Technical Note Citric acid-assisted phytoextraction of lead: A field experiment Eriberto Vagner Freitas a , Clístenes Williams Nascimento b,⇑ , Adailson Souza a,b , Fernando Bruno Silva a,b a UFRPE, Depto. de Agronomia, R. Dom Manuel de Medeiros, s/n – Dois Irmãos, 52171-900 Recife, PE, Brazil b UFPB, Campus II 58397-000 Areia, PB, Brazil highlights " Field experiments are fundamental to study the feasibility of phytoextraction. " Results from a phytoextraction field experiment in a real-life contaminated soil are provided. " Commercial citrate is an environmentally–friendly and cost effective chelant for phytoextraction. " Drawbacks for phytoextraction in soils with high Pb concentration are discussed. article info Article history: Received 27 August 2012 Received in revised form 24 January 2013 Accepted 25 January 2013 Available online 13 March 2013 Keywords: Phytoremediation Organic chelants Heavy metal Soil contamination abstract Soil contamination with heavy metals has become a serious environmental problem that requires afford- able strategies of remediation. This study was carried out to assess the performance of maize and vetiver in the phytoextraction of Pb from a soil contaminated by battery recycling activities. The species were planted with different spacings between rows (0.80, 0.65 and 0.50 m). Citric acid (40 mmol kg 1 ) was applied on each experimental plot on the 61st d of cultivation in order to solubilize the Pb and assist the phytoextraction. The results showed that the chelating agent promoted a 14-fold increase in the Pb concentration in maize shoots as compared to the control, which accumulated only 111 mg kg 1 of the metal. The citric acid induced a Pb concentration in vetiver shoots that was 7.2–6.7-fold higher than the control at both the 0.65 and 0.50 m plant spacing, respectively. The use of citric acid increased sub- stantially the uptake and translocation of Pb to the shoots, regardless of plant spacing. Citric acid was effi- cient in solubilizing Pb from the soil and inducing its uptake by both species. Environmentally-friendly and cost effective, commercial citric acid is recommended for assisting Pb-phytoextraction in the studied area. Due to the low natural solubility of Pb and a time frame needed of longer than 150 yr to accomplish the clean-up, phytoextraction with no chelate assistance is not recommended for the area. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Lead is one of the most common inorganic pollutants in soils. This metal has a high persistence in the soil and is potentially toxic, even at low concentrations. The United States Environmental Pro- tection Agency (EPA) considers levels of Pb in soil at between 400 and 500 mg kg 1 as high risk to human health. In Brazil, Resolution 420 of the National Environment Council defines 180, 300 and 900 mg kg 1 Pb as the maximum levels for agricultural, residential and industrial areas, respectively. Conventional techniques such as excavation, backfilling, fixa- tion and leaching are remediation strategies available for soils con- taminated by heavy metals. Alternatively, emerging technologies such as phytoremediation can also be used. Phytoextraction is often proposed for the remediation of soils contaminated with metals due to lower cost, public acceptance and reduced environ- mental impact. The solubilization of metals through the application of natural chelating agents on the ground, along with the cultivation of plants of high biomass production may be attractive due to the mitigation of adverse effects related to synthetic chelates. Citric acid has been one of the most studied natural chelates for phytoextraction, but studies in this area have shown conflicting results. While some studies reported a low effectiveness of citric acid in inducing phy- toextraction of Pb (Melo et al., 2008), others showed that the che- lating agent can be potentially used as an inducer in the phytoextraction of Pb from a soil contaminated by automotive bat- teries (Freitas et al., 2009; Araújo and Nascimento, 2010). There has been little field research in induced phytoextraction, especially with natural acids, but this is essential for assessing the technical and environmental feasibility of the process. In this con- text, the present study aimed to evaluate the field performance of maize and vetiver in the citric acid-induced phytoextraction of Pb 0045-6535/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.chemosphere.2013.01.103 ⇑ Corresponding author. Tel.: +55 81 3320 6236. E-mail address: clistenes@depa.ufrpe.br (C.W. Nascimento). Chemosphere 92 (2013) 213–217 Contents lists available at SciVerse ScienceDirect Chemosphere journal homepage: www.elsevier.com/locate/chemosphere