Accumulation of metals and metalloids in radish (Raphanus sativus L.) and spinach (Spinacea oleracea L.) irrigated with domestic wastewater in the peri-urban areas of Khushab City,Pakistan

Accumulation of different metals and metalloids was assessed in two vegetables radish (Raphanus sativus L.) and spinach (Spinacea oleracea L.) irrigated with domestic wastewater in the peri-urban areas of Khushab City, Pakistan. In general, the metal and metalloid concentrations in radish and spinach were higher at site-II treated with sewage water than those found at site-I treated with canal water. In case of radish at both sites the levels of metals (Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Mo, Cd, and Pb) were below the permissible level except those of Mn, Ni, Mo, Cd, and Pb. At both sites, the transfer factor ranged from 0.047–228.3 mg kg^?1 with Cr having the highest transfer factor. The metal pollution index in soil was in the following order: As > Fe > Ni > Zn > Cd > Mo > Se > Co > Pb > Mn > Cr > Cu, respectively. While in case of spinach at both sites, the concentrations of metals and metalloids in vegetable samples irrigated with canal and sewage water were observed below the permissible level except Mn, Ni, Zn, Mo, and Pb. At both sites, the transfer factor ranged from 0.038–245.4 mg kg^?1 with Cr having the highest transfer factor. The metal pollution index in soil was in the following order: Cd > Ni > Co > Se > Mn > Zn > Mo > Pb > Fe > Cr > As > Cu, respectively.     

Assessment of Hazardous and Essential Elements in a Food Crop Irrigated with Municipal Sewage Water: Risk Appraisal for Public Health

To assess the impact of sewage water on metal accretion in selected diverse varieties of wheat (i.e., Lasani-2008, ARRI-10, Faisalabad-83, Punjab-85, Aas-2010, and Sehar-2006), their seeds were sown in pots containing soil. The results showed that the concentration of heavy metals in grains from the wheat plants supplied with sewage water was considerably higher than the plants supplied with canal irrigation water (control). In canal water irrigated wheat grains the metal concentrations (mg/kg) ranged from 2.20–3.5 for Cu, 12.50–32.4 for Zn, 22.45–35.22 for Mn, 0.05–0.15 for Pb, 0.012–0.029 for Cd, 2.5–5.3 for Ni, 18.16–29.63 for Fe, and 0.90–3.64 for Cr in different wheat varieties, whereas the wheat grains raised from sewage water, had metal concentrations (mg/kg): 3.8–5.30 for Cu, 29.60–40.50 for Zn, 32.9–50.40 for Mn, 1.14–7.50 for Pb, 0.26–0.42 for Cd, 3.90–7.55 for Ni, 32.21–40.35 for Fe, and 2.88–7.84 for Cr. Since these metals bioaccumulate in wheat grains with unremitting use of metal-enriched wastewater, care has to be taken for irrigating wheat plants with household wastewater for a longer time, particularly in those soils where this crop is grown regularly.     

The content of protein,fibre and minerals of leaves of selected Acacia species indigenous to north-western Tanzania

Abstract

Browse tree leaves of six species of Acacia (A. angustissima L., A. drepanolobium L., A. nilotica L., A. polyacantha L., A. senegal L., A. tortilis L.) were screened for chemical composition, including minerals and trace elements. Crude protein (CP) varied among the species from 145 (A. senegal) to 229 g/kg DM (A. angustissima). The species had moderate to high levels of minerals. The concentrations of Ca, P, Mg and S varied among the species from 14.6 – 31.5, 3.5 – 4.9, 1.4 – 3.0 and 1.7 – 2.8 g/kg DM, respectively. The forages showed relatively low concentrations of trace elements. Content of trace elements varied among the species from 4.5 – 23.8, 99.4 – 173.6, 146.2 – 432, 41.0 – 90.1, 10.9 – 22.2 and 0.05 – 0.65 mg/kg DM for Cu, Mo, Fe, Mn, Zn and Co, respectively. All leaves of browse species would meet the normal requirements for Ca, P, Mg and S in ruminants, although some species had higher levels of Ca than tabulated mineral requirements in livestock. Assayed Cu, Mn, Zn and Co would satisfy the lower range of recommended requirements of trace elements depending on their bioavailability. Therefore, browse leaves from Acacias could form good sources of CP and mineral supplements to ruminants.     

Medicago sativa - Sinorhizobium meliloti Symbiosis Promotes the Bioaccumulation of Zinc in Nodulated Roots

In this study we investigated effects of Zn supply on germination, growth, inorganic solutes (Zn, Ca, Fe, and Mg) partitioning and nodulation of Medicago sativa This plant was cultivated with and without Zn (2 mM). Treatments were plants without (control) and with Zn tolerant strain (S532), Zn intolerant strain (S112) and 2 mM urea nitrogen fertilisation. Results showed that M. sativa germinates at rates of 50% at 2 mM Zn. For plants given nitrogen fertilisation, Zn increased plant biomass production. When grown with symbionts, Zn supply had no effect on nodulation. Moreover, plants with S112 showed a decrease of shoot and roots biomasses. However, in symbiosis with S532, an increase of roots biomass was observed. Plants in symbiosis with S. meliloti accumulated more Zn in their roots than nitrogen fertilised plants. Zn supply results in an increase of Ca concentration in roots of fertilised nitrogen plants. However, under Zn supply, Fe concentration decreased in roots and increased in nodules of plants with S112. Zn supply showed contrasting effects on Mg concentrations for plants with nitrogen fertilisation (increase) and plants with S112 (decrease). The capacity of M. sativa to accumulate Zn in their nodulated roots encouraged its use in phytostabilisation processes.     

Phytoremediation as a prospective method for rehabilitation of areas contaminated by long-term sewage sludge storage: A Ukrainian–Greek case study

Soil contamination by heavy metals could be caused by long-term storage of sewage sludge on the territory of most municipal wastewater treatment plants (WWTPs) worldwide. Different methods to deal with heavy metal pollution and rehabilitation can be applied, but they are costly. Phytoremediation is a method using plants in order to extract, sequester and/or detoxify pollutants such as heavy metals. Phytotechnologies are more advantageous economically, than other in situ and ex situ remedial approaches (they estimated to be at least 40% less costly) (ITRC, 2001).In this work the suitability of several plant species for phytoremediation under natural conditions was studied. Brassica napus, Medicago sativa, Zea mays, Triticum aestivum and Hordeum vulgare were grown in pots with sewage sludge from “Bezludivka” WWTP in Kharkiv, Ukraine and from Sindos WWTP in Thessaloniki, Greece.Plants in the experimental series were compared to those in the control samples (the same species grown in compost). In experimental series, shoot growth was less reduced in T. aestivum and H. vulgare than in the other plant species studied. M. sativa had the lowest germination rate. Generally B. napus and M. sativa, giving less biomass production than Z. mays and T. aestivum, were characterized by higher ability to accumulate heavy metals (Cd, Cu, Ni, Pb, Zn, Cr, As and Hg).     

The Amount of γ-Amino Butyric Acid and the Activity of Glutamic Decarboxylase in Aging Leaves

The amount of γ-amino butyric acid as measured by thin-layer chromatography, and the specific activity of glutamic decarboxylase as measured both by Warburgapparatus (CO₂) and by thin-layer chromatography (γ-ABA) were determined in leaves of different ages. Datura suaveolens, Medicago sativa and Salvinia natans were used as experimental plants. The amount of γ-ABA increases in the leaves of Salvinia natans, Medicago sativa and Datura suaveolens in proportion to the age of the leaves. In the case of Salvinia natans, the amount of γ-ABA in old leaves is about twice as much as in young ones: in the case of Medicago sativa and Datura suaveolens the increase is slightly less. In Salvinia natans the amount of γ-ABA reaches its greatest value in the third to fifth leaf, in Medicago sativa and Datura suaveolens later. This increase in the amount of γ-ABA with respect to the age variation of the leaves, is reflected in the growth of leaves. In Salvinia natans the third or fourth leaf is full-grown, in Medicago sativa and Datura suaveolens this stage is reached in the seventh or eighth leaf. The activity of glutamic decarboxylase parallels the γ-ABA accumulation in that it increases when the leaves grow. The increase of glutnmic decarboxylase activity takes place more rapidly in the aging leaves of Medicago sativa than in those of Datura suaveolens. The activities observed are somewhat higher when the amounts of γ-ABA are analysed than when the CO₂ evolved is measured. K_M-values for glutamic decarboxylase were calculated using various substrate concentrations to test the enzyme activity. The K_M-values obtained were 7.0 · 10^?3M in the case of Medicago sativa, and 7.9 · 10^?3M in the case of Datura suaveolens.     

Restoration of a Mediterranean Postfire Shrubland: Plant Functional Responses to Organic Soil Amendment

We investigated the potential of plant functional responses to speed up restoration in a postfire ecosystem. The patterns of change in plant nutrient uptake and water potential after compost amendment were monitored for 2 years in a 7‐year‐old postfire shrubland in southeastern France. We studied four different stress‐tolerant species with contrasting life traits: three shrub species and a perennial herb. Three treatments were applied: control, 50 and 100 Mg/ha of fresh cocomposted sewage sludge and green waste. In both compost treatments, concentrations of all the macronutrients increased. The amendment improved N and cation nutrition, but the positive effect of compost on plant nutrient status was most apparent on leaf P concentrations, indicating that P was a limiting nutrient in this shrubland. Compost had no significant short‐term effect on trace metal concentrations in plants. The plant nutrition response of different species to the compost varied; the nutritional status of Brachypodium retusum and Cistus albidus improved the most, whereas that of Quercus coccifera and Ulex parviflorus improved the least. Woody species exhibited no increase in N stocks. Phosphorus accumulation was also about three times higher in plots amended at 50 Mg/ha than in control plots for B. retusum and C. albidus. The severe summer drought of 2003 altered the compost effect. Contrary to our expectations, plants on amended plots did not exhibit a better water status in summer: the effect of the summer drought had a greater effect on water status than did the compost treatment.     

A study of the impacts of Zn and Cu on two rhizobial species in soils of a long-term field experiment

Two agriculturally important species of rhizobia, Rhizobium leguminosarum biovar viciae (pea rhizobia) and R. leguminosarum bv. trifolii (white clover rhizobia), were enumerated in soils of a long-term field experiment to which sewage sludges contaminated predominantly with Zn or Cu, or Zn plus Cu, were added in the past. In addition to total soil Zn and Cu concentrations, soil pore water soluble Zn and free Zn²⁺, and soluble Cu concentrations are reported. Pea and white clover rhizobia were greatly reduced in soils containing ≥200 mg Zn kg^-1, and soil pore water soluble Zn and free Zn²⁺ concentrations ≥7 and ≥3 mg l^-1, respectively, in soils of pH 5.9–6. Copper also reduced rhizobial numbers, but only at high total soil concentrations (>250 mg kg^-1) and not to the same extent as Zn. Yields of field grown peas decreased significantly as total soil Zn, soil pore water soluble Zn and free Zn⁺² increased (R² = 0.79, 0.75 and 0.75, respectively; P < 0.001). A 50% reduction in seed yield occurred at a total soil Zn concentration of about 290 mg kg^-1, in soils of pH 5.9–6. The corresponding soil pore water soluble Zn and free Zn²⁺ concentrations were about 9 and 4 mg l^-1, respectively. Pea seed yields were not significantly correlated with total soil Cu (R² = 0.33) or soil pore water soluble Cu (R² = 0.39). Yield reductions were due to a combination of greatly reduced numbers of free-living rhizobia in the soil due to Zn toxicity, thus indirectly affecting N₂-fixation, and Zn phytotoxicity. These effects were exacerbated in slightly acidic soils due to increased solubility of Zn, and to some extent Cu, and an increase in the free Zn²⁺ fraction in soil pore water. The current United Kingdom, German and United States limits for Zn and Cu in soils are discussed in view of the current study. None of these limits are based on toxicity thresholds in soil pore water, which may have wider validity for different soil types and at different pH values than total soil concentrations. This revised version was published online in June 2006 with corrections to the Cover Date.     

Phytoavailability of Heavy Metals and Metalloids in Soils Irrigated with Wastewater,Akaki, Ethiopia: A Greenhouse Study

Irrigation with untreated wastewater from several industrial, commercial, and domestic discharges for decades caused accumulation of various heavy metals and metalloids in soils along the Akaki River in Ethiopia. Assessment of environmental threats and the potential phytoremediation of the soils require understanding of the toxic elements’ uptake and distribution in plant parts. Hence, a greenhouse study was performed to examine the phytoavailability and distribution of Cr, Ni, Co, Cu, Zn, Cd, Pb, Hg, Se, V, and As in forage grasses: Oat (Avena sativa), Rhodes grass (Chloris gayana), Setaria (Setaria sphacelata), and the legumes Alfalfa (Medicago sativa) and Desmodium (Desmodium unicinatum). The average contents of Cr, Ni, Co, Cu, Zn, Pb, Hg, Se, and V in the plants were generally higher than the background levels for forage grasses/legumes, and some of these elements were in the phytotoxic range. Root bioconcentration factor (BCF = root to soil concentration ratio) > 1 was observed for Cu (Oat, Rhodes, Desmodium, and Setaria: Fluvisol), Zn (Setaria: Fluvisol), Cd (Rhodes: Fluvisol; Setaria from both soils) and Hg (Oat and Alfalfa: Fluvisol). Alfalfa and Desmodium displayed translocation factor > 1 (TF = shoot to root concentration ratio) for most heavy metals. Most heavy metals/metalloids may pose a health threat to humans and stock via introduction to the food chain. The plant factors (species and plant part), soil factors (soil type, soil fractions, pH, and CEC), and their interactions significantly (p < 0.05) influenced plant heavy metal and metalloid levels. However, the role of plant part and species emerged as the most important on heavy metal uptake, translocation, sequestration, and ultimately transfer to the food chain. Accordingly, the uptake and distribution of heavy metals/metalloids in the plants reflect the potential environmental and health hazards attributable to the use of fodder grasses, legumes, and cultivation of vegetables in soils with polymetallic and metalloid contamination.     

A field study on heavy metals phytoattenuation potential of monocropping and intercropping of maize and/or legumes in weakly alkaline soils

The study focused on the phytoattenuation effects of monocropping and intercropping of maize (Zea mays) and/or legumes on Cu, Zn, Pb, and Cd in weakly alkaline soils. Nine growth stages of monocropping maize were chosen to study the dynamic process of extraction of heavy metals. The total content of heavy metals extracted by the aerial part of monocropped maize increased in a sigmoidal pattern over the effective accumulative temperature. The biggest biomass, highest extraction content, and lowest heavy metals bioaccumulation level occurred at physiological maturity. Among the different planting patterns, including monocropping and intercropping of maize and/or soybean (Glycine max), pea (Pisum sativum), and alfalfa (Medicago sativa), the extraction efficiency of Cu, Zn, Pb, and Cd varied greatly. Only intercropping of maize and soybean yielded relatively higher extraction efficiency for the four metals with no significant difference in the total biomass. Moreover, the heavy metals concentrations in dry biomass from all the planting patterns in the present study were within China's national legal thresholds for fodder use. Therefore, slightly polluted alkaline soils can be safely used through monocropping and intercropping of maize and/or legumes for a range of purposes. In particular, this study indicated that intercropping improves soil ecosystems polluted by heavy metals compared with monocropping.     

喀斯特典型地区烟管荚蒾AM真菌多样性研究

烟管荚蒾是喀斯特地区灌木丛的主要组成植物。以茂兰喀斯特森林为采样地点,对烟管荚蒾AM真菌进行了分离、鉴定与多样性分析,并对优势菌种进行初步的接种研究。结果表明:烟管荚蒾根系的菌根侵染率为82.1%,从根际土壤分离到AM真菌2属16种,球囊霉属(Glomus)7种,无梗囊霉属(Acaulospora)9种。优势种为根内球囊霉(Glomus intraradices)、皱壁无梗囊霉(Acaulospora rugosa)和刺无梗囊霉(A. spinosa)。优势菌种接种紫花苜蓿(Medicago sativa),促生作用明显,并显著提高了SOD、POD和CAT酶活性。该研究对于探讨喀斯特地区AM真菌的多样性与独特性,筛选优良的宿主植物和与之高效共生的AM真菌具重要意义。     

New mitochondrial genome organization in three interspecific somatic hybrids of Medicago sativa including the parent-specific amplification of substoichiometric mitochondrial DNA units

Three somatic hybrid plants produced by protoplast fusion between Medicago sativa and each of the three species Medicago coerulea, Medicago falcata and Medicago arborea have been analysed for the composition of their mitochondrial DNA. Restriction fragment length polymorphism (RFLP) analysis of mitochondrial genes in somatic hybrids and their parental lines showed various degrees of rearrangement. The M. sativa+M. coerulea hybrid retained all of the M. coerulea-specific bands but lost all the major M. sativa- specific bands. The M. sativa+M. falcata hybrid showed only M. sativa-specific bands together with non-parental bands, and the M. sativa+M. arborea hybrid showed a partial incorporation of bands from both parents together with non-parental bands. The three different outcomes were attributed mainly to differences in the genetic distance between the parents of each hybrid. Analysis of the sexual progeny of the M. sativa+M. coerulea hybrid showed that a residual mitochondrial DNA subunit of M. sativa was retained in the hybrid cytoplasm. This subunit was amplified and inherited in a mutually exclusive, allelic-like fashion with its M. coerulea homologous counterpart in the sexual progeny of the hybrid. Possible mechanisms for the partitioning of mitochondrial DNA in the generative lineage of the somatic hybrids are discussed in relation to the creation of new nucleus-cytoplasm assortments otherwise impossible to obtain by a sexual cross in Medicago. Received: 5 January 2001 / Accepted: 23 March 2001     

Use of the green alga Ulva rigida C. Agardh as an indicator species to reassess metal pollution in the Thermaikos Gulf, Greece, after 13 years

The concentrations of metals (Mn, Pb, Fe, Zn, Cu, Cd,Co, Ni, Cr, Na, K, Ca, Mg) were determined in thegreen alga Ulva rigida, in the sediment andseawater of Thermaikos Gulf (Greece) during monthlysamplings in 1994–1995. This Gulf is the recipientof domestic and industrial effluents. Pb, Fe, Cu, Coand Cr concentrations in U. rigida at the studyarea were higher than those 13 years earlier andapparently came from different sources than those forZn, Cd and Ni. The relative abundance of metals inthe alga decreased in the order: Mg > Na > K >Ca > Pb > Fe > Mn > Zn > Cr, Cu > Ni >Co > Cd. Only Cu concentrations in the alga fromKalochori and Cd ones from Viamyl showed significantseasonal changes. Cu and Cd concentrations ingeneral followed the same pattern of variation, withminimum values in winter-spring. This pattern isdiscussed in relation to growth dynamics and tissueage. Only Pb concentrations in the alga showed asignificant positive correlation with concentrationsin the seawater. There were both positive andnegative correlations among some metals in the alga. It is concluded that U. rigida can be used as anindicator species, especially for Pb.     

Bioaccumulation and translocation of heavy metals by nine native plant species grown at a sewage sludge dump site

In the present study, nine native plant species were collected to determine their potential to clean up nine heavy metals from soil of a sewage sludge dump site. Almost all nine plant species grown at sewage sludge dump site showed multifold higher concentrations of heavy metals as compared to plants grown at the reference site. All the investigated species were characterized by a bioaccumulation factor (BF) > 1.0 for some heavy metals. BF was generally higher for Cd, followed by Pb, Co, Cr, Cu, Ni, Mn, Zn, and Fe. The translocation factor (TF) varied among plant species, and among heavy metals. For most studied heavy metals, TFs were <1.0. The present study proved that the concentrations of all heavy metals (except Cd, Co, and Pb) in most studied species were positively correlated with those in soil. Such correlations indicate that these species reflect the cumulative effects of environmental pollution from soil, and thereby suggesting their potential use in the biomonitoring of most heavy metals examined. In conclusion, all tissues of nine plant species could act as bioindicators, biomonitors, and remediates of most examined heavy metals. Moreover, Bassia indica, Solanum nigrum, and Pluchea dioscoridis are considered hyperaccumulators of Fe; Amaranthus viridis and Bassia indica are considered hyperaccumulators of Pb; and Portulaca oleracea is considered hyperaccumulator of Mn.     

Effect of Medicago sativa L. and compost on organic and inorganic pollutant removal from a mixed contaminated soil and risk assessment using ecotoxicological tests

Several Gentle Remediation Options (GRO), e.g., plant-based options (phytoremediation), singly and combined with soil amendments, can be simultaneously efficient for degrading organic pollutants and either stabilizing or extracting trace elements (TEs). Here, a 5-month greenhouse trial was performed to test the efficiency of Medicago sativa L., singly and combined with a compost addition (30% w/w), to treat soils contaminated by petroleum hydrocarbons (PHC), Co and Pb collected at an auto scrap yard. After 5 months, total soil Pb significantly decreased in the compost-amended soil planted with M. sativa, but not total soil Co. Compost incorporation into the soil promoted PHC degradation, M. sativa growth and survival, and shoot Pb concentrations [3.8 mg kg^?1 dry weight (DW)]. Residual risk assessment after the phytoremediation trial showed a positive effect of compost amendment on plant growth and earthworm development. The O₂ uptake by soil microorganisms was lower in the compost-amended soil, suggesting a decrease in microbial activity. This study underlined the benefits of the phytoremediation option based on M. sativa cultivation and compost amendment for remediating PHC- and Pb-contaminated soils.     

Trace metal concentrations in the tropical sponge Spheciospongia vagabunda at a sewage outfall: synchrotron X-ray imaging reveals the micron-scale distribution of accumulated metals

Major and trace elements were measured in sponges, seawater and sediment in Darwin Harbour (Australia) to test the hypothesis that metals are elevated in sponges closer to a sewage outfall compared with unimpacted sites. Seawater and sediment at the sewage discharge site contained high, but localised, concentrations of phosphorus (P), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), arsenic (As) and lead (Pb) compared with background sites. Metal concentrations in the sponge Spheciospongia vagabunda were highly elevated compared with other sponges and, although site specific, high metal concentrations were unrelated to the presence of sewage effluent. X-ray fluorescence microprobe imaging was used to investigate the metal distribution pattern in S. vagabunda. High Fe, Ni and Zn concentrations were either localised in circular patches (100–200 μm size) near water canals or in the pinacoderm, or scattered in spots (approximately 10 μm) throughout the tissue. This supports a microflora-mediated metal bioaccumulation hypothesis. In contrast, Co and Mn were highly dispersed and probably associated with aluminium- and iron-oxide rich sediment inclusions. Although the lack of association between sewage effluent and metal accumulation precludes the use of S. vagabunda as a biomonitor, the apparent differential mechanisms of metal accumulation warrants further investigation.     

Bioconcentration of some macrominerals in soil,forage and buffalo hair continuum: A case study on pasture irrigated with sewage water

The present study aimed to evaluate the bioaccumulation of some macrominerals in grazing buffaloes fed forage irrigated with sewage water or canal water. In particular, the transfer of sodium (Na), magnesium (Mg), potassium (K) and calcium (Ca) from soil to plant and in turn to animals was evaluated under sub-tropical environmental conditions. Samples of soil, forage and buffalo hair were collected and digested by wet method. Sodium and K concentrations were significantly higher in the soil but lower in the forages; however, Mg and Ca concentrations in both soil and forages were higher. The correlation between soil, forage and hair showed an imbalanced flow of Na, Mg and K and a balanced flow of Ca from soil to forage and then to animals. Based on the findings, the highest rates of transfer of minerals were found for sewage water treatment, whereas lowest rates were found for canal water treatment, except for Na. As the transfer of minerals depends on their bioavailability, the highest values may be due to the high rates of mineral uptake by plants. Thus, the high transfer rate of some elements by plants could become toxic in future causing detrimental effect to grazing livestock.     

Assessment of Heavy Metals and Metalloids in Solanum tuberosum and Pisum sativum Irrigated with Urban Wastewater in the Suburbs of Sargodha City,Pakistan

Dietary exposure to heavy metals (viz., Ni, As, Fe, Cr, Mn, Co, Mo, Cu, Zn, Se, Cd, and Pb) has been recognized as a potential hazard to human health. This study investigates the level of contamination at two different sites in Pakistan, one irrigated with canal water (Site-I) and the other with urban wastewater (Site-II). At Site-II, irrigation with wastewater resulted in a significant increase in heavy metals and metalloids in soil and a subsequent build-up in two vegetables selected for study (Solanum tuberosum [potato] and Pisum sativum [pea]). Results showed that mean concentrations of heavy metals and metalloids in soil at Site-I were lower than those of Site-II. Mean concentrations of As and Cd in soil at both sites and for both vegetables were found above maximum permissible levels, while for both vegetables As at both sites and Cd, Mo, and Pb exceeded the suggested maximum levels for vegetables. High levels of some metals in the soils and vegetables could be due to unnecessary use of fertilizers and disposable water for irrigating the soils and the environmental cues prevalent in the areas, such as presence of ions that may bind the metals, often play an important role in uptake.     

Heavy metals uptake by vegetables growing in sewage irrigated soil: relationship with heavy metal fractionation in soil

Abstract

Concentrations of the heavy metals Cd, Ni, Cr, Zn, Mn, Co and Cu in soils and vegetable samples (i.e. green chili and gourd) taken from six vegetable fields in the vicinity of Lahore, Pakistan were measured. These soils have been irrigated for a long time with untreated sewage effluents. A control site was selected that has history of fresh canal water irrigation. The sequential extraction procedure developed by Tessier was adopted to demarcate five metal fractions: exchangeable, acid soluble, reducible, oxidizable and residual. The extractants and digests were analysed by atomic absorption spectrometry. The fractionation procedure showed that all the metals were dominant (>50%) in the residual phase in control as well as in waste waster irrigated soils. The concentrations of all the metals in edible parts of the vegetables collected from wastewater irrigated soils, were above critical levels. The total metal concentrations in wastewater irrigated soils followed the order Mn> Co> Zn> Cr> Ni> Cu> Cd, while in control soils the ord er was Mn> Zn> Ni> Co> Cr> Cu> Cd. In order to understand the uptake of metals from soil to vegetables, correlation analyses were performed between metal concentrations in different fractions of soil and their concentrations in vegetables. Correlation analysis was performed at 95% and 99% confidence level. The meaningful significant negative correlation was observed between Cd_F5–Cd_chili,Cr_Total–Cr_gourd,Mn_F5–Mn_Chili,Gourd, Co_F5, _Total–Co_chili, Cu_Total–Cu_Chili which indicate the non availability of total content and residual fraction to studied vegetables. The positive correlation was observed between Cd_Fl-Cd_ChiU, Cd_Fl–Cd_gourd, Ni_{Fi, F3}–Ni_Gourd, Cr_{Fi, F3}, _F4–Cr_ChiU, Cr_F2–Cr_Gourd, Zn_{Fi, F2}–Zn_Gourd, Mn_F3–Mn_Chili, Mn_Fi–Mn_Gourd, Co_F2–Co_Chili, Cu_Fi–Cu_Chili. The positive correlation, especially for the first (exchangeable) second (acid soluble) and for the third (reducible) extraction steps, was obtained which indicate the bioavailability of these metal fractions to plant.     

Effect of plant growth promoting bacterium; Pseudomonas putida UW4 inoculation on phytoremediation efficacy of monoculture and mixed culture of selected plant species for PAH and lead spiked soils

Plant growth promoting bacteria (PGPB) enhanced phytoremediation (PEP) is an attractive remedial strategy for the remediation of polycyclic aromatic hydrocarbon (PAH) and heavy metal (HM) contaminated sites. The effect of PGPB; Pseudomonas putida UW4 inoculation on the phytoremediation efficiency of Medicago sativa, Festuca arundinacea, Lolium perenne, and mixed plants (L. perenne and F. arundinacea) was assessed. This involved two contaminant treatments; “PAH” (phenanthrene; 300?mg·kg^?1, fluoranthene; 200?mg·kg^?1, and benzo[a]pyrene; 5?mg·kg^?1) and “PAH?+?HM” (‘PAH’ treatments +100?mg of Pb/kg). PGPB inoculation significantly enhanced root biomass yield of F. arundinacea in PAH treatment, and the mixed plant shoot biomass and L. perenne root biomass yields of the PAH?+?HM treatment. PGPB significantly enhanced dissipation of phenanthrene and fluoranthene for M. sativa-PAH?+?PGPB treatment and fluoranthene for F. arundinacea-PAH?+?HM?+?PGPB treatment. In others, PGPB inoculation either had no impact or inhibited PAH dissipation. PAH dissipation for the single and mixed plant treatments with PGPB inoculation were not different. The efficiency of PEP is dependent on different factors such as PGPB inoculum biomass, plant species, plant–microbe specificity and type of contaminants. Exploiting PEP technology would require proper understanding of plant tolerance and growth promoting mechanisms, and rhizosphere activities.