Fate and Transport of Hexavalent Chromium in Undisturbed Heterogeneous Soil

Abstract

The disposal of toxic metals [e.g., Cr(VI)] generated by the Department of Energy during the cold war era has historically involved shallow land burial in unconfined pits and trenches. The objectives of this study were to investigate the impact of coupled hydrologic and geochemical processes on the fate and transport of Cr(VI) in undisturbed soil cores obtained from a fractured, acidic inceptisol that are commonly used in the disposal of waste at the Oak Ridge National Laboratory. The mobility of Cr(VI) was significantly retarded relative to a nonreactive Br- tracer, and the mobility decreased with increased loading of the solid phase with natural organic matter (NOM). A significant portion of added Cr(VI) did not elute from the columns, and X-ray absorption near-edge structure (XANES) revealed that both Cr(VI) and Cr(III) resided on the soil mineral surfaces. The reduction of Cr(VI) to Cr(III) was dramatically more significant on soils with higher levels of surface-bound NOM. This indicated that NOM was serving as a suitable reductant during Cr(VI) transport even in the presence of potentially competing geochemical oxidation reactions involving Cr. The redox reaction was catalyzed by the presence of soil mineral surfaces, and the reduced product Cr(III) was immobilized as a tightly bound moiety. The effectiveness of surface-bound NOM to reduce toxic Cr(VI) to Cr(III) under acidic conditions has important implications regarding the design and implementation of in situ remedial strategies.

Controlling Stormwater Quality with Filter Soil—Event and Dry Weather Testing

“…Potential introduction of Cr during the construction of curb extensions is therefore something to be aware of. The retention of the applied Cr was very low and the majority of the Cr in the effluent was found as dissolved Cr, which is similar to what has been observed in laboratory column experiments [44,45]. Since the Cr added with the synthetic pulse was added as Cr(VI), no direct comparison with the stormwater data can be made.…”

Evaluation of the effects of various culture conditions on Cr(VI) reduction by Shewanella oneidensis MR‐1 in a novel high‐throughput mini‐bioreactor

“…concentrations as low as 15 µM) strongly inhibits cell growth and its own reduction. However, 15 the experiments described herein demonstrate that the aerobic chromate reduction rate can be 16 significantly improved under specific conditions. We tested MR-1's ability to reduce 50 or 100 17 µM Cr(VI) at three different growth stages (Figure 6).…”

Soil humic acids may favour the persistence of hexavalent chromium in soil

“…On the other hand, transport and reduction of Cr(VI) in soil ultimately reflects the interdependent influences of chemical, physical and microbial processes in the contaminated soil. More than three decades ago Bartlett and Kimble (1976) and recently also several other scientists (Banks et al, 2006;Jardine et al, 1999), recognised that Cr(VI) can be rapidly reduced to Cr(III) by soil organic matter. In fact, Cr(VI), being a strong oxidant, can be readily reduced to Cr(III) in the presence of various electron donors (Nakayasu et al, 1999;Palmer and Wittbrodt, 1991).…”