Behavior of mercury in the Valdeazogues riverbank soil and transfer to Nerium oleander L.

The Almadén mining district (Spain) is a singular case of natural mercury concentration in the World. The intensive mining activities during the last two thousand years have caused a dispersion and remobilization of mercury within the area. This has generated interactions between soil and mercury as well as the incorporation of this trace element into living organisms of the area. As mercury is a global pollutant, well known for its toxicological and harmful effects, it is necessary to gather more knowledge about the environmental behavior of this metal. In this framework, the study is focused on the mercury behavior in soil from the banks of the Valdeazogues River, the main water course traversing the Almadén mining district, and to evaluate the mercury transfer to Nerium oleander shrubs that grow on the riverbanks.The results show that total Hg concentrations in soil range from 116.7 ± 24.3 to 245.5 ± 59.6 mg kg− 1 of Hg, with peak concentrations reaching 350.9 ± 68.6 mg kg− 1. However, using a six-step Sequential Extraction Procedure, it could be determined that the available Hg concentration is a smaller percentage than 0.16% of the total Hg measured in the samples, while the metal is associated with the more resistant soil fractions: crystalline Fe–Mn oxyhydroxides, organic matter absorbed and final residue. Regarding Hg absorption by N. oleander L., results show that the distribution of Hg in the plant is not homogeneous in the aerial part. Values are significantly higher in the leaves, followed by stems and fruits.

► Mercury behavior in riverbank soils in Almadén mining district.
► Differences between mercury, lead and zinc in SEP fractions.
► Influence of soil parameters on mercury transfer to N. oleander L. shrubs.
► Distribution of mercury throughout stems, leaves and fruits of N. oleander L.