clays and clay-organic complexes, as well as a comparison of immobilization efficiency by organic matter entrapment.
In particular, for this kind of studies, an instrument, innovative in soil science, was realized in our laboratory, based on generation of cold oxygen plasma activated by radiofrequencies to produce a Low Temperature Ashing (LTA). It allows to progressively remove the organic matter from the mineral matrix with minimal disturbance and damage of the inorganic constituents. Since the organic matter is located at the interface of soil-mineral particles, the LTA treatment, by oxidising the organic matter layer by layer without altering or damaging the residual layers, changes only the physico-chemical surface properties of the particles related to the organic matter presence.
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