Showing papers on "Arsenic published in 1989"

Groundwater contamination with arsenic and other trace elements in an area of the pampa, province of Córdoba, Argentina

Abstract: A geochemical study of groundwater of the pampa in the province of Cordoba, Argentina, was performed; the area covered approximately 10,000 km2. Physical-chemical parameters, dissolved solids, and seven trace elements were determined in 60 selected water samples. Systematic and accurate measurements of arsenic, flourine, and vanadium were performed for the first time. Three trace element contaminants not reported earlier were found: an important one, selenium, and two others of less known effects, uranium and molybdenum. Eighty-four percent of the water analyzed showed arsenic contents over 0.05 mg/L, maximum contaminant level established by the U.S. Environmental Protection Agency (1982). The frequency distribution of trace elements was analyzed, and its fit to the lognormal distribution was proved by means of the Pearson and Kolmogorov-Smirnov test; the geographic distribution of the seven trace elements was mapped and its correlation with the anion-cation composition of the water was studied. The maximum arsenic, fluorine, vanadium, and uranium contents were found in the western part of the area under study, in waters containing dominant alkali metals in the cation composition. Maximum selenium and antimony contents were found in the eastern part of the area, while molybdenum distribution does not show any relationship with the other two groups. In addition, the geographic distribution of the trace elements seems to be related to the subsurface structure, which has been inferred using interactive digital analysis of Landsat imagery. The movements of the subsoil have disturbed surface and subsurface drainage influencing the water salinity and trace element contents. In order to investigate the origin of the contamination, 54 loess samples were collected in wells at depths ranging from the surface down to the water table. This loess, which has a high proportion of volcanic components, mainly rhyolitic glass, exhibits a chemical composition corresponding to that of a dacite. The loess and the volcanic glass show anomalous contents of all contaminant trace elements, mainly arsenic and selenium. For this reason loess is considered the most important contamination source in the groundwater under study.

Arsenic in ground-water under oxidizing conditions, south-west United States.

Abstract: Concentrations of dissolved arsenic in ground-water in alluvial basins of Arizona commonly exceed 50 μg L−1 and reach values as large as 1,300 μg L−1. Arsenic speciation analyses show that arsenic occurs in the fully oxidized state of plus 5 (As+5), most likely in the form of HAsO4∼2, under existing oxidizing and pH conditions. Arsenic in source areas presumably is oxidized to soluble As before transport into the basin or, if after transport, before burial. Probable sources of arsenic are the sulphide and arsenide deposits in the mineralized areas of the mountains surrounding the basins. Arsenic content of alluvial material ranged from 2 to 88 ppm. Occurrence and removal of arsenic in ground-water are related to the pH and the redox condition of the ground-water, the oxidation state of arsenic, and sorption or exchange. Within basins, dissolved arsenic correlates (P<0.01) with dissolved molybdenum, selenium, vanadium, and fluoride and with pH, suggesting sorption of negative ions. The sorption hypothesis is further supported by enrichment of teachable arsenic in the basin-fill sediments by about tenfold relative to the crustal abundance and by as much as a thousandfold relative to concentrations found in ground-water. Silicate hydrolysis reactions, as defined within the alluvial basins, under closed conditions cause increases in pH basinward and would promote desorption. Within the region, large concentrations of arsenic are commonly associated with the central parts of basins whose chemistries evolve under closed conditions. Arsenic does not correlate with dissolved iron (r = 0.09) but may be partly controlled by iron in the solid phase. High solid-phase arsenic contents were found in red clay beds. Large concentrations of arsenic also were found in water associated with red clay beds. Basins that contain the larger concentrations are bounded primarily by basalt and andesite, suggesting that the iron content as well as the arsenic content of the basin fill may play a role in the occurrence of arsenic in ground-water. Under oxidizing conditions in Arizona, arsenic in ground-water appears to be controlled in part by sorption or desorption of HAsO4∼2 on active ferric oxyhydroxide surfaces.

Evolution of a broadlands-type epithermal ore fluid along alternative P-T paths; implications for the transport and deposition of base, precious, and volatile metals

Abstract: Boiling and acidification of hydrothermal solutions are important mechanisms that lead to the deposition of base, precious, and volatile metals in epithermal systems. Computer models of these processes with a Broadlands-type geothermal water are presented in a three-part study: boiling, gas phase metal transport, and acid reactions with metal-bearing waters. Revised and partly rederived thermodynamic data necessary for such a study are presented as an appendix.Boiling of a Broadlands-type water along alternative P-T-enthalpy paths induces the precipitation of base metal sulfides, sulfosalts, and electrum. The precipitation of base metals results from the pH increase due to CO 2 degassing, and the precipitation of electrum results from the pH increase as well as sulfide loss to the gas phase. Heat transfer to or from wall rocks controls the amount of boiling; thus, because the extent of boiling controls pH, heat transfer controls the precipitated mineral assemblage.Oxyacids and hydroxides are generally the dominant aqueous species of arsenic and antimony, respectively. At low temperatures, elevated sulfide concentrations, and intermediate pH, arsenic and antimony thiosulfides become dominant. Upon boiling, the precipitation of copper, lead, and silver sulfosalts instead of sulfides is most likely at low temperatures and low pH values. Calculated low-temperature sulfosalt precipitation is consistent with shallow arsenic and antimony mineralization in epithermal systems and also with the commonly observed late precipitation of these metals as temperature decreases with time. Calculated electrum compositions do not exceed 56 mole percent gold. These compositions vary with temperature but depend mainly on the amount of other silver-bearing minerals competing with electrum.Upon boiling, all mercury fractionates into the gas phase from 300 degrees to 101 degrees C. Numerical condensation by cooling the gas phase below 101 degrees C at a constant pressure induces the precipitation of cinnabar between 80 degrees and 100 degrees C, depending on the mercury concentrations (0.8-800 ppb). Arsenic and antimony, however, do not fractionate significantly into the gas phase as long as an aqueous phase is present. Upon 100 percent boiling of the solution, antimony stays in the dry gas phase down to 220 degrees C where stibnite precipitates, and arsenic down to 130 degrees C where realgar precipitates. The transport of base metals in the dry gas phase requires temperatures above 400 degrees C.The acidification of the boiled Broadlands-type water by acid sulfate waters or by H 2 SO 4 produced from magmatic SO 2 leads to the precipitation of gold-rich electrum or gold with copper sulfides (at 200 degrees , 150 degrees , and 101 degrees C), sulfosalts (at 150 degrees and 101 degrees C), and enargite (at 101 degrees C). Acidification in a hot spring environment at 90 degrees C causes orpiment and stibnite to precipitate. Comparative results between H 2 SO 4 and HCl acidification reactions indicate that the replacement of copper, lead, and silver sulfides by sulfosalts is driven by pH decrease and is favored by higher sulfide and sulfate activities. The enargite-covellite-tetrahedrite-chalcopyrite downward zoning of acid sulfate-type epithermal deposits can be explained by acidification at constant sulfide activity. Also, the formation of shallow epithermal deposits rich in gold, relative to silver, can be explained by the reaction at shallow depths between ascending boiling waters and downward percolating acid sulfate waters.

Determination of arsenic species by high-performance liquid chromatography-inductively coupled plasma mass spectrometry

Abstract: Arsenic(III), AsV, monomethylarsonic acid (MMAA), dimethylarsinic acid (DMAA) and arsenobetaine (AsB) were separated by high-performance liquid chromatography (HPLC) and determined on-line by inductively coupled plasma mass spectrometry (ICP-MS). Two forms of HPLC were used: ion pairing and ion exchange, with absolute detection limits for arsenic ranging between 50 and 300 pg. These detection limits were independent of the arsenic species when peak area was used for quantification. Anion pairing was found generally to be more sensitive to changes in the matrix of the sample injected. Anion exchange was more tolerant because of the higher buffering capacity of the mobile phase. Cation pairing was found suitable for the determination of DMAA and AsB in a biological sample containing high concentrations of salts.

Speciation of arsenic in urine using high-performance liquid chromatography with inductively coupled plasma mass spectrometric detection

Abstract: High-performance liquid chromatography (HPLC) has been coupled with inductively coupled plasma mass spectrometry (ICP-MS) for the speciation of four arsenic compounds commonly found in urine. Arsenite (As3+), arsenate (As5+), dimethylarsinate (DMA) and monomethylarsonate (MMA) were separated via anion-exchange HPLC and detected on-line using ICP-MS. The absolute detection limits ranged from 20 to 91 pg of arsenic in aqueous media and 36–96 pg in urine. The four species were determined in two freeze-dried urine standards using the method of standard additions. The total of the four species was found to be within 13% of the average reported total arsenic concentration for both freeze-dried urine standards containing elevated levels of As5+. The relative standard deviation of peak-height measurements was less than 10% for each of the four species in urine. The determination of As3+ is complicated by the presence of an interfering peak, which is believed to arise from the co-elution of chlorine-containing species and subsequent formation of 40Ar35CI+ ions (m/z= 75).

Mechanisms of arsenic-induced cell transformation

Abstract: Arsenic is a well-established carcinogen in humans, but there is little evidence for its carcinogenicity in animals and it is inactive as an initiator or tumor promoter in two-stage models of carcinogenicity in mice. Studies with cells in culture have provided some possible mechanisms by which arsenic and arsenical compounds may exert a carcinogenic activity. Sodium arsenite and sodium arsenate were observed to induce morphological transformation of Syrian hamster embryo cells in a dose-dependent manner. The trivalent sodium arsenite was greater than tenfold more potent than the pentavalent sodium arsenate. The compounds also exhibited toxicity; however, transformation was observed at nontoxic as well as toxic doses. At low doses, enhanced colony forming efficiency of the cells was observed. To understand the mechanism of arsenic-induced transformation, the genetic effects of the two arsenicals were examined over the same doses that induced transformation. No arsenic-induced gene mutations were detected at two genetic loci. However, cell transformation and cytogenetic effects, including endoreduplication, chromosome aberrations, and sister chromatid exchanges, were induced by the arsenicals with similar dose responses. These results support a possible role for chromosomal changes in arsenic-induced transformation. The two arsenic salts also induced another form of mutation-gene amplification. Both sodium arsenite and sodium arsenate induced a high frequency of methotrexate-resistant 3T6 cells, which were shown to have amplified copies of the dihydrofolate reductase gene.(ABSTRACT TRUNCATED AT 250 WORDS)

Biological Monitoring of Arsenic exposure of Gallium Arsenide- and Inorganic Arsenic-Exposed Workers by Determination of Inorganic Arsenic and Its Metabolites in Urine and Hair

Abstract: In an attempt to establish a method for biological monitoring of inorganic arsenic exposure, the chemical species of arsenic were measured in the urine and hair of gallium arsenide (GaAs) plant and copper smelter workers. Determination of urinary inorganic arsenic concentration proved sensitive enough to monitor the low-level inorganic arsenic exposure of the GaAs plant workers. The urinary inorganic arsenic concentration in the copper smelter workers was far higher than that of a control group and was associated with high urinary concentrations of the inorganic arsenic metabolites, methylarsonic acid (MAA) and dimethylarsinic acid (DMAA). The results established a method for exposure level-dependent biological monitoring of inorganic arsenic exposure. Low-level exposures could be monitored only by determining urinary inorganic arsenic concentration. High-level exposures clearly produced an increased urinary inorganic arsenic concentration, with an increased sum of urinary concentrations of inorganic arse...

Relation of arsenic exposure to lung cancer among tin miners in Yunnan Province, China.

Abstract: The relation of mining and smelting exposure to arsenic and lung cancer was studied among tin miners in Yunnan Province in the People's Republic of China. Interviews were conducted in 1985 with 107 living tin miners who had lung cancer and an equal number of age matched controls from among tin miners without lung cancer to obtain information on risk factors for lung cancer including detailed history of employment and tobacco use. Occupational history was combined with industrial hygiene data to estimate cumulative arsenic exposure. Similar methods were also used to estimate radon exposure for simultaneous evaluation in this analysis. The results indicate that subjects in the highest quarter of cumulative arsenic exposure have a relative risk of 22.6 compared with subjects without exposure after adjusting for tobacco and radon exposure, and a positive dose response relation was observed. Simultaneous evaluation of arsenic and tobacco exposure indicates a greater risk for arsenic, whereas simultaneous assessment of arsenic and radon exposure suggests radon to be the greater risk. There is no evidence of synergism between arsenic and tobacco exposure. Among arsenic exposed individuals, cases of lung cancer have longer duration but lower average intensity of arsenic exposure than controls, indicating that duration of exposure to arsenic may be more important than intensity in the aetiology of lung cancer. Finally, risk of lung cancer among workers exposed to arsenic only in mining is only slightly less than for miners whose exposure to arsenic was limited to smelting, although risks are highest when workers were exposed to both mining and smelting.

Simple approach to reducing polyatomic ion interferences on arsenic and selenium in inductively coupled plasma mass spectrometry

Abstract: The addition of small amounts of an organic solvent (e.g., propanol) or a molecular gas (e.g., nitrogen or oxygen) is shown to reduce the interferences on arsenic and selenium of polyatomic ions (ArCl+, Ar2+) at masses 75, 77 and 78 in inductively coupled plasma mass spectrometry.

Arsenopyrite: a spectroscopic investigation of altered surfaces

Abstract: Surfaces of a natural sample of arsenopyrite (FeAsS) were oxidized by a range of inorganic oxidants, and the resultant surface alteration products studied using various spectroscopic techniques. The oxidants used were air during heating to relatively low temperatures (150~ steam, ammonium hydroxide, hydrogen peroxide, and sulphuric acid. Electrochemical oxidation in water was also undertaken. X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and spectral reflectance measurements, were used to characterize the surface compositions. New data are proposed for the binding energies of core electrons in arsenopyrite based on the fitted XPS spectra: 706.9 eV for the Fe 2p 3~2 level, 161.2eV for the S 2p level, and 40.7eV for the As 3d level. Spectroscopic analyses of the surfaces following oxidation indicated a range of iron oxides and hydroxides (Fel_xO , Fe304, Fe203, FeOOH and Fe(OH)3), arsenic oxides (As203 and As205) , sulphur and iron sulphates (FeSO4, Fe2(SO4)3). The relative proportions of the different phases present in the surface layer are related to the strength of the oxidant employed and, where relevant, the Eh/pH conditions prevalent during oxidation. The conclusions regarding the nature of the oxidation of arsenopyrite are discussed in relation to arsenopyrite extraction by flotation and leaching, and the breakdown of arsenopyrite in natural systems. KEYWORD S: arsenopyrite, sulphides, surface, spectroscopy, XPS, AES.

Pathways of arsenic uptake and incorporation in estuarine phytoplankton and the filter-feeding invertebrates Eurytemora affinis, Balanus improvisus and Crassostrea virginica

Abstract: Arsenic uptake from water and from phytoplankton was followed in the copepod Eurytemora affinis and the barnacle Balanus improvisus collected from the Patuxent River estuary, Chesapeake Bay, eastern coast of the USA in 1987, and in the oyster Crassostrea virginica obtained from a hatchery on the shore of Chesapeake Bay in 1987. Dissolved arsenic was readily taken up by phytoplankton and by shell material of B. improvisus and C. virginica; however, no dissolved arsenic was incorporated into the invertebrate tissues. When E. affinis, B. improvisus and C. virginica were fed phytoplankton containing elevated arsenic contents, significant arsenic incorporation occurred. Juvenile B. improvisus incorporated relatively more arsenic than adults of all three species. Compared to the 100 to 200% increase in arsenic content by phytoplankton exposed to dissolved arsenic, the 25 to 50% increase in these invertebrate species via trophic transfer is relatively small. Even though the trophic pathway for arsenic transfer is the major one for higher trophic levels within an ecosystem, the potential for direct arsenic impact to trophic levels other than phytoplankton appears to be minimal.

Dissolved arsenic species in the Schelde estuary and watershed, Belgium

Abstract: The Schelde watershed drains a densely populated and industrialized region in central Europe. The Zenne River, a tributary which flows through the centre of the Brussels industrial region, contributes most of the arsenic to the river-estuary system. Inputs of industrial and domestic effluents create a region of anoxic conditions in the water column of the upper estuary. A study of arsenic concentrations and speciation in the rivers of the Schelde watershed shows that the ratio of As(III) to As(V) is elevated in the anoxic part of the estuary and those tributaries that are depleted in oxygen. The combination of a near-constant anthropogenic arsenic emission and seasonally fluctuating water discharge creates a variable arsenic concentration in the river endmember. This variability can explain the non-linearity in the arsenic-salinity relationship in the estuary, where a pronounced arsenic maximum is seen in a region without local arsenic sources. The As(III) As(V) ratio in the estuary has typical marine values in the lower estuary and increases sharply at the oxic/anoxic interface near the head of the estuary. The feasibility of using a numerical model incorporating fluctuating river composition and discharge, tidal mixing, zero-order reduction of arsenate and first-order oxidation of arsenite to model the distribution and redox speciation of arsenic in the estuary under non-steady-state conditions is explored.

The discovery of hidden arsenic species in coastal waters

Abstract: The analysis of ultraviolet (UV)-irradiated and untreated seawater samples has shown that the dissolved arsenic content of marine waters cannot be completely determined by hydride generation–atomic absorption spectrophotometry without sample pretreatment. Irradiation of water samples obtained during a survey of arsenic species in coastal waters during the summer of 1988 gave large increases in the measured speciation. Average increases in the measured speciation. Average increases in total arsenic, monomethylarsenic and dimethylarsenic were 0.29 μg As dm−3 (25%), 0.03 μg As dm−3 (47%) and 0.12 μg As dm−3 (79%), respectively. Overall, an average 25% increase in the concentration of dissolved arsenic was observed following irradiation. This additional arsenic may be derived from compounds related to algal arsenosugars or to their breakdown products. These do not readily yield volatile hydrides when treated with borohydride and are not therefore detected by the normal hydride generation technique. This has important repercussions as for many years this procedure, and other analytical procedures which are equally unlikely to respond to such compounds, have been accepted as giving a true representation of the dissolved arsenic speciation in estuarine and coastal waters. A gross underestimate may therefore have been made of biological involvement in arsenic cycling in the aquatic environment.

Contaminants in foods of aquatic birds at Kesterson Reservoir, California, 1985

Abstract: Plants, aquatic insects, and mosquitofish (Gambusia affinis) were collected from Kesterson Reservoir, Merced County, California, and a nearby reference site (Volta Wildlife Area) to compare concentrations of three contaminants found in 1985 with those reported in 1983 and 1984. Mean selenium concentrations in food-chain organisms from sites at Kesterson in 1985 ranged from 26.0 μg/g (dry wt) in water boatman (Corixidae) to 119 μg/g in mosquitofish. All mean selenium concentrations at Kesterson were significantly higher than those from Volta and were sufficient to have caused the impaired avian reproduction observed at Kesterson. Boron concentrations were also significantly higher at Kesterson, and, at one pond, the mean concentration in widgeongrass (Ruppia mari-tima) (1,630 μg/g) was high enough to impair avian reproduction. There were no differences in arsenic concentrations between locations, and concentrations in all food-chain organisms (<1.9 μg/g) were lower than those reported to cause adverse effects in wildlife. Within-location differences were observed for all three contaminants at Kesterson and for selenium at Volta, but there was no consistent pattern to these differences. Between-year comparisons showed that selenium concentrations in mosquitofish generally decreased at Kesterson, but remained about the same at Volta over the 3 years. Selenium concentrations in insects from 1985 were lower at Kesterson than 1983, but were similar to 1984. Concentrations in plants were generally higher in 1983 and lower in 1984 compared with 1985. Boron concentrations in plants were generally higher in 1985, but in mosquitofish and insects, boron concentrations remained about the same all 3 years. Most arsenic concentrations did not change significantly between years.

The determination of heavy metals in water, suspended materials and sediments from Langat River, Malaysia

Abstract: The distributions of heavy metals in the Langat River were studied for a period of six months between September 1984 and February 1985. Heavy metals such as arsenic, cadmium, cerium, cobalt, chromium, caesium, lanthanum, rubidium, antimony, scandium, thorium and zinc were determined in water, suspended materials and sediment samples from the Langat River by neutron activation and atomic absorption spectrometry. The concentrations of arsenic, cadmium, cerium, cobalt, scandium, antimony, and zinc were generally highest in the suspended materials, whereas the concentrations of chromium, rubidium and thorium were always highest in the sediments: Arsenic concentrations in the river were slightly higher than the natural concentration, while other elements were generally at their natural concentration levels. The use of arsenical herbicides in plantations along the river could be a source of arsenic pollution.

Selective Separation of Cu, Zn, and As from Solution by Flotation Techniques

Abstract: The selective precipitation and flotation of copper, zinc, and arsenic ions from dilute aqueous solutions were investigated. Phase separation was accomplished effectively by the dissolved-air technique for the production of fine gas bubbles, and a short-chain xanthate was applied as the collector for copper ions, dialkyldithiocarbamate for zinc, and ferric sulfate for the pentavalent arsenic. The procedures followed were ion flotation for copper and zinc, and adsorbing colloid flotation for arsenic (without a surfactant).

Field Experience With Point-of-Use Treatment Systems for Arsenic Removal

Abstract: Point-of-use (POU) treatment devices can be effective for removing inorganic contaminants. This article describes the investigation of POU treatment systems used for arsenic removal in four homes in Alaska and Oregon. Small systems utilizing activated alumina, ion exchange, and reverse osmosis techniques were field-tested on waters naturally contaminated with arsenic. The waters contained arsenic in concentrations ranging from 0.1 to 1.0 mg/L, which were successfully lowered to below the 0.05mg/L maximum contaminant level.

Comparison of different pre-concentration methods for the determination of trace levels of arsenic, cadmium, copper, mercury, lead and selenium

Abstract: Three methods have been considered for trace metal concentration: (a) liquid-liquid extraction using either ammonium pyrrolidinedithiocarbamate or 8-hydroxyquinoline-5-sulphonic acid; (b) the use of a synthetic poly(dithiocarbamate) resin; and (c) reductive precipitation with NaBH4. The suitability of method (a) for the determination of metal ions in samples with a complex matrix and high salinity has been investigated. Method (b) was especially useful for speciation studies of trace levels of AsIII, AsV, SeIV and SeVI. Method (c) gave 1000-fold pre-concentration factors with total recoveries.

Physical and chemical characteristics of a metal‐contaminated overbank deposit, west‐central South Dakota, U.S.A.

Abstract: A metal-contaminated overbank deposit in west-central South Dakota resulted from the discharge of a large volume of mine tailings into a river system between the late 1800s and 1977. The deposit along the Belle Fourche River is typically up to 2 m thick and extends about 90 m away from the channel along the insides of meander bends. The sediments contain above-background levels of copper, iron, manganese, zinc, and particularly arsenic, which is commonly two orders of magnitude above background level in the contaminated sediments. Carbonate minerals in the deposit limit the desorption of arsenic by preventing acid formation. Arsenic concentrations provide a measure of the dilution of mine tailings by uncontaminated sediment. The arsenic appears to have been transported and deposited as arsenopyrite, but is now at least partially associated with iron oxides and hydroxides. Within individual samples, arsenic concentration has an inverse relation with grain size that results from the more efficient accumulation of arsenic on the greater surface area of the smaller particles. Arsenic concentration is inversely related to the sample weight percent finer than 16 μm, however, as a consequence of the dilution of the contaminated sediments by uncontaminated sediment with a finer grain-size distribution. Dilution by uncontaminated sediment from tributaries cause arsenic concentrations to decrease by a factor of 3 along 100 km of floodplain. An influx at high streamflow of uncontaminated sediment from terraces and the premining floodplain as well as from tributaries causes arsenic concentrations in parts of the contaminated deposit that are farthest away from the channel to be two to three times less than arsenic concentrations in overbank sediment that is immediately adjacent to the channel.

Extraction of geological materials with mineral acids for the determination of arsenic, antimony, bismuth and selenium by hydride generation atomic absorption spectrometry

Abstract: Data are presented for the hydride generation atomic absorption spectrometric determination of arsenic, antimony, bismuth and selenium in stream sediments and a certified reference material (CPB-1 Lead Concentrate) using six different extraction media, viz., hydrochloric acid; nitric acid; 7 M nitric acid; nitric acidsulphuric acid (9 + 1); aqua regia; and reversed aqua regia (HNO3+ HCl, 3 + 1). Extraction with 7 M nitric acid was performed in test-tubes placed in a drilled out heating block (110 °C, 3.5 h). All other extractions were carried out overnight in 50-ml calibrated flasks placed in a water-bath. Bismuth was extracted quantitatively by all the extraction media. Arsenic and selenium were extracted completely by each of the media used, except for hydrochloric acid. Antimony was extracted completely by only two of the media, viz., aqua regia and reversed aqua regia. Selenium is converted to the +4 oxidation state on extraction with aqua regia and reversed aqua regia, i.e., selenium(VI) is reduced to selenium(IV), and the lower oxidation states are oxidised to selenium(IV). Hence the extracts can be analysed for selenium without pre-reduction to selenium(IV), which is necessary for hydride generation atomic absorption spectrometry. The nitric acid-hydrochloric acid mixtures used bring arsenic, antimony, bismuth and selenium quantitatively into solution and are, therefore, suitable for the sequential or simultaneous determination of these elements in a single sample solution. The speciation of selenium in stream sediments and surface waters is discussed.