Bacterial community analysis in chlorpyrifos enrichment cultures via DGGE and use of bacterial consortium for CP biodegradation

The organophosphate pesticide chlorpyrifos (CP) has been used extensively since the 1960s for insect control. However, its toxic effects on mammals and persistence in environment necessitate its removal from contaminated sites, biodegradation studies of CP-degrading microbes are therefore of immense importance. Samples from a Pakistani agricultural soil with an extensive history of CP application were used to prepare enrichment cultures using CP as sole carbon source for bacterial community analysis and isolation of CP metabolizing bacteria. Bacterial community analysis (denaturing gradient gel electrophoresis) revealed that the dominant genera enriched under these conditions were Pseudomonas, Acinetobacter and Stenotrophomonas, along with lower numbers of Sphingomonas, Agrobacterium and Burkholderia. Furthermore, it revealed that members of Bacteroidetes, Firmicutes, α- and γ-Proteobacteria and Actinobacteria were present at initial steps of enrichment whereas β-Proteobacteria appeared in later steps and only Proteobacteria were selected by enrichment culturing. However, when CP-degrading strains were isolated from this enrichment culture, the most active organisms were strains of Acinetobacter calcoaceticus, Pseudomonas mendocina and Pseudomonas aeruginosa. These strains degraded 6–7.4 mg L^?1 day^?1 of CP when cultivated in mineral medium, while the consortium of all four strains degraded 9.2 mg L^?1 day^?1 of CP (100 mg L^?1). Addition of glucose as an additional C source increased the degradation capacity by 8–14 %. After inoculation of contaminated soil with CP (200 mg kg^?1) disappearance rates were 3.83–4.30 mg kg^?1 day^?1 for individual strains and 4.76 mg kg^?1 day^?1 for the consortium. These results indicate that these organisms are involved in the degradation of CP in soil and represent valuable candidates for in situ bioremediation of contaminated soils and waters.     

Heavy Metals Bioconcentration from Soil to Vegetables and Assessment of Health Risk Caused by Their Ingestion

The present study was undertaken to assess the non-carcinogenic human health risk of heavy metals through the ingestion of locally grown and commonly used vegetables viz. Raphanus sativus (root vegetable), Daucus carota (root vegetable), Benincasa hispida (fruit vegetable) and Brassica campestris leaves (leafy vegetable) in a semi-urbanized area of Haryana state, India. Heavy metal quantification of soil and vegetable samples was done using flame atomic absorption spectrophotometer. Lead, cadmium and nickel concentration in vegetable samples varied in range of 0.12–6.54 mg kg^?1, 0.02–0.67 mg kg^?1 and <0.05–0.41 mg kg^?1, respectively. Cadmium and lead concentration in some vegetable samples exceeded maximum permissible limit given by World Health Organization/Food and Agriculture Organization and Indian standards. Much higher concentrations of Pb (40–190.5 mg kg^?1), Cd (0.56–9.85 mg kg^-1) and Ni (3.21–45.87 mg kg^?1) were reported in corresponding vegetable fields’ soils. Correlation analysis revealed the formation of three primary clusters, i.e. Cu–Cd, Cd–Pb and Ni–Zn in vegetable fields’ soils further supported by cluster analysis and principal component analysis. Bioconcentration factor revealed that heavy metals’ uptake was more by leafy vegetable than root and fruit vegetables. Hazard index of all the vegetables was less than unity; thus, the ingestion of these vegetables is unlikely to pose health risks to the target population.     

Does radial oxygen loss and iron plaque formation on roots alter Cd and Pb uptake and distribution in rice plant tissues?

Background and Aims

Metal (e.g. Cd and Pb) pollution in agricultural soils and crops have aroused considerable attention in recent years. This study aimed to evaluate the effects of ROL and Fe plaque on Cd and Pb accumulation and distribution in the rice plant.

Methods

A rhizobag experiment was employed to investigate the correlations among radial oxygen loss (ROL), Fe plaque formation and uptake and distribution of Cd and Pb in 25 rice cultivars.

Results

Large differences between the cultivars were found in rates of ROL (1.55 to 6.88 mmol O₂ kg^?1 root d.w. h^?1), Fe plaque formation (Fe: 6,117–48,167 mg kg^?1; Mn: 127–1,089 mg kg^?1), heavy metals in shoot (Cd: 0.13–0.35 mg kg^?1; Pb: 4.8–8.1 mg kg^?1) and root tissues (Cd: 1.1–3.5 mg kg^?1; Pb: 45–199 mg kg^?1), and in Fe plaque (Cd: 0.54–2.6 mg kg^?1; Pb: 102–708 mg kg^?1). Rates of ROL were positively correlated with Fe plaque formation and metal deposition on root surfaces, but negatively correlated with metal transfer factors of root/plaque and distributions in shoot and root tissues.

Conclusions

ROL-induced Fe plaque promotes metal deposition on to root surfaces, leading to a limitation of Cd and Pb transfer and distribution in rice plant tissues.     

Distribution and mobility of toxic metals in Thymus alsarensis Ronniger in the Allchar As–Sb–Tl mine,Republic of Macedonia

Abstract

The Allchar district is an abandoned antimony–arsenic–thallium deposit located in the north-western region of Ko?uf mountain in the Republic of Macedonia. The locality of Allchar has a complex and unique mineral composition. The current study sought to investigate the levels of uptake and distribution of different heavy metals, such as As, Sb and Tl, in the different organs of Thymus alsarensis Ronniger, an endemic plant species of the area. Root, stem, leaf and flower samples, as well as corresponding soils, were processed, digested and then analysed by inductively coupled plasma atomic emission spectrometry. Significant accumulation of As, Sb and Tl in this endemic species was observed. Total As content in the soil ranged from 34.7 to 5288 mg kg^–1, and the content of As in plants ranged from 0.25 to 140 mg kg^–1. The content of Sb in soil and plants ranged from 6.3 to 130 mg kg^–1 and 0.25 to 1.51 mg kg^–1, respectively. Lastly, the content of Tl in soil and plants ranged from 2.0 to 330 mg kg^–1 and 0.10 to 496 mg kg^–1, respectively. Similar results were obtained from extraction tests of soil samples using various solvents.     

Sulfur and molybdenum fractionation in marine and riverine alluvium paddy soils

Intermittently submergence and drainage status of paddy fields can cause alterations in morphological and chemical characteristics of soils. We conducted a sequential fractionation study to provide an insight into solubility of Sulfur (S) and Molybdenum (Mo) in flooded alluvial paddy soils. The samples (0–15 and 15–30 cm) were taken from marine and riverine alluvial soils in Kedah and Kelantan areas, respectively, and were sequentially extracted with NaHCO₃, NaOH, HCl, and HClO₄–HNO₃. Total S in upper and lower layers of Kedah and Kelantan ranged between 273 and 1121 mg kg^?1, and 177 to 1509 mg kg^?1, respectively. In upper layers and subsoil of Kedah, average total Mo were 0.34 and 0.27 mg kg^?1, respectively. Average total Mo in Kelantan were 0.25 mg kg^?1 (surface layer) and 0.28 mg kg^?1 (subsoil). Cation exchange capacity (CEC) was positively correlated with plant available amounts of Mo in upper layers of Kedah area. Also, total and medium-term plant-available S was correlated with total carbon (C) at lower layers of Kelantan soil series. But in surface layers of Kelantan soil series, CEC was strongly correlated with total and medium-term plant-available S. Our results indicates that the influence of flooding conditions on soil S and Mo contents in paddy fields may cause long-term changes in S and Mo chemical reactivities.     

A Counter-Current Acid Leaching Process for the Remediation of Contaminated Soils from a Small-Arms Shooting Range

The objective of this research was to use a counter-current leaching process (CCLP) with leachate treatment to develop a remediation process for contaminated soils at a small-arms shooting range (SASR). The soil contaminant concentrations were 245 mg Cu kg^?1, 3,368 mg Pb kg^?1, 73 mg Sb kg^?1, and 177 mg Zn kg^?1. The CCLP includes three acid leaching steps (1M H₂SO₄ + 4M NaCl, t = 1 h, T = 20°C, soil suspension = 100 g L^?1), followed by one water rinsing step (1 h). Seven counter-current remediation cycles were completed, and the average resulting metal removals were 93.2 ± 3.5% of Cu, 91.5 ± 5.7% of Pb, 82.2 ± 10.9% of Sb, and 30.0 ± 11.4% of Zn. The metal leaching performances decreased with the number of completed cycles. Soil treated with the CCLP with leachate treatment process met the USEPA threshold criteria of 5 mg Pb L^?1 in the TCLP leachate. The CCLP allows a decrease of the water use by 32.9 m³ t^?1 and the chemicals’ consumption by approximately 2,650 kg H₂SO₄, 6,014 kg NaCl, and 1,150 kg NaOH per ton of treated soil, in comparison to standard leaching processes. This corresponds to 78%, 69%, 83%, and 67% of reduction, respectively.     

Effects of Groundwater Irrigation and Petroleum Exploiting on Soil Arsenic Levels

In order to evaluate the combined effects of drip irrigation and petroleum extraction activities on As contamination and distribution in local soils, a total of 141 soil and 30 groundwater (GW) samples from field sites drip-irrigated with GW in Kuitun, Xinjiang, China were collected and analyzed arsenic (As) levels. Soil As levels ranged from 6.74 to 23.10 mg·kg^?1. For the field irrigated with As-loaded GW for 0.5-10 years, As levels in soils increased by 0.50-9.10 mg·kg^?1 as compared with the control soils. As levels in all top-layer (0-10 cm in thickness) irrigated soils A (0-5 cm away from dripper) were found to be higher than those in top-layer irrigated soils B (5-10 cm away from dripper). It was estimated that As in agricultural soils increased by approximately 11～3789 g·yr^?1·ha^?1 under drip irrigating, most of which in top-layer soils covering the plant roots. The widely used drip irrigation system in Kuitun enhanced the ecological and human-health threats of As via affecting its spread into soils. Furthermore, the petroleum exploiting activity further promoted As levels in local soils. Within a distance of 10～1000 m away from petroleum exploiting sites, the soil As level decreases significantly with the distance.     

The critical soil P levels for crop yield, soil fertility and environmental safety in different soil types

Background and aims

Sufficient soil phosphorus (P) is important for achieving optimal crop production, but excessive soil P levels may create a risk of P losses and associated eutrophication of surface waters. The aim of this study was to determine critical soil P levels for achieving optimal crop yields and minimal P losses in common soil types and dominant cropping systems in China.

Methods

Four long-term experiment sites were selected in China. The critical level of soil Olsen-P for crop yield was determined using the linear-plateau model. The relationships between the soil total P, Olsen-P and CaCl₂-P were evaluated using two-segment linear model to determine the soil P fertility rate and leaching change-point.

Results

The critical levels of soil Olsen-P for optimal crop yield ranged from 10.9 mg kg^?1 to 21.4 mg kg^?1, above which crop yield response less to the increasing of soil Olsen-P. The P leaching change-points of Olsen-P ranged from 39.9 mg kg^?1 to 90.2 mg kg^?1, above which soil CaCl₂-P greatly increasing with increasing soil Olsen-P. Similar change-point was found between soil total P and Olsen-P. Overall, the change-point ranged from 4.6 mg kg^?1 to 71.8 mg kg^?1 among all the four sites. These change-points were highly affected by crop specie, soil type, pH and soil organic matter content.

Conclusions

The three response curves could be used to access the soil Olsen-P status for crop yield, soil P fertility rate and soil P leaching risk for a sustainable soil P management in field.     

Regional distribution characteristics and ecological risk assessment of heavy metal pollution of different land use in an antimony mining area – Xikuangshan,China

Abstract

Mining activities have introduced various heavy metals and metalloids to surrounding soil environments, causing adverse impacts to the ecological environment system. The extremely high concentration of various heavy metals and metalloids make the Xikuangshan (Hunan, China) an excellent model to assess their ecological risk. In this study, the soil samples from 26 locations of different land use methods in four areas (smelting area, road nearby ore, mining area, and ore tailing area) in Xikuangshan with different levels of various heavy metals and metalloids (Sb, As, Pb, and Cd) were analyzed; in addition, the index of geo-accumulation and the potential ecological risk index were used to evaluate ecological risk. The results showed that the average contents of Sb, As, Pb, and Cd in all soil samples were 4368.222?mg·kg^?1, 40.722?mg·kg^?1, 248.013?mg·kg^?1, and 40.941?mg·kg^?1, respectively, implying serious contamination of compound pollution of heavy metals in soil. The concentration of heavy metals in soil among smelting area, road nearby ore, mining area, and ore tailing area showed significant distribution characteristics of region because different mining activities such as smelting, mining, transportation, and stacking caused different pollution intensity. Moreover, the contents of Sb in soil samples decreased successively in residue field, wasteland, forestland, sediment, grassland, and vegetable field, and the contents of Sb in vegetable-field and ecological restoration grassland were relatively low, which indicate that the method of grassland ecological restoration is an effective method to control antimony pollution in soil. The results of ecological risk assessment showed that the antimony mining area was seriously polluted by Sb, As, Pb, and Cd, and had strong ecological risk, and Sb and Cd were the most important pollution factors, which indicated that the pollution of Sb and Cd should be a major concern of relevant departments of environment and health.     

Spatial distribution of total halogenated organic compounds (TX), adsorbable organic halogens (AOX), and heavy metals in wetland soil irrigated with pulp and paper wastewater

Long-term irrigation using wastewater from paper industry may cause seriously problems to the receiving soil. This work surveyed and monitored the soil quality of a wastewater irrigation wetland system in Yancheng City, Jiangsu Province in China in 2014 and 2015. Τhe wetland soil showed different soil properties and TX, AOX, heavy metal contents after long-term wastewater irrigation. Long-term irrigation also accumulated the heavy metals such as Cu, Cd, Zn, and Pb in the wetland soil. Compared to the control, TX in the irrigated soil increased by 47.7–69.8% (2014) and 61.5–83.1% (2015). AOX varied in concentration from 1.7 to 55.0 mg kg^?1 (2014) and 11.0 to 53.0 mg kg^?1 (2015). The long-term irrigation of wastewater to wetland systems caused the accumulations of heavy metals, TX, and AOX in the soil and the levels of accumulations were related to several factors including soil properties, wastewater quality, and irrigation time.     

Hydrocarbons,Pb-Concentrations,and Pb-Isotope Ratios in Contaminated Alluvial Soils (Southern Québec,Canada)

Hydrocarbon-contaminated layers found over 100 kilometers of riverbanks (southern Québec) were investigated. Analytical results for hydrocarbons, trace metals, Pb concentrations, and Pb isotopic signatures (²⁰⁶Pb/²⁰⁷Pb, ²⁰⁸Pb/²⁰⁶Pb, ²⁰⁴Pb/²⁰⁶Pb) of contaminated soil are presented. Soil samples show hydrocarbon concentrations (C₁₀-C₅₀) ranging from <60 to 660 mg kg^?1. Higher concentrations were found in the Richmond site (southern Québec). The values for Pb-concentrations ranged between 7 and 149 mg kg^?1 with median value of 23 mg kg^?1. For the Pb isotope ratios, the values obtained in the hydrocarbon layer range from 1.124 to 1.175 ± 0.011 (²⁰⁶Pb/²⁰⁷Pb), 2.085 to 2.126 ± 0.011 (²⁰⁸Pb/²⁰⁶Pb), and 0.054 to 0.057 ± 0.000 (²⁰⁴Pb/²⁰⁶Pb). The combination of various techniques used allows us to distinguish the various sources of contaminants. The study also reveals that Pb and other trace metal elements continue to be found in the fluvial environment, even after many years, and this soil pollution could affect the quality of streams and living organisms.     

Rare earth elements and relation between their potential bioavailability and soil properties, Nidda catchment (Central Germany)

Rare earth elements (REEs) are widely used in industry and the entry of REEs into the pedosphere is assumed. Data about REEs in soils are scarce since only a few studies discuss their ecologically relevant behavior. Hence, we investigated total contents (aqua regia digestion) and potentially bioavailable contents (EDTA extraction) of REEs in soils from the Nidda catchment in Hesse (Central Germany). The study site covers a 1,600 km² sized area and 232 soil samples from 63 soil profiles were examined. The total REE content varied considerably, ranging from 544 mg kg^?1 to 41 mg kg^?1 (mean 201.1 mg kg^?1) with a high proportion of light REEs. Highest REE contents were found in the soilscape VB, followed by LVB, WNE, T, WSW and BF with the smallest concentrations. With respect to the parent material the contents decreased in the following order: basalt > clay slate > loess > sandstone. On average 15.9% of the total REEs belong to the potentially bioavailable fraction. They range greatly by a factor of 100, between 1.3 and 171.3 mg kg^?1 (average 33.5 mg kg^?1). Remarkably, Yttrium has a maximum available proportion of 75%. In contrast, Ce showed the highest total contents with the smallest potentially bioavailable proportion of all elements. Regression analyses established relation between soil properties and the potential bioavailability of REEs. Around 53% (range from 29.9 to 76.8%) of the REE’s potential bioavailability variations could be explained by the chosen variables (pH, clay and C_org contents and the total element concentrations). Occurrence patterns and concentrations of REEs lie within the range of the results found in the available literature. Bioavailability is linked to soil properties and varies greatly according to the individual element. In comparison with the chosen soil properties the pH value shows the least impact on bioavailability.     

Counter-Current Metal Leaching and Precipitation for Soil Remediation

Chemical acid leaching is an effective technique for extracting toxic metals from the finest fractions of polluted soils. Nevertheless, the use of large quantities of reagents and process water results in prohibitive operating costs. The purpose of this study was to evaluate the technical and economic advantages of recirculating water in a counter-current leaching process (CCLP). Five 1-h sulfuric acid extraction steps (at pH = 1.5) followed by three 5-min water-washing steps were applied to the fine particle fraction (<0.125 mm) of an industrial soil polluted by Cd (13.2 mg·kg^?1), Cu (3 100 mg·kg^?1), Mn (685 mg kg^?1), Pb (550 mg·kg^?1), and Zn (2 840 mg·kg^?1). The leaching experiments were carried out at ambient temperature using a 10% soil suspension and in 1-L working volume stirred tank reactors. This paper presents results of conventional and counter-current leaching process (CCLP) tests and shows that the CCLP yields removal results for Cu (85%), Zn (86%), Mn (75%), and Cd (90%) that are similar to those obtained using the conventional leaching process. Moreover, the CCLP uses half of the quantity of acid and one-eighth of the amount of water that the conventional process uses. Metal precipitation with NaOH and Ca(OH)₂ was applied to treat the acidic leachates, and good metal removal yields were achieved with both reagents. However, the large consumption of chemicals implies high operating costs. In addition, the precipitation causes considerable sludge production, particularly when using Ca(OH)₂. Overall, the CCLP coupled to metal precipitation using NaOH and water recycling appears to be the most attractive option for the removal of toxic metals from this industrial soil.     

Phytoremediation of fuel oil and lead co-contaminated soil by Chromolaena odorata in association with Micrococcus luteus

Phytoremediation is widely promoted as a cost-effective technology for treating heavy metal and total petroleum hydrocarbon (TPH) co-contaminated soil. This study investigated the concurrent removal of TPHs and Pb in co-contaminated soil (27,000 mg kg^?1 TPHs, 780 mg kg^?1 Pb) by growing Siam weed (Chromolaena odorata) in a pot experiment for 90 days. There were four treatments: co-contaminated soil; co-contaminated soil with C. odorata only; co-contaminated soil with C. odorata and Micrococcus luteus inoculum; and co-contaminated soil with M. luteus only. C. odorata survived and grew well in the co-contaminated soil. C. odorata with M. luteus showed the highest Pb accumulation (513.7 mg kg^?1) and uptake (7.7 mg plant^?1), and the highest reduction percentage of TPHs (52.2%). The higher TPH degradation in vegetated soils indicated the interaction between the rhizosphere microorganisms and plants. The results suggested that C. odorata together with M. luteus and other rhizosphere microorganisms is a promising candidate for the removal of Pb and TPHs in co-contaminated soils.     

Strategies for lead distribution in organs of <Emphasis Type="Italic">Phragmites australis</Emphasis> (Cav.) Trin. ex Steud. (Common reed) subjected to Pb pollution in flood and drought environments

Heavy metal allocation in clonal organs, stems, leaves, and roots has not been systematically studied for rhizomatous perennial plants. Here, pot experiments have been designed to investigate lead (Pb) distribution in different organs of Phragmites australis (Cav.) Trin. ex Steud. Common reed subjected to 0–4500 mg Pb kg^?1 under both flood and drought conditions. In either water treatment, Pb concentrations in offspring shoots were lower than in parent shoots; however, the opposite response was observed for biomass allocation for which parent shoots protected offspring shoots. Lower allocation of Pb to leaves rather than stems in offspring shoots could be a protective strategy of leaves under flood conditions. Lower Pb allocation to rhizomes is better for rhizome growth. This further provides energy for the growth of buds and offspring shoots, because the rhizome biomass and the number of buds and offspring shoots were not significantly inhibited by Pb levels of?≤?3000 mg kg^?1 in the flooded environment. These Pb allocation strategies could enhance the resistance capacity of reeds to Pb contamination by stabilizing population propagation and productivity, especially at Pb levels of?≤?3000 mg kg^?1 under flood conditions.     

Heavy-Metal Phytostabilizing Potential of Agrostis castellana Boiss. & Reuter

The soils of many abandoned mine sites in the central region of Spain are heavily polluted with a number of different metals. Having frequently found Agrostis castellana growing at these old mine sites, this study was designed to assess its remediation capacity for this type of setting. In an initial field study, plant specimens were collected from 4 abandoned mine sites to determine pollutant concentrations in their roots and shoots. This was followed by a 4-year bioassay in a controlled environment in which soils collected from the mines were used to set up microcosms. Maximum root concentrations of the most polluting elements present in the bioassay were 3625 mg kg^?1 Zn, 2793 mg kg^?1 Cu, 13042 mg kg^?1 Pb, 49 mg kg^?1 Cd and 957 mg kg^?1 As. These concentrations represent root bioaccumulation indices of over 1 and usually >2. In contrast, indices of transfer to above-ground phytomass were always < 1, indicating this species is a good candidate for use as a phytostabilizer. However, the high metal concentrations that could reach the above-ground mass of this plant determines a need for close monitoring and avoiding the use of areas under restoration for hunting or grazing.     

Brassica juncea tested on urban soils moderately contaminated by lead: Origin of contamination and effect of chelates

Urban garden soils are a potential repository of heavy metal pollution, resulting from either anthropogenic or geogenic origin. The efficiency of phytoextraction was compared on two garden soils with the same texture and topsoil Pb concentration (170 mg kg^?1) but not the same origin: one geogenic, the other anthropogenic. Two varieties of Brassica juncea were tested with citric acid (25 mmol kg^?1) or ethylenediaminetetraacetic acid (EDTA, 2.5 mmol kg^?1). Geogenic Pb was shown to be two times less available than anthropogenic Pb, as a result of which the phytoextraction efficiency was reduced by 59%. Pb mobility in the soil was solely enhanced with EDTA, which increased the Pb concentration in shoots of B. juncea by between 14 and 26 times in comparison with the control. The highest Pb concentration in shoots still remained low, however (i.e., 45 mg kg^?1 dry weight). Regardless of the chelates introduced, B. juncea 426308 accumulated roughly twice as much lead as B. juncea 211000, but only for the anthropogenic contaminated soil. Under these conditions, the amount of Pb accumulated by B. juncea (even when assisted by EDTA) was not high enough to envision achieving soil clean-up within a reasonable time frame.     

Assessment of EDDS and vermicompost for the phytoextraction of Cd and Pb by sunflower (Helianthus annuus L.)

The effects of Ethylenediamine disuccinic acid (EDDS) (0 and 5?mmol·kg^?1) as a synthetic chemical amendment, vermicompost (0 and 5%w/w) as an organic amendment and their combined application were evaluated for the phytoextraction by sunflower (Helianthus annuus L.) of cadmium (Cd) and lead (Pb) at three artificial contamination levels in soils (0, 50, and 100?mg·kg^?1 for Cd and 0, 100, and 200?mg·kg^?1 for Pb). The results showed that the application of EDDS was the most effective method to increase Pb and Cd concentrations in both parts of the plant. The results also showed that the application of EDDS increased 9.27% shoot Pb content at 200?mg·kg^?1 but decreased 15.95% shoot Cd content at 100?mg·kg^?1 contamination level with respect to the respective controls. The bioavailable concentrations of Cd at 100?mg·kg^?1 and Pb at 200?mg·kg^?1 contamination level in the soil at the end of experiment increased 25% and 26%, respectively after the application of EDDS but vermicompost decreased 43.28% the bioavailable Pb concentration relative to their controls. Vermicompost increased the remediation factor index of Cd, thus making it the best treatment for the phytoextraction of Cd. The combined application of EDDS and vermicompost was the best amendment for Pb phytoextraction.     

Phosphorus in pasture plants: potential implications for phosphorus loss in surface runoff

Phosphorus (P) loss from land can impair surface water quality. Losses can occur from soil and plant components. While it is known that P losses increase with soil P concentration, it is not known how losses from pasture plants vary with soil P concentration or between different forages. We examined total P and filterable reactive P (FRP) in water extracts of plant shoots, used as a measure of potential P loss to surface runoff, in different forage species relative to soil P concentration in field trials and a glasshouse experiment. The mean total P concentration of 16 forage species in grazed field plots was greater (P?<?0.01; LSD₀₅?=?117 mg kg^?1) in legumes (3,480 mg kg^?1) than for grasses (3,210 mg kg^?1). Total plant P concentrations of grasses and legumes increased with soil Mehlich-3 P concentrations in both glasshouse and field trials with concentrations close to 6,000 mg kg^?1 in arrowleaf clover at 680 mg kg^?1 Mehlich-3 soil P. FRP in water extracts of plant shoots increased relative to plant total P as soil Mehlich-3 P increased, with the greatest concentrations shown by crimson clover and arrowleaf clover. Analysis of water extracts of ryegrass and clover herbage from a field trial showed that while FRP was increasing, phytase-available-P decreased significantly from about 70% of filterable unreactive P at the lowest Mehlich-3 P concentrations, to close to zero at 200 mg kg^?1 Mehlich-3 P. The wide variation, and enrichment of FRP in water extracts and total P with increasing Mehlich-3 P among species, indicates that cultivar and site selection and sward management provide a potential option to mitigate P loss to surface waters.     

Screening of Indigenous Ornamental Species from Different Plant Families for Pb Accumulation Potential Exposed to Metal Gradient in Spiked Soils

Contamination of surface soils with lead (Pb) is a global concern due to the release of hazardous materials containing the metal element. In order to explore ways to remediate contaminated soils with less impact on environment and costs, this study aimed at screening ornamental plant species exposed to Pb gradient in spiked soils for Pb phytoextraction. Twenty-one ornamental plant species that currently grow in Pakistan, were selected to assess their potential for Pb accumulation. Pot experiments were conducted to evaluate the accumulative properties of the different plant species in unspiked control (Pb = 0) and spiked soils with different levels of Pb at 500, 1000, 1500 and 2000 mg Pb kg^?1 of soil. Biotranslocation factor (TF), Enrichment factor (EF) and Bioconcentration factor (CF) were calculated to assess the phytoremediation potential of tested plant species after seven weeks of exposure. Out of 21 plant species, Pelargonium hortorum and Mesembryanthemum criniflorum performed better and accumulated more than 1000 mg Pb kg^?1 of shoot dry biomass when they were grown in 500, 1000 and 1500 mg Pb kg^?1 contaminated soils. Both plants had no significant (P < 0.05) variation in the total dry biomass with increasing soil Pb concentration indicating a high tolerance to Pb. Considering the capacity of Pb accumulation, total dry biomass, TF, EF &; CF indices, Pelargonium hortorum and Mesembryanthemum criniflorum could be considered as Pb hyperaccumulators and could have the potential to be used in phytoremediation.