Available online at www.sciencedirect.com Environmental and Experimental Botany 62 (2008) 78–85 Phytofiltration of mercury-contaminated water: Volatilisation and plant-accumulation aspects Fabio N. Moreno a,∗ , Christopher W.N. Anderson b , Robert B. Stewart b , Brett H. Robinson c a Institute of Geosciences, University of S˜ ao Paulo, R. do Lago, 562, Cidade Universit´ aria, CEP 05508-080 S ˜ ao Paulo, SP, Brazil b Soil and Earth Sciences, Institute of Natural Resources, Massey University, Private Bag 11222, Palmerston North, New Zealand c Institute of Terrestrial Ecosystems, Swiss Federal Institute of Technology (ETH), Universit¨ atstrasse 16, CH-8092 Z¨ urich, Switzerland Received 12 July 2007; accepted 25 July 2007 Abstract Phytofiltration may be a cost-effective approach for treating Hg-contaminated wastewater. We investigated the removal of Hg from solutions by Indian mustard [Brassica juncea (L.) Czern.] grown in hydroponic conditions with solutions containing Hg concentrations from 0 to 10 mg/L. Plants were enclosed in gastight volatilisation chambers to assess the effect of Hg concentrations on plant transpiration, accumulation and volatilisation. We also determined the speciation and site of origin of volatilised Hg. Solution Hg concentrations of 5 and 10mg/L detrimentally affected transpiration. Roots concentrated Hg 100–270 times (on a dry weight basis) above initial solution concentrations. The plants translocated little Hg to the shoots, which accounted for just 0.7–2% of the total Hg in the plants. Volatilisation from planted vessels increased linearly as a function of Hg concentrations in solutions. Most Hg volatilisation occurred from the roots. Volatilised Hg was predominantly in the Hg(0) vapour form. Volatilisation was dependant on root uptake and absorption of Hg from the ambient solution. Production of Hg(0) vapour in the solutions may result from the activity of root-associated algae and Hg-resistant bacteria. Phytofiltration effectively removed up to 95% of Hg from the contaminated solutions by both volatilisation and plant accumulation. However, Hg(0) vapours released from living roots may have unforeseen environmental effects. © 2007 Elsevier B.V. All rights reserved. Keywords: Mercury; Translocation; Root absorption; Hg(0) vapour; Phytoremediation 1. Introduction Although developed nations have long banned the use of metallic mercury (Hg) for gold (Au) extraction, miners from the developing world still employ it in artisanal and small-scale gold mining (ASM) operations. In developing countries, ASM may release up to 450–800 tonnes per year of metallic Hg into the environment (Lacerda, 2003; Veiga, 2004). This figure corre- sponds to 10–20% of global Hg anthropogenic emissions. Veiga (2004) estimated that Brazil and China together contribute with as much as 300 tonnes per year of metallic Hg because of ASM. Gold extraction using metallic Hg consists of four main steps: amalgamation, separation of mineral portion, amalgam decomposition and gold melting (Veiga and Hinton, 2002). ∗ Corresponding author. Tel.: +55 11 3277 5461; fax: +55 11 3277 5461. E-mail address: fabionmoreno@terra.com.br (F.N. Moreno). Environmental contamination due to ASM mostly occurs from atmospheric deposition of emitted Hg(0) because of amalgam decomposition and gold smelting. Mercury also contaminates water bodies and soils after the discharge of water used to wash away amalgam residues (Veiga and Hinton, 2002). The amalgam residues may contain up to 450 mg/kg of residual Hg, whereas the Hg concentration in the wastewater varies from 0.5 to 3 mg of Hg per kg of suspended matter (Oliveira et al., 2004). Organic acids oxidise the metallic Hg deposited in surface soils and waters, thus forming soluble Hg(II) complexes, which may be transported to areas away from the pollution source (Veiga, 2004). Owing to the toxicity and biomagnification poten- tial of methylmercury in the food chain, Hg(II) methylation is a critical step in the Hg biogeochemical cycle. Biotic and abi- otic methylmercury pathways include enzymatic transference of CH 3 radicals from methylcobalamin to Hg(II) via sulphate- reducing bacteria (Barkay et al., 2003) and methylation in the presence of alkylated and methyl tin compounds (Cerrati et al., 0098-8472/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.envexpbot.2007.07.007