Plant and Soil 227: 301–306, 2000. © 2000 Kluwer Academic Publishers. Printed in the Netherlands. 301 Natural and induced cadmium-accumulation in poplar and willow: Implications for phytoremediation Brett H. Robinson 1,3 , Tessa M. Mills 1 , Daniel Petit 2 , Lindsay E. Fung 1 , Steve R. Green 1 & Brent E. Clothier 1 1 Horticulture and Food Research Institute of New Zealand, Palmerston North, New Zealand. 2 Laboratoire de G´ en´ etique et Evoloution des Plantes, CNRS, Universit´ e de Lille 1, Villeneuve d’Ascq, 59655 France. 3 Corresponding author ∗ Received 30 December 1999. Accepted in revised form 23 August 2000 Key words: bioaccumulation coefficient, cadmium, phytoremediation, poplar, willow Abstract 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 μgg −1 dry soil) of Cd concentrations. The willow clone accumulated significantly more Cd (9–167 μgg −1 dry matter) than the two poplar clones (6–75 μgg −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 μgg −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 −1 NTA) 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. Introduction Elevated Cd concentrations in soils are of concern be- cause of their risks to human health and the productiv- ity of plants and animals (Underwood and Suttle, 1999). They could even be used as a non-tariff trade barrier to exports. Many years of fertilisation with Cd- rich superphosphate has increased concentrations of Cd in New Zealand soils, in some cases to levels above a self-imposed limit of 3 μgg −1 in dry soil (Zanders, 1998). Conventional treatments for Cd-contaminated soils fall into three general categories: Isolation, cleansing and ‘inerting’. Isolation may involve removal of the topsoil, covering with concrete or non-contaminated soil, or hydraulic isolation from surrounding areas. Cleansing involves the leaching of pollutants with ∗ FAX No: +64(6) 3546731. E-mail: brobinson@hort.cri.nz acids. ‘Inerting’ is the addition of other chemicals to the soil that render the pollutants into a non- toxic form. Conventional procedures cost between US$ 100 000 and 1 000 000 per hectare (Russel et al., 1991). Furthermore, these methods may leave the soil infertile, cause further pollution by leaching or only be a temporary solution. Chaney (1983) suggested that some heavy-metal contaminated soils may be cleaned up by growing a crop of plants which accumulate the pollutants, then harvesting the plants and disposing of them in a ‘safe area’. This process was termed phytoremediation. The first feasibility experiments using ‘hyperaccumulator’ plants (see below) were conducted by McGrath et al. (1993), although Huiyi et al. (1991) had already shown that some forest species, including poplar, could be used to remove Cd from polluted soils. The cost of these operations is estimated to be US$ 60 000 to 100 000 per hectare (Salt et al., 1995) considerably