Kinetics,biochemical and factorial analysis of chromium uptake in a multi-ion system by Tradescantia pallida (Rose) D. R. Hunt

Discharge of wastewater from electroplating and leather industries is a major concern for the environment due to the presence of toxic Cr⁶⁺ and other ions, such as sulfate, nitrate, phosphate, etc. This study evaluated the potential of Tradescantia pallida, a plant species known for its Cr bioaccumulation, for the simultaneous removal of Cr⁶⁺, SO₄^2?, NO₃^?, and PO₄^3?. The effect of different co-ions on Cr⁶⁺ removal by T. pallida was examined following the Plackett-Burman design of experiments carried out under batch hydroponics conditions. The results revealed a maximum removal of 84% Cr⁶⁺, 87% SO₄^2?, 94% NO₃^? and 100% PO₄^3? without any phytotoxic effect on the plant for an initial Cr⁶⁺ concentration in the range 5–20 mg L^?1. SO₄^2? and NO₃^? enhanced Cr uptake at a high initial Cr concentration (20 mg L^?1), whereas PO₄^3? did not affect Cr uptake both at high and low initial Cr concentrations. The Cr⁶⁺ removal kinetics in the presence of different ions was well described by the pseudo-second-order kinetic model which revealed that both biosorption and bioaccumulation of the metal played an important role in Cr⁶⁺ removal. Increase in the total carbohydrate and protein content of the plant following Cr⁶⁺ and co-ions exposure indicated a good tolerance of the plant toward Cr⁶⁺ toxicity. Furthermore, enhancement in the lipid peroxidation and catalase activity in T. pallida upon Cr⁶⁺ exposure revealed a maximum stress-induced condition in the plant. Overall, this study demonstrated a very good potential of the plant T. pallida for Cr⁶⁺ removal from wastewater even in the presence of co-ions.     

Response Surface Modeling for Co-Remediation of Cr6+ and Pentachlorophenol by Bacillus cereus RMLAU1: Bioreactor Trial and Structural and Functional Characterization by SEM-EDS and FT-IR Analyses

This is the first report on optimization of process variables for simultaneous bioremediation of pentachlorophenol (PCP) and Cr⁶⁺ employing traditional and response surface methodology (RSM). In a one-factor-at-a-time approach, the effect of PCP level exhibited maximum bacterial growth and Cr⁶⁺ (82%) and PCP (91.5%) removal at initial 100 mg PCP L^?1 with simultaneous presence of 200 mg Cr⁶⁺ L^?1 within a 36-h incubation. However, at varied Cr⁶⁺ concentrations, maximum growth and Cr⁶⁺ (97%) and higher PCP (59%) removal were achieved at 50 mg Cr⁶⁺ L^?1 with simultaneous presence of 500 mg PCP L^?1 within a 36-h incubation. The Box-Behnken design suggested 100% Cr⁶⁺ and 95% PCP remediation at 36 h under optimum conditions of 75?mg PCP and 160 mg Cr⁶⁺ L^?1, pH 7.0, and 35°C; Cr⁶⁺ removal was further enhanced to 97% in bioreactor trial. Fourier transform infrared (FT-IR) analysis revealed the likely involvement of hydroxyl, amide, and phosphate groups in Cr³⁺ binding. Scanning electron microscopy and energy-dispersive x-ray spectroscopy (SEM-EDS) showed biosorption of reduced chromium on bacterial cell surface. This isolate can be employed for eco-friendly and effective in situ bioremediation of Cr⁶⁺ and PCP simultaneously.     

In Situ Cultivation of Subsurface Microorganisms in a Deep Mafic Sill: Implications for SLiMEs

An in situ culturing device was incubated within a flowing borehole in a mafic sill at 1.474 km depth in Evander Au mine, South Africa. The device was designed to enrich methanogenic, Fe^{3 +}-reducing and SO₄ ^{2 ?}-reducing microorganisms using acetate, formate, methanol, Fe^{3 +}-citrate and SO₄ ^{2 ?} enriched agar and sand cartridges. At the end of the 33 day incubation geochemical analyses detected elevated H₂, acetate, CH₄ and Fe concentrations and depleted SO₄ ^{2 ?} concentrations. 16S rDNA sequences and PLFA analyses revealed that the microbial community composition of the substrate-bearing cartridges were distinct from that of the original borehole water and the non-substrate-bearing control cartridge. 16S rDNA and dissimilatory sulfite reductase, dsrAB, gene sequences indicated the device successfully targeted SO₄ ^{2 ?} reducing bacteria (SRB), which were not detected in the original borehole water. 16S rDNA sequences also revealed a shift in the microbial community from one relying on H₂ based methanogenesis to one suggestive of H₂ based acetogenesis supporting aceticlastic methanogenesis and SO₄ ^{2 ?} reduction compatible with the subsurface lithoautotrophic hypothesis.     

A Counter-Current Acid Leaching Process for the Remediation of Contaminated Soils from a Small-Arms Shooting Range

The objective of this research was to use a counter-current leaching process (CCLP) with leachate treatment to develop a remediation process for contaminated soils at a small-arms shooting range (SASR). The soil contaminant concentrations were 245 mg Cu kg^?1, 3,368 mg Pb kg^?1, 73 mg Sb kg^?1, and 177 mg Zn kg^?1. The CCLP includes three acid leaching steps (1M H₂SO₄ + 4M NaCl, t = 1 h, T = 20°C, soil suspension = 100 g L^?1), followed by one water rinsing step (1 h). Seven counter-current remediation cycles were completed, and the average resulting metal removals were 93.2 ± 3.5% of Cu, 91.5 ± 5.7% of Pb, 82.2 ± 10.9% of Sb, and 30.0 ± 11.4% of Zn. The metal leaching performances decreased with the number of completed cycles. Soil treated with the CCLP with leachate treatment process met the USEPA threshold criteria of 5 mg Pb L^?1 in the TCLP leachate. The CCLP allows a decrease of the water use by 32.9 m³ t^?1 and the chemicals’ consumption by approximately 2,650 kg H₂SO₄, 6,014 kg NaCl, and 1,150 kg NaOH per ton of treated soil, in comparison to standard leaching processes. This corresponds to 78%, 69%, 83%, and 67% of reduction, respectively.     

Biosorption of heavy metal ions by brown seaweeds from southern coast of Korea

Heavy metal ions (Pb²⁺, Cd²⁺, Mn²⁺, Cu²⁺, and Cr₂O₇ ^2?) were biosorbed by brown seaweeds (Hizikia fusiformis, Laminaria japonica, and Undaria pinnatifida) collected from the southern coast of South Korea. The biosorption of heavy metal ions was pH-dependent showing a minimum absorption at pH 2 and a maximum biosorption at pH 4 (Pb²⁺, Cd²⁺, Mn²⁺, and Cr₂O₇ ^2?) or pH 6 (Cu²⁺). Biosorption increased most noticeably for pH changes from 2 to 3. In the latter pH range, biosorption increased, because a higher pH decreased the electrostatic repulsion between metal ions and functional groups on the seaweed. In the pH range of 2 ～ 4, biosorption of negatively-charged chromium species (Cr₂O₇ ^?2) followed the pattern of positively-charged metal ions (Pb²⁺, Cd²⁺, Mn²⁺, and Cu²⁺). This suggests that the most prevalent chromium species were positively-charged Cr³⁺, reduced from Cr⁶⁺ in Cr₂O₇ ^?2. Whereas positively-charged heavy metal ions (Pb²⁺, Cd²⁺, Mn²⁺, and Cu²⁺) reached a plateau after the maximum level, biosorption of chromium ions decreased noticeably between pH 5 and 8. Kinetic data showed that biosorption by brown seaweed occurred rapidly during the first 10 min, and most of the heavy metals were bound to the seaweed within 30 min. Equilibrium adsorption data for a lead ion could fit well in the Langmuir and Freundlich isotherm models with regression coefficients (R ²) between 0.93 and 0.98.     

Cr6+ bioremediation efficiency of Oscillatoria laete-virens (Crouan & Crouan) Gomont and Oscillatoria trichoides Szafer: kinetics and equilibrium study

Two species of cyanobacteria, Oscillatoria laete-virens (Crouan & Crouan) Gomont and Oscillatoria trichoides Szafer, were isolated from a polluted environment and studied for their Cr⁶⁺ removal efficiency from aqueous solutions. The parameters studied included the solution pH, contact time, initial concentration of Cr⁶⁺ and culture density. Living biomass is more efficient than dead biomass in Cr⁶⁺ removal. Removal by living biomass involves bioreduction and biosorption. Below pH 3.1, bioreduction is favored and biosorption is dominant at higher pH. The highest removal through biosorption for living biomass was achieved between pH 5 and 5.9 and for dead biomass at pH 2. The maximum removal was on the tenth day of exposure for both the species. Cr⁶⁺ removal increased from 0.2 to 0.4 g L^?1 of culture biomass with a decrease with further increase in biomass. Increased Cr⁶⁺ concentration decreases growth of both the species over time. Both species tolerate a concentration as high as 30 mg L^?1 Cr⁶⁺. There was no evidence of bioreduction in the case of dead biomass. Living biomass of O. laete-virens followed both Langmuir and Freundlich models with maximum sorptive capacity (q _max) of 21.88 mg g^?1. The results of dead biomass were well fitted only to Langmuir isotherm. O. trichoides living biomass did not follow either of the isotherms, but removed the metal to a maximum extent of 38.7mg g^?1. The removal was better described by Freundlich isotherm in case of dead biomass. The pseudo-first-order model describes the kinetics better than the pseudo-second-order model in the case of living biomass. Participation of carboxylic, carbonyl, and amino groups in Cr⁶⁺ removal was confirmed by FTIR analysis. Both species seem to be promising biosorbents for Cr⁶⁺.     

Cr6+对人工湿地薏苡光合特性和微量元素吸收的影响

为深入了解Cr⁶⁺胁迫对人工湿地植物薏苡光合特性和微量元素吸收的影响,该文通过构筑微型垂直流薏苡(Coix lacryma-jobi)人工湿地,采用1/2 Hoagland’s营养液配制的含0、5、20、40 mg·L^-1 Cr⁶⁺废水为灌溉用水,研究铬胁迫对人工湿地植物生长、光合特性、抗氧化酶活性和微量元素吸收等的影响。结果表明：(1)低浓度(5 mg·L^-1)Cr⁶⁺对薏苡的株高、茎粗和分蘖影响不显著,高浓度(20、40 mg·L^-1)Cr⁶⁺则显著抑制薏苡的生长。(2)低浓度Cr⁶⁺处理下,薏苡叶片净光合速率(P_n)、气孔导度(G_s)和蒸腾速率(T_r)有不同程度的提高,提高幅度分别为6.8%～54.8%、13.0%～40.3%和9.1%～36.4%。高浓度Cr⁶⁺处理下,叶片P_n、G_s     

Soil properties and turf growth on a sandy soil amended with fly ash

Field lysimeters of a sandy soil were amended to a depth of 100 mm with four rates (0, 5, 10 and 20%, wt/wt) of fly ash, and effects on soil water content, nutrient leaching, turf growth and nutrition, and uptake of trace elements by turf were assessed. Measurements were taken for 70 days for lysimeters either planted with rhizomes of Cynodon dactylon(L.) Pers., cv. `Wintergreen', or left bare. When irrigated daily, soil water content increased progressively with increasing rates of fly ash and leachate volumes were decreased by 17–52% for lysimeters containing fly ash amended soil. Fertiliser was applied equivalent to 28.4 g N m<sup>–2</sup> and 10.3 g P m<sup>–2</sup> for the entire 70 days (including pre-plant application). Macronutrient concentrations in leaf tissue were within levels regarded as sufficient. Total dry mass (root plus shoot) decreased when fertiliser application rates were reduced by 25%, irrespective of fly ash treatment. In `bare' lysimeters containing fly ash amended soil, cumulative leaching of NO₃ ^–, NH₄ ⁺and P were 0.32–0.88 of the values in non-amended soil. When planted with turf, leaching of those nutrients was minimal (equivalent to 3% of total N applied) and leaching loses did not differ among fly ash rates. Extractable soil P levels were increased 2.5–4.5-fold in the fly ash amended zone, compared with non-amended soil. Root mass in the top 100 mm was 1.2–1.5-fold larger for turf in fly ash amended soil, compared to non-amended soil. The Se concentrations were higher in leaf tissue grown in fly ash amended soil (being at most 0.63 g g^–1), but there was no effect of fly ash amended soil on As, Ba, B, Cd, Co, Cr, Cu, Pb, Hg, Mn, Ni, Ag or Zn in leaf tissues. Thus, fly ash amendment may be a suitable management option for turf culture on sandy soils, since fly ash improved soil water holding capacity and root growth in the amended zone.     

Insolubility of Cr2O3 in Bioaccessibility Tests Points to Requirement for a New Human Oral Reference Dose for Trivalent Chromium

Bioaccessibility measurements have the potential to improve the accuracy of risk assessments and reduce the potential costs of remediation when they reveal that the solubility of chemicals in a matrix (e.g., soil) differs markedly from that in the critical toxicity study (i.e., the key study from which a toxicological or toxicity reference value is derived). We aimed to apply this approach to a brownfield site contaminated with chromium, and found that the speciation was Cr^III, using a combination of alkaline digestion/diphenylcarbazide complexation and X-ray absorption near edge structure analysis. The bioaccessibility of Cr₂O₃, the compound on which a reference dose for Cr^III is based, was substantially lower (<0.1%) than that of the Cr^III in the soils, which was a maximum of 9%, giving relative bioaccessibility values of 13,000% in soil. This shows that the reference dose is based on essentially an insoluble compound, and thus we suggest that other compounds be considered for toxicity testing and derivation of reference dose. Two possibilities are CrCl₃·6H₂O and KCr(SO₄)₂·12H₂O, which have been used for derivation of ecological toxicity reference values and are soluble at a range of dosing levels in our bioaccessibility tests.     

Development of a Laboratory-Scale Leaching Plant for Metal Extraction from Fly Ash by Thiobacillus Strains

Semicontinuous biohydrometallurgical processing of fly ash from municipal waste incineration was performed in a laboratory-scale leaching plant (LSLP) by using a mixed culture of Thiobacillus thiooxidans and Thiobacillus ferrooxidans. The LSLP consisted of three serially connected reaction vessels, reservoirs for a fly ash suspension and a bacterial stock culture, and a vacuum filter unit. The LSLP was operated with an ash concentration of 50 g liter⁻¹, and the mean residence time was 6 days (2 days in each reaction vessel). The leaching efficiencies (expressed as percentages of the amounts applied) obtained for the economically most interesting metal, Zn, were up to 81%, and the leaching efficiencies for Al were up to 52%. Highly toxic Cd was completely solubilized (100%), and the leaching efficiencies for Cu, Ni, and Cr were 89, 64, and 12%, respectively. The role of T. ferrooxidans in metal mobilization was examined in a series of shake flask experiments. The release of copper present in the fly ash as chalcocite (Cu₂S) or cuprite (Cu₂O) was dependent on the metabolic activity of T. ferrooxidans, whereas other metals, such as Al, Cd, Cr, Ni, and Zn, were solubilized by biotically formed sulfuric acid. Chemical leaching with 5 N H₂SO₄ resulted in significantly increased solubilization only for Zn. The LSLP developed in this study is a promising first step toward a pilot plant with a high capacity to detoxify fly ash for reuse for construction purposes and economical recovery of valuable metals.     

Ecophysiological responses of water hyacinth exposed to Cr3+ and Cr6+

Due to its wide industrial use, chromium (Cr) is considered a serious environmental pollutant of aquatic bodies. In order to investigate the ecophysiological responses of water hyacinth [Eichhornia crassipes (Mart.) Solms] to Cr treatment, plants were exposed to 1 and 10 mM Cr₂O₃ (Cr³⁺) and K₂Cr₂O₇ (Cr⁶⁺) concentrations for two or 4 days in a hydroponic system. Plants exposed to the higher concentration of Cr⁶⁺ for 4 days did not survive, whereas a 2 days treatment with 1 mM Cr³⁺ apparently stimulated growth. Analysis of Cr uptake indicated that most of the Cr accumulated in the roots, but some was also translocated and accumulated in the leaves. However, in plants exposed to Cr⁶⁺ (1 mM), a higher translocation of Cr from roots to shoots was observed. It is possible that the conversion from Cr⁶⁺ to Cr³⁺, which immobilizes Cr in roots, was not total due to the presence of Cr⁶⁺, causing deleterious effects on gas exchange, chlorophyll a fluorescence and photosynthetic pigment contents. Chlorophyll a was more sensitive to Cr than chlorophyll b. Cr³⁺ was shown to be less toxic than Cr⁶⁺ and, in some cases even increased photosynthesis and chlorophyll content. This result indicated that the F_v/F₀ ratio was more effective than the F_v/F_m ratio in monitoring the development of stress by Cr⁶⁺. There was a linear relationship between qP and F_v/F_m. No statistical differences were observed in NPQ and chlorophyll a/b ratio, but there was a tendency to decrease these values with Cr exposure. This suggests that there were alterations in thylakoid stacking, which might explain the data obtained for gas exchanges and other chlorophyll a fluorescence parameters.     

Removal of Cr6+ from groundwater using zero-valence iron in the laboratory

Abstract

In this paper, we describe a series of laboratory experiments which quantify the rate of Cr⁶⁺ reduction by Fe⁰. The main goal of these experiments was to determine the removal efficiency of Cr⁶⁺ by iron. The results indicate that Fe⁰ reduces Cr⁶⁺ to Cr³⁺ under alkaline and slightly acidic conditions. The removal efficiency rises with an increase of the initial concentration of Cr⁶⁺ (1 mg/L to 10 mg/L) when the quantity of Fe⁰ is stable. The removal efficiency increases as the quantity of Fe⁰ is raised when other conditions are constant. The removal efficiency would not be affected by other inorganic ions unless they were present at very high concentrations. When the initial concentration Cr⁶⁺ is 10mg/L and pH is 6.5–7.7, the final concentration of Cr⁶⁺ in effluent is less than 0.05 mg/L and the total Fe is less than 0.3 mg/L in effluent.     

Nitrogen pollution of leachate at a sea-based solid waste disposal site and its nitrification treatment by immobilized acclimated nitrifying sludge

It was found that changes in the nitrogen concentration of leachate from the Osaka North Port sea based disposal site were closely related to the way in which dumping was carried out. The nitrogen concentration of the leachate was low due to the low nitrogen content and slow nitrogen dissolution rate of materials dumped previously in the landfill. The dumping of incinerator ash, noncombustible garbage, waterworks sludge and incinerated ash from sewage sludge were followed, and it was found that they caused a sharp increase in nitrogen concentration in the leachate. The main nitrogen form of leachate was NH₄-N, and its concentration reached 50 mg/l after 6 years of landfilling. Successful nitrification treatment of leachate (more than 80% nitrification) was possible by using polyvinyl alcohol immobilized acclimated marine nitrifying sludge with an NH₄-N loading rate of 2.9 mg-NH₄-N/g-pellets/d. Low NO₂-N was detected throughout the continuous nitrification experiments, so the rate limiting step in the nitrification treatment was revealed to be a nitrification step (NH₄⁺→NO₂⁻). The addition of inorganic carbon to the test leachate enabled us to perform nitrification treatment even with a high NH₄-N loading rate. Dolomite limestone was shown experimentally to be able to replace inorganic chemicals.     

Screening Perennial Warm-Season Bioenergy Crops as an Alternative for Phytoremediation of Excess Soil P

A recent alternative strategy to reduce environmental problems associated with P transport from agricultural soils is the use of bioenergy crops to remediate excess soil P. In addition to the positive impacts associated with P mitigation, harvested biomass used as a renewable energy source can also offset the cost associated with plant-based P remediation strategies. The objective of this study was to identify potential crop species that can be used for remediation of soil P and as a cellulosic feedstock for production of renewable energy in South Florida. Fifteen crop entries were investigated for their potential to remove P from a P-enriched soil. Dry matter (DM) yield varied among crop species with greatest yield observed for elephantgrass (Pennisetum purpureum Schum.) and sugarcane (Saccharum spp.) (43 and 39 Mg?ha^?1 year^?1, respectively). Similarly, greater P removal rates were observed for elephantgrass (up to 126 kg?P?ha^?1 year^?1 in 2008) followed by sugarcane (62 kg?P?ha^?1 year^?1 in 2008). Although there was no effect (P?=?0.45) of crop species on P reduction in the soil, soil P concentrations decreased linearly during the 3-year study. Because of its relatively greater DM yield and P removal rates, elephantgrass was shown to be a good candidate for remediation of excess soil P in South Florida Spodosols.     

Co-remediation of pentachlorophenol and Cr6+ by free and immobilized cells of native Bacillus cereus isolate: Spectrometric characterization of PCP dechlorination products,bioreactor trial and chromate reductase activity

In this study, Bacillus cereus isolate efficiently remediated 57% PCP and 74% Cr⁶⁺ simultaneously with uptake rate of 0.65 mg Cr⁶⁺ g^?1 biomass h^?1 at initial 200 mg Cr⁶⁺ and 500 mg PCP l^?1 concentration under optimized 0.4% glucose, 0.2% NH₄Cl, pH 7.0, 35 °C, 1.0% inoculum during 60 h incubation. Optimization of agitation (100 rpm) and aeration (0.6 vvm) in bioreactor further enhanced PCP dechlorination by ～5.0% and Cr⁶⁺ removal 7.5%. Presence of other heavy metals variedly affected bioremediation of both the toxicants. Maximum and minimum inhibition was exhibited by mercury and lead, respectively. Out of 74% Cr⁶⁺ remediated, 90% reduced to Cr³⁺, of which 52.8% was associated with cell biomass and 37.2% with culture supernatant. Maximum chromate reductase activity was evident in culture supernatant followed by cytosolic fraction and cell debris. A direct correlation existed between chromate reductase activity and reduced Cr³⁺ in different cell fractions. Among matrices, alginate was most suitable for biomass immobilization, which enhanced Cr⁶⁺ removal by 20.2% compared to free cells at 36 h. Gas chromatography and mass spectrometry detected 2,3,4,6-tetrachlorophenol, 2,4,6-trichlorophenol, 2,6-dichlorophenol and 6-chlorohydroxyquinol as PCP dechlorination products. Our promising strain can be efficiently employed for simultaneous bioremediation of PCP and Cr⁶⁺ under wide environmental conditions.     

Development of recycled aggregate bio-carrier with sulfate reducing bacteria for the elimination of heavy metals from seawater

In this study, we fabricated a novel recycled aggregate (RA) bio-carrier with sulfate-reducing bacteria (SRB) for the effective removal of the heavy metals Zn²⁺, Ni²⁺, and Cr⁶⁺ from contaminated seawater. By using only RA carriers, Zn²⁺, Ni²⁺, and Cr⁶⁺ could be removed up to 35.6, 11.0, and 61.3% and SRB-immobilized RA biocarriers could effectively lead to the removal of Zn²⁺, Ni²⁺, and Cr⁶⁺ up to 100.0, 98.0, and 87.8% for 100 ppm concentration of the heavy metals at 37°C, respectively. These results indicate that recycled aggregate bio-carriers with SRB hold great potential for use in the removal of cationic heavy metal species from marine environment.     

Contrasting responses of two Sitka spruce forest plots in Ireland to reductions in sulphur emissions: results of 20 years of monitoring

Long-term trends in ion concentrations of bulk precipitation, throughfall, forest floor leachate (humus water) and shallow and deep soil water were assessed at two Sitka spruce (Picea sitchensis) stands—one on an Atlantic peat bog in the west of Ireland (Cloosh), the other on the east coast on a peaty podzol (Roundwood). Deposition at Cloosh was dominated by marine ions (sodium, [Na⁺], chloride [Cl^?], and magnesium [Mg²⁺]), whereas bulk precipitation and throughfall at Roundwood was characterized by inputs of non-marine sulphate (nmSO₄ ^2?), acidity and inorganic nitrogen (NH₄ ⁺, NO₃ ^?). Significant declines in concentrations of nmSO₄ ^2? and acidity in bulk precipitation and throughfall were observed at both sites. The decline in throughfall nmSO₄ ^2? was significantly related to reductions in European sulphur dioxide (SO₂) emissions. At Roundwood, SO₄ ^2? declined significantly in humus, shallow and deep soil water. In deep soil water this was accompanied by a long-term increase in pH and a reduction in total aluminum (Al_tot). The recovery from acidification was delayed by high concentrations of NO₃ ^?, which strongly influenced acidity and Al_tot concentrations. At Cloosh, there was a significant decline in SO₄ ^2? in humus water but long-term trends were not evident in shallow or deep soil water; SO₄ ^2? concentrations at these depths fluctuated in response to drought-events. Marine ions strongly influenced soil water chemistry at both sites; at Cloosh soil water acidity was strongly related to Na⁺ and Cl^?, while at Roundwood, Na⁺, Cl^? and Mg²⁺ influenced Al_tot concentrations. Dissolved organic carbon increased significantly in humus and soil water at Roundwood, where it was associated with declining acidity. Soil water at both sites was influenced by a combination of anthropogenic sulphur (S) and nitrogen (N) deposition, drought and sea-salt events. The study highlights the value of long-term monitoring in assessing the response of forest soils to S and N deposition against a background of climate influences on soil water through drought and sea-salt events.     

The effect of selenium on sulfur uptake by barley and rice

Because of their chemical and physical similarities, plant uptake of S and Se are closely related. Barley (Hordeum vulgare L.) and rice (Oryza sativa L.) were grown in greenhouse solution culture to examine the synergistic interactions between SO₄ and Se⁶⁺ in plant uptake. In the presence of low concentrations of solution SO₄, shoot and root yields were decreased with additions of Se⁶⁺. However, when SO₄ was present in elevated concentrations, no Se-induced yield reduction occurred. A synergistic interaction between SO₄ and Se⁶⁺ caused an increase in the shoot S concentrations with increasing concentrations of Se⁶⁺ at low SO₄ solution concentrations. At elevated SO₄ concentrations, no synergism was osberved. Selenium had a lesser effect on the S concentration in plant roots.     

Seasonal and spatial patterns of S,Ca, and N dynamics of a Northern Hardwood forest ecosystem

Seasonal dynamics of S, Ca and N were examined at the Huntington Forest, a northern hardwood ecosystem in the central Adirondacks of New York for a period of 34 months (1985–1988). Solute concentrations and fluxes in bulk precipitation, throughfall (TF) and leachates from the forest floor, E horizon and B horizon were quantified. Both above and below-ground elemental fluxes mediated by vegetation (e.g. uptake, litter inputs, and fine roots production) were also determined. The roles of abiotic and biotic processes were ascertained based on both changes in solute concentrations through the strata of the ecosystem as well as differences between dormant and growing seasons. Concentrations of SO₄ ²⁻, NO₃ ⁻, NH₄ ⁺ and Ca²⁺ were greater in TF than precipitation. Forest floor leachates had greater concentrations of SO₄ ²⁻, NO₃ ⁻ + NH₄ ⁺ and Ca²⁺ (9, 6 and 77 μeq L⁻¹, respectively) than TF. There were differences in concentrations of ions in leachates from the forest floor between the dormant and growing seasons presumably due to vegetation uptake and microbial immobilization. Concentrations and fluxes of NO₃ ⁻ and NH; were greatest in early spring followed by a rapid decline which coincided with a demand for N by vegetation in late spring. Vegetation uptake (44.7 kg N ha⁻¹ yr⁻¹ ) could account for the low leaching rates of N0₃ ⁻. Within the mineral soil, changes with soil depth and the absence of seasonal patterns suggest that cation exchange (Ca⁺) or anion sorption (SO₄ ²⁻) are primarily responsible for regulating solute concentrations. The increase in SO₄ ²⁻ concentration after leachates passed through the mineral soil may be attributed to desorption of sulfate that was adsorbed during an earlier period when SO₄ ²⁻ concentrations would have been greater due to elevated S inputs.     

Reduction of pentaamminenitrocobalt(III) by hexaaquachromium(II) ion. Reinvestigation of the mechanism

Products of the reduction of [CoNO₂(NH₃)₅]²⁺ by Cr²⁺ were separated and identified under the conditions of [Cr²⁺]₀/[Co(IlI)]₀⩽3 and 0.02 M ⩽[H⁺] ⩽ 0.75 M. The product distribution was dependent on both [Cr²⁺]_o and [H⁺]. The following mechanism is proposed: [CoNO₂(NH₃)₅]²⁺ + Cr²⁺→Co²⁺ + [CrONO(H₂O)₅]²⁺ (i) [CrONO(H₂O)₅]²⁺ + H⁺→[Cr(H₂O)₆]³⁺ + HNO₂ (ii) [CrONO(H₂O)₅]²⁺ + Cr²⁺→Cr(IV) + [CrNO(H₂O)₅]²⁺ (iii) Cr(IV) + Cr²⁺→[(H₂O)₄Cr(OH)₂Cr(H₂O)₄]⁴⁺ (iv) HNO₂ + 2Cr²⁺→[Cr(H₂O)₆]³⁺ + [CrNO(H₂O)₅]²⁺ (v)