Selenium cycling across soil - plant - atmosphere interfaces : 7 a critical review 8

Selenium (Se) is an essential element for humans and animals, which 28 occurs ubiquitously in the environment. It is present in trace amounts in both 29 organic and inorganic forms in marine and freshwater systems, soils, biomass and 30 in the atmosphere. Low Se levels in certain terrestrial environments have resulted 31 in Se deficiency in humans, while elevated Se levels in waters and soils can be 32 toxic and result in the death of aquatic wildlife and other animals. Human dietary 33 Se intake is largely governed by Se concentrations in plants, which are controlled 34 by root uptake of Se as a function of soil Se concentrations, speciation and 35 bioavailability. In contrast, biomethylation by plants and microorganisms can 36 result in a loss of Se to the atmosphere. The mobilization of Se across soil-plant37 OPEN ACCESS