David Krauth - Trace Element Biogeochemistry
San Jose City College, California
Chemical Analysis of Trace Metal Phytoextraction on the Rhode River Watershed
Phytoextraction, a type of phytoremediation, is the process in which higher plants absorb metal contaminants through their roots and eventually translocate them into their leaves/stems. It is already known that certain plant species possess the genetic potential to accumulate excessive amounts of trace metals in their above-ground systems. Such hyperaccumulating plants are often specific for a certain metal contaminant, and the idea of using these plants to remediate metal contaminated soils makes the identification of new hyperaccumulator plants increasingly more important.
The current study evaluated five herbaceous, upland plant species native to the Chesapeake region for their differing abilities to accumulate nickel (Ni), copper (Cu), cadmium (Cd), and lead (Pb) in their leaf tissues. Virginia Creeper (Parthenocissus quinquefolia), Jewel Weed (Impatiens capensis), Hay-Scented Fern (Dennstaedtia punctilobula), Sensitive Fern (Onoclea sensibilis), and Lizard Tail (Saururus cernuus) were closely analyzed for the aforementioned metals by using Inductively-Coupled Plasma Mass Spectrometer (ICP-MS).
A block design experiment which included four dominant field sites and five sub-sites within each dominant site allowed the authors to sample the selected species over a greater geographical area. Composite soil samples, corresponding to each of the five plant species, were also evaluated in order to measure any correlations between metal uptake and soil chemistry. Analysis of Variance and t-tests using Bonferroni post-hoc tests of all paired contrasts indicated significant differences between Ni uptake in Jewel Weed and Ni uptake in Hay-Scented Fern, Lizard Tail, Sensitive Fern, and Virginia Creeper. Soil data failed to show any significant correlation between the amount of Ni in the soil and subsequent plant accumulation of Ni. Jewel Weed and Lizard Tail also accumulated Cu at rates that were statistically different than Cu uptake in Hay-Scented Fern, Sensitive Fern, and Virginia Creeper. Only Jewel Weed soil data showed direct relationships for Cu, which indicates that increases in soil copper make it more bioavailable to Jewel Weed relative to the other plant species. Jewel Weed and Hay-Scented Fern also accumulated Cd at significantly higher rates when compared to Sensitive Fern, Lizard Tail, and Virginia Creeper. Although Jewel Weed, Sensitive Fern, and Hay-Scented Fern showed direct relationships between soil Cd fluxes and plant uptake of Cd, only Jewel Weed accumulated the metal at rates 100-fold to Virginia Creeper and Lizard Tail, the non-accumulators of Cd. This study’s highest accumulator of lead was Hay-Scented Fern. Significant differences were reported between lead uptake in Hay-Scented Fern and lead uptake within the other plant species.
Overall, this study’s results showed little correlation between plant accumulation and soil concentrations. Field data for the various metals also varied widely within individual field sites and across the landscape (i.e. between field sites). The significance of the current study’s results suggests that phytoextraction is site specific, plant specific, and metal specific. Impatiens capensis was the best accumulator of Ni, Cu, and Cd, while Hay-Scented Fern absorbed Pb at the highest concentrations, and it is Impatiens capensis that, by definition, appears to be a hyperaccumulator of cadmium.
Funding was provided by the National Science Foundation – Research Experience for Undergraduates