Elevated Levels Of Cd Research Articles

Differential uptake, partitioning and transfer of Cd and Zn in the soil-pea plant-aphid system.

The biomagnification of trace metals during transfer from contaminated soil to higher trophic levels may potentially result in the exposure of predatory arthropods to toxic concentrations of these elements. This study examined the transfer of Cd and Zn in a soil-plant-arthropod system grown in series of field plots that had received two annual applications of municipal biosolids with elevated levels of Cd and Zn. Results showed that biosolids amendmentsignificantly increased the concentration of Cd in the soil and the shoots of pea plants and the concentration of Zn in the soil, pea roots, shoots, and pods. In addition, the ratio of Cd to Zn concentration showed that Zn was preferentially transferred compared to Cd through all parts of the system. As a consequence, Zn was biomagnified by the system whereas Cd was biominimized. Cd and Zn are considered to exhibit similar behaviors in biological systems. However, the Cd/Zn ratios demonstrated that in this system, Cd is much less labile in the root-shoot-pod and shoot-aphid pathways than Zn.

Contamination by Cd, Cu, Pb, and Zn in mine wastes from abandoned metal mines classified as mineralization types in Korea

The objective of this study was to investigate heavy metal contamination and geochemical characteristics of mine wastes, including tailings, from 38 abandoned mines classified as five mineralization types. Mine waste materials including tailings and soils were sampled from the mines and the physical and chemical characteristics of the samples were analyzed. The particle size of tailings was in the range of 10-100 microm. The pH of the waste covered a wide range, from 1.73 to 8.11, and was influenced by associated minerals and elevated levels of Cd, Cu, Pb, and Zn, extracted by a Korean Standard Method (digestion with 0.1 mol L(-1) HCl), which were found in the wastes. Half of the samples contained heavy metals at levels above those stipulated by the Soil Environmental Conservation Act (SECA) in Korea. In addition, extremely high concentrations of the metals were also found in mine wastes extracted by aqua regia, especially those from mines associated with sulfide minerals. Thus, it can be expected that trace elements in mine wastes may be dispersed both downstream and downslope through water and wind. Eventually they may pose a potential health risk to residents in the vicinity of the mine. It is necessary to control mine wastes by using a proper method for their reclamation, such as neutralization of the mine wastes using a fine-grained limestone.

Metallothionein gene and protein expression as a biomarker for metal pollution in natural gudgeon populations

Gudgeons ( Gobio gobio) from historically Cd and Zn contaminated sites in Flanders (Belgium) were found to be resistant to elevated Cd levels. In previous work, this increased resistance was largely explained by increased metallothionein (MT) expression. Recently, environmental cleanup efforts resulted in a significant decrease in Cd concentrations in the surface water. In this study, we evaluated the use of hepatic metal and metallothionein (MT) concentrations as biomarkers of metal exposure before and after the cleanup. Hepatic MT mRNA levels were determined after the environmental metal levels decreased in order to assess the applicability of MT gene expression as an environmental biomarker in natural fish populations. Our data show that both metallothionein protein and gene expression have the potential to be sensitive biomarkers for metal exposure. Significant correlations were found (a) among accumulated metal concentrations and both MT protein and mRNA levels, and (b) between MT protein and mRNA levels. However, our data illustrated that while MT protein and gene expression give a quantitative picture of metal load at a single time point, quantitative information in natural populations cannot always be obtained when different time points (including different years) are compared, since MT gene and protein expression are affected by many other factors in addition to the metal load. Furthermore, the result of the environmental cleanup was reflected in a decrease of hepatic Cd concentrations. Zn remained the most important factor determining MT concentrations. Finally, two differently sized MT mRNAs were amplified to test the hypothesis that 3′-UTR length can offer a protective advantage in conditions of environmental stress. Our data provided no evidence to support this hypothesis. In contrast, the ratio of the long mRNA variant relative to total MT mRNA was surprisingly constant, and independent of exposure history.

Biological and ecological factors related to trace element levels in harbour porpoises (Phocoena phocoena) from European waters

Selected trace elements (Cd, Cu, Hg, Se, Zn) were measured in the kidneys and the liver of 104 harbour porpoises (Phocoena phocoena) stranded along the coasts of France, Galicia (Spain), Ireland, Scotland (UK), and the Netherlands. Generally, relatively low concentrations of toxic elements were encountered in the tissues of European porpoises, except for two individuals, which displayed high hepatic Hg concentrations. Also, elevated Cd levels obtained in Scottish porpoises could be related to their feeding preferences and this result suggests an increase of the proportion of cephalopods in their diet with latitude. Moreover, significant geographical differences were seen in hepatic Zn concentrations; the elevated Zn concentrations displayed by porpoises from the Netherlands may relate their poor health status. Variation in metal concentrations within porpoises from the North Sea is likely to reflect a long-term segregation between animals from northern (Scotland) and southern areas (the Netherlands), making trace elements powerful ecological tracers.

Enhanced cadmium accumulation in maize roots—the impact of organic acids

Low molecular weight organic acids are important components of root exudates and therefore, knowledge regarding the mechanisms of cadmium (Cd) uptake and distribution within plants under the influence of organic acids, is necessary for a better understanding of Cd behavior in the plant–soil system. In this study, acetic and malic acids increased the uptake of Cd by maize (Zea mays L. cv. TY2) roots and enhanced Cd accumulation in shoots under hydroponic conditions. Concentration-dependent net Cd influx in the presence and absence of organic acids could be resolved into linear and saturable components. The saturable component followed Michaelis–Menten kinetics, which indicated that Cd uptake across the plasma membrane was transporter-mediated. While the K m values were similar, the V max values in the presence of acetic and malic acids were respectively 6.0 and 3.0 times that of the control. Zinc transporters were the most probable pathways for Cd accumulation. It was hypothesized that Cd(II)–organic acid complexes associated with the root zone, could decompose and liberate Cd2+ for subsequent absorption by maize roots; and that in the layer of the roots or within the root free space, depletion of Cd2+ was buffered by the presence of Cd(II)–organic acid complexes. Plant response to elevated Cd levels involved overproduction of organic acids in maize roots as a resistance mechanism to alleviate Cd toxicity.

3-1: The Elatsite porphyry Cu–Au deposit, Bulgaria: Ore deposit: Lat. 42° 45′ N, Long. 24° 02′ E

The aim of this study was to assess the spatial distribution of arsenic and heavy metals (Cd, Cr, Cu Hg, Ni, Pb and Zn) in a riparian area influenced by periodical flooding along a considerable stretch of the Danube River. This screening was undertaken on soil and plant samples collected from 43 sites along 2386 km of the river, collected during the international Joint Danube Survey 3 expedition (ICPDR, 2015). In addition, data on the concentration of these elements in river sediment was used in order to describe the relationship between sediment, riparian soil and riparian plants. A significant positive correlation (Spearman r, for p < 0.05) was found for trace metal concentrations in river sediment and soil (r = 0.817). A significant correlation between soil and plants (r = 0.438) and sediment and plants (r = 0.412) was also found for trace metal concentrations. Elevated levels of Cd, Cr, Cu, and Ni were found at certain sites along the Serbian stretch, while elevated concentrations of Hg were also detected in Hungary, of Pb along the Romanian stretch and of As along the Bulgarian stretch (the Lower Danube). These results point to the presence of naturally-occurring metals derived from ore deposits in the Danube River Basin and anthropogenic metals, released by mining and processing of metal ores and other industrial facilities, which are responsible for the entry of metals such as Cu, Ni and Zn. Our results also indicated toxic Cd and Zn levels in plant samples, measured at the Hercegsznato site (Middle Danube, Hungary), which highlighted these elements as a potential limiting factor for riparian vegetation in that area. The distribution of the analysed elements in plant material also indicates the species-specific accumulation of trace metals. Based on our results, the Lower and Middle Danube were found to be more polluted in terms of the analysed elements.

A field study examining metal elimination kinetics in juvenile yellow perch ( Perca flavescens)

Currently little is known about how and at what rate fish eliminate metals in natural environments. To address this knowledge gap we examined metal elimination kinetics in the field using juvenile yellow perch ( Perca flavescens) that were caught in a metal-contaminated lake (elevated levels of Cd, Cu and Zn) and transplanted to cages held within a reference lake. Fish were sampled from the cages over 75 d and changes in metal concentrations were measured in the gills, gut, liver and kidney. In transplanted fish, Cd concentrations decreased most rapidly in the gills and gut, i.e. from organs in contact with the ambient water and food; biological half lives ( t 1/2) were 18 and 37 d, respectively, for each organ. Longer half-lives were observed in the liver (75 d) and kidney (52 d) for this metal. Elimination of excess Cu by the liver and gut occurred much more rapidly, with estimated half-lives of labile Cu being 8 and 4 d, respectively, for these two organs. In contrast to Cd and Cu, there was little Zn elimination. To compare how the liver handles different metals during elimination, we used a differential centrifugation approach to examine changes in metal concentrations (Cd and Cu) at the sub-cellular level. Consistent with the long half-life observed for Cd at the whole organ level, there was no significant loss of Cd from any of the sub-cellular fractions. Copper, on the other hand, was lost from both the organelle and cellular debris fractions. As these fractions likely contain structures such as lysosomes, we suggest that Cu is depurated from the liver by direct elimination of these sub-cellular vesicles. These field results clearly demonstrate how the liver handles essential (Cu, Zn) and non-essential metals (Cd) differently during depuration.

The penguin feathers as bioindicator of Antarctica environmental state

Concentrations of biogenic and toxic elements (Na, K, Mg, Ca, P, S, Fe, Cu, Zn, Co, Mn, Se, Ni, Sr, Al, Cd, Pb, As) were determined for the first time in feathers of gentoo penguin ( Pygoscelis papua) and chinstrap penguin ( Pygoscelis antarctica) from Antarctica. A comparison of element levels was performed among these species in years 2002–2003. Penguins molt annually and this fact allows defining precisely the concentrations of accumulated toxic elements and heavy metals in plumage every year. A continual environmental biomonitoring could establish a possible trend to contamination of the Antarctica sea zones. The penguin feather is an excellent subject for monitoring because penguins have long life span, permanent ecological niche and dominate the aviafauna in Antarctica. Because of its remoteness, Antarctica is believed to be unpolluted. The relatively elevated levels of Cd established are due to the Cd-enrichment of the Antarctic marine food chain. Because of great bioaccumulation of lead in feathers, the concentration of Pb in penguin feather was higher (4–8 times) compared to that of Cd. In both penguin species the levels of Zn were 1.9 times higher than respective Fe levels. The concentrations of most of the investigated elements were significantly higher in P. papua than in P. antarctica and this probably could be explained by the different diet and feeding habit of these species.

Bioavailability of Cd in a soil–rice system in China: soil type versus genotype effects

Human exposure to toxic heavy metals via dietary intake is of increasing concern. In this regard, the bioavailability of heavy metals in the soil–crop system is considered to be a key factor controlling plant uptake and, therefore, public health risk through food chain transfer [J. Environ. Sci. Health B 34(4) (1999) 681]. In 2002, a pot experiment was conducted to elucidate the relative significance of soil types and rice genotype on the bioavailability, uptake and partitioning of Cd by two rice cultivars with distinct affinity for Cd. The results indicated that the total uptake of Cd and accumulation in grain was dependent on both soil type and genotype effects. Cd spiking enhanced high Cd uptake and partitioning in grain. Inherent differences in soil type effecting Cd bioavailability were less significant under the Cd spiking regime as compared to non-Cd spiking. In the case of Soil-P, with low Cd bioavailability as indicated by the comparatively lower MgCl2 extractable Cd, differences in metal affinity between genotypes dominated uptake. Conversely, inherent differences in soil type affecting Cd bioavailability dominated uptake in the low metal affinity cultivar treatments. Under the experimental conditions evaluated, the positive interaction between soil type and genotype results in elevated levels of Cd in rice grain with the Cd values exceeding the Chinese food guideline limit of 0.2 mg kg−1. The results indicated that Cd bioavailability and plant uptake is dependent on soil chemical and physical properties affecting Cd mobility, rice genotype and soil pollution status. The results further suggested that caution should be paid to rice production with the new high metal affinity genotypes on soils with inherent Cd bioavailability as with acidic Red Soils of Jiangxi Provinces, China.

Effect of alkaline pH and associated Zn on the concentration and total uptake of Cd by lettuce: comparison with predictions from the CLEA model

An eight-fold underestimate of the potential Cd exposure to humans via ingestion of lettuce grown in moderately alkaline soil has been measured experimentally. Current models of Cd uptake by leafy vegetables, which are used in risk assessment (e.g. CLEA in UK) predict higher concentration factors in acid than in alkaline soils. Experimental evidence shows that Cd uptake, although it decreases with increasing pH from acid to neutral soils, increases again in alkaline soils, confirming recent finding from other workers. The concentration of Zn in the soil also significantly affects the uptake of Cd, although this is not included in the current prediction models either. The effect of Zn on the uptake of Cd by plants is greater in slightly alkaline soils (pH 7.7) than in slightly acidic or neutral soils. High concentrations of Zn in soil (1000 mg/kg), which are often associated with elevated Cd levels, further increase the Cd concentration factor to values 12 times higher than that predicted by the CLEA model. This is due in part to the effect of the high soil Zn on reducing the above-ground biomass of the plants.

Toxic Risk Assessment and Environmental Contamination of Heavy Metals around Abandoned Metal Mine Sites in Korea

In order to investigate the levels of heavy metal contamination and to assess the risk of the adverse health effects on human exposure to toxic heavy metals influenced by past mining activities, environmental geochemical surveys were undertaken around abandoned metal mine sites (Okdong Cu-Pb-Zn, Dokok Au-Ag-Cu and Hwacheon Au-Ag-Pb-Zn mines). High concentrations of heavy metals were found in tailings from the Okdong (72 As mg/kg, 53.6 Cd mg/kg, 910 Cu mg/kg, 1,590 Pb mg/kg, 5,720 Zn mg/kg), the Dokok (254 As mg/kg, 98.2 Cd mg/kg, 2,550 Cu mg/kg, 4,200 Pb mg/kg, 18,020 Zn mg/kg) and the Hwacheon (72 As mg/kg, 12.4 Cd mg/kg, 580 Pb mg/kg, 1,300 Zn mg/kg) mines. Elevated levels of As, Cd, Pb and Zn were also found in agricultural soils from these mine areas. Human risk effects are classified into a cancer effect and a toxic (noncancer) effect. The hazard index representing a toxic risk for As was higher value than 1.0 in the Okdong and the Hwacheon mine sites, as was that for Cd in the Okdong and Dokok mine sites. Therefore, toxic risks for As and Cd exist via exposure (ingestion) to the contaminated soil, groundwater and rice grains in these mine areas. The cancer risk for As by the consumption of groundwater used as drinking water from the Okdong and the Hwacheon mine areas was 7E-4 and 1E-4, respectively. These risk levels exceed the acceptable risk (1 in 100,000) for regulatory purposes.

Molecular Monitoring of SRB Community Structure and Dynamics in Batch Experiments to Examine the Applicability of in situ Precipitation of Heavy Metals for Groundwater Remediation (15 pp)

Background, Aims and Scope Sulfate-reducing bacteria (SRB) are known for their capacity to reduce and precipitate heavy metals (HM) as metal sulfides, offering the opportunity to create an in situ reactive zone for the treatment of heavy metal-contaminated groundwater, a process called in situ metal precipitation (ISMP). The applicability of the ISMP technology first has to be investigated at a laboratory scale before going into an on site application. The evaluation and optimization of the ISMP process is facilitated when physical/chemical analysis techniques are combined with molecular tools that specifically monitor the abundance, diversity and dynamics of the indigenous sulfate reducing microbial community. In this study, batch experiments were conducted in order to investigate the feasibility of ISMP as a groundwater remediation strategy for an industrial site contaminated with elevated levels of Zn, Cd, Co and Ni.

The plant P 1B-type ATPase AtHMA4 transports Zn and Cd and plays a role in detoxification of transition metals supplied at elevated levels

The transition metal Zn is essential for many physiological processes in plants, yet at elevated concentrations this, and the related non-essential metal Cd, can be toxic. Arabidopsis thaliana HMA4, belonging to the Type P 1B subfamily of P-type ATPases, has recently been implicated in Zn nutrition, having a role in root to shoot Zn translocation. Using Arabidopsis insertional mutants, it is shown here that disruption of AtHMA4 function also results in increased sensitivity to elevated levels of Cd and Zn, suggesting that AtHMA4 serves an important role in metal detoxification at higher metal concentrations. AtHMA4 and a truncated form lacking the last 457 amino acids both confer Cd and Zn resistance to yeast but a mutant version of the full-length AtHMA4 (AtHMA4-C357G) does not; this demonstrates that the C-terminal region is not essential for this function. Evidence is presented that AtHMA4 functions as an efflux pump.

Levels of Cd, Hg and Zn in some surface waters from the Eastern Cape Province, South Africa

Total trace metals levels - Cd, Hg and Zn, which may affect human health and the "health" of the aquatic ecosystem, were determined in the Umtata, Buffalo, Keiskamma and Tyume Rivers and in the Sandile and Umtata Dams. These elements were also determined in sediment samples from some of these surface waters. Normal levels of the metals were detected in water samples from the Umtata River and the Umtata Dam but samples from Buffalo, Keiskamma and Tyume Rivers contained elevated levels of Cd. Generally the levels of Hg and Zn were normal in samples from all the surface waters. The probable sources of the metals in the rivers are diffuse, originating from rural and urban runoff and from agricultural runoff in the catchments although there could be contribution from natural and point sources. Water SA Vol.29(4): 375-380

Cadmium Bioaccumulation in Yellow Foxtail (Setaria glauca L. P. Beauv): Impact on Seed Head Morphology

Yellow foxtail (Setaria glauca L. P. Beauv) growing on a cadmium-contaminated site was sampled to determine the extent of cadmium bioaccumulation in aerial tissues and the impact of cadmium on growth and development. Water-extractable Cd concentrations in the soil ranged from 5.0 to 18.0 mg L-1. Aerial tissues contained elevated concentrations of Cd (16-48 μg g-1 DW), with mean concentration ratios of &gt;3.0. Since foxtail frequently colonizes disturbed sites, the bioaccumulation of Cd in aerial tissues of foxtail suggests that wildlife feeding upon this plant species could be exposed to elevated Cd levels. A significant negative correlation (r2=0.98) was observed between water-extractable Cd in the soil and seed head length in foxtail, indicative of an adverse effect of Cd on reproductive development. This correlation further suggests seed head length as a biomarker for soluble Cd in contaminated soils. KEYWORDS: Cadmium, bioaccumulation, biomarker, phytotoxicity

Groundwater Effects from Highway Tire Shred Use

Approximately 250,000 shredded tires have been used to construct a highway exit ramp as part of a demonstration project. One upgradient well was installed before the tire shreds were put in place. Two downgradient wells and two tire fill sampling ports were installed during the project. Levels of organic compounds and metals have been monitored since the project was completed in May of 2001. Organic compounds were not detected in the leachate or downgradient groundwater in significant amounts. Arsenic (As), barium (Ba), cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), lead (Pb), manganese (Mn), mercury (Hg), selenium (Se), silver (Ag), and zinc (Zn) were quantified in both filtered and unfiltered samples. Of most concern is the source of elevated levels of Ba, Cd, Fe, Mn, and Zn in filtered samples when compared with water quality standards. Zn, Cd, and Ba are elevated in one of the tire fill ports, whereas Fe and Mn have been consistently elevated in the downgradient wells. The elevated Zn, Cd, and Ba may be related to the use of shredded tires. The elevated Fe and Mn may be associated with traffic on the adjacent interstate and ramp and the hydrogeology of the site. The concentrations of iron and manganese in the downgradient groundwater would be a public health concern if the water were used for human consumption. It is important to evaluate the combined long-term effects of tire shreds and runoff from roadways on groundwater quality where tire shreds are used in highway construction.

Distribution of heavy metals in marine bivalves, fish and coastal sediments in the Gulf and Gulf of Oman

An assessment of marine contamination due to heavy metals was made in the Gulf and Gulf of Oman based on marine biota (fish and various bivalves) and coastal sediment collected in Bahrain, Oman, Qatar, and the United Arab Emirates (UAE) during 2000–2001. Sediment metal loadings were generally not remarkable, although hot spots were noted in Bahrain (Cu, Hg, Pb, Zn) and on the east coast of the UAE (As, Co, Cr, Ni). Concentrations of As and Hg were typically low in sediments and the total Hg levels in top predator fish commonly consumed in the region were <0.5 μg g −1 and posed no threat to public health. Very high Cd concentrations (up to 195 μg g −1) in the liver of some fish from southern Oman may result from food-chain bioaccumulation of elevated Cd levels brought into the productive surface waters by upwelling in the region. Very high As concentrations (up to 156 μg g −1) were measured in certain bivalve species from the region. Although not certain, the As is probably derived from natural origins rather than anthropogenic contamination.

Exposure assessment of heavy metals on abandoned metal mine areas by ingestion of soil, crop plant and groundwater

In order to assess the risk of adverse health effects on human exposure to arsenic and heavy metals influenced by past mining activities, environmental geochemical survey was undertaken in the abandoned metal mine areas (Dongil Au-Ag-Cu-Zn mine, Okdong Cu-Pb-Zn mine, Myungbong Au-Ag mine). Arsenic and other heavy metals were highly elevated in the tailings from the Dongil mine (8720 As mg/kg, 5.9 Cd mg/kg, 3610 Cu mg/kg, 5850 Pb mg/kg, 630 Zn mg/kg). Heavy metals except As from the Okdong mine (53.6 Cd mg/kg, 910 Cu mg/kg, 1590 Pb mg/kg, 5720 Zn mg/kg) and As from the Myungbong mine (5810 As mg/kg) were also elevated. Elevated levels of As, Cd and Zn were also found in agricultural soils from these mine areas. The H.I. (hazard index) values of As and Cd from the Dongil, the Okdong and Myungbong mine areas are higher than 1.0. Therefore, toxic risk for As and Cd exist via exposure (ingestion) of contaminated soil, groundwater and rice grain in these mine areas.

Role of type 1 versus type 2 immune responses in liver during the onset of chronic woodchuck hepatitis virus infection

Immune response messenger RNAs (mRNA) were compared in liver during self-limited (resolved) and chronic neonatal woodchuck hepatitis virus (WHV) infection. At week 14 postinfection (mid-acute phase), mRNAs for leukocyte markers (CD3, CD4, CD8), type 1 cytokines and related transcription factors (IFN-γ, TNF-α, STAT4, T-bet), and IL-10 were increased in livers from resolving infections, but mRNAs of other type 1 (IL-2) and type 2 (IL-4, STAT6, and GATA3 markers remained at baseline levels. Increased coexpression of IFN-γ and TNF-α mRNAs correlated in most cases with lower levels of intrahepatic WHV covalently closed circular DNA (cccDNA). At the same time point postinfection, livers from woodchucks that eventually progressed to chronic infection had baseline or slightly elevated levels of CD and type 1 mRNAs, which were significantly lower (or elevated less frequently) compared with resolving woodchucks. Earlier, at week 8, there were no differences between the two outcome settings. During these early time points and at a later stage in chronic infection (15 months), type 2 mRNAs in carrier liver remained at baseline levels or, when elevated, were never in excess of those in resolving woodchucks. In conclusion, the onset and maintenance of neonatal chronic WHV infection are not associated with antagonistic type 2 immunoregulation of type 1 responses in liver. Accordingly, chronicity develops in association with a primary deficiency in the intrahepatic CD responses, especially involving CD8 + T lymphocytes, and in both extracellular (cytokine) and intracellular (transcriptional) type 1 response mediators. This has relevant implications for future treatment of chronic hepatitis B virus (HBV) infection in humans. (H epatology 2003;37:771-780.)

Geochemical controls for Al, Fe, Mn, Cd, Cu, Pb, and Zn during experimental acidification and recovery of Little Rock Lake, WI, USA

Concentrations of Al, Fe, Mn, Cd, Cu, Pb, and Zn were measured in thereference and treatment basins of Little Rock Lake (Vilas County, Wisconsin), alow-alkalinity, seepage system (pH ∼6.1, alkalinity25 μeq/L) during six years of a whole-basinacidificationand the first four years of the lake's recovery. The treatment basin wasacidified with H2SO4 in three two-year steps to pH∼5.6, ∼5.1, and ∼4.7. By the end of year 4 of recovery, treatmentbasin pH increased to ∼5.3 as a result of internal alkalinity generation.During acidification, dissolved Mn and Fe (0.4 μmpore-size filters) increased at pH ∼5.6; dissolved Al, Cd, and Zn becameelevated at pH ∼5.1; and dissolved Pb at pH ∼4.7. Dissolved Cu remainedsimilar in both basins to pH ∼4.7. Al, Fe and Mn levels declinedsignificantly during the recovery period, approaching values at pH 5.3intermediate between the concentrations at pH 5.6 and 5.1 during acidification.Dissolved Al and Fe in the reference basin were near the equilibrium levels forsolubility of gibbsite (Al(OH)3) and amorphousFe(OH)3(s).The acidified basin was undersaturated relative to gibbsite, and dissolved Alwas limited by pH disequilibrium between the water column and sediments andpossibly by Al-DOC precipitation. Dissolved Fe apparently was controlled bysolubility of amorphous Fe(OH)3(s) and Fe-DOC precipitation.Dissolved Mn levels in both basins were consistent with manganite[γ-MnOOH(s)] solubility. Elevated levels of Cd, Pb, and Zn in thetreatment basin during acidification probably resulted from less efficientscavenging of atmospherically-deposited Cd, Pb, and Zn by settling particles.