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.     

Occurrence of metals in soil and ground water near chromated copper arsenate-treated utility poles

To thoroughly investigate the metal contamination around chromated copper arsenate (CCA)/polyethylene glycol (PEG)-treated utility poles, a total of 189 soil samples obtained from different depths and distances near six treated poles in the Montreal area (Canada) were analyzed for Cu, Cr, and As content. Various soil physicochemical properties were also determined. Ground water samples collected below the poles were analyzed for metals and bioassays with Daphnia magna were conducted. Generally, sandy soils had lower contaminant levels than clayey and organic soils. Copper concentrations in soil were highest followed by As and Cr. The highest Cu (1460 +/- 677 mg kg(-1)), As (410 +/- 150 mg kg(-1)), and Cr (287 +/- 32 mg kg(-1)) concentrations were found at the ground line and immediately adjacent to the pole. Contaminant levels then decreased with distance, approaching background levels within 0.1 m from the pole for Cr and 0.5 m for Cu and As. Chromium and Cu levels generally approached background levels at a depth of 0.5 m. Average As content near the pole on all study sites was three to eight times higher than Quebec's Level C criterion (50 mg kg(-1)), although it dropped to 31 mg kg(-1) at 0.1 m. Results also showed that As persisted up to 1 m in soil depth (17-54 mg kg(-1)). Copper and Cr concentrations in ground water samples were always <1.000 mg L(-1) and <0.05 mg L(-1), respectively and Cr(VI) was <0.02 mg L(-1). One sample contained an As concentration >0.025 mg L(-1) but bioassays showed that, overall, ground water had a low ecotoxic potential.     

In situ accumulation of copper, chromium, nickel, and zinc in soils used for long-term waste water reclamation

We studied the long-term in situ accumulation of Cu, Cr, Ni, and Zn in the soil profile of a large-scale effluent recharge basin after 24 yr of operation in a wastewater reclamation plant using the Soil Aquifer System approach in the Coastal Plain of Israel. The objective was to quantify metals accumulation in the basin's soil profile, clarify retention mechanisms, and calculate material balances and metal removal efficiency as the metal loads increase. Effluent recharge led to measurable accumulation, relative to the pristine soil, of Ni and Zn in the 0- to 4-m soil profile, with concentration increases of 0.3 to 1.3 mg kg(-1) and 2.9 to 6.4 mg kg(-1), respectively. Copper accumulated only in the 0- to 1-m top soil layer, with concentration increase of 0.28 to 0.76 mg kg(-1). Chromium concentration increased by 3.1 to 7.3 mg kg(-1) in the 0- to 1-m horizon and 0.9 to 2.3 mg kg(-1) at deeper horizons. Sequential selective extraction showed Cu tended to be preferentially retained by Fe oxides and organic matter (OM), Cr by OM, Ni by OM, and carbonate and Zn by carbonate. The average total retained amounts of Cu, Cr, Ni, and Zn were 0.7 +/- 1.0, 13.6 +/- 4.8, 4.3 +/- 3.6, and 28.7 +/- 5.4 g per a representative unit soil slab (1 m(2) x 4 m) of the basin, respectively. This amounts to 3.6 +/- 4.9%, 79.5 +/- 28.0%, 8.0 +/- 6.9%, and 9.3 +/- 1.8% of the Cu, Cr, Ni, and Zn loads, respectively, applied during 24 yr of effluent recharge (total of approximately 1880 m effluent load). The low long-term overall removal efficiency of the metals from the recharged effluent in the top horizon may be due to the metals' low concentrations in the recharged effluent and the low adsorption affinity and retention capacity of the sandy soil toward them. This leads to attainment of a quasi-equilibrium and a steady state in element distribution between the recharged effluent solution and the soil after few years of recharge and relatively small cumulative effluent loadings.     

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.     

The availability of copper in soils historically amended with sewage sludge, manure, and compost

Metals in soils amended with sewage sludge are typically less available compared with those in soils spiked with soluble metal salts. However, it is unclear if this difference remains in the long term. A survey of copper (Cu) availability was made in soils amended with sewage sludge, manure, and compost, collectively named organic amendments. Paired sets of amended and control soils were collected from 22 field trials where the organic amendments had aged up to 112 yr. Amended soils had higher total Cu concentrations (range, 2-220 mg Cu kg; median, 15 mg Cu kg) and organic C (range, 1-16 g kg; median, 4 g kg) than control soils. All samples were freshly spiked with CuCl, and the toxicity of added Cu to barley was compared between amended and control soils. The toxicity of added Cu was significantly lower in amended soils than in control soil in 15 sets by, on average, a factor of 1.4, suggesting that aged amendments do not largely increase Cu binding sites. The fraction of added Cu that is isotopic exchangeable Cu (labile Cu) was compared between control soils freshly spiked with CuCl and amended soils with both soils at identical total Cu concentrations. Copper derived from amendments was significantly less labile (on average 5.9-fold) than freshly added Cu in 18 sets of soils. This study shows that Cu availability after long-term applications of organic amendments is lower than that of freshly added Cu salts, mainly because of its lower availability in the original matrix and ageing reactions than because of increased metal binding sites in soil.     

Cupric ion activity in peat soil as a toxicity indicator for maize

Copper phytotoxicity in soils is difficult to assess because Cu accumulates at and damages roots, and is not readily transferred to shoots. Soil chemical properties strongly influence Cu speciation, so that total soil Cu alone is not a broadly useful indicator of potential toxicity to plants. The present study measured free Cu2+ activity in Cu-enriched peat soils using the ion selective electrode. The soil Cu2+ activity was related to the severity of phytotoxicity as measured by several indicators in a maize (Zea mays L.) bioassay, including leaf chlorosis, root stunting, and reduced shoot growth and Fe concentration. A soil Cu2+ activity of 10(-7.0) to 10(-7.5), corresponding to total Cu of about 275 mg/kg in the peat soil, caused phytotoxicity in maize seedlings. It is proposed that Cu2+ activity is more directly related to phytotoxic effects than other soil tests, such as extractions with strong acids or chelating agents, because it is the free Cu2+ in soil solution that has the most direct toxic effects on roots. There was very limited uptake of Cu into maize shoots, and even when Cu2+ activity and total soil Cu were raised into the extreme toxicity range of 10(-5) and 4,000 mg/ kg, respectively, shoot Cu remained less than 35 mg/kg. These results indicate the inadequacy of the USEPA risk assessment of potential for Cu toxicity to crops amended with sewage sludge, which assumed a no-effect level of maize shoot Cu of 40 mg/kg.     

Tolerance (PICT) of the bacterial communities to copper in vineyards soils from Spain

To detect effects of Cu pollution, the Cu tolerance of soil bacterial communities extracted from several vineyards located in NW Spain was measured. Bacterial community tolerance was estimated by means of the thymidine (TdR) and leucine (Leu) incorporation techniques using either IC(50) values (the log of the metal concentration that reduced incorporation to 50%) or the percentage of activity at one specific Cu concentration (10(-6) mol L(-1)). The tolerance measurements by the TdR incorporation technique were similar to those obtained by the Leu incorporation method, indicating that the two methods were equivalent in terms of suitability for detecting the toxicity of Cu to soil bacterial communities. The two tolerance indices considered (IC50 values and percentage of activity) were closely correlated (r = 0.975, P < 0.001), showing that both were equally good in measuring Cu tolerance of the bacterial community. An increased bacterial community tolerance to Cu, indicating a pollution effect, was observed in vineyard soils with more than 100 mg Cu kg(-1) soil. Thus, the long-term use of Cu in vineyards has a toxic effect on the soil bacterial community, resulting in an increased tolerance. An effect of increased levels of Cu could not be detected when measuring bacterial community activity, pointing to the increased sensitivity to detect toxicity in field studies using tolerance measurements.     

Trace element concentrations in soil, corn leaves, and grain after cessation of biosolids applications

From 1974 to 1984, 543 Mg ha(-1) of biosolids were applied to portions of a land-reclamation site in Fulton County, IL. Soil organic C increased to 5.1% then decreased significantly (p < 0.01) to 3.8% following cessation of biosolids applications (1985-1997). Metal concentrations in amended soils (1995-1997) were not significantly different (p > 0.05) (Ni and Zn) or were significantly lower (p < 0.05) (6.4% for Cd and 8.4% for Cu) than concentrations from 1985-1987. For the same biosolids-amended fields, metal concentrations in corn (Zea mays L.) either remained the same (p > 0.05, grain Cu and Zn) or decreased (p < 0.05, grain Cd and Ni, leaf Cd, Cu, Ni, Zn) for plants grown in 1995-1997 compared with plants grown immediately following termination of biosolids applications (1985-1987). Biosolids application increased (p < 0.05) Cd and Zn concentrations in grain compared with unamended fields (0.01 to 0.10 mg kg(-1) for Cd and 23 to 28 mg kg(-1) for Zn) but had no effect (p > 0.05) on grain Ni concentrations. Biosolids reduced (p < 0.05) Cu concentration in grain compared with grain from unamended fields (1.9 to 1.5 mg kg(-1)). Biosolids increased (p < 0.05) Cd, Ni, and Zn concentrations in leaves compared with unamended fields (0.3 to 5.6 mg kg(-1) for Cd, 0.2 to 0.5 mg kg(-1) for Ni, and 32 to 87 mg kg(-1) for Zn), but had no significant effect (p > 0.05) on leaf Cu concentrations. Based on results from this field study, USEPA's Part 503 risk model overpredicted transfer of these metals from biosolids-amended soil to corn.     

Plant availability of zinc and copper in soil after contamination with brass foundry filter dust: effect of four years of aging

We investigated the effect of 4 yr of aging of a noncalcareous soil contaminated with filter dust from a brass foundry (80% w/w ZnO, 15% w/w Cu0.6Zn0.4) on the chemical extractability of Zn and Cu and their uptake by barley (Hordeum vulgare L.), pea (Pisum sativum L.), and sunflower (Helianthus annus L.). Pot experiments were conducted with the freshly contaminated soil (2250 mg kg-1 Zn; 503 mg kg-1 Cu), with the contaminated soil aged for 4 yr in the field (1811 mg kg-1 Zn; 385 mg kg-1 Cu), and with the uncontaminated control soil (136 mg kg-1 Zn; 32 mg kg-1 Cu). In comparison with the uncontaminated soil, the growth of barley and pea was clearly reduced in both contaminated soils, while toxicity symptoms did not systematically vary from the freshly contaminated to the 4 yr aged soil. The sunflower did not grow in the contaminated soils. The slow oxidative dissolution of the brass platelets led to an increase in the solubility and the plant uptake of Cu from the freshly contaminated to the 4 yr aged soil. In an earlier study, we found that the fine-grained ZnO dissolved in the field soil within 9 mo and that about half of the released Zn was incorporated into a layered double hydroxide phase and about half was adsorbed to the soil matrix. These changes in Zn speciation did not lead to a reduction of the Zn contents in the shoots and roots of barley and pea grown in the aged soil as compared with the freshly contaminated soil.     

Accelerated weathering of biosolid-amended copper mine tailings

Application of municipal biosolids to mine tailings can enhance revegetation success, but may cause adverse environmental impacts, such as increased leaching of NO3- and metals to ground water. Kinetic weathering cells were used to simulate geochemical weathering to determine the effects of biosolid amendment on (i) pH of leachate and tailings, (ii) leaching of NO3- and SO4(2-), (iii) leaching and bioavailability (DTPA-extractable) of selected metals, and (iv) changes in tailing mineralogy. Four Cu mine tailings from southern Arizona differing in initial pH (3.3-7.3) and degree of weathering were packed into triplicate weathering cells and were unamended and amended with two rates (equivalent to 134 and 200 Mg dry matter ha(-1)) of biosolids. Biosolid application to acid (pH 3.3) tailings resulted in pH values as high as 6.3 and leachate pH as high as 5.7, and biosolids applied to circumneutral tailings resulted in no change in tailing or leachate pH. Concentrations of NO3--N of up to 23 mg L(-1) occurred in leachates from circumneutral tailings. The low pH of the acidic tailing apparently inhibited nitrification, resulting in leachate NO3--N of <5 mg L(-1). Less SO4(2-)-S was leached in biosolid-amended versus unamended acid tailings (final rate of 0.04 compared with 0.11 g SO4(2-)-S wk(-1)). Copper concentrations in leachates from acidic tailings were reduced from 53 to 27 mg L(-1) with biosolid amendment. Copper and As concentrations increased slightly in leachates from biosolid-amended circumneutral tailings. Small increases in DTPA-extractable Cu, Ni, and Zn occurred in all tailings with increased biosolid rate. Overall, there was little evidence of potential for adverse environmental impacts resulting from biosolid application to these Cu mine tailings.     

The role of nitrilotriacetate in copper uptake by tobacco

In growth chamber experiments we studied the effect of nitrilotriacetate (NTA) on Cu uptake by tobacco (Nicotiana tabacum L.). Plants were exposed for 6 d to 126 microM Cu and 500 microM NTA in nutrient solutions without and with 10 g L(-1) montmorillonite. Approximately seven times less Cu was dissolved in the montmorillonite solutions than in the nutrient solutions alone. In the absence of NTA, montmorillonite effectively competed with plant roots for Cu, although Cu remained bound to the roots. Nitrilotriacetate increased Cu uptake and translocation into shoots of tobacco by a factor of 3.5 from the nutrient solution and by a factor of 26 from the montmorillonite nutrient solution. Neither growth reduction nor any other visible sign of Cu toxicity was found in the presence of NTA with Cu concentrations of 190 mg kg(-1) in the shoots. In the absence of NTA, high Cu concentrations in root samples led to a brownish discoloration of the roots.     

Accumulation, distribution, and toxicity of copper in sediments of catfish ponds receiving periodic copper sulfate applications

Copper sulfate (CuSO4) is applied periodically to commercial channel catfish (Ictalurus panctatus) ponds as an algicide or parasiticide. Current understanding of the chemistry of copper in soil-water systems suggests that copper may accumulate in pond sediments, although the forms and potential bioavailability of copper in catfish pond sediments are not known. This study investigated the accumulation and distribution of copper in the sediment of catfish ponds receiving periodic additions of CuSO4.5H2O. All ponds were constructed in Sharkey (very-fine, smectitic, thermic Chromic Epiaquert) soil. Nine 0.40-ha ponds received 59 applications of 2.27 kg CuSO4.5H2O per application per pond over 3 yr; no CuSO4.5H2O applications were made to nine additional ponds. Total Cu concentration in the sediments of CuSO4.5H2O-amended catfish ponds (172.5 mg kg(-1)) was four to five times higher than that in the sediments of nonamended ponds (36.1 mg kg(-1)). Copper accumulated in catfish pond sediments at a rate of 41 microg kg(-1) dry sediment for each 1 kg ha(-1) of CuSO4. 5H2O applied to ponds. Copper in the sediments of amended ponds was mainly in the organic matter-bound (30.7%), carbonate-bound (31.8%), and amorphous iron oxide-bound (22.1%) fractions with a considerable fraction (3.4%; 3 to 8 mg kg(-1)) in soluble and exchangeable fractions. This indicates that Cu accumulates differentially in various fractions, with proportionally greater initial accumulation in potentially bioavailable forms. However, toxicity bioassays with amphipods (Hyallela azteca) and common cattail (Typha latifolia L.) indicated that the effect of exposure to amended or nonamended pond sediments was not different.     

Geochemical partitioning of copper, lead, and zinc in benthic, estuarine sediment profiles

The geochemical partitioning of copper (Cu), lead (Pb), and zinc (Zn) was examined in benthic sediment profiles (0- to 20-cm depth interval) composed of relatively coarse (65-90% sand-sized particles), noncohesive, suboxic material (Eh +120 to +260 mV). Total Cu, Pb, and Zn concentrations ranged from 8.3 to 194, 16.3 to 74.8, and 30.1 to 220 mg/kg, respectively, and were related to vertical trends in sediment texture. The observed distribution coefficients describing solid-solution partitioning were in the range of 100 to 1000 L/kg. The geochemical partitioning of solid-phase Cu, Pb, and Zn between six operationally defined fractions was examined with a sequential extraction scheme. The association of Cu, Pb, and Zn with amorphous oxides, crystalline oxides, and organic matter was linearly dependent on the abundance of each respective phase. For retention by amorphous oxide minerals, the observed stoichiometry ranged from 5.2 to 23.7 mg/g for Cu, 12.8 to 21.5 mg/g for Pb, and 23.1 to 85.7 mg/g for Zn. Corresponding values for association with crystalline oxides were an order of magnitude less than those for amorphous oxides, indicating a lesser affinity of trace metals for crystalline oxides. The stoichiometric relationships describing association with organic matter ranged from 17.6 to 54.0 mg/g for Cu, 6.1 to 9.6 mg/g for Pb, and 6.4 to 16.4 mg/g for Zn. The results from this study provide an insight into processes controlling trace metal partitioning in coarse-textured, suboxic, estuarine sediments.     

Trace element speciation in poultry litter

Trace elements are added to poultry feed for disease prevention and enhanced feed efficiency. High concentrations are found in poultry litter (PL), which raises concerns regarding trace element loading of soils. Trace metal cation solubility from PL may be enhanced by complexation with dissolved organic carbon (DOC). Mineralization of organo-As compounds may result in more toxic species such as As(III) and As(V). Speciation of these elements in PL leachates should assist in predicting their fate in soil. Elemental concentrations of 40 PL samples from the southeastern USA were determined. Water-soluble extractions (WSE) were fractionated into hydrophobic, anionic, and cationic species with solid-phase extraction columns. Arsenic speciation of seven As species, including the main As poultry feed additives, roxarsone (ROX; 3-nitro-4-hydroxyphenylarsonic acid) and p-arsanilic acid (p-ASA; 4-aminophenylarsonic acid), was performed by ion chromatography-inductively coupled plasma-mass spectrometry (IC-ICP-MS). Total As concentrations in the litter varied from 1 to 39 mg kg(-1), averaging 16 mg kg(-1). Mean total Cu, Ni, and Zn concentrations were 479, 11, and 373 mg kg(-1), respectively. Copper and Ni were relatively soluble (49 and 41% respectively) while only 6% of Zn was soluble. Arsenic was highly soluble with an average of 71% WSE. Roxarsone was the major As species in 50% of PL samples. However, the presence of As(V) as the major species in 50% of the PL samples indicates that mineralization of ROX had occurred. The high solubility of As from litter and its apparent ready mineralization to inorganic forms coupled with the large quantity of litter that is annually land-applied in the USA suggests a potential detrimental effect on soil and water quality in the long term.     

Distribution of copper, zinc, and phosphorus in coastal plain soils receiving repeated liquid biosolids applications

Continuous N-based application of biosolids contributes to a gradual increase of trace elements and P in soils. The objectives of this study were to assess the accumulation and vertical transport of Cu, Zn, C, N, and P within the profile of two coastal plain soils. Liquid (6-8% total solids) biosolids were applied to an Acredale silt loam (fine silty, mixed, thermic typic Ochraqualfs) and Bojac loamy sand (coarse loamy, mixed, thermic typic Hapludult) annually from 1984 to 1998. The repeated applications supplied 70, 204, and 3823 kg ha(-1) of Cu, Zn, and P, respectively, to the Acredale and 81, 225, and 4265 kg ha(-1) of Cu, Zn, and P, respectively, to the Bojac. The total C and N contents were not different than background levels in the Bojac soil and were slightly higher in the Acredale soil 7 years after cessation of biosolids application. Phosphorus, Cu and Zn are still concentrated in the top 0.25 m of the Acredale soil. Enrichment of P, Cu, and Zn were detected to the deepest soil increment in the coarse-textured Bojac soil. Approximately 20 to 40% of the Cu and Zn applied in the biosolids could not be accounted, which was likely due to a combination of leaching and incomplete extraction. Excessive Mehlich 1-P concentrations and a high degree of P saturation were found in amended soil, raising the potential for P release to runoff or leaching water.     

Heavy metals distribution in an Iowa suburban landscape

This study investigated the degree to which human activities through urbanization influence heavy metal concentrations in a suburban landscape in Ankeny, IA. Residential areas from different years in nine time periods of development were identified from aerial photos. Soil cores were collected from the center of the front yard of 10 randomly selected homes. Cores were subdivided into 0- to 5-, 5- to 10-, and 10- to 20-cm increments from a composite of five cores. The soils were analyzed for organic C, pH, and total Cd, Co, Cr, Cu, Ni, Pb, and Zn. Results showed that organic C increased and pH decreased with time, and that there was a general decreasing trend in heavy metal concentrations from the pre-1939 period until 1983-1990, after which there was a sharp increase in the concentrations of most of the metals. The mean Cu concentration ranged from 21 mg kg(-1) for the pre-1939 time period of development to 14.9 mg kg(-1) for the recent period of development (2003-2005). Nickel concentrations increased significantly with depth with means of 21.3 mg kg(-1) at depth 0 to 5 cm, 22.5 mg kg(-1) at depth 5 to 10 cm, and 23.0 mg kg(-1) at depth 10 to 20 cm. The concentrations of heavy metals were significantly intercorrelated, except Zn, suggesting their coexistence as mineral constituents or common contamination source. The concentrations of Cu and Pb in some locations could be due to anthropogenic inputs or higher organic matter content in soils adjacent to older homes. There appears to have been a source that caused an increase in Cd, Cr, Co, Cu, Pb, and Ni concentrations in soil adjacent to homes built between 1983 and 1990.     

Cadmium content of wheat grain from a long-term field experiment with sewage sludge

Grain Cd concentrations were determined in the wheat (Triticum aestivum L.) cultivars Soissons, Brigadier, and Hereward grown in 1994,1996, and 1999, respectively, in soils of a long-term field experiment to which sewage sludges contaminated with Zn, Cu, Ni, or Cr had previously been added. Soil pore water soluble Cd and free Cd2+ increased linearly with increasing total soil Cd (R2=0.82 and 0.84, respectively; P<0.001). Similarly, soil pore water free Cd2+ increased linearly with increasing soil pore water soluble Cd (R2=0.98; P<0.001). There was no evidence of a plateau in soil pore water Cd concentrations with increasing soil Cd concentrations. Grain Cd concentrations were significantly correlated with total soil Cd (P<0.001), soil pore water Cd (P<0.001), and free Cd2+ (P<0.001). A slight curvilinear relationship between grain Cd and soil Cd was apparent, but there was no plateau, even at the maximum soil Cd concentration of about 2.7 mg kg(-1). The relationship between soil pore water Cd and grain Cd was linear for all three cultivars. The slopes were in the order 1994 > 1996 > 1999, with more Cd being taken up into the grain by Soissons grown in 1994, and least by Hereward grown in 1999. For Soissons, Cd concentration in the grain greater than the EU limit (0.24 mg kg(-1) dry wt.) occurred at soil Cd less than the current UK limit of 3 mg kg(-1) for soils receiving sewage sludge. In contrast, for Brigadier and Hereward, grain Cd concentrations were near to and less than the EU limit, respectively, at soil Cd concentrations of 3 mg kg(-1).     

Relationships between bacterial tolerance levels and forms of copper and zinc in soils

The effects of various fractions of copper (Cu) and zinc (Zn) on soil bacteria were evaluated by the heavy metal tolerance level of the bacterial community (IC50) in soil samples collected near a mine. The IC50 values had no relationship with the total concentrations of Zn and Cu in the soils, but were weakly correlated with the 0.05 M CaCl2-extractable form of each metal in the soils (Cu: R2 = 0.670, p < 0.01; Zn: R2 = 0.453, p < 0.05). It was found that the IC50 correlated strongly with the total concentration of each metal in the extracts from water-saturated soil samples, described below as "soil solution" (Cu: R2 = 0.789, p < 0.01; Zn: R2 = 0.617, p < 0.01). The speciation of these metals in the soil solutions was estimated using an equilibrium thermodynamic computer model, SOILCHEM. Simulated free Cu ion ranged from 18 to 98% of total Cu, and organic complexes of Cu ranged from < 1 to 56%. In all samples, Zn existing as the free ion was estimated to be more than 80% of total Zn in the soil solutions. The IC50 values were also correlated with the estimated free metal ion activities, but with slightly lower correlation coefficients than found for total concentration in the soil solutions (Cu: R2 = 0.735, p < 0.01; Zn: R2 = 0.610, p < 0.01). The results suggest that not only high metal ion activities, but also total dissolved metal concentrations in soil solutions may affect the bacterial community.     

Soil profile distribution of phosphorus and other nutrients following wetland conversion to beef cattle pasture

Largely influenced by the passage of the Swamp Land Act of 1849, many wetlands were lost in the coastal plain region of the southeastern United States, primarily as a result of drainage for agricultural activities. To better understand the chemical response of soils during wetland conversion, soil core samples were collected from the converted beef cattle pastures and from the natural wetland at Plant City, FL in the summers of 2002 and 2003. Data collected from the natural wetland sites were used as reference data to detect potential changes in soil properties associated with the conversion of wetlands to improved beef cattle (Bos taurus) pastures from 1940 to 2003. The average concentration of total phosphorus (TP) in pasture soils (284 mg kg(-1)) was significantly (p 相似文献   

Macroscopic and molecular investigations of copper sorption by a steam-activated biochar

Excessive Cu concentrations in water systems can negatively affect biological systems. Because Cu can form strong associations with organic functional groups, we examined the ability of biochar (an O-C-enriched organic bioenergy by-product) to sorb Cu from solution. In a batch experiment, KOH steam-activated pecan shell biochar was shaken for 24 h in pH 6, 7, 8, or 9 buffered solutions containing various Cu concentrations to identify the effect of pH on biochar Cu sorption. Afterward, all biochar solids from the 24-h shaking period were air-dried and analyzed using X-ray absorption fine structure (XAFS) spectroscopy to determine solid-phase Cu speciation. In a separate batch experiment, biochar was shaken for 30 d in pH 6 buffered solution containing increasing Cu concentrations; the Cu sorption maximum was calculated based on the exponential rise to a maximum equation. Biochar sorbed increasing amounts of Cu as the solution pH decreased from 9 to 6. The XAFS spectroscopy revealed that Cu was predominantly sorbed onto a biochar organic phase at pH 6 in a molecular structure similar to Cu adsorbed on model humic acid (Cu-humic acid [HA]). The XAFS spectra at pH 7, 8, and 9 suggested that Cu was associated with the biochar as three phases: (i) a complex adsorbed on organic ligands similar to Cu-HA, (ii) carbonate phases similar to azurite (Cu(CO)(OH)), and (iii) a Cu oxide phase like tenorite (CuO). The exponential rise equation fit to the incubated samples predicted a Cu sorption maximum of 42,300 mg Cu kg. The results showed that KOH steam-activated pecan shell biochar could be used as a material for sorbing excess Cu from water systems, potentially reducing the negative effects of Cu in the environment.