Retention of Cd, Cu, Pb and Zn by Wood Ash, Lime and Fume Dust

Heavy metals are of interest due to their deleterious impacts on both human and ecosystem health. This study investigated the effectiveness of wood ash in immobilizing the heavy metals Pb, Cd, Cu and Zn from aqueous solutions. The effects of initial metal concentrations, solution pH, ash dose and reaction time on metal sorption, as well as the metal sorption mechanisms were studied. To investigate the effect of initial metal concentrations, solutions containing Cd, Zn (25, 50, 75, 100 or 125 mg L^?1), Cu (25, 50, 75, 100, 125, 150 or 175 mg L^?1) or Pb (250, 500, 750, 1000, 1250, or 1500 mg L^?1) were reacted with 10 g L^?1 ash for two hours. For the effect of pH, solutions containing 100 mg L^?1 of Cd, Cu or Zn or 1500 mg L^?1 of Pb were reacted with 15 g L^?1 ash over a pH range of 4 to 7. The wood ash was effective in immobilizing the four metals with a sorption range of 41–100 %. The amounts of metals retained by the ash followed the order of Pb > Cu > Cd > Zn. As expected, absolute metal retention increased with increasing initial metal concentrations, solution pH and ash dose. Metal retention by the ash exhibited a two-phase step: an initial rapid uptake of the metal followed by a period of relatively slow removal of metal from solution. Metal retention by the ash could be described by the Langmuir and Freundlich isotherms, with the latter providing a better fit for the data. Dissolution of calcite /gypsum minerals and precipitation of metal carbonate/sulfate like minerals were probably responsible for metal immobilization by the ash in addition to adsorption.     

Surface loading effect on Cd and Zn sorption by kaolinite and montmorillonite from low concentration solutions

Studies of Cd and Zn sorption using Na-saturated kaolinite and montmorillonite, and low metal solution concentrations similar to those found in the environment, showed that metal sorption affinity (measured by K _d values) decreased markedly with increasing surface metal loading for both layer silicates. For equilibrium solution concentrations <0.1 μmol L^?1 for Cd, and < 1 μmol L^?1 for Zn, both metals were sorbed with greater affinity by kaolinite than montmorillonite. These results were probably due to the higher proportion of weakly acidic edge sites present on kaolinite surfaces. In the case of Zn there was an affinity reversal for equilibrium solution concentrations > 1 μmol L^?1, which was attributed to the permanent charge sites of montmorillonite. Cadmium ions were sorbed, by kaolinite, with greater affinity than Zn for equilibrium solution concentrations between 0.3 to 1.5 μmol L^?1. This result was attributed to retention of these metal ions through electrostatic attraction by permanent charge sites present on the kaolinite used in this work. According of these results it seems that metal sorption by these layer silicates involves predominantly edge weak acid sites at lower surface coverages (higher affinity sites), and permanent charge sites at higher metal coverages (lower affinity sites). It was concluded that Cd and Zn sorption by those two layer silicates is greatly influenced by surface metal coverage, and results cannot be extrapolated from low to high surface coverages, and viceversa.     

Impacts of coal pile leachate on a forested wetland in South Carolina

This study was conducted to: (1) determine the probable cause of several areas of stressed and dead vegetation adjacent to a 15-yr-old reject coal pile in western South Carolina and (2) identify the factors limiting successful revegetation of the site. Data from an earlier study suggested that solution pH, total dissolved solids (TDS) and electrical conductivity (EC), and/or elevated trace element concentrations may have contributed to the stress and dieback. Soil water in the two vegetation kill zones is saline (TDS>10 000 mg L^?1 and EC>4 dS m^?1), highly acidic (soil pH<3.5), and high in Al and Mn (Al conc.>200 mg L^?1 and Mn conc.>10 mg L^?1). Soil water in areas of sparse vegetation is brackish (TDS>1000 mg L^?1 and EC>2 dS m^?1) and acidic (soil pH<4.0), with elevated Al values (> 40.5 mg Al L^?1). Tissue samples were collected from volunteer loblolly pine (Pinns taeda L.) seedlings growing in the study area and analyzed for essential and non-essential elements. Seedling tissues did not contain abnormal concentrations of nutrients or trace elements. The strong relationship between the zones of vegetation stress and dieback and solution pH and soluble salt concentrations, and the lack of excessive metal accumulations by tree seedlings which have become established in the less toxic portions of the study area, suggest that low solution pH and high soluble salts are more important factors limiting plant establishment on this site than solution metal concentrations. The results of this study demonstrate the importance of site hydrology in determining the impacts of coal waste disposal on adjacent ecosystems.     

Chromium-resistant microorganisms isolated from evaporation ponds of a metal processing plant

Chromium occurs naturally at trace levels in most soils and water, but disposal of industrial waste and sewage sludge containing chromium compounds has created a number of contaminated sites, which could pose a major environmental threat. This study was conducted to enumerate and isolate chromium-resistant microorganisms from sediments of evaporation ponds of a metal processing plant and determine their tolerance to other metals, metalloids and antibiotics. Enumeration of the microbiota of Cr-contaminated sediments and a clean background sample was conducted by means of the dilution-plate count method using media spiked with Cr(VI) at concentrations ranging from 10 to 1000 mg L^?1. Twenty Cr(VI) tolerant bacterial isolates were selected and their resistance to other metals and metalloids, and to antibiotics was assessed using a plate diffusion technique. The number of colony-forming units (cfu) of the contaminated sediments declined with increasing concentrations from 10 to 100 mg L^?1 Cr(VI), and more severely from 100 to 1000 mg L^?1 Cr(VI). The background sample behaved similarly to 100 mg L^?1 Cr(VI), but the cfu declined more rapidly thereafter, and no cfu were observed at 1000 mg L^?1 Cr(VI). Metals and metalloids that inhibited growth (from the most to least inhibitory) were: Hg > Cd > Ag > Mo = As(III) at 50 μg mL^?1. All 20 isolates were resistant to Co, Cu, Fe, Ni, Se(IV), Se(VI), Zn, Sn, As(V), Te and Sb at 50 μg mL^?1 and Pb at 100 μg mL^?1. Eighty-five percent of the isolates had multiple antibiotic resistance. In general, the more metal-tolerant bacteria were among the more resistant to antibiotics. It appears that the Cr-contaminated sediments may have enriched for bacterial strains with increased Cr(VI) tolerance.     

Heavy metal pollutant tolerance of Azolla Pinnata

The effects of Hg, As, Pb, Cu, Cd, and Cr (1, 2, and 5 mg L^?1 each) on Azolla pinnata R. Br. were analyzed. The treatments (2 and 5 mg L^?1) of the heavy metal pollutants decreased Hill activity, chlorophyll, protein and dry wt, and increased tissue permeability over control values. The effects were most pronounced with the treatment of 5 mg L^?1. The harmful effects of the metals were, in general, found by the treatments in the order: Cd 〉 Hg 〉 Cu 〉 As 〉 Pb 〉 Cr. There was no significant change in these parameters at 1 mg L^?1 of the metals over control. Thus Azolla pinnata shows tolerance to the heavy metals tested up to 1 mg L^?1 each.     

The Effects of Copper and Lead on Growth and Zinc Accumulation of Thlaspi Caerulescens J. and C. Presl: Implications for Phytoremediation of Contaminated Soils

Thlaspi caerulescens J. and C. Presl is a Zn-hyperaccumulatingplant which has aroused considerable interest with respect to its possible use for phytoremediation of Zn-contaminated soils. In this work, a British population of T. caerulescens, from a soil which was found to have relatively high concentrations of water-extractable Cu (0.22 mg L^-1), Pb (0.99 mg L^-1) and Zn (6.49 mg L^-1), was studied. Its ability to grow and accumulate Zn from hydroponic nutrient solution in the presence of elevated concentrations of Cu and/or Pb was investigated. The chosen concentrations of Cu, Pb and Zn were based on reported water-soluble concentrations of these heavy metals in contaminated soils. When supplied with 32.7 mg L^-1 Zn, plants accumulated 19 780 mg kg^-1 Zn in their shoot dry matter. This concentration declined by 9.3, 87 and 84% respectively when 5.0 mg L^-1 Pb, 1.0 mg L^-1 Cu or 2.0 mg L^-1 Cu were included in the nutrient solution. Despite the apparent adaptation of this population of T. caerulescens to a Zn/Pb/Cu-contaminated soil, these Cu treatments strongly inhibited growth, but the Pb treatment did not affect growth significantly.     

A Laboratory Study on Revegetation and Metal Uptake in Native Plant Species from Neutral Mine Tailings

Lygeum spartum, Zygophyllum fabago and Piptatherum miliaceum are typical plant species that grow in mine tailings in semiarid Mediterranean areas. The aim of this work was to investigate metal uptake of these species growing on neutral mine tailings under controlled conditions and their response to fertilizer additions. A neutral mine tailing (pH of soil solution of 7.1–7.2) with high total metal concentrations (9,100 and 5,200 mg kg^?1 Zn and Pb, respectively) from Southern Spain was used. Soluble Zn and Pb were low (0.5 and <0.1 mg l^?1, respectively) but the major cations and anions reached relatively high levels (e.g. 2,600 and 1,400 mg l^?1 Cl and Na). Fertilization caused a significant increase of the plant weight for the three species and decreased metal accumulation with the exception of Cd. Roots accumulated much higher metal concentrations for the three plants than shoots, except Cd in L. spartum. Shoot concentrations for the three plants were 3–14 mg kg^?1 Cd, 150–300 mg kg^?1 Zn, 4–11 mg kg^?1 Cu, and 1–10 mg kg^?1 As, and 6–110 mg kg^?1 Pb. The results indicate that neutral pH mine tailings present a suitable substrate for establishment of these native plants species and fertilizer favors this establishment. Metal accumulation in plants is relatively low despite high total soil concentrations.     

Acute and sub-chronic toxicity of lead to the early life stages of smallmouth bass (Micropterus Dolomieui)

The early life stages of smallmouth bass (Micropterus dolomieui) were exposed to Pb in acute (96 hr) and sub-chronic (90 day) bioassays (water hardness = 152 mg L^?1 as CaCO₃). After 96-hr static exposures at nominal Pb concentrations up to 15.9 mg L^?1, eggs and sac fry showed no increased mortality over that in controls. Swim-up fry (96-hr LC₅₀ = 2.8 mg Pb L^?1) were more sensitive to Pb exposure than were fingerlings (96-hr LC₅₀ of 29.0 mg Pb L^?1 ). The relation between dissolved Pb and mortality was non-significant for either swim-up fry or fingerlings. Fingerlings were exposed to Pb concentrations as high as 405 μg L^?1 for 90 day to evaluate effects on substrate selection, locomotor activity, hematology, and weight. Dark or light substrate selection (cover-seeking) and locomotor activity, weight and hemoglobin concentration in the blood were not significantly altered by any treatment. Hematocrit and leucocrit varied significantly but not in relation to Pb levels. Sub-chronic Pb exposure did not appear to represent a threat to smallmouth bass in waters of medium hardness and above-neutral pH (7.1 to 7.9).     

Avian Urine: Its Potential as a Non-Invasive Biomonitor of Environmental Metal Exposure in Birds

Current non-invasive biomonitoring techniques to measure heavy metal exposure in free ranging birds using eggs, feathers and guano are problematic because essential metals copper (Cu) and zinc (Zn) deposited in eggs and feathers are under physiological control, feathers accumulate metals from surface contamination and guano may contain faecal metals of mixed bioavailability. This paper reports a new technique of measuring lead (Pb), Cu and Zn in avian urate spheres (AUS), the solid component of avian urine. These metal levels in AUS (theoretically representing the level of metal taken into the bloodstream, i.e. bioavailable to birds) were compared with levels in eggs (yolk and shell), feathers and whole guano from chickens (Gallus gallus domesticus) exposed to a heavy metal-contaminated soil (an allotment soil containing Pb 555?mg?kg^?1 dry mass (dm), Cu 273?mg?kg^?1?dm and Zn 827?mg?kg^?1?dm). The median metal levels (n?=?2) in AUS from chickens exposed to this contaminated soil were Pb 208???g?g^?1 uric acid, Cu 66???g?g^?1 uric acid and Zn: 526???g?g^?1 uric acid. Lead concentrations in egg yolk and shell samples (n?=?3) were below the limit of detection (<2?mg?kg^?1), while Cu and Zn were only consistently detected in the yolk, with median values of 3 and 70?mg?kg^?1 (dm), respectively, restricting the usefulness of eggs as a biomonitor. Feathers (n?=?4) had median Pb, Cu and Zn levels respectively of 15, 10 and 140?mg?kg^?1 (dm), while whole guano samples (n?=?6) were 140, 70 and 230?mg?kg^?1 (dm). Control samples were collected from another chicken flock; however, because they had no access to soil and their diet was significantly higher in Cu and Zn, no meaningful comparison was possible. Six months after site remediation, by top soil replacement, the exposed chickens had median Pb, Cu and Zn levels respectively in whole guano (n?=?6) of 30, 20 and 103?mg?kg^?1 (dm) and in AUS (n?=?4) of 147, 16 and 85???g?g^?1 uric acid. We suggest the persistent high Pb level in AUS was a consequence of bone mobilised for egg production, releasing chronically sequestered Pb deposits into the bloodstream. In contrast, AUS levels of Cu and Zn (metals under homeostatic control and sparingly stored) had declined, reflecting the lower current exposure. However because pre- and post-remediation samples were measured using different methods carried out at different laboratories, such comparisons should be guarded. The present study showed that metals can be measured in AUS, but no assessment could be made of availability or uptake to the birds because tissue and blood samples were not concomitantly analysed. A major short coming of the study was the inappropriate control group, having no access to uncontaminated soil and being fed a different diet to the exposed birds. Furthermore guano and urine analysis should have been carried out on samples from individual birds, so biological (rather than just technical) variation of metal levels could have been determined. Future studies into using AUS for biomonitoring environmental heavy metals must resolve such experimental design issues.     

Toxicity of lead to clarias lazera,oreochromis niloticus,chironomus tentans and benacus sp.

The 48 and 96-hr LC50 values of Pb (Pb(NO₃)₂) with O. niloticus were 3.34 and 2.15 mg L^?1, respectively, compared to 1.91 and 1.72 mg L^?1, respectively, for C. lazera. C. tentans larvae and Benacus sp. demonstrated 48-hr LC 50 of 2.68 and 1.89 mg l^?1 respectively. The 96-hr LC50 value was 1.77 mg L^?1 for Chironomus and 1.36 mg L^?1 for Benacus. Clarias appeared to be the most susceptible of the four to Pb poisoning; Chironomus being the least susceptible. Uptake pattern of Pb by fingerlings of O. niloticus and C. lazera exposed to 0.33 and 0.27 mg L^?1 Pb, respectively, and the clearance of accumulated Pb were curvilinear. There was an initial ‘fast’ phase of accumulation occurring during the first 96 hr, followed by a slower phase over the remaining 240 hr. Mean Pb concentrations in gills, intestine, liver, muscle, bone, skin and whole body of O. niloticus were 33.30, 22.2, 5.3, 2.8, 1.8 and 14.9 μg g^?1, respectively, compared to 28.7, 6.5, 11.5, 2.5, 5.6, 5.9 and 6.8 µg g^?1 respectively in C. lazera. The half life of Pb in Oreochromis was 20 hr compared to 43 hr in C. lazera. Bioconcentration factors in Oreochromis and Clarias were 78.3 and 33.8, respectively. The data suggest that O. niloticus accumulates and eliminates Pb faster than C. lazera.     

Residual heavy metal (Cu and Cd) removal byIris Pseudacorus

The uptake of Cu and Cd by the roots ofIris pseudacorus and its transport to rhizome and leaves were examined using solutions containing 0.5 and 5.0 mg L^?1 of Cu and Cd. Heavy metal accumulation was measured while replacing the metal absorbed by the plants with daily introduction to restore the initial concentrations. The heavy metal accumulation by Iris p. was 1.01 g Cu and 0.69 g Cd kg^?1 of fresh plant at the end of the tests for the solutions of 5.0 mg L^?1 metal concentration, respectively.     

Bulk deposition of metals in Tulsa,Oklahoma

Samples of bulk precipitation were collected at six sites adjacent to the Arkansas River in Tulsa, Oklahoma for a period of 11 mo (June 1980 to April 1981). Collected samples were analyzed by flameless atomic absorbtion spectrophotometry for Cd, Cr, Ni, Pb, and Zn. The data were reported as volume-weighted metal concentrations (μg L¹) and metal deposition (mg m^?2 yr^?1). Metal deposition was fairly constant from site to site and appeared to be proportional to the amount of precipitation collected. Zinc was by far the largest contributing metal, 497 mg m^?2 yr^?1 followed by Pb. Cr, Ni, and Cd with depositions of 25.5, 25.7, 7.02, and 0.95 mg m^?2 yr^?1 respectively. Concentration data varied greatly over the collection period. Compared to data previously reported in the literature, all of the metal concentrations obtained in this study fall within the ranges observed by other investigators with the exception of Zn which was slightly higher. The average volume-weighted concentrations in μg L^?1 were Cd-2.1, Cr-57.0, Ni-15.6, Pb-56.6, and Zn-1100.     

Hg, Cu, Pb, Cd, and Zn Accumulation in Macrophytes Growing in Tropical Wetlands

The concentrations of Hg, Cu, Pb, Cd, and Zn accumulated by regional macrophytes were investigated in three tropical wetlands in Colombia. The studied wetlands presented different degrees of metal contamination. Cu and Zn presented the highest concentrations in sediment. Metal accumulation by plants differed among species, sites, and tissues. Metals accumulated in macrophytes were mostly accumulated in root tissues, suggesting an exclusion strategy for metal tolerance. An exception was Hg, which was accumulated mainly in leaves. The ranges of mean metal concentrations were 0.035?C0.953 mg g^?1 Hg, 6.5?C250.3 mg g^?1 Cu, 0.059?C0.245 mg g^?1 Pb, 0.004?C0.066 mg g^?1 Cd, and 31.8?363.1 mg g^?1 Zn in roots and 0.033?C0.888 mg g^?1 Hg, 2.2?C70.7 mg g^?1 Cu, 0.005?C0.086 mg g^?1 Pb, 0.001?C0.03 mg g^?1 Cd, and 12.6?C140.4 mg g^?1 Zn in leaves. The scarce correlations registered between metal concentration in sediment and plant tissues indicate that metal concentrations in plants depend on several factors rather than on sediment concentration only. However, when Cu and Zn sediment concentrations increased, these metal concentrations in tissues also increased in Eichhornia crassipes, Ludwigia helminthorriza, and Polygonum punctatum. These species could be proposed as Cu and Zn phytoremediators. Even though macrophytes are important metal accumulators in wetlands, sediment is the main metal compartment due to the fact that its total mass is greater than the corresponding plant biomass in a given area.     

Water Remediation Using Calcium Phosphate Derived From Marine Residues

The processing of natural resources in marine and freshwater ecosystems, directly operated by industries related to maritime sector, contributes annually to several million tons of waste. The reuse and economic recovery of this waste would be very desirable and profitable, either economically or environmentally. In this work, the remediation of hazardous divalent metal ions from aqueous solutions using biological apatites derived from marine residues was addressed. The biological apatite (calcium phosphate particles) was produced by heat treatment of fish bones. Experimental sorption studies of kinetics and equilibrium of the metal ions as well as an evaluation of competitive sorption behavior for lead immobilization were carried out in batch operation mode. The efficiency and mechanisms of lead sorption on two different particle sizes of calcium phosphate from aqueous solution were investigated. The results showed a high adsorption capacity of the biosorbent for Pb²⁺ (above 370 mg/g_ads.), in opposition to Cd²⁺ and Zn²⁺. For the case of low initial concentrations of the metal ion, reducing the biosorbent particles size increases the sorption rate. It was possible to verify that lead immobilization proceeds with a rapid surface complexation of the lead on the sorption sites before partial dissolution of calcium phosphate and formation of pyromorphite-like compounds. By the selectivity experiments, performed using binary systems—Pb/Cd and Pb/Zn—it was evidenced a competitive process between the divalent ions, which leads to a considerable decrease on the adsorption capacity of the adsorbent material for all the metals.     

Cadmium Removal by Two Strains of Desmodesmus pleiomorphus Cells

The capacity of microalgae to accumulate heavy metals has been widely investigated for its potential applications in wastewater (bio)treatment. In this study, the ability of Desmodesmus pleiomorphus (strain L), a wild strain isolated from a polluted environment, to remove Cd from aqueous solutions was studied, by exposing its biomass to several Cd concentrations. Removal from solution reached a maximum of 61.2 mg Cd g^?1 biomass by 1 day, at the highest initial supernatant concentration used (i.e., 5.0 mg Cd L^?1), with most metal being adsorbed onto the cell surface. Metal removal by D. pleiomorphus (strain ACOI 561), a commercially available ecotype, was also assessed for comparative purposes; a removal of 76.4 mg Cd g^?1 biomass was attained by 1 day for the same initial metal concentration. Assays for metal removal using thermally inactivated cells were also performed; the maximum removal extent observed was 47.1 mg Cd g^?1 biomass, at the initial concentration of 5 mg Cd L^?1. In experiments conducted at various pH values, the highest removal was achieved at pH 4.0. Both microalga strains proved their feasibility as biotechnological tools to remove Cd from aqueous solution.     

Trace Element Concentrations in Saltmarsh Soils Strongly Affected by Wastes from Metal Sulphide Mining Areas

Soil and water samples were analysed for trace metals and As in two watercourses and 14 sampling plots in a salt marsh polluted by mine wastes in SE Spain. Groundwater levels, soil pH and Eh were measured ‘in situ’ for a 12-month period in each sampling plot, and total calcium carbonate was also determined. Low concentrations of soluble metals (maximum Mn 1.089 mg L^?1 and maximum Zn 0.553 mg L^?1) were found in the watercourses. However, total metal contents were extremely high in the soils of a zone of the salt marsh (maximum 1,933 mg kg^?1 of Mn, 62,280 mg kg^?1 of Zn, 16,845 mg kg^?1 of Pb, 77 mg kg^?1 of Cd, 418 mg kg^?1 of Cu and 725 mg kg^?1 of As), and soluble metals in the pore water reached 38.7 mg L^?1 for Zn, 3.15 mg L^?1 for Pb, 48.0 mg L^?1 for Mn, 0.61 mg L^?1 for Cd and 0.29 mg L^?1 for As. Variable concentrations with depth indicate a possible re-mobilisation of the metals, which could be related to spatial and temporal variations of water table level, pH and Eh and to the presence of calcium carbonate. A tendency for the Eh to decrease in the warmest months and to increase in the coldest ones was found, especially, in plots that received water with a high content of dissolved organic carbon. Hence, the existence of nutrient effluent-enriched water may modify the physical–chemical conditions of the soil–water system and influence metal mobility.     

Pilot-scale counter-current acid leaching process for Cu,Pb, Sb,and Zn from small-arms shooting range soil

Purpose

The main objective of this study was to evaluate the potential of a counter-current leaching process (CCLP) on 14 cycles with leachate treatment at the pilot scale for Pb, Cu, Sb, and Zn removal from the soil of a Canadian small-arms shooting range.

Materials and methods

The metal concentrations in the contaminated soil were 904?±?112 mg Cu kg^–1, 8,550?±?940 mg Pb kg^–1, 370?±?26 mg Sb kg^–1, and 169?±?14 mg Zn kg^–1. The CCLP includes three acid leaching steps (0.125 M H₂SO₄?+?4 M NaCl, pulp density (PD)?=?10 %, t?=?1 h, T?=?20 °C, total volume?=?20 L). The leachate treatment was performed using metal precipitation with a 5-M NaOH solution. The treated effluent was reused for the next metal leaching steps.

Results and discussion

The average metal removal yields were 80.9?±?2.3 % of Cu, 94.5?±?0.7 % of Pb, 51.1?±?4.8 % of Sb, and 43.9?±?3.9 % of Zn. Compared to a conventional leaching process, the CCLP allows a significant economy of water (24,500 L water per ton of soil), sulfuric acid (133 L H₂SO₄ t^–1), NaCl (6,310 kg NaCl t^–1), and NaOH (225 kg NaOH t^–1). This corresponds to 82 %, 65 %, 90 %, and 75 % of reduction, respectively. The Toxicity Characteristic Leaching Procedure test, which was applied on the remediated soil, demonstrated a large decrease of the lead availability (0.8 mg Pb L^–1) in comparison to the untreated soil (142 mg Pb L^–1). The estimated total cost of this soil remediation process is 267 US$ t^–1.

Conclusions

The CCLP process allows high removal yields for Pb and Cu and a significant reduction in water and chemical consumption. Further work should examine the extraction of Sb from small-arms shooting range.     

Toxicity of uranium to Daphnia magna

The toxicity of U to Daphnia magna was determined in acute and chronic tests. The 48-hr LC₅₀ of U (VI) in Columbia River water was 6 mg L^?1. Acute toxicity diminished by a factor of 7.5 as mean water hardness and alkalinity values increased from 70 mg L^?1. and 57 mg L^?1. to 195 mg L^?1. and 130 mg L^?1. respectively. This effect was most likely the result of complexation of uranyl ion with carbonate ions. D. magna reproduction was suppressed in Columbia River water at U concentrations between 0.5 and 3.5 mg L^?1. Potential hazards of U to aquatic life are discussed as they relate to mining practices.     

Stress Induced by Heavy Metals Cd and Pb in Bean (Phaseolus Vulgaris L.) Grown in Nutrient Solution

The increasing number of cases of soil contamination by heavy metals has affected crop yields, and represents an imminent risk to food. Some of these contaminants, such as cadmium (Cd) and lead (Pb), are very similar to micronutrients, and thus can be absorbed by plants. This study evaluated the translocation of increasing amounts of cadmium and lead and the effects of these metals in the production of beans. Bean plants were grown in nutrient solution Clark and subjected to increasing levels of Cd (from 0 to 0.5 mg L^?1) and Pb (from 0 to 10 mg L^?1). Cadmium concentration of 0.1 mg L^?1 translocated 39.8% to the shoot, and dry matter production was reduced by 45% in shoots and 80% in roots, compared to the control treatment. Lead showed impaired movement in the plant, however the concentration of 1.0 mg L^?1 was observed in 5.7% of metal translocation to the leaves. The concentration of 10 mg L^?1 Pb reduced dry matter production of roots and shoots in 83% and 76%, respectively, compared to the control treatment.     

Catalytic effect of various metal ions on the methylation of mercury in the presence of humic substances

Methylation of Hg²⁺ (Hg(NO₃)₂) in the presence of fulvic acid (FA) and various metal ions has been studied. The concentrations of Hg²⁺ and FA ranged from 5 to 20 mg L^?1 and 171 to 285 mg L^?1 DOC, respectively. The pH range was 3 to 6.5. FA was isolated from an acid brown-water lake by XAD-8 polymeric adsorbent. Methylmercury production in the dark during 2 to 4 days incubation at 30 °C increased with increasing concentrations of Hg²⁺ ion and FA as well as with additions of metal ions (5 to 10 × 10^?5 mole L^?1 The observed catalytic activity of metal ions followed the order Fe³⁺ (Fe²⁺) > Cu²⁺ ≈ Mn²⁺, > Al³⁺. The production of methylmercury had a pH-optimum around 4 to 4.5 at the conditions tested.