Trace Metal Chemistry Research Articles

Effects of acidification on minor and trace metal chemistry in little rock lake, wisconsin

Little Rock Lake is a low-alkalinity (25 μeq/L, pH 6.1) seepage lake in north-central Wisconsin. The two main basins of the lake were separated by a polyvinyl barrier in 1984, and acidification of the north basin with H2SO4 began in spring 1985; the south basin is being maintained as a reference. The effects of acidification on dissolved concentrations of Al, Fe, Mn, Cd, Cu, Ni, Pb and Zn have been studied at three scales at Little Rock Lake: (A) laboratory-scale experiments with well-mixed sediments; (b) large (4- to 5-m dia) in situ enclosures maintained at pH 4.5 to 6.0; and (c) the lake itself. In general, qualitative agreement is good between the three approaches, but some differences have been observed, especially for Al and Fe. The most significant trace metal response observed in acidifying the north basin from pH 6.1 to 5.1 has been a large increase in dissolved Mn, apparently as a result of hindered oxidation of Mn2+ at lower pH. Dissolved Al and Fe also increased at pH 5.1 but not at 5.6. Water column levels of Cd, Cu, Pb and Zn have not increased at pH 5.1 in the lake, but results of lab and enclosure studies suggest that increased concentrations of Cd and Zn will occur when the lake is acidified to pH 4.6. Sediment cores and surface sediments from both basins of the lake have been collected and analyzed for Al, Fe, Mn, Cd, Cu, Hg, Ni, Pb and Zn. Similar concentrations of most metals were found in surface sediments from both basins of the lake. Near-surface sediments were enriched in Hg and Pb relative to deeper sediment layers; the enrichment is presumed to be caused by increased atmospheric inputs during the past century, not diagenetic activity. No consistent differences in the Hg content of zooplankton, periphyton and benthic invertebrates were found at pH 5.6 and 5.1 in the acidified basin compared with the pH 6.1 reference basin.

The impact of atmospheric aerosols on trace metal chemistry in open ocean surface seawater: 3. Lead

Atmospheric aerosols collected at Enewetak Atoll in the tropical North Pacific were exposed to seawater in laboratory experiments to assess the impact of atmospheric aerosols on lead chemistry in surface seawater. The net atmospheric flux of soluble lead to the ocean is between 16 and 32 pmol cm−2 yr−1 at Enewetak. The stable lead isotopic composition of soluble aerosol lead indicates that it is of anthropogenic origin. Anthropogenic aerosol lead from Central and North America appears to be less soluble and/or to dissolve less rapidly than that from Asia. Dissolved organic matter and possibly lower pH appear to increase the nonaluminosilicate aerosol lead solubility and/or dissolution rate. The isotopic composition of lead in air, seawater and dry deposition suggests that after deposition in the ocean, nonaluminosilicate paniculate lead can be reinjected into the atmosphere during sea salt aerosol production.

Short-Term Changes in the Chemistry of Trace Metals Following Calcium Carbonate Treatment of Acidic Lakes

Marked changes were evident in the concentrations of trace metals (aluminum, manganese, and zinc) following base application to two acidic lakes in the Adirondack region of New York. Immediately after calcite treatment, epilimnitic pH values increased above 9.0. This response coincided with a shift in the speciation of aluminum from acid-soluble to labile (inorganic) monomeric forms. Following the manipulation, pH values decreased below 8.0 as the epilimnion equilibrated with atmospheric CO2. Within 1–2 mo, aluminum, manganese, and zinc concentrations were greatly reduced, typically by an order of magnitude. The mechanism(s) for immobilization of trace metals following base treatment is not entirely clear. However, chemical equilibrium calculations suggest that at the higher pH resulting from base addition, lake water was oversaturated with readily forming aluminum and manganese minerals. Therefore, removal of these metals from the water column may have been due to direct precipitation. Solutions were highly undersaturated with zinc minerals, so zinc retention probably occurred by adsorption or coprecipitation reactions. Acidic Adirondack Lakes are generally net sinks for aluminum, and conservative with respect to transport of manganese and zinc. Base addition greatly enhanced retention of all three metals.

Some atomic-absorption spectrometric applications to clinical-biomedical trace-metal analyses

Following the introduction of atomic absorption spectrometric (AAS) instrumentation about 30 years ago, many specific and sensitive methods for determining trace metal concentrations in biological materials were developed. Yesterday's rare and esoteric investigations are today's routine clinical analyses. Levels of essential and toxic metals can be determined with relative ease for diagnostic purposes and following response to treatment. There is greater understanding of the chemistry and biochemistry of trace metals in health and disease as a consequence.

The impact of atmospheric aerosols on trace metal chemistry in open ocean surface seawater, 1. Aluminum

Significant quantities of aerosol aluminum are transported from continental regions through the atmosphere to the oceans. Enrichments in the concentration of dissolved aluminum in open ocean surface seawater suggest that dissolution of aerosol aluminum is an important source of dissolved aluminum to these waters. Atmospheric aerosols collected at Enewetak Atoll were exposed to seawater and artificial rain water to determine directly the importance of atmospheric deposition as a source of marine dissolved aluminum. The results of these experiments indicate that ∼ 8–10% of the aluminum in atmospheric aerosols of crustal origin over the North Pacific is soluble in seawater. Approximately 5–6% dissolves very rapidly ( < 0.6 hr). An additional 3–4% dissolves within 60 hr. This bimodal dissolution of aerosol aluminum of crustal origin suggests that this aluminum is present in two forms. The rapidly dissolving fraction is likely aluminum already weathered from primary minerals, while the more slowly dissolving fraction is probably aluminum from the aluminosilicate matrix. Nearly the same amount of aerosol aluminum dissolved in artificial rain water ( pH= 5.5) in 6 hr as dissolved in seawater ( pH= 8) in 60 hr. The lower pH appears to not only increase the dissolution rate but may also increase the quantity of aerosol aluminum that dissolves. Dissolved organic matter in seawater appears to have relatively little effect on aerosol aluminum dissolution. Considering measured total aerosol aluminum fluxes, aluminum dissolution of 5–10% would constitute the major source for dissolved aluminum in surface waters of the open North Pacific. The calculated residence time of dissolved aluminum in the upper 100 m of the tropical North Pacific ranges from 2 to 6 years.

Atmospheric trace elements at Enewetak Atoll: 2. Transport to the ocean by wet and dry deposition

The concentrations of trace elements in precipitation and dry deposition are presented for samples collected at Enewetak Atoll (11°N, 162° E) during SEAREX experiments in 1979. The concentrations of Al, Sc, Mn, Fe, Co, and Th in rain are dominated by crustal material, and for these elements, wet deposition evidently exceeds dry deposition. For most of these elements the present rates of atmospheric deposition at Enewetak are similar to their mean rate of accumulation in sediments over the past 5–10,000 years, suggesting that the air‐to‐sea exchange of particles is closely tied to the sedimentary cycle of the mid‐Pacific. Noncrustal sources govern the concentrations of Pb, Zn, Cu, Se, and Cd in wet and dry deposition samples. Analyses of dry deposition collected from a flat plastic plate indicate that the amount of material recycled from the sea surface varies markedly between samples, and even though these estimates do not necessarily reflect the dry deposition to the ocean surface, the results suggest that recycled sea spray often amounts to more than 50% of the total dry deposition of the enriched elements. Recycled sea spray also makes up a significant fraction of the total wet deposition of the enriched elements. The net deposition rates of elements such as Cu and Zn are greater than or equal to their inputs from vertical mixing, but the net deposition of Pb clearly exceeds the input from upwelling. The current net deposition rates of the enriched elements are also similar to their rates of removal to sediments. These results indicate that air‐sea exchange processes may significantly affect the chemistry of trace metals in the open ocean.

Trace Metal Chemistry in Arid‐Zone Field Soils Amended with Sewage Sludge: IV. Correlations Between Zinc Uptake and Extracted Soil Zinc Fractions

AbstractThe surface horizons of two field soils that had been amended with composted or liquid sewage sludge for 3 to 6 y were extracted with a series of reagents [KNO3, H2O, NaOH, EDTA (ethylenedinitrilotetraacetic acid), HNO3, in sequence] and with DTPA (1,4,7‐triazaheptane‐1,1,7,7‐pentaacetic acid) to characterize the zinc (Zn) pool in the soils with respect to lability and bioavailability. Statistical correlation analysis, comparing the extracted Zn fractions with the concentration of Zn in the leaves of barley (Hordeum vulgare L.) grown on the two soils, led to the following conclusions: (i) Zinc extracted by KNO3 and H2O in sequence is associated with the highly labile, soluble pool, dominated by Zn2+, which determines immediate bioavailability. (ii) Zinc extracted by KNO3, H2O, and NaOH in sequence has a strong, positive, 1:1 correlation with DTPA‐extractable Zn and, therefore, is associated with the labile, plant‐available Zn pool. (iii) EDTA‐extractable Zn represents a reservoir of potentially bioavailable Zn, and (iv) HNO3‐extractable Zn is associated with a nonlabile pool that is not bioavailable. These general relationships between extracted Zn fractions and bioavailability were applicable to both soils investigated and did not depend on the type of sludge applied or the length of time of sludge application.

Trace Metal Chemistry in Arid‐Zone Field Soils Amended with Sewage Sludge: III. Effect of Time on the Extraction of Trace Metals

AbstractThe surface horizons of two arid‐zone field soils that either had received amendments of composted sewage sludge annually since 1975, or had received amendments of liquid sludge between 1976 and 1978, were fractionated by sequential extraction for 4 years annually, beginning in 1979, to compare the solid‐phase forms of Ni, Cu, Zn, Cd, and Pb. The total concentration of each trace metal in the soils continually receiving composted sludge increased with time, whereas the total concentration of the metals in the soil that had received liquid sludge until 1978 did not increase with time. Regardless of the time variation of total metal concentration, the percentages of the metals in either the EDTA (ethylenedinitrilote‐traacetic acid)‐extractable fraction or the HNO3‐extractable fraction often tended to increase with time in the soils. This trend was more evident in the lighter‐textured field soil receiving composted sludge. It was concluded that the observed increase in EDTA‐extractable trace metals with time could be the result of the formation of trace metal carbonates accompanying the gradual mineralization of the organic matter in the applied sludge in the soil environment.

Trace metal complexation in high ligand variety natural media

A relatively small variety of ligand number two, three, and four complexes is sufficient to generate a very large number of mixed-ligand species. A simple model is presented which quantitatively accounts for the sum complexation intensity due to very large numbers of mixed-ligand complexes. Mixed-ligand complexes can dominate the solution chemistry of trace metals in ligand-rich, high ligand variety media. A probable consequence of neglecting mixed-ligand complexation in high ligand variety systems is substantial underestimation of a metal's degree of complexation.

Sediment trace metal chemistry of Second Marsh, Oshawa, Ontario

A study was made on the sediment distribution of the trace metals Cd, Cu, Ni, Pb, and Zn in Second Marsh located on the northern shoreline of Lake Ontario near Oshawa, Ontario. Forty surficial samples and four cores were collected from the marsh. Comparing results with other Lake Ontario marshes, Ni and Zn were higher, while Cu and Pb were comparable, and Cd somewhat lower in concentration. Metals in cores exhibited a complex distribution with depth due to past disposals of dredged materials into the marsh. Major sources of such contaminants include a sewage treatment plant, automobile-related industries, a tannery, and land disposal of sludge.

Trace Metal Chemistry in Arid‐zone Field Soils Amended with Sewage Sludge: I. Fractionation of Ni, Cu, Zn, Cd, and Pb in Solid Phases

AbstractThe surface horizons of two arid‐zone field soils that had received amendments of either liquid or dried, anaerobically digested sewage sludge for 4 years were sampled to determine the forms of selected trace metals in the solid phase. The soils had been amended with sludge twice annually at rates of 0, 22.5, 45.0, or 90.0 tons · ha−1 · year−1. Barley and sorghum had been grown on the soils in randomized experimental plots. The soil samples were analyzed for total Ni, Cu, Zn, Cd, and Pb and were fractionated by sequential extraction to estimate the quantities of these metals in “exchangeable,” “sorbed,” “organic,” “carbonate,” and “sulfide” forms.The total contents of the five metals in the two field soils were governed by the total content of the metals in the sludges applied and by the rate of sludge application. The accumulation of metals in the surface horizons of field plots receiving liquid sludge was less than that in the plots receiving composted sludge, possibly because of a lesser reduction in soil bulk density resulting from sludge applications. The percentage of the total metal content in exchangeable and sorbed forms was very low, averaging between 1.1 and 3.7% for all of the metals regardless of the type of soil, the form of sludge applied, or the sludge application rate. The application of sludge tended to reduce the sulfide fraction and to increase the organic and carbonate fractions of all five trace metals. At the highest rate of sludge application, the predominant forms of the metals were: Ni, sulfide; Cu, organic; and Zn, Cd, and Pb, carbonate.

Trace Metal Chemistry in Arid‐zone Field Soils Amended with Sewage Sludge: II. Comparative Study of the Fulvic Acid Fraction

AbstractThe elemental composition, infrared spectrum, and proton titration curve were determined for (i) the fulvic acid fraction of a Domino soil which had received applications of composted sewage sludge for three years in a field experiment, and (ii) a commercially available fulvic acid extracted from a spodosol. Data showed that the Domino fulvic acid more resembled a typical sludge‐derived fulvic acid than a fulvic acid extracted from natural soil organic matter. The distinguishing features of the Domino fulvic acid which led to this conclusion were: (i) a high total sulfur (S) content and the presence of sulfonyl groups, (ii) a significant content of anionic surfactants and S‐containing amino acids, (iii) a low glucosamine/galactosamine ratio, and (iv) more than two classes of acidic functional groups. However, the Domino fulvic acid had a much larger content of carboxyl and other acidic functional groups than a typical sludge‐derived fulvic acid, evidently because of partial oxidation of the sludge in the Domino soil.

Voltammetric trace analysis in ecological chemistry of toxic metals

Abstract

Computer modeling of trace metal speciation in soil solutions: Correlation with trace metal uptake by higher plants

Abstract The study of trace metal chemistry in soils which support crop plants is made complicated by the large number of reactions possible between trace metals and soil constituents and by the web of interrelations among trace metals and the macrocomponents of soil solutions which is created by these reactions. In a typical soil solution, there may be 10–20 different metal cations present (including trace metals) which can react with as many different inorganic and organic ligands to form 300–400 soluble complexes and up to 80 solid phases. In addition, redox, ion exchange, and specific adsorption reactions occur. GEOCHEM is a multipurpose computer program that calculates the chemical equilibrium in a soil solution where all of the reactions mentioned above can take place. The chemical principles and computational scheme on which this program is based are described. One important application of the program is to calculate the speciation of trace metals in the aqueous solution phase of an agricultural so...

Moderne voltammetrische Verfahren in der Spurechemie toxischer Metalle in Trinkwasser, Regen‐ und Meerwasser

AbstractModern voltammetric methods in trace chemistry of toxic metals in drinking water, rainwater and seawater. In environmental research and protection, toxic metals (particularly Cd, Pb and Hg) are becoming increasingly significant owing their biological nondegradability and the chronic toxicity resulting from their accumulation in vital organs of man. Aquatic systems, such as the sea, inland waters, drinking water, rainwater etc., are important stages in the biogeochemical cycle. Although the dissolved levels are usually in the trace range of μg/1 to ng/1 they still remain significant, because their entry into the food chain and interactions with suspended particulates and sedimnts largely occur via the dissolved state. General comparative considerations suggest modern voltammetric methods, particularly differential pulse stripping voltammetry (DPSV), to be the most promising choice for the determination and characterization of dissolved toxic heavy metal traces. Voltammetry combines extreme sensitivity with high inherent reliability, good precision, scope for simultaneous determination of several metals and modest costs. Moreover, due to its substance specificity, voltammetry permits identification and physicochemical characterization of dissolved complexes and chelates. The striking and comprehensive scope of voltammetry in trace metal chemistry of aquatic ecosystems is illustrated by examples from drinking water control, investigations on rainwater, extended studies in European coastal waters and the oceans, and by fundamental work on the occurrence and behaviour of toxic trace metal species in the sea.

The seeding of two red tide blooms by the germination of benthic Gonyaulax tamarensis hypnocysts

Complementary laboratory and field data are presented that demonstrate the seeding of a spring and a fall bloom of the toxic dinoflagellate Gonyaulax tamarensis by the temperature-induced germination of benthic hypnocysts. Nutrient, salinity, temperature and rainfall data collected before, during, and after a spring bloom in a Cape Cod salt pond indicate that germination of the overwintering hypnocysts was initiated by a temperature increase. Laboratory experiments with hypnocysts exposed to a gradual temperature increase after storage at 5 °C for four months verified this result. The fall bloom was apparently seeded by hypnocyst germination as well, but with excystment initiated by a temperature decrease from the summer level of 20–22 °C. This result was also confirmed in the laboratory using hypnocysts stored at 22 °C and subjected to a gradual decrease in temperature. The reasons for the eventual decline of both blooms are not known, but it is proposed that the motile populations were transformed into new hypnocysts that settled to the sediments. Immediately after both bloom peaks, there was a sharp decrease in the percentage of hypnocysts that germinated during laboratory incubation after isolation from fresh, unstored sediment samples. The duration of these periods of limited excystment after the declines suggests that cold storage (or overwintering) is not a required conditioning mechanism prior to germination but that a prolonged period of conditioning at higher temperatures will suffice. Finally, data are presented that suggest that the extreme localization of the blooms within the salt pond was due to limited tidal advection of the motile population and the favourable trace metal chemistry of the estuarine environment compared to the adjacent coastal waters.

Variable influence of the atmospheric flux on the trace metal chemistry of oceanic suspended matter

The particulate concentrations of 17 trace metals, Al, Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Se, Ag, Sb, Au, Hg, Pb and Th have been measured in the marine atmosphere (58 samples) and in the deep waters (35 samples) of the Tropical North Atlantic. For oceanic suspended matter, our results are similar to those in samples from the Atlantic and the Pacific Oceans collected during the GEOSECS Program. Based on these results, we have made a flux balance for the mixed layer between input via the atmosphere and removal through small and large particles. These data show that the primary flux of suspended aluminosilicates in the Tropical North Atlantic is attributable to the atmospheric input. Elements Sc, Th, Fe, V, Mn, Co and Cr show high correlation with Al in the marine atmosphere. Of these elements, Fe, Mn, V, Co and Cr are influenced by additional processes such as biological, in the marine environment. For elements Ni, Cu, Zn, Se, Ag, Sb, Au, Hg and Pb, we observe high enrichments (relative to average crustal material) in the marine atmosphere which may be due, at least partially, to the influence of anthropogenic sources. These metals also show similar enrichments in deep ocean suspended matter. Model calculations indicate that the atmospheric flux may not control the deep ocean particulate chemistry of Ni, Cu, Zn, Ag, Sb, Au and Hg. Hence it is likely that, for these elements, the enrichment in the ocean is due to processes within the marine regime, for example their involvement in the biological cycle of the ocean. For Se and Pb, the atmospheric source looks to be the dominant contribution to their particulate concentration in seawater. In the deep North Atlantic, particulate Pb appears to be mostly of anthropogenic origin, which is not the case for Se.

The flocculation of dissolved Fe, Mn, Al, Cu, Ni, Co and Cd during estuarine mixing

A laboratory experiment was carried out in which the flocculation products, formed from the mixing of filtered (0.4 μm) river water and seawater, were analysed. This study established that Fe, Mn, Al, Cu, Ni, Cd and Co have resolvable and well-defined estuarine chemistries. Copper, Ni, Mn and Co have salinity dependences of removal which are similar to those of dissolved Fe and humic acids. The amount of removal of the above trace metals increases between 0 and 15–18‰, after which little additional removal occurs. The extents of removal from river water are very different: Fe, 95%; Al, 20%; Cu, Ni, 40%; Co, 10%; Cd, 5% and Mn, 25–45%. The basic removal mechanism appears to be the estuarine flocculation of trace metals which exist, in part, in river water as colloids in association with colloidal humic acids and hydrous iron oxides. A qualitative model, based on this mechanism, supports the observations of this flocculation study. The results of this study give the most complete and consistent set of data presently available, from which to postulate the most important processes controlling the estuarine chemistry of trace metals. The generality of their behaviours still needs to be determined by future investigations.

Complexing Capacity of Natural Water--Its Significance and Measurement

Most of the trace metals in natural waters are believed to exist in complexed or chelated forms with the miscellaneous organic ligands of both natural and pollutants origin which regulate the availability of these metals in the system (1–5). Such a mechanism maintains a reservoir of metals ready for biological uses. The abundance of complexing ligands in a body of water thus determines the complexing capacity of the water and hence its regulating capability. The measurement of complexing capacity will add a new parameter to the chemistry of trace metals in the aquatic environment, especially in areas of biological uptake and toxicological studies (6,7). Such information is also pertinent in bioassay work where the knowledge of the possible forms of the metals after being added to a system is important. The measurement of complexing capacity of a water sample is based on the amount of copper ion being complexed by the organic ligands through direct complexation and/or displacement reaction. It is done by spiking several aliquots of a sample with increasing amounts of a copper solution. Then the uncomplexed copper is measured by a differential pulse anodic stripping voltammetric technique (8,9). After the complexing ligands in the sample have been saturated with copper, the peak current of free copper will increase linearly with the amount of the copper spikes. By extrapolating this linear curve back to zero peak current, the intercept on the X-axis represents the complexing capacity of the water expressed as equivalents of μ mole Cu/l. As the differential pulse anodic stripping voltammetry measurement of “free” copper is carried out in a system containing excess of copper ions, the peak current thus obtained represents the concentration of “free” copper. The amount of copper plated out from the labile complexes, if any, becomes insignificant (8). Table I illustrates some complexing capacity values of natural waters. Preliminary work on the chemical characterization of the complexing substances in lake water, using ultra-filtration techniques, indicated that these complexing compounds fall in an arbitrary molecular range of 1,000–10,000. Further investigations are being carried out to isolate and to characterize this fraction (9). The significance of complexing capacity of water on the effect and toxicity of copper ion on algal photosynthesis has also been investigated (10) using the 14C uptake technique with lake waters of different complexing capacity and with the original plankton species. It was observed that complexing capacity of a water body does not imply that the equivalent amount of copper can be taken up (masked) by the water without affecting the plankton growth, although it has been a recognized fact that chelating agents such as NTA, EDTA can mask up the toxicity of copper. Further studies are being carried out to find out the quantitative biological meaning of complexing capacity. The chemical and biological aspects of the problem must go hand in hand.