Arsenic forensic modeling leads to decommission of downgradient/off-site monitoring wells

Arsenic was detected at concentrations exceeding the regulatory limit of 0.010 milligrams per liter (mg/L) in an off-site bedrock monitoring well downgradient of a former electroplating facility in Merrimack, New Hampshire. The bedrock underlying the site is associated with naturally occurring high concentrations of groundwater arsenic. Geochemical modeling was used to evaluate whether the arsenic in bedrock groundwater at the off-site monitoring location was site-related or naturally occurring. The hydrogeochemical signature of the off-site bedrock well did not resemble signatures of site-impacted bedrock wells. Multiple lines of evidence support that the arsenic observed in off-site bedrock groundwater was not a result of adverse impacts from site-related groundwater contamination.     

Arsenic mobility in contaminated lake sediments

An arsenic contaminated lake sediment near a landfill in Maine was used to characterize the geochemistry of arsenic and assess the influence of environmental conditions on its mobility. A kinetic model was developed to simulate the leaching ability of arsenic in lake sediments under different environmental conditions. The HM1D chemical transport model was used to model the column experiments and determine the rates of arsenic mobility from the sediment. Laboratory studies provided the information to construct a conceptual model to demonstrate the mobility of arsenic in the lake sediment. The leaching ability of arsenic in lake sediments greatly depends on the flow conditions of ground water and the geochemistry of the sediments. Large amounts of arsenic were tightly bound to the sediments. The amount of arsenic leaching out of the sediment to the water column was substantially decreased due to iron/arsenic co-precipitation at the water-sediment interface. Overall, it was found that arsenic greatly accumulated at the ground water/lake interface and it formed insoluble precipitates.     

Arsenic speciation in plants growing in arsenic-contaminated sites

Concentrations of total arsenic and of arsenic species were determined by ICPMS and HPLC-ICPMS in terrestrial plant samples. The arsenic concentration in plant samples from the contaminated sites ranged from 1.14 to 98.5 mg kg(-1) (dry mass). However, a very high value, exceeding largely this range was found in a moss sample growing in the contaminated area (1750 mg kg(-1)). Plants growing in a non-contaminated area with similar geological characteristics contained 0.06-0.58 mg As kg(-1). Plant samples from different species were selected and extracted with water, water/methanol (9+1, v/v), and water/methanol (1+1, v/v). Water/methanol (9+1, v/v) was selected as extractant for the speciation analysis for all the plant samples. The extraction efficiencies ranged from 3.0% to 41.4%, with good agreement between samples from the same plant species. Arsenite and/or arsenate were found in all the plant samples. Additionally, methylarsonate (MA), dimethylarsinate (DMA), trimethylarsine oxide (TMAO) and tetramethylarsonium ion (TETRA) were also identified in several plants, and in some cases MA and DMA were the main species found. TMAO, which is usually found as a trace constituent in organisms, was also a significant arsenical in one of the studied samples, where it constituted 24% of the extracted arsenic. In the present study, the patterns of arsenic species varied with the plant species and much higher proportion of organoarsenicals was found in plants from the more contaminated sites.     

Statistical Issues in Assessing Anthropogenic Background for Arsenic

Conceptual and statistical issues surrounding the estimation of a background concentration distribution for arsenic are reviewed. How background area is defined and samples collected are shown to impact the shape and location of the probability density function that in turn affects the estimation and precision of associated distributional parameters. The overall background concentration distribution is conceptualized as a mixture of a natural background distribution, an anthropogenic background distribution and a distribution designed to accommodate the potential for contamination site samples being included into the background sample set. This concept is extended to a discussion of issues surrounding estimation of natural and anthropogenic background distributions for larger geographic areas. Finally, the mixture model is formally defined and statistical approaches to estimating its parameters discussed.     

Statistical Issues in Assessing Anthropogenic Background for Arsenic

Conceptual and statistical issues surrounding the estimation of a background concentration distribution for arsenic are reviewed. How background area is defined and samples collected are shown to impact the shape and location of the probability density function that in turn affects the estimation and precision of associated distributional parameters. The overall background concentration distribution is conceptualized as a mixture of a natural background distribution, an anthropogenic background distribution and a distribution designed to accommodate the potential for contamination site samples being included into the background sample set. This concept is extended to a discussion of issues surrounding estimation of natural and anthropogenic background distributions for larger geographic areas. Finally, the mixture model is formally defined and statistical approaches to estimating its parameters discussed.     

Arsenic compounds accumulated in pearl oyster Pinctada fucata

We investigated the water-soluble arsenic compounds present in the soft tissues of both the pearl-free and the pearl-containing pearl oysters. After dividing the soft tissue into five parts, i.e., adductor muscle, foot, mantle, viscera and gill, each part was analyzed by high-performance liquid chromatography-inductively coupled plasma mass spectrometry for the arsenic compounds accumulated in it. Arsenic concentration of each tissue part ranged from 22.1 to 45.7 microg g(-1) of dry tissue in the pearl-free pearl oyster and from 27.4 to 50.4 microg g(-1) of dry tissue in the pearl-containing pearl oyster. On the grounds of the present evidence the major water-soluble arsenic compound accumulated in each part was identified as arsenobetaine without exception in both types of pearl oysters (94.3-99.7% in the pearl-free pearl oyster and 87.2-99.7% in the pearl-containing pearl oyster). Trace or small amounts of arsenic compounds including tetramethylarsonium ion and arsenocholine were also detected in some parts. The levels of these minor arsenicals were a little higher in pearl-free pearl oyster than in the pearl-containing pearl oyster. This study confirms the hygienic safety of the soft tissues of both the pearl-free and the pearl-containing pearl oysters, as food.     

Arsenic in sediments from the southeastern Baltic Sea

Arsenic occurs as a persistent constituent in many of the chemical weapons dumped into the Baltic Sea; it can be used as an indicator of leakage and dispersal of released munitions to the marine environment. Total arsenic was analysed in sediment samples taken from the Lithuanian economic zone in the Baltic Sea, which included samples from the chemical munitions dumpsite in the Gotland Basin and national monitoring stations in the southeastern Baltic Sea. Arsenic concentrations in sediments ranged from 1.1 to 19.0 mg kg(-1), with an average of 3.4 mg kg(-1). Although there was evidence of slightly elevated arsenic content in sediments near the weapons dumpsite, arsenic concentrations were nevertheless quite low relative to other investigations in the Baltic and North Seas.     

Contamination in Ontario farmstead domestic wells and its association with agriculture:: 1. Results from drinking water wells

Groundwater provides about 30% of water requirements in Ontario, but farm families depend almost entirely on private wells. Major potential contaminants on farms are nitrate (NO₃⁻), pathogenic microorganisms, pesticides and petroleum derivatives. A survey of farm drinking-water wells was conducted throughout the Province of Ontario, Canada, in 1991 and 1992 and tested for these contaminants. The main objectives of the survey were to determine the quality and safety of drinking water for farm families, and determine the effect of agricultural management on groundwater quality at a provincial scale. Four farm wells were chosen in each township where >50% of the land area was used for agricultural production. Elsewhere one well per township was usually sampled. Within each township the types of farming activity and dominant soils were additional criteria for selection. The network comprised 1292 of the estimated 500,000 water-wells in Ontario, and the study conformed to a stratified random survey. A subset of 160 wells, chosen by farm type, soil, and the presence or absence of a fuel storage tank, was investigated for the presence of petroleum derivatives: benzene, toluene, ethyl benzene, and xylene. About 40% of farm wells tested contained one or more of the target contaminants above the maximum acceptable concentration; 34% of wells had more than the maximum acceptable number of coliform bacteria, 14% contained NO₃⁻-N concentrations above 10 mg l⁻¹ limit and about 7% were contaminated with both bacteria and NO₃⁻. Only six wells contained pesticide residues above the interim maximum acceptable concentration (IMAC), but pesticides were detected in 7% of wells in winter and in 11% in summer. No wells contained detectable petroleum derivatives. These results for NO₃⁻ contamination were not significantly different from those reported for a survey of Ontario wells for the period 1950–1954, but the frequency of contamination by Escherichia coli was greater in the present study. None of the point sources investigated contributed significantly to the NO₃⁻ contamination. The percentage of wells contaminated by coliform bacteria decreased significantly with increasing separation of the well from the feedlot or exercise yard on livestock farms. A full statistical model including the type of well construction, depth, age and soil hydrologic group was developed to describe the frequency of NO₃⁻ contamination.     

Extraction wells and biogas recovery modeling in sanitary landfills

A general methodology is established that permits the characterization and evaluation of the optimum potential of biogas extraction at each vertical well in the sanitary landfill of Asturias, Spain. Twenty wells were chosen from a total of 225 for the study, and the maximum production flow of biogas, which is a result of the degradation of the municipal solid waste deposited within its area of influence, was determined for each well. It was found that this flow varied with time and is characteristic of each extraction well. The maximum extractable flow also was determined as a function of the composition of the biogas needed for its subsequent utilization. The biogas extraction yield in the wells under study varied between approximately 26 and 97%, with a mean recovery value of 82%. The low yields found in certain cases were generally caused by a sealing defect, which leads to excessive incorporation of air into the landfill gas through the surrounding soil or through the extraction shaft, and which make its subsequent utilization difficult.     

Arsenic speciation in field-collected and laboratory-exposed earthworms Lumbricus terrestris

Mature Lumbricus terrestris were host soils and leaf litter were collected from a former arsenic mine in Devon, UK (Devon Great Consols), a former gold mine in Ontario, Canada (Deloro), and an uncontaminated residential garden in Nottingham, UK. Arsenic concentrations determined by inductively coupled plasma-mass spectrometry (ICP-MS) in soils were 16-348 mg kg⁻¹, 6.0-239 mg kg⁻¹ in the earthworms and 8.6 mg kg⁻¹ in leaf litter sampled at Deloro (all dry weight). High performance liquid chromatography (HPLC-ICP-MS) analysis revealed arsenite (As^III), arsenate (As^V) and five organoarsenic species; arsenobetaine (AB), methylarsonate (MA^V), dimethylarsinate (DMA^V), arsenosugar 1 (glycerol sugar), arsenosugar 2 (phosphate sugar), and trimethylarsineoxide (TMAO) in field-collected L. terrestris. Differences were observed in the variety of organoarsenic species present between field sites. Several organoarsenic species were observed in the leaf litter (DMA^V, arsenosugar 2 and TMAO) but not AB. Depuration resulted in higher concentrations of inorganic As being detected in the earthworm whereas the concentration or variety of organoarsenic species was unchanged. Commercially sourced L. terrestris were exposed to As contaminated soil in laboratory mesocosms (1.0, 98, 183, 236, 324 and 436 mg kg⁻¹) without leaf litter and were additionally analyzed using X-ray absorption near edge structure (XANES). Only inorganic As^III and As^V was observed. It is proposed that ingestion of leaf litter and symbiotic processes in the natural soil environment are likely sources of organoarsenic compounds in field-collected L. terrestris.     

Arsenic species and chemistry in groundwater of southeast Michigan

Groundwater samples, taken from 73 wells in 10 counties of southeast Michigan in 1997 had arsenic concentrations in the range of 0.5 to 278 microg/L the average being 29 microg/l. About 12% of these wells had arsenic concentrations that exceeded the current USEPA's maximum contaminant level of 50 microg/l. Most (53-98%) of the arsenic detected was arsenite [As(III)] and other observations supported the arsenic species distribution (low redox potential and DO). In shallow groundwater (< 15 m), arsenic concentrations are low likely due to the formation of insoluble ferrosoferric hydroxide complex. In deep groundwater (> 15 m), the concentration of arsenic is possibly controlled by reductive dissolution of arsenic-rich iron hydroxide/oxyhydroxide and dissolution of arsenic sulfide minerals.     

Arsenic immobilization in soils amended with drinking-water treatment residuals

Use of Fe/Al hydroxide-containing materials to remediate As-contaminated sites is based on the general notion that As adsorption in soils is primarily controlled by Fe/Al (hydr)oxides. A low-cost and potentially effective substitute for natural Fe/Al hydroxides could be the drinking-water treatment residuals (WTRs). Earlier work in our laboratory has shown that WTRs are effective sorbents for As in water. We hypothesized that land-applied WTRs would work equally well for As-contaminated soils. Results showed that WTRs significantly (p<0.001) increased the soil As sorption capacity. All WTR loads (2.5, 5, and 10%) significantly (p<0.001) increased the overall amount of As sorbed by both soils when compared with that of the unamended controls. The amount of As desorbed with phosphate (7500 mg kg(-1) load) was approximately 50%. The WTR effectiveness in increasing soil As sorption capacities was unaffected by differences in both soils' chemical properties.     

Arsenic uptake in orchard trees: implications for dendroanalysis

The distribution of arsenic in the stems of fruit trees grown in soils exposed to arsenical pesticides has been studied using neutron activation analysis. The results show arsenic to be confined mainly to heartwood near the pith and active xylem tissue in the most recent annual growth rings. These results suggest that dendroanalysis for arsenic in fruit trees will not yield a reliable chronology of arsenic exposure.     

Speciation of Arsenic in Ambient Aerosols Collected in Los Angeles

First-time measurements of the potentially toxic inorganic species of arsenic (arsenite arid arsenate) have been obtained in fine (<2.5 µm AD) and coarse (>2.5 µm AD) atmospheric particles in the Los Angeles area. A recently developed method that includes procedures for sample collection, preparation, and analysis was used in this study. Size-fractlonated aerosol samples were collected with a high-volume dichotomous virtual impactor that employed polytetrafluoroethylene filters. Results were obtained for the recovery of arsenic standards added to unexposed and collected filters. Data from this study, indicated that the recently developed speciation method can be used to determine concentrations of As(lll) and As(V) In atmospheric particulate matter samples.

Size-fractionated aerosol samples were collected in the city of Industry during January and February 1987. In most samples, As(lll) and As( V) were above the detection limit (approximately 1 ng m^-3 of either species) in both aerosol size fractions. A greater portion (about 75 percent) of the two species were observed in the fine particles. The As(lll)/As(V) ratio for both particle sizes was close to 1 (I.e., an equal mixture of both species). Comparison of total suspended particulate arsenic measured by the speciation method to that measured by a routine California Air Resources Board-approved procedure showed good agreement (r = 0.94), indicating both methods were approximately equivalent for the collection and analysis of aerosol arsenic.     

Arsenic and chromium speciation in an urban contaminated soil

The distribution and speciation of As and Cr in a contaminated soil were studied by synchrotron-based X-ray microfluorescence (μ-XRF), microfocused X-ray absorption spectroscopy (μ-XAS), and bulk extended X-ray absorption fine structure spectroscopy (EXAFS). The soil was taken from a park in Wilmington, DE, which had been an important center for the leather tanning industry along the Atlantic seaboard of the United States, until the early 20th century. Soil concentrations of As, Cr, and Pb measured at certain locations in the park greatly exceeded the background levels of these heavy metals in the State of Delaware. Results show that Cr(III) and As(V) species are mainly present in the soil, with insignificant amounts of Cr(VI) and As(III). Micro-XRF maps show that Cr and Fe are distributed together in regions where their concentrations are diffuse, and at local spots where their concentrations are high. Iron oxides, which can reduce Cr(VI) to Cr(III), are present at some of these hot spots where Cr and Fe are highly concentrated. Arsenic is mainly associated with Al in the soil, and to a minor extent with Fe. Arsenate may be sorbed to aluminum oxides, which might have transformed after a long period of time into an As-Al precipitate phase, having a structure and chemical composition similar to mansfieldite (AlAsO(4)?2H(2)O). The latter hypothesis is supported by the fact that only a small amount of As present in the soil was desorbed using the characteristic toxicity leaching procedure tests. This suggests that As is immobilized in the soil.     

土壤固相吸附砷的研究进展

砷是一种常见的有毒元素,土壤砷污染与修复问题已引起世界范围的广泛关注。土壤原位修复是消除土壤砷污染的有效方法,其中砷在土壤固相上的吸附也是近年来的研究热点。土壤固相广泛存在于土壤中,并具有表面积大和表面电荷等理化性质,它可通过与砷酸根阴离子发生表面配位反应,形成内外层配位体等方式来固定土壤中的砷,以降低金属离子的迁移能力和有效性,是一种有效的原位减轻砷污染的方法。文中简单介绍了砷污染的现状、危害和赋存状态,重点介绍了铁铝锰的氧化物和氢氧化物、粘土矿物、有机质等土壤固相对砷的吸附机理及其影响因素,旨在更好地掌握砷的吸附行为。     

Arsenic speciation in marine fish and shellfish from American Samoa

We speciated arsenic compounds in marine fish and shellfish from two islands of the United States Territory of American Samoa in the South Pacific, and found that inorganic arsenic occurred as a minor fraction. The proportion of inorganic arsenic was generally far below the levels of prevailing assumptions typically used in human health risk assessments when only total arsenic is analysed. Fish and shellfish were collected from Tutuila and Ofu between May 2001 and March 2002 (n=383 individual specimens, with 117 composites); sites were selected based on habitat type and were representative of those frequented by local fishers. These islands have moderately developed reef fish fisheries among artisanal fishers, are far removed from any industrial or mining sources of arsenic, and presented an opportunity to study arsenic variations in marine biota from un-impacted environments. Target species were from various trophic levels and are among those frequently harvested for human consumption. We found evidence that arsenic concentrated in some marine species, but did not tend to follow classic trophic patterns for biomagnification or bioaccumulation. For the majority of samples, inorganic arsenic was less than 0.5% of total arsenic, with only a few samples in the range of 1-5%, the latter being mollusks which are recognized to have unusually high arsenic levels in general. This work supports the importance of speciation analysis for arsenic, because of the ubiquitous occurrence of arsenic in the environment, and its variable toxicity depending on chemical form.     

Arsenic leachability and speciation in cement immobilized water treatment sludge

Arsenic leachability and speciation in cement immobilized water treatment sludge were investigated with leaching tests and X-ray absorption near edge structure (XANES) spectroscopy. The As leachability in the sludge determined with the toxicity characteristic leaching procedure (TCLP) and the waste extraction test (WET) was 283 and 7490 microgl(-1), respectively. Extractions with a lower liquid to solid ratio, under anaerobic conditions, and using citric acid buffer solution dramatically increased the leachate As concentration. XANES results showed that the As(III) composition was reduced from 51.1% of the total As content in the sludge to 16.3% in the cement treated sample with 28 days of cure. When the cement treated sample was cured for two years, the As(III) composition was decreased to 7.4%. The cement treatment reduced the As leachability. The leachate As(III) and total As concentrations were of the same order of magnitude in the samples cured for 28 days as for 2yr. However, consistently lower concentrations were detected in samples with longer cure time. The results of this study improve our understanding of arsenic speciation and leachability in the cement matrix after long cure times.