Seasonal variation of total dissolved arsenic and arsenic speciation in a polluted surface waterway

Seasonal differences in the dissolved arsenic concentration and speciation in a contaminated urban waterway in northwest England have been determined using a coupled ion chromatography-inductively coupled plasma-mass spectrometry (IC-ICP-MS) technique. Waters sampled in the vicinity of an industrial works during relatively dry conditions in April 2000 were found to contain total arsenic concentrations (As) of up to 132 g L^–1, more than an order magnitude greater than the 4 g L^–1 maximum found in December 2000. The difference in As between the April and December sampling periods is speculated to be largely due to the irregular anthropogenic supply of arsenic to the watercourse. For both sampling periods, the dissolved arsenic was exclusively inorganic in nature and had an As(V)/As ratio of between 0.6 and 0.8. Analysis of samples taken downstream of the industrial site, after the confluence with a relatively As-poor stream, revealed that As(III), As(V) and As concentrations were lower than would be expected from conservative mixing. The As(V)/As ratio was also observed to decrease markedly. The loss of arsenic from solution is thought to be due to adsorption on the iron oxyhydroxide-rich sediment observed to coat the riverbed downstream of the confluence. The reduction in the As(V)/As ratio is believed to be due to the more rapid adsorption of As(V) compared to that of As(III). Deviations from conservative behaviour were more marked during the relatively dry April 2000 sampling period and suggest the increased importance of adsorption processes controlling arsenic availability during this time.     

Field based speciation of arsenic in UK and Argentinean water samples

A field method is reported for the speciation of arsenic in water samples that is simple, rapid, safe to use beyond laboratory environments, and cost effective. The method utilises solid-phase extraction cartridges (SPE) in series for selective retention of arsenic species, followed by elution and measurement of eluted fractions by inductively coupled plasma mass spectrometry (ICP-MS) for “total” arsenic. The method is suitable for on-site separation and preservation of arsenic species from water. Mean percentage accuracies (n = 25) for synthetic solutions of arsenite (As^III), arsenate (As^V), monomethylarsonic acid (MA), and dimethylarsinic acid (DMA) containing 10 μg l⁻¹ As, were 98, 101, 94, and 105%, respectively. Data are presented to demonstrate the effect of pH and competing anions on the retention of the arsenic species. The cartridges were tested in the UK and Argentina at sites where arsenic was known to be present in surface and groundwaters, respectively, at elevated concentrations and under challenging matrix conditions. In Argentinean groundwater, 4–20% of speciated arsenic was present as MA and 20–73% as As^III. In UK surface waters, speciated arsenic was measured as 7–49% MA and 12–42% DMA. Comparative data from the field method using SPE cartridges and the laboratory method using liquid chromatography coupled to ICP-MS for all water samples provided a correlation of greater than 0.999 for As^III and DMA, 0.991 for MA, and 0.982 for As^V (P < 0.01).     

Urinary arsenic methylation profile in children exposed to low arsenic levels through drinking water

There is a lack of information on arsenic metabolism in children exposed chronically to low levels of arsenic (<50 µg L^?1). The objective of this study was to determine the methylation profile of urinary arsenic metabolites in children exposed to low-level concentrations of arsenic via their drinking water. A cross-sectional study was undertaken in 50 children from four towns in the Yaqui Valley, Sonora, with total arsenic values of 39.9, 16.8, 7.3, and 5.5 µg L^?1 in their drinking water, respectively. First morning void samples were analyzed for inorganic-As (InAs), mono and dimethyl arsenic (MMA and DMA). The total arsenic excreted in urine ranged from 23.1 to 99.1 µg L^?1 and these levels did not vary by sex. Children with the highest level of total arsenic in their drinking water excreted the highest amount in urine and the length of residence and age also had significant contribution. Children with a lower range of arsenic exposure (16.8–5.5 µg L^?1) had similar amounts of arsenic in urine with values of 23.1, 28.2, and 32.6 µg L^?1, respectively. DMA had the highest proportion in urine (52.1–74.7%), followed by InAs (16.3–34.9%) and MMA (4.4–8.4%). Compared to other reports, these children excreted a low %MMA (6.1%), and children from the towns with the lowest levels of arsenic had the highest %InAs and the lowest %DMA. This variability in arsenic methylation was partially explained by arsenic concentration in drinking water, years of residence and age, and may reflect genetic differences or more contribution from different exposure routes. In conclusion, our results show that at low levels of exposure the children's ability to metabolize InAs did not have a linear association with the levels of arsenic, and overall children from the Yaqui Valley excrete a lower %MMA than expected.     

Fractionation and speciation of arsenic in fresh and combusted coal wastes from Yangquan, northern China

In this study, the content and speciation of arsenic in coal waste and gas condensates from coal waste fires were investigated, respectively, using the digestion and sequential extraction methods. The fresh and fired-coal waste samples were collected from Yangquan, which is one of the major coal production regions in northern China. High-performance liquid chromatography-inductively coupled plasma-mass spectrometry (HPLC-ICP-MS) was used to determine the concentrations of four major arsenic species [As(III), As(V), monomethylarsonic acid (MMA) and dimethylarsenic acid (DMA)] in the extracts, while ICP-MS was used to measure total As content. Arsenic content in the investigated coal wastes and the condensate ranges between 23.3 and 69.3 mg/kg, which are higher than its reported average content in soils. Arsenic in coal waste exists primarily in the residual fraction; this is followed in decreasing order by the organic matter-bound, Fe–Mn oxides-bound, exchangeable, carbonates-bound, and water-soluble fractions. The high content of arsenic in the condensates indicates that combustion or spontaneous combustion is one of the major ways for arsenic release into the environment from coal waste. About 15% of the arsenic in the condensate sample is labile and can release into the environment under leaching processes. The water extractable arsenic (WEA) in the fresh coal waste, fired coal wastes, and the condensate varied between 14.6 and 341 μg/kg, with As(V) as the major species. Furthermore, both MMA and DMA were found in fresh coal wastes, fired coal wastes, and the condensate.     

An assessment of sampling,preservation, and analytical procedures for arsenic speciation in potentially contaminated waters

This study was undertaken to ascertain optimal methods of sampling, preserving, separating, and analyzing arsenic species in potentially contaminated waters. Arsenic species are readily transformed in nature by slight changes in conditions. Each species has a different toxicity and mobility. The conventional field sampling method using filters of 0.45 μm in size could overestimate the dissolved arsenic concentrations, as passing suspended particles that can act as a sink or source of arsenic depending on the site condition. For arsenic species in neutral pH and iron-poor waters, the precipitation can be stable for up to 3 days without any treatment, but for longer periods, a preservative, such as phosphoric acid, is required. Also, the analytical procedure must be selected carefully because the levels and hydride generation efficiencies of arsenic in different species can vary, even for the same amount of arsenic. For arsenic speciation in samples that also include organic species, a hybrid high-performance liquid chromatography (HPLC) column and inductively coupled plasma mass spectrometry (ICP-MS) gave the best resolution and lowest detection limits. However, the procedure using a solid phase extraction (SPE) cartridge can be used economically and conveniently for analyzing samples containing only inorganic arsenic species, such as groundwater, especially that related to mine activity.     

Arsenic speciation in rice consumed in south-western Nigeria,and estimation of dietary intake of arsenic species through rice consumption

This study determined concentrations and speciation of arsenic (As) in rice samples obtained from the cities of Akure, Ore, Ondo and Ikare in Ondo State, south-western Nigeria. The estimated dietary intake of As from rice consumption for total As and the identified As species were compared with the As benchmark dose lower confidence limit. Analyses of rice from the four cities identified three As species: inorganic As, monomethylarsonic, acid and dimethylarsinic acid. Concentrations of total As and the As species differed significantly across the sampling locations (by a factor of 2.5 for total As). Mean levels (±S.D.) were 58.8 ± 0.7 µg/kg total As, 47.0 ± 0.6 µg/kg inorganic As, 0.33 ± 0.03 µg/kg monomethylarsonic acid, and 11.5 ± 0.1 µg/kg dimethylarsinic acid. The estimated mean dietary intakes were 4.1 µg/d total As, 3.3 µg/d inorganic As, 0.02 µg/d monomethylarsonic acid, and 0.8 µg/d dimethylarsinic acid. These values are below the benchmark dose lower confidence limit and comparable to, or lower than, those reported for other countries. Thus, consumption of rice cultivated in south-western Nigeria does not appear to have inherent As-associated health risks.     

Influence of groundwater recharge and well characteristics on dissolved arsenic concentrations in southeastern Michigan groundwater

Arsenic concentrations exceeding 10 μg/l, the United States maximum contaminant level and the World Health Organization guideline value, are frequently reported in groundwater from bedrock and unconsolidated aquifers of southeastern Michigan. Although arsenic-bearing minerals (including arsenian pyrite and oxide/hydroxide phases) have been identified in Marshall Sandstone bedrock of the Mississippian aquifer system and in tills of the unconsolidated aquifer system, mechanisms responsible for arsenic mobilization and subsequent transport in groundwater are equivocal. Recent evidence has begun to suggest that groundwater recharge and characteristics of well construction may affect arsenic mobilization and transport. Therefore, we investigated the relationship between dissolved arsenic concentrations, reported groundwater recharge rates, well construction characteristics, and geology in unconsolidated and bedrock aquifers. Results of multiple linear regression analyses indicate that arsenic contamination is more prevalent in bedrock wells that are cased in proximity to the bedrock-unconsolidated interface; no other factors were associated with arsenic contamination in water drawn from bedrock or unconsolidated aquifers. Conditions appropriate for arsenic mobilization may be found along the bedrock-unconsolidated interface, including changes in reduction/oxidation potential and enhanced biogeochemical activity because of differences between geologic strata. These results are valuable for understanding arsenic mobilization and guiding well construction practices in southeastern Michigan, and may also provide insights for other regions faced with groundwater arsenic contamination.     

Urinary arsenic levels influenced by abandoned mine tailings in the Southernmost Baja California Peninsula,Mexico

Gold has been mined at San Antonio-El Triunfo, (Baja California Sur, Mexico) since the 18th century. This area has approximately 5,700 inhabitants living in the San Juan de Los Planes and El Carrizal hydrographic basins, close to more than 100 abandoned mining sites containing tailings contaminated with potentially toxic elements such as arsenic. To evaluate the arsenic exposure of humans living in the surrounding areas, urinary arsenic species, such as inorganic arsenic (iAs) and the metabolites mono-methylated (MMA) and di-methylated arsenic acids (DMA), were evaluated in 275 residents (18–84 years of age). Arsenic species in urine were analyzed by hydride generation-cryotrapping-atomic absorption spectrometry, which excludes the non-toxic forms of arsenic such as those found in seafood. Urinary samples contained a total arsenic concentration (sum of arsenical species) which ranged from 1.3 to 398.7 ng mL^?1, indicating 33 % of the inhabitants exceeded the biological exposition index (BEI = 35 ng mL^?1), the permissible limit for occupational exposure. The mean relative urinary arsenic species were 9, 11 and 80 % for iAs, MMA and DMA, respectively, in the Los Planes basin, and 17, 10 and 73 %, respectively, in the El Carrizal basin. These data indicated that environmental intervention is required to address potential health issues in this area.     

Daily intake of selenium and concentrations in blood of residents of Riyadh City, Saudi Arabia

Concentrations of selenium (Se) in food from local markets of Riyadh, Kingdom of Saudi Arabia (KSA) were measured and daily intake calculated based on information from a questionnaire of foods eaten by healthy Saudis. The daily intake of Se was then compared to concentrations of Se in blood serum. Primary sources of Se in the diet of Saudis were as follows: meat and meat products (31%), egg (20.4%), cereals and cereal products (16%), legumes (8.7%), fruits (6.8%), milk and dairy products (2.0%), beverages (2%), sweets (1.8%), pickles (0.2%), and oil (0.02%). Daily intake of Se, estimated to be 93 μg Se/person/day, was slightly greater than that calculated from the Food and Agriculture Organization (FAO) food balance sheet for KSA, which was approximately 90 μg Se/person/day. The daily intake of Se by Saudis in Riyadh was greater than that of Australians or Dutch but less that of Canadians and Americans. There was a statistically significant correlation (R = +0.38, P < 0.05) between daily intake of Se and concentrations of Se in blood serum of Saudis in Riyadh. The mean concentration of Se in serum was 1.0 × 10(2) ± 30.5 μg Se/l. Taken together, the results suggest that the average Se intake and Se serum concentrations are within the known limits and recommendations, making it unlikely that Saudis are on average at risk of deficiency or toxicity.     

Anomalous arsenic concentrations in groundwaters of an island community, Bowen Island, British Columbia

Recently, occurrences of elevated arsenic concentrations in bedrock groundwaters used for individual and municipal water supplies have been recognised along the mainland coast of southern British Columbia, Canada. An area on Bowen Island (Queen Charlotte Heights community) was chosen to investigate the source(s) of arsenic, geochemical processes controlling its aqueous uptake, the role of geology and structure in the formation of these waters, and the use of hydrogeochemical survey methods for detecting arsenious groundwater regions. Pyrite- arsenopyrite-Cu mineralisation in the Queen Charlotte Heights area is present as veins associated with NE-trending fault zones and as disseminations in marginal breccia and stockwork zones of a ryhodacite porphyry stock. Near surface mineralisation was later altered by supergene events to form minor pyrite- arsenopyrite in a matrix of limonite and clay. Geochemical factors that control the concentration and mobility of arsenic in these groundwaters include: (a) anion exchange of arsenic from clay minerals during cation divalent/univalent exchange processes (water softening) which leads to waters of high pH and high anion exchange capacities; (b) desorption of arsenic from Fe and Al oxyhydroxide minerals during pronounced shifts in pH from acid to alkaline conditions brought on by the water softening process; and (c) stepwise oxidation of arsenopyrite mineralisation to form arsenious sulphate-bearing groundwaters. The inconsistent behaviour of the As3+ and As5+ ions during the complex waterrock interaction processes described above, precludes the use of detailed chemical analyses to predict relative abundances of the more toxic As3+ species. For a full appreciation of the toxic impact of groundwaters containing total arsenic concentrations that are above regulatory guidelines an arsenic speciation analysis is required.     

The influence of arsenic speciation (AsIII & AsV) and concentration on the growth, uptake and translocation of arsenic in vegetable crops (silverbeet and amaranth): greenhouse study

We examined arsenic (As) uptake by vegetable crops (amaranth, Amaranthus gangeticus, and silverbeet, Beta vulgaris) as affected by As speciation (As^III and As^V) and their concentrations in nutrient solution. Amaranth and silverbeet were grown in a nutrient solution containing four levels of arsenate (As^V): 0, 1, 5, and 25 mg As/l and three levels of arsenite (As^III): 0, 5, 10 mg As/l. Both As^V and As^III are phytotoxic to these crops with the latter being five times more toxic. Amaranth treated with As^III exhibited As toxicity symptoms within 48 h of exposure and was close to death within 1 week. However, As^V treatment did not show clear toxicity symptoms other than wilting and yield reduction at the highest dose rate of 25 mg As^V/l. The main mechanism used by vegetable crops to tolerate As^V is probably avoidance—limiting As transport to shoots and increasing As accumulation in the root system. When As^V was added to the nutrient solution, the uptake of As in shoots increased and, at the highest dose (25 mg As^V/l), 60 μg As/g DW (3.6 mg/kg FW) accumulated in the edible portion, which exceeds the WHO recommended limit for food stuffs (2 mg/kg FW) as the water contents of the crops were 94%. It is therefore important to determine the nature of the As species and their bio-accessibility. Iron treatment with 0.5 mg NaFe(III)EDTA/l dose decreased silverbeet As uptake by 45% given its affinity to bind As at the root surface or root rhizosphere and so restrict As translocation to the shoots.     

Developmental arrest in Japanese medaka (Oryzias latipes) embryos exposed to sublethal concentrations of atrazine and arsenic trioxide

Embryos of the Japanese medaka (Oryzias latipes) were exposed to serial concentrations of atrazine (0, 25, 50, and 100 ppm) and arsenic trioxide (0, 0.025, 0.05, 0.1 ppm) until hatching. Stasis of circulation, blood islands, titanic convulsions, tube heart and mortality were observed in atrazine-treated embryos. Each endpoint exhibited a concentration-response relationship. Only 4% of the embryos hatched in the 25 ppm, and none in the 50 and 100 ppm, probably due to cell death attributed to the embryos' inability to break from the chorion. With arsenic exposure, hatching was inversely correlated to chemical concentration: 86%, 75% and 54% for 0.025, 0.05 and 0.1 ppm, respectively. Hatching periods were also reduced from 7-13 days in controls to 7-11 days in arsenic-treated embryos. This observation was more pronounced with the 0.05 ppm concentration, showing a reduction of about 4 days. Despite this shortage in hatching time, there were no observable morphological abnormalities, as seen with atrazine. The ecological significance of these findings and implications for the development of sublethal toxicity tests using Japanese medaka embryos are important.     

Species and speciation in poikilothermal animals

On the basis of current scientific information related to intraspecific and interspecific variability of eco-physiological properties at the individual (organismic) and subindividual (tissues, cells, and molecules) levels and his own experimental data, the author comes to the conclusion that eco-physiological adaptation is one of the major processes determining speciation. During sequential multi-step adaptation at the most sensitive and plastic levels of organisation (whole organisms and their labile cells and proteins) to changed abiotic (physico-chemical) environmental factors, the latter directly affect the conservative proteins and polynucleotides that maintain the species' genetic information. Transition from phenotypical to genotypical changes may be achieved if the organisms have attained the limit of their phenotypical plasticity, via selection at cellular and molecular levels. The high rate of cellular mytotic division and a promiment rise in the speed of interrelated DNA-RNA protein synthesis under sudden and profound environmental changes may account for the high rates of speciation indicative of cataclysmic climatic changes. Evolutionary morphological changes are considered to follow physiological changes. The adaptive nature of morphological peculiarities in higher taxonomic categories (type, class, order, family; more seldom genus) may be accounted for by the selection of phenotypes possessing morphological peculiarities best suited to the ecological niches of the species concerned. These peculiarities (although often neutral to physiological changes that have determined the speciation) are transferred from species to species, manifesting both historical relationship and morphological unity. The suggested scheme of speciation is in accord with the conceptions of the intermittent character of speciation, which can proceed only if extreme, directed, climatic changes cover a larger portion of the species' area. As the organisms' organisation becomes more complex during phylogenesis, intraspecific variability decreases; this trend manifests itself in the progressive stabilization of body shape and other morphological properties, and in the increase of eco-physiological stability of cells and proteins.     

Risk assessment of bioaccessible arsenic and cadmium exposure through rice consumption in local residents of the Mae Tao Sub-district,Northwestern Thailand

Environmental Geochemistry and Health - Consumption of contaminated rice is a toxin exposure route in Asian populations. Since total concentrations generally overestimate health risks, the...     

Predicting arsenic concentrations in groundwater of San Luis Valley,Colorado: implications for individual-level lifetime exposure assessment

Consumption of inorganic arsenic in drinking water at high levels has been associated with chronic diseases. Risk is less clear at lower levels of arsenic, in part due to difficulties in estimating exposure. Herein we characterize spatial and temporal variability of arsenic concentrations and develop models for predicting aquifer arsenic concentrations in the San Luis Valley, Colorado, an area of moderately elevated arsenic in groundwater. This study included historical water samples with total arsenic concentrations from 595 unique well locations. A longitudinal analysis established temporal stability in arsenic levels in individual wells. The mean arsenic levels for a random sample of 535 wells were incorporated into five kriging models to predict groundwater arsenic concentrations at any point in time. A separate validation dataset (n = 60 wells) was used to identify the model with strongest predictability. Findings indicate that arsenic concentrations are temporally stable (r = 0.88; 95 % CI 0.83–0.92 for samples collected from the same well 15–25 years apart) and the spatial model created using ordinary kriging best predicted arsenic concentrations (ρ = 0.72 between predicted and observed validation data). These findings illustrate the value of geostatistical modeling of arsenic and suggest the San Luis Valley is a good region for conducting epidemiologic studies of groundwater metals because of the ability to accurately predict variation in groundwater arsenic concentrations.     

Geological and geochemical factors affecting the radon concentration in homes in Cornwall and Devon,UK

Recently collected data for radon levels in houses in Devon and Cornwall are compared with geological and geochemical information. The region is underlain by granites intruded into folded sedimentary rocks. The highest incidence of affected houses is on granites. The granites are characterised by moderate uranium concentrations, a deep weathering profile and uranium in mineral phase which is easily weathered. However, while the uranium may be removed, radium, the immediate precursor of radon, can remain in situ. Radon is emanated easily from the host rock, and high values of radon in ground and surface waters and soil gases have been detected. The granite areas are also characterised by high values of uranium in stream sediments and waters. In contrast, other zones of high uranium in stream sediment samples do not necessarily exhibit high house radon concentrations, especially when underlain by relatively impermeable rocks. Permeable ground can give rise to high incidences, of affected houses despite having uranium levels close to the crustal abundance. It is concluded that the most efficient method of identifying zones of high radon potential is the soil gas radon survey.     

Biochemical speciation in chromium genotoxicity

The biochemical speciation of chromium compounds in mammalian cells is discussed with respect to uptake, metabolism, DNA binding and damaging. Whereas soluble hexavalent chromium is taken up rapidly and accumulated intracellularly after its reduction, compounds of trivalent chromium penetrate biomembranes about three orders of magnitude slower. Cr(VI) after its uptake is metabolised by electron donating compounds via Cr(V) to Cr(III) compounds. Chromium from various Cr(III) compounds, but not chromate, binds to chromatin in isolated cell nuclei. The DNA‐protein crosslinks and DNA strand breaks observed in rat liver and kidney after chromate administration are also found in vitro, when Cr(III) compounds (but not chromate) interacts with isolated nuclei. In the Chinese Hamster cell HGPRT mutation assay, three out of four tested Cr(III) complexes were found to be mutagenic. In a direct DNA strand break assay with supercoiled bacteriophage PM 2 DNA, neither chromate nor the four Cr(III) compounds tested caused nicks. However, the combined action of chromate plus glutathione as well as the isolated complex of pentavalent chromium, Na₄Cr(glutathione)₄, did cause DNA breaks. Reactive oxygen species are inferred to be the ultimate DNA nicking agents in this assay. In conclusion there appear to be two mechanisms of chromate genotoxicity; one with direct DNA damage caused by Cr(V) species and one via DNA‐protein crosslinks formed with Cr(III), the final reduction state of chromate.