Net alkalinity and net acidity 2: Practical considerations

The pH, alkalinity, and acidity of mine drainage and associated waters can be misinterpreted because of the chemical instability of samples and possible misunderstandings of standard analytical method results. Synthetic and field samples of mine drainage having various initial pH values and concentrations of dissolved metals and alkalinity were titrated by several methods, and the results were compared to alkalinity and acidity calculated based on dissolved solutes. The pH, alkalinity, and acidity were compared between fresh, unoxidized and aged, oxidized samples.Data for Pennsylvania coal mine drainage indicates that the pH of fresh samples was predominantly acidic (pH 2.5–4) or near neutral (pH 6–7); ≈ 25% of the samples had pH values between 5 and 6. Following oxidation, no samples had pH values between 5 and 6.The Standard Method Alkalinity titration is constrained to yield values >0. Most calculated and measured alkalinities for samples with positive alkalinities were in close agreement. However, for low-pH samples, the calculated alkalinity can be negative due to negative contributions by dissolved metals that may oxidize and hydrolyze.The Standard Method hot peroxide treatment titration for acidity determination (Hot Acidity) accurately indicates the potential for pH to decrease to acidic values after complete degassing of CO₂ and oxidation of Fe and Mn, and it indicates either the excess alkalinity or that required for neutralization of the sample. The Hot Acidity directly measures net acidity (= −net alkalinity). Samples that had near-neutral pH after oxidation had negative Hot Acidity; samples that had pH < 6.3 after oxidation had positive Hot Acidity. Samples with similar pH values before oxidation had dissimilar Hot Acidities due to variations in their alkalinities and dissolved Fe, Mn, and Al concentrations. Hot Acidity was approximately equal to net acidity calculated based on initial pH and dissolved concentrations of Fe, Mn, and Al minus the initial alkalinity. Acidity calculated from the pH and dissolved metals concentrations, assuming equivalents of 2 per mole of Fe and Mn and 3 per mole of Al, was equivalent to that calculated based on complete aqueous speciation of Fe^II/Fe^III. Despite changes in the pH, alkalinity, and metals concentrations, the Hot Acidities were comparable for fresh and most aged samples.A meaningful “net” acidity can be determined from a measured Hot Acidity or by calculation from the pH, alkalinity, and dissolved metals concentrations. The use of net alkalinity = (Alkalinity_measured − Hot Acidity_measured) to design mine drainage treatment can lead to systems with insufficient Alkalinity to neutralize metal and H⁺ acidity and is not recommended. The use of net alkalinity = −Hot Acidity titration is recommended for the planning of mine drainage treatment. The use of net alkalinity = (Alkalinity_measured − Acidity_calculated) is recommended with some cautions.     

Colloidal and truly dissolved metal(oid) fractionation in sediment pore waters using tangential flow filtration

The partitioning of trace metal(oid)s between colloidal and “truly” dissolved fractions in sediment pore waters is often overlooked due to the analytical challenge; indeed, only small volumes are available and filtration membranes are rapidly clogged. Moreover, metal(oid)s are subject to co-precipitate with Fe. In this study, tangential flow filtration (TFF) was assessed for the fractionation of Fe, Mn, Cu, As, Co, Ni, Zn and Cd in sediment pore waters with a 5 kDa cut-off size membrane. Five natural sediments were collected and used for different tests. Results on blank samples showed that this technique was appropriate for Fe, Mn, Co, Zn, As and Cd. Although the applied concentration factors (CF) were low (<7.4) due to the small available volume of pore waters (50 mL), it was shown that colloidal concentrations obtained from the TFF procedure were similar whatever the applied concentration factor. The mass balance approach showed satisfying results (100 ± 25%) for Mn, Co, Zn and As. Mass balances were higher than 130% and highly variable for Cd, Ni and Cu. For Fe, mass balance was reproducible but low (71 ± 10%), probably due to sorption of positively charged Fe oxides on the membrane. Applying this method to five contrasting metal(oid)-contaminated sediments, it was shown that Mn, As, Co and Fe were mainly present in the “truly” dissolved phase (<5 kDa). This technique is a necessary step to assess sediment toxicity and bioavailability of metal(oid)s and could be of great interest for emergent pollutants such as nanometals.     

Direct characterization of airborne particles associated with arsenic-rich mine tailings: Particle size,mineralogy and texture

Windblown and vehicle-raised dust from unvegetated mine tailings can be a human health risk. Airborne particles from As-rich abandoned Au mine tailings from Nova Scotia, Canada have been characterized in terms of particle size, As concentration, As oxidation state, mineral species and texture. Samples were collected in seven aerodynamically fractionated size ranges (0.5–16 μm) using a cascade impactor deployed at three tailings fields. All three sites are used for recreational activities and off-road vehicles were racing on the tailings at two mines during sample collection. Total concentrations of As in the <8 μm fraction varied from 65 to 1040 ng/m³ of air as measured by proton-induced X-ray emission (PIXE) analysis. The same samples were analysed by synchrotron-based microfocused X-ray absorption near-edge spectroscopy (μXANES) and X-ray diffraction (μXRD) and found to contain multiple As-bearing mineral species, including Fe–As weathering products. The As species present in the dust were similar to those observed in the near-surface tailings. The action of vehicles on the tailings surface may disaggregate material cemented with Fe arsenate and contribute additional fine-grained As-rich particles to airborne dust. Results from this study can be used to help assess the potential human health risks associated with exposure to airborne particles from mine tailings.     

Metal species in a Boreal river system affected by acid sulfate soils

The bioavailability of metals and their potential for environmental pollution depends not simply on total concentrations but on their chemical form. Consequently, knowledge of aqueous metal speciation is essential in investigating potential metal toxicity and mobility. Dissolved (<1 kDa), colloidal (1 kDa–0.45 μm) and particulate (>0.45 μm) size fractions of sulfate, organic C (OC) and 18 metals/metalloids were investigated in the extremely acidic Vörå River system in Western Finland, which is strongly affected by acid sulfate (AS) soils. In addition, geochemical modelling was used to predict the formation of free ions and complexes in these acidic waters. The most important finding of this study is that the very large amounts of elements known to be released from AS soils (including Al, Ca, Cd, Co, Cu, Mg, Mn, Na, Ni, Si and U) occur and can prevail mainly in toxic forms throughout acidic river systems; as free ions and/or sulfate-complexes. This has serious effects on the biota and particularly dissolved Al can be expected to have acute effects on fish and other organisms. In the study area, only the relatively forested upstream area (higher pH and contents of OC) had significant amounts of a few bioavailable elements (including Al, Cu, Ni and U) due to complexation with the more abundantly occurring colloidal OC in the upstream area. It is, however, notable that some of the colloidal/particulate metals were most likely associated with metal bearing phyllosilicates eroded from clay soils. Moreover, the mobilisation of Fe and As was small and As was predicted to be associated with Fe oxides, indicating a considerable influence of Fe oxides on the mobilisation/immobilisation processes of As. Elements will ultimately be precipitated in the recipient estuary, where the acidic metal-rich river water will gradually be diluted/neutralised with brackish seawater in the Gulf of Bothnia. According to speciation modelling, such a pH rise may first cause precipitation of Al, Cu and U together with organic matters closest to the river mouth, in line with previous sediment studies from the estuary.     

Arsenic mobility in mildly alkaline drainage from an orogenic lode gold deposit,Bralorne mine,British Columbia

The historical (1932–1971) Bralorne mine produced over 87 million grams of Au from an archetypal orogenic lode gold deposit in southwest British Columbia. High concentrations of As in mine drainage, however, represent an on-going environmental concern prompting a detailed study of effluent chemistry. The discharge rate at the mine portal was monitored continuously over a fourteen-month period during which effluent samples were collected on a quasi-weekly basis. Water samples were also collected on synoptic surveys of the adit between the portal and the main source of flow in the flooded workings. Total concentrations of As in the mildly alkaline (pH = 8.7) portal drainage average 3034 μg/L whereas at the source they average 5898 μg/L. As emergent waters from the flooded workings flow toward the portal, their dissolved oxygen content and pH increase from 0 to 10 mg/L and from 7.7 to 9, respectively. Near the emergence point, dissolved Fe precipitates rapidly, sorbing both As(III) and As(V). With increasing distance from the emergence point, dissolved As(III) concentrations drop to detection limits through sorption on hydrous ferric oxide and through oxidation to As(V). Concentrations of dissolved As(V), on the other hand, increase and stabilize, reflecting lower sorption at higher pH and the lack of available sorbent. Nonetheless, based on synoptic surveys, approximately 35% of the source As load is sequestered in the adit resulting in As sediment concentrations averaging 8.5 wt%. The remaining average As load of 1.34 kg/d is discharged from the portal. Partitioning of As(V) between dissolved and particulate phases in portal effluent is characterized by a sorption density of 0.37 mol As (mol Fe)⁻¹ and by a distribution coefficient (K_d) of 130 L/g HFO. The relatively high sorption density may reflect co-precipitation of As with Fe oxyhydroxides rather than a purely adsorption-controlled process. Results of this study show that the As self-mitigating capacity of drainage from orogenic lode gold deposits may be poor in high-pH and Fe-limited settings.     

Environmental assessment of abandoned mine tailings in Adak,Västerbotten district (northern Sweden)

Sulfide-rich mine tailings in Adak that are exposed to weathering cause acid mine drainage characterized by low pH (2–4) and high SO₄ (up to 800 mg L⁻¹). Surface water, sediment and soil samples collected in this study contain higher concentrations of As, Cu, Fe and Zn, compared to the target and/or intervention limits set by international regulatory agencies. In particular, high As concentrations in water (up to 2900 μg L⁻¹) and sediment (up to 900 mg kg⁻¹) are of concern. There is large variability in trace element concentrations, implying that both physical (grain size) and chemical factors (pH, secondary phases as sulfides, Al-oxides or clay minerals) play an important role in their distribution. The low pH keeps the trace elements dissolved, and they are transported farther downstream. Trace element partition coefficients are low (log K_d = 0.3–4.3), and saturation indices calculated with PHREEQC are <0 for common oxide and sulfidic minerals. The sediment and soil samples indicate an enhanced pollution index (up to 17), and high enrichment factors for trace elements (As up to 38,300; Zn up to 800). Finally, leaves collected from different plant types indicate bioaccumulation of several elements (As, Al, Cu, Fe and Zn). However, some of the plants growing in this area (e.g., Salix, Equisétum) are generally resistant to metal toxicity, and hence, liming and phytoremediation could be considered as potential on-site remediation methods.     

Tracing source and evolution of suspended particles in the Rio Negro Basin (Brazil) using chemical species of iron

Suspended solids found in porewaters obtained in waterlogged soil sequences that included representative laterite–podzol transitions, associated brooks and major rivers of the Rio Negro watershed (Brazil) were studied using electron paramagnetic resonance (EPR) and Fourier-transform infrared spectroscopies. The main goal was to ascertain sources and track the evolution of suspended matter using a ubiquitous chemical species, FeIII complexed to organic matter (FeOM). Three size fractions were separated by tangential-flow (ultra)filtration: particulate (> 0.2 μm), dense (P) and light (Ps), and colloidal (5 kD < Col. < 0.2 μm) fractions. Quantitative results were acquired for Col. and Ps fractions which are predominantly organic in nature.FeOM concentration (in ‰ dry weight) was determined to be relatively low in suspended solids found in black waters from podzol porewaters and brooks whereas in the main rivers it was several times higher. FeOM concentrations were also correlated with Fe(II)/Fe(III) ratios in solution; these ratios were high in podzol porewaters and low in the rivers. Considering that organic complexation of Fe(II) is minor when compared to that of Fe(III), two interpretations were proposed to account for the above observation. First, [FeOM] was assumed to be distributed along a mixing line, with the clear waters from laterites and the black waters from podzols being its end-members. Consequently, [FeOM] can be used to trace the source of suspended material. Second, dissolved Fe(II) from podzol areas was considered to be progressively oxidized as pore waters move towards the mainstream. According to this mechanism, iron is complexed by organic matter or precipitated as oxides, thus producing an evolution of colloidal matter. As a result of these mechanisms' action, both the high production of Fe(II) and organic matter at the waterlogged podzol–laterite transition areas are major factors affecting iron export in the Rio Negro watershed.     

Arsenic,iron and organic matter in sediments and groundwater in the Pannonian Basin,Hungary

In the central part of the Pannonian Basin, factors controlling the distribution of As in sediments and groundwater of the upper 500 m were studied. In core samples, the amounts of As, Fe and Mn extractable with hydroxylamine hydrochloride (NH₂OH · HCl) in 25% acetic acid, the proportion of the <0.063 mm size fraction, and the sediment organic C (C_org) contents were measured. In the groundwaters concentrations of As, humic substances, and selected major chemical components were determined. In most core samples extractable Fe, as FeOOH, and C_org are correlated, but some samples have excess Fe, or organic matter. In cases where either excess Fe or excess organic matter is found, the amount of As is also elevated. The spatial distribution of As in the groundwater and the lack of a consistent correlation of As with a single component indicate that there is no single factor controlling the concentration of dissolved As over the entire study area. The only consistent feature is enrichment of As relative to Fe in the groundwater, compared to the sediments. This suggests that the dissolution of Fe minerals, which primarily adsorb As, is not congruent. In reducing conditions Fe(III) oxyhydroxides together with adsorbed As dissolve, and siderite with little or no As precipitates. When sub-regions are separated and studied individually, it can be shown that hydrogeological features of the sediments, the proportions of Fe minerals and sedimentary organic matter, and the concentration of dissolved humic materials, all influence the accumulation and mobilization of As. The significance of the different mobilizing processes, however, and the mean concentration of As, is different in the recharge, through-flow and discharge areas.     

Potential for the formation and migration of colloidal material from a near-surface waste disposal site

Organic material typically constitutes a substantial volume (∼ 90%) of the low-level radioactive wastes (LLRW) intended for near-surface disposal at Chalk River Laboratories (CRL), Ontario, Canada. These wastes can contain a large variety of organic materials, including paper, cardboard, plastic bags, used clothing, and mop heads. After emplacement in a disposal facility, leaching of the LLRW by water can mobilize inorganic and organic substances, ranging from small molecules such as acetic acid to unidentifiable material of colloidal size range. This study determined the potential for colloid formation produced by LLRW degradation, because colloid-facilitated transport of contaminants could affect the safety performance of a disposal facility.The decomposition of compacted LLRW was simulated by recirculating water in a closed system over several compacted bales of waste to determine the potential composition and colloid content of leachates. Size fractionation of organic matter was performed on leachate samples that had been aged for 18 months to simulate the microbial degradation of organic matter within leachates during migration out of the LLRW disposal facility. The aged leachates contained high concentrations of dissolved organic matter, ranging between 74 and 5074 mg/l as C. In most of the leachates, volatile fatty acids accounted for a significant fraction (up to 81%) of the dissolved organic carbon. Although 5–110 mg/l of organic colloids were observed in leachates, in most cases, the organic colloids made up a very small fraction of the total leached organic carbon. Therefore, since the complexation properties of dissolved and colloidal organics are probably similar, contaminants complexed to organics are most likely to be dissolved and not affected by colloid transport. The leachates also contained significant quantities of Fe and Al, which could potentially precipitate Fe and Al as colloids after oxidation. Although a significant portion of the dissolved Fe may have been produced by the corrosion of the ☐es used to contain the bales, the high Fe concentrations could be representative of leachates from LLRW that contain metallic Fe components. If Fe and Al colloids are stable, stable concentrations in LLRW leachates could be high enough to affect contaminant transport. Therefore, the Fe and Al content of LLRW should be minimized. The concentrations of natural colloids in sandy aquifers, such as those found at CRL are too low to affect contaminant migration significantly.     

Arsenic attenuation in geothermal streamwater coupled with biogenic arsenic(III) oxidation

In the present study, we investigated As behavior in a high-As hot spring (Sambe hot spring, Shimane, Japan) by coupling direct chemical speciation by synchrotron-based XAFS and HPLC–ICP-MS with microbial As-redox transformation gene analysis. The concentration of soluble As in the spring streamwater decreased immediately along the flow in correlation with Fe behavior, indicating that As in the streamwater was naturally attenuated in the streamwater. Iron XAFS analysis suggested deposition of Fe(III) oxyhydroxides along the flow. Thus, considering the strong affinity of As to Fe oxyhydroxides, the observed attenuation in As was possibly caused by sorption (or incorporation) of As on Fe(III) oxyhydroxides. Both dissolved As(III) and As(V) were present in the aqueous phase, and As(III) was rapidly oxidized to As(V) (<30 s) along the flow. The oxidation kinetics indicated the occurrence of biotic As(III) oxidation, because obtained As(III) oxidation rate (6.7–7.8 μM min⁻¹) was much faster than the reported abiotic oxidation rates. Furthermore, the bacterial arsenite oxidase gene (aioA) was detected in DNA extracted from all samples (average of 2.0 × 10⁵ copies dry g⁻¹), which also supported potential attributes of biological As(III) oxidation in situ. In solid phase samples from sampling points analyzed by XAFS, most of the As existed as oxidized pentavalent form, As(V). This result indicated that this form was preferentially partitioned to the solid phase because of the much higher affinity of As(V) than of As(III) to Fe(III) oxyhydroxides. Considering the kinetic and microbiological findings, it is indicated that biotic process was predominantly responsible for As(III) oxidation at the present site, and this biotic As(III) oxidation to As(V) controlled the observed attenuation of As, because oxidized As(V) was removed from the aqueous phase by Fe(III) oxyhydroxides more efficiently.     

Adsorption of molybdate by synthetic hematite under alkaline conditions: Effects of aging

Hematite is a common primary/secondary mineral in mine drainage and mine waste settings that can adsorb dissolved metals and metalloids. This study explored the ability of synthetic hematite to retain one such contaminant, molybdate, on its surfaces under highly alkaline (pH = ∼10) conditions. X-ray diffraction (XRD), Raman spectroscopy (RS), scanning electron microscopy (SEM), and specific surface area (BET) analyses show that synthetic hematite particles are stable and able to adsorb molybdate. Raman spectra show that the hematite efficiently adsorbs molybdate and retains it on its surfaces via strong inner-sphere surface complexation. Inductively coupled plasma-mass spectrometry (ICP-MS) data indicate that hematite aged (7 and 9 days) at high and room temperatures (75 and 25 °C) retains adsorbed molybdate and that molybdate sorption increases with aging. SEM images show that aged hematite particles with adsorbed molybdate are similar in size and shape to pure hematite and exhibit no significant reduction in surface area. These findings are valuable for understanding the fate of Mo in mine wastes and mill tailings environments where the 2-line ferrihydrite to which it is adsorbed can transform to hematite.     

Laboratory study of calcite–gypsum sludge–water interactions in a flooded tailings impoundment at the Kristineberg Zn–Cu mine,northern Sweden

Due to liming of acid mine drainage, a calcite–gypsum sludge with high concentrations of Zn (24,400 ± 6900 μg g⁻¹), Cu (2840 ± 680 μg g⁻¹) and Cd (59 ± 20 μg g⁻¹) has formed in a flooded tailings impoundment at the Kristineberg mine site. The potential metal release from the sludge during resuspension events and in a long-term perspective was investigated by performing a shake flask test and sequential extraction of the sludge. The sequentially extracted carbonate and oxide fractions together contained ⩾97% of the total amount of Cd, Co, Cu, Ni, Pb and Zn in the sludge. The association of these metals with carbonates and oxides appears to result from sorption and/or coprecipitation reactions at the surfaces of calcite and Fe, Al and Mn oxyhydroxides forming in the impoundment. If stream water is diverted into the flooded impoundment, dissolution of calcite, gypsum and presumably also Al oxyhydroxides can be expected during resuspension events. In the shake flask test (performed at a pH of 7–9), remobilisation of Zn, Cu, Cd and Co from the sludge resulted in dissolved concentrations of these metals that were significantly lower than those predicted to result from dissolution of the carbonate fraction of the sludge. This may suggest that cationic Zn, Cu, Cd and Co remobilised from dissolving calcite, gypsum and Al oxyhydroxides were readsorbed onto Fe oxyhydroxides remaining stable under oxic conditions. In a long-term perspective (≳10² a), ⩾97% of the Cd, Co, Cu, Ni, Pb and Zn content of the sludge potentially is available for release by dissolution of calcite and reductive dissolution of Fe oxyhydroxides if the sludge is subject to a soil environment with lower dissolved Ca concentrations, pH and redox than in the impoundment.     

Seasonal variations of arsenic at the sediment–water interface of Poyang Lake,China

Arsenic species including arsenite, arsenate, and organic arsenic were measured in the porewaters collected from Poyang Lake, the largest freshwater lake of China. The vertical distributions of dissolved arsenic species and some diagenetic constituents [Fe(II), Mn(II), S(−II)] were also obtained in the same porewater samples in summer and winter. In sediments the concentration profiles of total As and As species bound to Fe–Mn oxyhydroxides and to organic matter were also determined along with the concentrations of Fe, Mn and S in different extractable fractions. Results indicate that, in the summer season, the concentrations of total dissolved As varying from 3.9 to 55.8 μg/L in sediments were higher than those (5.3–15.7 μg/L) measured in the winter season, while the concentrations of total As species in the solid phase varied between 10.97 and 25.32 mg/kg and between 7.84 and 30.52 mg/kg on a dry weight basis in summer and winter, respectively. Seasonal profiles of dissolved As suggest downward and upward diffusion, and the flux of dissolved As across the sediment–water interface (SWI) in summer and winter were estimated at 3.88 mg/m² a and 0.79 mg/m² a, respectively. Based on porewater profiles and sediment phase data, the main geochemical behavior of As was controlled by adsorption/desorption, precipitation and molecular diffusion. The solubility and migration of inorganic As are controlled by Fe–Mn oxyhydroxides in summer whereas they appear to be more likely controlled by both amorphous Fe–Mn oxyhydroxides and sulfides in winter. A better knowledge of the cycle of As in Poyang Lake is essential to a better management of its hydrology and for the environmental protection of biota in the lake.     

Forms of phosphorus in sediments from the Goczałkowice Reservoir

The occurrence of Total P (P-Tot) and the mineral forms of P (P-Min) in sediments from Goczałkowice Reservoir were investigated using inductively coupled plasma-optical emission spectrometer (ICP-OES). The method is based on sequential extractions of the sediment samples, each releasing four forms of inorganic P: loosely bound P, P bound to Al (P-Al), P bound to Fe (P-Fe) and P bound to Ca (P-Ca). Sediment samples for studies presented in this work were collected in April, August and November of 2009 from four sites of the Goczałkowice Reservoir. Significant variations in the P forms with sediment grain size were observed. The most abundant form of inorganic P in the bottom sediment was P-Fe. Other P forms were as follows: P-Ca > P-Al > loosely bound-P. Moreover, P compounds were studied using ³¹P NMR. It was found that the predominant form was inorganic orthophosphate.     

A national-scale geochemical and mineralogical survey of soils of the conterminous United States

In 2007, the US Geological Survey initiated a low-density (1 site per 1600 km², c. 4800 sites) geochemical and mineralogical survey of soils of the conterminous USA. The ideal sampling protocol at each site includes a sample from 0–5 cm depth, a composite of the soil A horizon, and a sample from the soil C horizon. The <2-mm fraction of each sample is analyzed for Al, Ca, Fe, K, Mg, Na, S, Ti, Ag, Ba, Be, Bi, Cd, Ce, Co, Cr, Cs, Cu, Ga, In, La, Li, Mn, Mo, Nb, Ni, P, Pb, Rb, Sb, Sc, Sn, Sr, Te, Th, Tl, U, V, W, Y and Zn by inductively coupled plasma-mass spectrometry and inductively coupled plasma-atomic emission spectrometry following a near-total digestion in a mixture of HCl, HNO₃, HClO₄ and HF. Separate methods are used for As, Hg, Se and total C on this same size fraction. The major mineralogical components are determined by a quantitative X-ray diffraction method. Sampling was completed in 2010 with chemical and mineralogical analysis currently underway. Preliminary results for a swath from the central USA to Florida clearly show the effects of soil parent material and climate on the chemical and mineralogical composition of soils. A sample archive will be established and made available for future investigations.     

Evaluation of the dissolved contaminant load transported by the Tinto and Odiel rivers (South West Spain)

The Tinto and Odiel rivers are heavily affected by acid mine drainage (AMD). However, the exact quantities of contaminants transported into the Huelva estuary and the Gulf of Cadiz are unknown. The existing previous investigations are, in general, based on studies with few data or incorrect methodology, and are therefore unreliable. This study aims to present a reliable estimation of the dissolved contaminant load transported by both rivers for the periods 1995/96 to 2002/03. The methodology used is based principally on the correlation between contaminant concentration and flow rate. The results show that both rivers transport enormous quantities of dissolved contaminants: 7900 t a⁻¹ of Fe, 5800 t a⁻¹ Al, 3500 t a⁻¹ Zn, 1700 t a⁻¹ Cu, 1600 t yr⁻¹ Mn and minor quantities of other metals. These values represent 60% of the global gross flux of dissolved Zn transported by rivers in to the ocean, and 17% of the global gross flux of dissolved Cu.     

Arsenic in agricultural and grazing land soils of Europe

Arsenic concentrations are reported for the <2 mm fraction of ca. 2200 soil samples each from agricultural (Ap horizon, 0–20 cm) and grazing land (Gr, 0–10 cm), covering western Europe at a sample density of 1 site/2500 km². Median As concentrations in an aqua regia extraction determined by inductively coupled plasma emission mass spectrometer (ICP-MS) were 5.7 mg/kg for the Ap samples and 5.8 mg/kg for the Gr samples. The median for the total As concentration as determined by X-ray fluorescence spectrometry (XRF) was 7 mg/kg in both soil materials. Maps of the As distribution for both land-use types (Ap and Gr) show a very similar geographical distribution. The dominant feature in both maps is the southern margin of the former glacial cover seen in the form of a sharp boundary between northern and southern European As concentrations. In fact, the median As concentration in the agricultural soils of southern Europe was found to be more than 3-fold higher than in those of northern Europe (Ap: aqua regia: 2.5 vs. 8.0 mg/kg; total: 3 vs. 10 mg/kg). Most of the As anomalies on the maps can be directly linked to geology (ore occurrences, As-rich rock types). However, some features have an anthropogenic origin. The new data define the geochemical background of As in agricultural soils at the European scale.     

Seasonal variations of ochreous precipitates in mine effluents in Finland

Ochreous precipitate and water samples were collected from the surroundings of seven closed sulphide mines in Finland. In the Hammaslahti Zn–Cu–Au mine, Otravaara pyrite mine and Paroistenjärvi Cu–W–As mine, the collection was repeated in different seasons to study mineralogical and geochemical variations of precipitates. The sampling was done in 1999–2002 from the ditches and drainage ponds of the tailings and waste rock piles that are susceptible to seasonal changes. Mineralogy of the precipitates was evaluated by X-ray diffraction (XRD) and infrared spectroscopy (IR), and precipitate geochemistry was examined by selective extractions. Schwertmannite (Fe₈O₈(OH)₆SO₄) was the most typical Fe hydroxide mineral found. Goethite was almost as common as schwertmannite, was often poorly ordered, and contained up to 10 wt.% of SO₄. Goethite and schwertmannite were commonly found as mixtures, and they occurred in similar pH and SO₄ concentrations. Ferrihydrite (nominally Fe₅HO₈ · 4H₂O) was typically found in areas not influenced by acid mine drainage, and also in acid mine waters with high organic matter or As content. Jarosite (KFe₃(SO₄)₂(OH)₆) was found only in one site. In addition, some gypsum (CaSO₄ · 2H₂O) and aluminous sulphate precipitates (presumably basaluminite, Al₄(SO₄)(OH)₁₀ · 5H₂O) were identified. Selective extractions showed that acid extracts Fe_tot/S_tot-ratios of schwertmannite and goethite samples were similar, but the ratio of oxalate-extractable to total Fe, Fe_ox/Fe_tot, of goethite samples were lower than those of the schwertmannite samples. Only Al, Si and As were bound to precipitates in substantial amounts, up to several wt.%. In schwertmannites and goethites, Al, Cu, Co, Mn and Zn were mostly structural, substituting for Fe in an Fe oxyhydroxide structure or bound to surface adsorption sites in pores limited by diffusion. In ferrihydrites, heavy metals were also partly bound in adsorbed form dissolving in acid ammonium acetate. Ferrihydrites and goethites were more enriched in Co, Mn and Zn than schwertmannites, but schwertmannites and ferrihydrites were more enriched in As than goethites. Mineralogical and geochemical evidence showed that in the spring, after the snowmelt, the acid mine drainage precipitates were predominantly schwertmannite, and were partly transformed during warm summer months to goethite. The phase transformation of precipitates was followed by a decrease in pH values and increase in SO₄ concentrations of waters. Adsorbed As retarded the phase transformation.     

Mobilization of arsenic from acid deposition – The Elbe River catchment,Czech Republic

Temporal changes of As concentration in surface waters were observed in some areas of the Czech Republic. Mobilized As originates from past atmospheric deposition. To understand the factors influencing As aqueous concentration and mobility the chemistry and runoff generation of a number of brooks, springs and rivers in the central part of the Elbe River catchment, Czech Republic, were monitored. Seasonal variations of As (from 0.5 to 10.5 μg L⁻¹), Fe (from 0.05 to 3.9 mg L⁻¹) and DOC (dissolved organic C – from 1.2 to 17.5 mg L⁻¹) were observed in monitored stream waters with maximum values of As and Fe in the summer months at pH values 7.6–7.8. The concentration of As in particles with a diameter < 60 μm correlates with the Fe concentration. There is no correlation between Fe and As in filtered samples (<0.45 μm). The As concentration in stream water colloids depends on an increase in DOC concentration and a decrease in ionic strength. The DOC stabilizes As in solution and reduces its re-adsorption on Fe colloids and consequently As concentration in the stream increases.     

Sicilian bottled natural waters: Major and trace inorganic components

Sixteen bottled waters of various Sicilian brands, 11 natural mineral waters and five normal drinking waters, were analyzed for major and trace inorganic components by ion chromatography (IC) and inductively coupled plasma-mass spectrometry (ICP-MS), respectively. The bottled waters represent a variety of water types with significantly different compositions in terms of salinity, major components and trace elements. Chemically, they range from Ca–HCO₃ and Ca–SO₄ to Na–HCO₃ types. Total dissolved solids ranges from 54 to 433 mg/L, total hardness from 25 to 238 mg/L CaCO₃, and measured Na content from 5.7 to 57 mg/L. According to total dissolved ions, all the bottled waters were classified as oligomineral (50 < TDS < 500 mg/L). All the bottled waters analyzed here had elemental concentrations which did not exceed the guideline and directive values, although a high concentration of Al was noted for one bottled water (O7, central Sicily) and high Rb and V in a bottled water (O1) from the Etna volcanic area. With regard to trace elements, the chemical quality of bottled waters was assessed by a metal index (MI). Chemical characteristics were compared with 10 tap water samples from private houses or public places, representative of the public water supply in Palermo, the largest and most densely populated city in Sicily. The municipal waters analyzed, belonging to HCO₃-alkaline earth and Cl–SO₄-alkaline earth waters, showed concentrations of chemical inorganic components well within drinking water limits. The data also indicated that the water supplied by the municipal authority is of fair quality, although fairly hard and high in Na concentration. Several considerations indicate that there is no sufficient reason to prefer bottled waters to tap waters.