The solid solution equilibria of lead and cadmium in polluted soils

A method for the measurement of Pb and Cd in equilibrium soil solutions involving soil equilibration with a dilute Ca electrolyte, centrifugation and filtration to <0.2 μm was evaluated. The procedure was subsequently used for the analysis of 100 Pb- and 30 Cd-contaminated soils. Solutions were analysed for Pb- and Cd using graphite-furnace AAS and the concentrations of Pb²⁺ and Cd²⁺ were estimated using standard speciation calculations. The concentrations of Pb and Cd found in the soil solutions were in the range 3.5–3600 μg dmp ^?3 and 2.7–1278 μg dm ^?3 respectively; both ranges represented less than 0.1% of the total metal concentration in the soils. Depending on solution pH, Pb ⁺² accounted for between 42–78% of Pb in solution while about 65% of Cd in solution was present as Cd⁺². The concentrations of Pb²⁺ and Cd²⁺ in solution suggested that the soil solutions were undersaturated with respect to the solid phases PbC0₃ and CdC0₃ but supersaturated with respect to Pb₅(P0₄)₃Cl and, for some samples, Cd₃(P0₄)₂ respectively. However, for both metals, a good empirical relationship was obtained between the total metal concentration in soil (mol kg^?1), free metal concentration in solution (mol dm^?3) and solution pH. The relationships took the general form of a pH-dependent Freundlich adsorption equation: For both lead and cadmium relationships, the values ofn and K₁ were close to unity, so that the distribution coefficient could be estimated from pH and a single metal-dependent constant, K₂. The algorithms appeared to be valid over a metal concentration range of four logarithmic units and pH range of 3.5–7.5.     

丛枝菌根真菌对蚕豆秸秆降解及玉米养分和镉铅吸收的影响

[目的]丛枝菌根真菌(arbuscular mycorrhizal fungi,AMF)有利于作物对养分的吸收.在镉、铅污染的土壤中,作物常将镉、铅积累在秸秆中,随着秸秆的还田而释放回土壤.探究前茬蚕豆秸秆还田和丛枝菌根真菌单施或联合施用对土壤肥力、后茬玉米的矿质养分与镉、铅吸收的影响,为AMF在调控污染农田轮作体系矿...     

Distribution of different fractions of cadmium,zinc, lead,and copper in unpolluted and polluted soils

McLaren and Crawford's method for fractionating soil Cu was modified, and used to fractionate soil Cd, Zn, Pb, and Cu in 38 soil samples from 11 soil profiles from industrially polluted and nearby unpolluted areas. Pollutant metals, especially Cd and Zn, were more soluble than the native soil metals. On average, approximately 45% of Cd was present in the CaCl₂ soluble (CA) fraction, whereas corresponding values for the other metals were below 10%. The percentages of each metal in the CA fraction followed the order Cd > Zn > Pb > Cu. The same order was observed for the acetic acid soluble (AAC) fraction. Approximately 30% of total Pb and Cu were present in the pyrophosphate soluble (PYR) fraction, and only 10% of total Cd and Zn. Approximately 20% of total Zn or Pb and 10% of Cd or Cu were present in the free oxide (OX) fraction. Only 20% of Cd and between 40–50% of the other 3 metals were present in the residual (RES) fraction. The results show that Cd is more labile than the other 3 metals.     

Distribution and budget of cadmium and lead in an agricultural region near Adelaide,South Australia

The principal natural and anthropogenic factors important in determining the regional distributions and relationships of Cd and Pb were studied by field sampling of stream waters, soils, pasture plants and rainfall of an agricultural area thought to represent typical ‘background’ for toxic metals. Cadmium in surface soils has a distribution associated with phosphate fertilizer use, geochemistry of parent materials, and atmospheric fallout of urban origin. Lead contamination of surface soils and rainfall decreases with distance from the urban area, the principal source of contaminant Pb being automotive emissions. For both elements, soil was the main sink. Losses of Pb and Cd in stream waters and agricultural products are negligible when compared with inputs, leading to a gradual accumulation in surface soils. With current fertilizer practice, extractable-Cd concentrations in surface soils will approximately double within about 20 yr. Similar increases in soil Pb will require at least 200 yr if the diminishing use of Pb in petrol remains the only significant source.

     

Effect of pH on chemical forms and plant availability of cadmium,zinc, and lead in polluted soils

The effect of pH on chemical forms and plant availability of heavy metals in three polluted soils was investigated. The soils were adjusted to pH values of 7.0, 6.0, and 4.5, then sequentially extracted so that Cd, Zn, and Pb could be partitioned into five operationally defined chemical fractions: exchangeable, carbonate, Fe-Mn oxide, organic, and residual. Kidney beans were grown in the soils to investigate plant availability of the metals in relation to changes of their levels in chemical forms resulting from alteration of soil pH. Alteration of pH resulted in changes of chemical forms of the metals in the soils, and at lower pH the changes were more significant. When soil pH values were decreased from 7.0 to 4.55, levels of Cd, Zn, and Pb in exchangeable form increased, decreased in carbonates and decreased slightly in Fe-Mn oxide forms. Their levels in organic and residual forms were unchanged. Although concentration of metals in plants increased with reduction in soil pH values, dry matter yields were also restricted, so that the amount of metal uptake were almost similar. The uptake rate of the metals in the exchangeable + carbonate forms was the same for the three elements in all the cases.     

微波消解-GFAAS测定肥料中铅、镉含量的方法

通过多个实验的研究分析建立了微波消解法作为样品前处理,原子吸收石墨炉(GFAAS)法同时测定肥料中铅、镉含量的方法。结果表明,铅的检出限为1.6μg/L,镉的检出限为0.11μg/L;7次平行相对标准偏差3%;3个浓度水平加标回收率均在90%～110%。微波消解-GFAAS法对肥料中铅镉测定结果准确、稳定,且更节约人力、物力以及时间,可作为推荐方法。     

Lead and cadmium contamination in the area immediately surrounding a lead smelter

Air, soil, and vegetation samples taken in the vicinity of a lead smelter were examined for Pb and Cd. The results indicate that the plant is a source of Pb and that this pollution may ose a threat to grazing animals but probably not directly to the local residents. Although Cd results are higher than normal no Cd pollution is directly attributed to the smelter.     

Contamination of soils near a copper smelter by arsenic,antimony and lead

Stack dust from a large Cu smelter near Tacoma, Washington has contaminated soil with As, Sb, and Pb. Within 5 km of the smelter 380 ppm (dry weight) As, 200 ppm Sb, and 540 ppm Pb have been measured in the surface soil (0–3 cm). Plants grown in these soils may be affected and also the consumption of plants coated with this heavy metal rich dust may be of concern.     

Survey of lead and cadmium in adult canned foods eaten by young children

A U.S. Food and Drug Administration survey of lead and cadmium in 10 adult canned foods commonly eaten by children less than 5 years old was conducted between October 1981 and September 1985. The survey, which included foods preserved by a commercial canning process and packaged in metal containers, found the highest mean levels of lead (0.32 micrograms/g) in tuna and of cadmium (0.02 micrograms/g) in tuna and tomatoes. Lead levels in foods packaged in lead-soldered cans were about 5 times as high as those in foods packaged in nonlead-soldered cans. Mean lead levels appeared to decline over the 4 years of the study. Cadmium levels were usually below the data reporting limit (0.01 micrograms/g).     

Relationships between the partitioning of lead in sediments and its accumulation in the marine mussel,Mytilus edulis near a lead smelter

Surficial sediment samples and specimens of the filter-feeding marine mussel, Mytilus edulis, were collected at thirteen sites near a Pb/Zn ore stockpile and smelting complex (Canada). Aside from measuring the total S content in the sediment samples, each of these samples were subjected to a sequential extraction procedure designed to determine the partitioning of Fe and Pb among various geochemical phases and compared with the Pb levels measured in the mussel tissues. About one third of the Fe and more than 90% of the Pb were extracted from the sediments. Sediments collected within Belledune Harbour generally yielded the greatest amount of Pb whereas the highest levels of S were measured in Dalhousie Harbour sediments. Regression analysis indicated that the total S content in the sediments played an important role in defining the Pb accumulation in the mussel tissues.     

Determination of cadmium, lead, and copper in margarines and butters by galvanostatic stripping chronopotentiometry

A galvanostatic stripping chronopotentiometric (GSCP) method for the simultaneous determination of cadmium, lead, and copper in commercial margarines and butters is described. Quantitative analyses of heavy metals in the mineralized fat samples, except standard addition method, were carried out automatically. The mean concentrations of Cd(II), Pb(II), and Cu(II) in different types of margarines and butters varied from 9.1 to 26.2, 9.2-14.2, 298.2-364.0 microg x kg(-)(1), respectively, that is below the legal requirements. The detection limits are 0.02, 0.02, and 0.06 microg x L(-)(1) for Cd(II), Pb(II) and Cu(II), while the reproducibilities are 3.3, 5.7, and 2.0%, respectively. The comparable precision (RSD = 0.76-4.5 and 0.87-4.9%) and recovery (96.7-102.2% and 96.1-103.2%) for the proposed GSCP and standard GFAAS methods, demonstrate the benefit of GSCP method in the routine analysis of heavy metal ions in fats.     

Influence of pH on copper, lead and cadmium binding by an ombrotrophic peat

The effect of pH on the adsorption of copper (Cu), lead (Pb) and cadmium (Cd) by a peat soil was studied, and the results compared with those corresponding to cation binding by a dissolved peat humic acid (HA), and interpreted with a NICA–Donnan model. A potentiometric titration technique was used to determine the adsorption isotherms for H⁺, at different ionic strengths, and for Cu²⁺, Pb²⁺ and Cd²⁺ at different pH values, in a peat soil. The effect of the ionic strength on proton binding was similar for the soil (solid) organic matter and for dissolved HA. The adsorption isotherms for cation–peat and the binding curves cation–dissolved HA are almost parallel, although more cation was adsorbed per kg of C in the dissolved HA. The effect of pH on cation binding is similar for dissolved organic matter and for the organic soil. At low metal concentration the amount of adsorbed metal followed the order Cu²⁺ > Pb²⁺ > Cd²⁺. The cation-binding parameters obtained with the NICA–Donnan model allow excellent simulation of the effect of pH on the adsorption of Cu, Pb and Cd ions in the studied peat soil. The binding constants for the peat suspension were greater than the corresponding generic parameters for dissolved HA. Speciation calculations showed that for Cu and Pb, the most abundant fraction was the metal adsorbed on peat, whereas for Cd the most abundant fraction was dissolved metal.     

Effect of heavy metals on microorganisms in soils near a secondary lead smelter

Soil samples were collected to a depth of 0 to 10 cm from several sites near a secondary Pb smelter during the summer of 1976 in order to determine heavy metal concentrations of soil and enumerate soil microorganisms and earthworms. Chemical analyses indicated that abnormally high concentrations of Pb, As, Cd, and Cu decreased with increasing distance from the source and population counts of bacteria, actinomyces, fungi, nematodes and earthworms increased with increasing distance from the smelter. The negative correlation coefficients between bacteria, actinomyces, fungi, and nematodes and the level of Pb, As, Cd, and Cu in the soil were statistically significant. The microflora of the contaminated soil was altered and the marked quantitative reduction or elimination of organisms were attributable to heavy metal pollution emission from the secondary Pb smelter.     

土壤环境质量铅镉基准值的研究综述

综述了分别用生物环境效应试验和土壤生态地球化学方法研究铅镉基准值的特点和进展。探讨了土壤生态地球化学，地球化学以及生态毒理学研究者对铅镉土壤环境质量基准值的研究思路。比较了国内外在确定铅镉基准值时存在的差异。列举了针对不同口的制订铅镉基准值的研究现状。为完善现有土壤环境质量标准提供了基础资料。     

Interference by tin in AOAC dry-ash voltammetric method for determination of lead and cadmium in canned foods

When lead and cadmium were determined in samples of canned food by the AOAC anodic stripping voltammetric method, an interference was observed which was believed to be tin(IV). This interference could cause false positive results for lead and cadmium. The electroactivity of tin(IV) was suppressed by increasing the concentration of tartaric acid in the supporting electrolyte from 0.005M to 0.1M after mixing with an equal volume of sample solution.     

Gel permeation chromatography studies on the speciation of lead in solutions of heavily polluted soils

Samples of solutions from soils contaminated with lead as a result of three different processes: natural weathering and dispersion from an ore body, mining and smelting, and sewage sludge-amendment to land, were fractionated on Sephadex gels. Solutions from the sludge-amended soil, dried sludge and calcareous mine soils were found to contain a proportion of lead eluted at the exclusion limit of the gel, accompanied by a peak in U.V. absorbance, implying the occurrence of a high molecular weight organo-lead complex. This fraction was proportionally highest in the solution from the dried sludge sample; however, low molecular weight organic peaks were also accompanied by elution of Pb in all samples except that from the low pH, naturally contaminated site. Association of Pb with organic matter was observed to be greater in samples of soil solution with a higher initial pH and this may be related to increased stability constants for Pb-organo complexes at higher pH.     

Leaching of zinc,lead and cadmium in columns of calcareous soils

Leaching of zinc, lead and cadmium was studied in columns packed with soil differing in pH, clay, organic matter and calcium carbonate contents. Distribution of 1 N HCI extractable heavy metals in different layers of the columns as a function of the amount of water leached was the criteria for measuring leachability of the three metals. Leachates contained only traces of the metals. Movement of surface applied metals could be observed only upto 30mm depth. Cadmium, which was observed to be the most mobile element, was leached to a depth of 30–40mm in a pH 7.5, light textured soil with 0.9 % calcium carbonate. Presence of superphosphate at the soil surface reduced the extent of leaching to an appreciable extent.     

The use of liquid chromatography in the study of cadmium speciation in soil solutions from polluted soils

Chromatographic methods were used in an attempt to identify the various species of cadmium in soil solution. Exclusion and reverse-phase chromatography using HPLC showed that cadmium existed in the form of low-molecular weight, highly polar species. Ion-exchange chromatography was used to divide soil solution cadmium into cationic, anionic and neutral species. Cadmium was found to be mainly in the form of inorganic cationic species, including the free ionic form, Cd²⁺, and some as neutral species, possibly organic as well as inorganic, especially in soils of higher pH. Anionic species were relatively unimportant. These results showed general agreement with those of other authors using computer models to predict cadmium speciation in soil solution.     

Competitive sorption of cadmium and lead in acid soils of Central Spain

The bioavailability and ultimate fate of heavy metals in the environment are controlled by chemical sorption. To assess competitive sorption of Pb and Cd, batch equilibrium experiments (generating sorption isotherms) and kinetics sorption studies were performed using single and binary metal solutions in surface samples of four soils from central Spain. For comparisons between soils, as well as, single and binary metal solutions, soil chemical processes were characterized using the Langmuir equation, ionic strength, and an empirical power function for kinetic sorption. In addition, soil pH and clay mineralogy were used to explain observed sorption processes. Sorption isotherms were well described by the Langmuir equation and the sorption kinetics were well described by an empirical power function within the reaction times in this study. Soils with higher pH and clay content (characterized by having smectite) had the greatest sorption capacity as estimated by the maximum sorption parameter (Q) of the Langmuir equation. All soils exhibited greater sorption capacity for Pb than Cd and the presence of both metals reduced the tendency for either to be sorbed although Cd sorption was affected to a greater extent than that of Pb. The Langmuir binding strength parameter (k) was always greater for Pb than for Cd. However, these k values tended to increase as a result of the simultaneous presence of both metals that may indicate competition for sorption sites promoting the retention of both metals on more specific sorption sites. The kinetic experiments showed that Pb sorption is initially faster than Cd sorption from both single and binary solutions although the simultaneous presence of both metals affected the sorption of Cd at short times while only a minor effect was observed on Pb. The estimated exponents of the kinetic function were in all cases smaller for Pb than for Cd, likely due to diffusion processes into micropores or interlayer space of the clay minerals which occurs more readily for Cd than Pb. Finally, the overall sorption processes of Pb and Cd in the smectitic soil with the highest sorption capacity of the studied soils are slower than in the rest of the soils with a clay mineralogy dominated by kaolinite and illite, exhibiting these soils similar sorption rates. These results demonstrate a significant interaction between Pb and Cd sorption when both metals are present that depends on important soil properties such as the clay mineralogy.