Biofiltration of Toxic Elements by Azolla Biomass

The aquatic fern Azolla binds heavy metals in a widerange of concentrations with high effectiveness, and it can therefore be used for the decontamination of polluted solutions.We have tested the application of its biomass as a practicalbiofilter for industrial waste treatment. In this report, we describe the properties of Azolla biomass which has been dried, rewetted and packed in columns, for use as an ion-exchange matrix. We used scanning electron microscopy in conjunction with an elemental analysis of the Azolla biomass to investigate its structure and to localize exchangeablecations. Azolla elemental content and model solutions containing Sr²⁺ eluted through the biofilter were analyzed.The Azolla biofilter bound Sr²⁺ ions efficientlyby ion exchange with K⁺, Na⁺, Ca²⁺ and Mg²⁺. K⁺ and Na⁺ ions were eluted during the initial phaseof Sr²⁺ binding, due to their lower affinity to the cation-binding groups in the Azolla cell wall. Ca²⁺ and Mg²⁺, bound with a higher affinity to theAzolla cation-binding groups, were exchanged during the secondary phaseof Sr²⁺ binding. Pre-loading of the metal-binding groups with K⁺ increased the removal of heavy metals from solutionby the Azolla biofilter. Our observations explain the mechanism of heavy-metal adsorption to the Azolla matrix.     

Interaction of cupric and cadmium ions with a protein-ovalbumin (OA)

The binding of Cu and Cd ions with ovalbumin has been measured indirectly by observing the displacement of H⁺ from acidic groups on the ovalbumin. The pH-measuring procedure agreed with values obtained by an equilibrium dialysis method. Both the metals were bound by carboxyl groups with log K values being 2.39 and 2.22, respectively. The extent of binding was found to be pH dependent with the involvement of the imidazole site yielding logK values of 3.23 and 2.80, respectively. Equilibrium dialysis results supported involvement of both carboxyl and imidazole groups of the protein in metal ion binding.     

pH and solubility of aluminium in acidic forest soils: a consequence of reactions between organic acidity and aluminium alkalinity

Data from two Podzol O and E horizons, sampled in 1-cm layers at 13 points within 2 m × 2 m plots, were used to test the hypothesis that the composition of hydrogen ions (H) and aluminium (Al) adsorbed to the solid-phase soil organic matter (SOM) determines pH and Al solubility in organic-rich acidic forest soils. Organically adsorbed Al was extracted sequentially with 0.5 m CuCl₂ and organically adsorbed H was determined as the difference between total acidity titrated to pH 8.2 and Al extracted in 0.5 m CuCl₂. The quotient between fractions of SOM sites binding Al and H (N_Al/N_H) is shown to determine the variation in pH and Al solubility. It is furthermore shown that models in which pH and Al solubility are linked via a pH-dependent solubility of an Al hydroxide and in which cation exchange between Al³⁺ and Ca²⁺, rather than cation exchange between Al³⁺ and H⁺, is the main pH-buffering process cannot be used to simulate pH or Al solubility in O and E horizons. The fraction of SOM sites adsorbing Al increased by depth in the lower O and throughout the E horizon at the same magnitude as sites adsorbing H decreased. The fraction of sites binding the cations Ca²⁺ + Mg²⁺ + K⁺ + Na⁺ remained constant. It is suggested that a net reaction between Al silicates (proton acceptors) and protonated functional groups in SOM (proton donors) is the long-term chemical process determining the composition of organically adsorbed H and Al in the lower part of the O and in the E horizon of Podzols. Thus, in the long term, pH and Al solubility are determined by the interaction between organic acidity and Al alkalinity.     

Influence of alkaline particulates on the chemistry of fog water at Delhi,North India

Chemical analysis of fog water collected by impaction in a pre-cooled chamber in Delhi has shown high concentrations of major ions. The dominant ions measured were Na⁺, K⁺, Ca⁺², and Mg⁺². The concentrations of acidic ions, SO₄ ^?2 and NO₃ ^?, were low. The pH values in the fog water were highly alkaline and varied from 6.4 to 7.6. The high concentrations of soil-oriented components, especially Ca⁺², were more than sufficient to neutralize the small acidity in the fog water and were responsible for maintaining high alkaline pH. The pH values of fog water did not attain the low values in India (Delhi), as found in other polluted environments of Europe and the northeast United States.     

Acid deposition and throughfall fluxes of elements as related to tree species in deciduous forests of South Sweden

The influence of tree species and soil properties on throughfall fluxes were studied for 5 tree species, growing on initially identical soil. In three mixed deciduous forests with different soil properties, throughfall fluxes of 11 elements were measured during 2 yr for 100 to 150 yr old individuals of Fagus sylvatica L., Quercus robur L., Carpinus betulus L., Tilia cordata Mill. and Acer platanoides L.. Throughfall : precipitation flux ratios were: PO₄ ^3? (11 to 37), K⁺ (7 to 22), Mn²⁺ (5 to 14), Mg²⁺ (3 to 9), Ca²⁺ (3 to 5), Cl^? (1.9 to 2.6), Na⁺ (1.1 to 2.2), NH₄ ⁺ (1.5 to 2), SO₄ ^2? (1.5 to 2.1), NO₃ ^? (0.7 to 1.3) and H⁺ (0.1 to 0.5). The annual input of S to the soil by throughfall was for Fagus 22 to 29, Quercus 25 to 37, Carpinus 20 to 25, Tilia 24 and Acer 29 kg ha^?1. The annual input of N to the soil by throughfall was for Fagus 20 to 29, Quercus 14 to 22, Carpinus 15 to 22, Tilia 22 and Acer 20 kg ha^?1. Throughfall fluxes of Na⁺ and Cl^? differed between species, depending on different canopy filtering capacity of sea aerosol, and were greatest for Fagus and Quercus. Throughfall of Ca²⁺, Mg²⁺ and K⁺ were characterized by increased flux from poor to rich sites, with the greatest soil effect on Carpinus, and by a high leaching part, which increased in the same manner. Manganese throughfall showed especially soil effects, characterized of decreased flux from poor to rich sites, but also species effects, of which Carpinus had the greatest flux. pH in throughfall showed a pronounced seasonal variation with pH 6 to 6.5 for Fagus in the foliated season and pH 4.0 to 4.3 in the defoliated season. Carpinus and especially Quercus had lower pH at the poor site, but the differences decreased at the richer sites. The calculated annual acid input to the trees was 4 to 12 times greater than the H⁺ flux measured as pH in throughfall. An inorganic anion deficit in throughfall, probably due to the presence of organic anions, was proportional to K⁺, Ca²⁺ and Mg²⁺.     

Formation of metal-humic acid complexes by titration and their characterization by differential thermal analysis and infrared spectroscopy

Humic acid (HA) extracted from a Eustis loamy sand (Psammentic Paleudult, Red Yellow Podzolic soil) was flocculated by titration with Al³⁺-, Fe³⁺-, Cu²⁺-, Zn²⁺-, Mn²⁺-, Ba²⁺-, Ca²⁺-, and Mn²⁺-chloride solutions, respectively, to determine possible development of metal-HA complexes, as reported by Flaig et al. (1975), and Tiurin and Kononova (1962). Titration was conducted with HA solutions with an initial pH 11.5 or 7.0. The results indicated that the cations used, except Mg²⁺, yielded insoluble complexes with HA, irrespective of initial pH. After titration, the pH of the metal-HA flocs was 6.0–7.0, which was expected in view of the presence of cation exchange and buffering capacity of HA compounds. More complex formation through electrovalent and covalent bonding by COO^? and phenolic OH groups of the HA molecule was only attained by the use of HA solutions with pH 11.5. On the other hand, less complex formation occurred by the use of HA solutions with an initial pH 7.0, through electrovalent bonding by COO^? groups. Differential thermal analysis (d.t.a.) curves of HA showed shifts in temperatures of the main decomposition peak as a result of flocculation with the different metals. Based on the type of the cations involved, the metal-humic acid flocs could be listed in the following decreasing order of thermal stability: Al³⁺ = Zn²⁺ = Mg²⁺ ≥ HA > Ca²⁺ > Ba²⁺ > Fe³⁺ > Cu²⁺ > Mn²⁺. A systematic relationship could not be found indicating that trivalent ions resulted in the formation of thermally less stable metal-humic acid flocs than divalent ions, as has been reported for HA-metal complexes. Physical mixtures of HA and metal hydroxides exhibited d.t.a. features resembling those of original (nontreated) HA, but not those of the HA-metal flocs.Infrared spectroscopy revealed increased absorption for COO^? vibrations at 1620 and 1400cm^?1 in spectrograms of metal-HA flocs compared to that of original humic acid, a phenomenon explained by many authors to be caused by bonding of the metal ions in hydrated form to the carboxyl or phenolic hydroxyl groups or both of the humic acid molecule. HA-flocs formed from solutions with an initial pH 11.5 had identical i.r. spectra compared with those formed from solutions with an initial pH 7.0.     

Preparation, Characterization, and Adsorption Behavior of Cu(II) Ions onto Alkali-Treated Weed (Imperata cylindrica) Leaf Powder

The adsorption of Cu(II) ions by sodium-hydroxide-treated Imperata cylindrica (SoHIC) leaf powder was investigated under batch mode. The influence of solution pH, adsorbent dosage, shaking rate, copper concentration, contact time, and temperature was studied. Copper adsorption was considered fast as the time to reach equilibrium was 40–90 min. Several kinetic models were applied and it was found that pseudo-second-order fitted well the adsorption data. In order to understand the mechanism of adsorption, spectroscopic analyses involving scanning electron microscope (SEM) coupled with energy-dispersive spectroscopy (EDS) and Fourier transform infrared (FTIR) spectrophotometer were carried out. Ion exchange was proven the main mechanism involved as indicated by EDS spectra and as there was a release of light metal ions (K⁺, Na⁺, Mg²⁺, and Ca²⁺) during copper adsorption. Complexation also occurred as demonstrated by FTIR spectra involving hydroxyl, carboxylate, phosphate, ether, and amino functional groups. The equilibrium data were correlated with Langmuir, Freundlich, and Dubinin–Radushkevich isotherm models. Based on Langmuir model, the maximum adsorption capacity was recorded at the highest temperature of 310 K, which was 11.64 mg g^?1.     

Heavy Metals Removal in a Horizontal Rotating Tubular Bioreactor

Mixed microbial culture was isolated from heavy metal-contaminated ground soils located inside iron, vinyl and cement factory area. Isolated mixed microbial culture was used for the heavy metal ions (Fe²⁺, Cu²⁺, Ni²⁺ and Zn²⁺) removal process in horizontal rotating tubular bioreactor (HRTB). In this research, the effect of bioreactor process parameters on the bioprocess dynamics in the HRTB was studied. Results of this research have shown that profiles of heavy metals concentration were gradually reduced along HRTB at all combinations of bioreactor process parameters [inflow rates (0.5?C2.0 L?h^-1) and rotation speed (5?C30 min^-1)]. Hydrodynamic conditions and biomass sorption capacity have main impact on the metal ions removal efficiency that was varied in the range of 38.1% to 95.5%. Notable pH gradient (cca 0.7 pH unit) along the HRTB was only observed at the inflow rate of 2.0 L?h^-1. On the basis of obtained results, it is clear that medium inflow rate (F) has higher impact on the heavy metal removal process than bioreactor rotation speed (n) due to the fact that increase of inflow rate was related to the reduction of equilibrium time for all examined metal ions. Furthermore, equilibrium times for all metal ions are significantly shorter than medium residence times at all examined combinations of bioreactor process parameters. The main impact on the biofilm sorption capacity has covalent index of metal ions and biofilm volumetric density. The sorption capacity of suspended microbial biomass is closely related to its concentration. Results of this research have also shown that the removal of heavy metals ion can be successfully conducted in an HRTB as a one-step process.     

Cu(II) Biosorption and Competitive Studies in Multi-ions Aqueous Systems by Arthrobacter sp. Sphe3 and Bacillus sphaericus Cells: Equillibrium and Thermodynamic Studies

Arthrobacter sp. Sphe3 and Bacillus sphaericus cells were used for Cu(II) biosorption. The effect of contact time, biosorbent dose, equilibrium pH, temperature and the presence of other ions on the efficiency of the process were extensively studied. Optimum pH value and biomass concentration were determined at 5.0 and 1.0?g/l, whereas contact time was found to be 5 and 10?min for Arthrobacter sp. Sphe3 and Bacillus sphaericus biomass, respectively. Equilibrium data fitted very well to Freundlich model (R ²?=?0.996, n?=?2.325, K _f?=?8.141) using Arthrobacter sp. Sphe3. In the case of B. sphaericus, a Langmuir adsorption model [R ²?=?0.996, Q _max?=?51.54?mg-Cu(II)/g] showed to better describe the results. Potentiometric titration and Fourier transform infrared (FTIR) spectroscopy showed that amine, carboxyl and phosphate groups participate in Cu(II)-binding. The calculated thermodynamic parameters indicated the spontaneous and feasible nature of Cu(II) biosorption on both biosorbents. Selectivity of Cu(II) biosorption was examined in binary and multi-ions systems with various anions and cations which are commonly found in municipal and industrial wastewater. A specificity towards Cu(II) was observed in binary mixtures with Cl^-, CO ₃ ^-2 , NO ₃ ^- , SO ₄ ^-2 , PO ₄ ^-3 , Mg⁺² and Ca⁺², and As(V) with the maximum uptake capacity remaining constant even at high competitive ion??s concentrations of 200?mg/l. Desorption studies showed that Cu(II) could be completely desorbed from Cu(II)-loaded Arthrobacter strain Sphe3 and B. sphaericus biomass using 1.0 and 0.8?M HCl, respectively, and both bacterial species could be effectively reused up to five cycles, making their application in wastewater detoxification more attractive.     

Comparison of Long-Term Precipitation Chemistry Measurements at the Hubbard Brook Experimental Forest,New Hampshire

From 1978 through 1989, a wet-onlyprecipitation collector operated for the NationalAtmospheric Deposition Program, an independantwet-only collector, and a bulk precipitation collectorwere co-located at the Hubbard Brook ExperimentalForest (HBEF) in central New Hampshire. A secondbulk precipitation collector was maintained at anotherlocation within the HBEF. There were statisticallysignificant differences between the chemistry fromco-located wet-only collections for Ca²⁺,K⁺, NH₄ ⁺, pH, and NO₃ ^-. Thedifferences for K⁺ and pH though statisticallysignificant were very small but consistant. Thedifferences for Ca²⁺ were related to earlycontamination problems, and differences inNH₄ ⁺ and NO₃ ^- were related toepisotic events. Bulk precipitation was significantlyricher in K⁺ than wet-only precipitation. Therewere no differences for any ions between the bulkcollections at the two locations. While there wereminor differences, after 1981 when the contaminationproblems had been resolved, data from all collectorsat all locations adequately characterized theprecipitation chemistry of the site.     

Effects of trace elements on urease activity in soils

Disposal of sewage sludges and effluents on agricultural land is becoming a widespread practice. Most sludge samples disposed on soils contain large quantities of various trace elements. Studies of 20 trace elements commonly found in sludge samples showed that they inhibit the activity of urease in soils and that their order of effectiveness as inhibitors of urease depends on the soil. When the trace elements were compared by using 5 μmiol·g^?1 soil, however, some of them showed the same order of effectiveness as urease inhibitors in the six soils studied i.e., for the monovalent and divalent ions, Ag⁺ ≥ Hg²⁺ >Cu²⁺ >Cd²⁺ >Zn²⁺ >Sn²⁺ >Mn²⁺, and generally, Fe²⁺ >Fe²⁺andCu²⁺ >Cu⁺. Other trace element ions that inhibited urease were Ni²⁺, Co²⁺, Pb²⁺, Ba²⁺, As³⁺ B³⁺, Cr³⁺, Al³⁺. V⁴⁺ Se⁴⁺ and Mo⁶⁺. Of the trace element ions studied, only As⁵⁺ and W⁶⁺ did not inhibit urease activity in soils.Studies on the distribution of urease activity showed that it is concentrated in surface soils and decreases with depth. Urease activity was proportional to organic C distribution in each soil profile and was significantly correlated with organic C in the surface soils studied.     

Development and validation of an acute biotic ligand model (BLM) predicting cobalt toxicity in soil to the potworm Enchytraeus albidus

An acute Biotic Ligand Model (BLM) was developed to predict the effect of cobalt on the survival of the potworm Enchytraeus albidus, exposed in nutrient solutions added to acid washed, precombusted sand. The extent to which Ca²⁺, Mg²⁺ and Na⁺ ions and pH independently mitigate cobalt toxicity to E. albidus was examined. Higher activities of Ca²⁺, Mg²⁺ and H⁺ linearly increased the 14 d LC50_Co²⁺ (LC50 expressed as Co²⁺-activity) whereas Na⁺-activity did not. Stability constants for the binding of Co²⁺, Ca²⁺, Mg²⁺ and H⁺ to the biotic ligand (BL) were derived, i.e. log K_CoBL=5.13, log K_CaBL=3.83, log K_MgBL=3.95 and log K_HBL=6.53. It was calculated that at Co-concentrations corresponding to the 14d-LC50 value, 32% of the BL sites were occupied by cobalt. An initial validation of the applicability of this BLM in true soil exposure systems was performed by comparing observed and model-predicted 14 d LC50 s in a standard artificial soil and a standard field soil. By assuming pore water to be the only route of exposure and assuming equilibrium between pore water Co²⁺ and solid phase Co, which is predicted by the geochemical WHAM-Model 6, LC50 s (as mg Co kg⁻¹ dry wt of soil) were predicted within an error of less than a factor two. Further validation in true soil exposures, combined with more detailed knowledge of Co binding to soil solid phases is needed, if this model is to be used as a tool for risk assessment and derivation of soil quality criteria for Co.     

THERMODYNAMICS AND THERMOCHEMISTRY OF THE EXCHANGE REACTION BETWEEN NH4+ AND Mn2+ IN A MONTMORILLONITE CLAY

The exchange reaction between NH₄⁺ and Mn³⁺ was studied on a montmorillonite clay at several temperatures and different ionic strengths. Manganese was preferred to ammonium; this preference increased with the temperature and dilution of the dialysate. Comparison with published data concerning exchanges involving NH₄⁺ and the alkaline-earths showed that in the sequence of increasing selectivity: Mg²⁺ < Ca²⁺ < Sr²⁺ < Ba²⁺, Mn²+ lies between Mg²⁺ and Ca²⁺. The enthalpy change was measured calorimetrically and calculated by application of the van't Hoff law to the temperature coefficient of the equilibrium constants. Both values were in good agreement. The excellent recoveries of Mn²⁺ at the end of the exchange reaction and the constancy of the cation exchange capacity over the whole range of surface composition ruled out the possibility of significant adsorption in the MnOH⁺ form. The behaviour of manganese was very similar to that of the alkaline-earth cations.     

Acid deposition and lake chemistry in southwest China

A water quality survey has been performed on selected lakes and streams in southwest China. The purpose of the study was to measure the concentrations of acidic deposition and surface water chemistry in a region of severe air pollution, forest decline, and relatively sensitive geology to acidic deposition. We show that, although there are some high elevation lakes of low acid neutralizing capacity (ANC<150μeq L^?1, acidification of lakes has not occurred in southwest China due to production of base cations in soil and dry deposition of dust that serves to neutralize acidic deposition. Water chemistry is buffered by high base cation concentrations (Ca²⁺, Mg²⁺, Na⁺, and K⁺ greater than 300μeq L^?1, and pH values are always greater than 6.5.     

Lupin and pea differ in root cell wall buffering capacity and fractionation of apoplastic calcium

Lupin (Lupinus angustifolius L.) and pea (Pisum sativum L.) differ substantially in their root growth at pH≥6. The mechanisms underlying such a variation are not fully understood. The H⁺ buffering capacity of isolated cell wall and calcium binding property of intact roots of these two species were compared under various experimental conditions. The shape of the H⁺/OH^‐ titration curves of cell wall for lupin and pea showed no major discrepancy except with differed magnitudes. There appeared to be two H⁺‐titratable groups in root cell wall of both species—below pH 6 and above 8. The wall H⁺ buffering capacity of pea roots was lower at pH 4–5, but was greater at pH above 5.5 than that of lupin roots. The fractionation of apoplastic calcium demonstrated that the proportion of easily exchangeable Ca²⁺ was greater while that of tightly bound Ca²⁺ was smaller in pea roots than in lupin roots. In addition, Ca²⁺ in cell wall was more easily exchanged by H⁺ in pea than in lupin roots. The results suggest that the different sensitivity in root growth at pH≥6 of lupin and pea is related to the difference in H⁺ buffering and Ca²⁺ exchange capacities in the root apoplast of these species, and that the greater sensitivity of lupin roots to pH≥6 is partly due to a higher threshold of H⁺ concentration required for cell wall loosening.     

SOLUBLE ALUMINIUM AND CALCIUM-ALUMINIUM EXCHANGE IN RELATION TO THE pH OF DILUTE CALCIUM CHLORIDE SUSPENSIONS OF ACID SOILS

Measurements of pH and A1 concentration were made on 10^-2 M CaCl₂, suspensions of a number of acid soils that had been limed to give 3 range of pH values, and exchangeable A1 and Ca+Mg were determined in 1.0 M NH₄Cl extracts. The variation of pH with A1 concentration did not support the theory that pH is controlled by the solubility of Al(OH)₃. For some of the soils, proton release on hydrolysis of A1₃₊ions in solution accounted for the pH values, and explained quantitatively the variation of pH with the Ca:Al balance of the exchange complex, taking account of the selectivity coefficient for exchange, K_ca→A1 Although K_ca→A1 was smaller for soils containing more humus, their pH values were also less than those predicted by the hydrolysis of A1³⁺ in solution, indicating that they contained other sources of protons, presumably the carboxyl groups in humus.     

Effects of Ca,Mg, K,Na, and pH on Copper Toxicity to Pakchoi (Brassica chinensis L.)

The influence of calcium, magnesium, sodium, and potassium (Ca²⁺, Mg²⁺, Na⁺, K⁺) ions and pH on copper (Cu) toxicity to pakchoi (Brassica chinensis L.) was independently estimated by measuring root elongation in nutrient solutions. Increases in Ca²⁺, Mg²⁺, and hydrogen (H⁺) significantly increased the 5-d EC50Cu_T (expressed as total soluble Cu) by a factor of 12 for all treatments, which clearly demonstrated the limitation of using total Cu concentration to predict Cu toxicity to pakchoi. EC50{Cu²⁺} (expressed as free Cu²⁺ activity) was not significantly influenced by changing the Ca²⁺, Mg²⁺, and H⁺ activities. The nonlinear relationship between EC50{Cu²⁺} and cations indicated that competition for binding sites between Cu²⁺ and cations was not a significant factor in determining toxicity of Cu²⁺ for pakchoi. The lower variation of EC50{Cu²⁺} suggests that free Cu²⁺ activity was a better predictor of toxicity to pakchoi than EC50Cu_T.     

The H+/M2+ exchange stoichiometry of calcium and zinc adsorption by ferrihydrite

The specific adsorption of Ca²⁺ and Zn²⁺ by ferrihydrite results in the net release of H⁺. The rate and H⁺/M²⁺ exchange stoichiometry of this reaction were monitored with a pH-stat. A rapid reaction of less than 6 min was followed by a slower reaction which continued at a diminishing rate for at least 2 days. Adsorption of Ca²⁺ at pH 7.8 and Zn²⁺ at pH 5.4 resulted in the net release of 0.92 and 1.70 mol H⁺/mol M²⁺ adsorbed, respectively. For Zn²⁺ adsorption, this stoichiometry was shown to be independent of pH. These estimates agree well with independent estimates based on the pH dependence of adsorption. The difference between the Ca²⁺ and Zn²⁺ stoichiometries was related to the differing acidity of the –OH₂ ligands attached to the adsorbed ions.     

COUNTER DIFFUSION OF Rb86 AND Sr89 IN COMPACTED SOIL

Counter-diffusion coefficients of Rb⁸⁶ and Sr⁸⁹ counter diffusing against H⁺ ions were measured in Dundee silt loam and Sharkey clay soils at differing soil bulk-densities. The cation exchange complex of each soil was saturated with either Rb⁺, Sr⁺⁺, or H⁺ and washed free of salts before making diffusion measurements. The water content of the soil on an oven-dry weight basis was maintained at a constant value for all bulk-densities; 14.2 and 28.0 per cent for the Dundee and Sharkey soils respectively. These moisture contents correspond to a tension of 2/3 bar for sieved soil. The diffusion coefficients were dependent upon concentration. Average counter-diffusion coefficients were calculated and related to soil bulk-density. Soil compaction of Dundee silt loam had little or no effect upon the counter diffusion of Rb⁸⁶. The average counter-diffusion coefficients of Sr⁸⁹ in Dundee silt loam and Sharkey clay were significantly and linearly related to bulk-density; as bulk-density increased the average counter-diffusion coefficients increased. The average counter-diffusion coefficients were approximately 0.5–0.75 of the corresponding self-diffusion coefficients measured previously in these soils. The applicability of counter- and self-diffusion data to practical field problems are discussed.     

Long Term Trend of Chemical Constituents in Tokyo Metropolitan Area in Japan

In recent years, acid rain has been a social problem all over the world. In Japan, it is also a big problem especially in the metropolitan area. Then, we have measured major ions such as H⁺, Na⁺, NH₄ ⁺, K⁺, Mg²⁺, Ca²⁺, Cl^?, NO₃ ^?, and SO₄ ^2? in precipitation and dry deposition samples which had been collected at 9 sampling sites at Hiyoshi, Mita, Kashiwa, Shiki, Fujisawa, Yokosuka, Mitaka, Hachiouji, and Ashikaga in Tokyo Metropolitan area for 10 years since 1990. The average pH of precipitation in their sites was 4.56 (n=1906). As the results of multiple regression analysis showed that pH of precipitation was determined by 5 ions such as NH₄ ⁺, nssCa²⁺(non sea salt calcium), nssCl^?(non sea salt chloride), NO₃ ^?, nssSO₄ ^2?(non sea salt sulfate) in the most of the sampling sites. Therefore, it is very important to investigate the behavior of these ions to understand the acidification of rain in Tokyo Metropolitan area. In this study, a long term trend of each ion concentration in precipitation and wet deposition was also investigated the base on the data we had observed at 7 sites for 10 years by the statistical method.