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Phytoremediation of heavy‐metal‐contaminated soils can be an inexpensive means to remove hazardous metals from soil. Two metallophytes, Thlaspi caerulescents (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 µM Zn + 0.063 µM Cd to 10000 µM Zn + 200 µM Cd. Thlaspi caerulescens showed much greater tolerance to Zn/Cd treatments than the other species, with toxicity stress only apparent at the 10000 µM Zn/200 µM 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 µM Zn/6.32 µM 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 Zncontaminated soils.

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Metal‐tolerant hyperaccumulator plants may be useful to phytoremediate contaminated soils. To evaluate agronomic management practices to maximize phytoremediation, two metallophytes, Thlaspi caerulescens J. and C. Presl (Zn hyperaccumulator) and bladder campion [Silene vulgaris (Moench) Garcke L.] (an indicator) were compared to ‘Rutgers’ tomato (Lycopersicon esculentum L.) in a pot study to assess Zn and Cd uptake patterns in relation to soil pH. Soils used for the study were gathered at three different sites in the vicinity of an old Zn smelter in Palmerton, PA, and contained 48 000, 4100, and 2100 mg kg−1 Zn and 1020, 37.4, and 35.2 mg kg−1 Cd, respectively. Each soil was adjusted to three pH levels ranging from 5.06 to 7.04. Thlaspi caerulescens showed much greater tolerance to the metals than the other plants (up to 18 455 mg kg−1 Zn and 1020 mg kg−1 Cd dry shoots without yield reduction) with metal stress apparent only in the low pH treatments of the two most contaminated soils. In all treatments except for the farm Soil (least contaminated) at pH 5.06, T. caerulescens had higher concentrations of both Zn and Cd than bladder campion and tomato. Thlaspi caerulescens was also more effective at translocating both Zn and Cd from soil to plant shoots. A variety of soil extractions were used to evaluate the correlation of shoot metal concentrations with quantitative measures of “available” soil metals. Concentrations of Cd measured in several common extractants (DTPA, water, 0.01 M Ca(NO3)2, and 1.0 M NH4NO3) were significantly correlated with Cd concentrations in tissue of each plant. Shoot Zn concentrations of bladder campion and tomato were significantly correlated with Zn extracted by the neutral salt extractants for all soils. For T. caerulescens, the neutral salt extractable Zn was significantly correlated with shoot Zn only in the two more contaminated soils. No extractant predicted shoot Zn concentration for T. caerulescens in the least contaminated soil.

No abstract

Abstract. High metal waste materials from the Bunker Hill, ID Superfund site are being collected in a central impoundment area. The waste materials have elevated metal concentrations with total Zn, Pb and Cd ranging from 6,000 -14,700, 2100 -4900, and 9 -28 mg kg' 1 , respectively. They also contained minimal amounts of organic matter. In June, 1997 different mixtures of biosolids, wood ash and logyard debris were surface applied to determine if these materials would enable vegetative cover to be established directly on the surface of the waste material. Surface application ofbiosolids in combination with other residuals was able to restore a vegetative cover to the metal contaminated materials for three years following amendment application. Plant biomass in 1999 was 0.01 Mg ha 1 in the control vs 3.4 Mg ha 1 in amended plots. Metal concentrations of the vegetation indicate that plants were within normal concentrations for the 3 years that data was collected. Zinc concentrations in plant tissue in the amended areas was all below 90 mg kg·' for the 1999 growing season. Surface application of amendments was also able to reduce CaN0 3 extractable Zn in the subsoil from 159 in the control to 10 mg kg' 1 • These results indicate that surface application of biosolids and wood ash +/-Iogyard debris are sufficient to restore a vegetative cover to high metal materials for up to 3 years following application.

Two metal tolerant plants, Thlaspi caerulescens J. and C. Presl. (hyperaccumulator), and Silene vulgaris L. (indicator) were grown with "Paris Island Cos" Romaine lettuce (Lactuca sativa var. longifolia) on longterm sewage sludge plots. Metal uptake patterns by plants in relation to total soil metal and soil pH were examined. The 2-year study used four treatments and two pH levels. Zinc and Cd uptake were measured. Zinc and Cd for Silene and lettuce were as expected with increasing plant concentration in the more contaminated treatments and lower pH levels. Thlaspi followed the same pattern for Cd but not for Zn. Concentrations of Cd were not significantly different between Thlaspi and the other plants. Zinc concentrations in Thlaspi(2000 and 4000 mg kg-1) were 10-fold greater than in Silene. They showed no relation to available soil Zn. Although Thlaspi appears to hyperaccumulate Zn on mildly contaminated soils, Cd uptake follows predictable patterns.

To manage biosolids in a sustainable manner, there is a need for further research in the following areas: achieving a higher degree of public understanding and acceptance for the beneficial use of biosolids, developing cost-efficient and effective thermal conversions for direct energy recovery from biosolids, advancing technology for phosphorus recovery, and selecting or breeding crops for efficient biofuel production.