Tessa Mills

Natural and induced cadmium-accumulation in poplar and willow: implications for phytoremediation.

Potentially poplars and willows may be used for the in situ decontamination of soils polluted with Cd, such as pasturelands fertilised with Cd-rich superphosphate fertiliser. Poplar (Kawa and Argyle) and willow (Tangoio) clones were grown in soils containing a range (0.6–60.6 μg g−1 dry soil) of Cd concentrations. The willow clone accumulated significantly more Cd (9–167 μg g−1 dry matter) than the two poplar clones (6–75 μg g−1), which themselves were not significantly different. Poplar trees (Beaupré) sampled in situ from a contaminated site near the town of Auby, Northern France, were also found to accumulate significant quantities (up to 209 μg g−1) of Cd. The addition of chelating agents (0.5 and 2 g kg−1 EDTA, 0.5 g kg−1 DTPA and 0.5 g kg−1NTA) to poplar (Kawa) clones caused a temporary increase in uptake of Cd. However, two of the chelating agents (2 g kg−1 EDTA and 0.5 g kg−1 NTA) also resulted in a significant reduction in growth, as well as abscission of leaves. If the results obtained in these pot experiments can be realised in the field, then a single crop of willows could remove over 100 years worth of fertiliser-induced Cd contamination from pasturelands.

Cadmium accumulation by willow clones used for soil conservation, stock fodder, and phytoremediation

Elevated levels of cadmium are often found in the soil of New Zealand pasturelands due to the long-term use of Cd-contaminated fertilisers. The accumulation of Cd in willow biomass used as stock fodder could therefore adversely affect agricultural productivity and human health. Alternatively, willows may be used for phytoremediation of Cd-contaminated soil at polluted sites. An investigation was carried out to determine the variation in Cd as well as Zn, Mn, and Fe accumulation in 15 willow clones that had been bred for soil conservation purposes. These clones were grown under controlled conditions in 20-L pots of soil containing Cd, Zn, Mn, and Fe at concentrations of 0.3, 64, 597, and 56000 mg/kg, respectively. Daily water use was measured over the final 2 weeks of the experiment and biomass accumulation was determined at the end of the experiment. We found that shrub willows had significantly higher leaf and stem Cd, Mn, and Zn concentrations than tree willows. Average leaf Cd concentrations varied widely between clones from 1.5 to 10 mg/kg. Clones with a high Cd accumulation capacity may be selected to improve the efficacy of Cd-phytoremediation, whereas clones that accumulated lower Cd concentrations may be used for stock fodder. Metal concentrations were not significantly correlated with plant water-use, or biomass production.

Trace element accumulation by poplars and willows used for stock fodder

Abstract Poplars and willows can accumulate high concentrations of some trace elements. We investigated the extent and nature of B, Cd, Co, Cu, Fe, Mn, and Zn accumulation in some commercial poplar and willow clones by using a lysimeter experiment and field collection of data. Trace element accumulation was a function of leaf age and the variety or species of tree. Leaf B, Cd, Mn, and Zn concentrations increased throughout the season, while Cu decreased and Fe remained unchanged. Poplars and willows accumulated high concentrations of the trace elements tested, relative to pasture. The accumulation of Cd is of concern, especially in willows. Stock exposure to Cd can be managed by judicious clone selection, harvesting young shoots, or harvesting early in the season. Poplars and willows may be used as feed supplements to increase Co and Zn intake by livestock. The varieties ‘Yeogi’ and ‘Crows Nest’ accumulated the highest concentrations of Co, yet their Cd concentrations were not significantly higher than pasture.

Chapter 26 Contaminants in the rootzone: Bioavailability, uptake and transport, and their implications for remediation

Publisher Summary This chapter focuses on the mechanisms that control the bioavailability, transport, and plant uptake of both metals and inorganic contaminants in soil. Their implications for phytoremediation of contaminated sites using poplars and willows are discussed. The chapter presents the results from screening experiments that have identified a huge range in the ability of willow clones to extract cadmium from contaminated soil. Beyond these pot experiments with willow clones, the emphasis is on the entire soil–plant–atmosphere continuum so that the dynamics and ultimate fate of water and contaminants in the rootzone can be detailed. A field project and large-scale lysimeter experiments are described in the chapter, exploring the ability of poplars to both dewater and remove the boron from contaminated sawdust piles. Experiments and analyses that have determined the fate of Cu, which is mobilized from soil by ethylenediamine tetra-acetic acid (EDTA) in an effort to enhance phytoextraction, are presented in the chapter. The power of quantitative modeling for providing predictions of the fate of rootzone water and contaminants is also demonstrated in the chapter.