Soil quality and vulnerability in a Mediterranean natural ecosystem of Central Italy.

Wet and dry atmospheric depositions and soil chemical and microbiological properties were determined in a Mediterranean natural ecosystem of Central Italy near Rome (Castelporziano Estate). The monitoring of depositions permitted us to quantify the exceedances of S and N compounds (expressed as eqH(+)ha(-1)year(-1)) over the critical loads of acidity. Critical loads, i.e. the quantity of a substance which a part of the environment can tolerate without adverse effects occurring, were determined adopting the level 0 methodology following the UN/ECE Convention on Long-range Transboundary Air Pollution. Deposition data were available for the period 1992-1997, and acidity exceedances were referred to the main vegetation types present in the area. Results showed that most part of the Estate has a medium degree of vulnerability to acidification, and the corresponding risk of acidification deriving from the exceedances of atmospheric deposition was rather low. The study of soil chemical and microbiological properties included mainly total soil organic carbon (SOC), microbial biomass-C, biomass-C/SOC, soil respiration, and metabolic quotient (qCO2). Soil organic C metabolism has been discussed on the basis of the results from eight sampling sites.

Morphological and functional alterations of human erythrocytes induced by SiO2 particles: An electron microscopy and dielectric spectroscopy study.

The interaction of aerosil particles with human erythrocytes was investigated by electron microscopy methods complemented with hemolysis and radio wave dielectric spectroscopy to elucidate the extent of morphological and functional modification induced by aerosil surface. Scanning electron microscopy and freeze-fracturing techniques were used to follow morphological and ultrastructural modifications and hemolysis tests and radio wave dielectric spectroscopy to monitor the membrane damage. All experimental results indicate that there is an effect depending on both silica concentration and incubation time. Our results are in good agreement with an interaction model based on membrane protein denaturation due to the electrostatic attraction between (-SiO-) groups at the silica surface and proteins embedded in the membrane. The process is time-limited and reaches saturation after about 20 min. The extent of the damage is determined mainly by the ratio between cell and aerosil surface, that is, aerosil concentration. Limited damage is observed, especially when little aerosil surface per cell is available. Conversely, strong membrane damage is obtained when aerosil surface is considerable. In any case, due to the high surface/volume of aerosil particles used in our experiments we obtained considerable membrane damage with small weight concentrations.