Trace and major element associations in basaltic ash soils of El Hierro Island

Abstract

Associations between major and trace elements (aqua regia) were studied in basaltic-ash soils from the island of El Hierro in order to distinguish possible non-lithological contributions to the large trace element concentration shown by the soils. Soil composition reflected the basaltic composition of the parent materials and their extended tendencies to ultrabasic and trachytic compositions. The obtained values did not differ from previously reported reference values for natural soils, pointing to a low intensity anthropic activity. Only Cd levels were above those predicted by parent materials. The large soil total phosphorus (P) concentrations were consistent with those reported for the parent materials, thus obscuring the hypothesis of the contribution of the phosphate-rich Saharan dust to soil Cd enrichment. The spatial distribution of trace and major elements helped to identify a larger concentration of trace elements in soils of the most humid zones where andic properties were more highly expressed. Anthropic influence was revealed by the association of P and Cd in a former intensive agricultural zone. The large metal concentrations could reach or exceed the Soil Quality Standards for heavy metal concentrations in relation to soil pH. Plant composition, however, did not approach hazardous levels, probably due to the effect of the organic and highly reactive mineral sorbing phases of the studied soil types. (C) 2014 Elsevier B.V. All rights reserved.