The effectiveness of four organic matter amendments for decreasing resin-extractable Cr(VI) in Cr(VI)-contaminated soils

This paper compared the effectiveness of four organic materials for decreasing the amounts of soil extractable Cr(VI) in Cr(VI)-contaminated soils using the DOWEX M4195 resin-extraction method. Organic matters were added into Cr(VI)-spiked soils [500 mg Cr(VI)(kgsoil)(-1)] in the form of sugarcane dregs compost (SCDC), cattle-dung compost (CDC), soybean meal (SBM) and rice bran (RB), in the amounts of 0, 1%, and 2% by dry weight, respectively. The results indicated that adding only 1% organic matter to the studied soils could effectively decrease the amount of soil resin-extractable Cr(VI) after 12 days of incubation. The decrease of resin-extractable Cr(VI) by organic materials was mainly the result from the reduction of Cr(VI) to Cr(III) supported by the XANES spectroscopy. Among the four tested organic materials, SBM and RB had higher effectiveness in decreasing soil resin-extractable Cr(VI) than CDC and SCDC. This result may be due to the fact that SBM and RB have more dissolved organic carbon (DOC) and protein than CDC and SCDC. Therefore, it was concluded that the contents of DOC and protein are the main factors that determine the effectiveness of organic materials for decreasing the amounts of soil available Cr(VI) in Cr(VI)-contaminated soils.