Report of the Selenium Working Group 2022

Abstract

In Finland selenium has been added to compound fertilizers since 1984. In the background of this action were studies of the low selenium contents of domestic foods and feeds and concern about its negative effects for public health. Climatic and soil conditions increase the conversion of selenium into forms unavailable to plants and selenium fertilization is needed annually to maintain adequate selenium levels in domestic foods and feeds. During the growing season plants convert inorganic fertilizer selenium into organic selenium compounds that humans and animals can utilize more efficiently than inorganic selenium. Already in the growing season 1985 the effects of selenium supplemented fertilization were seen in domestic foods and feeds. Selenium contents increased 3–4-fold. With fertilization selenium concentrations in foods have been at adequate level to maintain the selenium adequate intake which is in accordance with recommendations. Additional selenium supplements are not needed. Selenium intake can be regulated by the amount of selenium in fertilizers (changed in 1990, 1998, 2007, 2013). Reasons behind these revisions were the changes in fertilization practises. Recent years interest towards bio-based fertilizers (BBFs) have increased due to both environmental and economic reasons. Fertilizing Products Regulation provides means for free movement of BBFs within the EU and a way to reduce EU:s dependency on imported mineral fertilizers. Due to various sources of materials for producing BBFs concentrations of selenium varies as well. However, bioavailability of selenium was poor. Changes in the selenium contents of fertilizers affect directly to the selenium intake of the population and selenium concentrations in human serum. 2010s selenium intake was about 0.08 mg/day/10 MJ and the serum selenium level 1.5 µmol/l. Both intake and serum selenium are at good and adequate level. Soluble selenium concentration in cultivated soils has remained about the same low level during the past 37 years despite annual application of selenium supplemented fertilizers. This is probably due to small annual application rates of selenium and its binding to insoluble form and thus requiring annual application to ensure adequate selenium uptake by plants. Selenium fertilization has not affected into amount of soluble selenium in cultivated soils during the 36 years of selenium fertilization. The input through fertilizers is small and during the growing season selenium is transferred into insoluble forms and binds into soil constituents. The selenium concentrations in surface waters and fishes have been at acceptable level. During floods and heavy rains soil erosion can increase selenium input somewhat, but generally selenium fertilization has not affected surface waters or any other environment. However, environmental issues should be followed regular basis.