Validation of TOF-SIMS and FE-SEM/EDS Techniques Combined with Sorption and Desorption Experiments to Check Competitive and Individual Pb2+ and Cd2+ Association with Components of B Soil Horizons

Sorption and desorption experiments were performed by the batch method on the B horizons of five natural soils: Umbric Cambisol, Endoleptic Luvisol, Mollic Umbrisol, Dystric Umbrisol, and Dystric Fluvisol. Individual and competitive sorption and desorption capacity and hysteresis were determined. The results showed that Pb²⁺ was sorbed and retained in a greater quantity than Cd²⁺ and that the hysteresis of the first was greater than that of the second. The most influential characteristics of the sorption and retention of Pb²⁺ were pH, ECEC, Fe and Mn oxides and clay contents. For Cd²⁺ they were mainly pH and, to a lesser extent, Mn oxides and clay content. The combined use of TOF-SIMS, FE-SEM/EDS and sorption and desorption analyses was suitable for achieving a better understanding of the interaction between soil components and the two heavy metals. They show the preferential association of Pb²⁺ with vermiculite, chlorite, Fe and Mn oxides, and of Cd²⁺ with the same components, although to a much lesser extent and intensity. This was due to the latter’s higher mobility as it competed unfavourably with the Pb²⁺ sorption sites. TOF-SIMS and FE-SEM/EDS techniques confirmed the results of the sorption experiments, and also provided valuable information on whether the soil components (individually or in association) retain Cd²⁺ and / or Pb²⁺; this could help to propose effective measures for the remediation of contaminated soils.     

Biogeochemistry of trimethyllead and lead in a forested ecosystem in Germany

Lead compounds, especially ionic organolead compounds (OLC), are highly toxic and mobile pollutants strongly affecting many ecosystems. Soil pools and fluxes with precipitation, litterfall and runoff of trimethyllead (TML), one of the dominant ionic OLC in the environment, and Pb_total were investigated in a forested ecosystem in NE-Bavaria, Germany. In addition, ad/desorption of TML to soils was studied in batch experiments and its degradation in soils was investigated using long term incubations. Total soil storage in the catchment was 11.56?mg Pb?ha^?1 for TML and 222?kg Pb?ha^?1 for Pb_total. More than 90% of the soil storage of TML was found in the wetland soils of the catchment representing only 30% of the area. Most Pb_total (>90%) was found in the upland soils. In upland soils, TML was only detectable in the forest floor. The annual total deposition from the atmosphere, estimated as throughfall?+?litterfall fluxes, amounted to 3.7?mg Pb?ha^?1 year^?1 for TML and 52?g Pb?ha^?1 year^?1 for Pb_total. The contribution of litterfall was 1.5 and 32%, respectively. The concentrations of TML and Pb_total in wet precipitation were: fog?>?throughfall?>?bulk precipitation. The annual fluxes with runoff from the catchment was 0.5?mg Pb?ha^?1 year^?1 for TML and 2.8?g Pb?ha^?1 year^?1 for Pb_total. TML degraded rapidly in the forest floor (Oa horizon) with a half-life (t) of 33.5 days. The degradation of TML in Fen (t?=?421 days) and in the mineral soil (Bw-C horizon, t?=?612 days) was much slower. Emission of tetramethyllead from wetland soils was not observed during the 1 year incubation. The adsorption affinity of TML to different soils was Fen?>?Oa?>?A?≥?Bw-C. The ratio of total soil storages to the present annual input were 3.6 years for TML. TML and Pb_total are still deposited in remote areas even after the use of tetraalkyllead as additives has been terminated for years. The rates of deposition are, however, much lower than in the past. Forest soils act as a sink for deposited TML and Pb_total. TML is accumulated mostly in wetland soils and seems to be stable under anoxic conditions for a long time. In upland soils, TML decomposes rapidly. Only small amounts of TML are transferred from soils into runoff.     

Biogeochemistry of trimethyllead and lead in a forested ecosystem in Germany

Lead compounds, especially ionic organolead compounds (OLC), are highly toxic and mobile pollutants strongly affecting many ecosystems. Soil pools and fluxes with precipitation, litterfall and runoff of trimethyllead (TML), one of the dominant ionic OLC in the environment, and Pb_total were investigated in a forested ecosystem in NE-Bavaria, Germany. In addition, ad/desorption of TML to soils was studied in batch experiments and its degradation in soils was investigated using long term incubations. Total soil storage in the catchment was 11.56 mg Pb ha^–1 for TML and 222 kg Pb ha^–1 for Pb_total. More than 90% of the soil storage of TML was found in the wetland soils of the catchment representing only 30% of the area. Most Pb_total (>90%) was found in the upland soils. In upland soils, TML was only detectable in the forest floor. The annual total deposition from the atmosphere, estimated as throughfall + litterfall fluxes, amounted to 3.7 mg Pb ha^–1 year^–1 for TML and 52 g Pb ha^–1 year^–1 for Pb_total. The contribution of litterfall was 1.5 and 32%, respectively. The concentrations of TML and Pb_total in wet precipitation were: fog > throughfall > bulk precipitation. The annual fluxes with runoff from the catchment was 0.5 mg Pb ha^–1 year^–1 for TML and 2.8 g Pb ha^–1 year^–1 for Pb_total. TML degraded rapidly in the forest floor (Oa horizon) with a half-life (t _1/2) of 33.5 days. The degradation of TML in Fen (t _1/2 = 421 days) and in the mineral soil (Bw-C horizon, t _1/2 = 612 days) was much slower. Emission of tetramethyllead from wetland soils was not observed during the 1 year incubation. The adsorption affinity of TML to different soils was Fen > Oa > A Bw-C. The ratio of total soil storages to the present annual input were 3.6 years for TML. TML and Pb_total are still deposited in remote areas even after the use of tetraalkyllead as additives has been terminated for years. The rates of deposition are, however, much lower than in the past. Forest soils act as a sink for deposited TML and Pbtotal. TML is accumulated mostly in wetland soils and seems to be stable under anoxic conditions for a long time. In upland soils, TML decomposes rapidly. Only small amounts of TML are transferred from soils into runoff.     

Highly selective and sensitive coumarin–triazole‐based fluorometric ‘turn‐off’ sensor for detection of Pb2+ ions

Exposure to even very low concentrations of Pb²⁺ is known to cause cardiovascular, neurological, developmental, and reproductive disorders, and affects children in particular more severely. Consequently, much effort has been dedicated to the development of colorimetric and fluorescent sensors that can selectively detect Pb²⁺ ions. Here, we describe the development of a triazole‐based fluorescent sensor L5 for Pb²⁺ ion detection. The fluorescence intensity of chemosensor L5 was selectively quenched by Pb²⁺ ions and a clear color change from colorless to yellow could be observed by the naked eye. Chemosensor L5 exhibited high sensitivity and selectivity towards Pb²⁺ ions in phosphate‐buffered solution [20 mM, 1:9 DMSO/H₂O (v/v), pH 8.0] with a 1:1 binding stoichiometry, a detection limit of 1.9 nM and a 6.76 × 10⁶ M^?1 binding constant. Additionally, low‐cost and easy‐to‐prepare test strips impregnated with chemosensor L5 were also produced for efficient of Pb²⁺ detection and proved the practical use of this test.     

Abiotic immobilization of nitrate in two soils of relic <Emphasis Type="Italic">Abies pinsapo</Emphasis>-fir forests under Mediterranean climate

Evidence for abiotic immobilization of nitrogen (N) in soil is accumulating, but remains controversial. Identifying the fate of N from atmospheric deposition is important for understanding the N cycle of forest ecosystems. We studied soils of two Abies pinsapo fir forests under Mediterranean climate seasonality in southern Spain—one with low N availability and the other with symptoms of N saturation. We hypothesized that biotic and abiotic immobilization of nitrate (NO₃ ⁻) would be lower in soils under these forests compared to more mesic temperate forests, and that the N saturated stand would have the lowest rates of NO₃ ⁻ immobilization. Live and autoclaved soils were incubated with added ¹⁵NO₃ ⁻ (10 μg N g⁻¹ dry soil; 99% enriched) for 24 h, and the label was recovered as total dissolved-N, NO₃ ⁻, ammonium (NH₄ ⁺), or dissolved organic-N (DON). To evaluate concerns about possible iron interference in analysis of NO₃ ⁻ concentrations, both flow injection analysis (FIA) and ion chromatography (IC) were applied to water extracts, soluble iron was measured in both water and salt extracts, and standard additions of NO₃ ⁻ to salt extracts were analyzed. Good agreement between FIA and IC analysis, low concentrations of soluble Fe, and 100% (±3%) recovery of NO₃ ⁻ standard additions all pointed to absence of an interference problem for NO₃ ⁻ quantification. On average, 85% of the added ¹⁵NO₃ ⁻ label was recovered as ¹⁵NO₃ ⁻, which supports our hypothesis that rates of immobilization were generally low in these soils. A small amount (mean = 0.06 μg N g⁻¹ dry soil) was recovered as ¹⁵NH₄ ⁺ in live soils and none in sterilized soils. Mean recovery as DO¹⁵N ranged from 0.6 to 1.5 μg N g⁻¹ dry soil, with no statistically significant effect of sterilization or soil type, indicating that this was an abiotic process that occurred at similar rates in both soils. These results demonstrate a detectable, but modest rate of abiotic immobilization of NO₃ ⁻ to DON, supporting our first hypothesis. These mineral soils may not have adequate carbon availability to support the regeneration of reducing microsites needed for high rates of NO₃ ⁻ reduction. Our second hypothesis regarding lower expected abiotic immobilization in soils from the N-saturated site was not supported. The rates of N deposition in this region may not be high enough to have swamped the capacity for soil NO₃ ⁻ immobilization, even in the stand showing some symptoms of N saturation. A growing body of evidence suggests that soil abiotic NO₃ ⁻ immobilization is common, but that rates are influenced by a combination of factors, including the presence of plentiful available carbon, reduced minerals in anaerobic microsites and adequate NO₃ ⁻ supply.     

Resonance Scattering Spectral Detection of Trace Pb<Superscript>2+</Superscript> Using Aptamer-Modified AuPd Nanoalloy as Probe

The resonance scattering spectral probe for Pb²⁺ was obtained using aptamer-modified AuPd Nanoalloy. In the pH 7.0 Na₂HPO₄–NaH₂PO₄ buffer solution, the aptamer interacted with AuPd nanoalloy particles to form stable aptamer-AuPd nanoalloy probe for Pb²⁺ that is stable in high concentration of salt. The probe combined with Pb²⁺ ions to form a G-quadruplex and to release AuPd nanoalloy particles that aggregate to form big particles which led the resonance scattering (RS) intensity enhancing. The reaction solution was filtered by 0.15 μm membrane to obtain the filtration containing aptamer-AuPd nanoalloy probe that has strong catalytic effect on the electrodeless nickel particle plating reaction between Ni(II) and PO₂³⁻ that exhibited a strong RS peak at 508 nm. The RS intensity at 508 nm decreased when the Pb²⁺ concentration increased. The decreased intensity (ΔI _508nm) is linear to the concentration of 0.08–42 nM Pb²⁺, with regress equation of DI_508nm = 16.3 c + 1.5 \Delta {I_{{5}0{\rm{8nm}}}} = {16}.{3}\,c + {1}.{5} , correlation coefficient of 0.9965, and detection limit of 0.04 nM Pb²⁺. The RS assay was applied to the analysis of Pb²⁺ in wastewater, with satisfactory results.     

Iron interference in the quantification of nitrate in soil extracts and its effect on hypothesized abiotic immobilization of nitrate

Human alteration of the nitrogen cycle has stimulated research on nitrogen cycling in many aquatic and terrestrial ecosystems, where analyses of nitrate (NO₃ ⁻) by standard laboratory methods are common. A recent study by Colman et al. (Biogeochemistry 84:161–169, 2007) identified a potential analytical interference of soluble iron (Fe) with NO₃ ⁻ quantification by standard flow-injection analysis of soil extracts, and suggested that this interference may have led Dail et al. (Biogeochemistry 54:131–146, 2001) to make an erroneous assessment of abiotic nitrate immobilization in prior ¹⁵N pool dilution studies of Harvard Forest soils. In this paper, we reproduce the Fe interference problem systematically and show that it is likely related to dissolved, complexed-Fe interfering with the colorimetric analysis of NO₂ ⁻. We also show how standard additions of NO₃ ⁻ and NO₂ ⁻ to soil extracts at native dissolved Fe concentrations reveal when the Fe interference problem occurs, and permit the assessment of its significance for past, present, and future analyses. We demonstrate low soluble Fe concentrations and good recovery of standard additions of NO₃ ⁻ and NO₂ ⁻ in extracts of sterilized Harvard Forest soils. Hence, we maintain that rapid NO₃ ⁻ immobilization occurred in sterilized samples of the Harvard Forest O horizon in the study by Dail et al. (2001). Furthermore, additional evidence is accumulating in the literature for rapid disappearance of NO₃ ⁻ added to soils, suggesting that our observations were not the result of an isolated analytical artifact. The conditions for NO₃ ⁻ reduction are likely to be highly dependent on microsite properties, both in situ and in the laboratory. The so-called “ferrous wheel hypothesis” (Davidson et al., Glob Chang Biol 9:228–236, 2003) remains an unproven, viable explanation for published observations.     

Dissolved organic carbon affects soil microbial activity and nitrogen dynamics in a Mexican tropical deciduous forest

Seasonal variation of dissolved organic C (DOC) and its effects on microbial activity and N dynamics were studied during two consecutive years in soils with different organic C concentrations (hilltop and hillslope) in a tropical deciduous forest of Mexico. We found that DOC concentrations were higher at the hilltop than at the hillslope soils, and in both soils generally decreased from the dry to the rainy season during the two study years. Microbial biomass and potential C mineralization rates, as well as dissolved organic N (DON) and NH₄⁺ concentrations and net N immobilization were higher in soils with higher DOC than in soils with lower DOC. In contrast, net N immobilization and NH₄⁺ concentration were depleted in the soil with lowest DOC, whereas NO₃⁻ concentrations and net nitrification increased. Negative correlations between net nitrification and DOC concentration suggested that NH₄⁺ was transformed to NO₃⁻ by nitrifiers when the C availability was depleted. Taken together, our results suggest that available C appears to control soil microbial activity and N dynamics, and that microbial N immobilization is facilitated by active heterotrophic microorganisms stimulated by high C availability. Soil autotrophic nitrification is magnified by decreases in C availability for heterotrophic microbial activity. This study provides an experimental data set that supports the conceptual model to show and highlight that microbial dynamics and N transformations could be functionally coupled with DOC availability in the tropical deciduous forest soils. Responsible Editor: Chris Neill     

Organic and inogranic lead inhibit neurite growth in vertebrate and invertebrate neurons in culture

Summary Neurons from brains of chick embryos and pond snails (Lymnaea stagnalis) were cultured for 3 to 4 d in the presence of no toxins, inorganic lead (PbCl₂), or organic lead (trielthyl lead chloride). In chick neurons, inorganic lead reduced the percentage of cells that grew neurites (IC₅₀=270μM total lead, approximately 70 nM free Pb²⁺) but did not reduce the number of neurites per cell or the mean neurite length. Triethyl lead reduced the percentage of cells that grew neuites (IC₅₀=0.24 μM) and the mean neurite length (extrapolated IC₅₀=3.6 μM) but did not reduce the number of neurites per cell. InLymnaea neurons, inorganic lead reduced the percentage of cells that grew neurites (IC₅₀=13 μM total lead; approximately 10 nM free Pb²⁺). Triethyl lead reduced the percentage of cells that grew neurites (IC₅₀=0.4 μM) and exerted significant toxicity at 0.2 μM. The two forms of lead affected neurite growth in qualitatively different ways, which suggests that their mechansms of action are different. These experiments were supported by grants from the Environmental Protection Agency, Washington, DC, and the National Institutes of Environmental Health Science, Research Triangle Park, NC.     

Effects of low pH and Pb2+ stress on living cyanobacterium, Phormidium angustissimum West & G.S.West : A test of its feasibility as a living biosorbent

Pb²⁺ adsorption by the living cyanobacterium, Phormidium angustissimum followed the Langmuir adsorption model, with the maximum adsorption capacity (q _max ) of 295.4?±?13.8 mg g^?1. This result suggests that P. angustissimum is a promising living biosorbent to remove Pb²⁺ from wastewaters. Living biosorbents are better able to remove Pb²⁺ from wastewater than dead biosorbents, however there are practical limitations for their use are encountered in extreme conditions such as low pH and high Pb²⁺ concentration. The feasibility of using cyanobacterium, P. angustissimum, as a living biosorbent for the extraction of Pb²⁺ from wastewater was studied by investigating its photosynthestic performance and tolerance under Pb²⁺ (0–5 mg ?L^?1) contamination and low pH (pH?3–7). Decreased photosynthetic performance caused by Pb²⁺ contamination and low pH stress was detected in this study by means of a reduction of the maximum photochemical efficiency of PSII (F_v/F_m). Detoxification mechanisms of P. angustissimum on Pb²⁺ appeared to increase its intracellular polysaccharides (IPS), exocellular polysaccharides (EPS), and protein. Living P. angustissimum could increase the pH of the solution which resulted in Pb²⁺ precipitation. The unique ability of P. angustissimum to remove Pb²⁺ and to grow under toxic conditions, demonstrated herein, indicates that it is a promising living biosorbent for mildly acidic water contaminated with Pb²⁺ in bioremoval systems in the which pH is not lower than 5 and Pb²⁺ is not higher than 5 mg L^?1.     

Pb2+ reduces voltage- andN-methyl-d-aspartate (NMDA)-activated calcium channel currents

Summary 1. While intracellular calcium concentrations are closely regulated, two types of ion channels in neurons allow calcium influx: both voltage-activated and NMDA-activated channels are significantly permeable to calcium. In this study we compare the effects of lead (Pb²⁺) on currents carried through voltage-activated calcium channels and NMDA-activated channels.2. Pb²⁺ reduces voltage-activated calcium channel currents elicited by a voltage jump from –80 to 0 mV at 0.1 to 1 µM, with an IC₅₀ of 0.64 µM and a Hill slope of 1.22. This effect was partially reversible and not voltage dependent. Sodium and potassium currents were relatively unaffected at Pb²⁺ concentrations sufficient to block calcium channel currents by more than 80%. Pb²⁺ is, thus, a potent, reversible and selective blocker of voltage-dependent calcium channel currents.3. A fast reversible and slow irreversible blocking action of Pb²⁺ was found on NMDA-activated currents. When Pb²⁺ was applied simultaneously with aspartate and glycine (Asp/Gly), the inward currents were rapidly and reversibly reduced in a dose-dependent manner with a minimum effective concentration below 2 µM and a total blockade (>80%) with 100 µM Pb²⁺. The IC₅₀ was 45 µM and the Hill coefficient 1.1. Preincubation with 50 µM Pb²⁺ resulted in a greater reduction in the response to Asp/Gly/Pb²⁺. This effect was reversed within 2 to 5 sec of wash. The lack of voltage dependence suggests that Pb²⁺ does not block the channel but rather alters the binding of agonists. Prolonged superfusion of a cell with the Asp/Gly/Pb²⁺-containing external solution resulted in a slow and irreversible decrease in the Asp/Gly activated current. No clear threshold concentration is found for this slow and irreversible effect of Pb²⁺. This slow action might be more important for neurotoxic effects of Pb²⁺.     

Moisture adsorption capacity and surface area as deduced from vapour pressure isotherms in relation to hygroscopic water of soils

Six calcareous and alluvial soil profiles differing in their texture, CaCO₃ and salinity were chosen from west and middle Nile Delta for the present study. The 1^st and 2^nd profiles from Borg El-Arab area were sandy loam in texture and > 30% CaCO₃, while the 3^rd and 4^th profiles (from Nubaria area) were sandy clay loam and < 30% CaCO₃. The 2^nd and 4^th profiles were taken from cultivated area with maize. The 5^th profile from Epshan area was non-saline clay alluvial soil and the 6^th from El-Khamsen was saline clay alluvial soil. The relation between soil moisture content (W%) and water vapour pressure (P/P _o) was established for the mentioned soils. Data showed that the specific surface area (S) values were 34–53 and 44–60 m²/g for calcareous soils of Borg El-Arab and Nubaria areas, 206–219 and 206–249 m²/g for non-saline and saline clay alluvial soils of Epshan and El-Khamsen areas, respectively. The corresponding values of the external specific surface area (S _e) were 16–21, 14–22, 72–86 and 92–112 m²/g. Submitting W _m+W _me as an adsorption boundary of moisture films (W _c) (where W _m is mono-adsorbed layer of water vapour on soil particles and W _me is the external mono-adsorbed layer), the maximum water adsorption capacity (W _a) was found to be W _c + W _me or W _m + 2W _me. It was ranged from 1.88 to 2.70%, 1.97 to 2.95%, 9.70–10.70% and 10.80 to 13.12% while the maximum hygroscopic water (M _H) values were 2.43–3.78%, 2.91–4.65%, 16–17% and 18.30–21.9% for the studied soil profiles respectively. The residual moisture content (θ _r) at pF 7 and P/P _o = 0 was ranged from 0.0005–0.0010%, 0.0007–0.0019% and 0.0043–0.0048% in Borg El-Arab, Nubaria and Epshan soil profiles, respectively. The inter-relations between the surface area and the hygroscopic moisture parameters of the soils under investigation were as follows Calcareous soils; W _m = 0.40 M _H, W _c = 0.55 M _H, W _a = 0.70 M _H, S = 14 M _H Non-saline soil; W _m = 0.35 M _H, W _c = 0.49 M _H, W _a = 0.63 M _H, S = 13 M _H Saline soil; W _m = 031 M _H, W _c = 0.45 M _H, W _a = 0.59 M _H, S = 12 M _H These relations give possibility to deduce the soil moisture adsorption capacities and specific surface area via maximum hygroscopic water, which can be obtained through the experimental determination of water vapor adsorption isotherms.     

Isolation and Molecular Characterization of Heavy Metal-Resistant Azotobacter chroococcum from Agricultural Soil and Their Potential Application in Bioremediation

Pollution of soil with heavy metals, herbicides, antibiotics and other chemicals is known to have a negative effect on microbial activities. Therefore, the aim of this study was to isolate cultures of Azotobacter sp. from polluted and unpolluted soils and to study the effect of these pollutants on their growth. A total of 120 Azotobacter sp. were isolated from soils irrigated with wastewater (contaminated soils) and groundwater (uncontaminated soils). These isolates were screened for resistance to heavy metals, herbicide and antibiotics. Also, the soils from which the cultures were isolated were analyzed for the concentrations of Zn²⁺, Cd²⁺, Cu²⁺, Pb²⁺ and Mn²⁺ they contained. Contaminated soil showed high levels of heavy metals as compared to uncontaminated soil. The size of the Azotobacter population in contaminated soil was lower than that in uncontaminated soil. Of the Azotobacter isolates, 64 that were recovered from contaminated soil exhibited high resistance to heavy metals (Hg²⁺, Cd²⁺, Cu²⁺, Cr³⁺, Co²⁺, Ni²⁺, Zn²⁺ and Pb²⁺) and herbicide 2,4-D compared to 56 isolates from uncontaminated soil. Also, isolates from contaminated soil showed high resistance to chloramphenicol, nitrofurantoin and co-trimoxazole compared to those isolated from uncontaminated soil. The majority of Azotobacter isolates from contaminated soil showed multiple-resistance to different metal ions and antibiotics. All isolates failed to grow at pH less than 6. Salt concentration (5%) was found to be inhibitory to all isolates. The most potent isolates from contaminated soil that showed multiresistance to all substances tested were identified on the basis of morphological and biochemical characteristics, and 16S rRNA as A. chroococcum. These resistant isolates could be employed in contaminated soils and/or bioremediation.     

Évaluation par des extractions sélectives de l'immobilisation du Cd après l'apport de matériaux inorganiques dans deux terres polluées

Two soils, contaminated by sludge application or by smelter activities, have been amended with : lime (CaO), lime + Al-pillared smectites (CaO + Sm), phosphate basic slags (SCO), manganese oxide (HMO), iron oxide (HFO) and steel shot (GA). Four single soil extractions (water, 0.1 M Ca(NO₃)₂ 0.05 M ED TA-NH₄ and acetic acid (0.43 M HAc)) and the two plant cultures (tobacco and ryegrass) were used to evaluate the effect of these inorganic additives on the mobility and plant-availability of cadmium in the soils. The Cd extracted by the different solutions was compared to the concentration of Cd in the shoots of ryegrass and tobacco. The effect of treatments on Cd mobility in soil was easily discriminated by the use of either water or Ca(NO₃)₂. The addition of HMO and GA reduced both the mobility and the phyto-availability of Cd in the two soils. Conversely, the alkaline additives and HFO decreased the Cd mobility, but not the Cd plant availability. Single soil extractions using either water or Ca(NO₃)₂ are a useful tool for estimating Cd immobilization, but not sufficient for assessing Cd plant availability ; a validation by plant tests must be conducted.     

Evaluation of Phosphate Fertilizers for the Immobilization of Cd in Contaminated Soils

A laboratory investigation was conducted to evaluate the efficiency of four phosphate fertilizers, including diammonium phosphate (DAP), potassium phosphate monobasic (MPP), calcium superphosphateon (SSP), and calcium phosphate tribasic (TCP), in terms of the toxicity and bioavailability of Cd in contaminated soils. The efficiency of immobilization was evaluated on the basis of two criteria: (a) the reduction of extractable Cd concentration below the TCLP regulatory level and (b) the Cd changes associated with specific operational soil fractions on the basis of sequential extraction data. Results showed that after 50 d immobilization, the extractable concentrations of Cd in DAP, MPP, SSP, and TCP treated soils decreased from 42.64 mg/kg (in the control) to 23.86, 21.86, 33.89, and 35.59 mg/kg, respectively, with immobilization efficiency in the order of MPP > DAP > SSP > TCP. Results from the assessment of Cd speciation via the sequential extraction procedure revealed that the soluble exchangeable fraction of Cd in soils treated with phosphate fertilizers, especially TCP, was considerably reduced. In addition, the reduction was correspondingly related to the increase in the more stable forms of Cd, that is, the metal bound to manganese oxides and the metal bound to crystalline iron oxides. Treatment efficiency increased as the phosphate dose (according to the molar ratio of PO₄/Cd) increased. Immobilization was the most effective under the molar ratio of PO₄/Cd at 4:1.     

Zinc biosorption from aqueous solution by a halotolerant cyanobacterium Aphanothece halophytica

We have investigated the characteristics of zinc biosorption by Aphanothece halophytica. Zinc could be rapidly taken up from aqueous solution by the cells with an equilibrium being reached within 15 min of incubation with 100 mg L⁻¹ ZnCl₂. The adsorbed zinc was desorbed by treatment with 10 mM EDTA. The presence of glucose, carbonyl cyanide m-chlorophenylhydrazone (CCCP), and N,N′-dicyclohexylcarbodiimide (DCCD) did not affect the uptake of zinc. The specific uptake of zinc increased at low cell concentration and decreased when cell concentration exceeded 0.2 g L⁻¹. The binding of zinc followed Langmuir isotherm kinetics with a maximum zinc binding capacity of 133 mg g⁻¹ and an apparent zinc binding constant of 28 mg L⁻¹. The presence of an equimolar concentration of Mn²⁺, Mg²⁺, Co²⁺, K⁺, or Na⁺ had no effect on zinc biosorption, whereas Ca²⁺, Hg²⁺, and Pb²⁺ showed an inhibitory effect. The biosorption of zinc was low at a pH range from 4 to 6, but increased progressively at pH 6.5 and 7. Received: 12 December 2001 / Accepted: 11 January 2002     

Characterization of Lead in Soils of a Rifle/Pistol Shooting Range in Central Florida,USA

The distribution of lead in soil samples collected from both surface (0 to 10?cm) and profile (O 0 to 10?cm, E 11 to 30?cm, Eb 31 to 50?cm, Bw 51 to 100?cm, and C 181 to 200?cm) at a 14-year-old rifle/pistol shooting range located in central Florida were determined using EPA Method 3051a (microwave, HNO₃/HCl=3:1, v/v). In addition to total lead analysis, Toxicity Characteristic Leaching Procedure (TCLP) analysis was performed on corresponding samples to determine whether the soils would require special handling as hazardous waste if the soils were to be removed from the range. Total lead in surface soils varied from 330 to 17 850?mg Pb kg^?1, with the greatest concentration in the middle of the backstop berm. The TCLP tests indicated that lead in all surface soils exceeded the 5?mg Pb L^?1 critical level of federal regulation for solid wastes and hazardous wastes provided by the Resource Conservation and Recovery Act (RCRA) and would be characterized as hazardous waste. Sequential fractionation and X-ray diffraction (XRD) analyses revealed that lead carbonate existed predominantly (91.3%) in the berm soil. The weathering of lead bullets in the soil environments formed primarily as hydrocerussite (Pb₃(CO₃)₂(OH)₂), with small amounts of massicot (PbO) and cerussite (PbCO₃). However, the elevated soil pH, caused by the oxidization and transformation process of elemental lead in lead bullets, could be a significant factor in limiting the migration of lead in the soil.     

Horizontal Gene Transfer of PIB-Type ATPases among Bacteria Isolated from Radionuclide- and Metal-Contaminated Subsurface Soils

Aerobic heterotrophs were isolated from subsurface soil samples obtained from the U.S. Department of Energy's (DOE) Field Research Center (FRC) located at Oak Ridge, Tenn. The FRC represents a unique, extreme environment consisting of highly acidic soils with cooccurring heavy metals, radionuclides, and high nitrate concentrations. Four hundred isolates obtained from contaminated soil were assayed for heavy metal resistance, and a smaller subset was assayed for tolerance to uranium. The vast majority of the isolates were gram-positive bacteria and belonged to the high-G+C- and low-G+C-content genera Arthrobacter and Bacillus, respectively. Genomic DNA from a randomly chosen subset of 50 Pb-resistant (Pb^r) isolates was amplified with PCR primers specific for P_IB-type ATPases (i.e., pbrA/cadA/zntA). A total of 10 pbrA/cadA/zntA loci exhibited evidence of acquisition by horizontal gene transfer. A remarkable dissemination of the horizontally acquired P_IB-type ATPases was supported by unusual DNA base compositions and phylogenetic incongruence. Numerous Pb^r P_IB-type ATPase-positive FRC isolates belonging to the genus Arthrobacter tolerated toxic concentrations of soluble U(VI) (UO₂²⁺) at pH 4. These unrelated, yet synergistic, physiological traits observed in Arthrobacter isolates residing in the contaminated FRC subsurface may contribute to the survival of the organisms in such an extreme environment. This study is, to the best of our knowledge, the first study to report broad horizontal transfer of P_IB-type ATPases in contaminated subsurface soils and is among the first studies to report uranium tolerance of aerobic heterotrophs obtained from the acidic subsurface at the DOE FRC.     

Association of Microbial Community Composition and Activity with Lead, Chromium, and Hydrocarbon Contamination

Microbial community composition and activity were characterized in soil contaminated with lead (Pb), chromium (Cr), and hydrocarbons. Contaminant levels were very heterogeneous and ranged from 50 to 16,700 mg of total petroleum hydrocarbons (TPH) kg of soil⁻¹, 3 to 3,300 mg of total Cr kg of soil⁻¹, and 1 to 17,100 mg of Pb kg of soil⁻¹. Microbial community compositions were estimated from the patterns of phospholipid fatty acids (PLFA); these were considerably different among the 14 soil samples. Statistical analyses suggested that the variation in PLFA was more correlated with soil hydrocarbons than with the levels of Cr and Pb. The metal sensitivity of the microbial community was determined by extracting bacteria from soil and measuring [³H]leucine incorporation as a function of metal concentration. Six soil samples collected in the spring of 1999 had IC₅₀ values (the heavy metal concentrations giving 50% reduction of microbial activity) of approximately 2.5 mM for CrO₄²⁻ and 0.01 mM for Pb²⁺. Much higher levels of Pb were required to inhibit [¹⁴C]glucose mineralization directly in soils. In microcosm experiments with these samples, microbial biomass and the ratio of microbial biomass to soil organic C were not correlated with the concentrations of hydrocarbons and heavy metals. However, microbial C respiration in samples with a higher level of hydrocarbons differed from the other soils no matter whether complex organic C (alfalfa) was added or not. The ratios of microbial C respiration to microbial biomass differed significantly among the soil samples (P < 0.05) and were relatively high in soils contaminated with hydrocarbons or heavy metals. Our results suggest that the soil microbial community was predominantly affected by hydrocarbons.     

Amberlite IR-120 Modified with 8-Hydroxyquinoline as Efficient Adsorbent for Solid-Phase Extraction and Flame Atomic Absorption Determination of Trace Amounts of Some Metal Ions

In this study, a solid-phase extraction method combined with atomic absorption spectrometry for extraction, preconcentration, and determination of iron (Fe³⁺), copper (Cu²⁺), and lead (Pb²⁺) ions at trace levels in water samples has been reported. The influences of effective parameters such as flow rate, pH, eluent conditions (type, volume, and concentration), sample volumes, and interference of matrix ions on metal ions recoveries were studied. Under optimized conditions, the limits of detection were found in the range of 0.7–2.2 μg L⁻¹, while preconcentration factors for Fe³⁺, Cu²⁺, and Pb²⁺ ions were found to be 166, 200, and 250, respectively, and loading half time (t _1/2) values were less than 2 min for all analyte ions. The proposed procedure was applied for the determination of metal ions in different water samples with recovery of >94.4% and relative standard deviation less than 4.4% for N = 5.