Discrepancy of the microbial response to elevated copper between freshly spiked and long-term contaminated soils

A systematic comparison of Cu toxicity thresholds was made between freshly spiked soils and soils in which elevated Cu concentrations have been present for various times. Three uncontaminated soils were spiked and experimentally leached or incubated outdoors for up to 18 months. Additionally, five field-contaminated soils with a 6- to 80-year-old Cu contamination were sampled, and corresponding uncontaminated soils were spiked to identical total concentrations. All soil samples were subjected to three microbial assays (nitrification potential, glucose-induced respiration, and maize residue C-mineralization). Experimental leaching or soil incubation after spiking reduced Cu toxicity (1.3- or 2.3-fold increase of dose, respectively, to inhibit process by 50% [ED50]). No significant effects of soil type, aging time (6, 12, or 18 months), or bioassay on the factor change of ED50 were found. Significant reductions of microbial activity in field-contaminated soils were only identified in 2 of the 15 series (three assays in five soils), whereas freshly spiking the corresponding control soils significantly affected these processes in 12 series. Soil solution Cu concentrations significantly decreased on leaching at corresponding total soil Cu, and smaller decreases were found during additional aging. Soil solution Cu concentrations largely explain changes in Cu toxicity on leaching and aging, although additional variation may be related to changes in the sensitivity of microbial populations. It is concluded that total Cu toxicity thresholds are lower in freshly spiked soils compared to soils in which Cu salts have equilibrated and leaching has removed excess soluble salts. The large variability of soil microbial processes creates a large uncertainty about the magnitude of the factor by which aging mitigates Cu toxicity.     

A protocol to estimate the release of anthropogenic hydrocarbons from contaminated soils

An operational protocol, appropriate for a tier 1 or tier 2 type relative risk evaluation of a site that has polycyclic aromatic hydrocarbon (PAH) or petroleum hydrocarbon impacted soils, was developed to estimate the fraction of anthropogenic hydrophobic hydrocarbons that will be released rapidly from such soils. The development of this protocol used over 400 datasets from 40 different field samples to establish and verify the operational protocol. The datasets resulted from four-month kinetic desorption studies of these field samples. Based on the chemicals evaluated, the protocol has greatest application to two, three, and four ring-PAH and to diesel range aliphatic hydrocarbons. The protocol is a simple batch desorption analysis that uses established methods and is conducted for 7 d. The protocol results were verified with specific correlation relationships (r2 = 0.81 to 0.96) to estimate the rapidly releasing fraction (F value) that is obtained in a full, four-month chemical release evaluation.     

镉污染土壤植物萃取技术的研究进展

植物萃取是指在受重金属污染的土壤上连续的种植专性植物并收割植物茎叶作离地处理 ,以降低土壤中的重金属浓度的新兴技术。利用此方法对镉污染土壤进行原位修复具有成本低、环境可持续性的优点。综述了近年来这一领域内的研究进展及其商业应用的可行性分析 ,并展望了此技术在我国的应用前景。     

Comparative toxicity of cadmium, zinc, and mixtures of cadmium and zinc to daphnids

Investigations were conducted to determine acute (48-h) effects of cadmium and zinc presented individually and in combination on Ceriodaphnia dubia, Daphnia magna, Daphnia ambigua, and Daphnia pulex. Toxicity tests were conducted with single metals to determine lethal effects concentrations (lethal concentrations predicted for a given percent [x] of a population, LCx value). These were used to derive metal combinations that spanned a range of effects and included mixtures of LC15, LC50, and LC85 values calculated for each metal and species. In single-metal tests, 48-h LC50 values ranged from 0.09 to 0.9 micromol/L and 4 to 12.54 micromol/L for cadmium and zinc, respectively. For each metal, D. magna was most tolerant and showed a different pattern of response from all others as determined by slope of concentration-response curves. In the combined metal treatments, all daphnids showed a similar pattern of response when LC15 concentrations were combined. This trend continued with few exceptions when LC15 concentrations of cadmium were combined with LC50 or LC85 values for zinc. However, when this treatment was reversed (LC15, zinc + LC50 or LC85, cadmium), responses of all species except D. magna indicated less-than-additive effects. For C. dubia, a near complete reduction in toxicity was observed when the LC15 for zinc was combined with LC85 for cadmium. Multimetal tests with D. magna did not differ from additive. Collectively, these studies suggest that D. magna may not be representative of other cladocerans.     

Biotests and biosensors in ecotoxicological risk assessment of field soils polluted with zinc, lead, and cadmium

The combined chemical and ecotoxicological hazard evaluation study was conducted on 60 smelter-influenced soils containing 1 to 13, 50 to 653, and 100 to 1,198 mg/kg of Cd, Pb, and Zn, respectively. For these soils (liquid-to-soil ratio = 10), water extractability of Zn, Cd, and Pb was less than 0.19% (median values). Acetic acid (0.11 M) extracted 23, 9.7, and 0.7% of Cd, Zn, and Pb, respectively. Although heavy metal concentrations in the studied soils were high, the toxic effects of water extracts were observed only in few samples and in few biotests (algae Selenastrum capricornutum and metal detector assay). For most of the aquatic test organisms (e.g., crustaceans, photobacteria), the bioavailable concentrations of metals in soil-water extracts were either subtoxic, or the adverse effects were compensated by soil nutrients, etc. However, analysis of the soils with recombinant Cd sensor Bacillus subtilis (pTOO24) showed that about 65% of these apparently subtoxic samples contained bioavailable Cd when analyzed in the suspension assay (detection limit 1.5 mg Cd/kg soil), indicating the desorption of Cd induced by direct contact of bacteria with soil particles. The median bioavailable fraction of Cd (1%) was 23-fold lower than the fraction extracted by acetic acid. The Pb-Cd sensor Staphylococcus aureus (pT0024) detected bioavailable Pb only in the suspensions of five of the most lead-polluted soils (>417 mg Pb/kg): the median bioavailability of Pb was 0.42%. Consequently, the hazard assessment relying on total metal levels in soils should be revised by critical comparison with data obtained from bioassays. Development and use of biosensors (excellent tools for mechanistic studies and signaling hazard already at subtoxic level) should be encouraged.     

Bioturbation effects on cadmium and zinc transfers from a contaminated sediment and on metal bioavailability to benthic bivalves

The two main objectives of this study were to compare cadmium and zinc fluxes from a contaminated sediment to the water column in bioturbated and unbioturbated systems and jointly to analyze accumulation kinetics of these released metals by benthic filter-feeder bivalves. The experimental approach was based on indoor microcosms containing a two-compartment biotope: natural contaminated sediment (45 +/- 5 microg Cd/g, dry wt, and 1,938 +/- 56 microg Zn/g, dry wt) and water column. Four experimental conditions were studied: no organism added to the sediment-water biotope, presence of bivalves Corbicula fluminea, presence of Hexagenia rigida nymphs (bioturbation source), and presence of C. fluminea and H. rigida simultaneously. Results reveal that bioturbation produces a significant metal release into the water column via the resuspended sediment particles. The use of C. fluminea as an indicator of transferred metals in the water column shows that the metal bioavailability is very limited, quantities of cadmium and zinc bioaccumulated in the soft bodies being less than those measured in unbioturbated systems. This experimental study demonstrates that only the dissolved fraction resulting from diffusive metal fluxes across the sediment-water interface is bioavailable for this bivalve species.     

Analysis of arsenic bioavailability in contaminated soils

The bioavailable arsenic (As) content of contaminated soils was determined by joint analyses of acid-soluble, total water-soluble, and biovailable As by using a luminescent bacterial sensor, Escherichia coli MC1061(pTOO31). According to the results of this study, a significant positive correlation was found between the concentration of total water-soluble As and the bioavailability of As. However, the bioavailability of As in soil varied between sampling sites and was not equal when compared to the concentration of total water-soluble As; bioavailable As was 3 to 77% of total water-soluble As in soil. Our experiments also showed that aging and sequestration of As occurs in contaminated soils and As compounds thus become progressively less bioavailable with time. As a consequence, the bioavailability and toxicity of As should be considered when evaluating the ecological risks of contaminated soils.     

Urinary excretion of cadmium, copper and zinc in workers exposed to cadmium

Changes in urinary cadmium, copper and zinc excretion in workers who had considerable exposure to cadmium oxide fumes were investigated over a 5-year period following the cessation of exposure. The 22 male subjects aged 22 to 55 had been welders on automobile parts for periods ranging from 7 months to 23 years, using silver solder which contained cadmium. They were divided into three groups according to levels of urinary cadmium in the first medical examination in 1975: 5 in the high excretion group, 11 in the moderate group, and 6 in the low group. Renal tubular dysfunctions were indicated in most workers in the high excretion group but not in the other two groups. The high and moderate groups showed a rapid decrease in the levels of urinary-excreted cadmium, with biological half-times of 1.42 and 1.21 years, respectively. Excreted cadmium levelled off in the two groups about 1.7 and 1.5 years after the last exposure. Urinary copper excretion in the high cadmium excretion group was about twice that in the moderate and low groups, the difference being statistically significant in comparison with the controls. Urinary zinc excretion was high in all subjects immediately after cessation of exposure but decreased rapidly. After three years it was found that the reduction of urinary zinc was greatest in the high cadmium group. Urinary cadmium showed significant correlations with both copper and zinc. Urinary copper showed a negative correlation with zinc excretion in the high cadmium excretion group and a significant positive correlation in the other two groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Relative bioavailability and bioaccessibility and speciation of arsenic in contaminated soils

Background: Assessment of soil arsenic (As) bioavailability may profoundly affect the extent of remediation required at contaminated sites by improving human exposure estimates. Because small adjustments in soil As bioavailability estimates can significantly alter risk assessments and remediation goals, convenient, rapid, reliable, and inexpensive tools are needed to determine soil As bioavailability.Objectives: We evaluated inexpensive methods for assessing As bioavailability in soil as a means to improve human exposure estimates and potentially reduce remediation costs.Methods: Nine soils from residential sites affected by mining or smelting activity and two National Institute of Standards and Technology standard reference materials were evaluated for As bioavailability, bioaccessibility, and speciation. Arsenic bioavailability was determined using an in vivo mouse model, and As bioaccessibility was determined using the Solubility/Bioavailability Research Consortium in vitro assay. Arsenic speciation in soil and selected soil physicochemical properties were also evaluated to determine whether these parameters could be used as predictors of As bioavailability and bioaccessibility.Results: In the mouse assay, we compared bioavailabilities of As in soils with that for sodium arsenate. Relative bioavailabilities (RBAs) of soil As ranged from 11% to 53% (mean, 33%). In vitro soil As bioaccessibility values were strongly correlated with soil As RBAs (R² = 0.92). Among physicochemical properties, combined concentrations of iron and aluminum accounted for 80% and 62% of the variability in estimates of RBA and bioaccessibility, respectively.Conclusion: The multifaceted approach described here yielded congruent estimates of As bioavailability and evidence of interrelations among physicochemical properties and bioavailability estimates.     

The effect of earthworms on copper fractionation of freshly and long-term polluted soils

We investigated the effects of earthworm activity on the bioavailability of Cu in soil. The bioavailable fraction was estimated using sequential extraction, and the results of diethylenetriaminepentaacetic acid (DTPA) extraction were analyzed for comparison. Changes in the Cu fraction were compared in Cu-spiked soil (high bioavailability) and long-term polluted field soil (low bioavailability) with approximately equivalent total Cu concentrations. Earthworm activity decreased the bioavailable fraction in the Cu-spiked soil, where earthworm body Cu concentrations did not affect the bioavailable fraction. Soil pH was not a factor in the bioavailability differences between soils with and without earthworms in this study. The bioavailable fraction appears to be more heavily affected by biological and physical mechanisms than by soil pH. The two extraction methods showed different trends; the bioavailable fraction method was better than DTPA extraction, because the former gives clear insight into the aging process of Cu in soil.     

The disposition of cadmium and zinc inPandalus montagui

Cadmium uptake rates in various tissues ofPandalus montagui exposed to sea water containing 37 gCd/L for 14 days ranged from 0.002–0.06 g/g dry tissue/hr. During depuration for 57 days, the levels in most tissues decreased slightly, but continued to rise in the hepatopancreas indicating Cd redistribution. Exposure to 65 g Zn/L produced no substantial change in Zn content of the tissues. An increase occurred in eggs and hepatopancreas during the first six days of depuration. During exposure to Cd and Zn combined (40 g Cd/L + 70 g Zn/L), tissue Zn levels responded as with Zn alone. In the presence of Zn, Cd concentration was doubled in the hepatopancreas, depressed by one-third in the carcass, and did not change in the other tissues. Increased amounts of Zn (up to 410 g Zn/L) had no effect on the Cd levels of the tissues except that the Cd level in the hepatopancreas was depressed, although the level was still greater than in the case of exposure to Cd alone. The possible role of metallothionein is discussed.     

锌镉毒性研究进展

目的:总结近年来国内外对于锌镉毒性的研究进展。方法:搜集、分析国内外相关文献。结果:动物实验研究表明:镉对鼠类的生殖系统、骨骼发育以及听力系统均有毒作用,镉可引起鱼类卵壳破裂,锌能拮抗镉对动物的毒性作用。人体研究表明:锌不仅能提高人体免疫力而且能拮抗镉对人体的毒性作用,镉对人体的健康效应主要表现在对人体呼吸、泌尿、消化、运动、生殖系统等方面的毒性作用。结论:锌镉相互拮抗,锌可预防和减轻镉中毒的危害。     

The influence of cadmium and zinc on cadmium turnover in the zebrafish,Brachydanio rerio

A study was made of the dynamics of non-dietary cadmium in fish exposed to different concentrations of cadmium and zinc in water. Zebrafish,Brachydanio rerio, were exposed to Cd and Zn for various periods. The fate of a short pulse of the radioactive tracer¹⁰⁹Cd (3 or 9 days) was studied during a post-pulse period of 53 or 83 days. The tracer elimination and accumulation were described by exponential equations. The constants obtained from regression analysis of the results were used as a tool for evaluation of the findings.The majority of the¹⁰⁹Cd taken up in the gills during the pulse period was retained in the gill tissue and slowly transferred to the internal organs or lost to the water during the post-pulse period. The retention of tracer in the gills after a 3-day¹⁰⁹Cd pulse was increased by Zn but not influenced by Cd. Continuous exposure to stable Cd increased the rate of turnover of the retained¹⁰⁹Cd. Both Cd and Zn increased the tracer accumulation in the liver and kidney. The results also indicated that the effect of Zn on the Cd turnover might be lost if the environmental Zn is withdrawn before the start of the¹⁰⁹Cd pulse.A tendency of increased mortality of the fish exposed to 1 g Cd/L for 2–3 months suggested that low concentrations of Cd is toxic to the fish during chronic exposure. The increased Cd uptake and transfer in the gills, caused by Zn, could have deleterious effects on the fish. It might also reflect a change in the form of transport and in the intracellular handling of the metal, which protects the fish from Cd toxicity. However, a Zn pre-exposure did not decrease the mortality, which suggests that Zn did not protect the fish from Cd toxicity.     

Interrelationships between cadmium, zinc and antioxidants in the liver of the rat exposed orally to relatively high doses of cadmium and zinc

Zinc (Zn) reduces cadmium (Cd)-induced toxicity in the liver although it increases Cd tissue burden in some conditions; hence, the present study is designed to study the relationships between Cd, Zn and antioxidants in the liver of rats exposed to Cd. Livers of male rats which received orally relatively high doses of Cd (200 mg Cd/L as Cd chloride or Cd (200 mg/L)+Zn (500 mg Zn as Zn chloride) during five weeks, were investigated. Cd induced an accumulation of Cd and Zn in parallel to depletion in important variables (GSH, GSH/GSSG, CuZn-SOD and GPx activities) and to elevation in others (Cd/Zn and GSSG). Cd, did not affect CuZn SOD/GPx, nor Mn-SOD in the liver. Cd accumulation, Cd/Zn, CuZn SOD activity and CuZn SOD/GPx, was increased remarkably under Zn action. Zn supply ameliorated GSH level and partially reversed the decrease in GSH/GSSG, but it did not ameliorate GPx activity. Analysis showed high correlations between Cd and the majority of the variables, while Zn was positively correlated with only GSSG. We suggest from our results that Zn has indirect ameliorative effects on Cd-induced toxicity in the liver and that the increase in Cd retention is probably the key mechanism modulating, in the case of relatively high doses of Cd, the antioxidant response during exposure to Cd and Zn.     

Assessment of lead, cadmium, and zinc contamination of roadside soils, surface films, and vegetables in Kampala City, Uganda

The relationship between traffic density and trace metal concentrations in roadside soils, surface films, and a selected vegetable weed, Amaranthus dubius Mart. Ex Thell., was determined in 11 farming sites along major highways around Kampala City in Uganda. Surface soil, atmospherically deposited surface films on windows, and leaves of Amaranthus dubius were sampled at known distances from the roads and analyzed for lead (Pb), zinc (Zn), and cadmium (Cd) using flame atomic absorption spectrophotometry. Atmospherically deposited trace metal particulates were sampled using window glass as an inert, passive collector. Total trace metal concentrations in soils ranged from 30.0+/-2.3 to 64.6+/-11.7 mg/kg Pb, 78.4+/-18.4 to 265.6+/-63.2 mg/kg Zn, and 0.8+/-0.13 to 1.40+/-0.16 mg/kg Cd. Total trace metal levels in soil decreased rapidly with distance from the road. Total Pb decreased with distance up to 30 m from the road, where it reached a background soil concentration of 28 mg/kg dry weight. The study found background values of 50 and 1.4 mg/kg for Zn and Cd in roadside soils, respectively. Similarly, Pb concentration in Amaranthus dubius leaves decreased with increasing distance from the road edge. The dominant pathway for Pb contamination was from atmospheric deposition, which was consistent with Pb concentrations in surface films. The mean Pb concentrations in leaves of roadside crops were higher than those in their respective roots, with the highest leaf-to-root ratio observed in the Brassica oleraceae acephala group. The lowest Pb and Zn concentrations were found in the fruit compared to the leaves of the same crops. Leaves of roadside vegetables were therefore considered a potential source of heavy metal contamination to farmers and consumers in urban areas. It is recommended that leafy vegetables should be grown 30 m from roads in high-traffic, urban areas.