Validation of an Arsenic Sequential Extraction Method for Evaluating Mobility in Sediments

Keon, N. E.; Swartz, Christopher H.; Brabander, Daniel J.; Harvey, Charles F.; Hemond, Harold F.

doi:10.1021/es001511o

Cited by 472 publications

(250 citation statements)

References 38 publications

(44 reference statements)

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“…No sulfide phases, either arsenic or iron, were detectable in bulk sediments with powder XRD (36). Sequential extraction of arsenic and iron from sediments using an extraction scheme optimized for arsenic (42) showed that arsenic is not dominantly associated with easily exchanged sorption sites or with reducible iron (36). This finding indicates that much of the arsenic is strongly sequestered in the sediments rather than surface-adsorbed or associated with easily dissolved phases, which is consistent with the presence of small particles.…”

Section: Xasmentioning

confidence: 99%

The influence of sulfur and iron on dissolved arsenic concentrations in the shallow subsurface under changing redox conditions

O’Day

Vlassopoulos

Root

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

415

306

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The chemical speciation of arsenic in sediments and porewaters of aquifers is the critical factor that determines whether dissolved arsenic accumulates to potentially toxic levels. Sequestration of arsenic in solid phases, which may occur by adsorption or precipitation processes, controls dissolved concentrations. We present synchrotron x-ray absorption spectra of arsenic in shallow aquifer sediments that indicate the local structure of realgar (AsS) as the primary arsenic-bearing phase in sulfate-reducing conditions at concentrations of 1-3 mmol⅐kg ؊1 , which has not previously been verified in sediments at low temperature. Spectroscopic evidence shows that arsenic does not substitute for iron or sulfur in iron sulfide minerals at the molecular scale. A general geochemical model derived from our field and spectroscopic observations show that the ratio of reactive iron to sulfur in the system controls the distribution of solid phases capable of removing arsenic from solution when conditions change from oxidized to reduced, the rate of which is influenced by microbial processes. Because of the difference in solubility of iron versus arsenic sulfides, precipitation of iron sulfide may remove sulfide from solution but not arsenic if precipitation rates are fast. The lack of incorporation of arsenic into iron sulfides may result in the accumulation of dissolved As(III) if adsorption is weak or inhibited. Aquifers particularly at risk for such geochemical conditions are those in which oxidized and reduced waters mix, and where the amount of sulfate available for microbial reduction is limited. Despite intensive study in recent years, quantitative biogeochemical models that explain and predict conditions controlling the uptake or release of dissolved arsenic in groundwaters remain incomplete, due partly to a lack of knowledge of arsenic speciation in subsurface sediments. Worldwide, elevated concentrations of arsenic (Ͼ10 g⅐liter Ϫ1 , the World Health Organization and new U.S. Environmental Protection Agency drinking-water standard) in groundwater have the potential to have an adverse impact on Ϸ90 million people (1, 2), including 13 million in the United States (3, 4). Arsenic is a known carcinogen and mutagen that can lead to both acute and chronic adverse health effects (5, 6). Arsenic in ground-and surface waters results from both natural and anthropogenic sources, but its mobility and attenuation, and thus impact on humans and other organisms, is directly tied to its chemical speciation (3,7,8).Recent studies using direct spectroscopic characterizations have begun to verify differing chemical states of arsenic in natural samples and their influence on arsenic mobility (9-12). Under oxic conditions, it is widely accepted that arsenic in sediments is removed from solution by adsorption to or coprecipitation with ferric oxyhydroxide and possibly by adsorption to manganese oxide and phyllosilicate minerals (7, 13). As subsurface conditions change from oxidized to progressively more reduced, As(V) is reduced to As(III...

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Section: Xasmentioning

confidence: 99%

The influence of sulfur and iron on dissolved arsenic concentrations in the shallow subsurface under changing redox conditions

O’Day

Vlassopoulos

Root

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

415

306

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“…Previous studies have shown that this method extracts As from Fe oxides, metal sulfides, and As sulfides. 53,54 Reductive extractions leached 0.9-1.1 nanomoles As per gram of sediment dry weight ͑nmol/g͒ from the Ͻ2 mm sizefraction of sediments collected adjacent to the tracer test site and from the Ͻ1 mm size-fraction of a composite sample comprised of sediments from the uncontaminated zone ͑Table III͒. Preparation of this composite sample has been described elsewhere.…”

Section: Chemical Extractions Of Sedimentsmentioning

confidence: 99%

The influence of groundwater chemistry on arsenic concentrations and speciation in a quartz sand and gravel aquifer

Kent

2004

Geochem. Trans.

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We examined the chemical reactions influencing dissolved concentrations, speciation, and transport of naturally occurring arsenic ͑As͒ in a shallow, sand and gravel aquifer with distinct geochemical zones resulting from land disposal of dilute sewage effluent. The principal geochemical zones were: ͑1͒ the uncontaminated zone above the sewage plume ͓350 M dissolved oxygen ͑DO͒, pH 5.9͔; ͑2͒ the suboxic zone ͑5 M DO, pH 6.2, elevated concentrations of sewage-derived phosphate and nitrate͒; and ͑3͒ the anoxic zone ͓dissolved iron͑II͒ 100-300 M, pH 6.5-6.9, elevated concentrations of sewage-derived phosphate͔. Sediments are comprised of greater than 90% quartz but the surfaces of quartz and other mineral grains are coated with nanometer-size iron ͑Fe͒ and aluminum ͑Al͒ oxides and/or silicates, which control the adsorption properties of the sediments. Uncontaminated groundwater with added phosphate ͑620 M͒ was pumped into the uncontaminated zone while samples were collected 0.3 m above the injection point. Concentrations of As͑V͒ increased from below detection ͑0.005 M͒ to a maximum of 0.07 M during breakthrough of phosphate at the sampling port; As͑III͒ concentrations remained below detection. These results are consistent with the hypothesis that naturally occurring As͑V͒ adsorbed to constituents of the coatings on grain surfaces was desorbed by phosphate in the injected groundwater. Also consistent with this hypothesis, vertical profiles of groundwater chemistry measured prior to the tracer test showed that dissolved As͑V͒ concentrations increased along with dissolved phosphate from below detection in the uncontaminated zone to approximately 0.07 and 70 M, respectively, in the suboxic zone. Concentrations of As͑III͒ were below detection in both zones. The anoxic zone had approximately 0.07 M As͑V͒ but also had As͑III͒ concentrations of 0.07-0.14 M, suggesting that release of As bound to sediment grains occurred by desorption by phosphate, reductive dissolution of Fe oxides, and reduction of As͑V͒ to As͑III͒, which adsorbs only weakly to the Fe-oxide-depleted material in the coatings. Results of reductive extractions of the sediments suggest that As associated with the coatings was relatively uniformly distributed at approximately 1 nmol/g of sediment ͑equivalent to 0.075 ppm As͒ and comprised 20%-50% of the total As in the sediments, determined from oxidative extractions. Quartz sand aquifers provide high-quality drinking water but can become contaminated when naturally occurring arsenic bound to Fe and Al oxides or silicates on sediment surfaces is released by desorption and dissolution of Fe oxides in response to changing chemical conditions.

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“…This means that the main leaching toxicity of As is caused by its residual fraction, which is different from the other metals that we investigated. A possible reason is that the residual fractions of As in all three fractionation procedures account for more than 97% of the total amount detected, and there are special SEPs developed for As (Keon et al, 2001) to account for its particularly reactive properties (Dold, 2003;Huang et al, 2007;Zhao et al, 2010;Zhao et al, 2009). Additionally, although the mean concentration of As detected in the TCLP leachate (4.46 ± 0.22 mg/L) was below the regulation limit, the concentration of As in the residues after each fraction for the three SEPs could exceed the regulation limit of 5 mg/L.…”

Section: Chemical Speciation Tests Combined With Tclpmentioning

confidence: 99%

Leaching assessments of toxic metals in waste plasma display panel glass

Chen

Jiang

Chen

et al. 2015

Journal of the Air & Waste Management Association

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The plasma display panel (PDP) is rapidly becoming obsolete, contributing in large amounts to the electronic waste stream. In order to assess the potential for environmental pollution due to hazardous metals leached from PDP glass, standardized leaching procedures, chemical speciation assessments, and bioavailability tests were conducted. According to the Toxicity Characteristic Leaching Procedure (TCLP), arsenic in back glass was present at 4.46 ± 0.22 mg/L, close to its regulation limit of 5 mg/L. Zn is not available in the TCLP, but its TCLP leaching concentration in back glass is 102.96 ± 5.34 mg/L. This is because more than 90% of Zn is in the soluble and exchangeable and carbonate fraction. We did not detect significant levels of Ag, Ba, or Cu in the TCLP leachate, and the main fraction of Ag and Ba is residual, more than 95%, while the fraction distribution of Cu changes SEP by SEP. Ethylenediamine tetraacetic acid (EDTA)-and diethylenetriamine pentaacetic acid (DTPA)-extractable Ag, As, Ba, Cu, Zn, and Ni indicate a lower biohazards potential. These results show that, according to the EPA regulations, PDP glass may not be classified as hazardous waste because none of the metals exceeded their thresholds in PDP leachate. However, the concentrations of As and Zn should be lowered in the manufacturing process and finished product to avoid potential pollution problems.Implications: The plasma display panel is rapidly becoming obsolete because of the liquid crystal display. In this study, the leachability of heavy metals contained in the waste plasma display panel glass was first examined by standardized leaching tests, typical chemical speciation assessments, and bioavailability tests, providing fundamental data for waste PDP glass recovery, recycling, and reuse.

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Validation of an Arsenic Sequential Extraction Method for Evaluating Mobility in Sediments

Cited by 472 publications

References 38 publications

The influence of sulfur and iron on dissolved arsenic concentrations in the shallow subsurface under changing redox conditions

The influence of sulfur and iron on dissolved arsenic concentrations in the shallow subsurface under changing redox conditions

The influence of groundwater chemistry on arsenic concentrations and speciation in a quartz sand and gravel aquifer

Leaching assessments of toxic metals in waste plasma display panel glass

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