Trace element loading of southern Lake Michigan by dry deposition of atmospheric aerosol

Aerosol samples and meteorological data were collected at a mid-southern Lake Michigan site (87° 00′ W, 42° 00′ N) from May through September 1977. Hi-volume samplers with cellulose fiber filters and a digital meteorological data recording system were operated on board the U.S. EPA's R/VRoger R. Simons during four intensive sampling periods. Aerosol samples were analyzed by atomic absorption spectroscopy for seventeen trace elements. A diabatic drag coefficient method was used to determine aerosol deposition velocity (v _d ) overlake. A meanv _d of 0.5 cm s^?1 was found for the 0.1v _d to a long-term climatological record, annual dry deposition loadings to the southern basin for nine elements were estimated. For four elements, Fe, Mn, Pb, and Zn, dry deposition loadings to the southern basin alone of at least 500, 30, 250, and 100 (×10³ kg yr^?1) were found. For Fe and Mn, these loadings represent about 15% of the total of all inputs to Lake Michigan. for Zn and Pb, about one-third to one-half of the annual loading from all sources is from dry deposition of atmospheric aerosol.     

Forms of trace metals from inorganic sources in soils and amounts found in spring barley

Barley (Hordeum vulgare L.) was grown on a sandy soil given different doses of cadmium carbonate (salt), copper carbonate (malachite), lead carbonate (cerussite), and zinc carbonate (smithsonite) in a pot experiment conducted in a greenhouse. The element compounds were added to the soil in amounts equivalent to the following levels of the metals: Cd 5, 10, 50 μq ^?1; Cu and Pb 50, 100, 500 μg g^?1; Zn 150, 300, 1500 μg g^?1. Sequential extraction was used for partition these metals into five operationally-defined fractions: exchangeable, bound to carbonates, bound to Fe-Mn oxides, bound to organic matter and residual. The residue was the most abundant fraction in the untreated soil for all the metals studied (43 to 61% of the total contents). The concentration of exchangeable Cd (0.2 μg g^?1), Cu (0.01 μg g^?1), Pb (0.1 μg g^?1), and Zn (1.4 μg g^?1) were relatively low in the untreated soil but increased markedly in the treated soils for Cd (up to 31 μg g^?1) and Zn (up to 83 μg g^?1), whereas only small changes were observed for Cu and Pb. The pot experiment showed a significant increase in the Cd and Zn contents of barley grown on the treated soils, but only small changes in Cu and Pb concentrations.     

A Study of Airborne Selected Metals and Particle Size Distribution in Relation to Climatic Variables and their Source Identification

Ten selected metals (Na, K, Fe, Zn, Pb, Mn, Cr, Co, Ni & Cd) were estimated in total suspended particulate (TSP) samples collected on glass fibre filters in urban Islamabad, Pakistan, from October 2002 to May 2003, using a high volume sampling technique. The wet digestion method (HNO₃/HClO₄) was used for metal analysis by the flame atomic absorption spectrophotometry (FAAS) method. Maximum mean contribution was noted for Na (1.949 μg m^?3), followed by K (0.900 μg m^?3), Zn (0.603 μg m^?3), Fe (0.584 μg m^?3) and Pb (0.214 μg m^?3). The particle size determination on % volume basis for four fractions (PM_{< 2.5}, PM_2.5–10, PM_10–100& PM_{> 100}) was also carried out. PM_10–100 were found to be the most abundant in the local atmosphere followed by PM_2.5–10, while the respirable fraction (PM_{< 2.5}) and giant fraction (PM_{> 100}) showed comparable and lower levels. The trace metals were found to be mainly associated with PM_{< 2.5} and PM_2.5–10. The influence of climatic variables on toxic trace metals and particle size fractions was also investigated statistically and it was revealed that temperature has a significant correlation with fine particle fractions and airborne trace metal levels. The source identification was carried out by Principal Component Analysis and Cluster Analysis. Four metal sources were identified: industrial (32.6%), soil-derived dust (21.9%), traffic/road dust (19.8%), and metallurgical/garbage incineration (12.4%). The metal levels were also compared with those reported for other parts around the world.     

Effects of pentachlorophenol on asymbiotic nitrogen fixation in soil

The effect of 50, 100, 150, and 400 μg sodium pentachlorophenate (Na-PCP) per gram soil was studied in nonsterile soil incubated under aerobic and anaerobic conditions, and in sterilized soil inoculated withAzotobacter sp. isolated from the soil. N₂ fixation was determined by acetylene reduction. Pentachlorophenate at a concentration of 50 μg g^?1 had an inhibitory effect in nonsterile soil incubated aerobically while strong inhibition of dinitrogen fixation in nonsterile soil occurred in the presence of 100 μg g^?1 and above. The EC₅₀ values for the inhibition of nitrogenase activity in nonsterile soil incubated aerobically and anaerobically and in sterilized soil inoculated withAzotobacter sp. suspensions were 49.8±1.4 μg Na-PCP g^?1, 186.8±2.8 μg Na-PCP g^?1, and 660.8±29.3 μg Na-PCP g^?1, respectively.     

Sur une nouvelle methode de dosage du dioxyde d'azote present dans les atmospheres polluees,derivee de la methode de Griess-Saltzmann

This paper discusses a procedure involving absorption of NO₂ on triethanolamine impregnated-papers according to a recent study of Levaggi, Siu and Feldstein. The used solid surfaces are Millipore filters, first impregnated by stirring them in a solution containing triethanolamine, glycerol and acetone before drying in an oven. Storage is made in a closed glass container. For sampling, check air flow rate to be about 30 l h^?1 through filters. The sampling time depends on the actual concentration. Samples are then analyzed in a laboratory under Saltzman's colorimetric reaction. The composition of the reagents is slightly modificated (acetic acid is replaced by phosphoric acid to obtain pH 1). Color development needs 30 min and then absorbance is compared with a standardization curve built from dilute solutions of Na NO₂. Absorption efficiencies of over 95% are attained with two impregnated filters in a filter holder and at about 301 h^?1 flow rate. Stability of filters after sampling is evaluated at 2 or 3 weeks, so it is possible to store several filters before sending them (for example by mail) to the laboratory for analysis. The stoichiometric factor depends on the weight (expressed in μg) of NO₂ collected on the filters and varies between 1.0 and 0.84. To measure NO, oxidation into NO₂ is first required, for example with an O₃ lamp.     

The Determination of Ozone in Ambient Air with Free Hanging Filters as Passive Samplers

This paper describes the use of dry free hanging filters, as passive samplers to determine ozone in the ambient air. The filters, with a diameter of 25?mm, were impregnated with 5,5??-disodium indigo disulphonate (IDS), a reagent for ozone. From the amount of reacted indigo compound, found on the filter, and the ozone concentration in the ambient air, a pseudo rate constant k ₁, of the reaction between ozone (O₃) and IDS on the filter, is calculated. The range of measurement is between 9 and 205???g/m³ ambient ozone. The dry filter method is specific for ozone, while the Dutch standard method NEN2789, based on an aqueous solution of IDS, has to be corrected for the presence of NO _x . From wind tunnel and field experiments, k ₁ proved to vary between 0.7 and 1.5?×?10^?6?m³?s^?1 (??g O₃)^?1 at wind velocities between 1 and 3?m/s and at an exposure time of 60?min. Within these conditions, ozone concentrations have been determined with free hanging filters in four busy streets in Yogyakarta, Indonesia and at two background sites using an average value of k ₁ of 1.2?×?10^?6. Subsequently, the traffic NO emission was estimated from the difference of the O₃ concentrations at both sides of a road. For an arbitrary situation, an NO emission of 255???g/s per metre road length was calculated. The filter method is inexpensive and practical, needs no electricity, is easily assembled and can be used to perform measurements in remote areas. It is shown here that this simple measurement technique may support air quality studies, e.g., in developing countries.     

Acid deposition and ion leaching from a podzolic soil under hardwood forest

The contribution of atmospheric acids to cation leaching from a podzolic soil under mature maple-birch forest in central Ontario was examined during 1983. The movement of base cations was associated largely with NO₃ ^?, SO₄ ^2? and organic acid anions in surface soil horizons, with SO₄ ^2? and NO₃ ^? below the effective rooting zone, and SO₄ ^2? and HCO₃ ^? in streamflow. Mineral soil horizons could adsorb little additional SO₄ ^2? or associated cations at current soil solution SO₄ ^2? concentrations. Therefore it is concluded that the soil in situ lacks a strong affinity for SO₄ ^2?. Current annual inputs to the forest of SO₄ ^2? and NO₃ ^? in bulk precipitation (26.4 and 18.2 kg ha^?1, equivalent to 8.8 kg S and 4.1 kg N ha^?1 , respectively) contributed significantly to cation leaching from the soil. In order to maintain exchangeable cations in soil at current levels, a rate of weathering yielding 29.6, 5.0, 4.4 and 2.2 kg ha^?1 yr^?1 of Ca²⁺, Na⁺, Mg²⁺ and K⁺, respectively, would be required.     

Characteristics of an amidase isolated from a soil bacterium

Amidase was extracted from a bacterium isolated from soil, and its properties were compared with those of amidase in soil. Amidase activity of the bacterial protein was lower than that of soil amidase, respectively, in its optimal pH (7.0 vs 8.5), optimal temperature (50 vs 60°C), K_m constant calculated by the Lineweaver-Burk plot (5.6 vs 17.9 mm), activation energy (18.9 vs 43.3 kJmol^?) and Q₁₀ (av. = 1.28 vs 1.75). Bacterial amidase was stable at temperatures ranging from 10 to 50°C and denatured at 55°C. Toluene inhibited both bacterial and soil amidase.When the inhibitions by 21 trace elements were compared by using 2 μmol 0.1 mg^?1 protein, the most effective inhibitors of bacterial amidase (> 25% inhibition) were: Ag(I), Cd(II), Cu(II), Hg(II), Ni(II), Pb(II), Zn(II), Al(III) and Se(IV). The effect of 16 pesticides on bacterial amidase varied considerably. By using 2 μg of active ingredient of pesticide 0.1 mg^?1 protein, the inhibition of bacterial amidase ranged from 7 to 49% with Dinitroamine and Butylate, respectively. The results show that soil constituents have a considerable influence on the reaction catalyzed by this enzyme.     

Acidity neutralization mechanism in a forested watershed in Central Japan

The contributions of cation exchange and mineral weathering to the neutralization of acidity in the Jingahata watershed in central Japan were estimated through a laboratory weathering experiment and runoff chemistry measurements. The laboratory experiment was conducted in a stirred-flow reactor for a whole soil sample collected from the C horizon in the watershed. The concentration ratios of base cations (Ca²⁺, Mg²⁺, K⁺ and Na⁺) to Si (BC/Si) released during the steady-state stage of the laboratory experiment were in good agreement with the ratios of the net flux of base cations to the flux of Si in the streamwater (BC _{N ET}/Si _L).This result suggests that the acidity in the watershed is neutralized primarily by mineral weathering without causing a net loss of base cations from exchange sites. The alkalinity/acidity balance estimated for the watershed shows that the total weathering rate of base cations is approximately 3.26 keq ha^?1 yr^?1. Weathering of plagioclase (An₄₁) contributes 83% of the total weathering rate. The dominant acidity source is CO₂ released within the soil horizons, accounting for roughly 85% of the total acidity flux (3.20 keq ha^?1 yr^?1). This high internal production of acidity suppresses the relative importance of atmospheric acidity inputs (0.3 keq ha^?1 yr^?1).     

Effect of cations on copper adsorption by kaolin

Varying amounts of CaCl₂ or MgCl₂ were first equilibrated with a dilute suspension of H⁺-kaolin and then with spiked (high activity radioactive ⁶⁴Cu) water. After filtration, through 0.45 μm Millipore membrane the amount of radioactivity on the filter and the filtrate was measured separately using a Gamma ray well counter. Adsorption of Cu (expressed as distribution coefficient ?K _d ) was plotted against Ca or Mg concentration. K _d values decreased sharply at Ca or Mg concentration from 0 to 10 mg l^?1 and changed only slightly from 10 to 200 mg l^?1. Increase in the concentration of Ca or Mg reduces the Cu binding capacity of the clay.     

Chemistry differences in two streams entering an acidic lake in the Adirondack Mountains,New York (U.S.A.)

Solution chemistry was measured in two major inlets, lake water column, lake outlet, and soils of the South Lake watershed in the Adirondack Mountains, New York. The east inlet had greater concentrations of H⁺, sulfate-S, and Al and smaller concentrations of base cations and silica than the west inlet (70, 116, 25, 90, 64 and 4, 99, 8, 228, 148 μeq L^?1 of H⁺ and sulfate-S, μmol L^?1 Al, μeq L^?1 total base cations and μmol L^?1 silica in east and west inlets, respectively). Concentrations of base cations in C horizon soil solutions (157 μeq L^?1 total base cations) were smaller and greater than west and east inlets, respectively. This suggests that water flowing into the west inlet contacted deeper mineral layers, whereas water reaching the east inlet did not. Lake and lake outlet concentrations were also intermediate between the two inlets, and the lake was acidic (pH 4.9 to 5.1) with relatively high total monomeric Al concentrations (8 to 9 μmol Al L^?1). The east inlet also had greater DOC concentrations than the west (0.38 and 0.24 μmol C L^?1, respectively), again indicating that soil solutions entering the east inlet passed through the forest floor but had more limited contact with deeper mineral layers in comparison with the west inlet. Differences between the streams are hypothesized to be related to contact of percolating solutions with mineral soil horizons and underlying glacial till, which provides neutralization of acidic solutions and releases base cations. This work indicates that processes controlling surface water acidification can be spatially quite variable over a small watershed.     

Effect of biosolid application to Mollisol Chilean soils on the bioavailability of heavy metals (Cu,Cr, Ni,and Zn) as assessed by bioassays with sunflower (Helianthus annuus) and DGT measurements

Purpose

This study assessed the effect of biosolid application on the bioavailable fraction of some trace elements (Cu, Cr, Ni, and Zn) using a bioassay with sunflower (Helianthus annuus) and a chemical assay, diffusion gradient in thin films (DGT).

Materials and methods

Five surface soil samples (0–20 cm) were collected from an agricultural zone in Central Chile where biosolids are likely to be applied. Municipal biosolids were mixed with the soil at concentrations of 0, 30, 90, and 200 Mg ha^?1. The experiment to determine the bioavailability of metals in the soil using the bioassay was performed using sunflower. The DGT technique and Community Bureau of Reference (BCR) sequential extraction were used to determine the bioavailable fractions of the metals.

Results and discussion

The application of biosolids increased the phytoavailability of Zn, Ni, and Cr in most of the soils, as indicated by the increasing concentrations in sunflower plants as the biosolid application rate increased. In two of the soils, Codigua and Pelvín, this increase peaked at an application rate of 90 Mg ha^?1. Decreases in the bioavailable fractions of Zn, Ni, and Cr were observed with higher biosolid application rates. The bioavailability of metals was estimated through multiple linear regression models between the metals in the sunflower plants and the different chemical fractions of metals in the soils treated with different biosolid rates, which displayed a positive contribution of the labile (water soluble, carbonate, and exchangeable), oxide, and organic metal forms in the soil, particularly with respect to Ni and Zn at application rates of 30 and 90 Mg ha^?1. The bioavailable fraction of metals was determined in soils using the DGT technique. The effective concentration (C _E) results were compared with those in sunflower plants. The DGT technique could effectively predict the bioavailable fractions of Cr, Ni, and Zn in the Taqueral soil but only that of Zn in the Polpaico soil.

Conclusions

The application of biosolids significantly increased the labile fraction of most of the metals in the studied soils, particularly at the highest biosolid application rate. C _E increased as the concentration of biosolids increased for most of the metals. The effectiveness of the DGT technique for predicting the bioavailability of metals was dependent on the soil type and the metal. However, the C _E for soil Cu was not related to plant Cu for all soils studied.     

Effect of elevated concentrations of Cd and Zn in soil on spring wheat yield and the metal contents of the plants

The effect of increasing concentrations of Cd and Zn in a sandy soil on spring wheat (Triticum vulgare L.) yields and the metal contents of the plants was examined in a pot experiment to establish critical levels of these metals in soil. The metals were added (individually and jointly) to the soil as sulfates in the following doses (in μg g^?1, dry wt.): Cd — 2, 3, 5,10, 15, 25, and 50; Zn ?200, 300, 500, 1000, 1500, 2500, and 5000. Cadmium added to soil did not affect yields of wheat. The Zn dose of 1000 μg g^?1 strongly reduced crop yields; at 1500 μg g^? Zn dose wheat did not produce grain. The metal contents of wheat increased with increasing concentrations of Cd and Zn in soil up to 10.3 and 1587 μ g^? of Cd and Zn in straw, respectively. The concentrations of both metals were higher in straw than in grain by factors of 3–7 and 1.5–2 for Zn and Cd, respectively. The relationships between Cd and Zn contents of the plants and soils were best expressed by exponential equations. High concentrations of Zn in soils (1042 and 1542 μg g^?1) enhanced uptake of Cd by plants. The tested threshold concentrations of the metals in soils (3 μg g^?1 for Cd and 200–300 μg g^?1 for Zn) are safe for Zn but are too high for Cd in terms of protecting plants from excessive metal uptake. The critical Cd content of sandy soil should not exceed 1.5 μg g^?.     

Development of annual xylem rings and shoot growth of young beech (Fagus sylvatica L.) grown in soil with various Cd and Zn levels

In a pot culture experiment two-year-old beech (Fagus sylvatica L.) were planted in soil amended with different concentrations of Cd and Zn or combinations of both. Concentrations ranged up to ca 180 μmol Cd and 7500μmol Zn kg^?1 soil dry weight (1 M ammonium acetate extracts). After 2 seasons of growth plants were harvested. Annual xylem growth rings in stems were significantly smaller at 50 μmol Cd kg^?1 and 1000 μmol Zn kg^?1 as compared to controls. Elongation of apical shoots was significantly reduced at 180 μmol Cd kg^?1 and 1000 μmol Zn kg^?1. The lowest treatment of 50 μmol Zn kg^?1 caused no significant growth depressions of stem diameter and shoot elongation. In the second year of treatment growth reductions were generally more pronounced than in the first season. Uptake and translocation of Cd and Zn into stem wood and leaves were marked and were correlated with substrate concentrations. The observed growth reductions are discussed with respect to possible adverse effects of trace elements on forest trees under field conditions.     

GREENHOUSE GAS EMISSIONS FROM AN ALKALINE SALINE SOIL CULTIVATED WITH MAIZE (ZEA MAYS L.) AND AMENDED WITH ANAEROBICALLY DIGESTED COW MANURE: A GREENHOUSE EXPERIMENT

Sludge derived from cow manure anaerobically digested to produce biogas (methane; CH₄) was applied to maize (Zea mays L.) cultivated in a nutrient-low, alkaline, saline soil with electrolytic conductivity 9.4 dS m^?1 and pH 9.3. Carbon dioxide (CO₂) emission increased 3.1 times when sludge was applied to soil, 1.6 times when cultivated with maize and 3.5 times in sludge-amended maize cultivated soil compared to the unamended uncultivated soil (1.51 mg C kg^?1 soil day^?1). Nitrous oxide (N₂O) emission from unamended soil was -0.0004 μg nitrogen (N) kg^?1 soil day^?1 and similar from soil cultivated with maize (0.27 μg N kg^?1 soil day^?1). Application of sludge increased the N₂O emission to 4.59 μg N kg^?1 soil day^?1, but cultivating this soil reduced it to 2.42 μg N kg^?1 soil day^?1. It was found that application of anaerobic digested cow manure stimulated maize development in an alkaline saline soil and increased emissions of CO₂ and N₂O.     

Heterotrophic N2-fixation in arid soil crusts

The cryptogamic soil crusts of the Great Basin Artemisia, Ceratoides, and Atriplex plant communities contain a significant heterotrophic N₂-fixing microbial population in addition to the predominating filamentous cyanobacteria. The bacterial association with the cyanobacteria exhibits a phycosphere-like effect. Heterotrophically fixed N gains reached 17.5 μg N· g^?1 of soil (23.1% increase above the initial soil N content) and 45.9 μg N·g^?1 of soil (57.4% increase) after 3 and 5 weeks, respectively. (NH₄)₂SO₄ and native plant material amendments to soil resulted in a 41–100% reduction in N₂-fixation. The potential input of N to soil crusts may be reduced in the presence of shrub-produced allelochemic agents and by concurrent denitrification.     

Forms of Cd,Cu, Pb,and Zn in soil and their uptake by cereal crops when applied jointly as carbonates

The cereal crops (barley -Hordeum vulgare L., maize -Zea mays L., wheat -Triticum vulgare L.) were grown in a greenhouse using a sandy soil type treated with various doses of cadmium carbonate (salt), copper carbonate (malachite), lead carbonate (cerussite), and zinc carbonate (smithsonite), added jointly. The following levels of these metals were used: Cd ? 5, 10, 50μg g^?1 soil; Cu and Pb - 50,100, 500 μg g^?1 soil; Zn-150, 300, 1500 μg g-1 soil. Sequential extraction was adopted to partition the metals into five operationally-defined fractions: exchangeable, carbonate, Fe-Mn oxides, organic, and residual. The residual was the most abundant fraction in the untreated (control) soil for all the metals studied (50 to 60% of the total metal content). The concentrations of exchangeable Cd, Cu, Pb, and Zn were relatively low in untreated soil but increased (over the three year period) in treated soils for Cd, Zn, and Cu, whereas only small changes were observed for Ph. This experiment showed a significant increase in Cd, Zn, and Cu in tissue of plants grown on the treated soil, but a non-significant change in plant tissue with respect to Pb concentration.     

Evaluating the fraction of electrically associated cations on surfaces of soil particles by extrapolation of strong-field Wien effect measurements in dilute suspensions

Purpose

For agricultural production and environment protection, it is cations loosely bound to the soil particles that have a great significance in short-term processes of adsorption–desorption, exchange, and transport. It is beneficial to be able to evaluate the fractions of these cations in order to correctly predict potential pollution of soils by heavy metals and availability of plant nutrients.

Materials and methods

The homionic suspensions of yellow-brown soil (YB) and black soil I (BI) saturated with Na⁺ and Ca²⁺ and three subsamples of black soil II (BII) saturated with Ca²⁺ and Cd²⁺ were prepared to determine the electrical conductivity (EC) of the suspensions. On the basis of electrical conductivity vs. field strength (EC-E) curve, the fraction of electrically associated cations on surfaces of soil particles was evaluated by extrapolation of strong-field Wien effect measurements in dilute suspensions.

Results and discussion

The maximum dissociation degree (α _max) of Na⁺ adsorbed on surfaces of yellow-brown soil and black soil I was about 0.21, which is approximately twice as much as those of Ca²⁺ (0.07–0.10) adsorbed on surfaces of two soils. The soil type was not the main factor in evaluating α _max, and the valence of the cations was. For divalent cations, α _max of Ca²⁺ and Cd²⁺ adsorbed on soil particles with different contents of organic matter descended in the order: top black soil II?>?bottom black soil II?>?OM-free bottom black soil II.

Conclusions

The relatively small fractions of electrically adsorbed cations—about 0.2 for Na⁺ and 0.1 for Ca²⁺ on yellow-brown and black soils particles indicated that even for the more loosely adsorbed Na⁺ ions, most of the cations in the double layers of soil particles were adsorbed strongly by other, more specific mechanisms and cannot be stripped off into the solution, which would increase its electrical conductivity in a strong applied field.

     

Aluminium chemistry and acidification processes in a shallow podzol on the Swedish westcoast

Processes pertinent to soil acidification with special emphasis on the solution chemistry of A1, were studied in three adjacent small catchments on the Swedish westcoast, with mixed coniferous forest and shallow podzols (average soil depth 50 cm). Soil solution from different depths, groundwater and stream-water were sampled. Separation of organic and inorganic Al species was done with an ion exchange technique. The concentration of organic A1 species was linearly correlated with the concentration of dissolved organic C (r,², varied from 0.38 to 0.69 with p, < 0.001). In the A horizon 83 to 97 % of the dissolved A1 consisted of organic species. The average concentration of total A1 varied from 3.3 to 9.8 μmole 1^?1, in soil leachates collected below the A₀, horizon, and from 29.3 to 47.0 pmole 1^?1, in leachates collected below the A₂, horizon. The organic Al species decreased in importance with increasing soil depth. Leachates collected below the B horizon had average total A1 concentrations ranging from 95.3 to 115 pmole 1^?1, with a contribution of organic species varying between 8 and 20% of the total concentration. Activity calculations indicated an equilibrium with A1(OH)SO₄, (pK _S = 17.23) in the lower part of the B horizon, while groundwater together with some of the leachates from the upper B horizon showed a better fit with A1₁₄(OH)₁₀SO₄ (pK₁ = 117.51). Streamwater was obviously influenced by the soil organic matter in the outflow areas in terms of A1- organic matter complexes and protolysis of dissolved organic acids. There was a net outflow of Al and sulphate from the lower part of the B horizon compared to input in throughfall precipitation. The relative concentration increase varied from 64.4 to 78.0 (A1) and from 1.52 to 1.92 (sulphate). The relative increase due to evapotranspiration was estimated to be 1.4. The corresponding concentration factors for Mg and Ca were from 2.06 to 2.38, and from 0.81 to 1.07, respectively, indicating a very low Ca weathering. Data were compared with other studies, both recent and older ones. The possible influence from present-day levels of H⁺ and sulphurous compounds in the atmospheric deposition is evaluated.     

Effects and relative toxicity of heavy metals on Cuscuta reflexa

The effects of four concentrations (0.5, 1, 5 and 10 μg mL^?1) of the heavy metals Hg, As, Pb, Cu, Cd, and Cr on some senescence variables of Cuscuta reflexa Roxb. were studied. All of the treatments, except 0.5 μg mL^?1, decreased Hill reaction activity, chlorophyll and protein contents and dry matter percentage in biomass and increased tissue permeability over control data. The harmful effects of the metals were best visible at 10 μg mL^?1. The general order of sensitivity was As > Cd > Pb > Hg > Cu > Cr (absolute metal concentration). The data suggest that Cuscuta reflexa shows tolerance to the heavy metals tested up to 0.5 μg mL^?1.