Effects of calcium peroxide on arsenic uptake by celery (Apium graveolens L.) grown in arsenic contaminated soil

The ability of calcium peroxide (CaO₂) to immobilize As of contaminated soil was studied using pot and field experiments. In pot experiment, CaO₂ applied at 2.5 and 5 g kg⁻¹ significantly increased celery shoot weight and decreased shoot As accumulation, which was ascribed to the formation of stable crystalline Fe and Al oxides bound As and the reduction of labile As fractions in the soil. The labile As fractions were pH dependent and it followed a “V” shaped profile with the change of pH. In field experiment, the dose of CaO₂ application at 750 kg ha⁻¹ was optimal and at which the celery was found to produce the highest biomass (63.4 Mg ha⁻¹) and lowest As concentration (0.43 mg kg⁻¹). CaO₂ probably has a promising potential as soil amendment to treat As contaminated soils.     

Feasibility of phytoextraction to remediate cadmium and zinc contaminated soils

A Cd and Zn contaminated soil was mixed and equilibrated with an uncontaminated, but otherwise similar soil to establish a gradient in soil contamination levels. Growth of Thlaspi caerulescens (Ganges ecotype) significantly decreased the metal concentrations in soil solution. Plant uptake of Cd and Zn exceeded the decrease of the soluble metal concentrations by several orders of magnitude. Hence, desorption of metals must have occurred to maintain the soil solution concentrations. A coupled regression model was developed to describe the transfer of metals from soil to solution and plant shoots. This model was applied to estimate the phytoextraction duration required to decrease the soil Cd concentration from 10 to 0.5 mg kg⁻¹. A biomass production of 1 and 5 t dm ha⁻¹ yr⁻¹ yields a duration of 42 and 11 yr, respectively. Successful phytoextraction operations based on T. caerulescens require an increased biomass production.     

Correlation of foliar MT2b expression with Cd and Zn concentrations in hybrid aspen (Populus tremula × tremuloides) grown in contaminated soil

Metal uptake and its effect on foliar metallothionein 2b (MT2b) mRNA levels were studied in hybrid aspen (Populus tremula × tremuloides) in field conditions. The trees were planted on a site contaminated with several metals, including cadmium (mean 5.1 mg kg⁻¹), chromium (80 mg kg⁻¹), copper (180 mg kg⁻¹), nickel (81 mg kg⁻¹), vanadium (240 mg kg⁻¹) and zinc (520 mg kg⁻¹). Of the ten trace elements analyzed, only Cd and Zn accumulated in the leaves with maximal foliar concentrations of 35 and 2400 mg kg⁻¹ (dry weight), respectively. There was a strong correlation between Cd and Zn concentrations and bioaccumulation factors (concentration in plant/soil) in the leaves, branches and roots, suggesting similar transport mechanisms for these two metals. The levels of MT2b correlated with Cd and Zn concentrations in the leaves, demonstrating that increased MT2b expression is one of the responses of hybrid aspen to chronic metal exposure.     

Response of Holm oak (Quercus ilex subsp. ballota) and mastic shrub (Pistacia lentiscus L.) seedlings to high concentrations of Cd and Tl in the rhizosphere

The impairment of root growth and photosynthetical functioning are the main impacts of trace elements on woody plant seedlings. In this work, we assessed the response of Holm oak (Quercusilex subsp. ballota) and mastic shrub (Pistacia lentiscus) seedlings to high concentrations of Cd and Tl in the rhizosphere. These are non-essential trace elements, with a potential high mobility in the soil-plant system. Seedlings of these species are frequently used in the afforestation of degraded soils in mining areas. Plants were exposed to different levels of Cd (20, 80 and 200 mg L⁻¹) and Tl (2, 10 and 20 mg L⁻¹) in a sand culture. Biomass allocation, growth rates, chlorophyll fluorescence and gas exchange were studied. Both metals affected root biomass. Cadmium produced an increase in the root mass ratio and a decrease in the specific leaf area of the plants in oak seedlings, while Tl did not provoke such response. Mastic plants were more sensitive to Tl and Cd than oak plants. Between elements, Tl provoked more severe toxic effects in the plants, affecting the antennae complexes and reaction centers of the photosystem II. Both elements decreased net assimilation rates (down to a 20% of the control plants) and stomatal conductance (5-10% of the values for the control plants). Cadmium was highly retained in the roots of both species, while Tl was highly translocated into the leaves. In general, Holm oak showed a higher tolerance for Cd than for Tl, and a higher resistance to both metals than mastic shrub, due to a high capacity for Cd retention at the root level. However, such accumulation in roots may induce water stress in the seedling exposed to Cd.     

Removal of Ni(II) and Cu(II) ions using native and acid treated Ni-hyperaccumulator plant Alyssum discolor from Turkish serpentine soil

Alyssum discolor biomass was collected from serpentine soil and was used for removal of metal ions. The plant species grown on serpentine soils are known to be rich with metals ions and thus have more capability for accumulating heavy metals. Native and acid-treated biomass of A. discolor (A. discolor) were utilized for the removal of Ni(II) and Cu(II) ions from aqueous solutions. The effects of contact time, initial concentration, and pH on the biosorption of Ni(II) and Cu(II) ions were investigated. Biosorption equilibrium was established in about 60 min. The surface properties of the biomass preparations were varied with pH, and the maximum amounts of Ni(II) and Cu(II) ions on both A. discolor biomass preparations were adsorbed at pH 5.0. The maximum biosorption capacities of the native, and acid-treated biomass preparations for Ni(II) were 13.1 and 34.7 mg g⁻¹ and for Cu(II) 6.15 and 17.8 mg g⁻¹ dry biomass, respectively. The biosorption of Ni(II) and Cu(II) ions from single and binary component systems can be successfully described by Langmuir and Freundlich isotherms. When the heavy metal ions were in competition, the amounts of biosorbed metal ions on the acid treated plant biomass were found to be 0.542 mmol g⁻¹ for Ni(II) and 0.162 mmol g⁻¹ for Cu(II), the A. discolor biomass was significantly selective for Ni(II) ions. The information gained from these studies was expected to indicate whether the native, and acid-treated forms can have the potential to be used for the removal and recovery of Ni(II) ions from wastewaters.     

Application of phosphate-solubilizing bacteria for enhancing bioavailability and phytoextraction of cadmium (Cd) from polluted soil

In this study, phosphate-solubilizing bacteria (PSB), Bacillus megaterium, were used to enhance Cd bioavailability and phytoextractability of Cd from contaminated soils. This strain showed a potential for directly solubilizing phosphorous from soils more than 10 folds greater than the control without inoculation. The results of pot experiments revealed that inoculation with B. megaterium significantly increased the extent of Cd accumulation in Brassica juncea and Abutilon theophrasti by two folds relative to the uninoculated control. The maximum Cd concentrations due to inoculation were 1.6 and 1.8 mg Cd g⁻¹ plant for B. juncea and A. theophrasti after 10 wk, respectively. The total biomass of A. theophrasti was not significantly promoted by the inoculation treatment, yet the total biomass of B. juncea increased from 0.087 to 0.448 g. It is also worth to mention that B. juncea predominantly accumulates Cd in its stems (39%) whereas A. theophrasti accumulates it in its leaves (68%) after 10 wk. The change of the Cd speciation indicated that inoculation of B. megaterium as PSB increased the bioavailabilty of Cd and consequently enhanced its uptake by plants. The present study may provide a new insight for improving phytoremediation using PSB in the Cd-contaminated soils.     

Recycling of EDTA solution after soil washing of Pb, Zn, Cd and As contaminated soil

Soil washing with EDTA is known to be an effective means of removing toxic metals from contaminated soil. A practical way of recycling of used soil washing solution remains, however, an unsolved technical problem. We demonstrate here, in a laboratory scale experiment, the feasibility of using acid precipitation to recover up to 50% of EDTA from used soil washing solution obtained after extraction of Pb (5330 mg kg⁻¹), Zn (3400 mg kg⁻¹), Cd (35 mg kg⁻¹) and As (279 mg kg⁻¹) contaminated soil. Up to 100% of EDTA residual in the washing solution and 100%, 97%, 98% and 100% of initial Pb, Zn, Cd and As concentration in the solution, respectively, were removed in an electrolytic cell using a graphite anode. We employed the recovered EDTA and treated washing solution to prepare recycled soil washing solution with the same potential for extracting toxic metals from soil as the original. The efficiency of soil washing depends on the EDTA concentration. Using twice recycled 30 mmol EDTA kg⁻¹ soil, we removed 44%, 20%, 53% and 61% of Pb, Zn, Cd and As, respectively, from contaminated soil.     

Effects of municipal solid waste compost and mineral fertilizer amendments on soil properties and heavy metals distribution in maize plants (Zea mays L.)

Soil amendments based on crop nutrient requirements are considered a beneficial management practice. A greenhouse experiment with maize seeds (Zea mays L.) was conducted to assess the inputs of metals to agricultural land from soil amendments. Maize seeds were exposed to a municipal solid waste (MSW) compost (50 Mg ha⁻¹) and NPK fertilizer (33 g plant⁻¹) amendments considering N plant requirement until the harvesting stage with the following objectives: (1) determine the accumulation of total and available metals in soil and (2) know the uptake and ability of translocation of metals from roots to different plant parts, and their effect on biomass production. The results showed that MSW compost increased Cu, Pb and Zn in soil, while NPK fertilizer increased Cd and Ni, but decreased Hg concentration in soil. The root system acted as a barrier for Cr, Ni, Pb and Hg, so metal uptake and translocation were lower in aerial plant parts. Biomass production was significantly enhanced in both MSW and NPK fertilizer-amended soils (17%), but also provoked slight increases of metals and their bioavailability in soil. The highest metal concentrations were observed in roots, but there were no significant differences between plants growing in amended soil and the control soil. Important differences were found for aerial plant parts as regards metal accumulation, whereas metal levels in grains were negligible in all the treatments.     

Critical Limits for Hg(II) in soils, derived from chronic toxicity data

Published chronic toxicity data for Hg(II) added to soils were assembled and evaluated to produce a data set comprising 52 chronic end-points, five each for plants and invertebrates and 42 for microbes. With end-points expressed in terms of added soil Hg(II) contents, Critical Limits were derived from the 5th percentiles of species sensitivity distributions, values of 0.13 μg (g soil)⁻¹ and 3.3 μg (g soil organic matter)⁻¹ being obtained. The latter value exceeds the currently recommended Critical Limit, used to determine Hg(II) Critical Loads in Europe, of 0.5 μg (g soil organic matter)⁻¹. We also applied the WHAM/Model VI chemical speciation model to estimate concentrations of Hg²⁺ in soil solution, and derived an approximate Critical Limit Function (CLF) that includes pH; log [Hg²⁺]_crit = −2.15 pH −17.10. Because they take soil properties into account, the soil organic matter-based limit and the CLF provide the best assessment of toxic threat for different soils. For differing representative soils, each predicts a range of up to 100-fold in the dry weight-based content of mercury that corresponds to the Critical Limit.     

Cadmium accumulation in and tolerance of rice (Oryza sativa L.) varieties with different rates of radial oxygen loss

Cadmium (Cd) uptake and tolerance were investigated among 20 rice cultivars based on a field experiment (1.2 mg Cd kg⁻¹ in soil) and a soil pot trial (control, 100 mg Cd kg⁻¹), and rates of radial oxygen loss (ROL) were measured under a deoxygenated solution. Significant differences were found among the cultivars in: (1) brown rice Cd concentrations (0.11-0.29 mg kg⁻¹) in a field soil, (2) grain Cd tolerance (34-113%) and concentrations (2.1-6.5 mg kg⁻¹) in a pot trial, and (3) rates of ROL (15-31 mmol O₂ kg⁻¹ root d.w. h⁻¹). Target hazard quotients were calculated for the field experiment to assess potential Cd risk. Significant negative relationships were found between rates of ROL and concentrations of Cd in brown rice or straw under field and greenhouse conditions, indicating that rice cultivars with higher rates of ROL had higher capacities for limiting the transfer of Cd to rice and straw.     

Effects of rapeseed residue on lead and cadmium availability and uptake by rice plants in heavy metal contaminated paddy soil

Rapeseed (Brassica napus L.) has been cultivated for biodiesel production worldwide. Winter rapeseed is commonly grown in the southern part of Korea under a rice-rapeseed double cropping system. In this study, a greenhouse pot experiment was conducted to assess the effects of rapeseed residue applied as a green manure alone or in combinations with mineral N fertilizer on Cd and Pb speciation in the contaminated paddy soil and their availability to rice plant (Oryza sativa L.). The changes in soil chemical and biological properties in response to the addition of rapeseed residue were also evaluated. Specifically, the following four treatments were evaluated: 100% mineral N fertilizer (N100) as a control, 70% mineral N fertilizer + rapeseed residue (N70 + R), 30% mineral N fertilizer + rapeseed residue (N30 + R) and rapeseed residue alone (R). The electrical conductivity and exchangeable cations of the rice paddy soil subjected to the R treatment or in combinations with mineral N fertilizer treatment, N70 + R and N30 + R, were higher than those in soils subjected to the N100 treatment. However, the soil pH value with the R treatment (pH 6.3) was lower than that with N100 treatment (pH 6.9). Use of rapeseed residue as a green manure led to an increase in soil organic matter (SOM) and enhanced the microbial populations in the soil. Sequential extraction also revealed that the addition of rapeseed residue decreased the easily accessible fraction of Cd by 5-14% and Pb by 30-39% through the transformation into less accessible fractions, thereby reducing metal availability to the rice plant. Overall, the incorporation of rapeseed residue into the metal contaminated rice paddy soils may sustain SOM, improve the soil chemical and biological properties, and decrease the heavy metal phytoavailability.     

Dry deposition and soil-air gas exchange of polychlorinated biphenyls (PCBs) in an industrial area

Ambient air and dry deposition, and soil samples were collected at the Aliaga industrial site in Izmir, Turkey. Atmospheric total (particle + gas) ∑₄₁-PCB concentrations were higher in summer (3370 ± 1617 pg m⁻³, average + SD) than in winter (1164 ± 618 pg m⁻³), probably due to increased volatilization with temperature. Average particulate ∑₄₁-PCBs dry deposition fluxes were 349 ± 183 and 469 ± 328 ng m⁻² day⁻¹ in summer and winter, respectively. Overall average particulate deposition velocity was 5.5 ± 3.5 cm s⁻¹. The spatial distribution of ∑₄₁-PCB soil concentrations (n = 48) showed that the iron-steel plants, ship dismantling facilities, refinery and petrochemicals complex are the major sources in the area. Calculated air-soil exchange fluxes indicated that the contaminated soil is a secondary source to the atmosphere for lighter PCBs and as a sink for heavier ones. Comparable magnitude of gas exchange and dry particle deposition fluxes indicated that both mechanisms are equally important for PCB movement between air and soil in Aliaga.     

Lindane removal by pure and mixed cultures of immobilized actinobacteria

Stereoselective dissipation of epoxiconazole had been studied in grape and soil during plant growing under field conditions in this paper. A sensitive and rapid chiral method was developed and validated for the determination of epoxiconazole stereoisomers in grape and soil based on liquid chromatography coupled with triple quadrupole mass spectrometry (LC-MS/MS). Phenomenex Lux Cellulose-1 column was used for enantioseparation with a mixture of acetonitrile/water (90/10, v/v) as mobile phase at flow rate of 0.3 mL min⁻¹. Fortified recoveries in grape and soil samples ranged from 76.0% to 91.9% and relative standard deviations were less than 11.4% with fortified levels of 0.025-1.0 mg kg⁻¹. The limits of detection and quantification were 0.005 mg kg⁻¹ and 0.025 mg kg⁻¹, respectively, with linear calibration curves extending up to 5.0 mg kg⁻¹. The field experimental results showed that dissipations of epoxiconazole stereoisomers in grape followed first-order kinetics (R² > 0.92) and stereoselectivity occurred in 2 h after spraying. The (−)-stereoisomer with half-life of 9.3 d degraded faster than (+)-stereoisomer with that of 13.2 d, and resulted in relative enrichment of (+)-stereoisomer. However, the stereoisomeric dissipations in soil were triphasic (“increase-decrease-steady”) with lower dissipation rates, and also occurred with preferential degradation of (−)-stereoisomer under field condition. The results for stereoselective dissipations can be applied for food and environmental assessments of chiral pesticides.     

Arbuscular mycorrhizal fungi enhance both absorption and stabilization of Cd by Alfred stonecrop (Sedum alfredii Hance) and perennial ryegrass (Lolium perenne L.) in a Cd-contaminated acidic soil

A greenhouse pot experiment was conducted to compare the phytoextraction efficiencies of Cd by hyper-accumulating Alfred stonecrop (Sedum alfredii Hance) and fast-growing perennial ryegrass (Lolium perenne L.) from a Cd-contaminated (1.6 mg kg⁻¹) acidic soil, and their responses to the inoculations of two arbuscular mycorrhizal (AM) fungal strains, Glomus caledonium 90036 (Gc) and Glomus mosseae M47V (Gm). Ryegrass and stonecrop were harvested after growing for 9 and 27 wk, respectively. Without AM fungal inoculation, the weekly Cd extraction by stonecrop (8.0 μg pot⁻¹) was 4.3 times higher than that by ryegrass (1.5 μg pot⁻¹). Both Gc and Gm significantly increased (P < 0.05) root mycorrhizal colonization rates, soil acid phosphatase activities, and available P concentrations, and thereby plant P absorptions (except for Gm-inoculated ryegrass), shoot biomasses, and Cd absorptions (except for Gm-inoculated stonecrop), while only Gc-inoculated stonecrop significantly accelerated (P < 0.05) the phytoextraction efficiency of Cd by 78%. In addition, both Gc and Gm significantly decreased (P < 0.05) phytoavailable Cd concentrations by 21–38% via elevating soil pH. The results suggested the potential application of hyper-accumulating Alfred stonecrop associated with AM fungi (notably Gc) for both extraction and stabilization of Cd in the in situ treatment of Cd-contaminated acidic soil.     

Root porosity and radial oxygen loss related to arsenic tolerance and uptake in wetland plants

The rates of radial oxygen loss (ROL), root porosity, concentrations of arsenic (As), iron (Fe) and manganese (Mn) in shoot and root tissues and on root surfaces, As tolerances, and their relationships in different wetland plants were investigated based on a hydroponic experiment (control, 0.8, 1.6 mg As L⁻¹) and a soil pot trail (control, 60 mg As kg⁻¹). The results revealed that wetland plants showed great differences in root porosity (9-64%), rates of ROL (55-1750 mmo1 O₂ kg⁻¹ root d.w. d⁻¹), As uptake (e.g., 8.8-151 mg kg⁻¹ in shoots in 0.8 mg As L⁻¹ treatment), translocation factor (2.1-47% in 0.8 mg As L⁻¹) and tolerance (29-106% in 0.8 mg As L⁻¹). Wetland plants with higher rates of ROL and root porosity tended to form more Fe/Mn plaque, possess higher As tolerance, higher concentrations of As on root surfaces and a lower As translocation factor so decreasing As toxicity.     

Comparative bioremediation potential of four rhizospheric microbial species against lindane

Four microbial species (Kocuria rhizophila, Microbacterium resistens, Staphylococcus equorum and Staphylococcus cohnii subspecies urealyticus) were isolated from the rhizospheric zone of selected plants growing in a lindane contaminated environment and acclimatized in lindane spiked media (5-100 μg mL⁻¹). The isolated species were inoculated with soil containing 5, 50 and 100 mg kg⁻¹ of lindane and incubated at room temperature. Soil samples were collected periodically to evaluate the microbial dissipation kinetics, dissipation rate, residual lindane concentration and microbial biomass carbon (MBC). There was a marked difference (p < 0.05) in the MBC content and lindane dissipation rate of microbial isolates cultured in three different lindane concentrations. Further, the dissipation rate tended to decrease with increasing lindane concentrations. After 45 d, the residual lindane concentrations in three different spiked soils were reduced to 0%, 41% and 33%, respectively. Among the four species, S. cohnii subspecies urealyticus exhibited maximum dissipation (41.65 mg kg⁻¹) and can be exploited for the in situ remediation of low to medium level lindane contaminated soils.     

Identification of Chinese cabbage genotypes with low cadmium accumulation for food safety

The pot-culture experiment and field studies were conducted to screen out and identify cadmium (Cd) excluders from 40 Chinese cabbage genotypes for food safety. The results of the pot-culture experiment indicated that the shoot Cd concentrations under three treatments (1.0, 2.5 and 5.0 mg Cd kg⁻¹ Soil) varied significantly (p < 0.05), with average values of 0.70, 3.07 and 5.83 mg kg⁻¹, respectively. The Cd concentrations in 12 cabbage genotypes were lower than 0.50 mg kg⁻¹. The enrichment factors (EFs) and translocation factors (TFs) in 8 cabbage genotypes were lower than 1.0. The field studies further identified Lvxing 70 as a Cd-excluder genotype (CEG), which is suitable to be planted in low Cd-contaminated soils (Cd concentration should be lower than 1.25 mg kg⁻¹) for food safety.     

Nitrogen leaching and acidification during 19 years of NH₄NO₃ additions to a coniferous-forested catchment at Gårdsjön, Sweden (NITREX)

The role of nitrogen (N) in acidification of soil and water has become relatively more important as the deposition of sulphur has decreased. Starting in 1991, we have conducted a whole-catchment experiment with N addition at Gårdsjön, Sweden, to investigate the risk of N saturation. We have added 41 kg N ha⁻¹ yr⁻¹ as NH₄NO₃ to the ambient 9 kg N ha⁻¹ yr⁻¹ in fortnightly doses by means of sprinkling system. The fraction of input N lost to runoff has increased from 0% to 10%. Increased concentrations of NO₃ in runoff partially offset the decreasing concentrations of SO₄ and slowed ecosystem recovery from acid deposition. From 1990-2002, about 5% of the total N input went to runoff, 44% to biomass, and the remaining 51% to soil. The soil N pool increased by 5%. N deposition enhanced carbon (C) sequestration at a mean C/N ratio of 42-59 g g⁻¹.     

Distribution of Se and its species in Myriophyllum spicatum and Ceratophyllum demersum growing in water containing Se (VI)

The uptake of Se (VI) by two aquatic plants, Myriophyllum spicatum L. and Ceratophyllum demersum L., and its effects on their physiological characteristics have been studied. Plants were cultivated outdoors under semi-controlled conditions and in two concentrations of Na selenate solution (20 μg Se L⁻¹ and 10 mg Se L⁻¹). The higher dose of Se reduced the photochemical efficiency of PSII in both species, while the lower dose had no effect on PSII. Addition of Se had no effect on the amounts of chlorophyll a and b. The concentration of Se in plants grown in 10 mg Se L⁻¹, averaged 212 ± 12 μg Se g⁻¹ DM in M. spicatum (grown from 8-13 d), and 492 ± 85 μg Se g⁻¹ DM in C. demersum (grown for 31 d). Both species could take up a large amount of Se. The amount of soluble Se compounds in enzyme extracts ranged from 16% to 26% in control, and in high Se solution from 48% to 36% in M. spicatum and C. demersum, respectively. Se-species were determined using HPLC-ICP-MS. The main soluble species in both plants was selenate (∼37%), while SeMet and SeMeSeCys were detected at trace levels.     

Levels,profile and distribution of Dechloran Plus (DP) and Polybrominated Diphenyl Ethers (PBDEs) in the environment of Pakistan

No scientific data is available on emerging contaminants including Polybrominated Diphenyl Ethers (PBDEs) and Dechloran Plus (DP) levels in the environment in Pakistan. Levels of PBDEs and DP were determined in the soil, sediment and atmospheric samples along the stretch of River Ravi in Punjab Province. Average concentrations of ΣPBDEs in atmosphere, soils and sediments were 36 pg m⁻³, 40 ng g⁻¹ and 640 ng g⁻¹. BDE-209 was the most abundant PBDE congener, showing that deca-BDE accounts for most of the total PBDE emitted in the environment of Pakistan. Total DP levels were calculated as 88 pg m⁻³, 0.8 ng g⁻¹ and 1.9 ng g⁻¹ in air, soil and sediment samples, respectively. The lower average fractions of anti-DP showed significant differences to those of the technical mixtures, indicating the lack of DP production source in Pakistan.