Selenium behavior in the soil environment and its implication for human health

Selenium (Se) is an important element that was discovered in 1817, and since the 1960s, it has been regarded as an essential micronutrient for both animals and humans, playing among other functions a relevant role in the antioxidant system of mammals. Inadequate blood Se levels in the human body is a well-known concern in many parts of the world. This malnutrition problem is often due to Se-poor diet, probably as a result of the low Se availability in soils where crops are growing. Nowadays, it is known that not only the total content, but also the inorganic and organic forms of Se contained in foods are important for human nutrition. However, paradoxically some regions of the world present high Se levels in soils causing several functional disorders and diseases in people who live in seleniferous areas. As essential micronutrient, Se should be supplied in controlled amounts to avoid harmful effects. Therefore, taking into account the importance of the soils as a way to ensure the adequate Se supply for the population, this review has dealt with Se behavior in soil environment (e.g., Se forms and adsorption and desorption reactions) and its relevance for the human health. As a final message, the further understanding of Se behavior in soils to predict its availability for crops in different systems will be a significant approach in future studies to establish forms and safe doses of Se to be added in fertilizers. Agronomic and genetic biofortification of staple crops with Se has been suggested as an important tool to improve Se intake by population in Se-poor sites.