Mobility Of Pb In Soil Research Articles

Remediation Effects of Different Concentration of Nano-Hydroxyapatite Level on Pb-Contaminated Soil

Phosphorus-containing amendments can reduce the mobility of Pb in soil. Hydroxyapatite (HAP) is one of the most commonly used phosphorus-containing amendments. With the development of nanotechnology, nano-hydroxyapatie (n-HAP) was gradually applied to remediate soil polluted by heavy metals. Considering the concentrations of HAP/n-HAP were not more than 5% in most studies, soil polluted by Pb was artificially prepared and three different concentrations of n-HAP: 5%, 7% and 10% by weight, were added into the Pb-polluted soil separately. The mixtures of soil and n-HAP were incubated for 180 d and sampled regularly. The bioaccessibility of Pb in soil was determined using simulated gastric juices of two in-vitro digestion tests: USPM (United States Pharmacopeia Methodology) and PBET (Physiologically-Based Extraction Test). The results showed that the immobilizing efficiency of 5% n-HAP to Pb in soil was the highest in PBET. The extractable Pb from soil by USPM was not affected by concentration of n-HAP. So, the least concentration of n-HAP, i.e. 5% n-HAP treatment, was the most cost-effective in USPM. Soil pH increased with concentration of n-HAP. However concentration of n-HAP had little effects on content of soil OM. According to regression analysis, more than 50% differences of the extractable Pb from soil by PBET can be explained by soil pH, while soil pH, organic matter content and incubation time together explained nearly 85% differences of extractable Pb from soil by USPM.

A new assay of bacterial selection with Pb reveals an unexpected effect of Pb on bacterial behavior: implications for remediation

Soil pollution by lead (Pb) is a major health concern due to Pb toxicity. Phytoextraction could remove Pb, but this technique is limited by the low Pb mobility in soils. Pb mobility can be increased by bioaugmentation, which consists in adding selected bacteria in soil to increase Pb bioavailability. Nonetheless, many bioaugmentation and phytoextraction experiments have failed because bacterial selections did not take into account the presence of metals. Therefore, we developed a microplate assay with Pb-enriched growth media for the rapid selection of bacterial strains. Selection criteria included the ability of bacteria to grow in soils, to promote plant growth and to increase Pb availability. Results show that 100-250 µM Pb induced a decrease of production of indole acetic acid (IAA), a plant growth promotor, by up to 49% for Cupriavidus metallidurans, compared to the control without Pb. This finding implies that application in real soil conditions with C. metallidurans would have probably failed, thus strengthening the value of our selection method in the presence of Pb. By contrast, 100-250 µM Pb induced a 8.5-11-fold higher degradation of aminocyclopropane carboxylic acid (ACC) by C. metallidurans. Surprisingly , Pseudomonas putida did not degrade ACC without Pb, but degraded ACC at 100-250 µM Pb. This observation means that Pb activates ACC degradation, which should reduce plant stress because ACC is the precursor of the ethylene phytohormone. Overall, our selection method in the presence of Pb allows to reveal new bacterial properties, which would not have been disclosed by current methods that do not take into account the effect of metals. Our method allows also to test simultaneously about 200 bacterial isolates. In addition, our findings show for the first time that Pb changes the production of IAA and the degradation of ACC.

Aging effects on the mobility of Pb in soil: Influence on the energy requirements in electroremediation

This paper studies the possible differences in the behavior of lead as a contaminant in soil samples when it is present as “naturally-aged” for decades after the contamination, and when it has been spiked in the laboratory. This behavior differences are stablished mainly in two ways: as changes in the fractionation analysis obtained after a sequential extraction procedure (SEP) and as changes in the efficiency of the acid-enhanced electroremediation (EKR) technique. Additionally, aging effects have been studied for almost five years. In the case of the lead-spiked soil the influence of storage conditions on contaminant behavior have also been explored: 1) samples stored in capped containers at constant moisture conditions, and 2) samples in containers open to the atmosphere, with periods of water flooding and drying.Lab-spiked and the “naturally-aged” contaminants show very different behavior with respect not only to SEP analysis but also to EKR experiments. The soil spiked with a soluble lead salt presents a higher percent in the more mobile fractions. Regarding storage conditions, some changes were observed in the lead distribution along the vertical soil profile for samples stored in uncapped containers. The EKR results were also in agreement with those from fractionation analysis. Energy requirements for the remediation were estimated by a mathematical model with important differences obtained for the different soil samples. Results are indicating that it will be very unreliable to draw estimations for the “naturally-aged” soils from contaminant-spiked samples.

Effects of inorganic and organic amendments on the uptake of lead and trace elements by Brassica chinensis grown in an acidic red soil

A greenhouse study was conducted to investigate the effects of inorganic (phosphate rock, single superphosphate and calcium magnesium phosphate) and organic amendments (peat, straw manure and pig manure) on the uptake of lead (Pb) and trace elements by Chinese Cabbage (Brassica chinensis) grown in an acidic red soil. The application of all organic amendments increased the soil pH while inorganic amendments such as single superphosphate did not. Both inorganic and organic amendments decreased the availability and uptake of Pb while the organic amendments were superior to the inorganic (phosphate) amendments in reducing the availability of the more labile (soluble and exchangeable Pb) forms of soil Pb. More Pb was taken up by roots than shoots with all soil amendments. Among the organic amendments, straw manure and pig manure caused the largest decrease in Pb availability at 456.5 and 457.3mgkg−1, respectively, when a high level of 30g organic amendments kg−1 was applied. The organic amendments greatly increased the fraction D targeted to Fe–Mn oxides bound Pb, and decreased the fraction A (water-soluble), B (exchangeable), and C (carbonate-bound), thereby decreasing the solubility and mobility of Pb in soil. The organic amendments also significantly improved the concentrations of Fe, Mn, Cu and Zn in the soil and shoots (except Fe in shoots and/or roots), which are essential for plant nutrition. The organic amendments of straw and pig manure lowered the availability and uptake of Pb but not that of other trace metals. Thus, these amendments have the potential to remediate Pb-contaminated soils in situ.

Cu and Pb accumulation in maize (Zea mays L.) and soybean (Glycine max L.) as affected by N, P and K application

Nitrogen (N), phosphorus (P) and potassium (K) fertilizer application affects soil properties and processes in many ways that remain unclear. The effects of N, P, and K application on plant growth and copper (Cu) and lead (Pb) accumulation, as well as their differences in plant species were thus evaluated in soil-maize and soil-soybean systems. Five treatments were arranged: N, P, and K application (NPK), N and P application (NP), N and K application (NK), P and K application (PK), and CK (no fertilization). Results showed that N application could significantly increase maize shoot Cu concentration and translocation from soil to above ground tissue (p<0.05). However, soybean shoot Cu concentration could not increase with N application. Phosphorus application could effectively decrease the bioavailability of Cu and Pb in both systems. Under nutrients deficiency, soil dissolved organic carbon (C) significantly increased, showing difference in plant species (p<0.05), which further enhanced Cu and Pb mobility in soils. Copper removal from soil positively correlated with plant biomass production with the NPK and NP treatments showing the greatest in both crops. Our results show that, an appropriate increase in P application and decrease in N application are recommended to reduce agro-ecological risks associated with Cu and Pb in soil-plant systems. Key words: Soil-plant system, heavy metals, Cu and Pb mobility, ecological risk, translocation.

Retention Capacity and Environmental Mobility of Pb in Soils along Highway Corridor

Although lead (Pb) emissions have dropped drastically with the phase-out of tetra-ethyl lead (TEL) as a fuel additive, Pb deposited along highway corridors continues to be of concern because of its toxicity. This paper provides comprehensive data on the extent and distribution of Pb in roadside soils, Pb interaction with soils as a function of soil composition, the retention capacity of soil based on batch adsorption tests, the retention mechanism of Pb using selective sequential extraction, the potential for mobility using batch desorption tests with simulated rain and winter road salt, and column leach tests. Highway soils on high-traffic sections near Burnaby, Canada were found to have Pb accumulations up to 1628mg/kg soil. Contamination was mainly in the top 0.3m, with concentrations rapidly decreasing to the background level at a depth of 0.6m. The top layer contained more organic material and had a high adsorption capacity. Highway soils were found to have 3–10 times higher Pb adsorption capacities than the amount currently deposited. Selective sequential extraction indicated low exchangeable Pb in highway soils. Batch desorption tests with leaching solutions of H2O (pH 5.5), HNO3 solution (pH 4.0) and aqueous NaCl solution (0.17M) indicate low likelihood of significant leaching. Selective sequential extraction, leachate extraction and desorption tests show that Pb has limited mobility in highway soil.

Lead phytoextraction from contaminated soil with high-biomass plant species.

In this study, cabbage [Brassica rapa L. subsp. chinensis (L.) Hanelt cv. Xinza No 1], mung bean [Vigna radiata (L.) R. Wilczek var. radiata cv. VC-3762], and wheat (Triticum aestivum L. cv. Altas 66) were grown in Pb-contaminated soils. Application of ethylenediaminetetraacetic acid (EDTA) (3.0 mmol of EDTA/kg soil) to the soil significantly increased the concentrations of Pb in the shoots and roots of all the plants. Lead concentrations in the cabbage shoots reached 5010 and 4620 mg/kg dry matter on Days 7 and 14 after EDTA application, respectively. EDTA was the best in solubilizing soil-bound Pb and enhancing Pb accumulation in the cabbage shoots among various chelates (EDTA, diethylenetriaminepentaacetic acid [DTPA], hydroxyethylenediaminetriacetic acid [HEDTA], nitrilotriacetic acid [NTA], and citric acid). Results of the sequential chemical extraction of soil samples showed that the Pb concentrations in the carbonate-specifically adsorbed and Fe-Mn oxide phases were significantly decreased after EDTA treatment. The results indicated that EDTA solubilized Pb mainly from these two phases in the soil. The relative efficiency of EDTA enhancing Pb accumulation in shoots (defined as the ratio of shoot Pb concentration to EDTA concentration applied) was highest when 1.5 or 3.0 mmol EDTA/kg soil was used. Application of EDTA in three separate doses was most effective in enhancing the accumulation of Pb in cabbage shoots and decreased mobility of Pb in soil compared with one- and two-dose application methods. This approach could help to minimize the amount of chelate applied in the field and to reduce the potential risk of soluble Pb movement into ground water.

Long-term migration of metals at historical smelting sites

The vertical migration of metals in soils and rocks is assessed at 3 historical Pb smelters ranging in age from ca. 600 to ca. 1800 a. Core samples were taken through contaminated soils into the underlying rocks and analysed for trace elements by ICP-AES. Surface soils contain high levels of metals, particularly Pb which often exceeds a concentration of 1%. Of the total amount of Pb and Zn present in contaminated soils, only relatively small amounts appear to be in a readily mobile form. Lead concentrations in heavily contaminated horizons were too high to be controlled entirely by exchange reactions. It is suggested that the metal is also present occluded in slag particles, precipitated as insoluble compounds and specifically adsorbed to soil constituents. The low Pb mobility in soils is also related to the elevation of pH in contaminated soils by the release of Ca compounds from the slag wastes during weathering. The rate of vertical migration of Pb varies with rock type with sandstone being greater than limestone which is greater than a clay/sandstone matrix.

Equilibrium studies of metal-ion complexes of interest to natural waters—VIII

Abstract A pH-titration study is reported at 25·0 ± 0·1°C and μ = 0·1 M (NaClO 4 ) of the equilibria and distribution of complexes in the 2-ligand systems, relevant to soils, (i) M 2+ -fulvate-NTA, (ii) M 2+ -fulvate-phosphate and (iii) M 2+ -NTA-phosphate, where M 2+ = Pb, Cd or Zn, NTA = nitrolotriacetic acid and phosphate = H n PO 4 . Equilibria in the Pb and Cd systems were confirmed using metal-ion-selective electrodes. In (i), M (NTA) and (NTA) M (fulvate) predominate in weakly acidic or neutral solution. In systems (ii) and (iii), (phosphate) M ′(fulvate) and (phosphate) M ′(NTA) predominate, where M ′ = Cd 2+ or Zn 2+ . However, Pb(fulvate) and (phosphate)Pb(fulvate) complexes are insoluble, which could account for the low mobility of Pb in soils and the low uptake of Pb by plants. The role of mixed-ligand complexes in soil chemistry is discussed.