Behavior of heavy metals in forest microcosms: II. Effects on nutrient cycling processes

Effects of heavy metals on forest nutrient cycling processes were investigated using intact forest microcosms. Baghouse dust from a primary Pb smelter in southeastern Missouri was applied on the microcosms to approximate one annual deposition of metals at 0.4 km from the smelter. Contaminated litter from a forest adjacent to the smelter was also placed on the microcosms. Total dosage of Pb, Cd, Zn, and Cu was 11.0, 0.128, 0.748, and 0.161 mg cm^?2, respectively. Sustained increases in leaching rates of Ca and NO₃-N were found in microcosms amended with heavy metals. After 20 mo, extractable Ca, NH3-N, NO₃-N and dissolved organic carbon (DOC) were significantly lower in treated soil to a depth of 5 cm. In addition, extractable NH₃-N, NO₃-N and DOC were significantly lowered to a depth of 10 cm. Results from this experiment indicate that forest microcosms can be used for determining the effect of heavy metals on forest ecosystems.     

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.     

Effect of controlled-release urea on heavy metal mobility in a multimetal-contaminated soil

Controlled-release N fertilizers can affect the availability of heavy metals in the contaminated paddy soil.A soil incubation experiment was conducted to investigate the effects of prilled urea(PU),S-coated urea(SCU),and polymer-coated urea(PCU)on the solubility and availability of heavy metals Cd,Pb,Cu,and Zn in a multimetal-contaminated soil.The results showed that the application of different coated urea significantly affected the solubility and availability of heavy metals.At 5 d of incubation,the application of PU,SCU,and PCU had significantly decreased the concentrations of water-soluble and available Cd,Pb,Cu,and Zn,when compared with the control.At 60 d of incubation,the depletory effects of PU on water-soluble and available heavy metals had reduced,and the initial decrease in the concentrations of water-soluble Cd,Pb,Cu,and Zn caused by SCU had changed to an increase.The concentrations of water-soluble Pb,Cu,and Zn in the SCU-treated soil were higher than those in the control.Application with PCU led to a higher water-soluble Cu than that in the control,while the available Cd,Pb,and Zn were lower than those in the control.The effect of different coated urea was much stronger on the water solubility of the heavy metals than on their availability.The effects of controlled-release urea on the transformation of heavy metals resulted in changes in the concentrations of NH4^+,water-soluble SO4^2-,and soil p H.The results further suggested that PCU could be used in dry farming operations in multimetal-contaminated acid soils.     

Contents and chemical forms of heavy metals in school and roadside topsoils and road-surface dust of Beijing

Purpose

The concentration of human activities in urban systems generally leads to urban environmental contamination. Beijing is one of ancient and biggest cities on the world. However, information is limited on Beijing’s soil contamination, especially for roadside and campus soils. Thus, the aims of this study were to investigate the contents and chemical forms of toxic heavy metals Cd, Cr, Cu, Ni, Pb, and Zn in the road-surface dust, roadside soils, and school campus soils of Beijing. In addition, enrichment and spatial variation of these toxic heavy metals in the soils and dust were assessed.

Materials and methods

Topsoil samples were collected from the schools and roadside adjacent to main ring roads, and dust samples were collected from the surface of the main ring roads of Beijing. These samples were analyzed for total contents and chemical forms of Cd, Cr, Cu, Ni, Pb, Sc, Zn, Al, and Fe. Enrichment factors (EFs, relative to the background content) were calculated to evaluate the effect of human activities on the toxic heavy metals in soils.

Results and discussion

Heavy metal contents in the road dust ranged from 0.16 to 0.80, 52.2 to 180.7, 18.4 to 182.8, 11.9 to 47.4, 23.0 to 268.3, and 85.7 to 980.9 mg kg^?1 for Cd, Cr, Cu, Ni, Pb, and Zn, respectively. In the roadside soil and school soil, Cd, Cr, Cu, Ni, Pb, and Zn contents ranged from 0.13 to 0.42, 46.1 to 82.4, 22.7 to 71.6, 20.7 to 29.2, 23.2 to 180.7, and 64.5 to 217.3 mg kg^?1, respectively. The average EF values of these metals were significantly higher in the dust than in the soils. In addition, the average EF values of Cd, Cu, Pb, and Zn in the soils near second ring road were significantly higher than those near third, fourth, and fifth ring roads. Anthropogenic Cd, Pb, and Zn were mainly bound to the carbonates and soil organic matter, while anthropogenic Cu was mainly bound to oxides. The mobility and bioavailability of these metals in the urban soils of Beijing generally decreased in the following order: Cd?>?Zn?>?Pb?>?Cu?>?Ni?>?Cr; while in the dust, they decreased in the following order: Zn, Cu, and Cd?>?Pb?>?Ni?>?Cr.

Conclusions

Both EF and chemical forms documented that Cr and Ni in the soils and dust mainly originated from native sources, while Cd, Cu, Pb, and Zn partially originated from anthropogenic sources. In overall, Beijing’s road dust was significantly contaminated by Cd and Cu and moderately contaminated by Cr, Pb, and Zn, while Beijing’s roadside soil and school soil were moderately contaminated by Cd and Pb. However, the maximal hazard quotients (HQs) for individual Cd, Cr, Cu, Ni, Pb, and Zn and comprehensive hazard index (HI) of these metals in the dust and soil were less than 1, indicating that the heavy metals in the dust and soil generally do not pose potential health effects to children, sensitive population.     

Relations Between Soil Properties and Selected Heavy Metal Concentrations in Spring Wheat (Triticum aestivum L.) Grown in Contaminated Soils

Spring wheat was grown in soils near a non-ferrous metals mining and smelting base in Baiyin city, Gansu province, P.R. China. The area studied is 501 km². Some of the croplandshad been contaminated by heavy metals mainly through wastewaterirrigation or aerial deposition. The soil samples were analyzedfor pH, organic matter and available phosphorous (P); also fortotal cadmium (Cd), lead (Pb), copper (Cu) and zinc (Zn) contents. Spring wheat grains were also analyzed for heavy metals. The results were interpreted using multiple linear correlation and stepwise regression analyses. The increment oftotal soil contents of selected heavy metals could enhance grain Cd accumulation, and the increment of total Zn content of soil could lower the grain Pb accumulation. The correlationswere markedly increased by including other soil properties forgrain Cd and Pb. Stepwise regression analyses indicated that the effect of soil pH and available P on the uptake of grain Cd were greater than that of the other total soil contents ofheavy metals. Grain Cd and Pb could be reliably predicted bythe total soil contents of Cd and Pb while the uptake of grainZn and Cu were not satisfactorily predicted.     

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.     

Effects of heavy metals in soil on microbial processes and populations (a review)

The effects of Cd, Cu, Zn, and Pb on soil microorganisms and microbially mediated soil processes are reviewed. The emphasis is placed on temperate forest soils. The sensitivity of different measurements is discussed, and data compiled to compare relative toxicity of different metals. On the whole the relative toxicity of the metals (on a μg g^?1 soil basis) decreased in the order Cd > Cu > Zn > Pb, but differences between different investigations were found. The influence of abiotic factors on metal toxicity is briefly discussed and especially examplified by different soil organic matter content. Evidence of tolerance and adaptation in the soil environment and the time scale involved in the evolution of a metal-tolerant microbial community after metal exposure are also considered.     

Heavy metal pollution of soil from industrial and municipal wastes in Chittagong,Bangladesh

Heavy metal pollution was assessed in soils collected from 0–15, 15–30 and 30–45-cm depths of three industrial (FMC, PMC and CMC), and two municipal (BSD and MLF) waste disposal sites around Chittagong city in 2008. Soils were analysed for pH, organic carbon, total nitrogen, available P, exchangeable Ca, Mg, K and Na, and total Cd, Pb, Cu, Mn and Zn. The pH, organic C, total N, available P, total Cd, Pb, Cu and Mn, and contamination indices for Cd and Pb varied significantly among sites. Mean Cd, Pb, Cu, Mn and Zn were in the range 0.5–1.9, 54–86, 25–50, 261–624 and 204–330 mg kg^?1, respectively. Contamination indinces for Cd, Pb, Zn and Cu were estimated by comparison with respective threshold values. Contamination indices showed that the sites MLF and FMC had low Cu contamination. Other sites were not contaminated with thisheavy metal. All sites except PMC were highly contaminated with Cd, FMC was moderately contaminated and the others had low Pb contamination. FMC was highly contaminated, but the others were moderately contaminated with Zn. The integrated contamination index revealed that PMC had low contamination and the other sites were highly contaminated with heavy metals.     

Retention of Metals in Agricultural Soils After Amending with MSW and MSW-Biosolids Compost

The goal of this study was to measure the As, Cu, Fe, Pb and Zn contents of soils amended with municipal solid waste (MSW) and MSW-biosolids compost and to determine the long-term transport of these metals to lower soil horizons. Lead, Cu, Cd and Zn contents in the composts were 3–20 times more concentrated in the compost compared to the soil at the Calverton, NY, U.S.A. farm. As a result, Pb, Cd, Cu and Zn were elevated in the upper 5 cm soil layer following compost application and the metal enrichment was proportional to the amount of compost applied (21–62 Mg ha^-1). In addition, Pb, As and Cu contents of the non-compost amended Calverton soils were enriched above the tillage depth (20–25 cm). Cu, Pb and As enrichment was attributed to the historical use of sodium arsenite, lead arsenate and copper sulfate insecticides and fungicides. Results of the metal analyses of soil cores collected 16 and 52 months following compost application showed that Cu, Zn and Pb remained confined to the upper 5 cm soil layer. The low water extractable fraction of these metals in MSW and MSW-biosolids compost was a major factor limiting the transport of these metals to lower soil horizons. In contrast, Cd leaching from the upper 0–5 and 5–10 cm soil layers was continuous over the 52 month study period and was attributed primarily to the presence of soluble Cd in phosphate fertilizer initially applied to the Calverton farm soil.     

Cadmium,Lead, Copper,Zinc, and Nickel in Lettuce and Dry Beans as Related to Mehlich-3 Extraction in Three Brazilian Latossols

Lettuce (Lactuca sativa L.) and dry beans (Phaseolus vulgaris L.) were grown in three Brazilian Red-Yellow Latossols (Oxisols) in greenhouse conditions with cadmium (Cd), lead (Pb), copper (Cu), zinc (Zn), and nickel (Ni) applied to soils in treatments arranged as a randomized complete block design. Plant metals were analyzed in lettuce shoots and dry beans roots, stems, leaves, and seeds. After plant growth, soil samples from the pots were extracted with Mehlich-3 (M-3) for metal availability evaluation. The release of Ni in the M-3 extraction was dependent on the soil exchangeable aluminum (Al^{3 +}). Mehlich-3 was efficient for determination of availability of Cd, Pb, Cu, Zn, and Ni for dry beans and availability of Cd and Ni for lettuce. The dry bean leaves Cd, Pb, Cu, Zn, and Ni were highly correlated with their recovering from soils with M-3. The same was observed for Cd and Ni in lettuce shoots and the M-3 recovered metals from soils.     

Heavy Metals in Polish Forest Stands of Quercus Robur and Q. Petraea

This study aimed to compare concentrations of Zn, Cd, Pb and Cu in wood of Quercus robur and Q. petraea and in the soil on 21 plots in different parts of Polish lowlands. Concentrations of those metals in growth rings taken with an increment borer were measured in 20-year periods. The curves of radial distribution of heavy metals in growth rings are highly variable, but usually a greater variation was observed in sapwood than in heartwood. This attests to transport of metals in the younger, functional xylem, and confirms earlier observations. Quercus petraea accumulated significantly more Zn but less Cd than Q. robur, while concentrations of other metals were similar in both species. No significant correlations between levels of different metals in oak wood were detected, except a strong correlation between Pb and Cd. Concentrations of heavy metals in oak wood were generally not correlated with their concentrations in the soil. Most of the forest stands can be regarded as free from pollution with heavy metals.     

Der Einfluß der natürlichen organischen Substanzen auf die Metallverteilung zwischen Boden und Bodenlösung in einem sauren Waldboden

The influence of organic matter in the translocation of metals between soil and soil solution of an acid forest soil Water extracts were prepared from soil samples which were collected from a soil profile showing very little variation in the texture down to a depth of 120 cm and thus only little translocation of clay in the soil profile. The aim of the study was to describe the distribution between soil and soil solution of several metals like Cu, Pb, Cd, Zn, Al and Mn as a function of humic substances, electrolyte concentration and pH. From the experimental results the following hypothesis on the reaction mechanisms involving metals and humus derived substances has been deduced. The metals Cu, Fe, Al and Pb are mobilized through complexation by soluble humus substances in addition to the usual pH dependent desorption and dissolution of hydroxides. This mobilization determines the solution concentration of Cu and Fe at pH > 3.7 and Al and Pb at pH > 4.2. Al, Fe and Pb are complexed selectively by high molecular weight humus derived substances which undergo adsorption on soil mineral surfaces. Cu interacts with low molecular weight humus derived substances which are not easily adsorbed by the mineral surfaces. Zn, Cd and Mn primarily undergo sorption and are thus controlled by pH and electrolyte concentration of solutions because their complexation with humus derived substances seems to be weak or nonexistant. It is further postulated that the humus derived substances mobilize Al³⁺ and Fe³⁺ ions. By this, other metals like Cd, Zn, Mn, Ca and Mg can occupy the free exchange sites.     

Fraction Distributions of Lead,Cadmium, Copper,and Zinc in Metal‐Contaminated Soil before and after Extraction with Disodium Ethylenediaminetetraacetic Acid

Abstract: The fraction distributions of heavy metals have attracted more attention because of the relationship between the toxicity and their speciation. Heavy‐metal fraction distributions in soil contaminated with mine tailings (soil A) and in soil irrigated with mine wastewater (soil B), before and after treatment with disodium ethylenediaminetetraacetic acid (EDTA), were analyzed with Tessier's sequential extraction procedures. The total contents of lead (Pb), cadmium (Cd), copper (Cu), and zinc (Zn) exceeded the maximum permissible levels by 5.1, 33.3, 3.1, and 8.0 times in soil A and by 2.6, 12.0, 0.2, and 1.9 times in soil B, respectively. The results showed that both soils had high levels of heavy‐metal pollution. Although the fractions were found in different distribution before extraction, the residual fraction was found to be the predominant fraction of the four heavy metals. There was a small amount of exchangeable fraction of heavy metals in both contaminated soils. Furthermore, in this study, the extraction efficiencies of Pb, Cd, and Cu were higher than those of Zn. After extraction, the concentrations of exchangeable Pb, Cd, Cu, and Zn increased 84.7 mg·kg^?1, 0.3 mg·kg^?1, 4.1 mg·kg^?1, and 39.9 mg·kg^?1 in soil A and 48.7 mg·kg^?1, 0.6 mg·kg^?1, 2.7 mg·kg^?1, and 44.1 mg·kg^?1 in soil B, respectively. The concentrations of carbonate, iron and manganese oxides, organic matter, and residue of heavy metals decreased. This implies that EDTA increased metal mobility and bioavailability and may lead to groundwater contamination.     

Untersuchungen zur Schwermetalladsorption in einem sauren Waldboden

Investigations of heavy metal adsorption in an acid forest soil To examine the adsorption of heavy metals in an acid forest soil (Pseudogley-Pelosol), undisturbed soil columns of 5 cm length were treated over a period of 276 days with solutions containing Pb, Cu, Zn and Cd. It can be shown that the heavy metals added were preferably adsorbed in the humus-rich, upper part of the soil. When treating the soil with the four heavy metals simultaneously, Pb, Cu and Cd were completely adsorbed in the soil matrix. However 20% of given Zn were leached out of the soil columns. Lowering pH in the percolation solution from pH 4 to 3 led to the mobilisation of previously adsorbed Cu, Cd and Zn, whereas Pb completely remained in the soil.     

Effects of Changed Soil Conditions on the Mobility of Trace Metals in Moderately Contaminated Urban Soils

Changes in the soil chemical environment can be expected to increase the leaching of trace metals bound in soils. In this study the mobility of trace metals was monitored in a column experiment for two contaminated urban soils. Four different treatments were used (i.e. rain, acid rain, salt and bark). Leachates were analysed for pH, dissolved organic carbon (DOC) and for seven trace metals (cadmium (Cd), chromium (Cr), copper (Cu), mercury (Hg), nickel (Ni), lead (Pb) and zinc (Zn)). The salt treatment produced the lowest pH values (between 5 and 6) in the effluent whereas the DOC concentration was largest in the bark treatment (40–140 mg L^?1) and smallest in the salt and acid treatments (7–40 mg L^?1). Cadmium, Ni and Zn were mainly mobilised in the salt treatment, whereas the bark treatments produced the highest concentrations of Cu and Pb. The concentrations of Cu, Cr, and Hg were strongly correlated with DOC (r ²?=?0.90, 0.91 and 0.96, respectively). A multi-surface geochemical model (SHM-DLM) produced values for metal dissolution that were usually of the correct magnitude. For Pb, however, the model was not successful indicating that the retention of this metal was stronger than assumed in the model. For all metals, the SHM-DLM model predicted that soil organic matter was the most important sorbent, although for Pb and Cr(III) ferrihydrite was also important and accounted for between 15 and 50% of the binding. The results confirm the central role of DOC for the mobilization of Cu, Cr, Hg and Pb in contaminated soils.     

Arbuscular Mycorrhizal Fungi Contribute to Resistance of Upland Rice to Combined Metal Contamination of Soil

A greenhouse pot experiment was conducted to investigate heavy metal [copper (Cu), zinc (Zn), lead (Pb), and cadmium (Cd)] uptake by two upland rice cultivars, ‘91B3’ and ‘277’, grown in a sterilized field soil contaminated by a mixture of Cu, Zn, Pb, and Cd. Rice plants were inoculated with each of three arbuscular mycorrhizal fungi (AMF), Glomus versiforme (GV), Glomus mosseae (GM), and Glomus diaphanum (GD), or remained noninoculated (NM). Both rice cultivars could be colonized by the three AMF used in this experiment. The percentage of mycorrhizal colonization by the three AMFs on the two rice cultivars ranged from 30% to 70%. Mycorrhizal colonization of both upland rice cultivars had a large influence on plant growth by increasing the shoot and root biomass compared with non-inoculated (NM) plants. The results indicate that mycorrhiza exert some protective effects against the combined toxicity of Cu, Zn, Pb, and Cd in the contaminated soil. This conclusion is supported by the partitioning of heavy metals (HMs) in the two cultivars. In the two cultivars, colonization by AMF reduced the translocation of HMs from root to shoot (except that the colonization of AMF increased the Cu translocation of HMs in cultivar ‘277’). Immobilization of the HMs in roots can alleviate the potential toxicity to shoots induced by the mixture of Cu, Zn, Pb, and Cd. The two rice cultivars showed significant differences in uptake of Cu, Zn, Pb, and Cd when uninoculated. GM inoculation gave the most protective effects on the two cultivars under the combined soil contamination.     

Competitivity,selectivity, and heavy metals-induced alkaline cation displacement in soils

Abstract

The simultaneous incorporation of heavy metals into the soil is still a matter of great concern. Interaction (competitive sorption) between these metals and the soil solid phase may result in a deterioration of soil quality which relies basically on amounts of alkaline cations saturating soils sorptive complex. Results of this study indicate that Pb, Cu, C d, and Zn have induced solution pH decreases which were more intensive at highest metal loading rates. Partition parameters (Kd)-based sequences showed that Pb and Cu were more competitive than Cd and Zn and the overall selectivity sequence followed: Pb > Cu > Cd > Zn. Metal loadings and their competitive sorption have led to a strengthened displacement of alkaline cations (i.e. Ca²⁺, Mg²⁺, K⁺, Na⁺), especially of Ca²⁺ as a factor “stabilizing” soil sorptive complex. Such metals impact jointly with soils acidification are of great environmental concern since tremendous amounts of alkaline cations (especially Ca²⁺) may be potentially leached out, irrespective of the degree of soil contamination, as evidenced in the current study. High and positive ΔG values implied that the studied soils were characterized by generally low concentrations of exchangeable potassium which required high energy to get displaced (desorbed). Further studies on heavy metal uncontaminated or contaminated areas should be undertaken to provide with data which should be used for predictions on changes related to soil buffering capacity as impacted by heavy metal inputs.     

The Effects of Copper and Lead on Growth and Zinc Accumulation of Thlaspi Caerulescens J. and C. Presl: Implications for Phytoremediation of Contaminated Soils

Thlaspi caerulescens J. and C. Presl is a Zn-hyperaccumulatingplant which has aroused considerable interest with respect to its possible use for phytoremediation of Zn-contaminated soils. In this work, a British population of T. caerulescens, from a soil which was found to have relatively high concentrations of water-extractable Cu (0.22 mg L^-1), Pb (0.99 mg L^-1) and Zn (6.49 mg L^-1), was studied. Its ability to grow and accumulate Zn from hydroponic nutrient solution in the presence of elevated concentrations of Cu and/or Pb was investigated. The chosen concentrations of Cu, Pb and Zn were based on reported water-soluble concentrations of these heavy metals in contaminated soils. When supplied with 32.7 mg L^-1 Zn, plants accumulated 19 780 mg kg^-1 Zn in their shoot dry matter. This concentration declined by 9.3, 87 and 84% respectively when 5.0 mg L^-1 Pb, 1.0 mg L^-1 Cu or 2.0 mg L^-1 Cu were included in the nutrient solution. Despite the apparent adaptation of this population of T. caerulescens to a Zn/Pb/Cu-contaminated soil, these Cu treatments strongly inhibited growth, but the Pb treatment did not affect growth significantly.     

Competitive adsorption of zinc,cadmium, copper,and lead in three highly‐weathered Brazilian soils

Abstract

Equilibrium adsorption experiments on zinc (Zn), cadmium (Cd), copper (Cu), and lead (Pb) were conducted in three horizons of two Ultisols and one Oxisol with and without liming, from Viçosa‐MG (Brazil). Equilibrium solutions were applied as a “cocktail”; containing 700 mg L^‐1 of Zn, 20 mg L#lb¹ of Cd, 200 mg L^‐1of Cu, and 300 mg L^‐1 of Pb and its dilutions of 1:5 and 1:20. After shaking, the mixture was centrifuged, the supernatant collected and the pH and the concentrations of metals in the mixture were determined. Soil order, soil horizon, and liming had significant effects on the metal adsorption. Some important changes in the adsorption characteristics of the metals, especially in Zn and Cd, were observed due to competition between the different cations present in the solution. Also, desorption of Zn and Cd was observed with an increasing concentration of the solution. The adsorption data for Zn and Cd did not fit the linear, Langmuir, Freundlich, and Temkin isotherm equations for most situations, as these equations do not consider the possibility of a decrease in the amount of metal adsorbed with increasing metal competition for the adsorption sites. Due to the competition with other metals, the equations, which offered the best fit for Zn and Cd, were quadratic polynomial models. On the other hand, for Cu and Pb, the equations, which showed the best fit were linear, Langmuir, and Temkin, for different situations. The reasons for this behavior were related to the strong competitive forces for the adsorption sites presented by these two metals.     

海泡石改良土壤效果研究

通过连续三季盆栽试验研究海泡石提高油菜生物量,降低油菜Cd、Pb、Cu、Zn浓度及土壤Cd、Pb、Cu、Zn有效态浓度的效果。结果表明:海泡石在不同程度上提高了三季油菜的生物量,适量的海泡石可降低油菜中Cd、Pb、Cu、Zn浓度及土壤Cd、Pb、Cu、Zn有效态浓度。海泡石降低油菜中重金属浓度效果,第一季,Zn>Pb>Cd>Cu,第二季,Pb>Zn>Cd>Cu,第三季,Zn>Cd>Pb>Cu;降低有效态浓度的效果,第一季,Cd>Cu>Pb>Zn,第二季,Cu>Cd>Zn>Pb,第三季,Pb>Cd>Cu>Zn。因此,海泡石可用于土壤改良,提高油菜生物量,降低油菜中Cd、Pb、Cu、Zn浓度及土壤中Cd、Pb、Cu、Zn有效态浓度。海泡石降低油菜中重金属浓度总效果为Zn>Pb>Cd>Cu;降低土壤重金属有效态浓度总效果为Cd>Cu>Pb>Zn。