Heavy metal uptake by marsh plants in hydroponic solution cultures

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Abstract
Eight marsh plants were grown in chemically controlled hydroponic solutions containing three concentrations of heavy metals to evaluate the ability of each plant species to take up and accumulate heavy metals. The marsh plants studited were Cyperus esculentus, Scirpus validus, Spartina patens, Scirpus robustus, Distichiis spicata, Triglochin maritima, Spartina alterniflora, and Spartina foliosa. These species represented freshwater, brackish water, and saltwater marsh plants. An experimental hydroponic solution was developed from a modified Hoagland solution to more closely simulate natural marshland environments for the plants studied. Sodium chloride was added to the basic experimental hydroponic solution to simulate various salinities. The heavy metals studied were zinc, cadmium, nickel, lead, and chromium, each at a concentration of 0.0, 0.5, and 1.0 ppm. Marsh plants were exposed to heavy metals for six weeks and harvested. Plants were separated into tops, lower stems, rhizomes, tubers, and roots and analyzed for heavy metals to locate plant parts where heavy metals may accumulate. Exposure to heavy metals adversely affected the growth of S. validus, S. Zpatens, D. spicata, and S. alterniflora. These plant species appeared to be more sensitive to heavy metals than the other species studied. Tissue analysis for heavy metals indicated different abilities among plant species for heavy metal uptake. Those species that appeared to have more potential in taking up zinc, cadmium, and nickel were C. esculentus, S. patens, D. spicata, and, to some extent, S. alternlflora. Those plant Ispecies of lower potential appeared to be S. validus, S. robustus, T. maritima, and, to some extent, S. foliosa. Lead and chromium Accumulated in the roots of all species with very little trans‐location into plant tops. Phosphorus and iron concentrations in plant roots appeared to be correlated closely with the accumulation of zinc, nickel, lead, and chromium in the roots of all marsh plants. Phosphorus and iron content in the roots may be a major factor in determining the ability of a marsh plant to translocate heavy metals from the roots into other plant parts. Cadmium transilocation was the only heavy metal unaffected by concentrations of phosphorus and iron in the roots. The experimental hydroponic solution technique described can be used to study the relative uptake of and tolerance to heavy metals by a wide range of plants from freshwater to saline environments.