CHROMIUM ACCUMULATION, TRANSLOCATION AND CHEMICAL SPECIATION IN VEGETABLE CROPS

Trivalent chromium (Cr3+) is essential for animal and human health, wh ereas hexavalent Cr (CrO42-) is a potent carcinogen and extremely toxi c to animals and humans. Thus, the accumulated Cr in food plants may r epresent potential health hazards to animals and humans if the element is accumulated in the hexavalent form or in high concentrations. This study was conducted to determine the extent to which various vegetabl e crops absorb and accumulate Cr3+ and CrO42- into roots and shoots an d to ascertain the different chemical forms of Cr in these tissues. Tw o greenhouse hydroponic experiments were performed using a recirculati ng-nutrient culture technique that allowed all plants to be equally su pplied with Cr at all times. In the first experiment, 1 mg L-1 Cr was supplied to 11 vegetable plant species as Cr3+ or CrO42-, and the accu mulation of Cr in roots and shoots was compared. The crops tested incl uded cabbage (Brassica oleracea L. var. capitata L.), cauliflower (Bra ssica oleracea L. var. botrytis L.), celery (Apium graveolens L. var. dulce (Mill.) Pers.), chive (Allium schoenoprasum L.), collard (Brassi ca oleracea L. var, acephala DC.), garden pea (Pisum sativum L.), kale (Brassica oleracea L. var. acephala DC.), lettuce (Lactuca sativa L.) , onion (Allium cepa L.), spinach (Spinacia oleracea L.), and strawber ry (Fragaria x ananassa Duch.). In the second experiment, X-ray absorp tion spectroscopy (XAS) analysis on Cr in plant tissues was performed in roots and shoots of various vegetable plants treated with CrO42- at either 2 mg Cr L-1 for 7 d or 10 mg Cr L-1 for 2, 4 or 7 d. The crops used in this experiment included beet (Beta vulgaris L. var, crassa ( Alef.) J. Helm), broccoli (Brassica oleracea L. var. Italica Plenck), cantaloupe (Cucumis melo L. gp. Cantalupensis), cucumber (Cucumis sati vus L.), lettuce, radish (Raphanus sativus L.), spinach, tomato (Lycop ersicon lycopersicum (L.) Karsten), and turnip (Brassica npn L. var, r apifera Bailey). The XAS speciation analysis indicates that CrO42- is converted in the root to Cr3+ by all plants tested. Translocation of b oth Cr forms from roots to shoots was extremely limited and accumulati on of Cr by roots was 100-fold higher than that by shoots, regardless of the Cr species supplied. Highest Cr concentrations were detected in members of the Brassicaceae family such as cauliflower, kale, and cab bage. Based on our observations and previous findings by other researc hers, a hypothesis for the differential accumulation and identical tra nslocation patterns of the two Cr ions is proposed.