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

Abstract

Mentha piperita L. (Lamiaceae) 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.

Cilj ovog rada je bio analiza limita tolerancije za usvajanje Cr(III) i Cr(VI) iz zagađenog zemljišta i određivanje kapaciteta medicinske biljke Mentha piperita (L. Lamiaceae) radi kontrole unosa ovog metala. Biljke su uzgajane u plastičnim posudama, pri sobnoj temperaturi od 25 °C i održavanoj vlažnosti zemljišta na oko 80% retencionog vodenog kapaciteta. Zemljište na kome su biljke uzgajane kontaminirano je rastvorom Cr(III)-nitrata (40, 80, 120, i 200 mg kg-1) i K2Cr2O7 (2,5; 5; 10; i 15 mg kg-1). Kontrolna grupa biljaka je rasla pod istim uslovima bez dodavanja hroma. Za svaku koncentraciju hroma u zemljištu pripremane su serije uzoraka na tri nivoa kiselosti: prirodni i za po jednu jedinicu kiseliji i bazniji (pH2 6, pH1 5 and pH3 7). Uzorci biljaka su pripremani za analizu prema standardnoj proceduri i hrom je određivan metodom atomske apsorpcione spektrometrije sa grafitnom kivetom, GFAAS. Za uzorke na sva tri nivoa kiselosti izračunat je transportacioni indeks i dobijene vrednosti su u sledećim intervalima: 0,21-0,80; 0,06-1,06; 0,04-0,52. Tačnost metode (72,73-115,3 %) je potvrđena analizom hroma u uzorcima standardnih referentnih materijala (NIST SRM 8433 - Corn Bran and NIST SRM 1547 - Peach Leaves). Mobilnost hroma iz korenovog sistema u nadzemni deo biljke je diskutovana i sa aspekta kompeticije sa gvožđem i manganom za ista transportna mesta, pa su u tom smislu u uzorcima određene i koncentracije ovih metala.