Effect of aging on arsenic and lead fractionation and availability in soils: Coupling sequential extractions with diffusive gradients in thin-films technique

doi:10.1016/j.jhazmat.2014.03.024

Journal of Hazardous Materials

Volume 273, 30 May 2014, Pages 272-279

https://doi.org/10.1016/j.jhazmat.2014.03.024 Get rights and content

Highlights

•
Diffusive gradients in thin-films (DGT) technique to monitor aging of As and Pb.
•
Sequential extraction methods to determine As and Pb fractionation and availability.
•
Distribution of As and Pb in spiked soils was significantly different from native soils.
•
Exchangeable Pb was likely source of DGT-measured labile Pb.
•
Non-specifically and specifically sorbed As were likely source of DGT-labile As.

Abstract

We coupled the diffusive gradients in thin-films (DGT) technique with two sequential extraction methods to investigate the influence of aging on As and Pb fractionation and availability in three soils spiked with As (40 or 400 mg kg⁻¹), Pb (150 or 1500 mg kg⁻¹) or As + Pb (40 mg kg⁻¹ As and 150 mg kg⁻¹ Pb). During aging, As moved from the more available (non-specifically and specifically sorbed) to less available (amorphous and crystallized Fe/Al) fractions while Pb moved from the first three fractions (exchangeable, carbonate and Fe/Mn hydroxide) to organic fraction. However, even after 33-week aging, much more As and Pb were in the least available residual fraction in spiked soils than native soils (11–59% vs. 1.2–12%). Relatively, As in spiked soils was much more available than Pb with 11–14% As and 46–59% Pb in the residual fraction. Correlation analysis indicated that As in the non-specifically and specifically sorbed fractions and Pb in the exchangeable fraction were likely sources of DGT-measured labile As and Pb. The fact that As and Pb distribution and availability in spiked soils were significantly different from native soils suggests caution needs to be exercised when using spiked soils for research.

Introduction

As and Pb often coexist at elevated concentrations in contaminated soils resulting from mining, smelting and insecticide application [1]. After addition to soils, the bioavailability of soluble As and Pb to plants decreases with time, which is termed aging [2]. Though the specific mechanism of aging is not well understood, the changes in As and Pb bioavailability during aging depend on their partitioning process in soils [3]. With time, their distribution in soils changes from more available forms to less available forms [4], [5].

Soil properties control bioavailability of As and Pb and therefore influence their potential risk in contaminated soils. Arsenic bioavailability in soils is governed by Fe hydroxides, which are strongly affined with dissolved organic carbon (DOC), so As competes with DOC for sorption sites [6]. For Pb, its solubility in soils is controlled by sorption onto Fe hydroxides and OC [7]. Also, DOC plays a key role in controlling Pb solubility in soils, and in fact most of labile Pb in alkaline soils exists as Pb–DOC complexes [8]. As a metalloid, As exists in soils as an oxyanion whereas Pb is present as a cation. As such, arsenic solubility increases with pH while Pb solubility decreases in soils [9], [10]. However, their bioavailability is related to other soil properties and so it is soil specific. Hence, it is necessary to examine their changes in different soils.

Sequential extraction has been widely used to determine the fractionation and bioavailability of metals in soils [11], [12]. The method identifies different pools of metals in soils with different bioavailability. However, the method does not target metals associated with discrete soil phases due to non-specificity and redistribution during extraction [13]. Still it provides valuable information regarding metal bioavailability in soils.

The diffusive gradients in thin-films (DGT) technique has been successfully used to predict metal bioavailability to plants [14]. The dynamic sampling technique integrates a wide range of key soil properties that impact metal release/adsorption [15], [16]. In addition, it mimics plant uptake in soils by lowering metal concentration locally and inducing diffusive supply and release of metals from complexes and solid phase [16]. Hence, the DGT technique coupled with sequential fraction was used to examine the changes in fractionation and bioavailability of As and Pb in soils during aging.

In this study, three soils with different properties were amended with different levels of As and Pb. Changes in their fractionation and bioavailability with time in the soils were measured using sequential extraction and DGT technique. The objectives were to investigate (1) how the amendment of As and Pb influenced the soil properties; (2) the aging effect on fractionation and bioavailability of As and Pb in soils; and (3) correlation of sequential extraction data to DGT labile fractions.

Section snippets

Soil sampling and characterization

Bulk samples of topsoil (0–20 cm) were collected from three sites in China: Tianjin (TJ), Lanzhou (LZ) and Tai’an (TA). They were air-dried, passed through a 2-mm sieve, and stored in plastic containers before use. Particle size analysis was carried out by a laser diffractometer (Mastersizer 2000, Malvern, UK). Soil pH was measured at a 1:5 solution-to-solid ratio in 0.01 M CaCl₂ after shaking for 1 h. Total organic and inorganic carbon in the soils was measured using a total carbon analyzer

Results and discussion

Three soils with different properties were spiked with As and Pb to determine their impact on changes in fractionation and bioavailability of As and Pb during 33-week of aging. Total concentrations of As and Pb in the soils were 5.0–7.5 mg kg⁻¹ and 15.2–19.4 mg kg⁻¹ (Table 1). They were not contaminated according to the Chinese Environmental Quality Standard for Soils (15 mg kg⁻¹ As and 35 mg kg⁻¹ Pb) (GB 15618-1995).

Conclusion

The present study showed that amendment with high level of As (400 mg kg⁻¹) increased the contents of DOC and soluble Fe in soils whereas high loading of Pb (1500 mg kg⁻¹) acidified the soil solution along with increasing soluble Fe. Data on C_DGT and water-soluble As and Pb demonstrated that the alkaline soil (LZ) was less effective in As sorption during the aging than the neutral and acidic soils (TJ and TA). Similarly, the acidic soil (TA) was less effective in Pb sorption than neutral and

Acknowledgments

This work was funded by the National Natural Science Foundation of China (No. 21207062 and 21277070), the Natural Science Foundation of Jiangsu Province (BK2012311), Special Research Fund for the Doctoral Program of Higher Education, Ministry of Education of China (20120091120016), and the Program for Postgraduates Research and Innovation in Jiangsu Province (No. CXZZ13_0058).

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Published by Elsevier B.V.

Effect of aging on arsenic and lead fractionation and availability in soils: Coupling sequential extractions with diffusive gradients in thin-films technique

Highlights

Abstract

Introduction

Section snippets

Soil sampling and characterization

Results and discussion

Conclusion

Acknowledgments

Stabilization of Pb and As in soils by applying combined treatment with phosphates and ferrous iron

J. Hazard. Mater.

Long-term aging of copper added to soils

Environ. Sci. Technol.

Partitioning of metals (Cd, Co, Cu, Ni, Pb, Zn) in soils: concepts, methodologies, prediction and applications—a review

Eur. J. Soil Sci.

The nature of Zn precipitates formed in the presence of pyrophyllite

Environ. Sci. Technol.

The ageing effect on the bioaccessibility and fractionation of arsenic in soils from China

Chemosphere

Natural organic matter affects arsenic speciation and sorption onto hematite

Environ. Sci. Technol.

Adsorption of free lead (Pb) by pedogenic oxides, ferrihydrite, and leaf compost

Soil Sci. Soc. Am. J.

Complexation with dissolved organic matter and solubility control of heavy metals in a sandy soil

Environ. Sci. Technol.

A review of the source, behaviour and distribution of arsenic in natural waters

Appl. Geochem.

Extractability and bioavailability of Pb and As in historically contaminated orchard soil: effects of compost amendments

Environ. Pollut.

Sequential extraction procedure for the speciation of particulate trace metals

Anal. Chem.

Arsenic fractionation in soils using an improved sequential extraction procedure

Anal. Chim. Acta

Sorption of copper, zinc and lead on soil mineral phases

Chemosphere

Labile Cd complexes increase Cd availability to plants

Environ. Sci. Technol.