Determination of chromium in Mentha piperita L. and soil by graphite furnace atomic absorption spectrometry after sequential extraction and microwave-assisted acid digestion to assess potential bioavailability

Abstract

Analysis of chromium in Mentha piperita and the soil where it is cultivated was done. The capacity of soil for chromium immobilization and the capacity of M. piperita L., to control its uptake were analyzed by spiking the soil with standard solutions of Cr(III). For each concentration three acidity levels: natural. one unit below and one above its natural acidity (pH(2) = 6, pH(1) = 5 and pH(3) = 7) were tested. Three-stage sequential extraction was performed (I stage: I M ammonium-acetate, II stage: 0.1 M hydroxylamine-chlorohydrate and III stage: 0.2/0.2 M oxalic acid/ammonium-oxalate mixture). The chromium content in the extracts was obtained after the measurements by GFAAS. The results (expressed in mg L(-1)), at pH(1), pH(2) and pH(3), respectively, were as follows: I stage: 4.64-10.93, 0.79-5.78 and 0.26-5.26; II stage: 1.14-15.99, 0.76-20.31 and 0.67-20.64: III stage: 0.67-20.64, 19.17-100.76 and 19.17-116.05. A high potential of the soil for chromium immobilization was observed. In parallel, soil and plant samples were prepared by microwave-assisted acid digestion for total chromium determination. By analysis of SRMs (NIST SRM 2711 - Montana II Soil, NIST SRM 8433 - Corn Bran and NIST SRM 1547 - Peach Leaves) good recoveries (72.7-115.3%) were obtained. Additionally, iron and manganese oxides and hydroxides were recognized as matrix components of special importance for mobility of chromium species within a soil structures so, the determination of Mn and Fe was done too.