ZINC AND CADMIUM UPTAKE BY HYPERACCUMULATOR THLASPI-CAERULESCENS GROWN IN NUTRIENT SOLUTION

Phytoremediation of heavy-metal-contaminated soils can be an inexpensive means to remove hazardous metals from soil. Two metallophytes, Thlaspi caerulescens (J. & C. Presl, a Zn and Cd hyperaccumulator) from Prayon, Belgium, and a Zn-tolerant ecotype of bladder campion [Silene vulgaris (Moench.) Garcke L.] from Palmerton, PA, were compared with tomato [Lycopersicon lycopersicum (L,.) Karsten, metal intolerant] in nutrient solution to characterize Zn and Cd uptake and tolerance. Zinc and Cd were added to solutions at a 50:1 molar ratio to simulate concentrations often found on contaminated sites. Seven treatment concentrations were used, ranging (in half-log increments) from 3.16 mu M Zn + 0.063 mu M Cd to 10000 mu M Zn + 200 mu M Cd. Thlaspi caerulescens showed much greater tolerance to Zn/Cd treatments than the other species, with toxicity stress only apparent at the 10000 mu M Zn/200 mu M Cd treatment. In this treatment, shoot concentrations of Zn and Cd were 33600 and 1140 mg kg(-1), respectively. Thlaspi caerulescens was also more effective at translocating both Zn and Cd from solution to shoots. Zinc concentration in shoots of T. caerulescens was higher than the other species at all Zn/Cd treatments. Cadmium concentration in shoots of T. caerulescens were significantly higher than in bladder campion only at the 316 mu M Zn/6.32 mu M Cd treatment. This genotype of T. caerulescens may not hyperaccumulate Cd. However, extreme Zn and Cd uptake and tolerance is evident in T. caerulescens, with >25000 mg Zn kg(-1) and 1000 mg Cd kg(-1) before yield is reduced. Results suggest that T. caerulescens may be a candidate for the phytoremediation of Zn-contaminated soils.