Fig. 8. Estimating the concentration of the native soil organic carbon (OC) that has an equivalent reactivity to Cr(VI) as tryptic soy broth (TSB). (A) Sterile soils, based on Eq. [5] and [6]. This graph indicates that the native soil contains 339 ± 88 mg kg^-1 of OC having the equivalent reactivity of TSB. (B) Nonsterile soils, based on Eq. [1] and [2]. This graph indicates that the native soil contains 332 ± 55 mg kg^-1 of OC having the equivalent reactivity of TSB.