Ethylenediaminedissuccinate as a new chelate for environmentally safe enhanced lead phytoextraction

Using a soil column experiment, we compared the effect of a single dose and weekly additions of ethylenediaminetetraacetic acid (EDTA) and ethylenediaminedissuccinate (EDDS) on the uptake of Pb, Zn, and Cd by Chinese cabbage [Brassica rapa L. subsp. pekinensis (Lour.) Hanelt], and on the leaching of heavy metals through the soil profile. The analysis of plant material revealed that both chelates increased the concentrations of Pb and, to a lesser extent, also of Zn and Cd in the leaves of the test plant. The most effective applications were single doses of 10 mmol EDTA and EDDS kg(-1) soil, which caused the concentrations of Pb in the shoots to increase 94.2- and 102.3-fold, respectively, relative to the control. The same dose of EDTA increased the concentration of Zn and Cd in the leaves 4.3- and 3.8-fold and of EDDS 4.7- and 3.5-fold, respectively. In treatments with weekly additions and lower concentrations of both chelates, EDTA was more effective than EDDS in increasing the plant uptake of Pb. In soil columns treated with weekly additions of 10 mmol kg(-1) EDTA, on average 22.7, 7.0, and 39.8% of initial total Pb, Zn, and Cd in the soil were leached through the soil profile. The same amount of EDDS caused much lower leaching of Pb and Cd--only 0.8 and 1.5% of initial total concentrations. Leaching of Zn, 6.2% of the total concentration, was comparable with the EDTA treatment. A biotest with red clover (Trifolium pratense L.) indicated a greater phytotoxic effect of EDTA than EDDS addition. EDDS was also less toxic to soil fungi, as determined by phospholipid fatty acid (PLFA) analysis, and caused less stress to soil microorganisms, as indicated by the trans to cis PLFA ratio. Chelate addition did not prevent the development of arbuscular mycorrhiza on red clover.     

Food safety assessment of planting patterns of four vegetable-type crops grown in soil contaminated by electronic waste activities

A field experiment was conducted to assess the effect of crop and planting pattern on levels of cadmium (Cd), lead (Pb), and copper (Cu) in crops grown in soil contaminated by electronic waste. The crops were maize (Zea mays L. var. Shentian-1), tomato (Solanum lycopersicum L. var. Zhongshu-4), cabbage (Brassica oleracea L. var. Jingfeng-1), and pakchoi (Brassica chinensis (L.) Makino. var. Youdonger-Hangzhou). The planting patterns were crop monoculture, crop co-planted with a legume, and crop co-planted with another crop. Metal concentrations in the edible parts of the crops varied with types of metals and crops. Pb concentration was higher in leafy vegetables (cabbage and pakchoi) than in maize or tomato, Cd concentration was higher in tomato and pakchoi than in maize or cabbage, and Cu concentration was higher in maize and pakchoi than in tomato or cabbage. Metal concentrations in the edible part were also influenced by planting pattern. Relative to monoculture, co-planting and especially co-planting with Japanese clover tended to decrease Pb accumulation and increase Cd accumulation. According to the maximum permissible concentration (MPC) standard of the National Standard Agency in China, only maize (under all planting patterns) could be safely consumed. Because co-planting tended to increase Cd accumulation even in maize, however, the results suggest that maize monoculture is the optimal crop and planting pattern for this kind of contaminated soil.     

Enhancing phytoextraction: the effect of chemical soil manipulation on mobility, plant accumulation, and leaching of heavy metals

For heavy metal-contaminated agricultural land, low-cost, plant-based phytoextraction measures can be a key element for a new land management strategy. When agents are applied into the soil, the solubility of heavy metals and their subsequent accumulation by plants can be increased, and, therefore, phytoextraction enhanced. An overview is given of the state of the art of enhancing heavy metal solubility in soils, increasing the heavy metal accumulation of several high-biomass-yielding and metal-tolerant plants, and the effect of these measures on the risk of heavy metal leaching. Several organic as well as inorganic agents can effectively and specifically increase solubility and, therefore, accumulation of heavy metals by several plant species. Crops like willow (Salix viminalis L.), Indian mustard [Brassica juncea (L.) Czern.], corn (Zea mays L.), and sunflower (Helianthus annuus L.) show high tolerance to heavy metals and are, therefore, to a certain extent able to use the surpluses that originate from soil manipulation. More than 100-fold increases of lead concentrations in the biomass of crops were reported, when ethylenediaminetetraacetic acid (EDTA) was applied to contaminated soils. Uranium concentrations could be strongly increased when citric acid was applied. Cadmium and zinc concentrations could be enhanced by inorganic agents like elemental sulfur or ammonium sulfate. However, leaching of heavy metals due to increased mobility in soils cannot be excluded. Thus, implementation on the field scale must consider measures to minimize leaching. So, the application of more than 1 g EDTA kg(-1) becomes inefficient as lead concentration in crops is not enhanced and leaching rate increases. Moreover, for large-scale applications, agricultural measures as placement of agents, dosage splitting, the kind and amount of agents applied, and the soil properties are important factors governing plant growth, heavy metal concentrations, and leaching rates. Effective prevention of leaching, breeding of new plant material, and use of the contaminated biomass (e.g., as biofuels) will be crucial for the acceptance and the economic breakthrough of enhanced phytoextraction.     

Preceding crop affects grain cadmium and zinc of wheat grown in saline soils of central Iran

Enhanced Cd concentrations in wheat (Triticum aestivum L.) grain produced on saline soils of central Iran have been recently reported. Because wheat bread is a major dietary component for the Iranian people, practical approaches to decrease Cd concentration in wheat grain were investigated. This study investigated the influence of sunflower-wheat vs. cotton-wheat rotations on extractable Cd and on Cd uptake by wheat in these salt-affected soils. Two fields with different levels of Cd contamination (1.5 and 3.2 mg total Cd kg(-1) dry soil) were cropped with different rotations (cotton-wheat and sunflower-wheat) in Qom province, central Iran. Seeds of cotton (Gossypium L.) or sunflower (Helianthus annuus L. cv. Record) were planted in plots. After harvesting of the plants and removal of crop residues, wheat (cv. Rushan) was seeded in all plots. For both studied soils, the concentrations of Cd extracted by 0.04 M EDTA and 1 M CaCl(2) were significantly (P < or = 0.05) greater after cotton than after sunflower. Accordingly, the total amount of Cd in sunflower shoot was significantly (P < or = 0.05) greater than in the cotton shoot. Shoot Cd content in wheat plants grown after cotton and sunflower were significantly different; wheat shoots after cotton accumulated more Cd (two to four times) than after sunflower. Wheat grain Cd concentration after sunflower was much lower (more than seven times) than after cotton. The results of this study showed that sunflower in rotation with wheat in salt-affected soils of central Iran significantly reduced the risk of Cd transfer to wheat grain.     

Source-separated municipal solid waste compost application to Swiss chard and basil

A growth room experiment was conducted to evaluate the bioavailability of Cu, Mn, Zn, Ca, Fe, K, Mg, P, S, As, B, Cd, Co, Cr, Hg, Mo, Na, Ni, Pb, and Se from a sandy loam soil amended with source-separated municipal solid waste (SSMSW) compost. Basil (Ocimum basilicum L.) and Swiss chard (Beta vulgaris L.) were amended with 0, 20, 40, and 60% SSMSW compost to soil (by volume) mixture. Soils and compost were sequentially extracted to fractionate Cu, Pb, and Zn into exchangeable (EXCH), iron- and manganese-oxide-bound (FeMnOX), organic-matter (OM), and structurally bound (SB) forms. Overall, in both species, the proportion of Cu, Pb, and Zn levels in different fractions followed the sequence: SB > OM > FeMnOX > EXCH for Cu; FeMnOX = SB > OM > EXCH for Pb; and FeMnOX > SB = EXCH > OM for Zn. Application of SSMSW compost increased soil pH and electrical conductivity (EC), and increased the concentration of Cu, Pb, and Zn in all fractions, but not EXCH Pb. Basil yields were greatest in the 20% treatment, but Swiss chard yields were greater in all compost-amended soils relative to the unamended soil. Basil plants in 20 or 40% compost treatments reached flowering earlier than plants from other treatments. Additions of SSMSW compost to soil altered basil essential oil, but basil oil was free of metals. The results from this study suggest that mature SSMSW compost with concentrations of Cu, Pb, Mo, and Zn of 311, 223, 17, and 767 mg/kg, respectively, could be used as a soil conditioner without phytotoxic effects on agricultural crops and without increasing the normal range of Cu, Pb, and Zn in crop tissue. However, the long-term effect of the accumulation of heavy metals in soils needs to be carefully considered.     

Uncertainty and sensitivity analysis of spatial predictions of heavy metals in wheat

Heavy metals seriously threaten the health of human beings when they enter the food chain. Therefore, policymakers require precise predictions of heavy metal concentrations in agricultural crops. In this paper we quantify the uncertainty of regression predictions of Cd and Pb in wheat (Triticum aestivum L.) and the contributions to the uncertainties in these predictions associated with inputs to the regression model. For each node of the 500- x 500-m grid covering the arable soils in The Netherlands, a latin hypercube sample size of 1000 is constructed from the uncertainty distributions of the explanatory variables (pH, soil organic matter [SOM], and heavy metal concentration in soil), the regression coefficients, and the random term of the regression model. This sample is used as input for the regression model to obtain 1000 values from the uncertainty distributions of the log(Cd) and log(Pb) concentration in wheat. There were no nodes where the recent EU quality standards for Cd and Pb (0.2 mg kg(-1) fresh wt.) in wheat were almost certain to be exceeded. For most nodes with clay soils, the quality standard for Cd in wheat almost certainly will not be exceeded; for Pb this is much less certain. The uncertainty in the Cd concentration in soil contributes most to the uncertainty in the predicted Cd concentrations in wheat (36% on the average), followed by the random term of the regression model (23%). For Pb the contribution of the random term is by far the largest (52%).     

Influence of plant growth on degradation of linear alkylbenzene sulfonate in sludge-amended soil

Widespread application of sewage sludge to agricultural soils in Denmark has led to concern about the possible accumulation and effects of linear alkylbenzene sulfonate (LAS) in the soil ecosystem. Therefore, we have studied the uptake and degradation of LAS in greenhouse pot experiments. Sewage sludge was incorporated into a sandy soil to give a range from very low to very high applications (0.4 to 90 Mg dry wt. ha(-1)). In addition, LAS was added as water solutions. The soil was transferred to pots and sown with barley (Hordeum vulgare L. cv. Apex), rape (Brassica napus L. cv. Hyola 401), or carrot (Daucus carota L.). Also, plant-free controls were established. For all additions there was no plant uptake above the detection limit at 0.5 mg LAS kg(-1) d.w, but plant growth stimulated the degradation. With a growth period of 30 d, LAS concentrations in soil from pots with rape had dropped from 27 to 1.4 mg kg(-1) dry wt., but in plant-free pots the concentration decreased only to 2.4 mg kg(-1) dry wt. When LAS was added as a spike, the final concentration in soil from planted pots was 0.7 mg kg(-1) dry wt., but in pots without plants the final concentration was much higher (2.5 mg kg(-1) dry wt.). During degradation, the relative fraction of homologues C10, C11, and C12 decreased, while C13 increased.     

Weathering of lead bullets and their environmental effects at outdoor shooting ranges

Lead contamination at shooting range soils is of great environmental concern. This study focused on weathering of lead bullets and its effect on the environment at five outdoor shooting ranges in Florida, USA. Soil, plant, and water samples were collected from the ranges and analyzed for total Pb and/or toxicity characteristic leaching procedure (TCLP) Pb. Selected bullet and berm soil samples were mineralogically analyzed with X-ray diffraction and scanning electron microscopy. Hydrocerussite [Pb3(CO3)2(OH)2] was found in both the weathered crusts and berm soils in the shooting ranges with alkaline soil pH. For those shooting ranges with acidic soil pH, hydrocerussite, cerussite (PbCO3), and small amount of massicot (PbO) were predominantly present in the weathered crusts, but no lead carbonate mineral was found in the soils. However, hydroxypyromorphite [(Pb10(PO4)6(OH)2] was formed in a P-rich acidic soil, indicating that hydroxypyromorphite can be a stable mineral in P-rich shooting range soil. Total Pb and TCLP Pb in the soils from all five shooting ranges were significantly elevated with the highest total Pb concentration of 1.27 to 4.84% (w/w) in berm soils. Lead concentrations in most sampled soils exceeded the USEPA's critical level of 400 mg Pb kg(-1) soil. Lead was not detected in subsurface soils in most ranges except for one, where elevated Pb up to 522 mg kg(-1) was observed in the subsurface, possibly due to enhanced solubilization of organic Pb complexes at alkaline soil pH. Elevated total Pb concentrations in bermudagrass [Cynodon dactylon (L.) Pers.] (up to 806 mg kg(-1) in the aboveground parts) and in surface water (up to 289 microg L(-1)) were observed in some ranges. Ranges with high P content or high cation exchange capacity showed lower Pb mobility. Our research clearly demonstrates the importance of properly managing shooting ranges to minimize adverse effects of Pb on the environment.     

Dissolution of trace element contaminants from two coastal plain soils as affected by pH

Trace element mobility in soils depends on contaminant concentration, chemical speciation, water movement, and soil matrix properties such as mineralogy, pH, and redox potential. Our objective was to characterize trace element dissolution in response to acidification of soil samples from two abandoned incinerators in the North Carolina Coastal Plain. Trace element concentrations in 11 soil samples from both sites ranged from 2 to 46 mg Cu kg(-1), 3 to 105 mg Pb kg(-1), 1 to 102 mg Zn kg(-1), 3 to 11 mg Cr kg(-1), < 0.1 to 10 mg As kg(-1), and < 0.01 to 0.9 mg Cd kg(-1). Acidified CaCl2 solutions were passed through soil columns to bring the effluent solution to approximately pH 4 during a 280-h flow period. Maximum concentrations of dissolved Cu, Pb, and Zn at the lowest pH of an experiment (pH 3.8-4.1) were 0.32 mg Cu L(-1), 0.11 mg Pb L(-1), and 1.3 mg Zn L(-1) for samples from the site with well-drained soils, and 0.25 mg Cu L(-1), 1.2 mg Pb L(-1), and 1.4 mg Zn L(-1) for samples from the site with more poorly drained soils. Dissolved Cu concentration at pH 4 increased linearly with increasing soil Cu concentration, but no such relationship was found for Zn. Dissolved concentrations of other trace elements were below our analytical detection limits. Synchrotron X-ray absorption near edge structure (XANES) spectroscopy showed that Cr and As were in their less mobile Cr(III) and As(V) oxidation states. XANES analysis of Cu and Zn on selected samples indicated an association of Cu(II) with soil organic matter and Zn(II) with Al- and Fe-oxides or franklinite.     

Effect of chloride in soil solution on the plant availability of biosolid-borne cadmium

Increasing chloride (Cl) concentration in soil solution has been shown to increase cadmium (Cd) concentration in soil solution and Cd uptake by plants, when grown in phosphate fertilizer- or biosolid-amended soils. However, previous experiments did not distinguish between the effect of Cl on biosolid-borne Cd compared with soil-borne Cd inherited from previous fertilizer history. A factorial pot experiment was conducted with biosolid application rates of 0, 20, 40, and 80 g biosolids kg(-1) and Cl concentration in soil solution ranging from 1 to 160 mM Cl. The Cd uptake of wheat (Triticum aestivum L. cv. Halberd) was measured and major cations and anions in soil solution were determined. Cadmium speciation in soil solution was calculated using GEOCHEM-PC. The Cd concentration in plant shoots and soil solution increased with biosolid application rates up to 40 g kg(-1), but decreased slightly in the 80 g kg(-1) biosolid treatment. Across biosolid application rates, the Cd concentration in soil solution and plant shoots was positively correlated with the Cl concentration in soil solution. This suggests that biosolid-borne Cd is also mobilized by chloride ligands in soil solution. The soil solution CdCl+ activity correlated best with the Cd uptake of plants, although little of the variation in plant Cd concentrations was explained by activity of CdCl+ in higher sludge treatments. It was concluded that chlorocomplexation of Cd increased the phytoavailability of biosolid-borne Cd to a similar degree as soil (fertilizer) Cd. There was a nonlinear increase in plant uptake and solubility of Cd in biosolid-amended soils, with highest plant Cd found at the 40 g kg(-1) rate of biosolid application, and higher rates (80 g kg(-1)) producing lower plant Cd uptake and lower Cd solubility in soil. This is postulated to be a result of Cd retention by CaCO3 formed as a result of the high alkalinity induced by biosolid application.     

接种根瘤菌和菌根真菌对三叶草生长及对土壤Pb2+吸收的影响

采用盆栽实验,设计了不接种(CK)、接种根瘤菌、接种丛枝菌根真菌、双接种根瘤菌和菌根真菌4种处理,探讨了三叶草的生长情况及对土壤中Pb2+吸收的影响。结果表明:三叶草对Pb具有一定的吸收能力,两次采样中,CK处理三叶草Pb浓度分别为15.38mg/kg和15.57mg/kg,均为各处理中最高;接种根瘤菌可明显提高三叶草生物量,接种菌根真菌能明显减少三叶草对土壤中Pb的吸收。接种根瘤菌和菌根真菌减少三叶草对Pb2+的吸收和向地上部运输。     

A washing procedure to mobilize mixed contaminants from soil: I. Polychlorinated biphenyl compounds

We conducted a laboratory study to assess the feasibility of a washing process with nonionic and anionic surfactants in combination with ethylenediaminetetraacetate (EDTA) for the simultaneous mobilization of heavy metals and polychlorinated biphenyls (PCBs) from a field-contaminated soil. Unit processes consisting of complexometric extraction and surfactant-assisted mobilization were combined with reagent regeneration and detoxification steps to generate innocuous products. Ten minutes of ultrasonic mixing of the soil with a combination of 30 mL L(-1) surfactant suspension and a sparing quantity (2 mmol) of EDTA mobilized appreciable quantities of PCBs, virtually all of the available Cd, Cu, Mn, and Pb, and lesser amounts of the Zn, Ni, and Cr but only small quantities of Al and Fe. Relative to individual reagents, combinations of surfactant (Brij 98, Triton X-301, or Triton XQS-20) with EDTA did not influence PCB extraction efficiencies perceptibly. Of the three surfactants, the Brij 98 proved to be the most efficient for three successive extractions with a single charge, mobilizing 83% of the PCBs, whereas companion extractions that used fresh reagent each time mobilized 87% of the soil PCB content. The decreased PCB mobilization with the same quantity of anionic surfactant (71 or 68%) resulted from losses during the EDTA regeneration process with zero-valent Mg. In toto, these studies demonstrate that PCB compounds and selected heavy metals can be coextracted efficiently from soil with three successive washes with the same washing suspension containing EDTA and a nonionic surfactant.     

In situ dynamics of phosphorus in the rhizosphere solution of five species

Root activity can modify the chemistry of the rhizosphere and alter phosphorus (P) availability and uptake. However, until recently, relatively little was known about the dynamics of soil solution P at the root surface because of our inability to measure in situ changes in solution P at the plant root. A mini-rhizotron experiment with corn (Zea mays L. cv. Stine 2250), soybean [Glycine max (L.) Merr. cv. Pioneer 3563), cottonwood (Populus deltoids L.), smooth brome (Bromus inermis Leyss.), and switchgrass (Panicum virgatum L.) was conducted to measure the spatial and temporal dynamics of P in the rhizosphere solution of a fine silty, P-rich calcareous soil (solid-phase total P concentration = 62 mg kg(-1), pH = 7.68) from western Iowa. Micro-suction cups were used to collect samples of soil solution from defined segments of the rhizosphere, and capillary electrophoresis (CE) was used to determine the P concentration of the soil solution. At the end of 10 d, a decreasing P concentration gradient in soil solution toward the root was observed in corn, cottonwood, and smooth brome. No clear rhizosphere effect was observed for soybean and switchgrass. Statistical analysis indicated significantly lower solution P concentrations in the rhizospheres of corn (p = 0.05), cottonwood (p = 0.01), and smooth brome (p = 0.01) compared with bulk soil solution. Results indicate that P depletion from rhizosphere soil solution depends on plant species. Under the conditions of this study, corn, cottonwood, and smooth brome were more effective in depleting solution P than soybean and switchgrass.     

Effects of near-surface hydraulic gradients on nitrate and phosphorus losses in surface runoff

Phosphorous (P) and nitrogen (N) in runoff from agricultural fields are key components of nonpoint-source pollution and can accelerate eutrophication of surface waters. A laboratory study was designed to evaluate effects of near-surface hydraulic gradients on P and N losses in surface runoff from soil pans at 5% slope under simulated rainfall. Experimental treatments included three rates of fertilizer input (control [no fertilizer input], low [40 kg P ha(-1), 100 kg N ha(-1)], and high [80 kg P ha(-1), 200 kg N ha(-1)]) and four near-surface hydraulic gradients (free drainage [FD], saturation [Sa], artesian seepage without rain [Sp], and artesian seepage with rain [Sp + R]). Simulated rainfall of 50 mm h(-1) was applied for 90 min. The results showed that near-surface hydraulic gradients have dramatic effects on NO(3)-N and PO(4)-P losses and runoff water quality. Under the low fertilizer treatment, the average concentrations in surface runoff from FD, Sa, Sp, and Sp + R were 0.08, 2.20, 529.5, and 71.8 mg L(-1) for NO(3)-N and 0.11, 0.54, 0.91, and 0.72 mg L(-1) for PO(4)-P, respectively. Similar trends were observed for the concentrations of NO(3)-N and PO(4)-P under the high fertilizer treatment. The total NO(3)-N loss under the FD treatment was only 0.01% of the applied nitrogen, while under the Sp and Sp + R treatments, the total NO(3)-N loss was 11 to 16% of the applied nitrogen. These results show that artesian seepage could make a significant contribution to water quality problems.     

Prediction of zinc, cadmium, lead, and copper availability to wheat in contaminated soils using chemical speciation, diffusive gradients in thin films, extraction, and isotopic dilution techniques

To predict the availability of metals to plants, it is important to understand both solution- and solid-phase processes in the soil, including the kinetics of metal release from its binding agent (ligand and/or particle). The present study examined the speciation and availability of Zn, Cd, Pb, and Cu in a range of well-equilibrated metal-contaminated soils from diverse sources using several techniques as a basis for predicting metal uptake by plants. Wheat (Triticum aestivum L.) was grown in 13 metal-contaminated soils and metal tissue concentrations (Zn, Cd, Pb, and Cu) in plant shoots were compared with total soil metal concentrations, total soluble metal, and free metal activities (pM2+) in soil pore waters, 0.01 M CaCl2-extractable metal concentrations, E values measured by isotope dilution, and effective metal concentrations, C(E), measured by diffusive gradients in thin films (DGT). In the DGT technique, ions are dynamically removed by their diffusion through a gel to a binding resin, while E values represent the isotopically exchangeable (labile) metal pools. Free metal activities (Zn2+, Cd2+, and Pb2+) in soil pore waters were determined using a Donnan dialysis technique. Plant Zn and Cd concentrations were highly related to C(E), while relationships for Zn and Cd with respect to the other measures of metals in the soils were generally lower, except for CaCl2-extractable Cd. These results suggest that the kinetically labile solid-phase pool of metal, which is included in the DGT measurement, played an important role in Zn and Cd uptake by wheat along with the labile metal in soil solution. Plant Pb concentrations were highly related to both soil pore water concentrations and C(E), indicating that supply from the solid phase may not be so important for Pb. Predictions of Cu uptake by wheat from these soils by the various measures of Cu were generally poor, except surprisingly for total Cu.     

Pesticide applications of copper on perennial crops in California, 1993 to 1998

Inorganic copper is used as a broad-spectrum fungicide and bacteriocide on a variety of agricultural crops. After application, the copper residue typically accumulates in the upper 15 cm of soil. Data from the California Pesticide Use Reports were used to estimate the augmentation of copper in the soil that resulted from pesticide applications for the six years from 1993 to 1998 on 12 crops that are grown without rotation. The estimated mean mg Cu kg(-1) soil added to the upper 15 cm during the six years was the following: walnut (Juglans regia L.), 28; peach [Prunus persica (L.) Batsch var. persica], 22; nectarine [Prunuspersica (L.) Batsch var. nucipersica (Suckow) C.K. Schneid], 19; cherry (Pseudolmedia oxyphyllaria Donn. Sm.), 18; rice (Orvza sativa L.), 16; apricot (Prunus armeniaca L.), 11; orange [Citrus sinensis (L.) Osbeck) and plum (Prunus domestica L. subsp. domestica ), 9; lemon [Citrus limon (L.) Burm.f.] and almond [Prunus dulcis (Mill.) D.A. Webb], 6; pear (Pyrus communis L.), 4; and grape (Vitis vinifera L.), 3. In addition, for the first five of these crops, we estimated the area that was treated with each level of kg Cu ha(-1). For example, for walnut orchards, we estimated that 12 500 ha, or 17% of the planted area, was treated with a quantity of Cu that would increase the total concentration of Cu in the upper 15 cm of soil by at least 50 mg Cu kg(-1) soil. A comparison of the amount of Cu per unit planted area that was applied in the first and second half of the study indicated that the intensity of copper use is either relatively constant or increasing, depending on the crop. The findings are discussed in relation to the potential effect of continued long-term use of Cu pesticides on soil sustainability.     

Apatite and phillipsite as sequestering agents for metals and radionuclides

Laboratory and greenhouse studies were conducted to quantify apatite and phillipsite (zeolite) sequestration of selected metal contaminants. The laboratory batch study measured the sorption of aqueous Co2+, Ba2+, Pb2+, Eu3+, and UO2(2+). Apatite sorbed more Co2+, Pb2+, Eu3+, and UO2(2+) from the spike solution than phillipsite, resulting in distribution coefficients (Kd values) of >200,000 L kg(-1). Phillipsite was more effective than apatite at sorbing aqueous Ba2+. Results from the laboratory study were used to design the greenhouse study that used a soil affected by a Zn-Pb smelter from Pribram, Czech Republic. Two application rates (25 and 50 g kg(-1)) of phillipsite and apatite and two plant species, maize (Zea mays L.) and oat (Avena sativa L.), were evaluated in this study. There was little (maize) to no (oat) plant growth in the unamended contaminated soil. Apatite and, to a slightly lesser extent, phillipsite additions significantly enhanced plant growth and reduced Cd, Pb, and Zn concentrations in all analyzed tissues (grain, leaves, and roots). The sequestering agents also affected some essential elements (Ca, Fe, and Mg). Phillipsite reduced Fe and apatite reduced P and Fe concentrations in oat tissues; however, the level of these elements in oat leaves and grains remained sufficient. Sequential extractions of the soil indicated that the Cd, Pb, and Zn were much more strongly sorbed onto the amended soil, making the contaminants less phytoavailable.     

Effect of biosolids processing on lead bioavailability in an urban soil

The potential for biosolids products to reduce Pb availability in soil was tested on a high Pb urban soil with biosolids from a treatment plant that used different processing technologies. High Fe biosolids compost and high Fe + lime biosolids compost from other treatment plants were also tested. Amendments were added to a Pb-contaminated soil (2000 mg kg(-1) Pb) at 100 g kg(-1) soil and incubated for 30 d. Reductions in Pb bioavailability were evaluated with both in vivo and in vitro procedures. The in vivo study entailed feeding a mixture of the Pb-contaminated soil and AIN93G Basal Mix to weanling rats. Three variations of an in vitro procedure were performed as well as conventional soil extracts [diethylenetriaminepentaacetic acid (DTPA) and Ca(NO3)2] and sequential extraction. Addition of the high Fe compost reduced the bioavailability of soil Pb (in both in vivo and in vitro studies) by 37 and 43%, respectively. Three of the four compost materials tested reduced Pb bioavailability more than 20%. The rapid in vitro (pH 2.3) data had the best correlation with the in vivo bone results (R = 0.9). In the sequential extract, changes in partitioning of Pb to Fe and Mn oxide fractions appeared to reflect the changes in in vivo Pb bioavailability. Conventional extracts showed no changes in metal availability. These results indicate that addition of 100 g kg(-1) of high Fe and Mn biosolids composts effectively reduced Pb availability in a high Pb urban soil.     

Application methods affect phosphorus-induced lead immobilization from a contaminated soil

Phosphate rock (PR) and phosphoric acid (PA) are an effective combination of P sources for immobilizing Pb in contaminated soils. This column experiment examined the effectiveness of different application methods on Pb immobilization in a contaminated soil. Phosphate was applied at a P/Pb molar ratio of 4 with half as PR and half PA. While PR was mixed with the soil or placed as a layer, aqueous PA was applied from the top of the column as one or two applications. After 4 wk of incubation, total and soluble Pb and P, TCLP-Pb (toxicity characteristic leaching procedure) and PBET-Pb (physiologically-based extraction test) in the P-treated soil were determined. Phosphate addition effectively reduced leachable Pb to below the EPA drinking water standard of 15 microg L(-1) in all treatments. Mixing both PA and PR with the soil was the most effective method in Pb immobilization, reducing TCLP-Pb by up to 95% and PBET-Pb by 25 to 42%. Application of PR as a layer in the soil column was the most effective in reducing Pb migration (by 73-79%) and minimizing soil acidification and P entrophication, potential drawbacks of PA. Applying PA in two applications was less effective than one application. Mixing PR and PA with the soil plus placing PR as a layer can be employed for effective remediation of Pb-contaminated soils, reducing Pb leachability, bioavailability, and mobility while minimizing soil acidification and P entrophication.     

Dietary crude protein and tannin impact dairy manure chemistry and ammonia emissions from incubated soils

Excess crude protein (CP) in dairy cow diets is excreted mostly as urea nitrogen (N), which increases ammonia (NH) emissions from dairy farms and heightens human health and environmental concerns. Feeding less CP and more tannin to dairy cows may enhance feed N use and milk production, abate NH emissions, and conserve the fertilizer N value of manure. Lab-scale ventilated chambers were used to evaluate the impacts of CP and tannin feeding on slurry chemistry, NH emissions, and soil inorganic N levels after slurry application to a sandy loam soil and a silt loam soil. Slurry from lactating Holstein dairy cows (Bos taurus) fed two levels of dietary CP (low CP [LCP], 155 g kg; high CP [HCP], 168 g kg) each fed at four levels of dietary tannin extract, a mixture from red quebracho (Schinopsis lorentzii) and chestnut (Castanea sativa) trees (0 tannin [0T]; low tannin [LT], 4.5 g kg; medium tannin [MT], 9.0 g kg; and high tannin [HT], 18.0 g kg) were applied to soil-containing lab-scale chambers, and NH emissions were measured 1, 3, 6, 12, 24, 36, and 48 h after slurry application. Emissions from the HCP slurry were 1.53 to 2.57 times greater ( < 0.05) than from the LCP slurry. At trial's end (48 h), concentrations of inorganic N in soils were greater ( < 0.05) in HCP slurry-amended soils than in LCP slurry-amended soils. Emissions from HT slurry were 28 to 49% lower ( < 0.05) than emissions from 0T slurry, yet these differences did not affect soil inorganic N levels. Emissions from the sandy loam soil were 1.07 to 1.15 times greater ( < 0.05) than from silt loam soil, a result that decreased soil inorganic N in the sandy loam compared with the silt loam soil. Larger-scale and longer-term field trails are needed to ascertain the effectiveness of feeding tannin extracts to dairy cows in abating NH loss from land-applied slurry and the impact of tannin-containing slurry on soil N cycles.