Smelting Operations Research Articles

Mobility and speciation of heavy metals in soils impacted by hazardous waste

This study describes the mobility and chemical fractionation of heavy metals (HMs) from a site impacted by auto battery slag that was generated from secondary lead smelting operations. Samples were collected from the waste pile and from the immediate surrounding soil at four depths to assess the migration and potential bioavailability of Pb, Cd, Cr, Ni and Zn. Total levels of the HMs and their fractionation were determined. The results indicate that highest levels of HMs are present in the uppermost layer with significant migration down the depth, thereby posing a threat to groundwater quality. In the fractions, the concentrations of the metals follow this sequence: Pb>Zn>Cd>Cr>Ni. The chemical fractions of Pb, Cd, Cr, Ni and Zn in the samples, expressed as mean concentrations of the sum of the individual chemical fractions, demonstrate that the HMs exist mainly in the non-residual fractions. For instance, the percentage of non-residual fractions of lead in the waste pile and the surrounding soil ranged from 48.9 to 95.6% and 69.4 to 98.3% respectively. The mobility factors of the heavy metals are significantly high indicating high potential mobility and bioavailable forms of these HMs. The high concentrations of the HMs particularly Pb in the non-residual fractions, as observed in this study, shows the impact of anthropogenic activities on enrichment of natural soil with bioavailable HMs. Consequently, there is a need to be cautious in the way waste that is generated from heavy metals projects is added to natural soil.

Three Missouri Alfisols Impacted by Aeolian Deposition of Lead-Zinc-Cadmium-Silver-Indium Bearing Mine Tailings

Modern mining technologies promote the nation's gross domestic product and reduce environmental impacts; however, previous mining activities in Missouri have a legacy of soil contamination. This study focuses on Pb-Cd-Zn-Ag-In soil contamination resulting from a closed Pb-Zn mine at St. Joe State Park in Missouri. Metal contamination is the result of ancestral smelting operations and presently exposed tailings. Three soil profiles located adjacent to a closed mine-smelting operation and two reference pedons located outside of the study area were examined to determine the concentrations of Pb, Cd, Zn, Ag, and In. Aqua regia digestion and selective chemical extractions were employed to assess metal availability. The near-surface soil horizons show dramatically greater Pb, Cd, Zn, Ag, and In concentrations than deeper soil horizons or the reference loess-derived soil profiles. Surface Pb concentrations in the study area range from 224 to 589 mg Pb kg − 1 , whereas the surface Cd concentrations range from 0.3 to 3.1 mg Cd kg− 1. Pyrophosphate and EDTA (Ethylenediaminetetraacetic Acid) extractions demonstrate that a small to substantial portion of the total Pb and Cd pool is potentially available. Water soluble metal concentrations infer that the risk of metal leaching from the soil is minimal.

Evaluation of extractable elements in artificial substratum made from sewage sludge: Approach to remediation of degraded land in the Arctic

AbstractThe Arctic (or subarctic) is characterized by a harsh climate and nutrient‐poor soil; what makes it even harsher in Monchegorsk (67°51′N and 32°48′E) is that metal pollution originating from the Ni–Cu smelting industry has severely damaged the soil and ground vegetation, resulting in formation of an industrial desert (barren ground). A pilot‐scale (4 ha) field test was carried out under such conditions to study how to apply municipal sewage sludge for rehabilitation of degraded land. After sewage sludge had been composted, an artificial substratum made from the compost was introduced to the remediation test field, and then willow, birch and grasses were planted on the substratum. The transformation of the artificial substratum was observed in the test field during 3 years. The portion of Cu in residual form was greater than that in other forms, it is hence considered that Cu has low bioavailability in the artificial substratum. Furthermore, the metal distributions statistically increased in fractions of humic acid (insoluble in water under acidic conditions), so the mobile amounts of Ni and Cu became small.The conclusion drawn from the field survey and analysis of extractable metals indicates that the lost vegetation is being restored even while pollution continues to be discharged from the smelter operation. Copyright © 2008 John Wiley & Sons, Ltd.

Analysis of silver in the water column of the Pra and the Eture estuaries in Ghana

Silver is a rare but naturally occurring metal, often found deposited as mineral ore in association with other elements like gold, manganese and aluminium. Emission from smelting and gold mining operations as well as indiscriminate disposal of waste from photographic laboratories and other chemical laboratories are some of the anthropogenic sources of silver in the environment. This work analysed the concentration of total recoverable silver in the water column of the Eture and the Pra estuaries in Ghana. The result indicated high concentrations in the two estuaries, higher than the values that should be tolerated in the estuarine environment. The high levels in the Pra estuary could be attributed to the numerous mining activities upstream and this was the same for the Eture estuary which also runs through Cape Coast and the University of Cape Coast. The higher levels of silver reported in this study area suggest that much work has to be done to monitor and improve the quality of these ecosystems in the Ghanaian environment.

English

The Golinsky site is a small underground copper mine complex consisting of abandoned mine workings and remnants of smelter operations located on a steep hillside above Little Backbone Creek, a tributary to Lake Shasta. The mine pool is typical acidic mining influenced water (MIW) with a pH of 2.5 to 4 containing heavy metals including Fe, Al, Cu, Zn, Cd, and Mn. The US Forest Service committed to a bench and pilot scale testing program to demonstrate that the SRBR technology would work at the remote site and reduce metal loading on Lake Shasta. A pilot scale SRBR test system was constructed in 2004 and decommissioned in September, 2006 after 26 months of year-round operation. Despite overloading and other operational challenges (e.g., the site is only accessible by boat), the pilot system performed as expected. At the conclusion of the pilot test run, the pilot scale effluent was field-titrated with raw MIW. The results of this effort suggest that SRBR-treated MIW has geochemical benefits beyond the expected straight dilution effects. That is, the elevated alkalinity and sulfide concentrations of the SRBR effluent appear to be capable of providing additional treatment of raw MIW in a simple mixing and settling operation. The titrated mixtures were also tested for toxicity using MetPLATE™ testing kits. A first-phase treatment module is being designed based on the pilot test results.

Dynamic Modelling of an Industrial Smelter Furnace and Converter Off-gas System

In smelters, metal ores or concentrates are smelted to reduce a metal oxide to a metal through a series of reactions and processes. In a smelting process, a large amount of off-gas emissions are often generated, which can cause serious environmental and plant hygiene problems if not properly treated. Off-gas systems extract and treat the off-gas emissions, and ensure that the smelter operation is in accordance with environmental and industrial hygiene regulations. In this paper, the dynamic models for an industrial smelter furnace and converter off-gas system, tackling hazardous sulfur dioxide (SO2), carbon monoxide (CO) and carbon dioxide (CO2), are developed using mass continuity, momentum and energy conservation laws. Based on the developed dynamic models, the effects of important variables on the system’s dynamics are studied via simulations. The developed dynamic models provide a necessary basis for high performance control development of smelter off-gas systems because online measurements are limited and additional ones must be justified.

インドにおけるアルミニウム精錬工場労働者の健康調査

This study reports a work-environmental assessment and workers' exposure in a major prebake type aluminium smelter in India. Levels of known health hazards in and near the main smelting operations viz., the Potroom, the Carbon area, the Butt section, the Rodding shop, the Bath preparing area and the Casthouse were measured. Dustiness in general was high to excessively high. Mean levels of respirable dust (PM10) in air in the three dustiest areas were 24.07 mg/m3 in the Carbon areas, 27.57 mg/m3 in the Bath preparing and 4.44 mg/m3 in the Rodding shop. 40- 60% of the particles were less than 5 microm in size. 0.5- 2.82% particulate fluoride was obtained in the size fraction 0.4- 4.7 microm of the Potroom air. Naturally, exposures to total dusts were very high in these processes. The background levels of NOx and SO2 and fluorides (gaseous and particulate) were found to be within the prescribed Indian Standards. Higher exposures to gaseous and particulate fluoride, 3.85 and 6.53 mg/m3 respectively, were observed among the Rodding shop workers. The levels ofpolycyclic aromatic hydrocarbons (PAHs) were deemed to be excessive in the Carbon area. Measurements of heat stress were made in winter and were found to be lower than the prescribed limit.

Heavy metal exposure, reproductive activity, and demographic patterns in white-footed mice ( Peromyscus leucopus) inhabiting a contaminated floodplain wetland

We examined the concentrations of selected metals and selenium (Se) in the tissues of white-footed mice ( Peromyscus leucopus) collected at a constructed wetland originally created as a retention basin for sediments dredged from Lake DePue, Illinois. These sediments were contaminated with high concentrations of cadmium (Cd), zinc (Zn), and other elements as a result of nearby smelting operations. White-footed mice inhabiting the former retention basin experienced greater exposure to Cd, Pb, and Se than those from nearby reference sites. Concentrations of Cu and Zn in livers of mice from the contaminated wetland and adjacent floodplain reference site were greater than in mice from the more-distant reference sites. Judging by concentrations in their kidneys, white-footed mice inhabiting the floodplain adjacent to the contaminated wetland had greater exposure to Cd than those from the two more-distant reference sites. Concentrations of Hg in tissues of mice did not vary appreciably among sites. Concentrations of Cd and Se in the tissues of some white-footed mice from the contaminated wetland exceeded critical concentrations observed in experimental studies of laboratory mice and rats; with few exceptions tissue Pb concentrations were below published effects levels. However, we did not detect changes in abundance, demographics, or reproductive activity that might suggest population-level effects of contaminant exposure. Mean weight of embryos expressed as a function of crown–rump length did not differ among locations sampled, and no gross lesions indicative of exposure to heavy metals were observed. Kidney and liver weight, corrected for body weight, were nominally, though not significantly, lowest in both male and female mice from areas of increased Cd and Pb exposure. Metals dredged from Lake DePue were still bioavailable 25 years after deposition. However, small mammal populations are resilient to environmental stressors and we did not detect differences in population parameters suggesting that the population of white-footed mice inhabiting the contaminated wetland was at risk from increased exposure to these contaminants.

Characterization of PM 2.5 fugitive metal in the workplaces and the surrounding environment of a secondary aluminum smelter

Fugitive metal in PM 2.5 at the blast furnace ( S 1), reverberatory furnace ( S 2), and surrounding environment ( S 0) of a secondary aluminum smelter (a secondary ALS) was studied. PM 2.5 mass concentration at the blast furnace exceeded that at the reverberatory furnace and this was especially apparent during operation, giving an early indication that the blast furnace is more important as a pollutant source. Further, PM 2.5 mass concentration levels and patterns at S 0 indicated that emissions from the blast furnace and reverberatory furnace were the major source of the observed fine particle pollution in the surrounding environment. Si and K were the main components and hence pollutants by mass in the PM 2.5 at S 1, S 2 and S 0 during both operation and non-operation. Hg was not detected in the PM 2.5 aerosol during smelter operation but was present at all three sampling locations during non-operation. This is due to the falling blast furnace and reverberatory furnace temperatures during non-operation which cause Hg vapor formed during operation to condense to form detectable Hg particles, and hence Hg contributes to the pollutant load during non-operation. Average S 1/ S 0 and S 2/ S 0 mass concentration ratios of 40.32 and 18.53, respectively, for all measured metals during operation and 7.83 and 5.73 for all measured metals during non-operation indicate that metal particulate pollution at the workplaces of secondary ALSs, particularly at the blast furnace during operation, is a serious issue. S 1/ S 0 mass concentration ratios were higher still for Pb (62.22), Ti (113.40) and Ba (248.64), while the S 2/ S 0 mass concentration ratio for Mo was 138.20. Principal component analyses produced a PC1 that explained 32.36–48.16% of the total variance during operation of the smelter and 47.86–69.Ten percent during non-operation. Their strong component loadings were mainly related to the fugitive PM 2.5 mass. Compared to atmospheric metal concentrations reported for other regions of the world, the toxic metals that have relatively higher concentrations in the secondary ALS emissions are Cr, Cd, Cu, As, Pb, Se, Al and Zn, especially during smelter operation. Concentrations of these toxic heavy metals are approximately 2–4 orders of magnitude higher than those reported for various industrial regions and metropolises with heavy traffic across the world.

COMPARISON OF DIFFERENT CONTROL METHODS FOR AN INDUSTRIAL NICKEL SMELTER ROASTER OFF-GAS SYSTEM

A roaster off-gas system constitutes an important component of the Nickel smelter operations, as it ensures the smelter operations in accordance with environmental regulations. It is important to control the off-gas pressure at the setpoint. In this paper, several control methods commonly used in industry are evaluated and compared via simulations. Comparison shows that the feedback control combining the conventional PI control with the steady state feedforward term can provide robust but effective control in rejecting the disturbance. The control method provides an improved control performances with an easily implementable form.

Variability in Copper and Bronze Casting Technology as Seen at Bronze Age Godin Tepe, Iran

AbstractGodin Tepe lies along the “High Road” leading from the Mesopotamian lowlands to the northern Iranian Plateau and beyond. This site acted as a center for the exchange of goods, transmission of ideas, and spread of technology; therefore the technology and manufacturing methods represented by the artifacts at this site provide information regarding the technology in use across the Iranian Plateau. Materials analyzed from Godin Tepe include crucibles, furnace and tuyere fragments, ore, and metal artifacts dating to the early third through late second millennium B.C.E. The production materials were concentrated in only a few locations throughout the site, and they are indicative of small scale production. SEM and microprobe analyses have allowed the determination of cooling rates and temperatures attained during smelting and casting operations in antiquity. In addition, the analysis of approximately 60 metal artifacts (out of the two-hundred plus that were excavated) have contributed greatly to understanding the variability in manufacture methods present during this time period. The results of this investigation support two significant conclusions. First, the measurement and evaluation of secondary dendrite arm spacing of cast artifacts and crucible prills provides insight to the processes and cooling methods employed by ancient craftsmen. Second, the wide range in manufacturing methods shown by the microstructures of non-utilitarian artifacts, offers strong evidence for the presence of multiple producers who copied styles and typology, but not technological methods from their contemporary craftsmen.

NOVEL APPROACH TO MODELING OF IMPERIAL SMELTING FURNACE BEHAVIOR

A mathematical model based on the heat and mass balance of the Imperial Smelting Furnace (ISF) has been proposed. This model can be used by operating engineers to evaluate furnace behavior without the necessity of generating an exhaustive data bank for rate parameters. The model formulation is based on Rist's model of iron blast furnace, consisting of separate reaction zones. In the adapted approach, the ISF has been conceived as a combination of a lead reduction zone and a zinc reduction zone, separated by an equilibrium zone. The mass and energy balances comprising oxygen balance, heat demand, and heat supply analyses lead to the construction of an operating line for the furnace describing its behavior. The model has been validated by 1) predicting furnace coke consumption based on analytical heat balance for an actual smelter operation as reported in the literature and 2) estimating the coke ratio as a function of the oxygen content of the blast. Both of these parameters have been satisfactorily correlated with available data. The model has been used for predictions of furnace behavior, accounting for: 1) the effect of increasing blast temperature on coke savings, and 2) the effect of change in the operating mode of oxygen enrichment on a specific carbon rate.

Fractionation change of hydrogen isotopes in trees due to atmospheric pollutants

Atmospheric pollution effects on hydrogen fractionation in trees are demonstrated for the first time in this study. The δ 2H ring-cellulose series obtained for black spruce trees at a site near a SO 2-emitting smelter display short-term fluctuations superimposed on a first order −11‰ shift coincident with the onset of smelter operations. The isotopic depletion in trees exposed to various levels of SO 2 diminish with increasing distance relative to the location of the smelter, and it is not detected at the most distant selected stand, 116 km downwind from the point source. Both the spatial and temporal isotopic trends likely result from the combined effects of leaf transpiration, biochemical processes and water uptake by the root system. The spatial and temporal trends of δ 2H values are the reverse of the δ 13C trends previously obtained for the same tree ring series. These coupled isotopic fractionations underline an important response of trees to pollution stresses likely generated by ambient atmospheric SO 2 concentrations. The degradation of global air quality during the last 150 yr likely generated large scale modifications in the way terrestrial vegetation grows. In this respect, hydrogen dendrogeochemistry combined with other tracers such as C isotope ratios constitutes a new tool to evaluate the past behavior of forest ecosystems in terms of C uptake and acclimation to various types of atmospheric pollution.

Zinc mobility and speciation in soil covered by contaminated dredged sediment using micrometer-scale and bulk-averaging X-ray fluorescence, absorption and diffraction techniques

The mobility and solid-state speciation of zinc in a pseudogley soil (pH = 8.2–8.3) before and after contamination by land-disposition of a dredged sediment ([Zn] = 6600 mg kg −1) affected by smelter operations were studied in a 50 m 2 pilot-scale test site and the laboratory using state-of-the-art synchrotron-based techniques. Sediment disposition on land caused the migration of micrometer-sized, smelter-related, sphalerite (ZnS) and franklinite (ZnFe 2O 4) grains and dissolved Zn from the sediment downwards to a soil depth of 20 cm over a period of 18 months. Gravitational movement of fine-grained metal contaminants probably occurred continuously, while peaks of Zn leaching were observed in the summer when the oxidative dissolution of ZnS was favored by non-flooding conditions. The Zn concentration in the <50 μm soil fraction increased from ∼61 ppm to ∼94 ppm in the first 12 months at 0–10 cm depth, and to ∼269 ppm in the first 15 months following the sediment deposition. Higher Zn concentrations and enrichments were observed in the fine (<2 μm) and very fine (<0.2 μm) fractions after 15 months (480 mg kg −1 and 1000 mg kg −1, respectively), compared to 200 mg kg −1 in the <2 μm fraction of the initial soil. In total, 1.2% of the Zn initially present in the sediment was released to the environment after 15 months, representing an integrated quantity of ∼4 kg Zn over an area of 50 m 2. Microfocused X-ray fluorescence (XRF), diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) spectroscopy techniques were used to image chemical associations of Zn with Fe and Mn, and to identify mineral and Zn species in selected points-of-interest in the uncontaminated and contaminated soil. Bulk average powder EXAFS spectroscopy was used to quantify the proportion of each Zn species in the soil. In the uncontaminated soil, Zn is largely speciated as Zn-containing phyllosilicate, and to a minor extent as zincochromite (ZnCr 2O 4), IVZn-sorbed turbostratic birnessite (δ-MnO 2), and Zn-substituted goethite. In the upper 0–10 cm of the contaminated soil, ∼60 ± 10% of total Zn is present as ZnS inherited from the overlying sediment. Poorly-crystalline Zn-sorbed Fe (oxyhydr)oxides and zinciferous phyllosilicate amount to ∼20–30 ± 10% each and, therefore, make up most of the remaining Zn. Smaller amounts of franklinite (ZnFe 2O 4), Zn-birnessite and Zn-goethite were also detected. Further solubilization of the Zn inventory in the sediment, and also remobilization of Zn from the poorly-crystalline neoformed Fe (oxyhydr)oxide precipitates, are expected over time. This study shows that land deposition of contaminated dredged sediments is a source of Zn for the covered soil and, consequently, presents environmental hazards. Remediation technologies should be devised to either sequester Zn into sparingly soluble crystalline phases, or remove Zn by collecting leachates beneath the sediment.

Sulfate Reduction Potential in Sediments in the Norilsk Mining Area, Northern Siberia

The purpose of this study was to characterize the distribution and activity of sulfate-reducing bacteria in tailings and sediments impacted by effluents from mining and smelting operations in the Norilsk area in northern Siberia. The Norilsk mining complex involves three smelter operations, a hydrometallurgical plant, and extensive tailings areas located in the permafrost zone. Sulfate reduction rates measured with a 35SO4 2− tracer technique under various in-situ conditions ranged from 0.05 to 30 nmol S cm−3 day−1. Acetate and glucose addition greatly stimulated sulfate reduction, whereas lactate had less effect. The most pronounced stimulation of sulfate reduction (6.5-fold) was observed with phosphate amendment. Most-probable-number (MPN) counts of sulfate-reducing bacteria in media with glucose, ethanol, lactate, and acetate as electron donors were generally highest at around 107 cells ml−1. The actual MPN counts varied with the sample, electron donor, and incubation conditions (pH 7.2 vs. pH 3.5; 28°C vs. 4°C). Enrichment cultures of sulfate-reducing bacteria were established from a sample that showed the highest rate of sulfate reduction. After multiple serial transfers, the dominant sulfate-reducers were identified by fluorescence in situ hybridization using genus and group-specific 16S rRNA-targeted oligonucleotide probes. Desulfobulbus spp. prevailed in ethanol and lactate enrichments and the Desulfosarcina-Desulfococcus group dominated in acetate and benzoate enrichments. Psychrophilic Desulfotalea-Desulfofustis and moderately psychrophilic Desulforhopalus spp. were identified in enrichments incubated at 4°C, but they were also found in mesophilic enrichments.

Control Analysis of the Operation of a Copper Smelter and Two Sulphuric Acid Plants

A control strategy analysis for the operation of a copper smelter and two different acid plants is performed. The gas, reach in sulphur dioxide and dust, is generated by the combined operation of two Teniente Converters and four Peirce Smith converters. The gas is treated to reach certain temperature and solid contents, and then distributed into two sulphuric acid plants, where afer a cleaning stage; the sulphur dioxide is catalytically converted into sulphur trioxide that finally is absorbed in concentrated sulphuric acid. The main goal of this project is to increase the acid plants availability, and therefore to increase copper production, by decreasing the occurrence of environmental events and acid plant shutdowns. Preliminary results are discussed. Copyright © 2004IFAC

Distribution of 36 Element Deposition Rates in a Historic Mining and Smelting Area as Determined Through Fine-Scale Biomonitoring Techniques. Part II: Relative Long-Term Accumulated Atmospheric Deposition Levels

The content of 36 elements in the H horizon of coniferous forest floor humus was determined for 56 sampling plots situated in linear transects running out radially to a distance of 14 km from a lead smelter. Fine-scale contour maps of element content in humus revealed five types of basic patterns for the positions of hot spots. Using PCA and contour maps the following four dominant pollution sources were identified that had influenced the accumulation of some elements in humus in the area (615 km2): operation of a lead smelter (Ag, Bi, Cd, Cu, Fe, Hg, In, Pb, S, Sb, Zn), gravel production from stones from uranium pit heaps (Al, Be, Co, Cr, Ga, Mn, Sc, Se, Th, U, V), operation of works processing heat resistant steel (Mo) and anthropogenic or local geogenic factors (Ce, Co, La, Nd, Pr, Y). Except in the case of Pb, Cd, Zn, (As, Hg), high current and long-term accumulated loads of the other elements named above have not previously been indicated in the literature for this area. In addition, no patterns of accumulated elements in humus in details of registers and allotments are known for this area. The interpolated hot spot area for heavy forest humus contamination was found to be 5–80 km2, however, U, Cd and Pb were highly accumulated in humus at 100, 320 and more than 630 km2, respectively. At a distance of 200 m and 22 km windward and 600 m and 22 km leeward from the lead smelter, the Pb content in the forest floor humus was 78 500 and 131 μg g-1 windward and 81 050 and 175 μg g-1 leeward, respectively. The normal Pb content in forest floor humus is less than 100 μg g-1 in the Czech Republic. Also patterns of accumulated elements in humus in details of registers and allotments have not been known for the area up to now. The distributions of the long-term accumulated elements in humus related to the distance from the source could be described nearly perfectly by exponential equations, while elevation, topography, leeward/windward exposure, and the geology of the sampling plots have not significantly influenced accumulation ofmost elements. Results of the forest floor humus analysis were fully supported by the parallel moss monitoring results. Humus monitoringtechniques can reliably determine the long-term effects of pollutionsources and reveal the hidden accumulated loads of elements in details in the landscape.

Geochemical and Health Policy Dimensions of the Controversy about Fluorides in Water Resources

Fluorine has natural and anthropogenic sources. Its presence in water resources and its addition to drinking water as fluoride to aid dental health have generated scientific controversies and policy disputes in many parts of the world during the past 15 years. The concentration of fluorine in the earth’s crust is about 0.3 g/kg. It is a constituent of rocks ~especially, volcanic rocks!, soils, and living matter. By virtue of its position in the periodic table of chemical elements, it is highly electronegative. Consequently, it tends to react with other substances under prevailing environmental conditions to form fluorides. Fluorides enter surface water and groundwater systems through dissolution and leaching of mineral deposits and rock formations; precipitation and flooding events; and release of inadequately treated or untreated wastes into the environment. The near-surface environment in which country rocks exist is dynamic and promotes the development of physicochemical interactions that have produced rocks that vary in geochemistry from one region to another. Globally, the reported levels of fluoride in groundwater are in the range of 1–35 mg/L. At a specific location, water that is taken from wells that penetrate fluoride-bearing bedrock is likely to have greater concentrations of fluoride than water from wells that terminate in the soil profile. Industrial operations conducted within the last 60 years constitute the main source of anthropogenic fluoride in groundwater. Fluoride is released during phosphate processing for fertilizers, aluminum smelting operations, and production processes of glass, bricks, and steel. In the United States and other technologically developed countries, the deployment of innovative ~and less polluting! technologies, voluntary environmental stewardship by industrial organizations, and enforcement of industrial effluent guidelines by local, regional, and national agencies have made it rare for fluoride concentrations to exceed 3 mg/L in groundwater. For example, in Nebraska, the reported range is 0.1–2.6 mg/L ~Headrick 1996!. In the State of New Hampshire, less than 1.0% of bedrock wells produce water with fluoride concentrations in excess of 4.0 mg/L ~NHDES 2002!. As a continuation of the practice that started in Grand Rapids, Michigan, on January 25, 1945, fluoride is added to drinking water by most municipalities in the United States. The known benefit is that it reduces tooth decay when it is taken at the appropriate dose. Daily consumption of water that has a fluoride concentration of 4 mg/L does not present a health risk. The World Health Organization recommends a fluoride content of 1.5 mg/L in drinking water. In general, in the United States, the optimum fluoride content in drinking water is considered to be 0.7–1.2 mg/L. It is also known that daily drinking of water with fluoride concentrations above 2.0 mg/L can cause dental fluorosis. Fluo-

Effects of smelter sulfur dioxide emissions: a spatiotemporal perspective using carbon isotopes in tree rings.

We wanted to test the hypothesis that forest exposure to phytotoxic gases indirectly affects their carbon uptake. We estimated that the reduction of photosynthesis may have reached 20 to 30% at a site located 9 km (test site) from the Horne copper smelter in Rouyn-Noranda, which is a point source of SO2. Twenty-one spruce trees older than 100 yr were selected from seven sites at various distances from the smelter to evaluate conditions prior to and during the periods of smelter operation. The carbon isotope results obtained from spruce tree rings at our test site reveal an unprecedented and abrupt shift of +4/1000 after the onset of smelter operations. This large and permanent shift exceeds natural variations in regional pre-smelter series or in the series at a remote control site. All trees up to 116 km downwind from the smelter show delta13C positive shifts following the onset of operations. There is also a clear inverse relationship between the amplitude of the first-order trends and distance from the smelter. Those delta13C trends indicate that trees exposed to high levels of SO2 decrease their level of CO2 uptake through activation of stomatal closure. This is strongly supported by the significant departure of the Rouyn-Noranda trends from those measured for trees from non-industrialized areas of the Northern Hemisphere, or calculated using global atmospheric conditions. Considering the large number of SO2 point sources in North America, our results imply that CO2 uptake by the boreal forest in the vicinity of these sources may be lower than previously thought.

Assessment of environmental impacts of active smelter operations and abandoned mines in Karabash, Ural Mountains of Russia

AbstractIndustrialization in the former USSR caused widespread environmental damage, which is graphically illustrated in the South Urals mining region of west‐central Russia. One of the most heavily polluted areas is the town of Karabash and its surrounding area, which has abandoned mines and a large active copper smelter close to its centre. The area is affected by effluents and gaseous and particulate emissions from the smelter, acid drainage from abandoned mines and leachates and dusts from waste dumps and tailings dams. This article outlines the methodologies employed under a 3 year instrumental‐ and bio‐monitoring assessment of mining‐related impacts in Karabash, designed to be sensitive to the natural setting and specific political, sociological and economic situation in the Ural mountains. The results of the preliminary, planning stage of the project are presented and discussed. Copyright © 2003 John Wiley &amp; Sons, Ltd and ERP Environment.