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An experimental technique based on image analysis was used to perform a Lagrangian description of passive pollutant particle motion in a three-dimensional saturated porous medium. To allow for optical access, the experiment was carried out with Pyrex grains as the solid matrix and glycerol as the liquid phase in order to have two phases with the same refractive index. Statistical analysis of the experimental data allowed for estimation of velocity and displacement probability density functions (pdf), velocity component correlation functions, Lagrangian integral scales, and mechanical dispersion coefficient tensor components. The results obtained suggest that the longitudinal velocity component has a log normal pdf while the transversal component has a symmetrical pdf, which is nevertheless not Gaussian for high values of the kurtosis. Furthermore, the velocity components' autocorrelation functions are well represented by exponential laws, and the integral scale is dependent on filtration velocity and grain size. As foreseen in the theory the total displacement pdf shows the tendency to reach normal distribution after many integral scales. The evaluated dispersion coefficient tensor components are dependent on travel time; the components start from zero and reach an asymptotic value after several integral scales. Furthermore, the tensor is anisotropic, with the longitudinal component greater than the transversal one by about 1 order of magnitude. Comparison with other experimental data shows agreement at least for the longitudinal dispersion component. Dagan's linear theory has been used for comparing the analytical longitudinal component of the dispersion tensor with that obtained by means of the experiments. [Bear, 1969[Bear, , 1972; Koch and Brady, 1985; Charlaix et al., 1987; Koch and Brady, 1987]. Comprehension of the phenomena at the microscopic level can furnish a valid aid in analyzing the process on a larger scale. Consequently, detailed analysis of the processes occurring when fluids flow inside the media is required. The approach should allow for determination of velocity field statistical parameters, which play an extremely important role in the Paper number 96WR00605. 0043-1397/96/96WR-00605 $09.00 dispersion process, and the influence that the various parameters involved have on the phenomenon. Both experimental and theoretical studies have been carried out on the "hydrodynamic dispersion coefficient" [Bear, 1972; Bear and l/errujit, 1987; Dagan, 1982, 1984, 1989] and the "mechanical dispersion coefficient" [Eidsath et al., 1983; Koch and Brady, 1985; Brady and Koch, 1988]. During experimental measurement of the longitudinal (i.e., parallel to the average motion direction) dispersion coefficient in the laboratory, its dependence on the Peclet number [Carberry and Bretton, 1958; Ebach and White, 1958; Neung-Won et al., 1985; Charlaix et al., 1987, 1988] and on filtration velocity [Rumer, 1962; Harleman and Rumer, 1963; Harleman et al., 1963; Carberry and Bretton, 1958; Ebach and White, 1958] have been...

Abstract:Glyphosate is a synthesis product and chemical substance that entered in the global market during the 70s. In the beginning, the molecule was used as an active principle in a wide range of herbicides, with great success. This was mainly due to its systemic and non-selective action against vegetable organisms and also to the spread of Genetically Modified Organism (GMO) crops, which over the years were specifically created with a resistance to glyphosate. To date, the product is, for these reasons, the most sprayed and most used herbicide in the world. Because of its widespread diffusion into the environment, it was not long before glyphosate found itself at the center of an important scientific debate about its adverse effects on health and environment. In fact, in 2015 the IARC (International Agency for Research on Cancer, Lyon, France), an organization referred to as the specialized cancer agency of the World Health Organization (WHO, Geneva, Switzerland), classified the substance as "likely carcinogenic" to humans. This triggered an immediate and negative reaction from the producer, who accused the Agency and claimed that they had failed to carry out their studies properly and that these conclusions were largely contradictory to published research. Additionally, in 2015, just a few months after the IARC monography published on glyphosate, the EFSA (European Food Safety Authority, Parma, Italy), another WHO related organization, declared that it was "unlikely" that the molecule could be carcinogenic to humans or that it could cause any type of risk to human health. The conflict between the two organizations of the World Health Organization triggered many doubts, and for this reason, a series of independent studies were launched to better understand what glyphosate's danger to humans and the environment really was. The results have brought to light how massive use of the herbicide has created over time a real global contamination that has not only affected the soil, surface and groundwater as well as the atmosphere, but even food and commonly used objects, such as diapers, medical gauze, and absorbent for female intimate hygiene. How human health is compromised as a result of glyphosate exposure is a topic that is still very debatable and still unclear and unambiguous. This paper is a review of the results of the main independent recent scientific studies.

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