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

Phytoremediation of heavy-metal-contaminated soils can be an inexpensi ve means to remove hazardous metals from soil. Two metallophytes, Thla spi caerulescens (J. & C. Presl, a Zn and Cd hyperaccumulator) from Pr ayon, Belgium, and a Zn-tolerant ecotype of bladder campion [Silene vu lgaris (Moench.) Garcke L.] from Palmerton, PA, were compared with tom ato [Lycopersicon lycopersicum (L,.) Karsten, metal intolerant] in nut rient solution to characterize Zn and Cd uptake and tolerance. Zinc an d Cd were added to solutions at a 50:1 molar ratio to simulate concent rations often found on contaminated sites. Seven treatment concentrati ons 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 showe d much greater tolerance to Zn/Cd treatments than the other species, w ith toxicity stress only apparent at the 10000 mu M Zn/200 mu M Cd tre atment. In this treatment, shoot concentrations of Zn and Cd were 3360 0 and 1140 mg kg(-1), respectively. Thlaspi caerulescens was also more effective at translocating both Zn and Cd from solution to shoots. Zi nc concentration in shoots of T. caerulescens was higher than the othe r 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. caerul escens may not hyperaccumulate Cd. However, extreme Zn and Cd uptake a nd tolerance is evident in T. caerulescens, with >25000 mg Zn kg(-1) a nd 1000 mg Cd kg(-1) before yield is reduced. Results suggest that T. caerulescens may be a candidate for the phytoremediation of Zn-contami nated soils.