Partitioning Of Trace Metals Research Articles

Distribution and partitioning of trace metals (Cd, Cu, Ni, Pb, Zn) in Galveston Bay waters

The distribution of several trace metals has been studied in the surface waters of Galveston Bay, Texas, in order to assess the impact of complexation with organic and reduced sulfur species on the partitioning of trace metals between particulate and aqueous species. The distribution of trace metals in the filter-passing fraction ( Cu>Cd>Zn>Pb>Mn>Fe, while an increasing trend was found in the same sequence for the acid-leachable fractions. The average values of Kd1, the particle-water partition coefficient, expressed as the ratio of weak acid-leachable particulate fractions to the filter-passing fractions, increased in the order Ni<Cu<Cd<Zn<Mn<Pb<Fe. This sequence is consistent with the relative importance of particulate transport of these trace metals from estuaries to coastal oceans. The observed decrease of Kd1 of Cu with increasing concentrations of suspended particulate matter (SPM), also called the “particle concentration effect” (PCE), can be eliminated when the free ionic, rather than the total concentration of Cu in the filter-passing fraction is used for calculating this ratio. A particle concentration effect would be expected if the binding of these trace metals by particles is mediated by solution (i.e., filter-passing) phase ligands. Complexation of Cd, Cu, Ni, Pb, and Zn with reduced sulfur species could be one of the causes for the observed linear correlations between metals and reduced sulfur species in both the filter-passing and filter-retained fractions. Significant correlations between Cu in the weak acid-leachable fraction and chlorophyll a (Chl a) concentrations suggest biological mediation of Cu uptake into the particulate fraction.

Insights into sequential chemical extraction procedures from quantitative XRD: a study of trace metal partitioning in sediments related to frog malformities

Sequential chemical extraction (SCE) and quantitative X-ray diffraction (QXRD) were used in combination to assess trace metal speciation and availability in sediment from two separate marshes in western Vermont, USA, one with high (45%) and one with low (<5%) northern leopard frog ( Rana pipiens) malformity rates. The types of malformities observed in the field are very similar to malformities produced in laboratory studies where frogs are exposed to waters and sediments with elevated levels of trace metals such as Co, Cu, Ni, and Zn. Total recoverable metals, as determined by US EPA method 200.2 (HCl–HNO 3), are statistically higher in the malformity-affected marsh than in the marsh with low malformity rates, suggesting possible causality. Analysis of trace metal speciation by SCE and QXRD, however, implies that the most common reservoir of Co, Cr, Cu, Ni, and Zn in the sediment is trioctahedral clay minerals, including chlorite, high charge smectite and vermiculite. The only trace metal that is not associated with trioctahedral clay is Pb, which appears to be contained in poorly crystalline or amorphous oxyhydroxides. The proportions of trace metals in the exchangeable fraction are variable, with values of ≤3% of total Cr and Pb, 2–17% of total Cu and Ni, and up to 24% of total Co and Zn. Total metals concentrations may be slightly elevated relative to background values, and the partitioning of Co, Cu, Ni, and Zn into the exchangeable fraction implies a mechanism for interaction with frogs. Furthermore, partitioning of Pb into poorly crystalline or amorphous oxyhydroxides suggests that it might be mobilized when water levels rise and cause reduction and dissolution of oxyhydroxides in submerged sediment. The difference in speciation between Pb on the one hand, and Co, Cr, Cu, Ni, and Zn on the other, implies that only Pb has an anthropogenic source. Mn speciation differs from all other metals in that it is subequally partitioned into exchange sites, hydroxides and trioctahedral clay. Fe is predominantly partitioned into trioctahedral clay, with lesser amounts in hydroxide form. QXRD indicates that expandable trioctahedral clay dissolves progressively throughout the SCE procedure, including during extractions intended to (1) oxidize sulfides and organic matter, and (2) reduce oxides and hydroxides, indicating that SCE procedures are not entirely phase selective. It also underscores the need for quantitative mineralogical analysis in conjunction with SCE, and has important implications for the interpretation of metal speciation by SCE alone and without corroborating QXRD analyses.

Sorption of trace metals to an aluminum precipitate in a stream receiving acid rock-drainage; Snake River, Summit County, Colorado

The quality of water in streams that are contaminated by acid drainage from mines and from the weathering of mineralized rocks improves as the water flows downstream. The purpose of this study was to investigate the geochemical processes that occur in one such stream and to determine the fate of the trace metals that are removed from the water. The stream chosen for this purpose was the Snake River, Summit County, Colorado, which is affected by natural acid rock-drainage (ARD) containing SO 4, Al, Fe, and various trace elements such as Zn, Cu, Pb, Ni, and others. Most of the Fe in the Snake River is removed from solution by the oxidation of Fe 2+ to Fe 3+ and the subsequent precipitation of Fe-oxyhydroxides that form a massive ferricrete deposit near the springs that feed the river. Further downstream, the Snake River (pH=3.0) mixes with water from Deer Creek (pH= 7.0) thereby increasing its pH to 6.3 and causing SO 4-rich precipitates of Al-oxyhydroxide to form. The precipitates and associated organic C complexes sorb trace metals from the water and thus have high concentrations of certain elements, including Zn (540–11,400 ppm), Cu (34–221 ppm), Pb (90–340 ppm), and Ni (11–197 ppm). The concentrations of these elements in the precipitates that coat the streambed rise steeply in the zone of mixing and then decline downstream. The trace element concentrations of the water in the mixing zone at the confluence with Deer Creek decrease by 75% or more and are up to 3 orders of magnitude lower than those of the precipitates. Sorption curves for Zn, Cu, Pb, Ni, and SO 4 were derived by stepwise neutralization of a sample of Snake River water (collected above the confluence with Deer Creek) and indicate that the trace metals are sorbed preferentially with increasing pH in the general order Pb, Cu, Zn, and Ni. Sulfate is removed between pH 4 and 5 to form an Al-hydroxysulfate and/or by sorption to microcrystalline gibbsite. The sorption data determined from the neutralization experiment were used to account for the downstream decrease of trace-metal concentrations in the precipitates. The results of this study demonstrate that the partitioning of trace metals in the Snake River is not only a function of pH, but also depends on the progressive removal of trace metals as the water of the Snake River flows through its confluence with Deer Creek. The chemical composition of the water also determines what compounds precipitate with increasing pH.

Modeling metal removal onto natural particles formed during mixing of acid rock drainage with ambient surface water.

Studies have examined partitioning of trace metals onto natural particles to better understand the fate and transport of trace metals in the environment, but few studies have compared model predictions with field results. We evaluate the application of an empirical modeling approach, using surface complexation parameters available in the literature, to complex natural systems. In this work, the equilibrium speciation computer program PHREEQC was used along with the diffuse double-layer surface complexation model to simulate metal removal onto natural oxide particles formed during the mixing of acid rock drainage with ambient surface water. End-member solutions sampled in the Coeur d'Alene (CdA) Mining District in September 1999 from the Bunker Hill Mine and the South Fork Coeur d'Alene (SFCdA) River were filtered and mixed in several ratios. Solution chemistry was determined for end-members and mixed solutions, and X-ray diffraction (XRD) was used to determine the mineralogy of precipitate phases. Predicted amounts of Fe precipitates were in good agreement with measured values for particulate Fe. Surface area and reactive site characteristics were used along with surface complexation constants for ferrihydrite (Dzombak, D. A.; Morel, F. M. M. Surface Complexation Modeling: Hydrous Ferric Oxide; John Wiley & Sons: New York, 1990) to predict ion sorption as a function of mixing fraction. Comparisons of model predictions with field results indicate that Pb and Cu sorption are predicted well by the model, while As, Mo, and Sb sorption are less well-predicted. Additional comparisons with particulate metal and Fe data collected from the CdA Mining District in 1996 and 1997 suggest that sorption on particulate Fe, including amorphous iron oxides and schwertmannite, may be described using universal model parameters.

Distribution and partitioning of trace metals in sediments of the lower reaches of the New Calabar River, Port Harcourt, Nigeria.

The distribution of trace metals in sediments of the lower reaches of the New Calabar River, Nigeria was evaluated together with the partitioning of their chemical species between five geochemical phases. Samplings were made in five zones at the lower reaches of the New Calaber River. All the trace metals were determined by AAS after selective chemical extractions and concentrations given in microg gm(-1) (dry weight basis). The average total concentrations found for trace metals in the sediment were ( mean +/- rsd.) Pb: 41.6 +/- 0.29, Zn: 31.60 +/- 0.42, Cd: 12.80 +/- 0.92, Co: 92 +/- 0.25, Cu: 25.5 +/- 0.65 and Ni: 3.2 +/- 0.25. Maxima and minima concentrations are inconsistent with previous studies in other rivers of this region. Spatial distribution revealed that the sources of trace metals into the river appeared to be of non-point. Five contamination indices were applied in studying the partitioning of the trace metals in the sediment. These indices provided bases for ascertaining the potential environmental risk of trace metals in the river system. The results denote high partition levels in the more mobile and more dangerous phases.

Spatial trends in the chemical composition of sediments on the continental shelf and slope off the Mediterranean coast of Israel

In order to determine whether observed trends in total trace metal content were natural or due to anthropogenic inputs, major and trace elements were measured on three size fractions (fine sand (250–63 μm), silt and clay (<63 μm) and clay (<2 μm)) of sediment collected off the Mediterranean coast of Israel. Partitioning of trace metals into carbonate/exchangeable, iron oxide and residual phases for each grain size was also determined. The dominant source of particles was Nile derived material. There was a decrease in Fe/Al, Ti/Al and non-carbonate Mg/Al in the fine sand fraction, interpreted as a decrease in heavy minerals towards the north and an increase in K/Al due to increased feldspars and micas. There was a simultaneous increase in CaCO 3 both towards the north and onshore in all grain size fractions due to a northward increase in local biogenic fragments and river detritus. This is consistent with circulation and sediment transport models for the southeast Levantine basin. The background trend in trace metals corresponds to changes in mineralogy. While the fine sand fraction appeared free of contamination, in the finer fractions there is a significant enrichment of Zn, and Cd towards the north, which is not accounted for by changes in mineralogy. The sediments were also enriched in Cu, Zn and Cd near Tel Aviv and Hadera. The peaks near Tel Aviv may correspond to waste discharged through the Yarqon and an old sewage pipe, whilst near Hadera, the Alexander and Hadera Rivers and the terminal for a coal-fired power station may be the source of contamination. There was also clear evidence for contamination by Pb in the finest sediments. However, there was no enrichment in Pb around the point sources of the other trace metals, therefore it was concluded that the majority of Pb contamination was from the atmosphere. All trace metal contamination may be subject to ‘smearing’ by sediment transport, particularly in the clay fraction.

Prediction of trace metal partitioning between minerals and aqueous solutions: a linear free energy correlation approach

Trace metal partitioning between authigenic minerals and aqueous solutions is of great interest to both geochemical and environmental communities. In this paper, we have developed a linear free energy correlation model that correlates metal partition coefficients with metal cation properties: −2.303 RT log K d + ΔG f,M Z+ 0 = a ∗ M H X Δ G n,M Z+ 0 + β ∗ M H X r M Z+ + b ∗ M H X where a ∗ M H X , β ∗ M H X , and b ∗ M H X are constants, which can be determined by a regression analysis. For isovalent metal partitioning, because of the constraint of K d = 1 for the host metal, this correlation can be also expressed as: −2.303 RT log K d = a ∗ M H X (Δ G n,M H Z+ 0 − Δ G n,M 0 ) + β ∗ M H X ( r M Z+ − r n,M H Z+ ) − (Δ G f,M Z+ 0 − Δ G 0 f,M H Z+ ). Host minerals from an isostructural family have the same linear free energy relationship, as long as the relationship is expressed as a function of the differences in cation properties between substituent and host metals. We have applied our model to both isovalent and non-isovalent metal partitioning in carbonate minerals. The model closely fits experimental data, demonstrating the robustness of the proposed linear free energy relationship. Using the model, we have predicted the partition coefficients of divalent and trivalent metals between various carbonate minerals and aqueous solutions. The differences between the predicted and experimental values are generally less than 1 logarithmic unit for divalent cations and less than 0.4 logarithmic unit for trivalent cations. Magnesite is predicted to have the largest partition coefficients among the carbonate minerals with a calcite structure and therefore, can be a good scavenger for toxic metals. The kinetic effect on metal partitioning can be described graphically by a “seesaw” line anchored at a host cation. To explain the rate dependence of partition coefficients, we have proposed a conceptual model that relates metal partitioning to surface adsorption. The conceptual model suggests that as the rate of host mineral precipitation increases, the ratio of substituent to host cation in a solid approaches what is in the adsorbed layer. The linear free energy correlation model developed in this paper provides a useful tool for systematizing the existing experimental data and for predicting unknown partition coefficients.

Partitioning of trace metals before and after biological removal of metals from sediments

Metal removal by biological solubilization in three strongly contaminated sediments was carried out in a two-liter stirred bioreactor. Biological treatment yielded metal removal efficiencies in the range of 11–30%, 43–57%, 60–79%, 61–90%, 18–21%, 0–10% for Pb, Cu, Zn, Cd, Ni and Cr, respectively. The treated sediments were then rinsed with a NaCl solution (0.5 M), resulting in an increase by nearly 47% in Pb removal for the three sediments, while for other metals (Cu, Zn, Cd, Ni, Cr), the NaCl rinse did not seem to allow any significant increase in metal solubilization. A standard procedure of sequential selective extraction (SSE) was applied to the sediments before and after each treatment. With regard to Pb, Zn and Cd, the carbonate bound fractions (2/3 sediments) represented 18–42% of metals prior to treatment, while the iron and manganese oxides bound fraction constituted 39–60% of metals for the three sediments. Between 90 and 100% of Pb, Zn and Cd removed by the process came from the fractions bound to carbonates and from those bound to Fe and Mn oxides. The organic matter and sulfide bound fractions contained 65–72% of total Cu present before treatment and the process removed, on average, 63% Cu present in this fraction. In contrast, Ni and Cr were found mainly in the residual fractions (50–80%). Finally, this biological treatment did not solubilize Cr appreciably, while removal of Ni mostly originated from the carbonate and Fe/Mn oxides fractions (70–80%).

Trace metal partitioning in Fe–Mn nodules from Sicilian soils, Italy

Concentrations of 20 elements (Mn, Fe, Na, Mg, Al, K, Ca, V, Co, Ni, Cu, Zn, Rb, Sr, Cd, Cs, Ba, La, Ce, Pb) were determined in 18 Fe–Mn nodules from two alfisols, which are subject to periodic waterlogging. The nodules are significantly enriched in most trace metals relative to the host soil, with Mn, Co, Ce, Pb, Ba, Cd, Ni more enriched than Fe, V, La, Cu, Sr, Zn. Cesium and rubidium show poor or no enrichment in the nodules, consistent with their aluminosilicate affiliation. Scanning electron microscopy (SEM) examination and energy dispersive X-ray spectrometer (EDS) microprobe analysis have shown different microstructures (an undifferentiated fabric and a distinctive Fe–Mn banded structure) in the nodules from the two soils. A clearer partitioning of trace elements between Mn and Fe oxide phases is observed in the nodules showing the Fe–Mn banded structure, with Ba, Sr, Ni, Cu, and Cd correlated with Mn, V, and Pb with Fe. The nodules with undifferentiated fabric exhibit lower element/Mn molar ratios, which could reflect a minor adsorption of trace elements by MnO 2 in relation to a more rapid growth of the nodules. As shown by elemental associations, the Cd and Ce distribution appears to be closely linked to the redox cycling of Mn.

Magmatic-hydrothermal evolution in a fractionating granite: a microchemical study of the sn-w-f-mineralized mole granite (Australia)

A large granitic pluton associated with numerous hydrothermal ore deposits (the Mole Granite, northeastern New South Wales, Australia) was used for an integrated study of the chemical evolution of silicate melts and aqueous fluids during the late magmatic to early hydrothermal transition. Major and trace-element compositions were obtained by electron microprobe analysis (EPMA) and laser-ablation iductively coupled plasma mass-spectrometry microanalysis of fluid inclusions and crystallized melt inclusions in magmatic phenocrysts and minerals from miarolitic cavities. Together with fluid-compositional data from the ore veins, these data allowed reconstruction of the evolving silicate melts and therefrom exsolving single-phase (supercritical) or two-phase (brine + vapor) fluids, from the time of initial fluid saturation through to the final solidification of F-rich residual melts. The analytical data and a Rayleigh fractionation model combining experimental partitioning data with constraints from the natural system demonstrate that the phase state, the salinity, and the ore-metal contents of the exsolving fluids vary dramatically with increasing degree of crystallization. Fluid properties vary even without variation of externally imposed parameters such as pressure or temperature, mainly because of the progressive enrichment of F in the melt. Early-saturating fluids are Cl-rich and immediately separate into coexisting brine and vapor phase due to the low pressure of the system (≈1 kbar). Increasing F content of the melt reduces the partitioning of Cl to the fluid, such that later exsolving fluids are single-phase and have low salinity (at unchanged pressure conditions). Due to the contrasting complexation behavior of different ore metals, this evolution leads to a significant change in trace-metal partitioning as magma crystallization proceeds. The resulting variation in fluid compositions in turn controls the major variation in ore-metal ratios observed in the ore deposits (notably Sn/W in this case). This conclusion agrees with recent data from porphyry-style systems, and indicates more generally that the magmatic-to-hydrothermal transition probably exerts the dominant control on the metal content of high-temperature hydrothermal ore deposits.

Contrasting the geochemistry of suspended particulate matter and deposited sediments within an estuary

The geochemistry, as defined by amounts of easily reducible Mn (ERMn; Mn oxides), reducible Fe (RFe; Fe oxides), organic matter (% loss on ignition), total metal (Cu, Pb and Zn) and metals associated with the ERMn, RFe and organic matter components of deposited sediments (DS) and suspended particulate matter (SPM) were contrasted over a 1-year period (two-way ANOVA with sediment type and month as the two factors) within the Fraser River Estuary, BC, Canada. The geochemistry of SPM as compared to DS was distinctly different. The geochemistry of SPM displayed a marked seasonality. By contrast, seasonal differences in the geochemistry of DS were much less pronounced over the 12-month sampling period. Concentrations of organic matter and RFe in SPM were significantly greater (two-way ANOVA; P<0.05) in winter months (maximums of 23% and 53 g kg −1, respectively) as compared to the rest of the year (maximums of 9.3% and 11 g kg −1, respectively). Concentrations of organic matter in DS did not change over the 12-month period; however, RFe in DS was significantly greater in winter months (7.3 g kg −1) as compared to summer months (2.3 g kg −1). Easily reducible Mn in both SPM and DS was highly variable throughout the year with no apparent seasonal dependence. Total concentrations of Cu, Pb and Zn and their partitioning among the 3 sediment components (i.e. ERMn, RFe and organic matter) were also month-dependent (two-way ANOVA, P<0.05); metal concentrations in SPM were up to 17 times greater than DS with a higher proportion of these metals associated with the easily reducible component (oxides of Mn and amorphous forms of Fe oxides) during winter as compared to summer months. Trace metal concentrations and partitioning in DS showed the same seasonal trends, although not to the same degree as occurred for SPM, throughout the 4 seasons of study. Seasonal changes in the partitioning of metals in addition to greater proportions of the metal occurring in an easily reducible form in SPM relative to DS has potentially important implications for sediment ingesting organisms capable of filter-feeding on both SPM and DS. Specifically, metal bioavailability to sediment ingesting organisms from SPM may be seasonally dependent with periods of greatest exposure occurring during winter months, as compared to DS where no seasonal dependence occurs. To identify main vectors of metal exposure to sediment ingesting organisms, both the type of sediment and when they are feeding on the particular type of sediment need to be determined.

Comparison of the feasibility of three extraction procedures for trace metal partitioning in sediments from south-west Spain

The feasibility of three sequential extraction schemes (a modification of the Tessier procedure, the scheme proposed by Meguellati and the protocol designed by BCR (now called the Standards, Measurements and Testing Programme, M&T) have been compared to study the distribution of As, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb and Zn in sediment samples. The comparison has been performed by analyzing Certified Reference Material (CRM-601), a test material (S-12) and seven sediments from the Odiel Marshes Natural Park (located at the Atlantic coast of southern Spain). Samples were classified as sandy (with low iron oxide and organic matter contents) and clay–silty (with high iron oxide and organic matter contents) sediments. A higher metal mobility, especially under reducing conditions, was more properly assessed using the modified Tessier scheme compared to both the BCR and Meguellati procedures, these two later presenting comparative results for the reducible and residual phases. Significant Hg losses were found using the BCR procedure but the quantification of the acid phase for Cd, Cr and Ni was more reliable than that obtained with the modified Tessier and Meguellati schemes.

99/03330 Study on trace metal partitioning in pulverized combustion of bituminous coal and dry sewage sludge

99/03330 Study on trace metal partitioning in pulverized combustion of bituminous coal and dry sewage sludge

Trace metal distribution in different chemical fractions of marine sediments along the eastern Aegean shelf

The major objective of this study was to carry out sequential chemical extraction for the partitioning of particulate trace metals in sediment samples, collected along the eastern Aegean shelf during cruises July‐August 1994, in the framework of a National Marine Measurement and Monitoring Programme for the Aegean Sea. Five metals, Cd, Pb, Cu, Zn and Cr were examined in each of sediment samples. Three chemical fractions of the sediments were separated and concentrations of the trace metals were determined by AAS techniques. The three different leaches used were hydroxylamine hydrochloride‐acetic acid, hydrogen peroxide and nitric‐perchloric acids. Metals were concentrated mainly in the fraction extracted by nitric‐perchloric acids. Lead in the first fraction were found in the sediments of Northern part of Aegean, where the concentration of organic material was high. The total concentrations of Cd, Cu, Zn, Cr were higher in Izmir Bay than the other sampling points. The distribution of Pb concentrations was the highest in Edremit Bay and Izmir Bay.

The influence of size distribution on the particle concentration effect and trace metal partitioning in rivers

The particle concentration effect (p.c.e.) is an unexpected decline in partition coefficients (K d) as suspended particulate matter (SPM) increases. This anomaly has been attributed to a variety of causes, but most often to the existence of colloidal forms of the adsorbate, which are included, in error, in the dissolved fraction when calculating K d. To test this hypothesis we have directly measured colloidal, macroparticulate, and truly dissolved metals (Cd, Cu, Pb, Zn, Fe, Al, Mn, Ag) monthly for one year (6/96–7/97) in four Connecticut rivers having a range of ancillary biogeochemical characteristics. These include factors that are all likely to influence partitioning between dissolved and solid phases, such as DOC, pH, and competing cations. The p.c.e. is clearly evident in these rivers, and explicit consideration of colloidal metals eliminates or reduces this anomaly in nearly all cases. Furthermore, a substantial portion of metals occurs in the colloidal fraction, and the amount of colloidal metals increases with SPM. Both of these conditions are necessary for the colloidal model to explain the p.c.e.. Important differences are observed among rivers and metals, and in some cases systematic decreases in K d continue even when colloidal metals are taken into account. This additional decrease can be eliminated by excluding large particles having negligible surface complexation sites. When corrections are applied for both colloids and large particles, K d values become truly constant.

Trace metal levels and partitioning in Wisconsin rivers

Trace metal clean-techniques were applied in the determination of the levels and particle partitioning of Al, Cd, Cu, Pb, Zn in 14 rivers in Wisconsin. Nine headwater and five receiving water sites, representing both major river systems and diverse physiographic regions were sampled in the fall of 1991 and 1992, and spring of 1993. Mean filterable concentrations (range) of Cd 9.5 (4.6–26), Cu 620 (110–1800), Pb 76 (20–200), and Zn 460 (160–930) ng L-1 are comparable with recent data from oceanic, Great Lakes, and other river systems determined by researchers using modern ‘clean’ methods. Metal partition coefficients at each site generally followed the trend (pooled mean log Kd): Pb (5.84) > Zn (5.54) > Cd (4.92) > Cu (4.94). Order-of-magnitude differences in Kds were observed between sites, however, a large fraction of this variance could be explained by dissolved organic carbon (DOC) levels and degree of anthropogenic perturbation. Watershed yields of Cd, Pb, and Zn, under baseflow conditions were a very small fraction, typically 1–2%, of atmospheric loading. Copper yields represented a much higher fraction, particularly during spring high flow conditions. Filterable levels and yields of Al, Pb, and Zn are significantly higher in non-calcareous systems than in calcareous ones, which correlates with the higher levels of DOC in non-calcareous, forested systems.

Nearshore Versus Offshore Copper Loading in Lake Superior Sediments: Implications for Transport and Cycling

A thorough understanding of the fate and transport of metals in Lake Superior is necessary in order to predict the ability of Lake Superior to recover from anthropogenic perturbations (copper mining). Sediment cores were collected from nearshore and offshore sites in Lake Superior and used to evaluate spatial and temporal variations in copper loading associated with mining-related activities. Although both settings have been strongly affected by anthropogenic releases of copper, copper concentrations in nearshore cores are significantly greater than those found in offshore cores, implying that nearshore copper loading is dominated by simple deposition and burial of sediment generated from mining activities. Temporal variations in copper profiles in sediments from nearshore environments closelymimic copper production rates. Conversely, copper loading histories derived from offshore sediments are not well correlated to production rates. The offshore sediment cores, when compared with analogous cores from Lakes Ontario and Michigan, show that the average, lake-wide intensity of copper loading in Lake Superior is comparable to the other two lakes, despite the fact that Lake Superior has received the largest total burden of anthropogenic copper. Cu/Zn ratios, used to evaluate the amount of copper loading derived from mining discharges, vary strongly in nearshore environments in response to loading. Cu/Zn ratios in offshore sediments are much less variable, implying that copper loading may be regulated by additional mechanisms (solution chemistry and/or biologic uptake). Study of trace metal partitioning within Lake Superior sediments indicates that the organic fraction of the sediment contains the majority of the copper. Copper concentrations in offshore sediments are significantly correlated to organic carbon content of the sediment whereas copper concentrations in nearshore sediments are not. These findings support the model that transport and deposition of particles released from mining discharges dominate copper loading in nearshore sediments, whereas biologic uptake and settling of particulate organic matter may regulate copper loading in offshore sediments.

Development of soil metal criteria to preserve groundwater quality

The principal impediment in the remediation of contaminated sites and in the protection of groundwater quality is the lack of appropriate and reasonable standards for heavy metals in soils. There are no standards applicable to predict the potential for groundwater contamination by heavy metals in Taiwan. Lack of these soil standards may result in subjective judgment regarding the remediation needed. The migration of heavy metals through the unsaturated zone to groundwater is controlled by sorption to the soil, a highly pH-dependent process, and the hydrological regime. Soil sorption behavior is the criterion upon which to establish a standard based on a maximum permissible concentration in groundwater. The maximum level of metal in soil for which the equilibrium soluble metal does not exceed the Drinking Water Standard can be computed, at any pH, from the measured adsorption coefficient for any metal and soil. These metal criteria can be used as soil standards that will be protective of groundwater quality. Criteria for soil remediation are based on specific soil types and the effect of pH on metal sorption because the partitioning of trace metals is highly dependent on the solution pH and the chemical nature of the soil.

Study on trace metal partitioning in pulverized combustion of bituminous coal and dry sewage sludge

A study of the influence of co-firing of dry municipal sewage sludge on the behavior of the metals Cr, Hg, Mn, Ni, Pb, Zn during pulverized coal combustion is presented. Sewage sludge contains higher concentrations of the metals listed above than the reference coal, but a lower concentration of Cl, that enhances the volatility of many metals. Experiments were performed in a semi-industrial scale pulverized fuel combustion chamber (500 kW). Ash was collected at four locations: bottom hopper ( T=850 K), air preheater ( T=750 K), cyclone ( T=620 K), and bag filter ( T=480 K). From the bottom hopper to the filter, the particle size decreased and ash particles were progressively enriched in volatile elements. Mass balances of the metals were performed and the enrichment trends on the ash collected at the different locations were calculated. Increasing the sewage sludge share in the blend caused a significant increase in the recovery rate in the solid phase. In spite of that, the calculated concentrations in the flue gas of Hg and Zn increased. Sewage sludge co-firing influences the combustion process and the post-combustion environment in many ways. This study focuses on the effect of the different flue gas composition on the condensation temperature of metal species. The system was modeled by assuming thermodynamic equilibrium. The results indicated that the increasing recovery of Zn might be caused by enhanced condensation and the increasing recovery of Hg by adsorption on ash particles. The increasing recovery of the other metals seemed referable to failure in vaporization and it cannot be studied with an equilibrium approach.

Geochemistry of rare elements in waters and sediments of alkaline lakes in the Sasykkul depression, East Pamirs

The saline lakes (Tuzkul, Chukurkul, Sasykkul Lakes) of the Sasykkul depression located in the semidesert part of the Pamirs provide a prominent example of the evaporative concentration of alkaline waters in a closed basin under arid climate conditions. Chemical evolution of the lake waters has resulted in the development of residual Na–Cl–CO 3–SO 4 and Na–Cl–CO 3 brines. The contents of a number of rare elements were determined in waters and sediments of the Sasykkul depression lakes. Speciation modelling suggests that the main aqueous species of Ag are chloride complexes, Cu, Pb, Zn, Mn are carbonate complexes, Be, Bi, Nb are hydroxocomplexes, Mo, W, As, V are oxyanions. It was established that the salt lake sediments are significantly enriched in B, Ba, Mo, W, U, Th. High contents of trace elements are considered to be due to chemical weathering of rocks within the catchment basin, significant contribution from thermal springs derived from the residual fluids associated with acid igneous and volcanic rocks, and following evapoconcentration in a closed basin. The processes of evaporative concentration, solution complexation, chemical precipitation, and water-sediment interaction lead to the partitioning of trace metals in the salt sediments.