Analysis of the bioavailability of Cr(III) and Cr(VI) based on the determination of chromium in Mentha piperita by graphite furnace atomic absorption spectrometry

Mentha piperita L. (Lamiace) was cultivated under the controlled laboratory conditions in the presence of varying levels of trivalent and hexavalent chromium in order to determine its capacity to control chromium uptake and its tolerance limit. The plants were grown in pots at 25?C with controlled soil moisture (about 80 % of the water retention capacity). The soil was treated with increasing concentrations of Cr(NO3)3 (40, 80, 120, and 200 mg kg-1) and K2Cr2O7 (2.5, 5, 10, and 15 mg kg-1). A control group of plants was grown without the addition of chromium to the soil. For each concentration, three acidity levels were tested: natural, one pH unit below and one above the natural acidity of the soil (pH2 = 6, pH1 = 5 and pH3 = 7). The plant samples were digested according to the standard procedure and chromium content was determined by GFAAS. For all plants, the transportation index was calculated and the results (expressed in mg kg-1) at pH1, pH2 and pH3, respectively, were: 0.21-0.80, 0.06-1.06 and 0.04-0.52. The recoveries were good (72.73-115.3 %) as evidenced by the analysis of certified reference materials (NIST SRM 8433 - Corn Bran and NIST SRM 1547 - Peach Leaves). The mobility of chromium through the plants tissues is discussed in regard to its competition with iron and manganese for transport binding sites; hence Mn and Fe were also determined.