Poplar for the phytomanagement of boron contaminated sites B.H. Robinson a, * , S.R. Green b , B. Chancerel b , T.M. Mills b , B.E. Clothier b a Institute of Terrestrial Ecosystems, Swiss Federal Institute of Technology (ETH), Universita ¨tstrasse 16, CH-8092 Zu ¨ rich, Switzerland b HortResearch, Private Bag 11030, Palmerston North, New Zealand Received 27 November 2006; received in revised form 12 January 2007; accepted 20 January 2007 Poplars reduce boron leaching from contaminated sites. Abstract Boron (B) is a widespread environmental contaminant that is mobile relative to other trace elements. We investigated the potential of hybrid poplar (Populus sp.) for B phytomanagement using a lysimeter experiment and a field trial on B-contaminated wood-waste. In both studies, poplars enhanced evapotranspiration from the wood-waste, reduced B leaching, and accumulated B in the aerial portions of the tree. When grown in a substrate containing 30 mg/kg B, poplar leaves had an average B concentration of 845 mg/kg, while the stems contained 21 mg/kg B. Leaf B concentrations increased linearly with leaf age. A decomposition experiment revealed that abscised leaves released 14% of their B during the winter months. Fertiliser application enhanced tree growth without decreasing the leaf B concentrations. Harvesting alter- nate rows of trees on a contaminated site would reduce leaching from the site while removing B. Harvested plant material may provide bioen- ergy, stock fodder, or an amendment for B-deficient soils. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Phyto-DSS; Phytoremediation; Boron; Biofuel 1. Introduction Phytomanagement is the use of vegetation/soil amendment systems to reduce the environmental risk posed by contami- nated sites (Ba~ nuelos, 1995). Poplars are often planted to reduce the water flux through contaminated sites because of their ease of propagation, rapid establishment, deep roots, and ability to coppice (Mills and Robinson, 2003). Poplars thrive in a wide range of soil and cli- matic conditions (McGee et al., 1981). Ba~ nuelos et al. (1999) reported that when irrigated with water containing 3 mg/L B, some poplar clones accumulated up to 543 mg/kg of B in their aerial tissues. Subsequently, we found that when grown in soil containing just 40 mg/kg B, poplars accumulated up to 1200 mg/kg in the leaves, some 20 times more than other spe- cies grown in the same environment (Robinson et al., 2003a). The high evapotranspiration of poplars combined with their high B uptake may reduce the environmental risk arising from B-contaminated sites. Poplars may reduce B leaching into ground and surface waters by returning rainfall to the atmo- sphere via evapotranspiration and by binding B in the plant tissue. Harvesting the trees would remove B from the site (Robinson et al., 2003a). 1.1. Boron as an environmental contaminant Boron (B) generally occurs only in small concentrations in soils, but has a disproportionately large impact on plants, both as an essential element and as a toxin. High levels of B occur naturally in soils in arid areas. Boron contamination results from a wide range of anthro- pogenic activities. Although most B (76%) is used in the man- ufacture of glass (Parks and Edwards, 2005), B in borosilicate * Corresponding author. E-mail addresses: brett.robinson@env.ethz.ch (B.H. Robinson), bclothier@ hortresearch.co.nz (B.E. Clothier). 0269-7491/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.envpol.2007.01.017 Environmental Pollution 150 (2007) 225e233 www.elsevier.com/locate/envpol