Abstract
The sources of mercury (Hg) variability in agricultural soils have been evaluated using 624 soil samples that were taken in the northeast of Spain. The Hg concentration ranges were 1-717 microg/kg. This was a wide range, although 90% of the values for Hg contents were estimated between 2.5 and 70 microg/kg. Other soil parameters (the pH, organic matter, carbonates and particle size) showed little correlation with the Hg content. The anthropogenic influence was linked to specific practises, in particular the application of slurries. Maps of the spatial distribution indicated various areas with high concentration levels that are attributed to anthropogenic influences. Evidence of human activity can be seen in the Ebro delta, which reflects the accumulation of metals in the basin over many years, and on the Ebro headwaters, characterized by intense mining and smelting activities in the past. A significant portion of the increased Hg content in the Ebro valley probably comes from the deposition of anthropogenic atmospheric Hg due to emissions from industrial activities.
Highlights
No essential biological function of mercury (Hg) is known
The anthropogenic influence was linked to specific practises, in particular the application of slurries
Evidence of human activity can be seen in the Ebro delta, which reflects the accumulation of metals in the basin over many years, and on the Ebro headwaters, characterized by intense mining and smelting activities in the past
Summary
No essential biological function of mercury (Hg) is known. Worldwide Hg concentrations in soils range between 10 and 200 μg kg-1 soil (Adriano, 1986; Tack et al, 2005) or according to other studies between 10 μg kg-1 and 500 μg kg-1 (Alloway, 1995). Many natural and antropogenic processes intervene in the release of Hg into the atmosphere in form of Hg0 This can remain present in the atmosphere between 0.5 and 2 years before it is deposited in the soil (Navarro et al, 1993), which permits transport over large distances. Hg released from mining and refining activities undergoes rapid deposition, Lacerda et al (2004) showed that Hg emitted from mining sites to the atmosphere is deposited in the first 40 km from sites. Another source of Hg emissions into the atmosphere is the paper mill. The purpose of this study was to characterize the Hg topsoil concentrations in quantitative terms and to evaluate the sources of variability in the Ebro basin
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