Solubility of organic acids in various methanol and salt concentrations: the implication on organic acid sorption in a cosolvent system

The well-known cosolvency-induced sorption model is not applicable to predict the sorption of carboxylic acids in cosolvent system. To investigate the phenomenon, sorption and solubility of chlorinated phenols (2,4-dichlorophenol (2,4-DCP) and 2,4,6-trichlorophenol (2,4,6-TCP)) and carboxylic acids (benzoic acid and 2,4-dichlorophenoxyacetic acid (2,4-D)) were measured in soil-methanol mixture with various ionic strengths. The sorption (K_m) of chlorinated phenols was explained by a cosolvency-induced sorption model; the inverse log-linear relationship between the K_m and methanol volume fraction (f_c). However, the K_m of carboxylic acids increased with increasing f_c. This discrepancy was attributed to the effect of the carboxylic moiety. To explain the effect, solubility was measured for benzoic acid and 2,4,6-TCP from various liquid conditions. For both solutes, the cosolvency power (σ) increased with CaCl₂ concentrations and the salting constant (K^s) became smaller as f_c increased. However, the σ value at a given salt concentration and the K^s value at a given f_c were greater for 2,4,6-TCP than for benzoic acid, both of which were due to the greater hydrophobicity of the former. Overall, the solubility profiles of the both solutes on combination of f_c and CaCl₂ concentration evidenced no specific role of the carboxylic moiety. Therefore, it can be reasonably concluded that the positive relationship between K_m and f_c for carboxylic organic acid can be attributed to the modification of the activity coefficient occurred in the solid phase, which cannot be traceable by cosolvency-based model.     

Characterizing As(III,V) adsorption by soils surrounding ash disposal facilities

Leachate derived from unlined coal ash disposal facilities is a potential anthropogenic source of arsenic to the environment. To establish a theoretical framework for predicting attenuation of arsenic by soils subject to ash landfill leachate, which is typically enriched in calcium and sulfate, the adsorption of As(V) and As(III) was characterized from 1 mM CaSO₄ for 18 soils obtained down-gradient from three ash landfill sites and representing a wide range in soil properties. As(V) consistently exhibited an order of magnitude greater adsorption than As(III). As(V) adsorption was best described by coupling pH with 15 s DCB-Fe (R² = 0.851,  = 0.001), although pH coupled to clay, DCB-Fe, or DCB-Al also generated strong correlations. For As(III), pH coupled to Ox–Fe (R² = 0.725,  = 0.001) or Ox–Fe/Al (R² = 0.771,  = 0.001) provided the best predictive relationships. Ca²⁺ induced increases in As(V) adsorption whereas sulfate suppressed both As(V) and As(III) adsorption. Attenuation of arsenic from ash leachate agreed well with adsorption measured from 1 mM CaSO₄ suggesting that the use of 1 mM CaSO₄ in laboratory adsorption tests is a reasonable approach for estimating arsenic behavior in soils surrounding ash landfills. We also showed that the impact of leachate-induced changes in soil pH over time may not be significant for As(V) adsorption at pH < 7; however, As(III) adsorption may be impacted over a wider pH range especially if phyllosilicate clays contribute significantly to adsorption. The benefits and limitations of predicting arsenic mobility using linearized adsorption coefficients estimated from nonlinear adsorption isotherms or from the relationships generated in this study are also discussed.     

Heavy metal immobilization in soil near abandoned mines using eggshell waste and rapeseed residue

Heavy metal contamination of agricultural soils has received great concern due to potential risk to human health. Cadmium and Pb are largely released from abandoned or closed mines in Korea, resulting in soil contamination. The objective of this study was to evaluate the effects of eggshell waste in combination with the conventional nitrogen, phosphorous, and potassium fertilizer (also known as NPK fertilizer) or the rapeseed residue on immobilization of Cd and Pb in the rice paddy soil. Cadmium and Pb extractabilities were tested using two methods of (1) the toxicity characteristics leaching procedure (TCLP) and (2) the 0.1 M HCl extraction. With 5 % eggshell addition, the values of soil pH were increased from 6.33 and 6.51 to 8.15 and 8.04 in combination with NPK fertilizer and rapeseed residue, respectively, compared to no eggshell addition. The increase in soil pH may contribute to heavy metal immobilization by altering heavy metals into more stable in soils. Concentrations of TCLP-extracted Cd and Pb were reduced by up to 67.9 and 93.2 % by addition of 5 % eggshell compared to control. For 0.1 M HCl extraction method, the concentration of 0.1 M HCl-Cd in soils treated with NPK fertilizer and rapeseed residue was significantly reduced by up to 34.01 and 46.1 %, respectively, with 5 % eggshell addition compared to control. A decrease in acid phosphatase activity and an increase in alkaline phosphatase activity at high soil pH were also observed. Combined application of eggshell waste and rapeseed residue can be cost-effective and beneficial way to remediate the soil contaminated with heavy metals.     

Sorption of acidic organic solute onto kaolinitic soils from methanol-water mixtures

The fate of the acidic organic solute from the soil-water-solvent system is not well-understood. In this study, the effect of the acidic functional group of organic solute in the sorption from cosolvent system was evaluated. The sorption of naphthalene (NAP) and 1-naphthoic acid (1-NAPA) by three kaolinitic soils and two model sorbents (kaolinite and humic acid) were measured as functions of the methanol volume fractions (f _c ≤ 0.4) and ionic compositions (CaCl₂ and KCl). The solubility of 1-NAPA was also measured in various ionic compositions. The sorption data were interpreted using the cosolvency-induced sorption model. The K _m values (= the linear sorption coefficient) of NAP with kaolinitic soil for both ionic compositions was log linearly decreased with f _c. However, the K _m values of 1-NAPA with both ionic compositions remained relatively constant over the f _c range. For the model sorbent, the K _m values of 1-NAPA with kaolinite for the KCl system and with humic acid for both ionic compositions decreased with f _c, while the sorption of 1-NAPA with kaolinite for the CaCl₂ system was increased with f _c. From the solubility data of 1-NAPA with f _c, no significant difference was observed with the different ionic compositions, indicating an insignificant change in the aqueous activity of the liquid phase. In conclusion, the enhanced 1-NAPA sorption, greater than that predicted from the cosolvency-induced model, was due to an untraceable interaction between the carboxylate and hydrophilic soil domain in the methanol-water system. Therefore, in order to accurately predict the environmental fate of acidic pesticides and organic solutes, an effort to quantitatively incorporate the enhanced hydrophilic sorption into the current cosolvency-induced sorption model is required.     

Influence of a soil enzyme on iron-cyanide complex speciation and mineral adsorption

Cyanide is commonly found as ferrocyanide [Fe(II)(CN)(6)](-4) and in the more mobile form, ferricyanide [Fe(III)(CN)(6)](-3) in contaminated soils and sediments. Although soil minerals may influence ferrocyanide speciation, and thus mobility, the possible influence of soil enzymes has not been examined. In a series of experiments conducted under a range of soil-like conditions, laccase, a phenoloxidase enzyme derived from the fungi Trametes versicolor, was found to exert a large influence on iron-cyanide speciation and mobility. In the presence of laccase, up to 93% of ferrocyanide (36-362ppm) was oxidized to ferricyanide within 4h. No significant effect of pH (3.6 and 6.2) or initial ferrocyanide concentration on the extent or rate of oxidation was found and ferrocyanide oxidation did not occur in the absence of laccase. Relative to iron-cyanide-mineral systems without laccase, ferrocyanide adsorption to aluminum hydroxide and montmorillonite decreased in the presence of laccase and was similar to or somewhat greater than that of ferricyanide without laccase. Laccase-catalyzed conversion of ferrocyanide to ferricyanide was extensive though up to 33% of the enzyme was mineral-bound. These results demonstrate that soil enzymes can play a major role in ferrocyanide speciation and mobility. Biotic soil components must be considered as highly effective oxidation catalysts that may alter the mobility of metals and metal complexes in soil. Immobilized enzymes should also be considered for use in soil metal remediation efforts.     

Gene expression analysis and classification of mode of toxicity of polycyclic aromatic hydrocarbons (PAHs) in Escherichia coli

Escherichia coli is known to respond to certain toxic chemicals through an increased expression of various stress genes. In this study, therefore, the expression of recA, katG, fabA and grpE genes was used as a representative for DNA, oxidative, membrane and protein damage, respectively, after E. coli was exposed to different polycyclic aromatic hydrocarbons (PAHs), i.e., phenanthrene, naphthalene and benzo[a]pyrene. To accomplish this, the expression levels of these four genes were quantified using a real-time RT-PCR analysis when E. coli cultures were under stressful conditions, such as those caused by an exposure to mitomycin C, hydrogen peroxide and phenol. It was found that the primary toxic effect of each chemical is clearly seen when the expression levels of the different genes are compared. Tests with the PAHs showed naphthalene and benzo[a]pyrene to be genotoxic, while phenanthrene had no clear effect on the expression of any of these genes. Based on these results, the effects due to these toxic chemicals and the extent of each stress can be evaluated with ease using the expression levels of different stress responsive genes.     

Summer cover crops reduce atrazine leaching to shallow groundwater in southern Florida

At Florida's southeastern tip, sweet corn (Zea Mays) is grown commercially during winter months. Most fields are treated with atrazine (6-chloro-N-ethyl-N'-[1-methylethyl]-1,3,5-triazine-2,4-diamine). Hydrogeologic conditions indicate a potential for shallow groundwater contamination. This was investigated by measuring the parent compound and three degradates--DEA (6-chloro-N-[1-methylethyl]-1,3,5-triazine-2,4-diamine), DIA (6-chloro-N-ethyl)-1,3,5-triazine-2,4-diamine, and HA (6-hydroxy-N-[1-methylethyl]-1,3,5-triazine-2,4-diamine)--in water samples collected beneath sweet corn plots treated annually with the herbicide. During the study, a potential mitigation measure (i.e., the use of a cover crop, Sunn Hemp [Crotalaria juncea L.], during summer fallow periods followed by chopping and turning the crop into soil before planting the next crop) was evaluated. Over 3.5 yr and production of four corn crops, groundwater monitoring indicated leaching of atrazine, DIA, and DEA, with DEA accounting for more than half of all residues in most samples. Predominance of DEA, which increased after the second atrazine application, was interpreted as an indication of rapid and extensive atrazine degradation in soil and indicated that an adapted community of atrazine degrading organisms had developed. A companion laboratory study found a sixfold increase in atrazine degradation rate in soil after three applications. Groundwater data also revealed that atrazine and degradates concentrations were significantly lower in samples collected beneath cover crop plots when compared with concentrations below fallow plots. Together, these findings demonstrated a relatively small although potentially significant risk for leaching of atrazine and its dealkylated degradates to groundwater and that the use of a cover crop like Sunn Hemp during summer months may be an effective mitigation measure.     

A hierarchical end-of-life decision model for determining the economic levels of remanufacturing and disassembly under environmental regulations

Remanufacturing, in contrast to material recycling and disposal, can reduce environmental impacts by retaining the geometrical form of the product, thereby regarded as a more eco-efficient approach. In this paper, an end-of-life (EOL) decision model for remanufacturing options is presented to facilitate remanufacturing. The proposed model, in order to maximize the economic value of remanufacturing options while meeting environmental regulations, takes an integrative approach to EOL-option decision-making. Also presented in this paper is a hierarchical approach that represents both the overall hierarchical structure of a product and the interconnections among components. Illustrative examples are provided to demonstrate the effectiveness of the model.     

Stabilization of Cu-contaminated army firing range soils using waste oyster shells

A stabilization/solidification (S/S) process was used to immobilize Cu in contaminated soils obtained from two army firing ranges sites (A and B) with total Cu concentrations of 520 and 380 mg/kg, respectively. Both waste oyster shells (WOS) and pretreated oyster shells (POS) were used to immobilize Cu in the contaminated soils. Waste oyster shells passing the #10 mesh and #20 mesh were used for the Sites A and B, respectively. WOS- and POS-treated soil samples cured for 28 days were evaluated for Cu leaching by the Korean Standard Leaching Test (KSLT) method. Slurry suspensions were prepared to investigate the Cu immobilization mechanism using X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM) energy dispersive X-ray spectroscopy (EDX) analyses. The treatment results showed that the POS treatment was more effective than the WOS treatment of 28 days. For Site A, 10 wt% WOS and 3 wt% POS dosages were required to pass the Korean warning standard of 50 mg/kg, while 10 wt% WOS and 5 wt% POS dosages were required for the Site B treatment. The XRPD and SEM-EDX results showed that Cu immobilization was strongly linked to both CSH/CAH and ettringite. Overall, the POS treatment was effective at immobilizing the Cu in the contaminated soils, very likely due to its CaO content.