The impact of selenium fertilisation on the distribution of selenium in rivers in Finland

Abstract

Finland is a country covered by thin layers of glacial deposits, mainly till, on top of Precambrian igneous and metamorphic rocks. The environment is characterised by low selenium (Se) concentrations. To improve the Se intake of the population, Se-supplemented fertilisers have been used nationwide since 1985. This raises the possibility of undesirable environmental effects of the operation. The present study, the first one dealing with Se concentration of stream waters and stream sediments in Finland, throws light on the mobilisation of Se in the environment. The median Se concentrations (range) in stream waters and stream sediments were 67.5 ng 1 −1 (32–180 ng 1 −1) and 258 μg kg −1 (29–3940 μg kg −1), respectively. There was a highly significant correlation between the Se concentration of stream waters and sediments ( r=0.313, P<0.001, n=204). The rainfall-related seasonal variations of the Se concentrations in stream water exceeded 100%. The stream water Se concentrations decreased from 1991 to 1992, possibly as the result of a reduction in the amount of Se added to fertilisers since 1991. The stream water Se concentrations correlated with those in well water and with cultivated field area per community. About 8.5% of the Se in stream waters was in particulate form. The fractions of the total Se in humic substances (36%) and selenate (35.7%) dominated the Se species of stream waters, while selenite comprised only 9.6% of the total Se. Cultivation and the use of Se-supplemented fertilisers may have temporarily increased the Se concentrations in headwater stream and river waters in Finland.