Biomonitoring of environmental pollution using dielectric properties of tree leaves.

In the present work, dielectric measurements were performed in plane-tree leaves collected from a polluted urban site and a natural unpolluted one, in order to investigate the sensitivity of dielectric relaxation spectroscopy to the detection of heavy metals pollution. Although heavy metal concentrations at the urban site are not found considerable higher than those at the natural site, the two samples exhibit different features in the recorded dielectric spectra. Evaluation of experimental data suggests that the dielectric modulus (M*(omega)) representation is the most suitable for accenting the different dielectric relaxation processes of each sample. The imaginary part of dielectric modulus M''(omega) was fitted using a three-term Havriliak-Negami relaxation function, with fitting parameters, which depend on the concentrations of heavy metals. The lower frequency relaxation process is attributed to the ionic conductivity of the samples, while the two others are due to different charge transport mechanisms of alpha-response. The investigation of plane-tree leaves in terms of their dielectric properties can be considered as a promising biomonitoring for environmental pollution.

Dielectric and conductivity measurements as proxy method to monitor contamination in sandstone.

The present work investigates whether dielectric spectroscopy can be used to detect contamination, which may leach in a natural porous material, due to the spreading of contaminants. For this purpose, dielectric and conductivity measurements, in the frequency range from 10 mHz to 1 MHz, were carried out in sandstone samples, partially filled or saturated with solutions of leachates, at different concentrations. The experimental results suggest the dominant role of free water to the measured electrical conductivity and dielectric permittivity in contaminated samples with high water content. On the other hand, various relaxation mechanisms were observed in dried samples at different leachate concentrations. Experimental data were fitted using the Havriliak-Negami dielectric relaxation function, superimposed with a conductivity term. The determined parameters of the fitting function may serve to distinguish between different amounts of leachate in sandstone samples.