Release of arsenic to the environment from CCA-treated wood. 2. Leaching and speciation during disposal

Wood treated with chromated copper arsenate (CCA) is primarily disposed within construction and demolition (C&D) debris landfills, with wood monofills and municipal solid waste (MSW) landfills as alternative disposal options. This study evaluated the extent and speciation of arsenic leaching from landfills containing CCA-treated wood. In control lysimeters where untreated wood was used, dimethylarsinic acid (DMAA) represented the major arsenic species. The dominant arsenic species differed in the lysimeters containing CCA-treated wood, with As(V) greatest in the monofill and C&D lysimeters and As(III) greatest in the MSW lysimeters. In CCA-containing lysimeters, the organoarsenic species monomethylarsonic acid (MMAA) and DMAAwere virtually absent in the monofill lysimeter and observed in the C&D and MSW lysimeters. Overall arsenic leaching rate varied for the wood monofill (0.69% per meter of water added), C&D (0.36% per m), and MSW (0.84% per m) lysimeters. Utilizing these rates with annual disposal data, a mathematical model was developed to quantify arsenic leaching from CCA-treated wood disposed to Florida landfills. Model findings showed between 20 and 50 t of arsenic (depending on lysimeter type) had leached prior to 2000 with an expected increase between 350 and 830 t by 2040. Groundwater analysis from 21 Florida C&D landfills suspected of accepting CCA-treated wood showed that groundwater at 3 landfills was characterized by elevated arsenic concentrations with only 1 showing impacts from the C&D waste. The slow release of arsenic from disposed treated wood may account for the lack of significant impact to groundwater near most C&D facilities at this time. However, greater impacts are anticipated in the future given that the maximum releases of arsenic are expected by the year 2100.     

Release of arsenic to the environment from CCA-treated wood. 1. Leaching and speciation during service

Insufficient information exists about the speciation of arsenic leaching from in-service chromated copper arsenate (CCA)-treated products and the overall impact to soils and groundwater. To address this issue, two decks were constructed, one from CCA-treated wood and the other from untreated wood. Both decks were placed in the open environment where they were impacted by rainfall. Over a one-year period, rainwater runoff from the decks and rainwater infiltrating through 0.7 m of sand below the decks was collected and analyzed for arsenic species by HPLC-ICP-MS. The average arsenic concentration in the runoff of the untreated deck was 2-3 microg/L, whereas from the CCA-treated deck it was 600 microg/L. Both inorganic As(III) and As(V) were detected in the runoff from both decks, with inorganic As(V) predominating. No detectable levels of organoarsenic species were observed. The total arsenic concentration in the infiltrated water of the treated deck had risen from a background concentration of 3 microg/L to a concentration of 18 microg/L at the end of the study. Data from the deck study were combined with annual CCA-treated wood production statistics to develop a mass balance model to estimate the extent of arsenic leaching from in-service CCA-treated wood structures to Florida soils. Results showed that during the year 2000, of the 28 000 t of arsenic imported into the state and utilized for in-service CCA-treated wood products, approximately 4600 t had already leached. Future projections suggest that an additional 11,000 t of arsenic will leach during in-service use within the next 40 years.     

Landfill disposal of CCA-treated wood with construction and demolition (C&D) debris: arsenic, chromium, and copper concentrations in leachate

Although phased out of many residential uses in the United States, the disposal of CCA-treated wood remains a concern because significant quantities have yet to be taken out of service, and it is commonly disposed in landfills. Catastrophic events have also led to the concentrated disposal of CCA-treated wood, often in unlined landfills. The goal of this research was to simulate the complex chemical and biological activity of a construction and demolition (C&D) debris landfill containing a realistic quantity of CCA-treated wood (10% by mass), produce leachate, and then evaluate the arsenic, copper, and chromium concentrations in the leachate as an indication of what may occur in a landfill setting. Copper concentrations were not significantly elevated in the control or experimental simulated landfill setting (alpha = 0.05). However, the concentrations of arsenic and chromium were significantly higher in the experimental simulated landfill leachate compared to the control simulated landfill leachate (alpha = 0.05, p < 0.001). This indicates that disposal of CCA-treated wood with C&D debris can impact leachate quality which, in turn could affect leachate management practices or aquifers below unlined landfills.     

Assessing influence of experimental parameters on formation of PCDD/F from ash derived from fires of CCA-treated wood

Ash residues from fires of radiata pine timber, both untreated and treated with chromated copper arsenate (CCA), were analyzed for the presence of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/F). Fire conditions were simulated using a cone calorimeter. The sensitivity of the magnitude and profile of PCDD/F in the ash under controlled experimental conditions were examined to gain an insight into the formation of PCDD/F in a system containing CCA. The total amount of PCDD/F increased from 2.0 ng/kg of ash (0.05 ng of TE/kg of ash, using WHO-TEF) for untreated radiata pine to a maximum of 2700 ng/kg of ash (78 ng of TE/kg of ash) for 0.94% CCA. Ash containing CCA showed a distinct preference for formation of PCDFs, particularly the tetrachloro homologue. It is concluded that PCDD/F formation predominantly occurred via de novo synthesis during smoldering of the char rather than during the initial flaming and pyrolysis. Furthermore, the composition of the CCA constituents present in the timber was controlled to assess whether the physical presence of Cu, a known catalyst in PCDD/F production, was sufficient to account for the formation of PCDD/F in fires of timber impregnated with CCA.     

Arsenic speciation and reactivity in poultry litter

Recent U.S. government action to lower the maximum concentration levels (MCL) of total arsenic (As) (10 ppb) in drinking water has raised serious concerns about the agricultural use of As-containing biosolids such as poultry litter (PL). In this study, solid-state chemical speciation, desorbability, and total levels of As in PL and long-term amended soils were investigated using novel synchrotron-based probing techniques (microfocused (micro) synchrotron X-ray fluorescence (SXRF) and micro-X-ray absorption near-edge structure (XANES) spectroscopies) coupled with chemical digestion and batch experiments. The total As levels in the PL were as high as approximately 50 mg kg(-1), and As(II/III and V) was always concentrated in abundant needle-shaped microscopic particles (approximately 20 microm x 850 microm) associated with Ca, Cu, and Fe and to a lesser extent with S, Cl, and Zn. Post-edge XANES features of litter particles are dissimilar to those of the organo-As(V) compound in poultry feed (i.e., roxarsone), suggesting possible degradation/transformation of roxarsone in the litter and/or in poultry digestive tracts. The extent of As desorption from the litter increased with increasing time and pH from 4.5 to 7, but at most 15% of the total As was released after 5 d at pH 7, indicating the presence of insoluble phases and/or strongly retained soluble compounds. No significant As accumulation (< 15 mg kg(-1)) was found in long-term PL-amended agricultural surface soils. This suggests that As in the PL may have undergone surface and subsurface transport processes. Our research results raise concerns about long-term PL amendment effects on As contamination in surrounding soil-water environments.     

Emissions of chromium, copper, arsenic, and PCDDs/Fs from open burning of CCA-treated wood

Aged and weathered chromated copper arsenate (CCA) treated wood was burned in an open burn research facility to characterize the air emissions and residual ash. The objectives were to simulate, to the extent possible, the combustion of such waste wood as might occur in an open field or someone's backyard; to characterize the composition and particle size distribution (PSD) of the emitted fly ash; to determine the partitioning of arsenic, chromium, and copper between the fly ash and residual ash; and to examine the speciation of the CCA elements. This work reports preliminary air emission concentrations and estimated emission factors for total particulate matter, arsenic (As), chromium (Cr), copper (Cu), and polychlorinated dibenzodioxins/dibenzofurans (PCDD/F) totals and toxic equivalents (TEQs). The partitioning of As, Cr, and Cu between the emitted fly ash and residual ash is examined and thermochemical predictions from the literature are used to explain the observed behavior. Results indicate a unimodal fly ash PSD between 0.1 and 1.0 microm diameter. In addition to a large carbonaceous component, between 11 and 14% of the As present in the burned CCA treated wood was emitted with the air emissions, with the remainder present in the residual ash. In contrast, less than 1% of both the Cr and Cu present in the wood was emitted with the air emissions. PCDD/F levels were unremarkable, averaging 1.7 ng TEQ/kg of treated wood burned, a value typical for wood combustion. Scanning electron microscopy (SEM) was unable to resolve inorganic particles consisting of Cu, Cr, or As in the wood samples, but X-ray absorption fine structure (XAFS) spectroscopy confirmed that the oxidation states of the CCA elements in the wood were Cu2+, Cr3+, and As5+. SEM examination of the fly ash samples revealed some inorganic microcrystals within the mostly carbonaceous fly ash, while XAFS spectroscopy of the same samples showed that the oxidation states after combustion were mixed Cu+ and Cu2+, Cr3+, and mixed As3+ and As5+. Estimates of the ratios of the mixed oxidation states based on the XAFS spectra were As3+/(total As) = 0.8-0.9 and Cu+/(total Cu) = 0.65-0.7. The Cu and Cr present in the fly ash were determined to coexist predominantly in the two oxide phases CuCrO2 and CuCr2O4. These results indicate that the open burning of CCA-treated wood can lead to significant air emissions of the more toxic trivalent form of As in particle sizes that are most respirable.     

Chemical structure of arsenic and chromium in CCA-treated wood: implications of environmental weathering

Chromated copper arsenate (CCA) has been used to treat lumber for over 60 years to increase the expected lifetime of CCA-treated wood. Because of the toxicity of the arsenic and chromium used in CCA treatment, regulatory and public attention has become focused on the potential risks from this exposure source. In particular, exposure of children to arsenic from CCA-treated wood used in decks and play sets has received considerable attention. X-ray Absorption Spectroscopy (XAS) was used to evaluate the chemical structure of As and Cr in three samples of CCA-treated materials: newly treated wood, aged wood (5 years as decking), and dislodgeable residue from aged (1-4 years as decking) CCA-treated wood. The form of the Cr and As in CCA-treated material is the same in fresh and aged samples, and between treated wood and dislodged residue. In all cases, the dominant oxidation state of the two elements is As(V) and Cr(III), and the local chemical environment of the two elements is best represented as a Cr/As cluster consisting of a Cr dimer bridged by an As(V) oxyanion. Long-term stability of the As/Cr cluster is suggested by its persistence from the new wood through the aged wood and the dislodgeable residue.     

Arsenic speciation and volatilization from flooded paddy soils amended with different organic matters

Arsenic (As) methylation and volatilization in soil can be increased after organic matter (OM) amendment, though the factors influencing this are poorly understood. Herein we investigate how amended OM influences As speciation as well as how it alters microbial processes in soil and soil solution during As volatilization. Microcosm experiments were conducted on predried and fresh As contaminated paddy soils to investigate microbial mediated As speciation and volatilization under different OM amendment conditions. These experiments indicated that the microbes attached to OM did not significantly influence As volatilization. The arsine flux from the treatment amended with 10% clover (clover-amended treatment, CT) and dried distillers grain (DDG) (DDG-amended treatment, DT2) were significantly higher than the control. Trimethylarsine (TMAs) was the dominant species in arsine derived from CT, whereas the primary arsine species from DT2 was TMAs and arsine (AsH(3)), followed by monomethylarsine (MeAsH(2)). The predominant As species in the soil solutions of CT and DT2 were dimethylarsinic acid (DMAA) and As(V), respectively. OM addition increased the activities of arsenite-oxidizing bacteria (harboring aroA-like genes), though they did not increase or even decrease the abundance of arsenite oxidizers. In contrast, the abundance of arsenate reducers (carrying the arsC gene) was increased by OM amendment; however, significant enhancement of activity of arsenate reducers was observed only in CT. Our results demonstrate that OM addition significantly increased As methylation and volatilization from the investigated paddy soil. The physiologically active bacteria capable of oxidization, reduction, and methylation of As coexisted and mediated the As speciation in soil and soil solution.     

Arsenic leaching from mulch made from recycled construction and demolition wood and impacts of iron-oxide colorants

Mulch made from recycled construction and demolition (C&D) wood has been reported to contain elevated levels of arsenic from inadvertent inclusion of chromated copper arsenate (CCA)-treated wood. Such mulch is also commonly colored with iron oxide, a compound known to bind arsenic. The objectives of this study were to quantify the releases of arsenic from mulch made from C&D wood, to evaluate the impacts of an iron-oxide colorant in potentially decreasing arsenic leaching rates, and to evaluate the relative significance of additional variables on leachate concentrations. Atotal of 3 sets of mulch samples (0%, 5%, or 100% CCA-treated wood) were prepared containing a sample either with or without colorant addition. Each sample was subjected to two tests: a field leaching test and the Synthetic Precipitation Leaching Procedure (SPLP). Results showed that arsenic concentrations in the field leachate from the 0% treated wood mulches were consistently low (<0.003-0.013 mg/L) whereas leachates from 5 and 100% treated wood mulches were characterized by higher arsenic concentrations (0.059-2.23 mg/L for 5%; 0.711-22.7 mg/L for 100%). The mass of arsenic leached from the field samples during the 1-year monitoring period was between 10 and 15% of the initial mass of arsenic. The colorant reduced the leaching of arsenic by more than 20% for the field leachate and 50% for the SPLP leachate, on average. However, the study showed that the effect may not last for long periods. Besides colorant addition other factors were observed to affect the amount of arsenic leached from contaminated mulch. These include the proportion of CCA-treated wood in the mulch, time, and pH of rainfall.     

Arsenic in rice: II. Arsenic speciation in USA grain and implications for human health

Rice is a potentially important route of human exposure to arsenic, especially in populations with rice-based diets. However, arsenic toxicity varies greatly with species. The initial purpose of the present study was to evaluate arsenic speciation in U.S. rice. Twenty-four samples containing high levels of arsenic and produced in different regions of the U.S were selected from a previous market-basket survey. Arsenite and dimethyl arsinic acid (DMA) were the major species detected. DMA increased linearly with increasing total As but arsenite remained fairly constant at approximately 0.1 mg kg(-1), showing that rice high in As was dominated by DMA. A similar result was obtained when our data was combined with other published speciation studies for U.S. rice. However, when all published speciation data for rice was analyzed a second population dominated by inorganic As and lower levels of DMA was found. We thus categorized rice into DMA and Inorganic As types. Rice from the U.S. was predominantly the DMA type, as were single samples from Australia and China, whereas rice from Asia and Europe was the Inorganic As type. We suggest that methylation of As occurs within rice and that genetic differences lead to the two rice types. Insufficient understanding of DMA toxicity precludes a firm assessment of the relative health risks associated with the two rice types but, based on current knowledge, we suggest that the DMA rice type is likely to be less of a health risk than the Inorganic As rice type and, on this basis, rice from the U.S. may be safer than rice from Asia and Europe.     

Strontium speciation during reaction of kaolinite with simulated tank-waste leachate: bulk and microfocused EXAFS analysis

Radioactive strontium (90Sr) is an important constituent of the complex wastes from past nuclear weapons production and has been stored in underground tanks at U.S. DOE sites (e.g., Hanford, WA). Using bulk and microfocused EXAFS spectroscopy, we examined temporal changes in solid-phase Sr speciation in kaolinite samples reacted for 1-369 d with high-pH, high ionic strength synthetic tank-waste leachate containing Sr(2+) and Cs(+) at 10(-3) mol kg(-1). Analyses of bulk EXAFS spectra showed that Sr initially forms a precipitate by 7 d with a local structure similar to SrCO(3-) (s). At 33 d, microfocused EXAFS of individual particles in one sample revealed a mixture of hydrated and dehydrated Sr associated with neoformed sodalite-type phases. At aging times of 93 d and longer, bulk EXAFS spectra and supporting characterizations indicated nonexchangeable Sr with a local structure consistent with incorporation into increasingly crystalline aluminosilicate particles, particularly sodalite. These experimental studies suggest that irreversible trapping of radionuclides occurs if they are present during the formation and aging of feldspathoid alteration products of local Si-bearing sediment minerals. This may serve as an effective contaminant sequestration mechanism at sites such as Hanford.     

Arsenic speciation in plankton organisms from contaminated lakes: transformations at the base of the freshwater food chain

The two complementary techniques high performance liquid chromatography-inductively coupled plasma-mass spectrometry (HPLC-ICP-MS) and X-ray absorption near edge structure (XANES) analysis were used to assess arsenic speciation in freshwater phytoplankton and zooplankton collected from arsenic-contaminated lakes in Yellowknife (Northwest Territories, Canada). Arsenic concentrations in lake water ranged from 7 μg L(-1) in a noncontaminated lake to 250 μg L(-1) in mine-contaminated lakes, which resulted in arsenic concentrations ranging from 7 to 340 mg kg(-1) d.w. in zooplankton organisms (Cyclops sp.) and from 154 to 894 mg kg(-1) d.w. in phytoplankton. The main arsenic compounds identified by HPLC-ICP-MS in all plankton were inorganic arsenic (from 38% to 98% of total arsenic). No other arsenic compounds were found in phytoplankton, but zooplankton organisms showed the presence of organoarsenic compounds, the most common being the sulfate arsenosugar, up to 47% of total arsenic, with traces of phosphate sugar, glycerol sugar, methylarsonate (MMA), and dimethylarsinate (DMA). In the uncontaminated Grace Lake, zooplankton also contained arsenobetaine (AB). XANES characterization of arsenic in the whole plankton samples showed As(V)-O as the only arsenic compound in phytoplankton, and As(III)-S and As(V)-O compounds as the two major inorganic arsenic species in zooplankton. The proportion of organoarsenicals and inorganic arsenic in zooplankton depends upon the arsenic concentration in lakes and shows the impact of arsenic contamination: zooplankton from uncontaminated lake has higher proportions of organoarsenic compounds and contains arsenobetaine, while zooplankton from contaminated area contains mostly inorganic arsenic.     

Chemical speciation and bioaccessibility of arsenic and chromium in chromated copper arsenate-treated wood and soils

This research compares the As and Cr chemistry of dislodgeable residues from chromated copper arsenate (CCA)-treated wood collected by two different techniques (directly from the board surface either by rubbing with a soft bristle brush or by rinsing from human hands after contact with CCA-treated wood) and demonstrates that these materials are equivalent in terms of both the chemical form and bonding of As and Cr and in terms of the As leaching behavior. This finding links the extensive chemical characterization and bioavailability testing that has been done previously on the brush-removed residue to a material that is derived from human skin contact with CCA-treated wood. Additionally, this research characterizes the arsenic present in biological fluids (sweat and simulated gastric fluid) following contact with these residues. The data demonstrate that in biological fluids the arsenic is present primarily as free arsenate ions. Arsenic-containing soils were also extracted into human sweat to evaluate the potential for arsenic dissolution from soils at the skin surface. For soils from field sites, only a small fraction of the total arsenic is soluble in sweat. Based on comparisons to reference materials that have been used for in vivo dermal absorption studies, these findings suggest that the actual relative bioavailability via dermal absorption of As from CCA residues and soil may be well below the current default value of 3% used by U.S. EPA.     

Arsenic speciation and phytoavailability in contaminated soils using a sequential extraction procedure and XANES spectroscopy

In this study, a sequential extraction procedure (SEP) and X-ray absorption near edge structure (XANES) spectroscopy were used to determine the solid-phase speciation and phytoavailability of arsenic (As) of historically contaminated soils from As containing pesticides and herbicides and soils spiked with As in the laboratory. Brassica juncea was grown in the contaminated soils to measure plant available As in a glasshouse experiment. Arsenic associated with amorphous Fe oxides was found to be the dominant phase using both SEP and XANES spectroscopy. Arsenic predominantly existed in arsenate (As(V)) form in the soils; in a few samples As was also present in arsenite (As(III)) form or in scorodite mineral. Arsenic concentration in shoots showed significant (p < 0.001-0.05) correlations with the exchangeable As (r = 0.85), and amorphous Fe oxides associated As evaluated by the SEP (r = 0.67), and As associated with amorphous Fe oxides as determined by XANES spectroscopy (r = 0.51). The results show that As in both fractions was readily available for plant uptake and may pose a potential risk to the environment. The combination of SEP and XANES spectroscopy allowed us the quantitative speciation of As in the contaminated soils and the identification of valence and mineral forms of As. Such detailed knowledge on As speciation and availability is vital for management and rehabilitation of As-contaminated soils.     

Volatilization of weathered chiral and achiral chlordane residues from soil

To mitigate the impact on the environment of persistent organic pollutants (POPs), we must understand thoroughly their environmental fate. Residues of many of these pollutants are still present in soil years after their legitimate uses were banned. In this report, the volatilization of one such persistent pollutant, chlordane, from a field where it was applied approximately 40 years ago, is examined in detail overthe course of several years. Ambient air samples were collected at three heights above the treated soil throughout the investigation. Air samples were also collected at several background sites in Connecticut for comparison. Analysis of these samples shows that chlordane volatilization from soil continues to occur long after initial application, at rates dependent on both temperature and cultivation of the soil. Comparison of relative concentrations and enantiomeric profiles for components of technical chlordane in atmospheric samples from a variety of sources suggests a regional, urban input of chlordane to the ambient air over Connecticut, possibly related to the widespread termiticidal use of chlordane in home foundation soils.     

Extraction of protein from expeller- and solvent-extracted coconut meal by dilute acid,alkali, and salt solutions

The extractability of protein (nitrogen) from poonac (the press-cake left after extraction of oil from dried coconut kernel) with dilute aqueous hydrochloric acid, sodium hydroxide, and salt solutions has been investigated. Experiments were carried out on both expeller poonac and solvent-extracted poonac, the protein of the former being more soluble. Approximately 40% and 55% of the poonac protein nitrogen was extractable with 0.15% aqueous acid and alkali, respectively, under optimum conditions. Dilute salt solutions were found to have a comparatively poor solubilising effect under the conditions employed. Increasing the fat content of expeller poonac to 10% increased the nitrogen extracted by acid but not by alkali solutions.     

In vitro synergistic anti-oxidant activities of solvent-extracted fractions from Astragalus membranaceus and Glycyrrhiza uralensis

Our study estimated the in vitro anti-oxidant activities of the solvent-extracted fractions from Astragalus membranaceus (AME), Glycyrrhiza uralensis (GU) and the combination of them (AG), using 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay, 2,2-azinobis (3-ethyl-benzothiazoline-6-sulfonic acid) (ABTS) free radical scavenging assay and ferric reducing anti-oxidant power (FRAP) assay. Different solvent extracts have different anti-oxidant activities. As to the herb pair (AG), the highest anti-oxidant capacity and total phenolic/flavonoid content were observed in the ethyl acetate fraction, which were exhibited in different solvent fractions of the individual herbs. The ethyl acetate extract of herb pair (EA-AG) showed significantly higher anti-oxidant capacity than the theoretical sum of two single herbs, and presented better cytoprotection and induced higher activity of anti-oxidant enzymes than the single herbs. Moreover, there’s a linear correlation between the increment of total phenolics/flavonoids and anti-oxidant capacities, especially between polyphenol content and TEAC values (correlation coefficient = 0.9^∗). These indicated that the phenolic and flavonoid may be the main compounds which caused the synergistic anti-oxidant capacity and cytoprotection in the combination of AME and GU.