Interactions Between Environmental Selenium and Sulphoxy Radicals

Chemical interactions between sulphoxy radical anions and elemental Se were investigated to show the influence of SO₂ pollution on the atmospheric fate of selenium. Laboratory experiments were performed with elemental Se plates or fine powder exposed to sulphoxy radicals formed in situ during the autoxidation of SO₂ dissolved in water. Impacts of the radicals were followed examining the topographic surface changes of Se (atomic force microscopy, AFM) and measuring the S(IV) autoxidation rate, essentially decreased in the presence of Se (conductometry). The experiments showed that remobilization of water insoluble selenium (elemental Se) may take place not only in atmosphere (cloud waters), but also in surface waters, soil and sediments contacting with SO₂ polluted air. By scavenging radicals, selenium causes the retardation of the S(IV) autoxidation to sulphuric acid (acid rain), thus contributing to long-distance transport of unreacted S(IV). The more general problem of sulphoxy radical-induced atmospheric corrosion has been brought forward into consideration, as the radicals appear capable to damage diverse solid surfaces.