LAUSR

Abstract Basic oxygen furnace slag (BOFS), a by-product of steel manufacturing, is efficient as liming material. It contains, however, trace amounts of heavy metals such as chromium (Cr). Under environmental conditions Cr exists in two stable oxidation states: +III and +VI. From those, Cr III is an essential nutrient, whereas Cr VI is highly toxic. In soils, soluble Cr III is potentially oxidized to Cr VI by manganese (hydr)oxides (MnO 2 ). We investigated the release of bioaccessible Cr III or Cr VI from BOFS to field soil. Prior to characterization of the bioaccessible, as well as less bioavailable Cr fractions, field soil was incubated with BOFS in quantities equivalent to 10 and 100 t ha − 1 (7 weeks at 22oC, moisture content at 50% of water holding capacity). Liming with BOFS elevated the acid soluble (known as semi-total) Cr but not the bioaccessible Cr III or Cr VI . In addition, potential oxidation of initially soluble Cr III (mimicking leachates of BOFS) was determined by a short-term net-oxidation test in soil suspension with 1 mM CrCl 3 (1:10 soil to solution). In field soil incubated with BOFS, the net-oxidation (oxidized Cr III –Cr VI reduced back to Cr III ) of added Cr III into Cr VI without MnO 2 was negligible. To produce highly oxidizing conditions, the test was further modified with excessive addition of synthetic Mn IV O 2 . Liming with BOFS diminished the production of Cr VI , whereas added Mn IV O 2 notably promoted oxidation of Cr III . Overall, the oxidation risk of Cr III in BOFS to Cr VI by innate soil MnO 2 can be expected to be minimal due to the low solubility of Cr III in field soil.