Variations In Metal Concentrations Research Articles

Heavy Metal Distribution in Open Canals and Drains in the Upper Rio Grande Basin

The inclusion of reclaimed effluents for irrigated agriculture may allow communities along the U.S.-Mexico border to use water resources more efficiently and reduce urban costs of wastewater treatment. However, metal inflow from industry and urbanization may threaten food safety. This study examines metal concentrations in sediments from open canal systems charged with flow from the Rio Grande and from effluents discharged from border communities. At the surface of canal beds, sediments were collected from six canal segments that began at the fringe of the El Paso/Juarez metroplex to rural areas downstream, and ranged from 9 to 24 km in length. Sediments were analyzed for Cd, Co, Cr, Cu, Ni, Pb, and Zn. These metals rarely exceeded 20 mg kg−1. Drainage and effluent conveyance increased the variability of metal concentrations in sediments. Geostatistical models did not significantly account for spatial variability of metals, except in Mexico. This may implicate multiple rather than single inflow sources of metals. Peaks in metal concentrations often coincided with growing rural communities. However, most metal concentrations were within conventional global ranges and were not at levels high enough to threaten food safety. Future sampling strategies will require reduced sampling intervals from 1 to <0.13 km.

Natural variation of copper, zinc, cadmium and selenium concentrations in Bembicium nanum and their potential use as a biomonitor of trace metals

Copper, zinc, cadmium and selenium were measured in the gastropod mollusc Bembicium nanum at two uncontaminated locations, Jervis Bay and Rosedale, NSW, to determine natural variability of metals associated with gender, mass, shore position and temporal variability. Trace metals were also measured in B. nanum at three industrialised locations to determine the accumulation of trace metals in contaminated environments. Copper, zinc, cadmium and selenium concentrations were not significantly different between male and female B. nanum. No significant relationships were found between zinc, cadmium and selenium concentrations and mass. There was a significant relationship between copper concentration and mass but only 19% of the variation was explained by mass. Generally inherent variability within samples had a greater influence than gender or variations in mass on trace metal concentrations. No trend was found in cadmium and selenium concentrations with variation in shoreline position. Copper and zinc concentrations increased further away from the low tide mark, with a decrease in metal concentrations at the furthest site from the water. Variability in metal concentrations is attributable to variations in food source, food availability and different immersion times. Copper, zinc, cadmium and selenium concentrations varied over a 12-month period. Copper, cadmium and selenium were taken up and lost over time, as metal body burden followed the same trend as metal concentrations. Zinc concentrations were influenced by mass. Copper and cadmium concentrations fluctuated throughout the 12-month period but with no clear seasonal trends. Selenium concentrations peaked in spring (October), with concentrations remaining uniform over the other months. These differences in mean concentrations between months were most likely due to inherent trace metal variability associated with differences in food availability and changes in metabolic rates associated with changes in temperature during the study period. Measurement of trace metals in B. nanum at contaminated sites showed that B. nanum accumulates metals in response to contamination. B. nanum meets most of the requirements to be a biomonitor of trace metal contamination as they are abundant, sedentary, easy to identify, provide sufficient tissue for analysis, tolerate high concentrations of pollutants and they accumulate trace metals in response to contamination. However, as trace metal concentration can vary with mass, shoreline position and temporally, care must be taken to collect individual organisms with similar mass from similar shoreline positions and times.

Hydrological and geochemical controls governing the distribution of trace metals in a mine-impacted lake

Factors controlling the distribution of mining-derived Cu, Pb and Zn in the waters and bottom sediments of a large Andean lake (Lago Junin, Peru) have been assessed based on sample collections in May/June 1997 (dry season) and February/March 1998 (wet season). Relatively low levels of trace metals detected in surface waters of the lake during the dry season contrasted greatly with the high values observed during the wet period. Dry season concentrations of total Zn, Cu and Pb in the central lake basin averaged 41, 4.4 and 0.24 µg/L, respectively. In contrast, the respective wet season concentrations of total Zn, Cu and Pb in areas of the main basin ranged up to 387, 52 and 40 µg/L. The seasonal variability in metal concentrations largely reflects an increase in the concentration of particulate metal phases during the wet season. Such observations can be attributed to changes in sediment loadings associated with mining-derived river inputs and changes in lake circulation resulting from hydroelectric dam operations. Surface sediments are characterized by lake-wide enrichments of Zn, Cu and Pb, with maximum concentrations reaching as high as 5, 0.25 and 0.7 wt%, respectively. Estimated rates of authigenic metal accumulation are not sufficient to account for the elevated metal concentrations in the main basin of the lake, indicating that metal distributions are governed by the accumulation of metal-rich particulates. Variations in the spatial distributions of Zn, Cu and Pb are suggested to be a function of varying host phases and textural sorting.

Stainless steel flow reactor for supercritical water oxidation: corrosion tests

One of the obstacles that is inhibiting the development of supercritical water oxidation (SCWO) into a viable industrial process, is the problem of corrosion. A bench scale stainless steel flow reactor for supercritical water oxidation studies was constructed. Corrosion of the reactor was studied under pressure of 400 bars and at temperatures of 250, 375 and 420 °C. The concentrations of various metals in the effluent were monitored by flame atomic absorption spectrometry. Higher corrosion rates were observed at 375 °C, or near the critical temperature. Addition of hydrogen peroxide also significantly increases the corrosion of stainless steel. Exposure of the reactor to open air between experiments is also found to be a contributing factor to the corrosion of SCWO experiment.

Generation of metal-rich felsic magmas during crustal anatexis

We show that partial melting of a preexisting mineral deposit during regional anatexis is likely to lead to incorporation of sulfide melt into silicate melt. Simple dissolution of metals in silicate melt during anatexis leads to minor metal addition to escaping magma, but physical entrainment of sulfide melt can lead to extreme enrichment and higher total metal incorporation. Metal enrichment is enhanced if melt segregation is structurally driven; only dissolved metal is incorporated if initial segregation is driven by buoyancy alone. However, once encapsulated within a larger volume of silicate melt, immiscible globules of sulfide melt are physically carried by buoyantly rising magma. Gradual dissolution of entrained sulfide melt globules is expected as the silicate magma migrates from the lower crust. This process may lead to significant variations in metal contents of silicate magmas above regions that underwent anatexis.

Metal concentrations in deciduous tree leaves from urban areas in Poland.

Accumulation of metals in deciduous tree foliage from urban areas in western-south Poland was monitored during the vegetation season of 2000 year. Concentrations of Al, Ba, Ca, Cd, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Sr, Ti and Zn were measured in birch, willow, linden and maple leaves using the ICP-AES method. Seasonal variations of metal concentrations and their relations with sampling site were investigated. The most dynamic accumulation of Al, Cd, Cr, Ni and Pb was observed for examined species. The highest differences in element concentrations for investigated sites were found for Ba, Cd, Mn and Ni. Interelement correlations were investigated. In all foliar samples synergistic relationships between Al-Cr and Ca-Sr were found. Statistically significant negative correlations were observed only for Cd and Ti in birch leaves.

Uptake of Metals by Plants Sharing a Rhizosphere with the Hyperaccumulator Thlaspi caerulescens

ABSTRACT The hyperaccumulator Thlaspi caerulescens was grown with Hordeum vulgare and Lepidium heterophyllum in a split pot experiment to examine the effect of rhizosphere interactions on metal uptake. The objective was to assess the viability of such intercropping as either (1) a system of ‘phytoprotection’ for nonaccumulating plants or (2) a means of enhancing phytoextraction with large-biomass crops through increased metal mobilization within the shared rhizosphere. The plants were separated by (1) an impermeable barrier, (2) a permeable root barrier, or (3) no physical barrier to allow different degrees of root interaction. Studies of rhizosphere effects using split pot experiments are subject to considerable uncertainty by the need to relate test results to appropriate control plants. This was resolved by comparing plant metal concentrations to ‘equivalent’ control plants, with the same yield, based on the observed variation in metal concentration with yield under similar growing conditions. Cadmium concentration in H. vulgare was increased by a factor of 2.4 when it was grown alongside T. caerulescens without a barrier. In contrast, the uptake of zinc by H. vulgare was significantly decreased, probably through metal depletion within the zone of the Zn-hyperaccumulator's rhizosphere. T. caerulescens also apparently increased the concentration of Cd in H. vulgare by a factor of 1.4 when the roots of the two plants were separated by a permeable barrier that allowed movement of soil solution but prevented physical mixing of roots. The concentrations of all the metals studied (Cd, Zn, Cu, Pb, Ni) were greater in T. caerulescens when the hyperaccumulator was grown alongside either L. heterophyllum or H. vulgare without a root barrier — probably through successful exploitation of a greater volume of soil. However, this effect was not seen in the presence of a partial barrier, except in the case of Cu when T. caerulescens was grown alongside H. vulgare. These results suggest that T. caerulescens may alter conditions in shared rhizospheres and thereby affect the availability of selected metals to neighboring plants. Thus, it is possible that under-sowing some plants with small hyperaccumulators may potentially offer an alternative form of management for marginally contaminated soils. There was limited evidence of an intercropped hyperaccumulator mobilizing selected metals and restricting the availability of others. However, changes in uptake of selected metals by the larger plant may be quite small compared with the requirements of crop protection or the short-term requirements of many land remediation programs.

Removal of Toxic Metals from Leachates from Hazardous Solid Wastes and Reduction of Toxicity to Microtox by the Use of Calcium Alginate Beads Containing Humic Acid

Improper disposal of hazardous wastes can lead to release of potentially harmful substances through leaching such as heavy metals, which ultimately contaminate soil, sediment surface water, and groundwater through runoff. To remove these toxic metals and avoid any adverse effect on the ecosystem, a novel approach involving calcium alginate (CA) beads containing humic acid (HA) was used. For this, 10% leachates of the waste obtained from two major industrial units with electroplating processess were prepared at neutral pH and analyzed by atomic absorption spectrophotometry (AAS). Both leachates contained Cd, Cu, Cr, Ni, Mn, Fe, and Zn. The concentrations of Ni, Mn, Fe, and Zn in the waste were found to be significant. The leachates analyzed were passed through columns packed with calcium alginate beads with or without humic acid. The concentrations of various metals in beads and in different fractions collected after adsorption were measured. Data recorded indicate that calcium alginate beads containing humic acids are more efficient in removal of all metals in substantial amounts from the two leachates. Along with removal of metals, this process led to considerable detoxification of the leachates as tested by Microtox assay, indicated by earlier protection and higher EC50. The significance of the results in relation to removal of toxic metals by beads containing humic acid is discussed.

Metal accumulation in aquatic macrophytes from southeast Queensland, Australia.

To determine the extent of metal accumulation in some aquatic macrophytes from contaminated urban streams in southeast Queensland, plants were sampled from six sites, along with contiguous sediments. In all, 15 different species were collected, the most common genera being Typha (Cattails or Bulrushes) and Persicaria (Knotweeds). Before heavy metal analysis, plants were further separated into various morphological tissues, and five selected samples were separated into various physiological tissues. The cadmium, copper, lead and zinc content of the plants were analysed using flames AAS. In general, plant roots exhibited higher metal concentrations than the contiguous sediments. Of the metals of interest, only for zinc was there a relatively clear pattern of increasing accumulation in aquatic macrophytes with increasing sediment metal concentrations. Comparison between morphological tissues of the sampled plants found that roots consistently presented higher metal concentrations than either the stems or leaves, however unlike previous studies, this investigation revealed no consistent trend of stems accumulating more metals than the leaves. For Typha spp., metal concentrations followed the order of roots > rhizomes > leaves, while for Persicaria spp. the order was roots > leaves > stems. The submerged species Myriophyllum aquaticum accumulated the highest levels of metals overall (e.g. Zn 4300 micrograms g-1 dry weight and Cd 6.5 micrograms g-1), and the emergent macrophytes also exhibited relatively high metal contents in their roots. The leaves of the submerged and floating-leafed species collected contained relatively high quantities of the four metals of interest, compared with the leaves of emergent aquatic macrophytes. In the Typha rhizome and Persicaria stem samples analysed for internal variation in metal content, there was a pattern of increasing metal concentrations towards the external sections of the stem, both for subterranean stems (rhizomes) and above-substrate stems. For Persicaria stems, no clear pattern was observed for cadmium and lead, the two metals investigated that are not required by plants for survival.

Mushrooms from two metal-contaminated areas in Norway: occurrence of metals and metallothionein-like proteins

This study tested the hypothesis that concentrations of metallothionein-like (MT-like) proteins in fruiting bodies of wild-growing macrofungi reflect exposure to the metals Cd, Cu and Zn. Screening for these proteins was done by taking 44 samples of seven species of macrofungi from two metal-polluted areas in Norway, namely Odda and Sulitjelma. Concentrations of Cd, Cu and Zn were measured in fruiting bodies and topsoil, the highest of which were observed in fruiting bodies – 126 μg g −1 for Cd, 427 μg g −1 for Cu and 396 μg g −1 for Zn. A large intra- and inter-specific heterogeneity in metal uptake was displayed between fruiting bodies from the same soils. Cd,Zn–MT-like proteins were detected in all samples, except one stipe of Boletus edulis , whereas only 72% of the samples contained detectable levels of Cu–MT-like proteins. However, concentrations of MT-like proteins did not reflect variations in metal concentrations. Low content of cysteine in Cd-binding protein fractions from Amanita muscaria collected in Odda indicates that no proteins of the metallothionein family were present in this species. Onthe contrary, these protein fractions share several characteristics with cadmium–mycophosphatins.

Should foliar cadmium concentrations be expressed on a dry weight or dry ash weight basis?

Foliar analysis is a valuable tool for evaluating the pollution status of forests. However, the use of foliar diagnosis in large-scale surveys is a complicated process owing to the high variability within the crown. The method used to express foliar concentrations has often been found to diminish the variability. The effect of the method used to express element concentrations on the spatial variability of cadmium (Cd) in the leaves of crack willow (Salix fragilis L.) was investigated by sampling the leaves of one willow at 292 locations in the crown, each sampling location having a volume of 0.027 m3 (0.3 m x 0.3 m x 0.3 m). Cadmium showed a distinct spatial trend in the crown of the tree. Concentrations as low as 2.4 mg kg(-1) dry weight (DW) or 23.1 mg kg(-1) dry ash weight (DAW) were obtained in the top of the crown, and 10.6 mg kg(-1) DW or 73.0 mg kg(-1) DAW in the bottom of the crown. The lower relative standard deviation and weaker correlation with the sampling height support the use of DAW in large-scale surveys especially. The lower variability of the DAW Cd concentration makes this variable less sensitive to fluctuations caused by differences in growing conditions and sampling methodology. However, the majority of publications in this field report metal concentrations on a DW basis. Therefore, the restrictions set on the use of results expressed on a DAW basis in large-scale surveys of foliar metal concentrations have to be offset against the advantages offered by a reduction of the variability in metal concentrations.

The effect of body size on metal accumulations in the bivalve Laternula elliptica

Variations of metal concentrations with body size were investigated in kidney, digestive gland and gill of the Antarctic clam, Laternula elliptica, collected from a near-shore habitat at King George Island. Positive relationships for metal concentrations with body size were common among the three organs for most of the metals, while an inverse relationship was found only in the digestive gland for Cu, Zn and Mn. In the gill, concentrations of eight out of the ten metals increased linearly with body size, whilst in the kidney concentrations of Cd, Zn, Pb, Co and Ni were best fitted by quadratic regression curves, viz. increasing continuously until reaching a peak at around an 80 mm shell length. This may reflect specific regulatory activities for the extremely high accumulation of these metals in the kidney, particularly Cd (28–354 μg g−1 tissue dry weight). The overall prevalence of positive relationships indicate net accumulation of these metals throughout life, which may be at least in part associated with the slow growth and long life span of this cold-water bivalve species. The study demonstrates distinct body size-metal concentration relationships in the three organs of L. elliptica, and suggests they may be useful as biomonitors for assessing changes in metal concentrations in Antarctic waters.

Synchrotron x‐ray fluorescence and secondary ion mass spectrometry in tree ring microanalysis: applications to dendroanalysis

AbstractMining operations in the Sudbury district of northern Ontario have resulted in environmental damage caused by acid rain and heavy metal pollution. Remedial liming (Ca/MgCO3) has been used in an attempt to restore the pH of the lake water and soil to natural levels. The spatial and temporal variation of metal concentrations in the annual growth rings of trees may be a useful indicator of the effects of the pollutants and the liming operation. We used synchrotron radiation‐induced x‐ray emission (SRIXE) and secondary ion mass spectrometry (SIMS) to examine the distribution of selected metals in the annual growth rings of red pine (Pinus resinosa) from an area damaged by acid rain and heavy metal pollution which had been subjected to remedial liming (Ca/MgCO3). The results show a non‐uniform distribution of metals in the stemwood, including seasonal variations and changes in the Ca/Mn ratio consistent with the increased soil pH following liming. Copyright © 2001 John Wiley &amp; Sons, Ltd.

Towards the characterisation of heavy metals in dredged canal sediments and an appreciation of ‘availability’: two examples from the UK

Canal sediments can act as sinks for a wide range of contaminants including heavy metals from various sources (e.g. industrial and waste water discharges). Dredging of canals is required to maintain navigational depth and prevent flooding. The sediments removed from canals are often disposed of to land, being deposited either straight on to the banks of the canal or, in recent years, in licensed disposal sites. The aim of this work was to investigate the nature of dredged sediment-derived soils and the heavy metals present in them. Two disposal sites in the United Kingdom (UK) were investigated and soil samples taken. A variety of analytical techniques were used, including Aqua regia digestion and sequential extraction, in order to assess the concentrations and associations of metals present. Diethylene triaminepenta-acetic acid extracts, performed to illustrate plant-available metal concentrations, reveal that up to 40% of the total extracted metals were in an ‘available’ form. Variations in metal concentrations with depth in the soil cores show a significant correlation with total organic carbon content.

The interpretation of background variation in regional geochemical surveys – an example from Nunavut, Canada

In glaciated terrains, geochemical maps portray bedrock provenance and the integrated effects of glacial processes affecting the distribution, concentration, and partitioning of minerals in sediments. In those maps, indicators of economic mineralization can be difficult to distinguish in the context of natural background, especially at low trace metal concentrations. Sample mineralogy, which can be inferred from lithophile elements, provides a key basis for interpreting sediment provenance and controls on background variation in metal concentrations. In non-carbonate terrain, the principal rock-forming minerals digested by aqua regia are Mg-bearing phyllosilicates, including trioctohedral chlorite, biotite, and phlogopite. Hence, Mg analyses directly reflect the concentrations of those minerals. In a regional geochemical survey of till in Nunavut, strong linear correlations ( r &gt;0.840, n =1842, p &lt;0.0001) for Cu and Cr with Mg concentrations indicate Mg-bearing phyllosilicates are the principal metal hosts, and that the metals are bound in mineral lattice structures in direct proportion to Mg. Thus, metal:Mg ratios express geochemical properties of the mineral(s) hosting the metal, and are independent of mineral partitioning among size fractions that results from either glacial or postglacial processes. Ratio maps can be used to establish till provenance and infer aspects of bedrock composition not evident in single-element geochemical maps. Ratio anomalies could indicate metals derived from economic indicators such as sulphide minerals, and metal-rich particulate from anthropogenic sources .

Short-term effects of alkaline biosolids on pH and trace metals in oligotrophic forest peat and on growth of Picea sitchensis

A field experiment was conducted in a 13‐year‐old Sitka spruce ( Picea sitchensis (Bong.) Carr.) plantation on shallow oligotrophic peat to investigate short‐term changes in soil pH and trace metal concentrations and in tree growth responses to applications of rural and urban alkaline biosolids. There were five treatments: (1) control (no amendment); (2)–(4) rural biosolids at application rates of 20, 40 and 60 t fresh material (FM) ha −1 ; and (5) urban biosolids applied at one rate (40 t ha −1 ) only. The biosolids were spread by hand on the ground surface of each plot on 12 March 1992. Peat and foliar samples were collected in February each year from 1993 to 1995. Annual tree height was also measured. The results show that alkaline biosolid‐derived Cu, Zn, Ni, Cd, Pb and Cr accumulated in the litter layer. The magnitude of surface soil metal enrichment was related to sludge type and application rate. There was spatial and temporal variation in metal concentrations, probably due to uneven distribution of the sludge biosolids and the uneven depth of the litter layer on the forest floor. Rural biosolids markedly increased the dilute acetic acid extractable Zn while urban biosolids greatly elevated extractable Cu in the litter layer, reflecting the different metal loadings in the two sources of sewage sludge. Alkaline biosolids raised the pH of the litter layer, and of the top 5 cm (and occasionally the top 10 cm) of the underlying peat profile and elicited tree growth responses. Small amounts of heavy metals such as Cu and Zn may have leached down the soil profile. Heavy metals that have accumulated in the litter layer may represent a potential pool for long‐term leaching as litter decomposition and acidification proceed. Long‐term monitoring would therefore be required to determine the full environmental impact following application of alkaline biosolids to spruce forests on oligotrophic peat.

Regional Variability of Cd, Hg, Pb and C Concentrations in Different Horizons of Swedish Forest Soils

Contents of cadmium (Cd), mercury (Hg), lead (Pb) and carbon(C) in the O, B and C horizons of podzolized forest soils inSweden were surveyed. Concentrations and storage of Cd, Hg andPb in the O and B horizons were high in southern Sweden and gradually decreased towards the north, though with considerablelocal variability. This pattern reflects the influence of anthropogenic emissions of these metals, as well as the effectsof soil-forming processes. Parent till material, as representedby the C horizon concentration of the respective metal, accountedfor little of the variation in metal concentration in the O horizon. For Cd and Pb, the correlations were not significant orslightly negative (R2 = 0.12 and 0.09 respectively) depending on region, while for Hg the correlation was not significant or slightly positive (R2 = 0.03 and 0.08). Furthermore, parent till material accounted for more of the variation in metal concentrations in the B horizons in the northern part of Sweden than in the middle and southernmost parts, where the concentration of total carbon had more influence. The correlation between the metal concentrationsin the B and C horizon was strongest for Pb (R2 = 0.63 and 0.36 in the two northernmost regions), lower for Cd (R2 = 0.19 and 0.16) and not significant for Hg. For allsoil horizons, total C concentration accounted for much of thevariation in Hg concentration in particular (O-horizon R2 = 0.15–0.69, B horizon R2 = 0.36–0.50, C horizon R2 = 0.23–0.50 and ns in one region). Ratios of metal concentrations between the B and C horizons were highest for Hg(maximum value of 30), indicating a relatively larger addition or retention of Hg compared to Cd and Pb (maximum value of 10)in the B horizon. This study indicate that factors other than parent material account for the large scale variation in O horizon concentrationsof metals but patterns correspond well with those of atmosphericdeposition of heavy metals and acidifying substances. Furthermore, the study highlights the importance of soil organicmatter and the intensity of pedogenic processes for the content and distribution of metals throughout the soil horizons.

Trace metal loss following whole-tree harvest of a northeastern deciduous forest, U.S.A.

We examined changes in the biogeochemistry of trace metals following a commercial whole-tree harvest (WTH) at the Hubbard Brook Experimental Forest in New Hampshire. Within 6 months after completion of the WTH, maximum streamwater concentrations of Ni, Cd, Ba, Sr, Mn, Zn and Fe increased two- to nine-fold. Streamwater concentration of Cu remained unchanged after harvest. Streamwater pH decreased from 5.2 to 4.5 after the harvest, and correlated strongly with trace metal concentrations except for Fe. The decrease in pH apparently resulted from increased nitrogen mineralization and nitrification following harvest. All streamwater metal concentrations (except Mn and Fe) in the disturbed watershed increased prior to the decrease in streamwater pH, suggesting that the loss of readily exchangeable metals, not increased mineral dissolution, was responsible for the initial increase in streamwater trace metal concentrations. In contrast, streamwater Mn concentrations did not increase until streamwater pH dropped to 4.5, due in part to increased mineral dissolution. Although pH related strongly to trace metal concentrations in the harvested watershed, it did not account for much of the variation in metal concentrations in the reference (W6) watershed. Annual flux of trace metals increased two- to eight-fold following WTH. Annual losses of Mn and Sr were 14% and 12%respectively of the forest floor pool for each element, and less than 10% of forest floor pools for all other elements. Except for Cd and Cu, annual trace metal losses in streamwater exceeded annual inputs in bulk precipitation.

Development of cermet microstructures during sintering

Six Ti(C,N)-TiN-WC-Co cermet materials originating from the same powder mixture but sintered to different stages of the sintering cycle have been studied using scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray analysis (EDX), electron energy-loss spectroscopy (EELS), and energy-filtered transmission electron microscopy (EFTEM). At 1350 °C, the binder phase exists both as solid and as liquid phase. The cobalt is nanocrystalline before melting, probably due to deformation during milling. A tungsten-rich inner rim starts to form and is very inhomogeneously distributed on the Ti(C,N) cores, indicating that it is difficult to nucleate the inner rim. The outer rim mainly forms at the sintering temperature and accounts for grain growth during the holding time. There are no major variations in metal content of the carbonitride phases in the materials sintered to 1350 °C or higher, although the N/(C+N) atomic ratio changes somewhat. Close to the core-rim boundary of the materials sintered at 1430 °C, there is often an enrichment of nitrogen in the core that is believed to be the result of nitrogen diffusion from the tungsten-rich rim to the titanium-rich core during cooling.

Spatial Distribution of Total Cadmium, Copper, and Zinc in the Zebra Mussel ( Dreissena polymorpha) Along the Upper St. Lawrence River

The zebra mussel ( Dreissena polymorpha) was utilized to assess the spatial distribution of three trace metals, cadmium, copper, and zinc, in the upper St. Lawrence River and to test the hypothesis that outflow from Lake Ontario influenced levels of these metals in near-shore biota. Zebra mussels, collected from twelve sites along the southern shore, were analyzed for total cadmium, copper, and zinc in their soft tissues. Total cadmium and copper concentrations were elevated at all sites compared to relatively uncontaminated waters and were highest at sites near the outflow of Lake Ontario and an industrial area farthest downstream. Total zinc concentrations approached levels found at uncontaminated sites. Concentrations were rarely related to animal size at any site. However, body burdens (metal content per individual) showed strong positive relationships with size. To facilitate comparisons among sites, body burdens were calculated for standard length (2.0 cm) mussels. Highest body burdens occurred at the outflow of the lake and at one relatively uncontaminated site downstream. Lowest body burdens occurred at sites in the industrial area, although concentrations in the tissues were high. Expected total cadmium concentrations in tissues were estimated using a bio-energetic based kinetic model. Observed cadmium concentrations were lower than predicted, suggesting that near-shore areas may comprise significant depositional areas subject to enrichment with contaminants carried in the outflow from Lake Ontario. Long-term studies of inter-annual variability in metal concentrations, metal burdens, and growth rates should enhance the usefulness of D. polymorpha as a biomonitor and help in understanding the fate of trace metals in the upper St. Lawrence River.