Leachate Properties and Cadmium Migration Through Freeze-thaw Treated Soil Columns

Soil column leaching experiments were conducted to study the effects of multiple freeze-thaw cycles on the vertical migration of cadmium (Cd). Three Cd-spiked leaching solutions of different properties were derived from snowmelt, sludge, and straw, designated as B, W and J, respectively. The leaching solutions varied in dissolved organic matter (DOM) concentrations in the order of J > W > B. Changes in leachate properties and Cd concentration were observed. The results showed that pH values of all the leachate solutions through freeze-thaw treated soil columns were higher than those of leachates through unfrozen soils. However, electrical conductivity (EC) values decreased compared with leachates in unfrozen treated soil columns. Although the concentrations of DOM in leachate solutions had no evident differences between the freeze-thaw and unfrozen treated soil columns, the concentrations of DOM in the leachate solutions B, W and J were different. Freeze-thaw cycles resulted in increased concentrations of Cd in the leachate solutions in the order J > W > B, and promoted a deeper migration of Cd in the soil columns. Thus, it was shown that freeze-thaw cycles may increase the risk of groundwater pollution by Cd.     

Sewage sludge applied to agricultural soil: Ecotoxicological effects on representative soil organisms

Application of sewage sludge to agricultural lands is a current practice in EU. European legislation permits its use when concentrations of metals in soil do not increase above the maximum permissible limits. In order to assess the fate and the effects on representative soil organisms of sewage sludge amendments on agricultural lands, a soil microcosm (multi-species soil system—MS 3) experiment was performed. The MS 3 columns were filled with spiked soil at three different doses: 30, 60 and 120 t ha^?1 fresh wt. Seed plants (Triticum aestivum, Vicia sativa and Brassica rapa) and earthworms (Eisenia fetida) were introduced into the systems. After a 21-d exposure period, a statistically significant increase for Cd, Cu, Zn and Hg concentrations was found for the soils treated with the highest application rate. Dose-related increase was observed for nickel concentrations in leachates. Plants and earthworm metal body burden offer much more information than metal concentrations and help to understand the potential for metal accumulation. Bioaccumulation factor (BAF_plant?soil) presented a different behavior among species and large differences for BAF_{earthworm?soil}, from control or sewage-amended soil, for Cd and Hg were found. B. rapa seed germination was reduced. Statistically significant decrease in fresh biomass was observed for T. aestivum and V. sativa at the highest application rate, whereas B. rapa biomass decreased at any application rate. Enzymatic activities (dehydrogenase and phosphatase) as well as respiration rate on soil microorganisms were enlarged.     

Soil pH Effect on Phosphate Induced Cadmium Precipitation in Arable Soil

The objective of this study was to determine soil pH conditions that allow cadmium (Cd) to precipitate as Cd minerals in phosphate (P) amended soil. Cadmium immobilization could be attributed primarily to Cd adsorption due to increase in pH and negative charge. Soil pH might not affect Cd precipitation as Cd₃(PO₄)₂ by direct reaction of Cd and P in the studied soil, even when soil pH increased up to 9.0. However, Cd might precipitate as CdCO₃ with increasing pH up to 9.0 in P untreated soil and up to 8.0 in P treated soil depending on CO₂ level.     

Efficiency of C3 and C4 Plant Derived-Biochar for Cd Mobility,Nutrient Cycling and Microbial Biomass in Contaminated Soil

Biochar is considered a novel soil amendment to reduce metal mobility, but its influence on soil chemical and biochemical properties is not fully understood. In the present study, biochar derived from rice straw (RSB), rice hull (RHB), and maize stover (MSB) was used to evaluate comparative efficiency on Cd mobility and soil biochemical properties. Ammonium nitrate extractable Cd significantly decreased among all the applied biochar types and application rates. The European Community Bureau of Reference (BCR) technique showed significant decrease in acid-soluble Cd by 24%–32%, 19%–23%, and 22%–27% for RSB, RHB, and MSB, respectively at the 1.5% and 3% rate. However, the concentration of Cd in the residual increased by 38%, 35% and 36% for RSB, RHB and MSB, respectively at a 3% application rate. Soil microbial biomass (C and N) and inorganic nitrogen forms (NH₄ and NO₃) significantly increased among all biochar applications. Overall, RSB demonstrated positive results as soil amendments for Cd immobilization, increasing soil nutrient availability, and enhancing soil microbial biomass.     

Relationships between physicochemical parameters and the toxicity of leachates from a municipal solid waste landfill

Landfills are used to dispose municipal solid wastes, and although on-site recycling in these places is an extensive practice in Latin America, diverse pollutants are incorporated into the leachates. The objective of this work was to establish relationships between composition and toxicity of leachates from the landfill of the city of Cartagena, Colombia. Leachates were characterized measuring Cd, Ni, Hg, Mn, Cu, and Pb concentrations, and physicochemical parameters including pH, conductivity, chemical oxygen demand (COD), and hardness. Bioassays were conducted diluting with synthetic sea water, recording toxicity against Artemia franciscana as median lethal concentrations (LC50 values) after 24 and 48 h exposure. Average LC₅₀ values oscillated between 3.20% and 39.33% (v/v). Multivariate analysis showed that toxicity was dependent on Cd and COD. The slope of the concentration–response curve correlated with Ni concentration independently from toxicity. Results suggest toxicity of these leachates depends on Cd concentrations associated with organic matter, this effect being modulated by Ni.     

Removal of toxic metals from leachates from hazardous solid wastes and reduction of toxicity to microtox by the use of calcium alginate beads containing humic acid

Improper disposal of hazardous wastes can lead to release of potentially harmful substances through leaching such as heavy metals, which ultimately contaminate soil, sediment surface water, and groundwater through runoff. To remove these toxic metals and avoid any adverse effect on the ecosystem, a novel approach involving calcium alginate (CA) beads containing humic acid (HA) was used. For this, 10% leachates of the waste obtained from two major industrial units with electroplating processess were prepared at neutral pH and analyzed by atomic absorption spectrophotometry (AAS). Both leachates contained Cd, Cu, Cr, Ni, Mn, Fe, and Zn. The concentrations of Ni, Mn, Fe, and Zn in the waste were found to be significant. The leachates analyzed were passed through columns packed with calcium alginate beads with or without humic acid. The concentrations of various metals in beads and in different fractions collected after adsorption were measured. Data recorded indicate that calcium alginate beads containing humic acids are more efficient in removal of all metals in substantial amounts from the two leachates. Along with removal of metals, this process led to considerable detoxification of the leachates as tested by Microtox assay, indicated by earlier protection and higher EC(50). The significance of the results in relation to removal of toxic metals by beads containing humic acid is discussed.     

Persistence of Bifenthrin in Sandy Loam Soil as Affected by Microbial Community

Soil was fortified with bifenthrin at the level of 10 μg g⁻¹ soil. Soil samples were drawn at regular intervals of 0, 10, 20, 30 and 40 days. For extraction of bifenthrin, soil was extracted with acetone. Clean up was done by liquid–liquid partitioning with dichloromethane after diluting with brine solution. Quantification of bifenthrin residues was done by GC using mega bore column and ECD detector. Recovery of bifenthrin in soil ranged between 92.6 % and 93.8 % at 0.5 and 1.0 μg g⁻¹. The instrumental limit of detection of bifenthrin was 0.005 μg mL⁻¹ and LOQ for soil by this method was found to be 0.05 μg g⁻¹. The calibration curve was found to be linear within range the range of 0.01 and 0.10 μg mL⁻¹ concentration. The DT₅₀ (disappearance time for 50 % loss) of bifenthrin at the level of 10 μg g⁻¹ in sterile and non sterile soil were found to be 330 and 147 days, respectively. A vast difference in the half life of sterile and non sterile soil indicated the presence of potential microbes for bifenthrin degradation.     

Release and leaching of plant DNA in unsaturated soil column

Little information is available on the process of DNA release from plants and neither is there much information to be found regarding DNA transport in the vadose zone. Unsaturated soil columns were used to examine the release and transport of DNA content in the leaf of tomato variety Palmiro, which was introduced into the soil columns after being dried at 35 degrees C for 3 days. Soil columns were leached with sterile water at a rate of 0.5mLh(-1) for 104 days. DNA from column leachate water was extracted and analysed. Both quantitative and qualitative measurements of extracted DNA were taken. Tomato gene sequences were detected using PCR amplification based on tomato specific 18S primers. The concentration of total DNA in soil column leachate water ranged from 6.7 to 50.4microgL(-1). Genomic analysis using agarose gel electrophoresis showed degradation of DNA after its passage through unsaturated soil columns. The presence of tomato genes in the leachate water of soil columns suggests a potential release of tomato DNA from leaves and potential transport of DNA over considerable distances in water-unsaturated soil. Consequently, transport of plant DNA in vadose zone is indicated, and there is a risk that the DNA may reach the groundwater.     

Exotic Earthworms Decrease Cd,Hg, and Pb Pools in Upland Forest Soils of Vermont and New Hampshire USA

Exotic earthworms are present in the forests of northeastern USA, yet few studies have documented their effects on pollutant metals in soil. The objective of this study was to identify if Cd, Hg, and Pb strong-acid extractable concentrations and pools (bulk inventories) in forest soils decreased with the presence of exotic earthworms. We compared ‘Low Earthworm Abundance’ (LEA) sites (≤10 g m^?2 earthworms, n?=?13) and ‘High Earthworm Abundance’ (HEA) (>10 g m^?2 earthworms, n?=?17) sites at five watersheds across Vermont and New Hampshire. Organic horizon Cd, Hg, and Pb concentrations were lower at HEA than LEA sites. Organic horizon and total soil pools of Cd and Hg were negatively correlated with earthworm biomass. Soil profile Cd and Hg concentrations were lower at HEA than LEA sites. Our results suggest earthworms are decreasing accumulation of Cd, Hg, and Pb in forest soils, potentially via greater mobilization through organic matter disruption or bioaccumulation.     

Effects of Peanut Shell Biochar on the Adsorption of Cd(II) by Paddy Soil

Soil from an experimental paddy field in southern China was incubated with peanut shell biochar to investigate effects of this additive on the adsorption and desorption characteristics of Cd(II) using batch methods. Incorporation of biochar increased adsorption of Cd(II) by the paddy soil at 20, 25, and 30°C; this trend was apparent both with increasing quantities of biochar and rising temperature. Incorporation of biochar primarily enhanced the non-electrostatic adsorption of Cd(II). In addition, supplementation with biochar decreased the adsorption rate of Cd(II), which decreased with increasing quantities of biochar. The Langmuir constant b and Freundlich constant k_f both increased with greater quantities of biochar at different temperatures. Adsorption of Cd(II) was an endothermic process and occurred spontaneously. Incorporation of biochar decreased availability and mobility of Cd(II) to plants primarily through increased non-electrostatic adsorption of Cd(II) by paddy soil.     

Effects of liming on uptake of lead and cadmium by Raphanus sativa

Although liming soil to reduce the heavy metal uptake by plants has been recommended generally, there is some disagreement with the practice based on the results of recent studies. Radishes, Raphanus sativa L. var. Paekyong, were grown in greenhouse pots which were filled with soils treated with 1.52 mg kg^–1 Cd and 25.37 mg kg^–1 Pb, respectively and amended with lime at five rates of 0, 0.25, 0.5, 1.0, and 2.0% by dry soil weight. Plants were harvested three times at 25, 50, and 75 days after sowing and the roots and shoots separated. After the plant samples were digested with HNO₃-HClO₄, Cd was analyzed by flame AAS and Pb by graphite furnace AAS. A large amount of Cd was translocated into the radishes, which accumulated dramatically with time. Compared to Cd, Pb uptake was very low and accumulated slowly. Cd contents were very much higher in the shoots than the roots, but Pb was not significantly different. Liming or increased soil pH decreased Cd uptake markedly with increased lime level; Pb influence was negligible. Yields were decreased with excessive liming, but not by the levels of Cd or Pb added.     

Immobilization of cadmium by microbial extracellular products

An axenic bacterial culture was isolated from Morrison loam soil (pH 6.4) and was capable of growth in the presence of CdO (175 g/mL of Cd). During the first two days of incubation, growth of the culture was accompanied by a decrease in the concentration of soluble Cd. This effect was due to two phenomena: (1) a decrease in the solubility of CdO in medium conditioned by the microorganisms; and (2) to sorption of Cd to bacterial cells. The solubility of CdO in filter-sterilized spent medium was very low (4–6 g/mL), yet the solubility was high (110–160 g/mL) in autoclaved, filtered spent medium. Changes in the pH value of the medium were not responsible for this effect. Incubation of spent medium in the presence of increasing concentrations of Cd as Cd(NO₃)₂ resulted in a decrease in the metal concentration of the liquid, due to the formation of a precipitate in quantities proportional to the amount of added Cd. Similar precipitate formation was observed when 100 g/mL of Hg, Cu, or Zn were added but not when 100 g/mL of Mg was introduced. The compound(s) responsible for the precipitate formation was not dialyzable from tubing with a pore size of 12,000–14,000 and was not retained by a C₁₈ Sep-Pak cartridge. Dialysis of a suspension of the precipitate against water (pH 3.0) resulted in partial dissolution of the complex. Approximately 50% of the bound Cd was released and this was accompanied by the release of a protein of molecular weight of 42,600 daltons. The results suggest that this microbial protein forms a water insoluble precipitate with Cd and therefore plays a major role in decreasing the concentration of soluble Cd during microbial growth.     

Fate of triclosan and triclocarban in soil columns with and without biosolids surface application

The leaching and transformation behaviors of triclosan (TCS) and triclocarban (TCC) in soil columns (20 cm high, 4 cm in diameter) packed with an agricultural soil (Roxana very fine sandy loam) with and without biosolids surface application were investigated. The column leachates and soil samples were analyzed for TCS, TCC, and their transformation products. Significantly more TCS was transformed compared with TCC. Surface application of biosolids significantly retarded their transformation. Downward movement of TCS and TCC occurred within a 10-cm soil depth. Methyl-TCS was not detectable in the leachates but was detected in the top 5-cm soil layer, with more appearing in the biosolids-applied soil. At the end of the column study, carbanilide (CBA) was the only detectable TCC reductive dechlorination product in the soil. No TCC reductive dechlorination products were detectable in the leachates. Detection of 3,4-dichloroaniline (3,4-DCA) and 4-chloroaniline (4-CA) suggested the occurrence of TCC hydrolysis. Rapid leaching of 4-CA through the soil column was observed. The 3,4-DCA was detected throughout the entire 20-cm depth of the soil column but not in the leachates. The fact that only small percentages of the transformed TCS and TCC appeared, after a 101-d column study, in the forms of the products analyzed suggested that either the investigated transformation pathways were minor pathways or further rapid transformation of those products had occurred.     

Kinetics of Cadmium Uptake and Subcellular Partitioning in the Earthworm <Emphasis Type="Italic">Eisenia fetida</Emphasis> Exposed to Cadmium-Contaminated Soil

To understand the bioaccumulation kinetics of cadmium (Cd) at the subcellular level, toxicokinetics and subcellular fractionation of Cd were determined for the terrestrial earthworm Eisenia fetida exposed to Cd-contaminated red soil. The bioaccumulation factor was 1.74 after exposure to soil containing 1 mg Cd/kg dry weight for 21 days. Four distinct compartments with different Cd-binding affinities were obtained by sequential centrifugations, including the cytosolic fraction (G), the organelles fraction (F), the granular fraction (D), and the tissue, cell membrane, and intact cell fraction (E). Most of the accumulated Cd in the organisms existed as fraction G. Cd bound to the tissue and cell membrane fraction (E) was <8% of total Cd. Only approximately 3% of Cd existed in fraction F, and <1% was found in fraction D. Accumulation and elimination kinetics of Cd in different fractions were accurately described by one-compartment models, and kinetic parameters (uptake rate constant k ₁ and elimination rate constant k ₂ ) were derived. Fractions G and F were responsible for the linear accumulation pattern during 3 weeks of exposure, whereas fractions D and E showed a nonlinear uptake curve, and steady state was achieved after 7 and 14 days of exposure, respectively.     

Effects of cadmium and simulated acid rain on ammonification and nitrification in soil

A perfusion technique was used to study the effects of 1) simulated acid rain on the mineralization and nitrification of glycine (NH₂-N) or ammonium sulfate (NH₄-N) by adjusting the pH of the perfusates to 3.0, 2.5, or 2.0 with H₂SO₄; and 2) 0, 50, 100, 500, and 1,000μg Cd/g dry weight of soil on the mineralization and nitrification of NH₂-N, both in soil adjusted with H₂SO₄ to pH 3.0 and in soil not exposed to acidity. Ammonification was relatively insensitive to both Cd and acidity, occurring even in soil exposed to pH 2.0 or 1,000 ppm Cd. Nitrification was more sensitive, being retarded in NH₂-N-supplemented soils exposed to pH 2.5 and inhibited in soil exposed to pH 2.O. In NH₄-N-supplemented soils, nitrification was retarded at pH 3.0 and inhibited at pH 2.5. This retardation and inhibition occurred despite the increase in the pH of the perfusates to a noninhibitory level. Nitrification was retarded at 500 ppm Cd and to a greater extent at 1,000 ppm Cd, where nitrite accumulated. The combined effect of exposure to Cd and H₂SO₄ at pH 3.0 was additive rather than synergistic, and even with 1,000 ppm Cd at pH 3.0 some nitrification eventually occurred.     

Adsorption of Cd on Soils with Various Particle Sizes from an Abandoned Non-ferrous Smelting Site: Characteristics and Mechanism

Soil particle size could intensively impact the Cd adsorption in soils. The adsorption characteristics of Cd on miscellaneous fill (MF) and weathered slate (WS), collected from a zinc smelting site, were studied by batch experiments under conditions of different initial Cd concentrations and soil particle sizes. The results showed that the adsorption kinetics of Cd for soil particles from MF and WS were well fitted with the pseudo-first-order model, and the Cd adsorption isotherms well conformed to the Freundlich model. Soil particle size had an inconspicuous influence on adsorption rate, while the adsorption capacity decreased with particle size increase. The Cd adsorption on soil particles could be due to the exchange with Fe/Al, and -OH/C=O sites were the predominant adsorption sites. The MF may cause secondary pollution risk due to its low adsorption ability for Cd in smelting sites.

     

Leaching Characteristics of Calcium and Strontium from Phosphogypsum Under Acid Rain

Phosphogypsum (PG) stored close to phosphorus chemical plants has caused worldwide environmental problems. Column leaching experiments were conducted to evaluate Ca and Sr leaching from PG under simulated acid rain at pH levels typical for rain in the study region (Shifang, China). High concentrations of Ca and Sr in leachates in the first five leaching events could pollute the soil and groundwater around the PG. Leachates pH was lower than and had no correlation with simulated rain pH. No correlations between simulated rain pH and cumulative Ca and Sr content in leachates were noted. Around 2.0%–2.2% of Ca and 0.5%–0.6% of Sr were leached out from PG by the simulated summer rainfall in Shifang. Electrical conductivity values, Ca and Sr concentrations at bottom sections of PG columns were higher than those of top sections, while pH values showed a reverse trend. More precautions should be taken to protect the environment around PG stacks.     

Geo-Accumulation Indices of Heavy Metals in Soil and Groundwater of Kanpur,India Under Long Term Irrigation of Tannery Effluent

Soil and groundwater from long-term (>50 years) tannery effluent irrigated areas of Kanpur were analyzed and significant buildup of heavy metals such as Cr, Ni, Cd, Pb, Zn, and As in the range of 252–972, 23–30, 2.3–14.1, 23.7–58.8, 138–338 and 6.8–11 mg kg^?1, respectively in soil was found. Few groundwater samples in the effluent irrigated areas also exhibited high Cr concentration above the permissible limit of United States Environmental Protection Agency. The tannery effluents contained 1.53–57.3 ppm Cr, 0–0.12 ppm Ni, 0–0.02 ppm Cd, 0–0.07 ppm Pb, 0–0.48 ppm Zn and 0–0.03 ppm As. The Geo-accumulation index (I_geo) revealed that soil samples were unpolluted to moderately polluted with Cu, Ni, Zn, Pb and As; moderately polluted in case of Cd; and heavily to extremely polluted by Cr.     

Methods for toxicity assessment of contaminated soil by oral or dermal uptake in land snails: metal bioavailability and bioaccumulation

Using two biological characteristics of the land snail (subspecies Helix aspersa aspersa and Helix aspersa maxima), i.e., soil eating and crawling on wet surfaces, methods were developed to assess the bioavailability of heavy metals (Cd, Cr, Pb, and Zn) from soil and aqueous leachates of soil. Measurement of heavy-metal concentrations in soil, leachates, and soft tissues of snails showed that contamination from ingested soil is the major route for metal uptake. Generally, the concentrations of metals were greater in the viscera than in the foot and rose with the proportion of spiked soil (Sl) in the diet. After ingestion of soil, bioaccumulation factors in the viscera were over two for Cd (3.5-27) and Zn (1.7-4.4) for both subspecies but were below one for Cr (0.04-0.6, except for H. aspersa maxima: 1.21) and Pb (0.02-0.23). Contamination by leachate Sl mainly caused accumulation of Cr in the tissues. Determining the metal burden per snail enables an estimation to be made of the risk of secondary poisoning encountered by predators. The present study provides data on the bioavailability of metals in soils and on the relationships between bioaccumulation and sublethal effects.     

The nature of cadmium binding in commercial Eastern Oysters (Crassostrea virginica)

In contrast to previous results which examined oysters exposed to artificially high cadmium (Cd) levels, the forms of cadmium occurring in “natural” commercially available oysters were partially characterized. About one-third of the Cd was associated with insoluble material. Of the soluble Cd, about 20% occurred in a high molecular weight protein of 40,000–50,000 daltons. The low molecular weight soluble Cd consisted of at least two different forms,i.e., that associated with amino acids (a small peptide) and inorganic Cd. The small peptide fraction also contained zinc and copper. The forms of Cd in commercial oysters were compared to those occurring in both commercial scallops and artificially cultured oysters. Scallops bind Cd to three soluble proteins, all of which are of higher molecular weight than the small oyster peptide. Oysters cultured in 10 ppb Cd medium contained binding sites similar to commercial oysters except that none of the soluble Cd in the cultured oysters was associated with a high molecular weight protein. The results suggest that extremely high environmental Cd levels are necessary to induce a metallothionein-like protein in oysters. Implications of the results to public health are discussed.