Riparian vegetation role in mercury uptake (Valdeazogues River, Almadén, Spain)

• Hg accumulation in two macrophytes and three riparian shrubs from Almadén
• Low Hg accumulation in aerial part of studied species
• The studied macrophytes had higher values of Hg in aerial part than riparian shrubs
• High Hg concentration in roots of the studied macrophytes
• The studied macrophytes are better candidates to be used in phytoremediation

The aim of the present study is to improve the knowledge on the role of riparian vegetation in Hg removal along Valdeazogues River that is located within the old mercury mining district of Almadén (Ciudad Real, Spain). In this framework, the accumulation of Hg in the aerial part of five different riparian plant species (three riparian shrubs: Flueggea tinctoria (L.) G.L. Webster, Tamarix canariensis Willd. and Nerium oleander L., and two macrophytes: Typha domingensis Pers. and Phragmites australis Cav.) grown in the same river site was studied, and their ability to accumulate Hg under natural conditions was compared between them. Furthermore, one macrophyte (T. domingensis) and one shrub (F. tinctoria) were chosen to study and compare their behavior dealing with Hg in several river sites affected by different degrees of Hg contamination.Generally, the studied macrophytes had higher values of Hg concentration in the aerial part (up to 1.1 mg kg− 1) than the riparian shrubs (up to 0.4 mg kg− 1). Hg accumulation in the studied plants along the river had a positive correlation with the total Hg in soils and sediments. Furthermore, T. domingensis was more efficient than F. tinctoria in Hg uptake and its accumulation in the aerial part when there was a low concentration of easily available Hg for plants in soils and sediments. In summary and taking into account the transfer factor values, Hg accumulation in the aerial part and the possibility of harvesting the subterranean part of macrophyte species, the results show that the studied macrophytes are better candidates than the studied shrubs to be used in phytoremediation.