Copper and zinc fractions affecting microorganisms in long-term sludge-amended soils

The influences of Zn and Cu on soil enzyme activities (acid phosphatase, alkaline phosphatase, arylsulfatase, cellulase, dehydrogenase, protease (z-FLase), urease, beta-D-glucosidase and beta-D-fructofuranosidase (invertase)) and microbial biomass carbon were investigated in agricultural soils amended with municipal sewage sludge or compost since 1978. The trace metals in the soils were fractionated using a sequential extraction method. Long-term application of the sewage sludge and composts caused accumulations of Cu and Zn in the soils, ranging from 140 to 144 and from 216 to 292 mg kg(-1), respectively. The percentage of Cu was highest in the NaOH- and HNO3-extractable fractions (44-51% and 38-46%, respectively), while the percentage of Zn was highest in the HNO3- and EDTA-extractable fractions (65-83% and 11-32%, respectively). Although the percentage of the bioavailable fractions (sum of KNO3 + H2O-, NaOH-, and EDTA-extractable amounts) of Cu (53-64%) was higher than that of Zn (15-37%), the percentage of the most labile fractions (KNO3 + H2O) of Zn (2.1-5.9%) was larger than that of Cu (1.1-2.4%). The size of the microbial biomass carbon increased with the application of sewage sludge or compost. For some enzymes, however, the ratio of the enzyme activity to microbial biomass was lower in the soils amended with sewage sludge or compost than that in the control soil. The soil enzyme activities were more adversely affected by Zn than by Cu. From a multiple regression analysis, it was found that dehydrogenase, urease, and beta-D-glucosidase activities were reduced by the KNO3 + H2O-extractable fraction of Zn in the soils. These microbial activities seem to be sensitive to Zn stress, indicating the possibility that they might be useful bioindicators for evaluation of the toxic effects of Zn on microorganisms in the soils.     

Movement of water and heavy metals (Zn, Cu, Pb and Ni) through sand and sandy loam amended with biosolids under steady-state hydrological conditions

New guidelines for using biosolids in UK agriculture favour the use of enhanced treated biosolids, such as dried and composted cakes, due to concerns about the potential for transfer of pathogens into the food chain. However, there is a need to ensure that their use is environmentally acceptable and does not increase the risk to potable water supplies or the food chain from other contaminants such as heavy metals and xenobiotic organic chemicals. The objective of this study was to determine whether the use of composted and dried mesophilic anaerobically digested dewatered (MADD) biosolids would increase the risk of heavy metal leaching from cultivated horizons when compared to more conventionally used MADD cake. Three biosolids (MADD sewage sludge cake - fresh, dried and composted) were mixed with a sand (typic quartzipsamments, %OM = 3.0, pH = 6.5) or a sandy loam (typic hapludalf, %OM = 4.8, pH = 7.6) at an application rate equivalent to 250 kg N/ha/y resulting in loadings of approximately Zn: 6 microg, Cu: 2 microg, Pb: 5 microg and Ni: 0.2 microg/g of soil dry weight basis. These amended soils were repacked into columns (0.4 m by 0.1 m internal diameter) and leaching of Zn, Cu, Pb and Ni was investigated following application of two 24 h simulated rainfall events of 4.5 mm/h. Water balance data and the use of conservative tracers (Cl- and Br ) showed that the hydrological regimes of each core were comparable and, thus, unlikely to account for differences in metal leaching observed. Although no significant difference (P = 0.05) was observed between biosolid amended and control soils, those amended with composted sludge consistently gave higher loss of all metals than did the control soils. Total losses of metals from compost amended soil over the two rainfall events were in the ranges, Zn:20.5-58.2, Cu:9.0-30.5, Pb:24.2-51.2 and Ni:16.0-39.8 microg metal/kg amended soil, compared with Zn:16.4-41.1, Cu:6.2-25.3, Pb:16.9-41.7, and Ni:3.7-25.4 microg metal/kg soil from the control soils. Losses of Zn, Cu, Pb and Ni from fresh MADD cake amended soils (19.8-41.3, 3.2-25.8, 21.6-51.6 and 7.6-36.5 microg metal/kg amended soil, respectively) and from dry MADD cake amended soils (10.7-36.7, 1.8-23.8, 21.2-51.2 and 6.8-39.2 microg metal/kg amended soil, respectively) were similar to the controls. Generally, quantities of metals leached followed the order Zn = Pb > Cu > Ni, which was consistent with the levels of metals in the original sludge/soil mixtures. These results suggest that composting or drying MADD biosolids is unlikely to increase the risk of groundwater contamination when compared to the use of MADD cake; therefore, the changes in UK sludge use in agriculture guidelines are satisfactory in this respect.     

Effects of Zn and P addition on the microbial biomass in a Zn deficient calcareous soil amended with glucose

A 35-day laboratory incubation experiment at 25°C was carried out to investigate the effects of Zn and P addition on microbial biomass C, N, and P in a Zn deficient calcareous soil, sampled at 15–40 cm depth in Central Anatolia, Turkey, amended with glucose. The underlying hypothesis was that P, but also Zn addition leads to a decrease in the microbial biomass C/N ratio. In the glucose-amended soil, the microbial biomass C/N ratio was not affected by the addition of P at day 5. At day 35 in this treatment, the significant P addition × day interaction revealed a significant decrease in the microbial biomass C/N ratio from 11.3 to 8.9. In the glucose-amended soil, Zn addition also had generally significant negative effects on microbial biomass C in comparison with the pure glucose treatment. A similar tendency was observed for microbial biomass N and consequently the microbial biomass C/N ratio remained unaffected. No evidence was found in the present incubation experiment that the microbial community suffered from Zn deficiency.     

Solubility and accumulation of metals in Chinese brake fern, vetiver and rostrate sesbania using chelating agents

Greenhouse experiments were conducted to study the effects of chelating agents on the growth and metal accumulation of Chinese brake fern (Pteris vittata L.), vetiver (Vetiveria zizanioides L.), and rostrate sesbania (Sesbania rostrata L.) in soil contaminated with arsenic (As), Cu, Pb, and Zn. Among the five chelating agents used [ethylenediaminetriacetic acid (EDTA), hydroxyethylenediaminetriacetic acid (HEDTA), nitrilotriacetic acid (NTA), oxalic acid (OA), and phytic acid (PA)], OA was the best to mobilize As, EDTA to mobilize Cu and Pb, and HEDTA to mobilize Zn from soil, respectively. The biomass of vetiver was the highest, followed by rostrate sesbania. All chelating agents inhibited the growth of Chinese brake fern and rostrate sesbania, but HEDTA significantly increased the aboveground biomass of vetiver. Dry weights of both Chinese brake fern and rostrate sesbania decreased with increasing EDTA concentrations amended in the soil, especially in treatments with high EDTA concentrations. EDTA and HEDTA enhanced Cu, Zn, and Pb, but lowered As accumulation in all three plant species, except for As in vetiver, while OA significantly enhanced As accumulation in the aboveground part of vetiver. Concentrations of Cu, Zn, and Pb in the aboveground parts of plants increased significantly with the increase of EDTA concentrations and treatment time. In addition to As, Chinese brake fern also accumulated the highest Cu, Pb, and Zn in its aboveground parts among the three plant species grown in metal-contaminated soil with EDTA/HEDTA treatments. This species, therefore, can be used to simultaneously clean up As, Cu, Pb, and Zn from contaminated soils with the aid of EDTA or HEDTA.     

Long-term effects of metals in sewage sludge on soils,microorganisms and plants

Summary This paper reviews the evidence for impacts of metals on the growth of selected plants and on the effects of metals on soil microbial activity and soil fertility in the long-term. Less is known about adverse long-term effects of metals on soil microorganisms than on crop yields and metal uptake. This is not surprising, since the effects of metals added to soils in sewage sludge are difficult to assess, and few long-term experiments exist. Controlled field experiments with sewage sludges exist in the UK, Sweden, Germany and the USA and the data presented here are from these long-term field experiments only. Microbial activity and populations of cyanobacteria,Rhizobium leguminosarum bv.trifolii, mycorrhizae and the total microbial biomass have been adversely affected by metal concentrations which, in some cases, are below the European Community's maximum allowable concentration limits for metals in sludge-treated soils. For example, N₂-fixation by free living heterotrophic bacteria was found to be inhibited at soil metal concentrations of (mg kg^–1): 127 Zn, 37 Cu, 21 Ni, 3.4 Cd, 52 Cr and 71 Pb. N₂-fixation by free-living cyanobacteria was reduced by 50% at metal concentrations of (mg kg^–1): 114 Zn, 33 Cu, 17 Ni, 2.9 Cd, 80 Cr and 40 Pb.Rhizobium leguminosarum bv.trifolii numbers decreased by several orders of magnitude at soil metal concentrations of (mg kg^–1): 130–200 Zn, 27–48 Cu, 11–15 Ni, and 0.8–1.0 Cd. Soil texture and pH were found to influence the concentrations at which toxicity occurred to both microorganisms and plants. Higher pH, and increased contents of clay and organic carbon reduced metal toxicity considerably. The evidence suggests that adverse effects on soil microbial parameters were generally found at surpringly modest concentrations of metals in soils. It is concluded that prevention of adverse effects on soil microbial processes and ultimately soil fertility, should be a factor which influences soil protection legislation.     

The long-term effect of sludge application on Cu, Zn, and Mo behavior in soils and accumulation in soybean seeds

A long-term greenhouse column experiment using two soils of different textures amended with dewatered, composted and alkaline-stabilized sludges (biosolids) tested the effect of aging on trace metal solubility, mobility and crop uptake over 15 cropping cycles. Specifically, soil chemical properties and extractability of Cu, Zn and Mo were measured after each cropping cycle, and soybeans (Glycine max (L.) Merr.) grown as the final crop were analyzed for those metal concentrations in the seeds. Significant Cu loss from the surface soil through leaching, and increased Zn extractability resulting from soil acidification were evident in the early cropping cycles shortly after sludge application, with the degree of Cu mobilization and soil acidification strongly dependent on the type of soil and sludge. Liming to counter acidification in later cycles enhanced Mo extractability and bioavailability substantially, with some sludge treatments producing soybean seeds with Mo concentrations up to 5 times greater than the control. Aging effects were difficult to discern for trace metals in this long-term study, since soil pH changes caused by sludge and liming amendments dominated metal solubility and crop uptake.     

Removal of copper, lead, and zinc from contaminated water by saltbush biomass: analysis of the optimum binding, stripping, and binding mechanism

Experiments performed on the Cu(II), Pb(II), and Zn(II) binding by saltbush biomass (Atriplex canescens) showed that the metal binding increased as pH increased from 2.0 to 5.0. The highest amounts of Cu, Pb, and Zn bound by the native biomass varied from 48-89%, 89-94%, and 65-73%, respectively. The hydrolyzed biomass bound similar amount of Pb and 50% more Cu and Zn than the native. The esterified biomass had a lower binding capacity than native; however, esterified flowers bound 45% more Cu at pH 2.0 than native flowers. The optimum binding time was 10 min or less. More than 60% of the bound Cu was recovered using 0.1 mM HCl, while more than 90% of Pb was recovered with either HCl or sodium citrate at 0.1 mM. For Zn, 0.1 mM sodium citrate allowed the recovery of 75%. Results indicated that carboxyl groups participate in the Cu, Pb, and Zn binding.     

Soil microbial activities and heavy metal mobility in long-term contaminated soils after addition of EDTA and EDDS

A 40-day incubation experiment was carried out in order to evaluate the microbial activities and heavy metal availability in long-term contaminated arable and grassland soils after addition of EDTA (ethylenediaminetetraacetic acid) or EDDS ([S,S]-ethylenediaminedisuccinic acid). Soils with similar contamination of heavy metal from the vicinity of a lead smelter were used in the experiment. The soil microbial carbon (C_mic) decreased significantly after addition of EDTA in the arable soil (CM1); lesser effects were observed in the grassland soil (CM2). Addition of EDDS caused a decrease of C_mic during the first 10 days of incubation. In the later phases of the experiment, C_mic increased, and even exceeded the amounts found in the control soils. Respiratory activities and metabolic quotients (qCO₂) increased after the addition of the chelating agents into the soils. Higher respiratory activities and qCO₂ were observed in the EDTA-treated soils. The readily available heavy metal fractions were extracted with NH₄NO₃ solution. Readily mobilizable heavy metal fractions of Cd, Pb, Zn, and (in part) Cu increased during the first 3-10 days of incubation in the presence of EDTA. The addition of EDDS particularly increased concentrations of available Cu. Significant correlations between NH₄NO₃-extractable metals, soil respiratory activities, and qCO₂ were found in both soil treatments with EDTA and EDDS. This indicates that enhanced metal mobility seriously affects the microbial processes in experimental soils. In addition, the relationships between NH₄NO₃-extractable Cd, Cu, and the microbial biomass were found in the CM1 soil amended with EDTA.     

Copper and zinc mixtures induce shifts in microbial communities and reduce leaf litter decomposition in streams

1. To assess the impact of metal mixtures on microbial decomposition of leaf litter, we exposed leaves previously immersed in a stream to environmentally realistic concentrations of copper (Cu) and zinc (Zn) (three levels), alone and in all possible combinations. The response of the microbial community was monitored after 10, 25 and 40 days of metal exposure by examining leaf mass loss, fungal and bacterial biomass, fungal reproduction and fungal and bacterial diversity.
2. Analysis of microbial diversity, assessed by denaturing gradient gel electrophoresis and identification of fungal spores, indicated that metal exposure altered the structure of fungal and bacterial communities on decomposing leaves.
3. Exposure to metal mixtures or to the highest Cu concentration significantly reduced leaf decomposition rates and fungal reproduction, but not fungal biomass. Bacterial biomass was strongly inhibited by all metal treatments.
4. The effects of Cu and Zn mixtures on microbial decomposition of leaf litter were mostly additive, because observed effects did not differ from those expected as the sum of single metal effects. However, antagonistic effects on bacterial biomass were found in all metal combinations and on fungal reproduction in metal combinations with the highest Cu concentrations, particularly at longer exposure times.     

Heavy metals fractionation and organic matter mineralisation in contaminated calcareous soil amended with organic materials

Degradation of organic matter (OM) from organic amendments used in the remediation of metal contaminated soils leads to changes in soil chemical properties shortly after their addition, which may affect the soil metal distribution. The effects of two differing organic amendments on OM mineralisation and fractionation of heavy metals in a contaminated soil were investigated in an incubation experiment. The treatments were: control unamended soil, soil amended with fresh cow manure, and soil amended with a compost having a high maturity degree. The soil used was characteristic of the mining area at La Unión (Murcia, Spain) with 28% CaCO(3) and sandy-loam texture (pH 7.7; 2602 mg kg(-1)Zn; 1572 mg kg(-1)Pb). Manure and compost C-mineralisation after 56 days (24% and 3.8%, respectively) were below values reported previously for uncontaminated soils. Both amendments favoured Zn and Pb fixation, particularly the manure. Mn solubility increased at the beginning of the experiment due to a pH effect, and only Cu solubility increased through organic matter chelation in both amended soils.     

Fine Root Decomposition and Cycling of Cu,Ni, Pb,and Zn at Forest Sites Near Smelters in Sudbury,ON, and Rouyn-Noranda,QU, Canada

This study determined rates of in situ fine root decomposition and changes in trace metals concentration during decomposition at sites in Sudbury, ON, and Rouyn-Noranda, QU, with elevated or background concentrations of Cu, Ni, Pb, and/or Zn in the soil, and correlated the depth gradients of Cu, Ni, Pb, and Zn for soils and roots at the same sites. Fine roots were extracted from soil cores within root traps several times over 12 months; biomass and metal concentrations were measured. Live roots were collected from 30-cm soil cores, separated into three depths. Elevated soil metal concentrations did not necessarily reduce fine root decomposition, and effects on decomposition were similar to those previously reported for surface foliar litter at the same sites. Decomposing roots at only the high metal sites demonstrated increased metal concentrations with time. Root tissue concentrations of Cu, Ni, and Zn, but not Pb, at lower soil depths were generally higher than expected from soil metal concentrations. This could be explained by reallocation of essential metals, although these metals were likely also more available for uptake at depth due to lower DOC concentrations. This study means that for risk assessment, separate determinations of altered decomposition for roots and leaf litter are likely not necessary for predicting ecosystem effects, a pragmatically useful conclusion given the labor intensity of the fine root studies. This study also suggests that for risk assessment of plant community exposure to metals, prediction of exposure to metals should probably consider soil layers that do not have substantially elevated metal concentrations, as their soil characteristics, or plant processes, may result in unexpected exposure.     

Effects of soil acidification on the chemical extractability of Fe,Mn, Zn and Cu and the growth and micronutrient uptake of highbush blueberry plants

Summary The effects of soil acidification and micronutrient addition on levels of extractable Fe, Mn, Zn and Cu in a soil, and on the growth and micronutrient uptake of young highbush blueberry plants (Vaccinium corymbosum L. cv. Blueray) was investigated in a greenhouse study.Levels of 0.05M CaCl₂-extractable Fe, Mn, Zn and Cu increased as the pH was lowered from 7.0 to 3.8. However, the solubility (CaCl₂-extractability) of Fe and Cu was considerably less pH-dependent than that of Mn and Zn. With the exception of HCl-and DTPA-extractable Mn, micronutrients extractable with 0.1M HCl, 0.005M DTPA and 0.04M EDTA were unaffected or raised only slightly as the pH was lowered from 6.0 to 3.8. Quantities of Mn and Zn extractable with CaCl₂ were similar in magnitude to those extractable with HCl, DTPA and EDTA whilst, in contrast, the latter reagents extracted considerably more Cu and Fe than did CaCl₂. A fractionation of soil Zn and Cu revealed that soil acidification resulted in an increase in the CaCl₂- and pyrophosphate-extractable fractions and a smaller decrease in the oxalate-extractable fraction.Plant dry matter production increased consistently when the soil pH was lowered from 7.0 to 4.6 but there was a slight decline in dry matter as the pH was lowered to 3.8. Micronutrient additions had no influence on plant biomass although plant uptake was increased. As the pH was lowered, concentrations of plant Fe first decreased and then increased whilst those of Mn, and to a lesser extent Zn and Cu, increased markedly.     

Functional stability of stream-dwelling microbial decomposers exposed to copper and zinc stress

1. We investigated the resistance of aquatic microbial decomposers to Cu and Zn stress and their ability to recover after release from metal exposure, by examining leaf mass loss, fungal reproduction and microbial biomass and diversity.
2. Alder leaves, colonised in a reference stream, were exposed in microcosms to copper (Cu) or zinc (Zn), alone or in mixtures, with metals added together or sequentially (at day 0 or after 10 days). After 20 days, half of the microcosms were released from metals.
3. Leaf mass loss and fungal reproduction were reduced in most metal treatments, and the structure of fungal and bacterial communities was altered as indicated by identification of conidia and DNA fingerprinting based on denaturing gradient gel electrophoresis. Metals reduced the biomass of bacteria, but not that of fungi.
4. After release from metal stress, the structure of fungal communities became similar to that of control, and a recovery of microbial activity seemed to occur as shown by the lack of differences in leaf mass loss, bacterial biomass and fungal reproduction between control and metal treatments.     

施用污泥对油菜根际养分和不同种类重金属的影响

根际是控制植物养分动态的重要因素,养分动态也影响着根际土壤环境。当土壤被污水污泥改良后,根际土壤中的养分和重金属性质也会发生变化。目前很少有人研究施用污泥的土壤中植物根系对根际重金属有效性和分布的影响。采用根垫—冰冻薄层切片法对施用污泥后土壤中油菜根际的养分和重金属分布情况进行研究,以期探明污泥改良土壤中根际重金属的活化特征。当土壤施用污泥后,根际土壤中DTPA提取态Zn,Cd,Ni,Mn,有效磷,有效钾和铵态氮被显著消耗,而根际土壤中DTPA提取态Cu没有明显的消耗或积累。当土壤中施用大量污泥时,根际土壤的pH值随着离根表面距离的增加而增加。无论土壤是否用污泥处理,油菜根际土壤中可交换态Cu都显著减少。当土壤被50%污泥改良时,在距离根表面0—2 mm处的油菜根际土壤中碳酸盐结合态,铁锰氧化物结合态,有机物结合态,残渣态的Cu和Zn都被消耗较多。污泥的施用对油菜的生长有促进作用。随着污泥施用量的增加,油菜地上部分Cu和Zn的含量没有显著变化。施用污泥量小于25%的土壤中,污泥没有增加重金属的可利用性和移动性。除了Cu,油菜根际土壤中DTPA提取态Zn,Cd,Ni的减少表明施用污泥的土壤中重金属的活化是非常有限的。     

Phytoextraction of zinc, copper, nickel and lead from a contaminated soil by different species of Brassica

In a pot culture experiment, five different species of Brassica (Brassica juncea, Brassica campestris, Brassica carinata, Brassica napus, and Brassica nigra) were grown for screening possible accumulators of heavy metals, viz. Zn, Cu, Ni, and Pb. The plants were grown to maturity in a soil irrigated with sewage effluents for more than two decades in West Delhi, India. The soil analysis showed enhanced accumulation of Zn, Cu, Ni, and Pb in this sewage-irrigated soil. Among all species, B. carinata showed the highest concentration (mg kg(-1)) as well as uptake (microg pot(-1)) of Ni and Pb at maturity. Although B. campestris showed a higher concentration of Zn in its shoots (stem plus leaf), B. carinata extracted the largest amount of this metal due to greater biomass production. However, B. juncea phytoextracted the largest amount of Cu from the soil. In general, the highest concentration and uptake of metal was observed in shoots compared to roots or seeds of the different species. Among the Brassica spp., B. carinata cv. DLSC1 emerged as the most promising, showing greater uptake of Zn, Ni, and Pb, while B. juncea cv. Pusa Bold showed the highest uptake of Cu. The B. napus also showed promise, as it ranked second with respect to total uptake of Pb, Zn, and Ni, and third for Cu. Total uptake of metals by Brassica spp. correlated negatively with available as well as the total soil metal concentrations. Among the root parameters, root length emerged as the powerful parameter to dictate the uptake of metals by Brassica spp. Probably for the first time, B. carinata was reported as a promising phytoextractor for Zn, Ni, and Pb, which performed better than B. juncea.     

Molecular and Functional Assessment of Bacterial Community Convergence in Metal-Amended Soils

Species diversity and the structure of microbial communities in soils are thought to be a function of the cumulative selective pressures within the local environment. Shifts in microbial community structure, as a result of metal stress, may have lasting negative effects on soil ecosystem dynamics if critical microbial community functions are compromised. Three soils in the vicinity of a copper smelter, previously contaminated with background, low and high levels of aerially deposited metals, were amended with metal-salts to determine the potential for metal contamination to shape the structural and functional diversity of microbial communities in soils. We hypothesized that the microbial communities native to the three soils would initially be unique to each site, but would converge on a microbial community with similar structure and function, as a result of metal stress. Initially, the three different sites supported microbial communities with unique structural and functional diversity, and the nonimpacted site supported inherently higher levels of microbial activity and biomass, relative to the metal-contaminated sites. Amendment of the soils with metal-salts resulted in a decrease in microbial activity and biomass, as well as shifts in microbial community structure and function at each site. Soil microbial communities from each site were also observed to be sensitive to changes in soil pH as a result of metal-salt amendment; however, the magnitude of these pH-associated effects varied between soils. Microbial communities from each site did not converge on a structurally or functionally similar community following metal-salt amendment, indicating that other factors may be equally important in shaping microbial communities in soils. Among these factors, soil physiochemical parameters like organic matter and soil pH, which can both influence the bioavailability and toxicity of metals in soils, may be critical.     

Partitioning of Zn,Cd, Pb,and Cu in organic-rich soil profiles in the vicinity of a zinc smelter

Abstract

A five-step sequential extraction procedure was applied to organic-rich soil samples from five soil profiles situated 1–8 km from a zinc smelter. The partitioning of Zn, Cd, Pb, and Cu into five operationally defined fractions (exchangeable, “carbonate’’-bound, reducible, oxidizable, and residual) was studied at different soil depths down to 35cm. In the surface soil (0–1 cm) a major part of Pb and Cu was extracted in the oxidizable fraction, whereas for Zn and Cd slightly more was extracted in the ‘‘carbonate”-fraction than in the other four fractions. Extracted metal proportions in the oxidizable fraction were respectively of the order of 30%, 20%, 50%, and 80% for Zn, Cd, Pb, and Cu in the surface soil for all sites, but these proportions decreased with soil depth. In the surface soil less than 20% of all the elements were extracted in the residual fraction, but the proportions associated with this fraction generally increased with soil depth. In the C-horizon, differences in extracted proportions of Pb and Cu in the residual fraction were probably due to geochemical factors, whereas for Zn the low extracted proportion at a highly contaminated site (20%) may be due to Zn migration to the C-horizon at this site. For Cd the extracted proportions in the C-horizon were lower than for the other elements, generally below 20%, presumably because Cd is weaker in terms of its adsorption to the soil than the other elements studied. Total concentrations of the metals decreased strongly with increasing distance from the smelter, but less systematic differences were observed for their distributions among fractions. Potentially bioavailable metal proportions (exchangeable + “carbonate”-bound fraction) in the surface soil were about 50%, 60%, 20%, and 10% for Zn, Cd, Pb, and Cu, respectively. In C-horizon soil the mobility sequence Cd>Zn>Pb = Cu was generally observed. The present results indicate that the concentrations and chemical fractionation of Zn, Pb, and Cd in these soils represent a considerable risk to natural terrestrial food chains.     

Biosorption of chromium, copper, manganese and zinc by Pseudomonas aeruginosa AT18 isolated from a site contaminated with petroleum

The study describes the sorption of Cr, Cu, Mn and Zn by Pseudomonas aeruginosa AT18 isolated from a site contaminated with petroleum and heavy metals. The concentrations studied were 50, 49, 60 and 70 (mg L(-1)) for Cr, Cu, Mn and Zn, respectively. The solution pH and ionic strength were very important factors in the metal biosorption performance and the biosorption capacity of P. aeruginosa AT18 for Cr3+,Cu2+, Mn2+ and Zn2+. In aqueous solution, the biosorption increased with increasing pH in the range 5.46-7.72. The results obtained in the experimental assays show that P. aeruginosa AT18 has the capacity for biosorption of the metallic ions Cr3+, Cu2+ and Zn2+ in solutions, although its capacity for the sorption of manganese is low (22.39 mg Mn2+/g of biomass) in comparison to the Cr3+, Cu2+ and Zn2+ ions, as shown by the individual analyses. However, 20% of the manganese was removed from an initial concentration of 49.0 mg L(-1), with a Qm value similar to that obtained in solutions containing mixtures of Cr3+, Cu2+, Mn2+and Zn2+. The chromium level sorbed by P. aeruginosa AT18 biomass was higher than that for Cu, Mn and Zn, with 100% removal in the pH range 7.00-7.72 and a Qm of 121.90-200.00 mg of Cr3+/g of biomass. The removal of Cr, Cu and Zn is also a result of precipitation processes.     

Arbuscular mycorrhizal contribution to heavy metal uptake by maize (Zea mays L.) in pot culture with contaminated soil

In two pot-culture experiments with maize in a silty loam (P2 soil) contaminated by atmospheric deposition from a metal smelter, root colonization with indigenous or introduced arbuscular mycorrhizal (AM) fungi and their influence on plant metal uptake (Cd, Zn, Cu, Pb, Mn) were investigated. Soil was -irradiated for the nonmycorrhizal control. In experiment 1, nonirradiated soil provided the mycorrhizal treatment, whereas in experiment 2 the irradiated soil was inoculated with spores of a fungal culture from P2 soil or a laboratory reference culture, Glomus mosseae. Light intensity was considerably higher in experiment 2 and resulted in a fourfold higher shoot and tenfold higher root biomass. Under the conditions of experiment 1, biomass was significantly higher and Cd, Cu, Zn and Mn concentrations significantly lower in the mycorrhizal plants than in the nonmycorrhizal plants, suggesting a protection against metal toxicity. In contrast, in experiment 2, biomass did not differ between treatments and only Cu root concentration was decreased with G. mosseae-inoculated plants, whereas Cu shoot concentration was significantly increased with the indigenous P2 fungal culture. The latter achieved a significantly higher root colonization than G. mosseae (31.7 and 19.1%, respectively) suggesting its higher metal tolerance. Zn shoot concentration was higher in both mycorrhizal treatments and Pb concentrations, particularly in the roots, also tended to increase with mycorrhizal colonization. Cd concentrations were not altered between treatments. Cu and Zn, but not Pb and Cd root-shoot translocation increased with mycorrhizal colonization. The results show that the influence of AM on plant metal uptake depends on plant growth conditions, on the fungal partner and on the metal, and cannot be generalized. It is suggested that metal-tolerant mycorrhizal inoculants might be considered for soil reclamation, since under adverse conditions AM may be more important for plant metal resistance. Under the optimized conditions of normal agricultural practice, however, AM colonization even may increase plant metal absorption from polluted soils.     

酸性矿山废水污染的水稻田土壤中重金属的微生物学效应

采样调查了广东大宝山地区受酸性采矿废水长期污染的亚热带水稻田的土壤理化性质 ,重金属 Cu、Pb、Zn、Cd的全量及其 DTPA浸提量 ,以及微生物生物量及其呼吸活性等指标。利用主成分和逐步回归分析了影响土壤重金属的有效性及其微生物学效应的因素。结果表明 :土壤高含硫 ,强酸性 ,有机碳、全氮较低 ,4种金属的全量普遍超标。DTPA可提取态金属含量较高 ,不仅与其全量呈显著正相关 ,而且与土壤酸度和粘粒含量正相关 ,和 Mn含量负相关。过量的金属显著降低了土壤微生物生物量 C、N、微生物商、生物量 N/全 N比 ,并抑制了微生物呼吸强度和对有机碳的矿化率 ,导致了土壤 C/N比的升高。同时 ,金属对微生物群落及生理代谢指标 ,如微生物生物量 C/N比和代谢商的影响不显著。 DTPA可提取态金属 ,特别是 DTPA- Cu是导致微生物生物量和活性指标变化的主要因素。以有机碳 (或全氮 )为基数的复合微生物指标降低了土壤性质差异造成的干扰 ,较单一指标更能准确指示微生物对金属胁迫的反应。土壤硫没有对金属有效性和微生物指标产生明显影响 ,但其氧化过程可能引起酸化和金属离子的释放