Chelating agents to solubilize heavy metals from Oxisols contaminated by the addition of organic and inorganic residues

Abstract

Phytoremediation is an attractive technique for soils contaminated with heavy metals, especially in conjunction with chelating agents to assist metal phytoextraction. Nevertheless, their studies in Brazil are rare. Thus, the objective of the present work was to evaluate the efficiency of the chelating agents EDDS and EDTA for the solubilization of heavy metals from two Oxisols contaminated by organic sources in Jaguariúna (LVJ) and inorganic sources in Paulínia (LVP), São Paulo State, Southeastern Brazil. First, the soil samples were fractionated and the DTPA method was used to quantify heavy metals available forms. The results indicated that the metals were highly available in the soil fractions and could be solubilized by the chelating agents. The soil was suspended for 24 h in a chelating agent solution (EDTA or EDDS) at rates of 0, 250, 500 and 750 mg kg -1 of soil. The concentration of solubilized heavy metals was determined in the resulting solution. The extent of metal solubilization varied according to soil type, the chelating agent added and the specific metal. The amount of iron solubilized, as compared to the total iron (LVJ) was 11% (EDTA) and 19% (EDDS). EDDS solubilized more Cu than EDTA in both soils but more Ni in LVJ, while EDTA solubilized more Zn in both soils but more Cd in LVP. Both EDTA and EDDS may be useful for phytoextraction from soils, although the iron content is an important factor regarding the phytoextraction of heavy metals with chelating agents in Oxisols. Key words: soil pollution, chelating agents, tropical soils, fractionation USO DE QUELANTES NA SOLUBILIZAÇÃO DE METAIS PESADOS DE LATOSSOLOS CONTAMINADOS PELA ADIÇÃO DE RESÍDUOS ORGÂNICO E INORGÂNICORESUMO: A fitoextração tem sido uma opção atrativa para remediar solos contaminados com metais pesados, principalmente quando associada à aplicação de quelantes ao solo, embora no Brasil seus estudos sejam muito incipientes. Portanto, o objetivo deste trabalho foi avaliar a eficiência dos quelantes EDTA e EDDS na solubilização de metais pesados em Latossolos contaminados por Cu, Zn, Cd e Ni, cujas fontes de contaminação foram: orgânica em Jaguariúna (LVJ) e inorgânica em Paulínia (LVP). Antes da solubilização dos metais com os quelantes as amostras de solo foram submetidas ao fracionamento seqüencial e à extração dos metais pesados pelo método do DTPA. Ainda, as amostras dos dois solos foram agitadas com as soluções dos quelantes, por 24 h, usando as seguintes doses: 0, 250, 500 e 750 mg kg -1 de solo, realizando-se a determinação dos metais pesados no sobrenadante. Tanto a extração com DTPA como o fracionamento seqüencial indicaram que os metais estavam nas frações disponíveis que poderiam ser solubilizados pelos quelantes. As quantidades solubilizadas de Cu, Fe, Zn e Ni variaram em função do tipo de solo, dos quelantes e das doses aplicadas. A solubilização do Fe em relação ao seu teor total no LVJ foi de 11% (EDTA) e 19% (EDDS). O EDDS solubilizou mais Cu em ambos os solos e Ni no LVJ, enquanto o EDTA apresentou maior s...

Heavy-Metal Phytoextraction Potential of Spinach and Mustard Grown in Contaminated Calcareous Soils

“…In this technique, soil is amended with certain chemicals, such as synthetic organic chelates {DTPA (diethylenetriaminepentaacetic acid), EDTA (ethylenediaminetetraacetic acid), CDTA (trans-1,2-diaminocyclohexane-N,N,N ,N -tetraacetic acid), EGTA (ethylene glycol-[-aminoethyl ether]-N,N,N_,N_-tetra-acetic acid), EDDHA (ethylenediamine-di(o-hydroxyphenylacetic acid), NTA (nitrilotriacetic acid), HEDTA (hydroxyethylenediaminetriacetic acid), EDDS (ethylenediamine-disuccinic acid), citric acid, and elemental sulfur (S)}, to increase the heavy-metal bioavailability in soil and thus enhance phytoextraction by plant and translocation of heavy metals from the roots to the green parts of tested plants (Cooper et al 1999;Lombi et al 2001;Zhen et al 2002). Laboratory studies showed that EDTA is more effective in removing Pb, Zn, Cu, and Cd from contaminated soils, although extraction efficiency depends on many factors such as the lability of heavy metals in soil, the strength of EDTA, electrolytes, pH, and soil matrix (Brown and Elliot 1992;Heil et al 1999;Coscione et al 2009 Much of the previous work on chelate-assisted soil washing and phytoextraction was focused on Pb. In this study, natural and chemically enhanced phytoextractions of Pb and Cd were compared by growing spinach and mustard plants on two soils contaminated with multiple metals that were treated with varying rates of EDTA.…”

Biodegradable chelate enhances the phytoextraction of copper by Oenothera picensis grown in copper-contaminated acid soils

“…Efficiency of these chelates mainly depends on the metal that is to be extracted and on the soil characteristics. In the case of copper, numerous studies show an advantage for biodegradable chelates over traditional synthetic ones (Gre ˇman et al, 2003;Luo et al, 2004;Tandy et al, 2004;Cao et al, 2007;Cosciones et al, 2009). In terms of environmental risk, studies by Cao et al (2007) and Gre ˇman et al (2003) have shown that the concentration of metals is significantly higher in the leachate from soils treated with the traditional chelate EDTA, than from soils treated with the biodegradable chelates MGDA or EDDS.…”

Sequential extraction and availability of copper in Cu fungicide-amended vineyard soils from Southern Brazil

“…By this prodecure, the concentration of the element in each soil fraction is measured. Further, it is possible to correlate the content in each fraction with the bioavailable contents to plants [6]. Several extractors are used to evaluate the metals' availability in soils, more frequently DTPA pH 7.3 [7], Mehlich-III [8] and 0.1 M HCl [9], but few studies were carried out to assess the efficacy of such extractors for Cu in soils from the humid tropic [10].…”