Elsevier

Environmental Pollution

Volume 156, Issue 3, December 2008, Pages 1139-1148
Environmental Pollution

Chelant-aided enhancement of lead mobilization in residential soils

https://doi.org/10.1016/j.envpol.2008.04.004Get rights and content

Abstract

Chelation of metals is an important factor in enhancing solubility and hence, availability to plants to promote phytoremediation. We compared the effects of two chelants, namely, ethylenediaminetetraacetic acid (EDTA) and ethylenediaminedisuccinic acid (EDDS) in enhancing mobilized lead (Pb) in Pb-based paint contaminated residential soils collected from San Antonio, Texas and Baltimore, Maryland. Batch incubation studies were performed to investigate the effectiveness of the two chelants in enhancing mobilized Pb, at various concentrations and treatment durations. Over a period of 1 month, the mobilized Pb pool in the San Antonio study soils increased from 52 mg kg−1 to 287 and 114 mg kg−1 in the presence of 15 mM kg−1 EDTA and EDDS, respectively. Stepwise linear regression analysis demonstrated that pH and organic matter content significantly affected the mobilized Pb fraction. The regression models explained a large percentage, from 83 to 99%, of the total variation in mobilized Pb concentrations.

Introduction

Lead (Pb) is a metal contaminant that poses a significant health risk to humans, especially children. Lead induces a multitude of physiological, biochemical, and behavioral dysfunctions; particularly in children (Banks et al., 1997). Chronic low-level Pb exposure primarily interferes with heme biosynthesis and the central nervous system. Exposure to Pb during the early stages of a child's development can result in significant reduction in their IQ levels. The greater absorptive capacity of the gastrointestinal tracts of children puts them at a higher risk group than the adults. In addition, exposure to Pb is associated with impaired skeletal growth in children. It has been estimated that in the United States alone Pb poisoning affects more than 800,000 children between the ages of 1 and 5 (Pirkle et al., 1998). Dust- and soil-Pb, derived from flaking, weathering, and chalking paint, alongside airborne Pb fallout and waste disposal over the years are the major proximate sources of potential childhood Pb exposure (CDC, 1991). Lead-based paint continues to be the root cause of the majority of the severe Pb poisoning cases in children reported in the United States (CDC, 2003). Lead-based paints have very high concentrations of Pb and are the most prevalent of the various sources, being found in approximately 38 million pre-1978 homes (US Census, 2000). Lead is added as lead oxide (PbO) in the paints; once introduced to the soil environment, Pb forms strong bonds with the soil components and is generally retained in the surface soil layer (Rieuwerts et al., 1998). Thus, the adverse impact of Pb on environmental quality and on human health persists for long periods. Hence, cleanup of Pb-contaminated soils typically requires their complete removal. Various techniques are used for cleaning up Pb-contaminated soils. Among these, phytoremediation, i.e., the use of plants for environmental remediation is an emerging cleanup technology for metal contaminated sites. However, the success of Pb phytoextraction primarily depends on the phytoavailability of Pb as it must be in either soluble or exchangeable form for plant uptake to occur. The term ‘mobilized Pb’ in this context refer to the soluble and exchangeable forms released from the soil solid phase to soil pore water in the presence of chelating agents (Wu et al., 2004, Wang et al., 2007). Literature to date indicates that Pb has limited solubility in soil environment due to complexation with various organic and inorganic soil colloids, sorption on oxides and clays, and precipitation as carbonates, hydroxides and phosphates (Zhang et al., 1997). Although total soil Pb concentrations are high in many of the contaminated residential sites, the mobilized or soluble fraction of Pb is often very low, typically less than 1%. Plants have the ability to extract soluble or free forms of Pb rather than the bound ones. Hence, mobilized Pb fraction is a limiting factor for Pb phytoremediation. For soils with pH between 5.5 and 7.5, where Pb solubility is controlled by carbonate and phosphate precipitates, the maximum activity of Pb2+ in soil solution is approximately 10−8.5 M (Lindsay, 1979). Extremes in soil pH above 7.5 or below 5.5 will either decrease or increase Pb solubility. Thus, increasing soluble and exchangeable Pb concentrations in the soil solution are key factors in phytoremediation of Pb-contaminated soils.

Recent research has focused on artificially inducing Pb desorption from complex soil matrices to enhance Pb phytoextraction. Several synthetic chelating/complexing agents, such as ethylenediaminetetraacetic acid (EDTA), ethylenetrinitrilopentaacetic acid (DTPA), N-hydroxy-ethylenediaminetriacetic acid (HEDTA), nitrilotriacetate (NTA) and a natural chelant like [S,S′] ethylenediaminedisuccinate (EDDS) have been used to enhance metal solubility during phytoextraction (Blaylock et al., 1997, Huang et al., 1997, Grčman et al., 2003). Kos and Leštan (2003) reported that addition of EDTA and EDDS increased Pb concentrations in the plant by 158 and 89 times, respectively, compared to the plants grown in soils with no chelant amendments. These chelants form strong Pb-ligand coordination complexes, thereby desorbing Pb from the soil matrix to soil solution (Aldrich et al., 2004, Lai and Chen, 2004).

In the present study, in a static incubation setup, we compared the effects of application of a biodegradable chelating agent, namely, ethylenediaminedisuccinic acid (EDDS) on enhancing the soluble form of Pb in Pb-based paint contaminated residential sites compared to that of a more commonly used, but non-biodegradable chelant, namely, ethylenediaminetetraacetic acid (EDTA). EDTA was chosen as a representative chelant in the soil environment that has been used for extracting many metals (Huang et al., 1997, Wu et al., 1999, Kim et al., 2003). EDDS is a new biodegradable chelant and is a structural isomer of EDTA. EDDS strongly complexes with transition metals and radionuclides and may be an effective alternative to synthetic chelating agents, which persist in the soil environment (Grčman et al., 2003). The type of chelants used and solubility of Pb by chelants in contaminated soils need to be understood prior to developing a phytoremediation strategy.

The nature and extent of the ‘soluble’ and ‘insoluble’ pool of Pb in soils is controlled by various soil physico-chemical properties. Understanding the soil properties is the first step towards developing a successful phytoremediation strategy (Datta and Sarkar, 2004). Knowledge on these properties helps to manipulate, and subsequently increase the potentially plant available form of Pb in soils, thereby enhancing plant uptake. We selected Pb-contaminated residential soils from two major metropolitan areas (San Antonio, TX and Baltimore, MD) with varying soil physico-chemical properties – the soils from San Antonio were primarily alkaline and those from Baltimore were acidic (Andra et al., 2006). In San Antonio, there are 340,532 pre-1978 housing units, accounting for 56.7% of the total housing units in the city (US Census, 2000). Baltimore, MD, has a severe lead poisoning problem, with a rate that is four times higher than the national average. The number of residential homes built prior to the 1950s in Baltimore is close to 530,000. Approximately, an estimated 976,000 homes were built in between 1950 and 1978, with 75% of these homes with likely Pb-based paint (Rioux, 2001). Although the total Pb concentrations in many of these contaminated residential soils exceed the EPA permissible limits, the phytoavailable Pb fraction (water soluble and exchangeable) is usually very low due to the strong association of Pb with organic matter, Fe–Mn oxides, and clays, and because of precipitation as carbonates, hydroxides, and phosphates (Huang et al., 1997).

The objectives of this study were to (i) investigate the effectiveness of two chelates (EDTA and EDDS) in enhancing mobilized Pb in paint contaminated residential soils collected from San Antonio and Baltimore; and (ii) establish a relationship between soil properties and the mobilized soil Pb fraction.

Section snippets

Pb-paint contaminated residential soils collection and characterization

Lead-based paint contaminated soils were collected from residential areas of San Antonio, TX and Baltimore, MD; six residential sites from each city were selected for this study. At each housing unit, three composite soil samples were collected from the sides of the houses, which are likely to have the highest Pb concentration. Each composite sample was a mixture of four samples taken at a depth of 0–15 cm from four locations within each housing unit. Handling of the soil samples followed the

Physico-chemical properties of the Pb-paint contaminated residential soils

The physico-chemical characteristics of Pb-contaminated San Antonio and Baltimore soils are summarized in Table 1, Table 2. Study soils collected from San Antonio were slightly alkaline in nature (pH ranging from 7.45 to 8.23), while those from Baltimore were slightly acidic (pH ranging from 5.51 to 6.10). The median pH is 7.73 in San Antonio soils, whereas it is 5.84 in Baltimore soils. In general, the San Antonio soils have relatively high soil salinity; the EC values ranged between 177 and

Conclusions

Results from our study demonstrated that both EDDS and EDTA were effective in increasing the solubility of Pb in paint-contaminated residential soils of San Antonio and Baltimore. The concentrations of mobilized Pb in EDDS- and EDTA- treated soils were upto four and seven times higher, respectively, compared to the untreated controls. Although EDTA was more effective in Pb solubilization than EDDS, the rapid kinetics of the Pb–EDTA complexation process and the prolonged persistency of EDTA in

Acknowledgments

The authors would like to thank the U.S. Department of Housing and Urban Development (HUD) for providing financial support for this study. We are also grateful to City of San Antonio, Neighborhood Action Department, TX and Coalition to End Childhood Lead Poisoning, Baltimore, MD for their assistance in collecting Pb-paint contaminated soils from residential areas.

References (44)

  • S. Tandy et al.

    Biodegradation and speciation of residual SS-ethylenediaminedisuccinic acid (EDDS) in soil solution left after soil washing

    Environ. Pollut.

    (2006)
  • L.H. Wu et al.

    EDTA-enhanced phytoremediation of heavy metal contaminated soil with Indian mustard and associated potential leaching risk

    Agricult. Ecosys. Environ.

    (2004)
  • M.V. Aldrich et al.

    Lead uptake and the effects of EDTA on lead-tissue concentrations in the desert species Mesquite (Prosopis spp.)

    Int. J. Phytoremediation

    (2004)
  • S.S. Andra et al.

    Lead in soils in paint contaminated residential sites at San Antonio, Texas and Baltimore, Maryland

    Bull. Environ. Contam. Toxicol.

    (2006)
  • E.C. Banks et al.

    Effects of low level lead exposure on cognitive function in children: a review of behavioral, neuropsychological and biological evidence

    Neurotoxicology

    (1997)
  • E. Ben-Dor et al.

    Determination of organic matter content in arid-zone soils using a simple “loss-on-ignition” method

    Commun. Soil Sci. Plant Anal.

    (1989)
  • M.J. Blaylock et al.

    Enhanced accumulation of Pb in Indian mustard by soil applied chelating agents

    Environ. Sci. Technol.

    (1997)
  • CDC(Centers for Disease Control and Prevention)

    Preventing Lead Poisoning in Young Children: A Statement by the U.S. Department of Health and Human Services

    (1991)
  • CDC(Centers for Disease Control and Prevention)

    National Center for Environmental Health: Children's Blood Lead Levels in the United States

    (2003)
  • R. Datta et al.

    Effective integration of soil chemistry and plant molecular biology in phytoremediation of metals: an overview

    Environ. Geosci.

    (2004)
  • B.E. Davies

    Heavy metal contaminated soils in an old industrial area of Wales, Great Britain: source identification through statistical data interpretation

    Water Air Soil Poll.

    (1997)
  • G.W. Gee et al.

    Particle size analysis

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