Element mobility and partitioning along a soil acidity gradient in central Ontario forests, Canada

The potential environmental risk posed by metals in forest soils is typically evaluated by modeling metal mobility using soil-solution partitioning coefficients (K(d)), although such information is generally restricted to a few well-studied metals. Soil-solution partitioning coefficients were determined for 17 mineral elements (Al, As, Be, Ba, Ca, Cr, Cu, Fe, Ga, K, Li, Mg, Rb, Sr, Tl, U and V) in A-horizon (0-5 cm) soil at 46 forested sites that border the Precambrian Shield in central Ontario, where soil pH(aq) varied from 3.9 to 8.1. Sites were dominated by mature sugar maple (Acer saccharum Marsh.), white birch (Betula papyrifera Marsh.), balsam fir (Abies balsamea (L.) Mill.) or white pine (Pinus strobus L.). Log K(d) values for all elements could be predicted by empirical linear regression with soil pH (r (2) = 0.17-0.77) independent of forest type, although this relationship was greatly affected by positive relationships between acid-extractable metal concentration and pH(aq) for 13 of the 17 elements. Elements that exhibited strong or moderate (r (2)> 0.29; p < 0.001) relationships with soil pH(aq) in soil water extracts include Al, Ba, Fe, Ga, K, Li, Rb, Tl, V (negative) and Ca (positive). Elemental partitioning in mineral soil was independent of forest type; tree species differed in their response to chemical differences in mineral soil. For example, Rb, Ba, and Sr concentrations in foliage of sugar maple and white birch significantly increased with increasing soil acidity, whereas Rb, Ba, and Sr concentrations in balsam fir and white pine foliage exhibited no response to soil pH(aq). While K(d) values can provide useful information on the potential mobility and bioavailability of mineral elements in forest soils, care must be used when interpreting the relative contribution of solid and aqueous phases to this relationship and the differing responses of vegetation in elemental cycling in forests must also be considered.     

Differentiation in low molecular weight organic acids exudation into rhizosphere and their creation in Ulmus laevis Pall organs treated by As – pot experiment

Two-year old Ulmus laevis Pall (U. laevis) seedlings were cultivated in a three-month hydroponic experiment with inorganic (aresenite – As(III) and arsenate – As(V)) and organic (dimethylarsenic acid – DMA(V)) arsenic forms, at 0.06 and/or 0.6?mM concentrations. Further, the profile and content of total low molecular weight organic acids (LMWOAs) were investigated in the rhizosphere, roots and leaves of U. laevis. Obtained results showed that the addition of As(III) or As(V) individually or in a mixture led to increased LMWOAs concentration in the rhizosphere, especially of oxalic and malonic acids, in comparison to the control, while in roots the overall content of the profiled LMWOAs decreased. In both rhizosphere and roots, addition of the DMA(V) form resulted in the inhibition of LMWOAs exudation into the rhizosphere and their creation in plant roots. Leaves were characterised by a higher content of LMWOAs than in the rhizosphere and roots for all experimental systems, where the profile and content of LMWOAs was strictly correlated with the analysed As forms. Our study indicated that creation of LMWOAs in U. laevis organs and their exudation to the rhizosphere could be responsible for the As toxicity tolerance of the plants.     

新型高分子螯合-絮凝剂制备条件的响应面法优化

以壳聚糖为原料,采用化学合成法将二硫代羧基引入到其高分子链上,制备出一种新型高分子螯合-絮凝剂二硫代羧基化壳聚糖(R′-N-(C=S)-SNa,简称DTCTS).以水样中Cd(Ⅱ)的去除率为考察对象,在单因素实验法的基础上,选取了制备DTCTS的主要影响因素,并采用中心复合设计实验和响应面分析法对DTCTS制备条件进行了优化.结果表明,建立的二次多项式模型回归性显著而失拟项不显著,决定系数R2为0.9829,模型拟合性良好;DTCTS最佳制备条件为:反应物CTS/CS2/NaOH摩尔比1:1.5:2、预反应时间30min、主反应温度60℃,此条件下制备的DTCTS对Cd(Ⅱ)的去除率可达99.52%,与模型预测值相对偏差为0.05%,模型可靠.     

植物铜耐性机理的研究进展

主要从植物根细胞壁积累固定、细胞膜对铜的吸收控制、金属配体的螯合作用、铜在系统液泡的分隔机制及胁迫蛋白的合成5个方面,分别阐述植物对铜分子的耐性机制的研究进展,全面了解了铜在植物中的亚细胞分布、铜在植物根系到地上部分运输过程的转运机制以及植物在铜胁迫下的抗性反应等。并在此基础上提出了存在的问题以及今后研究的重点。     

Formation of methyl mercury in an aquatic macrophyte

In the nature, inorganic forms of mercury (Hg) may be transformed to the organic, very toxic, methyl-Hg. Occasionally methyl-Hg has been detected in plants, also so in the aquatic macrophyte water spinach (Ipomoea aquatica), which is a popular vegetable in tropical regions. The objectives of this study were to investigate if methyl-Hg is formed and/or degraded in water spinach. Water spinach plants were exposed to inorganic Hg via spiked soil or spiked nutrient solution. Tests were performed in a climate chamber and in experimental units, one for each individual plant, that were equipped with separated shoot and root compartments. Plant tissues were analysed for total- and methyl-Hg. The results showed that methyl-Hg was accumulated in water spinach, especially in young metabolically active parts, when exposed to external inorganic Hg, even at sterilized conditions. Results also showed that methyl-Hg was formed in water spinach in the absence of external Hg, i.e., during recovery in a not Hg-spiked medium following after HgCl₂-exposure. There was however, no sign of demethylation. Summarizing, most of the Hg that is taken up by the plants is bound in the roots, but of the comparatively small amounts of Hg that reach the young growing shoots, a part will be methylated. Since the young shoots of this plant make a delicious and very appreciated vegetable, Hg in I. aquatica may contribute to human health problems.     

Lead and cadmium biosorption by extracellular polymeric substances (EPS) extracted from activated sludges: pH-sorption edge tests and mathematical equilibrium modelling

The sorption of Cd and Pb by extracellular polymeric substances (EPS) extracted from activated sludges originated from wastewater treatment plants (WWTPs) or Lab-scale bioreactors was investigated as a function of pH. The study was carried out using a polarographic method in the SMDE (stripping mercury dropping electrode) mode which is suited to determine labile metals in solution containing soluble ligands such as EPS. The results obtained provide evidence of the presence of a pH-sorption/desorption edge for Cd and Pb by EPS. The use of Kurbatov’s model gives information on the mechanisms involved through the determination of “relative complexation constants” (operationally defined) and the number of protons exchanged. The use of this model demonstrates that proton exchange with metals is not the only mechanism involved in metal biosorption by EPS. Other mechanisms such as cation exchange with Ca or Mg, global electric field surrounding the ligand or micro-precipitation of metals could be involved in metal sorption by EPS. The position of the pH-sorption edge curves and the “relative complexation constants” show that Pb displays a greater affinity for EPS than Cd. The studied EPS have large differences regarding binding strength of Cd and Pb. These differences are not correlated with the organic parameters measured to characterize the EPS, however the mineral fraction of the EPS could be involved to a large extent in the sorption of metal.     

Amelioration of acute mercury toxicity by a novel,non-toxic lipid soluble chelator N,N′bis-(2-mercaptoethyl)isophthalamide: effect on animal survival,health, mercury excretion,and organ accumulation

The toxic effects of mercury are known to be complex with specific enzyme inhibitions and subsequent oxidative stress adding to the damaging effects. There are likely other factors involved, such as the development of impaired metal ion homeostasis and depletion of thiol- and selenium-based metabolites such as cysteine and selenium. Much of the toxicity of mercury occurs at the intracellular level via binding of Hg²⁺ to thiol groups in specific proteins. Therefore, amelioration of mercury toxicity by the use of chelation would likely be enhanced by the use of a chelator that could cross the cell membrane and the blood brain barrier. It would be most favorable if this compound was of low toxicity, had appropriate pharmacokinetics, bound and rendered mercury cation non-toxic and had antioxidant properties. Herein we report on such a chelator, N,N′-bis(2-mercaptoethyl)isophthalamide (NBMI), and, using an animal model, show that it prevented the toxic effects associated with acute exposure induced by injected mercury chloride.     

Deposition and resorption of organic aerosol constituents in the respiratory tract as calculated from particle size distribution data

Data on the particle size distributions of organic aerosol constituents were used as input for a study, designed to calculate the fractions of the particulate concentrations of these compounds, deposited into the respiratory tract. The known relation between the deposition probability and the particle size as described by the ICRP‐model was used. The organic constituents were from the classes of the aliphatic hydrocarbons, carboxylic acids, polycyclic and aza‐heterocyclic aromatic hydrocarbons. Aerosol samples were obtained by Hi‐Vol cascade impactor sampling at suburban, rural and sea shore background stations as well as in an industrial emission site (coke oven).

Our approach uses the measured concentrations, being average values within each impactor particle size interval, as well as the integrated average deposition probabilities. This procedure was validated experimentally for eight model distributions from the literature, for which an infinitesimal calculation of the deposited fractions was possible.

Dilution reduces total particulate concentrations in the remote areas and predominantly determines the total deposited pollutant concentrations. Of these, pulmonary and nasopharyngeal deposition are most significant and, as a first approximation, correspond largely to the relative importance of the accumulation and dispersion modes of the sampled aerosol. A particle size distribution shift toward larger particles within the accumulation mode occurs upon ageing of the aerosol and reduces the pulmonary deposited fraction of the measured compounds in the background sites, compared to the one in the suburb. The total deposited fraction, however, increases. The contributions of biogenic higher odd n‐alkanes and, to a lesser extent, of even carboxylic acids to the dispersion mode of the aerosol result in an increased nasopharyngeal deposition at the background sites mainly during summer.

Since little information on the bio‐availability of organic aerosol constituents is available in the literature, the fractions of the particulate pollutant concentrations, resorbed in the tissues from the deposited material, were calculated, assuming an average efficiency of 70% for pulmonary and of 10% for nasopharyngeal and tracheobronchial resorption. A nearly constant total resorbed fraction of 20±2% resulted, independent of the sampling station or the season chosen, in contrast with the total deposited fractions, for which significant differences were observed. The predominant pulmonary resorption as well as compensating effects of the nasopharyngeal resorption level out the relatively small differences in particle size distributions observed. Based on these data, a first estimate in nanogram of the daily intake by inhalation of the organic pollutants studied can be formulated as four times the particulate pollutant concentration, expressed in ngm^‐3.     

Metal transport phases in rivers around Jameshedpur†

Transport phases of four metals of geochemical and water quality importance were investigated in rivers around Jamshedpur. The metals iron, manganese, zinc and copper were partitioned into dissolved, adsorbed and or ion exchangeable, solid organic, oxide coating and crystalline phases applying filtration for the dissolved phase and a chemical fractionation scheme for the particulates. Iron and copper were transported mainly in the particulate phases at all sites, while manganese and zinc were found in the dissolved phase up to a hundred percent depending on the pH of water sample and pollution at the site concerned. Except copper more than 75 percent of all other three metals occurred in transport modes thought to be available to aqueous and biotic interactions. Copper was in available phases from 50 to 70 percent. The significance of metal partitioning as a factor in controlling metal availability and toxicity to biota is discussed.     

Induction of gene mutations in salmonella and Drosophila by soluble Cr(Vi) compounds: Synergistic effects of nitrilotriacetic acid

The interaction between NTA and soluble Cr(VI) (K₂Cr₂O₇) was studied by the Ames test on S. typhimurium and the sex‐linked recessive lethal test on D. melanogaster. In both systems a synergistic effect of NTA on Cr(VI) mutagenicity took place at sub‐toxic doses of Cr(VI). The synergism could depend on the action of NTA on intracellular Cr(VI) reduction, as more Cr(VI) was reduced in vitro to Cr(III) by Salmonella and Drosophila protein extracts in the presence of NTA. A similar enhancement of soluble Cr(VI) mutagenicity was produced by low doses of EDTA.