Mercury content in topsoils, and geostatistical methods to identify anthropogenic input in the Ebro basin (Spain)

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 mu g kg(-1). This was a wide range, although 90% of the values for Hg contents were estimated between 2.5 and 70 mu g kg(-1). 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.