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The distribution of mercury (Hg) species in soils, as affected by (i) the physicochemical and biological properties of the soils, (ii) the lithogenic vs. anthropogenic sources of soil Hg pollution, and (iii) soil–plant interactions, was investigated in a model pot experiment in which Sinapis alba (Brassicaceae) was planted. The pseudototal (aqua regia-soluble) Hg contents in soils originating from the vicinity of the former cinnabar mine varied between 16.6 and 44.7 mg/kg, whereas in soils from sites where the amalgamation technique had been used for the extraction of gold from ore-bearing materials, the pseudototal Hg values varied between 1.63 and 10.1 mg/kg. However, Hg accessibility was low, with mobilizable Hg(II) accounting for 3–11% of total soil Hg and mobilizable methylmercury (MeHg) remaining below 1%, indicating a limited bioavailable pool under the studied conditions. Mobilizable Hg(II) showed significant negative relationships with total soil carbon and cation exchange capacity (CEC), reflecting its strong association with charged functional groups of the soil sorption complex. The low Hg accessibility in the soil resulted in low Hg contents in plants, not exceeding the feed safety thresholds, with a significant proportion of Hg taken up by the plants being retained in the roots. The results of the determination of gaseous elemental mercury (GEM) indicated its relevance in soil mercury cycling, where further research on the role of plants in GEM emissions is necessary. In this context, the GEM concentrations increased in plants found in soils collected close to the former cinnabar mine. These aspects should be investigated further in future studies. Full article

The box and flux model is a mathematical tool used to describe and forecast the major and trace elements perturbations of the Earth biogeochemical cycles. This mathematical tool describes the biogeochemical cycles, using kinetics of first, second and even third order. The theory and history of the box and flux modeling are shortly revised and discussed within the framework of Jim Lovelok’s Gaia theory. The objectives of the investigation were to evaluate the natural versus anthropic load of Potentially Toxic Elements (PTEs) of the Scottish soils, investigate the soil components adsorbing and retaining the PTEs in non-mobile species, evaluate the aging factor of the anthropic PTEs and develop a model which describes the leaching of PTEs in layered soils. In the Scottish land, the soil-to-rock enrichment factorinversely correlates with the boiling point of the PTEs. The same is observed in NW Italy and USA soils, suggesting the common source of the PTEs. The residence time in soils of the measured PTEs linearly correlates with the Soil Organic Matter (SOM). The element property which mostly explains the adsorption capacity for PTEs’ is the ionic potential (IP). The downward migration rates of the PTEs inversely correlate with SOM, and in Scottish soil, they range from 0.5 to 2.0 cm·year⁻¹. Organic Bentoniteis the most important soil phase adsorbing cation bivalent PTEs. The self-remediation time of the polluted soil examined ranged from 50 to 100 years. The aging factor, the adsorption of PTEs’ into non-mobile species, and occlusion into the soil mineral lattice was not effective. The box and flux model developed, tested and validatedhere does not describe the leaching of PTEs following the typical Gaussian shape distribution of the physical diffusion models. Indeed, the mathematical model proposed is sensitive to the inhomogeneity of the layered soils. Full article