Induced plant uptake and transport of mercury in the presence of sulphur-containing ligands and humic acid

The induced accumulation of mercury (Hg) by plants was investigated for the species Phaseolus vulgaris (Bush bean), Brassica juncea (Indian mustard), and Vicia villosa (Hairy vetch). All plants were grown in modified Hg-contaminated mine tailings and were treated with sulphur-containing ligands to induce Hg accumulation. The effects of varied substrate Hg concentration and humic acid (HA) level on the induced plant-Hg accumulation for B. juncea were examined. Thiosulphate salts (ammonium and sodium) mobilised Hg in the substrates and caused an increase in the Hg concentration of roots and shoots of all tested plant species. Root Hg accumulation was positively correlated to extractable Hg for (NH4)2S2O3-treated B. juncea plants grown in HA-amended substrates. However, shoot Hg translocation for this species was inhibited at 1.25 g HA kg(-1) of substrate. Mercury-thiosulphate complexes could be translocated and accumulated in the upper parts of the plants up to 25 times the Hg concentration in the substrate. We conclude that shoot Hg accumulation in the presence of thiosulphate salts is dependent upon plant species characteristics (e.g. root surface area) and humic acid content.     

Phytofiltration of mercury-contaminated water: Volatilisation and plant-accumulation aspects

Phytofiltration may be a cost-effective approach for treating Hg-contaminated wastewater. We investigated the removal of Hg from solutions by Indian mustard [Brassica juncea (L.) Czern.] grown in hydroponic conditions with solutions containing Hg concentrations from 0 to 10 mg/L. Plants were enclosed in gastight volatilisation chambers to assess the effect of Hg concentrations on plant transpiration, accumulation and volatilisation. We also determined the speciation and site of origin of volatilised Hg. Solution Hg concentrations of 5 and 10 mg/L detrimentally affected transpiration. Roots concentrated Hg 100–270 times (on a dry weight basis) above initial solution concentrations. The plants translocated little Hg to the shoots, which accounted for just 0.7–2% of the total Hg in the plants. Volatilisation from planted vessels increased linearly as a function of Hg concentrations in solutions. Most Hg volatilisation occurred from the roots. Volatilised Hg was predominantly in the Hg(0) vapour form. Volatilisation was dependant on root uptake and absorption of Hg from the ambient solution. Production of Hg(0) vapour in the solutions may result from the activity of root-associated algae and Hg-resistant bacteria. Phytofiltration effectively removed up to 95% of Hg from the contaminated solutions by both volatilisation and plant accumulation. However, Hg(0) vapours released from living roots may have unforeseen environmental effects.     

Difference in bonding behaviour of azide and thiocyanate to Hg(II)-azoimidazoles

Mercury(II) acetate reacts with the 1-alkyl-2-(arylazo)imidazoles [RaaiR′ where R = H (a), Me (b); R′ = Me (1/3/5), Et (2/4/6)] and sodium azide in methanol solution to afford azido bridged polymeric complexes [Hg(RaaiR′)(N₃)₂]_n (3/4). On setting up similar reaction condition, the reaction of Hg(OAc)₂ with RaaiR′ and NH₄SCN has yielded, instead of polymer, an ion-pair [Hg(RaaiR′)₄][Hg(SCN)₄] (5/6). The complexes are characterised by elemental analysis, IR, UV-Vis, ¹H NMR spectral data and single-crystal X-ray structures of [Hg(HaaiEt)(μ-1,1-N₃)₂]_n (4a) and [Hg(HaaiEt)₄][Hg(SCN)₄] (6a). The complex 4a is a coordination polymer with end-on (μ-1,1) azido bridge and 6a has tetrahedral structure.     

Effect of lime, dicyandiamide and soil water content on ammonia and nitrous oxide emissions following application of liquid hog manure to a marshland soil

The loss of nitrogen (N) from field-applied animal manure through ammonia (NH₃) volatilisation and nitrous oxide (N₂O) emission is of major environmental concern. Both lime and dicyandiamide (DCD) have been suggested as amendments that can mitigate N₂O emissions, but simultaneously increase the risk of NH₃ volatilisation. This study evaluated the impact of lime and DCD on NH₃ and N₂O emissions following application of liquid hog manure. Hydrated lime (Ca(OH)₂) was added to an acidic soil to achieve three pH levels (4.7, 6.3 and 7.4). Soil samples (100 g) were then placed in 500 ml screw-top Mason-jars and de-ionised water was added to bring the samples to 50, 70 and 90% water-filled pore space (WFPS). Slurry was applied at a rate equivalent to 116,000 l ha⁻¹, while DCD was applied at 30% of the NH₄-N rate applied. Jars were sealed and incubated at 21°C for 21 d. Ammonia volatilisation was quantified using boric acid traps, while N₂O gas concentration was analysed using gas chromatography. Dicyandiamide had no effect (P>0.05) on either NH₃ or N₂O emissions. Both NH₃ and N₂O emissions increased (P<0.05) as WFPS increased, with emissions ranging from 0.9 to 1.4 kg NH₃-N ha⁻¹ and 123 to 353 g N₂O-N ha⁻¹, respectively. Liming decreased (P<0.01) N₂O emissions from 547 to 46 g N₂O-N ha⁻¹, but increased (p<0.01) NH₃ volatilisation from 0.36 to 1.92 kg NH₃-N ha⁻¹. Results suggest that liming to a pH ≥6.3 can reduce N₂O emissions, however, this reduction will be accompanied by a substantial loss of NH₃. Section Editor: H. Lambers     

Mercury translocation in and evaporation from soil. II. Evaporation of mercury from podzolized soil profiles treated with HgCl2 and CH3HgCl

Mercury evaporation from soil columns of an iron humus podzol treated with various amounts of HgCl₂ and CH₃HgCl was measured over 3500 h. The effects of rain acidity, rain duration, and rain intensity were investigated. Hg evaporation from CH₃HgCl‐treated soil columns seems to be a biologically determined process. Hg evaporation from HgO₂‐treated soil probably is mainly an abiotic process, following a pseudo first‐order reaction with rapidly decreasing evaporation rate due to a decreasing amount of available Hg. The added Hg compounds were transformed to highly volatile Hg⁰ and/or (CH₃)₂Hg. The Hg evaporation rate decreased with increasing rain acidity, which may cause accumulation of Hg in the soil. No effects of rain duration and rain intensity were found.     

Dissociation of Human αB-Crystallin Aggregates by Thiocyanate Is Structurally and Functionally Reversible

Conformational modifications and changes in the aggregation state of human αB-crystallin were investigated at different concentrations of SDS, KBr, urea, and NH₄SCN and at different temperatures. Intrinsic fluorescence measurements indicated complete and reversible unfolding of the protein at 2 M NH₄SCN, whereas the concentration of urea required for complete and irreversible unfolding was 6 M. Gel permeation chromatography indicated almost complete dissociation of the micelle-like aggregate of αB-crystallin in 2 M NH₄SCN, but only partial dissociation into large-sized aggregates in 6 M urea. Thiocyanate-treated αB-crystallin recovered its chaperone-like activity upon dilution of the dissociating agent, whereas the urea-treated protein did not.     

Addition compounds of bis(trifluoromethyl)mercury with tetraphenylphosphonium and tetraphenylarsonium halides and thiocyanates

Addition compounds of Hg(CF₃)₂ with [Ph₄P]X and [Ph₄As]X in the 1:1 ratio for X = Cl, Br, I as well as in the 1:2 ratio for X = SCN, were isolated from aquaeous solution and identified by elemental analysis and infrared spectroscopy. Molar conductance of the thiocyanate compounds in nitrobenzene solution points to its complex-salt nature defined as [Ph₄P]₂[Hg(CF₃)₂(SCN)₂] and [Ph₄As]₂[Hg(CF₃)₂-(SCN)₂], but not for the halide compounds. However, in the monoclinic crystals of the chloride ccompound, as shown by X-ray diffractometry, pairs of [Hg(CF₃)₂ molecules are bridged over by two chlorides in a centro-symmetrical dimer with the CHgC bond angle of 160.5(8)° and the Hg…Cl bond length of 2.823(3) and 2.837(4) Å. The structure was refined to the R factor of 0.053. When X = CN no addition compounds were obtained, the reaction products were HCF₃ and the complex salts [Ph₄P]₂- [Hg(CN)]₄ and [Ph₄As]₂[Hg(CN)]₄, not described so far.     

Phosphorus Sequestration in Lake Sediment with Iron Mine Tailings

Internal phosphorus loading can lead to eutrophication in lakes when anoxic sediments release bioavailable phosphorus into the water column. In laboratory experiments, iron mine tailings helped to sequester phosphorus in sediment from a eutrophic lake. Phosphorus release from the sediments after extraction with distilled water or 0.02 N H ₂ SO ₄ was significantly reduced when mine tailings were added (1:1 w/w), even when the system was anaerobic (～ 1 mg O ₂ /L). The degree of sequestration was enhanced when glucose (1% w/w) was added to stimulate the growth of microorganisms, suggesting that the process was microbially mediated. We suggest that oxidized iron in the mine tailings served as an electron sink for microbial respiration via dissimilatory Fe³⁺ reduction. The reduced iron released into solution sequestered phosphorus, either as it re-oxidized and formed hydrous ferric oxide complexes containing phosphorus (HFO-P), or through precipitation. Since mine tailings are inexpensive, they may prove useful for preventing phosphorus from entering surface waters, as well as reducing internal phosphorus loading.     

A wood based low-temperature biochar captures NH3-N generated from ruminant urine-N, retaining its bioavailability

Aims

Ammonia (NH₃) can be volatilised from the soil surface following the surface application of nitrogenous fertilisers or ruminant urine deposition. The volatilisation of NH₃ is of agronomic and environmental concern, since NH₃-N is a form of reactive nitrogen. Ammonia adsorption onto biochar has the potential to mitigate NH₃ losses, but to date no studies have examined the potential for reducing NH₃ losses when biochar is present in the soil matrix.

Methods

We used ¹⁵N-enriched urine to examine the effect of incorporating a wood based low-temperature biochar into soil on NH₃ volatilisation. Then, we extracted the urine-treated biochar and compared its potential to act as a plant N source with fresh biochar, while growing ryegrass (Lolium perenne).

Results

The NH₃ volatilisation from ¹⁵N-labelled ruminant urine, applied to soil, was reduced by 45% after incorporating either 15 or 30?t ha^?1 of biochar. When the urine-treated biochar particles were transferred into fresh soil, subsequent plant growth was not affected but the uptake of ¹⁵N in plant tissues increased, indicating that the adsorbed-N was plant available.

Conclusions

Our results show that incorporating biochar into the soil can significantly decrease NH₃ volatilisation from ruminant urine and that the NH₃-N adsorbed onto the biochar is bioavailable. Further studies are now required to assess the temporal dynamics of the N pools involved.     

Temperature and preillumination dependence of delayed fluorescence of spinach chloroplasts

Delayed fluorescence (luminescence) from spinach chloroplasts, induced by short saturating flashes, was studied in the temperature region between 0 and ?40 °C. At these temperatures, in contrast to what is observed at room temperature, luminescence at 40 ms after a flash was strongly dependent, with period four, on the number of preilluminating flashes (given at room temperature, before cooling). At ?35 °C luminescence of chloroplasts preilluminated with two flashes (the optimal preillumination) was about 15 times larger than that of dark-adapted chloroplasts. The intensity of luminescence obtained with preilluminated chloroplasts increased steeply below ?10 °C, presumably partly due to accumulation of reduced acceptor (Q^?), and reached a maximum at ?35 °C.In the presence of 50 mM NH₄Cl the temperature optimum was at ?15 °C; at this temperature luminescence was increased by NH₄Cl; at temperatures below ?20 °C luminescence at 40 ms was decreased by NH₄Cl. At room temperature a strongly enhanced 40-ms luminescence was observed after the third and following flashes. The results indicate that both the S₂ to S₃ and the S₃ to S₄ conversion are affected by NlH₄Cl.Inhibitors of Q^? reoxidation, like 3-(3, 4-dichlorophenyl)-1, 1- dimethylurea, did only slightly affect the preillumination dependence of luminescence at sub-zero temperatures if they were added after the preillumination. This indicates that these substances by themselves do not accelerate the deactivation of S₂ and S₃.     

Allantoin-induced changes of microbial diversity and community in rice soil

The effects of slurry application method and weather conditions after application on ammonia volatilisation are well documented, however, the effect on slurry N recovery in herbage is less evident due to large variability of results. The objective of this field experiment was to determine the recovery of cattle slurry NH₄-N in herbage and soil in the year of application as affected by application method (trailing shoe versus broadcast) and season of application (spring versus summer), using ¹⁵N as a tracer. In 2007 and 2008, ¹⁵N enriched slurry was applied on grassland plots. N recovery in herbage and soil during the year of application was determined. Both spring and trailing shoe application resulted in significantly higher herbage DM yields, N uptake and an increased recovery of ¹⁵NH₄-N in herbage. Additionally, the recovery of slurry ¹⁵NH₄-N in the soil at the end of the growing season was increased. Spring and trailing shoe application reduced the losses of slurry ¹⁵NH₄-N by on average 14 and 18 percentage points, respectively, which corresponded closely to ammonia volatilisation as predicted by the ALFAM model. It was concluded that slurry N recovery in temperate pasture systems can be increased by adjusting the slurry application method or timing.     

Using Earthworms to Assess Hg Distribution and Bioavailability in Gold Mining Soils

Between 1980 and 2000, the municipality of Cachoeira do Piriá, located in Pará State, Brazil, experienced an intense gold rush with approximately 5,000 artisanal miners discharging more than four tonnes of mercury into soils, air and aquatic systems. Mercury is dispersed across an area of approximately 2,100 ha and concentrations in soils and sediments frequently exceed 1,000 μg.kg^?1. The metallic mercury discharged by miners into the environment has the potential to be transformed into a highly toxic form of mercury, methylmercury. A 28-day bioassay with the earthworm Eisenia fetida was used to assess mercury bioavailability in mine tailings, soils, and sediments. Experiments indicated that the highest Hg concentration in earthworms was associated with low-Hg-organic-rich soils collected from densely vegetated areas despite higher mercury concentrations in organic-poor tailings. This indicates that reaction with organic acids is an important pathway for mercury incorporation into food chains. The quick, inexpensive, and simple bioassay also provided a means to evaluate remedial measures (i.e. by capping “hotspots” with local soils). Earthworm experiments indicate that covering “environmental hotspots” (sites with high Hg bioavailability) with local clay-rich sediments is very effective in terms of preventing uptake of mercury from tailings, while organic-rich sediments are relatively ineffective.     

Metal complexes of polycyclic tertiary amines. Part VII. Preparation and crystal structure determination of polymeric hexamethylenetetramine—mercury(II) thiocyanate (12), (CH2)6N4·2Hg(SCN)2

A 1:2 complex of hexamethylenetetramine with mercury(II) thiocyanate, (CH₂)₆N₄·2Hg(SCN)₂, was prepared and shown by X-ray crystallography to be polymeric. The mixed-ligand complex crystallizes in the space group P2₁/m, with a = 6.059(2), b = 19.710(5), c = 7.895(2) Å, β = 105.63(2)°, and Z = 2. The structure was refined to R_F = 0.060 for 1634 observed MoKα diffractometer data. Mercury(II) atoms in a row are linked pairwise by two thiocyanato groups in an end-to-end bridging mode, to give an infinite chain running in the a direction. Two neighboring chains are further laterally connected, successively by bidentate organic ligands which lie on a crystallographic mirror plane. The coordination geometry about Hg(II) is distorted tetragonal pyramidal, the metal atom binding strongly to two S atoms and a tertiary amino N atom (apex), and weakly to two thiocyanato N atoms.     

Dissociation of human alphaB-crystallin aggregates by thiocyanate is structurally and functionally reversible

Conformational modifications and changes in the aggregation state of human B-crystallin were investigated at different concentrations of SDS, KBr, urea, and NH₄SCN and at different temperatures. Intrinsic fluorescence measurements indicated complete and reversible unfolding of the protein at 2 M NH₄SCN, whereas the concentration of urea required for complete and irreversible unfolding was 6 M. Gel permeation chromatography indicated almost complete dissociation of the micelle-like aggregate of B-crystallin in 2 M NH₄SCN, but only partial dissociation into large-sized aggregates in 6 M urea. Thiocyanate-treated B-crystallin recovered its chaperone-like activity upon dilution of the dissociating agent, whereas the urea-treated protein did not.     

Effects of Different Wetland Plant Species on Fresh Unweathered Sulphidic Mine Tailings

Vegetation cover with two Eriophorum species on old unweathered sulphidic mine tailings has earlier been found to reduce the element levels and to prevent production of acidity in drainage water. The present study aims to find out if Carex rostrata Stokes, Eriophorum angustifolium Honck. and Phragmites australis (Cav.) Steud. had other effects on metal and As release in fresh unweathered sulphidic mine tailings, if the species showed different effects and if this depended on plant mechanisms such as O₂, carbonate or organic acid release. Plants were grown in pots with fresh sulphidic mine tailings for 13 months. Arsenic, Cd, Cu, Fe, Pb, Zn, pH, SO ₄ ²⁻ , alkalinity and organic acids in the drainage water as well as metals and As in roots and shoot and O₂ and redox potential in pore water were analysed. The tailings weathered slowly due to high buffering capacity thus no pH decrease was found and therefore similar buffering effects by plants as shown in the previous investigation could not be found. The plants increased the total release of metals and As from the tailings. The release did not depend on carbonate or organic acid release from plants. However, the Fe and As release was due to changed redox potential, caused by O₂ release, and high concentration of Fe and As was found in plant roots. Phragmites australis released more As and Fe but less Cd than E. angustifolium and C. rostrata which make P. australis not suitable for plant establishment on sulphidic mine tailings containing high levels of As. Plants did take up the elements and the lowest translocation of elements to the shoot was found in P. australis while the highest in E. angustifolium.     

Synthesis, crystal structure, magnetic properties and EPR studies of Cu/Hg bimetallic thiocyanato-bridged coordination polymer

The new Cu/Hg bimetallic thiocyanato-bridged coordination polymer, [Cu(2-bzpy)Hg(SCN)₄]_n, has been synthesized and characterized by elemental analysis, magnetic measurements, EPR, and X-ray crystallography. X-ray diffraction analysis reveals that the title complex structure creates 3D network.     

Effect of Methionine Sulfoximine on the Accumulation of Ammonia in C(3) and C(4) Leaves : The Relationship between NH(3) Accumulation and Photorespiratory Activity

Additions of methionine sulfoximine (MSX), an inhibitor of glutamine synthetase (GS), result in an increase in NH₃ in seedling leaves of C₃ (wheat [Triticum aestivum cv. Kolibri] and barley [Hordeum vulgare var Perth]) and C₄ (corn [Zea mays W6A × W182E] and sorghum [Sorghum Vulgare var MK300]) plants. NH₃ accumulation is higher in C₃ (about 17.8 micromoles per gram fresh weight per hour) than in C₄ (about 4.7 micromoles) leaves. Under ideal conditions, when photosynthesis is not yet inhibited by the accumulation of NH₃, the rate of NH₃ accumulation is about 16% of the apparent rate of photosynthesis. A maximum accumulation of NH₃ was elicited by 2.5 millimolar MSX and was essentially independent of the addition of NO₃⁻ during either the growth or experimental period. When O₂ levels in the air were reduced to 2%, MSX resulted in some accumulation of NH₃ (6.0 micromoles per gram fresh weight per hour). At these levels of NH₃, there was no significant inhibition of rates of CO₂ fixation. There was also a minor, but significant, accumulation of NH₃ in corn roots treated with MSX. Inhibitors of photorespiration (isonicotinic hydrazide, 70 millimolar; 2-pyridylhydroxymethanesulfonic acid, 20 millimolar) or transaminase reactions (aminooxyacetate, 1 millimolar) inhibited the accumulation of NH₃ in both C₃ and C₄ leaves. These results support the hypothesis that GS is important in the assimilation of NH₃ in leaves and that the glycine-serine conversion is a major source of that NH₃.     

Effect of calcium ions and anaerobic microbial activity on sedimentation of oil sands tailings

Oil sands tailings ponds contain large volumes (∼10⁸ m³) of fine tailings, originating from bitumen production by surface mining. These sediment rapidly in dilute suspension but then form a network, which consolidates much more slowly. The overall process increases solid content to up to 85% (w/w) and is referred to as tailings densification. Addition of gypsum (CaSO₄·2H₂O) to a mixture of sand and fines gives a non-segregating, consolidated tailings slurry in which calcium ions serve as a cross-linking agent. Tailings ponds also harbor active anaerobic microbial consortia, which are thought to contribute to densification through microbial activity, including gas production, creating dewatering channels. To determine the roles of calcium ions and anaerobic microbial activity in tailings sedimentation, we placed 70% (v/v) tailings, containing 77% (w/w) solids, and 30% (v/v) defined medium with various amendments in anaerobic test tubes with an N₂–CO₂ headspace. Following mixing the initial sedimentation rate R of the water-tailings boundary and the final percentage (v/v) of sedimentation S_F were measured. Amendment with 0–20 mM CaCl₂ increased R from 0.006 to up to 0.012 day⁻¹, but decreased S_F from 14–15% to 8–10% (v/v), whereas subsequent amendment with lactate increased both R and S_F. To determine the effect of the type of anaerobic microbial activity, tubes were amended with (i) 20 mM NaCl or 10 mM CaCl₂, (ii) 10 mM Na₂SO₄ or 10 mM CaSO₄, (iii) 20 mM NaNO₃ or 10 mM Ca(NO₃)₂, or (iv) no additions. Following mixing, duplicate tubes were monitored continuously to determine S_F, whereas another set of duplicate tubes was re-mixed once per week to determine R, as well as headspace methane, and the concentrations of sulfate, sulfide, nitrate and nitrite in the supernatant fluid. Microbial activity was boosted after 63 days by adding 20 mM lactate to all tubes. The data for this experiment also indicated that R increased, whereas S_F decreased by addition of calcium ions. Lactate significantly boosted microbial activity with increased methanogenesis, sulfate reduction or nitrate reduction being observed in tubes amended with no electron acceptor, sulfate or nitrate, respectively. Addition of lactate increased S_F by 2–4% (v/v) in most tubes, except in tubes with Ca(NO₃)₂ in which S_F increased by 15% (v/v). The solids content increased from 69 to 78% under these conditions, representing a significant progression to the maximum values observed in tailings ponds over a short period of time.     

Hydrogen peroxide is required for abscisic acid-induced NH4+ accumulation in rice leaves

The role of H₂O₂ in abscisic acid (ABA)-induced NH₄⁺ accumulation in rice leaves was investigated. ABA treatment resulted in an accumulation of NH₄⁺ in rice leaves, which was preceded by a decrease in the activity of glutamine synthetase (GS) and an increase in the specific activities of protease and phenylalanine ammonia-lyase (PAL). GS, PAL, and protease seem to be the enzymes responsible for the accumulation of NH₄⁺ in ABA-treated rice leaves. Dimethylthiourea (DMTU), a chemical trap for H₂O₂, was observed to be effective in inhibiting ABA-induced accumulation of NH₄⁺ in rice leaves. Inhibitors of NADPH oxidase, diphenyleneiodonium chloride (DPI) and imidazole (IMD), and nitric oxide donor (N-tert-butyl-α-phenylnitrone, PBN), which have previously been shown to prevent ABA-induced increase in H₂O₂ contents in rice leaves, inhibited ABA-induced increase in the content of NH₄⁺. Similarly, the changes of enzymes responsible for NH₄⁺ accumulation induced by ABA were observed to be inhibited by DMTU, DPI, IMD, and PBN. Exogenous application of H₂O₂ was found to increase NH₄⁺ content, decrease GS activity, and increase protease and PAL-specific activities in rice leaves. Our results suggest that H₂O₂ is involved in ABA-induced NH₄⁺ accumulation in rice leaves.