The effects of agricultural practice and land-use on the distribution and origin of some potentially toxic metals in the soils of Golestan province, Iran

Soil samples were collected from the agricultural lands of Golestan province, north of Iran and analyzed for 24 elements including eight toxic metals of As, Cd, Co, Cr, Cu, Pb, Se and Zn. Electrical conductivity, pH, organic matter, soil texture, calcium carbonate content as well as soil cation exchange capacity were also determined. The possible sources of metals are identified with multivariate analysis such as correlation analysis, principal component analysis (PCA), and cluster analysis. In addition, enrichment factors were used to quantitatively evaluate the influences of agricultural practice on metal loads to the surface soils. The PCA and cluster analysis studies revealed that natural geochemical background are the main source of most elements including Al, Co, Cr, Cs, Cu, Fe, K, Li, Ni, Pb, V and Zn in the arable soils of the province (more than 90 %), however, those soils which have been developed on the mafic and metamorphic rocks were considerably contributed on metal concentration (43 %). Calcium and Sr were constituents of calcareous rocks and Na and S were mainly controlled by saline soils in the north of the province. Loess deposits was also accounting for high levels of selenium concentration. Phosphorous was mostly related to application of P-fertilizers and organophosphate pesticides. The comparison of metal load and enrichment factor for dry and irrigated farmlands showed that Cd, Co, Pb, Se and Zn had higher concentrations in the irrigated lands where considerable amounts of agrochemicals had been applied. However, it also found that proximity of arable lands to urban and industrial areas resulted in higher Pb and Cd values in the irrigated agricultural sources relative to dry ones.     

Iron(III) reduction and phosphorous solubilization in humid tropical forest soils

Phosphorus is one of the nutrients most commonly limiting net primary production in soils of humid tropical forests, mainly because insoluble Al and Fe phosphates and strong sorption to Fe(III) (hydr)oxides remove P from the bioavailable pool. Recent field studies have suggested, however, that this loss may be balanced by organic P accumulation under a wet moisture regime (>3350 mm annual precipitation). It has been hypothesized that, as the moisture regime changes from dry to mesic to wet, periods of anoxic soil conditions increase in intensity and duration, depleting Fe(III) (hydr)oxides and releasing sorbed P, but also slowing organic matter turnover, thus shifting the repository of soil P from minerals to humus. Almost no quantitative information is available concerning the coupled biogeochemical behavior of Fe and P in highly weathered forest soils that would allow examination of this hypothesis. In this paper, we report a laboratory incubation study of the effects of biotic Fe(III) (hydr)oxide reduction on P solubilization in a humid tropical forest soil (Ultisol) under a wet moisture regime (3000-4000 mm annual rainfall). The objectives of our study were: (1) to quantify Fe(III) reduction and P solubilization processes in a highly weathered forest soil expected to typify the hypothesized mineral dissolution-organic matter accumulation balance; (2) to examine the influence of electron shuttling on these processes using anthraquinone-2,6-disulfonate (AQDS), a well-known surrogate for the semiquinone electron shuttles in humic substances, as an experimental probe; and (3) to characterize the chemical forms of Fe(II) and P produced under anoxic conditions, both with and without AQDS. Two series of short-term incubation experiments were carried out, one without AQDS and another with an initial AQDS concentration of 150 μM. We measured pH, pE, and the production of Fe(II), total Fe [Fe(II) + Fe(III)], inorganic P, total P (inorganic P + organic P), and biogenic gases (CO₂, H₂ and CH₄). The same positive correlation was found between soluble P release and soluble Fe(II) production throughout incubation, implying that reduction of Fe(III) solubilized P. The Fe(II) produced was mainly particulate, evidently due to the formation of Fe(II) solid phases. Thermodynamic calculations indicated that precipitation of siderite and, in the presence of AQDS, vivianite was favored under the anoxic conditions that developed rapidly in the soil suspensions. Inorganic soluble P released during incubation was very small, indicating that the soluble P produced was mainly in organic form, which is consistent with the hypothesis that P accumulates in soil humus. Our net CO₂ production, H₂ consumption, and Fe(II) production data all suggested that reductive dissolution of Fe(III) (hydr)oxides was a terminal electron-accepting process coupled both to H₂ consumption and organic C oxidation by the native population of microorganisms in the soil. Addition of AQDS accelerated the production of Fe(II) and the release of soluble P, while hastening the decline in H₂ gas levels and suppressing CH₄ production. However, throughout incubation, the same quantitative relationships between soluble Fe(II) and P, and between pE and pH, were found, irrespective of AQDS addition. Thus we conclude that, in our soil incubation experiments, added AQDS functioned with the native microbial population solely as an electron shuttle catalyzing Fe(III) reduction. Whether humic substances in the soil also can act as electron shuttles in this way is a matter for future investigation.     

Natural radionuclides and trace elements in rice field soils in relation to fertilizer application: study of a chronic kidney disease area in Sri Lanka

The rising number of chronic kidney disease patients with no identifiable cause (CKD of uncertain aetiology), prevalent in some areas of the dry zone of Sri Lanka is suspected to be related to the environmental exposure to heavy metals. Agricultural soils are well recognized as being contaminated with potentially toxic metals from various forms of fertilizers and agro-chemicals, which could easily enter the human body through the food chain. The objective of this paper is to determine the content of heavy metals and activity concentration of background radionuclides such as K-40, Ra-226 and Th-232, in rice field soils. Rice farming is the most common agricultural practice in the affected region and possible heavy metal sources such as fertilizers are applied in abundance in the rice fields. Soils collected from a rice field in a non-CKD region was used for the comparison. In dry zone soils, Ca, K, Ba, Pb and Zr contents were higher and Fe, Mn, Cr, Ni and Zn contents were lower compared to that of soils from the wet zone non-CKD region. However, the activity concentration of soils was mostly the same in all samples, except for the K-40 contents of the soils, which were higher in the rice field soils compared to the undisturbed forest soils and also to the world averages. The mean U content was 3.6 mg/kg in the studied soils, although extremely high uranium contents were found in some fertilizer samples particularly in the triple superphosphates. Most uranium applied via fertilizer could contaminate the drinking water sources and even low uranium concentrations in drinking water may cause nephrotoxic effects.     

The effect of organic matter on chemical weathering: study of a small tropical watershed: nsimi-zoétélé site,cameroon

The effect of organic matter during soil/water interaction is still a debated issue on the controls of chemical weathering in a tropical environment. In order to study this effect in detail, we focused on the weathering processes occurring in a small tropical watershed (Nsimi-Zoetélé, South Cameroon). This site offers an unique opportunity to study weathering mechanisms in a lateritic system within a small basin by coupling soil and water chemistry.The lateritic cover in this site can reach up to 40 m in depth and show two pedological distinct zones: unsaturated slope soils on the hills and/or elevated areas; and water-saturated soils in the swamp zone which represent 20% of the basin surface. The study present chemical analysis performed on water samples collected monthly from different localities between 1994–1997 and on soil samples taken during a well drilling in December 1997. The results suggest the existence of chemical and spatial heterogeneities of waters in the basin: colored waters flooding the swamp zone have much higher concentrations of both organic matter (i.e., DOC) and inorganic ions (e.g., Ca, Mg, Al, Fe, Th, Zr) than those from springs and groundwater from the hills. Nevertheless, these organic-rich waters present cation concentrations (Na, Ca, Mg, K) which are among the lowest compared to that of most world rivers. The main minerals in the soils are secondary kaolinite, iron oxi-hydroxides, quartz, and accessory minerals (e.g., zircon, rutile). We mainly focused on the mineralogical and geochemical study of the swamp zone soils and showed through SEM observations the textural characterization of weathered minerals such as kaolinite, zircon, rutile, and the secondary recrystallization of kaolinite microcrystals within the soil profile. Water chemistry and mineralogical observations suggest that hydromorphic soils of the swamp zone are responsible for almost all chemical weathering in the basin. Thus, in order to explain the increase of element concentration in the organic-rich waters, we suggest that organic acids enhance dissolution of minerals such as kaolinite, goethite, and zircon and also favors the transport of insoluble elements such as Al, Fe, Ti, Zr, and REE by chemical complexation. SiO₂(aq) concentrations in these waters are above saturation with respect to quartz. Dissolution of phytholithes (amorphous silica) may be responsible for this relatively high SiO₂(aq.) concentration. Al/Mg ratios obtained for the soil and the Mengong river waters show that a significant amount of Al does not leave the system due to kaolinite recrystallisation in the swamp zone soils. Geochemical data obtained for this watershed show the important contribution of vegetation and organic matter on chemical weathering in the swamp zone. Quantitatively we propose that the increasing amount in total dissolved solid (TDS) due to organic matter and vegetation effect is about 35%. In summary, this interaction between soils and waters occurs mostly in soils that are very depleted in soluble elements. Thus, the low concentration of major elements in these water is a direct consequence of the depleted nature of the soils.     

Effects of soil types and forms of arsenical pesticide on rice growth and development

For decades, repeated and widespread use of arsenical pesticides has significantly contributed to arsenic contamination in soils. Residues from the overuse of these arsenicals may result in phytotoxicity to crops, which will depend on soil types, plant species and the toxicity of arsenical pesticides. A greenhouse column study was conducted to evaluate the effect of two pesticides, i.e. one organic (dimethylarsinic acid) and one inorganic (sodium arsenate), on the vegetative response of rice as a function of soil properties. Four soils with varying arsenic retention capabilities at two different pesticide amendment rates (675 and 1500 mg/kg) representing the worst case scenarios in superfund sites were used. Results showed that arsenic availability to rice was mainly influenced by soil physicochemical properties. The soil with the lowest arsenic retention capacity had the highest arsenic concentration in the leachate as well as in the plant tissue. In contrast, for soils with higher arsenic retention capacity, higher concentrations of arsenic were found in the surface soil which resulted in the inhibition of plant growth. There was no significant difference between labile arsenic / plant-available arsenic irrespective of the form of arsenical pesticide used. Plant growth parameters such as biomass, shoot height, root length decreased with increased arsenic concentrations in all soils. A significant negative correlation (P<0.05) was observed between the phytoavailable arsenic and plant growth response. Interestingly, the form of arsenical pesticide used did not impact arsenic uptake or shoot growth but significantly impacted root growth.     

Arsenic geochemistry in forested soil profiles as revealed by solid-phase studies

Arsenic concentrations in soils may be elevated either because of anthropogenic activity or because of a high natural abundance of the parent material. In the unsaturated zone of seven forest soils in northern Sweden, inorganic As(V) generally dominated the solid-phase speciation while non-NaBH₄-reducible organic As associated with isolated humic substances (humic As) was present in low amounts. In unpolluted soils, absorbed As(V) was more or less constant through the B and C horizons and did not show any obvious relationship with secondary short-range ordered Fe or Al minerals-this suggested that most As(V) had formed early during pedogenesis as a result of sulphide weathering. When a small amount of As(V) was added to the mineral soils, adsorption was almost complete and the amount of remaining As(V) in solution depended on the ratio of pyrophosphate-C to oxalate-(Fe + Al). On higher As(V) additions, the amount of adsorption sites governed the As solubility. As regards the humic As, the XAD-4 acid fulvates were more enriched with As as compared to the hydrophobic acids. The As content of the forest floor was highly dependent on the distance from the Rönnskärsverken non-ferrous metal smelter, but did not reflect the As content of the underlying horizons; thus, biological uptake of As from the mineral soil appeared to be very low.     

Arsenic distribution and hydrochemical factors in urban groundwater,Foshan City,South China

The distribution of arsenic （As） in shallow groundwater of eastern Chancheng District in Foshan City as a function of season and water table was investigated, and the influence of hydrochemical factors on the As distribution was discussed. The groundwater samples were collected from 20 sites in dry season and 9 sites in wet season. As concentrations in 20% groundwater samples exceeded value of the WHO guideline （10 μg/L）, and the highest As concentration of 23.5 μg/L occurred in dry season. It is observed that groundwater As concentration decreased with the increase of depth of water table in dry season, and were generally higher in wet season than that in dry season, indicating that ground surface As might be one of the main sources for shallow groundwater As in study area, especially in wet season. Groundwater As concentration in study area had significantly positive correlation with the concentration of Fe, Mn, NH4, F, and COD, and was positively correlated to pH, but negatively correlated to Eh and K, indicating that reductive dissolution of Fe and Mn （oxy）hydroxides might be one of the main control mechanisms for groundwater As mobilization, while pH and F also played an important role in controlling the groundwater As mobilization in study area.     

Geochemical evolution of solutions derived from experimental weathering of sulfide-bearing rocks

The chemical composition of natural waters is affected by the weathering of geologic materials at or near the surface of the Earth. Laboratory weathering experiments of whole-rock sulfide rocks from the Shoe-Basin Mine (SBM) and the Pennsylvania Mine (PM) from the Peru Creek Basin, Summit County, Colorado, indicate that the mineral composition of the sulfide rocks, changes in pH, the duration of the experiment, and the formation of sorbents such as Fe and Al oxyhydroxides affect the chemical composition of the resulting solution. Carbonate minerals in the rock from SBM provide buffering capacity to the solution, contribute to increases in the pH and enhance the formation of Fe and Al oxyhydroxides, which sorb cations from solution. The final solution pH obtained in the experiments was similar to those measured in the field (i.e., 2.8 for PM and 5.0 for SBM). At PM, acidic, metal-rich mine effluent is discharged into Peru Creek where it mixes with stream water. As a result, the pH of the effluent increases causing Fe and Al oxyhydroxide and schwertmannite to precipitate. The resulting solids sorb metal cations from the water thereby improving the quality of the water in Peru Creek.     

Arsenic mobility and impact on recovered water quality during aquifer storage and recovery using reclaimed water in a carbonate aquifer

Arsenic release from aquifers can be a major issue for aquifer storage and recovery (ASR) schemes and understanding the processes that release and attenuate As during ASR is the first step towards managing this issue. This study utilised the first and fourth cycles of a full scale field trial to examine the fate of As within the injectant plume during all stages of the ASR cycle, and the resultant water quality. The average recovered As concentration was greater than the source concentration; by 0.19 μmol/L (14 μg As/L) in cycle 1 and by 0.34 μmol/L (25 μg As/L) in cycle 4, indicating that As was being released from the aquifer sediments during ASR and the extent of As mobilisation did not decline with subsequent cycles. In the injection phase, As mobilisation due to oxidation of reduced minerals was limited to an oxic zone in close proximity to the ASR well, while desorption from Fe oxyhydroxide or oxide surfaces by injected P occurred further in the near well zone (0–4 m from the ASR well). With further aquifer passage during injection and greater availability of sorption sites there was evidence of attenuation via adsorption to Fe oxyhydroxides which reduced concentrations on the outer fringes of the injectant plume. During the period of aquifer storage, microbial activity resulting from the injection of organic matter resulted in increased As mobility due to reductive Fe oxyhydroxide dissolution and the subsequent loss of sorption sites and partial reduction of As(V) to the more mobile As(III). A reduced zone directly around the ASR well produced the greatest As concentration and illustrated the importance of Fe oxyhydroxides for controlling As concentrations. Given the small spatial extent of this zone, this process had little effect on the overall recovered water quality.     

Mobilization and speciation of arsenic from hydrothermally altered rock containing calcite and pyrite under anoxic conditions

The effects of water residence time and anoxic conditions on the mobilization and speciation of As in a calcite- and pyrite-bearing altered rock excavated during a road-tunnel project has been evaluated using batch and column laboratory experiments. Higher infiltration rates (i.e., shorter water residence times) enhanced the leaching of As due to the higher pH values of the effluents and more rapid transport of dissolved As through the columns. The concentration of As in the effluent also increased under anoxic conditions regardless of the water residence time. This enhanced leaching of As under anoxic conditions could be attributed to a significant pH increase and decreased Fe oxyhydroxide/oxide precipitation compared to similar experiments done under ambient conditions. Processes that controlled the evolution of pH and the temporal release mechanisms of As under anoxic conditions were identical to those previously observed under ambient conditions: the dissolution of soluble phases, pyrite oxidation, co-precipitation and/or adsorption/desorption reactions. Speciation of As in the column experiments could partly be attributed to the pH-dependent adsorption of As species onto Fe oxyhydroxide/oxide precipitates. Moreover, apparent equilibrium of the total As and As[III] concentrations was delayed under anoxic conditions in both batch and column experiments.     

Arsenic distribution during formation and capping of an oxidised sulphidic minesoil, Macraes mine, New Zealand

A minesoil has developed over 5 years oxidative exposure on sulphide concentrate tailings (ca. 1 wt.% As) at the Macraes mesothermal gold mine, New Zealand. The minesoil has a dry crust which has formed due to evaporative drying. This dry crust is enriched in arsenic (ca. 5 wt.% As) as scorodite (FeAsO₄·2H₂O) because of upward mobility of dissolved arsenic during drying. Similar enrichment of arsenic has occurred along the walls of desiccation cracks which extend over 1 m into the minesoil. Capping of the tailings and minesoil with wet tailings (pH=8) results in dissolution of scorodite and remobilization of arsenic on the millimetre scale. Experimental capping of the minesoil with wet calcium carbonate remobilized some arsenic from scorodite on the centimetre scale, but much original arsenic enrichment was preserved after 400 days. A layer of gypsum (CaSO₄·2H₂O) and iron oxyhydroxide cementation developed at the interface between the minesoil and the experimental calcium carbonate cap, restricting water flow. This layer was ca. 1 mm thick after 400 days. Theoretical comparison between advection and diffusion in the minesoil suggests that diffusion is an important mechanism for chemical mobility on the 1–50-year time scale. However, advection can be important in secondary porosity of the dry crust of the minesoil and water penetrates this zone at a rate of 1.5 mm/day.     

Iron oxyhydroxide coating of pyrite for acid mine drainage control

When pyrite oxidizes at near neutral pH in the presence of sufficient alkalinity, Fe oxyhydroxide coatings develop on the surface. As these coatings grow thicker and denser they block oxidant transport from the solution to the pyrite surface and reduce the rate of pyrite oxidation. The authors’ measurements of pyrite oxidation rates in a NaHCO₃ solution show that the coating grows in two stages. In the first stage Fe oxyhydroxide colloids form and then attach to the pyrite surface to produce a slight reduction in oxidant transport. In the second stage interstitial precipitation of Fe oxyhydroxide material between the colloidal particles reduces the oxidant’s diffusion coefficient by more than five orders of magnitude. This causes the pyrite oxidation rate to decline as the square root of time. The kinetic predominance diagram, which compares the rates of Fe transformation reactions, shows that when pyrite oxidation releases Fe quickly enough for the total Fe concentration to rise to about 10⁻⁸ m, ferrihydrite forms but lower rates of Fe release will not produce coatings. Extrapolation of the results to longer times predicts that pyrite-bearing materials need to be treated with an extra source of alkalinity for several decades to produce coatings that are thick enough to be sustained by alkalinity levels typical of groundwater. However, once the coatings develop no additional treatment is needed and further pyrite oxidation simply causes the coating to grow thicker and denser until the entire pyrite grain is pseudomorphically replaced by goethite.     

Phosphate sorption desorption characteristics of some ferruginous soils of tropical region in Eastern India

Phosphate sorption and desorption experiments were conducted with four ferruginous soils (alfisols) of Eastern India, in view of the low native phosphate concentrations in tropical Indian soils. From the P-isotherm curve, standard P requirement (SPR) of the soils was determined. Phosphate sorption data were fitted to both Langmuir and Freundlich equations and mean sorption maximum values obtained for the different soil series were in the decreasing order as Matimahal > Anandapur > Mrigindih > Kashipur. The fraction of added P sorbed followed the same trend as SPR, P sorption maximum (P_max), phosphate affinity constant (K), maximum phosphate buffering capacity (MPBC), Freundlich constant K′ and phosphate desorption values. Phosphate sorption maximum was significantly correlated with MPBC, Freundlich 1/n, SPR, clay and different forms of Fe and Al. The value of K (bonding energy) was significantly correlated with MPBC, Freundlich K′ and pyrophosphate extractable Fe and Al. The MPBC was significantly correlated with Freundlich K′, Freundlich constant 1/n, clay, oxalate and dithionite extractable, amorphous and crystalline form of Fe and Al. Freundlich K′ was significantly correlated with Freundlich 1/n, pH_water, clay, dithionite extractable and crystalline form of Fe and Al. The results suggested that the soils having higher amount of extractable and reactive Fe and Al shared higher P sorbtion capacity and such soils may need higher levels of P application     

Abundance, Sources and Speciation of Trace Elements in Humus-Rich Streams Affected by Acid Sulphate Soils

The behaviour of trace elements (Al, As, Cd, Co, Cr,Cu, Fe, Mn, Ni, V, Zn) was studied in five humus-richstreams (dissolved organic carbon = 14–40 mg/L)impacted by acid sulphate soils developed in marinesulphide-bearing fine-grained sediments. During heavyrainfalls in autumn, on which the study focusses, themetals Al, Cd, Co, Cu, Mn, Ni and Zn are extensivelyleached from these acidic soils (pH = 2.5–4.5), whileAs, Cr, Fe and V are not leached more strongly fromthis soil type than from areas of till and peat. Aspeciation experiment, based on anion and cationexchange of the stream waters in the field, showedthat (1) the metals Al, Cd, Co, Mn, Ni and Zn aretransported in the streams mainly as inorganiccations, (2) Cu exists mainly in cationic form but isalso to a significant extent associated with dissolvedhumic substances, (3) Fe occurs mainly in the anionicfraction explained by organic coating on colloidal Feoxyhydoxides and (4) the hydrochemistry of As, Cr andV is complex as these elements may exist in severalunquantified anionic fractions and to a minor extentin cationic species/forms. Whereas the proportion ofacid sulphate soils in the catchments had a largeimpact on concentrations levels of several elements inthe stream waters, these soils did not have a largeaffect on the speciation of elements in water.     

Field-scale evaluation of the chemical–biological stabilization process for the remediation of hydrocarbon-contaminated soil

Developing countries face the challenge of growing their economy while reducing the negative environmental impacts of industry, thus requiring treatment technologies that are economical and effective. One recent technology developed in the tropical part of Mexico for the remediation of petroleum-contaminated soil was tested in this scale-up project at an industrial level, whereas previously it had only been tested at laboratory scale; 150 m³ of bentonitic mud, contaminated with weathered hydrocarbons (3.4°API) at ~50,000 ppm, was treated with 4 % Ca(OH)₂, 4 % organic amendment, and a fine-root tropical grass. Hydrocarbons in soil and in leachates, as well as pH, and acute toxicity (Microtox) were monitored for 28.8 months. At the end of the study, basal respiration, root density, and earthworm toxicity were also measured. The hydrocarbon concentration in soil was reduced to 45 %, and toxicity was eliminated. Hydrocarbons in leachates were reduced to ~1 mg/l, safe for human consumption. The pH adjustment depended on low soil moisture and was stabilized at 7.1. Intense revegetation resulted in good root density, within 90 % of nearby uncontaminated soil under pasture. Basal respiration was increased to levels comparable to uncontaminated tropical soils with agricultural use, pasture and gallery forest. At an industrial scale, strict moisture control was necessary for good pH stabilization. By controlling these conditions and applying this novel treatment process, it was possible to transform a heavily contaminated geological material into a non-toxic, fertile, soil-like substrate capable of maintaining a complete vegetative cover and microbial activity comparable to similar soils in a tropical environment.     

The contribution of organic and mineral colloidal nanoparticles to element transport in a podzol soil

The aim of this work is to analyze the size-distribution and composition of nanoparticles in a water-extract of a podzol B horizon. AsFlowFFF coupled to ICP–MS and a UV/VIS detector was used for particle fractionation and simultaneous measurement of the composition of the nanoparticles. Detected nanoparticles were organic and mineral particles; the mineral particles were dominated by clay and Fe-(hydr)oxides. Both organic- and inorganic particles contributed to the mobility of Fe, Al, trace metals and P. For Zn, Pb and P respectively 73%, 92% and 72% of the colloidal concentrations were associated with clay minerals. The large contribution of clay particles to the mobility of trace metals and P can be partly explained by the high amount of dispersed clay due to drying, sieving and rewetting of the soil. Inorganic nanoparticles can contribute significantly to the mobility of metals and P in soils.     

Serpentine geology links to water quality and heavy metals in sediments of a stream system in central Queensland,Australia

Serpentinite soils, common throughout the world, are characterized by low calcium-to-magnesium ratios, low nutrient levels and elevated levels of heavy metals. Yet the water quality and heavy metal concentrations in sediments of streams draining serpentine geology have been little studied. The aim of this work was to collect baseline data on the water quality (for both wet and dry seasons) and metals in sediments at 11 sites on the Marlborough Creek system, which drains serpentine soils in coastal central Queensland, Australia. Water quality of the system was characterized by extremely hard waters (555–698 mg/L as CaCO₃), high dissolved salts (684–1285 mg/L), pH (8.3–9.1) and dissolved oxygen (often >110% saturation). Cationic dominance was Mg > Na > Ca > K and for anions HCO₃ > Cl > SO₄. Al, Cu and Zn in stream waters were naturally high and exceeded Australian and New Zealand Environment and Conservation Council guidelines. Conductivity displayed the highest seasonal variability, decreasing significantly after wet season flows. There was little seasonal variation in pH, which often exceeded regional guidelines. Stream sediments were enriched with concentrations of Ni, Cr, Co and Zn up to 35, 21, 10 and 2 times the world average for shallow sediments, respectively. Concentrations for Ni and Cr were up to 60 and 16 times those of the relevant Interim Sediment Quality Guidelines Low Trigger Values, respectively. The distinctive nature of the water and sediment data suggests that it would be appropriate to establish more localized water quality and sediment guidelines for the creek system for the water quality parameters conductivity, Cu and Zn (and possibly Cr and Cd also), and for sediment concentrations of Cd, Cr and Ni.     

Arsenic in groundwater affected by phosphate fertilizers at São Paulo, Brazil

. This paper studies metalloid mobility in soils produced by conventional farming methods. The mobility of arsenic in soils depends on several factors including redox potential, soil mineralogy, pH, and the presence of other anions that compete with As for soil retention sites, for example, phosphate. Phosphate enhances the mobility of As in soils by competing for adsorption sites. Arsenic may accumulate in soil through the application of fertilizers. Ingestion of inorganic arsenic contained in drinking water is known to cause cancer. Studies were carried out in an area of Jundiaí, São Paulo in Brazil with high arsenic levels in natural water from domestic wells. The mobility of arsenic in the soil of Jundiaí was studied in the period 1998–2001. The application of phosphate fertilizers on a wide scale is a common agricultural practice. Based on data from the field and laboratory experiments, the deterioration of soil and groundwater quality is a result mainly of fertilizer use due to excessive P application, overdosing of soil with phosphate, and undesirable additions of arsenic in P fertilizers.     

Geochemical modeling approach to predicting arsenic concentrations in a mine pit lake

Between 1968 and 1983, the North pit at the Getchell Mine, Humboldt County, NV, filled with water to form a lake. In 1983, water quality data were collected with the following results: As concentrations of 0.29 to 0.59 mg/L, pH of 7.1 to 7.9, SO₄ concentrations of 1490 to 1640 mg/L, and TDS of 2394 to 2500 mg/L. Using geochemical modeling techniques presented here, pit lake waters have been theoretically allowed to react for 8.5 a, the approximate time that the North pit had been completely full by 1983. Modeling results predict pH of 7.9 to 8.2, SO₄ concentrations of 1503 to 1644 mg/L, TDS of 2054 to 2366 mg/L, and As concentrations ranging from 0.57 in the hypolimnion to 96 mg/L in the epilimnion. In the epilimnion, model results do not match observed As concentrations, suggesting that mechanisms, such as precipitation of arsenate salts or adsorption to mineral surfaces, may control As levels in an actual pit lake system. Adsorption to Fe oxyhydroxide surfaces is questioned by the authors because of the low Fe content in the Getchell system, but adsorption to Al(OH)₃ (gibbsite) and clay mineral surfaces may be important in controlling natural As concentrations.