Evaluation of four chemical extractants for metal determinations in wetland soils

Abstract

Wetland soils (hydric soils) are unique in their chemical characteristics compared to upland soils. It is known that they are capable of removing a variety of wastes from polluted water entering the wetland including metals and potentially toxic heavy metals. When these metals are determined in wetland soils, it is necessary to use the proper chemical extractant(s). Four commonly used chemical extractants (Mehlich 1, Mehlich 3, 0.1M HCl, and DTPA) for soil fertility evaluation were selected to measure metal concentrations of three different wetland soils/spoils. Soil samples were collected from the constructed wetland cells which were lined with Abernathy silt loam topsoil and two different mine spoil materials [collected from active coal strip‐mined sites in Alabama (pH 5.9) and Tennessee (pH 3.2)]. Mehlich 3 extracted the most zinc (Zn), iron (Fe), manganese (Mn), calcium (Ca), magnesium (Mg), potassium (K), sodiumm (Na), and aluminum (Al), while 0.1M HC1 extracted more cadmium (Cd), copper (Cu), and lead (Pb). Extractants followed the same trend in removing quantities of the metals from the three soil/spoil materials, with DTPA generally extracting the least amount of the metal (the trend was Mehlich 3 > 0.1N HCl > Mehlich 1 > DTPA). However, DTPA removed larger quantities of metals from Tennessee spoil compared to Alabama spoil and topsoil, suggesting the higher effectiveness of DTPA under acidic conditions. Metal concentrations in plant tissue did not show a definite trend in correlation with metals extracted by the four chemical extractants.     

Comparison of four extractants and chemical fractions for assessing available zinc and copper in soils of India

Abstract

Relative suitability of different extraction procedures for estimating available zinc (Zn) and copper (Cu) in soils was assessed using DTPA, 0.1 N HCl, ammonium acetate+EDTA, and double acid (HCl+ H₂SO₄) as extractants and rice as a test crop in Neubauer experiment. The relationships between Zn concentration and uptake of Zn by rice plants and Zn extracted by the different methods showed that DTPA‐TEA, pH 7.3, could very suitably be used to assess Zn availability in soils. However, 0.1 N HCl was better for assessing the Cu availability in soils to the rice plants. Water‐soluble and exchangeable fractions of Zn and Cu had significant positive correlations with Zn and Cu concentrations, respectively obtained by all the four extractants tested. The results also showed that DTPA and ammonium acetate+EDTA extracted organically bound Zn, whereas DTPA, 0.1 N HCl and ammonium acetate+EDTA extracted organically bound Cu. Water‐soluble, exchangeable and organic matter bound fractions exhibited significant relationships with Zn and Cu concentrations, their uptake and rice dry matter yield.     

Effect of cobalt treatments on dry matter production of wheat and DTPA extractable cobalt content in soils

Abstract

The effect of different concentrations of cobalt added to two soil types, a sandy and a sandy loam soil, was studied on growth performance and tissue cobalt concentration of wheat plants. DTPA‐extractable cobalt was significantly higher in the sandy soil than in the sandy loam soil. Plants grown in the sandy soil accumulated significantly higher amount of cobalt in comparison to plants grown in the sandy loam soil. Roots were significantly richer in cobalt than shoots in both the soil types. Lower (1 μg g^‐1) administration of cobalt resulted in an enhancement in the growth whereas higher (5–625 μg g^‐1) addition inhibited growth. A significant inverse relationship between relative wheat yield and tissue cobalt concentration was observed. The results indicate a possible requirement of cobalt for higher plants.     

Kinetics of acid phosphatase in calcium chloride extractable soil organic matter

The aim of this work was to compare the kinetic parameters of acid phosphatase (EC 3.1.3.2.) extracted from two forest soils under oak or pine. Soil was extracted with 4 mM CaCl₂ and the extract was divided into two fractions by filtration: one >0.2 μm containing microbial cells and soil particulates, and the other <0.2 μm containing fine particles and dissolved organic compounds of soil. The >0.2 μm fraction had higher K_m (0.26–0.82 vs. 0.12–0.39) and V_max (0.07–0.79 vs. 0.06–0.16) values than the <0.2 μm fraction, indicating a higher enzyme-substrate affinity and smaller amount of enzyme in fine particles and dissolved organic matter.     

Soil solution and extractable calcium in gypsumamended coastal plain soils used for peanut culture

Abstract

Peanut (Arachis hypogaea L.) fruits absorb Ca directly from the soil solution; therefore, the concentration of soil solution Ca in the fruiting zone (0–8 cm) is important in determining the availability of adequate Ca during fruit development. Since the critical period for Ca requirement for peanut fruit may extend from 25–65 d after flowering, a measure of extractable Ca (Quantity factor) is also important in determining the replenishment of soil solution Ca over the fruiting period. A laboratory study was conducted to evaluate the effects of varying soil moisture regimes on soil solution and extractable Ca in gypsumamended Bonifay sand (loamy, siliceous, thermic, grossarenic, Plinthic Paleudult) and Greenville sandy loam (clayey, kaolinitic, thermic, Rhodic Kandiudult) soils over a 70‐d period. Soil solution Ca increased in both soils with increasing soil moisture, 14 d after incubation of gypsum‐amended soils. Subsequently, the soil solution Ca decreased for all moisture regimes in the Bonifay soil, but only in the driest regime in the Greenville soil. Soil solution Ca concentrations were 1.0 and 3.2 cmolc/L in the Bonifay soil and 2.7 and 1.6 cmolc/L in the Greenville soil for the wettest and driest regimes, respectively, 70 d after incubation. Gypsum amendment also increased the concentrations of K and Mg in soil solution in both soils; therefore, leaching of excess K and Mg below the fruiting zone may be facilitated in field situations.     

Comparative evaluation of residual and total metal analyses in polluted soils

Abstract

Two digestion procedures, employing aqua regia‐HF (ARHF) and HNO₃‐HCIO4‐HF (HHH), were used to analyze residual metals (following a chemical fractionation scheme) and total metal content of two soils, one moderately polluted by municipal sludge applications and the other a grossly‐contaminated sample (20.8% Pb) from a battery recycling site. Although commonly used in sequential extraction analyses, the ARHF method solubilized only 53% (significant at p = 0.05) of the HHH‐determined residual Pb in the battery soil. For the sludge‐amended soil, residual Cd, Pb, and Zn were not statistically different by the two methods. For the battery soil, a single ARHF extraction also underestimated total Pb and Cu relative to HHH, but both methods gave statistically‐similar total Cd, Cu, Pb, and Zn for the sludge‐amended soil. As the sample metal concentration increased, the ability of ARHF to solubilize HHH‐equivalent metal quantities generally decreased. Since the degree of contamination is often unknown for environmental samples, the HHH method is more reliable for assessing residual and total metals in polluted soils     

Evaluation of P sorption capacity and P extractants for assessing P requirements of maize in Western Nigeria savannah soils.

Abstract

Most of the P extractants developed for soils in temperate countries have not been able to successfully predict P requirements of crops in the tropics. Some workers have, however, suggested the use of sorption capacity at standard equilibrium P concentration to estimate fertilizer P requirements. Phosphorus sorption capacity (psc), determined at 0.2 and 2.0 ug/ml equilibrium P concentrations, were evaluated by greenhouse and field fertilizer experiments on savannah soils of western Nigeria. Correlation coefficients between psc at 0.2 and 2.0 ug/ml P and yield attributes were very low and not statistically significant. The sorption values were also not able to predict P requirement in these soils because psc, and therefore, buffer capacity were low, difficult to measure accurately and did not approximate values required for maximum crop yields.

Field P rates usually exceeded P requirements obtained from psc measurements. However, extractants which were able to indicate P status and availability in the soils correlated significantly with yield. It is suggested, therefore, that soil tests with suitable P extractants in addition to fixation studies which would evaluate P needed to increase soil F to a given level would have to be investigated for meaningful fertilizer recommendations.     

Comparative evaluation of Ca chloride and Ca phosphate for extractable sulfur in soils with a wide range in pH

Deficiency of sulfur (S) is becoming widespread in the rainfed systems of India, and there is increasing need for diagnosing the deficiency. Calcium chloride and Ca phosphate are commonly used for extracting available S in soils. Because of cost and the ease of availability locally, we prefer using Ca chloride as an extractant over Ca phosphate, for extracting available S. However, there is paucity of data on the comparative evaluation of the two extractants to extract available S, especially in soils having a wide range in natural pH (from acidic to alkaline range). It is recognized that soil pH plays a dominant role in the adsorption–desorption and extractability of sulfate‐S in soils. We compared the extraction of S by Ca chloride and Ca phosphate in 86 Indian soils having a wide range in pH (4.5 to 10.6). Sulfur in the extracts was determined by ICP‐AES. Considering all the 86 soil samples tested, there was an excellent agreement between the values of extractable S determined by using the two extractants (r = 0.96, p < 0.001). However, the correlation coefficient (r) between the values of extractable S by the two reagents, although highly significant, varied among the groups of soil samples according to the range in soil pH. The highest correlation coefficient (r = 0.99, p < 0.0001, n = 17) was found for soils with pH in the alkaline range (8.5–10.6), and the lowest correlation coefficient (r = 0.71, p < 0.0001, n = 58) was obtained with a set of soil samples with pH in the acidic range (4.5–6.5). For soil samples having pH in the near‐neutral range (6.7–7.3), an excellent agreement was observed (r = 0.93, p < 0.0001, n =11) between the extractable‐S values obtained by the two extractants. While Ca phosphate extracted higher amount of S compared to Ca chloride in soil samples with pH in the acidic range, the two extractants were equally effective for soil samples with pH in the neutral or alkaline range. Our results suggest that for most of the soils in the semiarid tropical regions, which have pH in the neutral to alkaline range, Ca chloride can replace Ca phosphate as an extractant for removing available S in such soils.     

Relationship between ph measured in water and calcium chloride for soils of Southwestern Australia

Abstract

Soil pH in southwestern Australia (WA) is usually measured either in water (pH_w) or 0.01M CaCl₂ (pH_Ca). There are no published relationships to convert one pH to the other. This has been done in this paper for 236 WA soils: pH_Ca=0.918 pH_w‐0.3556, r²=0.9401. It is, therefore, concluded that, for the majority of soils within WA, it is likely that the linear model proposed for all soils would give the best relationship.     

用模糊综合评判法评价土壤重金属污染程度

通过对南宁市郊 1 2个主要菜区土壤中重金属 ( Cu、Zn、Cd、Pb)含量的调查和分析测定 ,采用模糊综合评判方法对土壤重金属污染状况进行评价。结果表明 :南宁市郊部分蔬菜区土壤不同程度地受到Cu、 Zn、 Pb、 Cd的污染 ,污染程度依次是 :Cd>Pb>Zn>Cu。 1 2个样点污染程度依次为 n2 =n6 =n1 1 >n7=n8=n9>n1 =n4 >n5>n1 2 >n3=n1 0     

Effects of excess manganese and metal chelators on micronutrient concentrations in the xylem sap of iron-deficient barley plants

Barley (Hordeum vulgare L.) plants were grown hydroponically in a greenhouse for 14 d under Fe-deficient conditions before treatment for 3 h with excess Mn (25 µM) and equimolar amounts of plant-borne (phytosiderophores, PS) or synthetic (ethylene diamine tetraacetic acid, EDTA) metal chelators. The xylem sap was collected for 3 h and analyzed for PS, Fe, Mn, Zn, Cu, and citrate concentrations. Excess Mn in the feeding medium decreased the concentrations of PS, Fe, Zn, and Cu in the xylem sap. Addition of 25 µM Mn and an equimolar amount of PS to the feeding medium increased the concentrations of PS, Fe, and Cu in the xylem sap, while EDTA decreased the concentrations of PS and the above nutrients. Excess Mn in the feeding medium increased the Mn concentration in the xylem sap and this increase was more pronounced with the addition of PS to the feeding medium, while EDTA had a depressing effect. These findings suggested that the roots of Fe-deficient barley plants can enhance the absorption and/or translocation of both Mn²⁺ and a PS-Mn complex. Addition of excess Mn to the feeding medium, irrespective of chelators, did not affect the xylem citrate concentration, indicating that citrate may not contribute to the translocation of metal micronutrients. In the xylem sap of Fe-deficient barley plants, the concentrations of metal micronutrients were positively correlated with the concentrations of PSG     

Comparison of extractants for the determination of available phosphorus,potassium, calcium,magnesium and sodium in some Ethiopian and German soils

Abstract

A study was conducted with the purpose of comparing the efficiency of Mehlich 1, Mehlich 3, and calcium acetate lactate (CAL) extractants for the deter‐ mination of available phosphorus (P) and exchangeable cations [potassium (K), calcium (Ca), magnesium (Mg), and sodium (Na)] on 22 Ethiopian and 10 German agricultural soils. The Olsen and NH₄OAc extractants were used as standards against which P and exchangeable cations values were compared. Results showed that, in general, highly significant correlations were found between all of the methods for available P and exchangeable cations determination on the Ethiopian soils. The highest correlation was, however, found with the Mehlich 3 extractant. On the ten soils from Germany, the Olsen method did not give significant cor‐ relation with the CAL method for P determination. The CAL and Mehlich 3 extrac‐ tants were also not good indicators of Na availability when compared with the NH₄OAc method. It can be generalized that the Mehlich 3 is a suitable extractant for P, K, Ca, Mg, and Na in Ethiopian soils, but further study is recommended to confirm these findings under field conditions.     

Total content and extractable fraction of cadmium,cobalt, copper,nickel, lead,and zinc in calcareous orchard soils

Abstract

The levels and availability of six heavy metals cadmium (Cd), cobalt (Co), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) in calcareous orchard soils were measured in an investigation of a method for the determination of total content and extractable fraction of these metals by atomic absorption spectrometry. The digestion step was performed comparatively using two different types of heating. Cadmium, Cu, Ni, Pb, and Zn were determined by flame atomic absorption spectrometry (F‐AAS) and Cd was determined by electrothermal or graphite furnace atomic absorption spectrometry (GF‐AAS) using the method of standard addition. The detection limits, precision values, and accuracy (recovery assays) show the reliability of the method. The conditions for the determination of the extractable fraction of the metals were also optimized. Extraction time for Cd and Zn was studied, and the application of two hours of shaking was selected. The tested method was applied to real samples corresponding to highly calcareous orchard soils characteristic of the Mediterranean area. Only Zn, Cu and Pb showed high levels in their extractable forms, whereas Cd and Co had highest levels in their total contents. An important bio‐availability was observed in all the studied metals, but mainly for Cd and Pb.     

Automated determination of micro amounts of phosphate in dilute calcium chloride extracts of soils

Abstract

An Auto Analyzer II method for the colorimetric determination of micro amounts of phosphorus (<100 μg/L) in 0.01 M CaCl₂ soil extracts is described. The automated procedure gave results not significantly different from manual determinations.

Using data derived from four soils extracted in triplicate on three separate occasions, the relative confidence intervals for a single sample determination were found to be ± 10.6%.     

Evaluation of some chemical extractants for determination of exchangeable ammonium in tropical rice soils

Abstract

Seven rice soils varying in texture, pH, organic matter and total nitrogen content were extracted with 1N and 2N KCl, 1N and 2N Nacl, 10% Nacl at pH 2.5, N CH₃ CooNa at pH 3.0, and Morgan's reagent using a soil: solution ratio of 1:10. The ammonium in the extracts was determined by steam distillation with MgO.

The normality of KCl or Nacl had no significant effect on the amount of NH₄ ⁺ ‐N extracted but KCl proved a better extractant than Nacl. However, Nacl at pH 2.5 generally extracted significantly higher amounts of NH₄ ⁺ ‐N as compared to the neutral salt solution. N CH₃ CooNa at pH 3.0 did not extract more NH₄ ⁺ than Morgan's reagent. Overall, KCl appeared to be better than Nacl; Nacl at pH 2.5 N CH₃ CooNa and Morgan's reagent were either equally effective or better for some of the soils as compared to KCl. However, when recovery of the known amount of NH₄ ⁺‐N applied to soils was used as a criterion, the efficiency of these chemicals were in the following descending order: KCl > NaCl, pH 2.5 > NaCl > CH₃CooNa, pH 3.0 > Morgan's reagent.     

Influence of different temperatures on metal tolerance measurements and growth response in bacterial communities from unpolluted and polluted soils

The effects of temperature on the growth rate and metal toxicity in soil bacterial communities extracted from unpolluted and polluted soils were investigated using the thymidine and leucine incorporation techniques. An agricultural soil, which was contaminated in the laboratory with Cu, Cd, Zn, Ni or Pb, and an uncontaminated forest soil were used. Measurements were made at 0°C and 20°C. Leucine incorporation was found to be as sensitive to heavy metals as thymidine incorporation in the short-term trial used to indicate heavy metal tolerance. Similar IC₅₀ values (the log of the metal concentration that reduced incorporation to 50%) were also obtained at 0 and 20°C, independently of the technique used. Metal tolerance could thus be measured using both techniques at any temperature in the range 0–20°C. In the long-term experiment different temperature-growth relationships were obtained on the basis of the rate of thymidine or leucine incorporation into bacterial assemblages from unpolluted and polluted soils, as judged from the minimum temperature values. This could not be attributed to the metal addition alone since different patterns were observed when different metals were added to the soil. Thus, the minimum temperature for thymidine incorporation was similar in Cu-polluted and unpolluted soil, while in soils polluted with Cd and Zn the minimum temperature increased by 2°C, and Ni and Pb additions increased the minimum temperature by 4°C compared to the unpolluted soil. This suggested that heavy metal pollution led to bacterial communities showing different temperature characteristics to those in the corresponding unpolluted soil. Similar observations were deduced from the minimum temperatures required for leucine incorporation. Three groups of bacterial communities were distinguished according to the growth response to temperature in polluted soils, one group in Cu-polluted soil, a second group in soil polluted with Zn and Cd, and a third group in soils polluted with Ni and Pb.     

Relationship between extractable Al and organic C in volcanic soils of Chile

In previous studies, Al extracted by acid ammonium acetate (Al_a) or Na-pyrophosphate (Al_p), rather than silt or clay content and climate conditions, was the most important factor that controls organic matter (OM) levels in volcanic soils. Here, the hypothesis was tested that Al_a is a comparable method (as much as CuCl₂) to quantify the proportion of Al bound to OM in allophanic soils. As far as we know, there are no previous antecedents in which selective dissolution method has been compared with this extractant. Secondly, we examine the effects of (a) Al, (b) silt plus clay content (particles size 0-53 µm) and (c) clay mineralogy on the control of organic carbon (OC) level in Chilean volcanic soils. This was achieved by sampling 16 soils series (11 Andisols, one Alfisol and four Ultisols, USDA classification) including 48 soil pedons up to 0.4 m depth. Soils were analyzed for Al_a, Al_p, oxalate (Al_o, Si_o and Fe_o), cold NaOH (Al_n) and un-buffered salts, CuCl₂ (Al_Cu), LaCl₃ (Al_La) and KCl (Al_k). We also measured the Al-humus as soluble C fraction after pyrophosphate extraction and the C associated to the silt plus clay fraction after sonication and gravity decantation. The statistical package (S)MATR was used to examine bivariate linear regressions among soil properties by computing the standardized major axis (SMA). Our results indicate that Al_a had a good correspondence with Al_p (R² = 0.76) in the top soil with Al_a/Al_p ratio of 0.19 and both extractans presented significant and positively relationship with soil OC (R² > 0.62). Acid ammonium acetate was as effective as Al_Cu to determine the Al-OM in allophanic soils. It is cheaper than Al_Cu and Al_p and 0.5 h shaking is required compared to 2 h of Al_Cu and 16 h of Al_p. The efficiency of the extraction was: Al_n ≥ Al_o > Al_p > Al_Cu ≥ Al_a > Al_La > Al_k. We also found that allophane content (estimated by Al/Si ratio) was strongly correlated (R² = 0.82) with the OC in the fine silt plus clay and that Al-humus together with C in the finest particles explained (R² > 0.60) the largest proportion of variation of soil OC across studied soils.     

The profile distribution of total and extractable zinc in selected Nigerian soils

Abstract

The profile distribution of total, DTPA‐ and 0.1 N HC1‐extractable Zn was determined in 11 Nigerian soil profiles formed on various parent Materials including the coastal plain sands, shales, basalt, granite and banded gneiss.

The total content ranged from 9 to 84 ppm. Generally soils developed on igneous rocks contained more Zn than those on sedimenatary deposits. Among the soils on sedimentary rocks, those on shale had more total Zn than those on sandstones. Total Zn was weakly correlated with organic matter but strongly associated vith clay content and free oxides of iron and manganese.

The amounts of Zn extracted by DTPA and 0.1 N HC1 ranged from 0.01 to 10.98 and from 0.23 to 6.25 ppm, respectively. The dilute acid generally removed more Zn from the soils than did the DTPA. The amounts extracted generally decreased vith depth especially vith DTFA extractant. Soils developed on basalt and shales contained the highest amounts of 0.1 N HCl‐extractable Zn while those on basement complex rocks gave the highest values of DTPA‐extractable Zn. Extractable Zn from soils on coastal plain sands remained relatively lev. The extractable Zn was more associated vith organic matter than vith clay content.     

The profile distribution of total and extractable copper in selected Nigerian soils

Abstract

The profile distribution of total, DTPA‐ and 0.1N HCl‐extractable Cu was determined in 11 Nigerian soil profiles formed from various parent materials including the coastal plain sands, shales, basalt, granite and banded gneiss.

Total Cu ranged from 7 to 72 ppm with a mean of 35 ppm₀ The soils formed from basalt had the highest values while those on coastal plains had the least content. Generally, there was a higher content in the subsoils than in the surface horizons. The total Cu significantly correlated with percent clay and the free oxide contents of Fe and Mn.

DTPA ‐ and 0.1N HCl‐extractable Cu ranged from 0.08 to 2.81 ppm and 0.10 to 7.78 ppm, respectively. Soils on metamorphic rocks gave the highest values of DTPA‐extractable Cu. The DTPA‐extractable Cu ‐was only related to pH but the acid extractable Cu was associated with total Cu, clay, free Fe₂O₃ and MnO₂ contents.     

矿区植物根内嗜鱼外瓶霉对重金属的耐性和超积累作用

从云南会泽铅-锌矿区自然生长植物密序野古草(Arundinella bengalensis(Spreng.)Druce)的健康根内分离得到一株深色有隔内生真菌(dark septate endophytes,DSE)。据其形态学特征和ITS1-5.8S-rDNA-ITS2序列分析,鉴定为一株嗜鱼外瓶霉(Exophiala pisciphila)。纯培养条件下研究了其对Pb2+、Zn2+、Cd2+的耐性和超积累作用。结果表明,此菌株在液体合成培养基上可以分别耐受2、3和0.5 g/L的Pb2+、Zn2+和Cd2+;在含Pb2+、Cd2+培养基中生长其菌丝可以富集超过其干重25%以上的Pb2+和5%以上的Cd2+;显示此菌株属于极端耐性并具有超积累作用的真菌。此真菌在植物根系的定殖或许可以通过菌丝体对金属离子的固持作用缓解植物根围土壤微环境中超量金属离子对植物的毒害作用。