Selenium distribution in topsoils and plants of a semi-arid Mediterranean environment.

Selenium was determined from 25 topsoils and 25 plants in the semi-arid Central Spain where large extents of soils are developed on evaporitic materials. Some species of vegetation associated with them are of the genera Astragalus, Salsola, Mercurialis, Phlomis, Thymus and Atriplex. Total selenium in soils was determined and its bioavailability assessed by chemical sequential fractionation. Se content in soils was adequate (in the range 0.17-0.39 mg kg(-1)) or large (in the range 0.50-4.38 mg kg(-1)) and appeared in highly and/or potentially available forms. Several plant species showed high Se levels (in the range 5-14.3 mg kg(-1)), which can be a potential risk of toxicity to animals. Data obtained from the study area can be used as a guide to the range of values in soils and plants of the European Mediterranean area that are relatively unpolluted from industrial sources, allowing comparison with more polluted areas.