Association mechanism between a series of rodenticide and humic acid: a frontal analysis to support the biological data

The binding constants (K) of a series of anticoagulant rodenticides with the main soil organic component, humic acid (HA), were determined using frontal analysis approach. The order of the binding constants was identical as the one obtained in a previous paper [J. Chromatogr. B 813 (2004) 295], i.e. bromadiolone>brodifacoum>difenacoum>chlorophacinone>diphacinone, confirming the power of this frontal analysis approach for the determination of binding constants. Moreover, and for the first time, the concentration of unbound rodenticide to HAs could be determined. Thanks this approach, we could clearly demonstrate that HA acid protected the human hepatoma cell line HepG2 against the cytotoxicity of all the rodenticides tested and that the toxicity of rodenticides was directly linked to the free rodenticide fraction in the medium (i.e. unbound rodenticide to HA).     

Adsorption of humic acid from aqueous solution onto irradiation-crosslinked carboxymethylchitosan

This paper presents the adsorption of humic acid from aqueous solution onto crosslinked chitosan derivative (carboxymethylchitosan), formed by additionless irradiation technique. The surface charge and swelling properties of crosslinked samples were investigated. The adsorption of humic acid onto crosslinked carboxymethylchitosan was carried out by the batch method at room temperature, and it was found to be strongly pH-dependent. Maximum amount of humic acid was adsorbed under acidic conditions at the optimum pH value of 3.5. Adsorption kinetic studies indicated the adsorption process was transport-limited at the same pH. The adsorption isotherm analysis data under various initial humic acid concentrations confirms that experimental data fitted well into the Langmuir equation. X-ray photoelectron spectroscopy (XPS) revealed that the amino groups of carboxymethylated chitosan were protonated, suggesting the formation of organic complex between the protonated amino groups and humic acid. From these preliminary evaluations, it was concluded that crosslinked carboxymethylated chitosan derivatives have a great potential in water treatment for the removal of humic acid and other polarized or electrically charged species.     

Mechanism of the desmutagenic effect of humic acid

The mechanism of an apparent desmutagenic effect of humic acid was investigated. Firstly, components of humic acid (resorcinol, vanillin, vanillic acid, ferulic acid, protochatechuic acid and benzoic acid) were tested and were not found to show a desmutagenic effect. By contrast, lignin did show a desmutagenic effect. The desmutagenic effect of humic acid was decreased by ozone treatment, and the degree of decrease corresponded with a decrease in KMnO4 consumption. Benzo[a]pyrene and humic acid were incubated at 37 degrees C for 1 h and extracted by ethyl acetate and the extract was investigated by gas chromatography (GC). The peak of the decomposition product did not appear, but the amount of benzo[a]pyrene was decreased. This suggests that the desmutagenic effect of humic acid was caused by adsorption of benzo[a]pyrene by humic acid rather than by decomposition of benzo[a]pyrene. Humic acid had the largest adsorption activity at its critical micelle concentration (CMC), while adsorbed benzo[a]pyrene could be released by ultrasonication. Fulvic acid and water-soluble humic substance showed a slight inhibitory effect on the mutagenicity of benzo[a]pyrene.     

Adsorption isotherms of lanthanum to soil constituents and effects of pH,EDTA and fulvic acid on adsorption of lanthanum onto goethite and humic acid

Abstract

La³⁺ adsorption isotherms to five soil constituents (quartz, feldspar, kaolinite, goethite and humic acid) are studied. EDTA, fulvic acid and pH effects are also investigated on the adsorption of lanthanum by goethite and humic acid because of their relative importance in affecting metal environmental behavior. Adsorption isotherms of La³⁺ to five constituents show differences in adsorption capacity and in shape in the studied range of La³⁺. These constituents can be classified according to their adsorption capacity: humic acid > goethite ≈ kaolinite > feldspar ≈ quartz. pH increase could promote humic acid and goethite adsorption of La³⁺ while EDTA could reduce the adsorption by these two adsorbents. Fulvic acid can reduce humic acid adsorption but has less effect on adsorption by goethite.     

Humic acid interference with virus recovery by electropositive microporous filters

The effects of humic acid on poliovirus type 1 recovery from water by Zeta Plus 60S filters were investigated. The humic acid interfered by preventing virus adsorption to the filters, and the interference increased as a function of the amount of humic acid filtered. Humic acid decreased virus adsorption when filtered before the virus, but did not elute virus which had adsorbed to the filters. The effects on virus recovery were not due to alterations in virus titer or neutralizability. The addition of AlCl3, which improved virus recovery by electronegative filters in the presence of humic acid, did not aid in overall virus recovery by the Zeta Plus filters in the presence or absence of humic acid. However, the salt and humic acid in combination improved virus adsorption and concurrently reduced virus elution efficiency. The addition of NaH2PO4 had no direct effect on virus recovery and did not alter the effect of humic acid. In an attempt to identify the components of humic acid responsible for the interference, humic materials were fractionated by size by using Sephadex gel chromatography and dialysis, and the fractions were tested for interfering activity. Interference was not associated with specific size fractions of the humic materials.     

Humic acid interference with virus recovery by electropositive microporous filters.

The effects of humic acid on poliovirus type 1 recovery from water by Zeta Plus 60S filters were investigated. The humic acid interfered by preventing virus adsorption to the filters, and the interference increased as a function of the amount of humic acid filtered. Humic acid decreased virus adsorption when filtered before the virus, but did not elute virus which had adsorbed to the filters. The effects on virus recovery were not due to alterations in virus titer or neutralizability. The addition of AlCl3, which improved virus recovery by electronegative filters in the presence of humic acid, did not aid in overall virus recovery by the Zeta Plus filters in the presence or absence of humic acid. However, the salt and humic acid in combination improved virus adsorption and concurrently reduced virus elution efficiency. The addition of NaH2PO4 had no direct effect on virus recovery and did not alter the effect of humic acid. In an attempt to identify the components of humic acid responsible for the interference, humic materials were fractionated by size by using Sephadex gel chromatography and dialysis, and the fractions were tested for interfering activity. Interference was not associated with specific size fractions of the humic materials.     

Direct enantioseparation of mandelic acid by high-performance liquid chromatography using a phenyl column precoated with a small amount of cyclodextrin additive in a mobile phase

Direct enantioseparation of mandelic acid by high-performance liquid chromatography (HPLC) with a reversed phase column and a mobile phase containing a small amount of hydroxylpropyl-β-cyclodextrin (HP-β-CD) was studied as an efficient method for saving consumption of the CD additive. As a result, it was proposed that racemic mandelic acid can be analyzed with a phenyl column by using a mobile phase composed of 10 mM ammonium acetate buffer (pH 4.2) and 0.02% (w/v) HP-β-CD at a flow rate of 1.0 mL/min at 40°C after the passage of 10 mM ammonium acetate buffer (pH 4.2) containing 0.1% (w/v) HP-β-CD as a precoating mobile phase for 60 min. It is suggested that HP-β-CD is bound with a phenyl group on the surface of the stationary phase to allow a phenyl column to act as a transient chiral column, and injected mandelic acid can form the ternary complex with the adsorbed HP-β-CD. The longer retention time of D-mandelic acid than the L-isomer for HPLC can be explained from the higher stability of the HP-β-CD complex with D-mandelic acid, which was confirmed by CE experiment with HP-β-CD as a selector. The efficiency of a phenyl column compared with other stationary phases was also discussed.     

Adsorption of lecithin liposomes to acid clay

The interaction between lecithin liposomes and acid clay was investigated to clarify the mechanism for liposome adsorption to the clay. It was found that the multilamellar vesicular structure of the liposomes was broken as a result of primary adsorption. The acid clay particles aggregated and were eventually covered by the lecithin layer structure. In the case of kaolin, on the other hand, the liposomes were weakly adsorbed to the clay and maintained the vesicular structure. The amount of primary adsorption to the clay surface, which was estimated from the adsorption isotherm, was more for acid clay than for kaolin, and the total amount adsorbed to the acid clay was also more than to kaolin. This result can be explained by the much higher density of the negative charge on the acid clay surface than that for kaolin. The liposomes are therefore considered to be adsorbed to the acid clay mainly by the choline positive charge residing at the end of the lecithin molecule, although this is of no net charge as a whole.     

海南热带雨林土壤中胡敏酸对Pb2+、Cu2+的吸附解吸特性研究

重金属元素在土壤-溶液界面的吸附反应深刻地影响重金属行为及其生态风险。以热带次生雨林土壤中提取的胡敏酸为材料, 采用傅立叶红外光谱、扫描电镜等技术对胡敏酸进行了表征, 通过批量吸附实验研究了胡敏酸对铅、铜的吸附特性, 通过连续解吸方法研究了在不同浓度下饱和吸附的胡敏酸对重金属吸附的形成过程。结果表明, 胡敏酸的腐殖化系数较高, 阳离子交换量为52.84 mmol·g-1, 表面含有羧基和酚羟基官能团。胡敏酸对铜的吸附符合准二级动力学模型, 对铅的吸附符合准一级动力学方程; Langmuir 模型能够更好地描述单一和复合污染条件下胡敏酸对Pb2+的等温吸附行为, Freundlich 模型能够更好的描述单一和复合污染条件下胡敏酸对Cu2+的等温吸附行为。通过连续解吸实验发现, 胡敏酸对铅的吸附过程中4种结合方式的先后饱和顺序为: 物理吸附、络合、离子交换和氢键结合。胡敏酸对铜的吸附过程中4种结合方式的先后饱和顺序为: 络合、氢键结合、离子交换和物理吸附。     

Influence of pH, salinity, and organic matter on the adsorption of enteric viruses to estuarine sediment.

This study was designed to determine the degree of adsorption of enteric viruses to marine sediment and factors controlling this association. Adsorption and elution characteristics of several enteroviruses and one rotavirus to estuarine sediments were studied under varying conditions of pH, salinity, and presence of soluble organics. Greater than 99% of the added poliovirus type 1 (LSc), coxsackievirus type B3 (Nancy), echovirus type 7 (Wallace), and rotavirus (SA-11) adsorbed to sediment. Echovirus 1 (Farouk) and a recent isolate typed as coxsackievirus B4 adsorbed significantly less than poliovirus 1 under similar conditions of varying salinity and pH. The presence of soluble organic matter, in the form of secondary sewage effluent or humic acid, did not affect these patterns of adsorption. Only echovirus 1 (Farouk) desorbed when the pH or salinity was altered and then only to a small extent. Three recent isolates of echovirus 1 and echovirus 29 (strain JV-10) also demonstrated varying amounts of adsorption to sediment. These data indicate that enteric viruses can become readily associated with sediment in the estuarine environment and that this association may play a major role in their hydrotransportation and survival.     

Conditions for nisin adsorption by Streptococcus lactis cells

Some conditions for absorption of nisin, a polypeptide antibiotic by the cells of Str. lactis were studied. The amounts of nisin adsorbed by the cells depended on the culture age: at the late stationary phase the adsorption level was 2 times higher than that at the logarithmic phase. The cells grown on a "poor" medium adsorbed 85-90 per cent of nisin added to the solution, while the cells grown on the "rich" medium adsorbed 50 per cent of the antibiotic. The adsorption level of nisin by the cells subjected to a thermal shock was higher than that by the live cells. Desorption of nisin from the cells with acid ethanol and bivalent cation solutions was insignificant. Nisin is adsorbed by the cells of other microorganisms, the adsorption levels by the cells of Bac. brevis being the same as those by the streptococcal cells, while the levels adsorbed by Bac. polymyxa being 4 times lower.     

Novel method to extract large amounts of bacteriocins from lactic acid bacteria.

Antimicrobial peptides, bacteriocins, produced by lactic acid bacteria were adsorbed on the cells of producing strains and other gram-positive bacteria. pH was a crucial factor in determining the degree of adsorption of these peptides onto cell surfaces. In general, between 93 and 100% of the bacteriocin molecules were adsorbed at pHs near 6.0, and the lowest (< or = 5%) adsorption took place at pH 1.5 to 2.0. On the basis of this property, a novel isolation method was developed for bacteriocins from four genera of lactic acid bacteria. By using this method we made preparations of pediocin AcH, nisin, sakacin A, and leuconocin Lcm1 that were potent and concentrated. This method produced a higher yield than isolation procedures, which rely on precipitation of the bacteriocins from the cell-free culture liquor. It is simple and can be used to produce large quantities of bacteriocins from lactic acid bacteria to be used as food biopreservatives.     

Novel method to extract large amounts of bacteriocins from lactic acid bacteria.

Antimicrobial peptides, bacteriocins, produced by lactic acid bacteria were adsorbed on the cells of producing strains and other gram-positive bacteria. pH was a crucial factor in determining the degree of adsorption of these peptides onto cell surfaces. In general, between 93 and 100% of the bacteriocin molecules were adsorbed at pHs near 6.0, and the lowest (< or = 5%) adsorption took place at pH 1.5 to 2.0. On the basis of this property, a novel isolation method was developed for bacteriocins from four genera of lactic acid bacteria. By using this method we made preparations of pediocin AcH, nisin, sakacin A, and leuconocin Lcm1 that were potent and concentrated. This method produced a higher yield than isolation procedures, which rely on precipitation of the bacteriocins from the cell-free culture liquor. It is simple and can be used to produce large quantities of bacteriocins from lactic acid bacteria to be used as food biopreservatives.     

Effects of humic materials on virus recovery from water

Humic and fulvic acids were tested for their ability to interfere with virus recovery by microporous filters. Two electropositively charged types of filter (Seitz S and Zeta Plus 60S) were used to concentrate poliovirus in the presence of humic materials. Humic acid inhibited virus adsorption, but even at the highest humic acid concentrations tested (200 mg/liter), 30 to 40% of the virus was recovered by the filters. Fulvic acid, tested with Zeta Plus filters, did not affect virus recovery. For comparison, two electronegatively charged filter types were tested (Cox and Balston). These two types of filter were more sensitive to interference at lower concentrations of humic acid than the more positively charged filters. With Balston filters, at humic acid concentrations above 10 mg/liter, most of the virus was recovered in the filtrate. Fulvic acid, tested with Balston filters, did not interfere with virus recovery. With the electropositively charged filters, the humic materials adsorbed efficiently, even at high input concentrations. Interference with virus adsorption occurred at humic acid concentrations which were below the level of saturation of the filters. In addition, in high-volume experiments, humic acid led to premature blockage of the filters. The efficiency of virus recovery by a second concentration step, organic flocculation of the filter eluate, was tested. For all the filter types tested, this procedure was not affected by the presence of humic or fulvic acid in the input water.     

Effects of humic materials on virus recovery from water.

Humic and fulvic acids were tested for their ability to interfere with virus recovery by microporous filters. Two electropositively charged types of filter (Seitz S and Zeta Plus 60S) were used to concentrate poliovirus in the presence of humic materials. Humic acid inhibited virus adsorption, but even at the highest humic acid concentrations tested (200 mg/liter), 30 to 40% of the virus was recovered by the filters. Fulvic acid, tested with Zeta Plus filters, did not affect virus recovery. For comparison, two electronegatively charged filter types were tested (Cox and Balston). These two types of filter were more sensitive to interference at lower concentrations of humic acid than the more positively charged filters. With Balston filters, at humic acid concentrations above 10 mg/liter, most of the virus was recovered in the filtrate. Fulvic acid, tested with Balston filters, did not interfere with virus recovery. With the electropositively charged filters, the humic materials adsorbed efficiently, even at high input concentrations. Interference with virus adsorption occurred at humic acid concentrations which were below the level of saturation of the filters. In addition, in high-volume experiments, humic acid led to premature blockage of the filters. The efficiency of virus recovery by a second concentration step, organic flocculation of the filter eluate, was tested. For all the filter types tested, this procedure was not affected by the presence of humic or fulvic acid in the input water.     

Land Use as a Driver of Patterns of Rodenticide Exposure in Modeled Kit Fox Populations

Although rodenticides are increasingly regulated, they nonetheless cause poisonings in many non-target wildlife species. Second-generation anticoagulant rodenticide use is common in agricultural and residential landscapes. Here, we use an individual-based population model to assess potential population-wide effects of rodenticide exposures on the endangered San Joaquin kit fox (Vulpes macrotis mutica). We estimate likelihood of rodenticide exposure across the species range for each land cover type based on a database of reported pesticide use and literature. Using a spatially-explicit population model, we find that 36% of modeled kit foxes are likely exposed, resulting in a 7-18% decline in the range-wide modeled kit fox population that can be linked to rodenticide use. Exposures of kit foxes in low-density developed areas accounted for 70% of the population-wide exposures to rodenticides. We conclude that exposures of non-target kit foxes could be greatly mitigated by reducing the use of second-generation anticoagulant rodenticides in low-density developed areas near vulnerable populations.     

Evaluation and optimization of immobilized lipase for esterification of fatty acid and monohydric alcohol

Commercial available lipases viz. Lipozyme™, Novozyme-735 and Candida antartica lipase-B (CAL-B) were immobilized on seven different supports by simple adsorption process. The importance of suitable enzyme–support combination in esterification of lauric acid and iso-propanol was validated experimentally. Effect of long chain fatty acids (C4–C18) and small chain monohydric alcohols (C1–C6) on specific activities of different immobilized lipases were evaluated. Lauric acid (C12) was found to be the most preferred fatty acid and t-amyl alcohol (C5) being the best alcohol. CAL-B adsorbed on Lewatit was the most efficient immobilized enzyme for esterification reaction. Selectivity constant for lauric acid (3.4) was the highest among all fatty acids tested, whereas there was not much difference in selectivity between different alcohols. Furthermore, increase in fatty acid unsaturation leads to decrease catalytic efficiency of immobilized CAL-B. The optimum conditions for t-amyllaurate synthesis were as follows: lauric acid—0.5 M, t-amyl alcohol—0.3 M and amount of immobilized enzyme—150 mg. Finally, CAL-B adsorbed on Lewatit was reused for three consecutive cycles.     

Studies on the potent bacterial mutagen, 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone: aqueous stability, XAD recovery and analytical determination in drinking water and in chlorinated humic acid solutions

3-Chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX) was detected by gas chromatography/mass spectrometry in drinking water samples from 3 locations in the U.S.A., and also in a chlorinated humic acid solution. MX appears to account for a significant proportion of the mutagenicity of these samples, as measured in the Ames test using strain TA100 without metabolic activation. Studies on recovery of MX from spiked water samples by XAD-2/8 resin adsorption/acetone elution indicated that sample acidification prior to resin adsorption was essential to the effective recovery of MX. The stability of MX in aqueous solution was pH and temperature dependent. At 23 degrees C the order of stability, based on persistence of mutagenic activity was found to be: pH 2 greater than pH 4 greater than pH 8 greater than pH 6. The half-life at pH 8 and 23 degrees C was 4.6 days. One of the degradation products has been tentatively identified as 2-chloro-3-(dichloromethyl)-4-oxo-2-butenoic acid, an open form of MX which appears to be in the "E" configuration. Overall, these results suggest that MX is formed during water chlorination as a result of reaction of chlorine with humic substances, and that a substantial fraction of the MX formed is likely to persist throughout the distribution system.     

A chromatographic approach to the determination of relative free energies of interaction between hydrophobic and amphiphilic amino acid side chains.

A liquid chromatographic stationary phase was prepared by covalently binding to the surface of microparticulate silica gel functionality (benzylsilane), which mimics the side chain of the amino acid phenylalanine. The chromatographic retentions of the N-acetyl C-(N'-methyl) amides of various hydrophobic and amphiphilic amino acids on this stationary phase were measured using an aqueous mobile phase. A retention order of Gly < Ala < Cys < Val < Met < Pro < Ile < Leu < Tyr < Phe < Trp is seen at room temperature. Chromatographic retentions were used to derive free energies of adsorption of the amino acid derivatives on the chromatographic support relative to that of the glycine derivative. The temperature dependencies of the retention of aromatic and aliphatic amino acid derivatives differ in curvature, indicating a qualitative difference in the absorption mechanism. An adsorption model for retention is proposed, and arguments are made as to the suitability of an adsorption model for describing the contacts between amino acid side chains during the initial steps of protein folding.     

Intraparticle diffusion processes during acid dye adsorption onto chitosan

The adsorption of five acid dyes onto chitosan was studied. The equilibrium capacities based on the Langmuir analysis were 1.54, 2.66, 1.11, 1.25 and 1.03 mmol/g chitosan for Orange 10 (AO10), Acid Orange 12 (AO12), Acid Red 18 (AR18), Acid Red 73 (AR73) and Acid Green 25 (AG25) respectively. The batch adsorption rate for the five systems based on an intraparticle diffusion rate parameter derived from the plots of dye adsorbed versus the square root of time indicated that the adsorption mechanism was predominantly intraparticle diffusion but there was also a dependence on pore size as the dye diffuses through macropore, mesopore and micropore respectively.