The influence of organic matter on sorption and fate of glyphosate in soil - Comparing different soils and humic substances

Soil organic matter (SOM) is generally believed not to influence the sorption of glyphosate in soil. To get a closer look on the dynamics between glyphosate and SOM, we used three approaches: I. Sorption studies with seven purified soil humic fractions showed that these could sorb glyphosate and that the aromatic content, possibly phenolic groups, seems to aid the sorption. II. Sorption studies with six whole soils and with SOM removed showed that several soil parameters including SOM are responsible for the strong sorption of glyphosate in soils. III. After an 80 day fate experiment, ∼40% of the added glyphosate was associated with the humic and fulvic acid fractions in the sandy soils, while this was the case for only ∼10% of the added glyphosate in the clayey soils. Glyphosate sorbed to humic substances in the natural soils seemed to be easier desorbed than glyphosate sorbed to amorphous Fe/Al-oxides.     

The role of humic substances in chromium sorption onto natural organic matter (peat)

To elucidate mechanisms of Cr³⁺ sorption onto the unaltered solid natural organic matter, the comparative studies of this ion binding from a solution at pH 4.0 onto three selected particle size fractions: 2000–1000 μm, 630–200 μm and 63–20 μm of markedly different HS content and structure, separated by a wet sieving from an overall sample of peat (Brushwood Peat Humus) were carried out. Comparable patterns of COOH groups and CEC_t confirmed that for cation exchange capacity were responsible mainly cations connected with COO⁻ functional groups. It was though found that aliphatic acids in the solid state did not take part in Cr³⁺ binding, thus the finest studied fraction 63–20 μm of the highest contents of functional groups showed the lowest sorption capacity for Cr³⁺, while similar patterns of sorbed Cr³⁺, soluble HS content and base CEC₀ indicated that these parameters were directly interrelated. The base ion exchange processes determined by CEC₀ (with Ca²⁺ as a predominant exchangeable cation) appeared to be not the major mechanisms responsible for Cr³⁺ sorption. For this metal, strong binding to insoluble large molecular weight organic pool two- to threefold prevailed over the ion exchange processes. Very low acid desorption indicated generally low mobility of Cr³⁺-organic compounds.     

Sorption of tebuconazole onto selected soil minerals and humic acids

The aim of the present study was to investigate tebuconazole sorption on common soil minerals (birnessite, ferrihydrite, goethite, calcite and illite) and humic acids (representing soil organic matter). Tebuconazole was used (i) in the commercial form Horizon 250 EW and (ii) as an analytical grade pure chemical. In the experiment with the commercially available tebuconazole, a significant pH-dependent sorption onto the oxides was observed (decreasing sorption with increasing pH). The highest sorption was found for ferrihydrite due to its high specific surface area, followed by humic acids, birnessite, goethite and illite. No detectable sorption was found for calcite. The sorption of analytical grade tebuconazole on all selected minerals was significantly lower compared to the commercial product. The sorption was the highest for humic acids, followed by ferrihydrite and illite and almost negligible for goethite and birnessite without any pH dependence. Again, no sorption was observed for calcite. The differences in sorption of the commercially available and analytical grade tebuconazole can be attributed to the additives (e.g., solvents) present in the commercial product. This work proved the importance of soil mineralogy and composition of the commercially available pesticides on the behavior of tebuconazole in soils.     

Reactions of compost-derived humic substances with lead, copper, cadmium, and zinc

Thermodynamic stability constants of the formation of complexes from the reactions of humic substances with various metals are usually used as parameters to judge the reactivities of both humic substances and metals. However, in calculating the thermodynamic stability constants, complicated processes for the acquisition of activities of components in reactions are absolutely inevitable. In this study, we investigated the average conditional concentration quotients of the complexes formed from the reaction of metals with humic substances and the relations of these quotients to thermodynamic stability constants. The characterized humic substances including HA (MW>1,000), FA (MW>1,000), and FA (MW<1,000) extracted from a swine compost were prepared to react with Pb, Cu, Cd, and Zn at 25 degrees C and at pH 4.00 and 6.50. Reactions of HA (MW>1,000), FA (MW>1,000), and FA (MW<1,000) with the four metals were carried out at 1:0.1, 1:0.5, 1:1, 1:5, and 1:10 ligand:metal stoichiometry. The concentrations of the free ions of Pb, Cu, Cd, and Zn in the reaction systems of metal-HA suspensions and metal-FA solutions were measured by anodic stripping voltammetry (ASV). The sequence of the average conditional concentration quotients of the formed complexes from the reaction of humic substances with metals was FA(MW<1,000)>FA(MW>1,000)>HA(MW>1,000), showing the relative reactivities of the fractions of swine compost-derived humic substances. The sequence of reacting metals with humic substances was Pb>Cu>Cd>Zn, which is in good agreement with the sequence reported by judging the thermodynamic stability constants. The average conditional concentration quotients of the formed complexes from the reaction of humic substances with metals were thus useful parameters that can be directly related to thermodynamic stability constants and other parameters.     

Effect of copper on the adsorption of p-nitrophenol onto soils

The effect of copper on adsorption of p-nitrophenol on two typical Chinese soils was investigated using a batch-equilibration method. Adsorption experiments were carried out when both copper and p-nitrophenol were adsorbed simultaneously, and when copper was previously adsorbed on soils. It was observed that adsorption of p-nitrophenol decreased with increasing copper concentrations thereby indicating a competition between copper and p-nitrophenol for occupying the adsorption sites on soils. Moisture increased the hydrated sphere and the acidity of water surrounding the cation, which further reduced the adsorption of p-nitrophenol. Fourier transform infrared spectroscopy study provided the direct evidence for the coordination of p-nitrophenol sorbed by soils with metal cation in n-hexane system. It was observed that the perturbations included a red shift of the nu(asym) (NO) band, a concomitant blue-shift of the nu(sym) (NO) band and a blue-shift of C-N band when compared with the infrared spectra obtained from water solution.     

The effect of dissolved glyphosate upon the sorption of copper by three selected soils

The effect of the pesticide glyphosate (GPS) on adsorption processes of copper onto three soils of different characteristics has been studied. Cu adsorption decreases in general with increasing GPS concentration in solution, due principally to the lower equilibrium pHs, although this is not the only variable affecting copper adsorption. For the same pH values, Cu adsorption is higher in two of the three soils in the presence of GPS, but for the third soil, Cu adsorption is higher in the absence of GPS. This behavior is explained by the possibility of GPS adsorption on these soils and by the formation of Cu-GPS complexes in solution. The soils showing a higher Cu adsorption in the presence of GPS than in its absence for the same pH are able to adsorb this pesticide. In these soils, copper can be adsorbed directly on the soil surfaces, and also through the formation of bonds with GPS previously adsorbed. The third soil was not able to adsorb GPS. Consequently, all the pesticide remained in solution, forming strong Cu complexes with low tendency to be adsorbed on this soil. For this reason, the concentration of free Cu in solution is drastically reduced, and the adsorption of copper on this soil is lower.     

Effects of pollution on humic substances

To assess effects of industrial and environmental pollution on analytical characteristics of humic substances, we isolated humic acids (HA's) and fulvic acids (FA's) from unpolluted and polluted soils and sediments. Following purification, the HA's and FA's were characterized by elemental (C, H, O, N, S) and functional group (CO2H, phenolic OH, total acidity) analyses, infrared (IR) spectrophotometry, differential thermal analysis (DTA) and by metal (Fe, Al, Cu, Mn, Pb, Ni, Co, Zn, Cr, Cd, Hg, Ca and Mg) analyses. Si was also determined in all samples. Polluted HA's and FA's contained more N and S but less O and were richer in all metals and Si than were unpolluted ones. IR spectra showed that polluted humic materials were enriched in COO- groups, secondary non-cyclic amides and possible also in SO3H groups. DTA curves indicated that polluted HA's and FA's were more thermostable than unpolluted HA's and FA's. Unusually high N, S, Cu, Cr, Zn and Hg contents of humic materials appear to be useful indicators of soil and sediment pollution.     

Effects of pollution on humic substances

Abstract

To assess effects of industrial and environmental pollution on analytical characteristics of humic substances, we isolated humic acids (HA's) and fulvic acids (FA's) from unpolluted and polluted soils and sediments. Following purification, the HA's and FA's were characterized by elemental (C, H, O, N, S) and functional group (CO₂H, phenolic OH, total acidity) analyses, infrared (IR) spectrophotometry, differential thermal analysis (DTA) and by metal (Fe, Al, Cu, Mn, Pb, Ni, Co, Zn, Cr, Cd, Hg, Ca and Mg) analyses. Si was also determined in all samples.

Polluted HA's and FA's contained more N and S but less 0 and were richer in all metals and Si than were unpolluted ones. IR spectra showed that polluted humic materials were enriched in COO^‐ groups, secondary non‐cyclic amides and possible also in SO₃H groups. DTA curves indicated that polluted HA's and FA's were more thermostable than unpolluted HA's and FA's. Unusually high N, S, Cu, Cr, Zn and Hg contents of humic materials appear to be useful indicators of soil and sediment pollution.     

Specific association of 36Cl with low molecular weight humic substances in soils

Soils initially contaminated with ³⁶Cl in the chloride form were subjected to solid–liquid extractions using a variety of reagents including deionised water and 1 M sodium hydroxide (NaOH). 1 M NaOH was found to result in the greatest recovery of ³⁶Cl from the soils, a result which provided initial evidence that radioactive chlorine became attached to humic substances present naturally within the soils. Deionised water and 1 M NaOH extracts were subjected to analysis involving separation by gel filtration chromatography (GFC). It was found that ³⁶Cl in 1 M NaOH extracts associated preferentially with low molecular weight (LMW) fractions of humic substances whereas, in deionised water extracts, ³⁶Cl appeared to be present exclusively in the chloride form. Previous literature evidence, mainly from highly organic forest soils, suggests that conversion of stable chlorine from chloride to organic forms can occur as a result of biological action. The present paper also presents good evidence for the specific attachment of stable chlorine (³⁷Cl) to a LMW humic fraction, again demonstrated using GFC separation. Current risk assessments of the deep geological disposal of solid radioactive wastes containing ³⁶Cl typically assume a very low degree of sorption based on the notion that the predominant environmental species of radiochlorine is chloride. This paper concludes with a brief discussion on the implications of organochlorine formation in the biosphere for assessment of the radiological impact of deep geological disposal of solid radioactive wastes.     

Quantifying the influence of humic acid adsorption on colloidal microsphere deposition onto iron-oxide-coated sand

This article describes an approach for quantifying microsphere deposition onto iron-oxide-coated sand under the influence of adsorbed Suwannee River Humic Acid (SRHA). The experimental technique involved a triple pulse injection of model latex microspheres (microspheres) in pulses of (1) microspheres, followed by (2) SRHA, and then (3) microspheres, into a column filled with iron-coated quartz sand as a water-saturated porous medium. A random sequential adsorption model (RSA) simulated the gradual rise in the first (microsphere) breakthrough curve (BTC). Using the same model calibration parameters a dramatic increase in concentration at the start of the second particle BTC, generated after SRHA injection, could be simulated by matching microsphere concentrations to extrapolated RSA output. RSA results and microsphere/SRHA recoveries showed that 1 μg of SRHA could block 5.90 ± 0.14 × 10⁹ microsphere deposition sites. This figure was consistent between experiments injecting different SRHA masses, despite contrasting microsphere deposition/release regimes generating the second microsphere BTC.     

Organic compounds adsorption onto activated carbon: the effect of association between dissolved humic substances and pesticides

The quantitative determination of pesticide binding to dissolved humic substances is relevant to both water treatment operation using activated carbon adsorption process and the application of transport models that predict the environmental distribution patterns of a given hydrophobic contaminant. In this study and in a first set of experiments, the extent of binding between (i) three pesticides of environmental concern, aldicarb, lindane and pentachlorophenol, and (ii) dissolved commercial humic acid and soil extracted fulvic acid, was determined using dialysis experiments and water solubility enhancement tests. In a second set of experiments, the influence of dissolved humic substances or pesticide on the retention of the other co-adsorbate onto activated carbon was investigated in binary systems. It was found that association was negligible for aldicarb and that the pesticide sorption onto activated carbon was not affected by humic acid (8.5 mg liter(-1) DOC). The association constants K for lindane and pentachlorophenol were identical in the presence of fulvic acid (logK=4.1) but lower than that observed with humic acid. In the presence of humic acid, binding affinity for pentachlorophenol (logK=4.6) was higher than the one observed for lindane (logK=4.4), despite its much higher water solubility. This observation suggests that the aromatic character of the pentachlorophenol molecule contributes to association interactions with humic acid. From co-adsorption experiments onto activated carbon it was found that fulvic acid (7.7 mg litre(-1) DOC) slightly enhances sorption kinetics of pentachlorophenol. Lindane (1 mg litre(-1)) does not affect sorption kinetics for fulvic acid but markedly enhances both the sorption kinetics and adsorptive capacity for humic acid. Activated carbon retention of dissolved humic substances or pesticide appears to be enhanced by the association potential that exists between these co-adsorbates in some binary systems.     

Potential availability of heavy metals to phytoextraction from contaminated soils induced by exogenous humic substances

Effective phytoremediation of soils contaminated by heavy metals depends on their availability to plant uptake that, in turn, may be influenced by either the existing soil humus or an exogenous humic matter. We amended an organic and a mineral soil with an exogenous humic acid (HA) in order to enhance the soil organic carbon (SOC) content by 1% and 2%. The treated soils were further enriched with heavy metals (Cu, Pb, Cd, Zn, Ni) to a concentration of 0, 10, 20, and 40 microg/g for each metal and allowed to age at room temperature for 1 and 2 months. After each period, they were extracted for readily soluble and exchangeable (2.5% acetic acid), plant-available (DTPA, Diethylentriaminepentaacetic acid), and occluded (1 N HNO(3)) metal species. Addition of HA generally reduced the extractability of the soluble and exchangeable forms of metals. This effect was directly related to the amount of added HA and increased with ageing time. Conversely, the potentially plant-available metals extracted with DTPA were generally larger with increasing additions of exogenous HA solutions. This was attributed to the formation of metal-humic complexes, which ensured a temporary bioavailability of metals and prevented their rapid transformation into insoluble species. Extractions with 1 N HNO(3) further indicated that the added metals were present in complexes with HA. The observed effects appeared to also depend on the amount of native SOC and its structural changes with ageing. The results suggest that soil amendments with exogenous humic matter may accelerate the phytoremediation of heavy metals from contaminated soil, while concomitantly prevent their environmental mobility.     

Increased retention of polycyclic aromatic hydrocarbons in soils induced by soil treatment with humic substances

The analytical recovery of a mixture of polycyclic aromatic hydrocarbons (PAHs) was determined from a soil before and after oxidation with hydrogen peroxide, and subsequently treated with increasing amounts of an exogenous humic acid and subjected to different incubation periods. The release of PAHs from soil depended on the specific structure and physico-chemical properties of each PAH, and increased with additions of exogenous humic materials for both the oxidized and non-oxidized soil as well as with time of PAH permanence in soil. PAH recoveries were lower in the non-oxidized soil, thereby revealing the importance of native organic matter in increasing PAH retention in soils. This study shows that mobility of PAHs in soils can be controlled by soil conditioning with humic substances.     

AhR-mediated and antiestrogenic activity of humic substances

Humic substances (HS) were for decades regarded as inert in the ecosystems with respect to their possible toxicity. However, HS have been recently shown to elicit various adverse effects generally attributed to xenobiotics. In our study, we used MVLN and H4IIE-luc cell lines stably transfected with luciferase gene under control of estrogen receptor (ER) and Ah receptor (AhR; receptor connected with so-called dioxin-like toxicity) for assessment of anti/estrogenic and AhR-mediated effects of 12 commercially available humic substances. Out of those, five humic acids were shown to induce AhR-mediated activity with relative potencies related to TCDD 2.6 x 10(-8)-7.4 x 10(-8). Organic extracts of HS solutions also elicited high activities what means that lipophilic molecules are responsible for a great part of effect. However, relatively high activity remaining in extracted solution suggests also presence of polar AhR-agonists. Contribution of persistent organic compounds to the observed effects was ruled out by H(2)SO(4) treatment. Eight out of twelve HS elicited significant antiestrogenic effects with IC(50) ranging from 40 to 164 mg l(-1). The possible explanations of the antiestrogenic effect include sorption of 17-beta-estradiol (E2) on HS, changes in membrane permeability for E2 or another specific mechanism.     

Co-contaminant effects on ofloxacin adsorption onto activated carbon,graphite, and humic acid

Given their voluminous application, significant amounts of fluoroquinolones are discharged into the environment through wastewater effluent. Adsorption has been shown to be a critical process controlling the environmental behaviors of fluoroquinolones. Competition between ofloxacin (OFL) and naphthalene (NAP)/bisphenol A (BPA) and their adsorption on activated carbon (AC), graphite (GP), and humic acid (HA) were investigated. The suppressed adsorption of OFL was observed on AC and GP, but not on HA, by NAP or BPA. Moreover, for AC, the competition by NAP was slightly stronger than that by BPA. However, for GP, the competition with BPA was higher than that with NAP. These observations indicate that competitive adsorption of OFL with respect to NAP/BPA depends on the degree of overlap of adsorption sites, as interpreted by the following: (i) AC can provide overlapping adsorption sites for OFL, BPA, and NAP, which include non-specific adsorption sites, such as hydrophobic sites, π-π interactions, and micropore filling; (ii) π-π interactions and hydrogen bonding might be responsible for the strong competitive adsorption between BPA and OFL on GP; and (iii) OFL adsorbs on HA through specific adsorption force—electrostatic attraction, with which NAP and BPA cannot compete.

     

Sorption of thallium(I) onto geological materials: influence of pH and humic matter

The sorption behaviour of the severely toxic heavy metal thallium (Tl) as a monovalent cation onto three representative materials (goethite, pyrolusite and a natural sediment sampled from a field site) was examined as a function of pH in the absence and presence of two natural humic acids (HAs), using ²⁰⁴Tl(I) as a radiotracer. In order to obtain a basic understanding of trends in the pH dependence of Tl(I) sorption with and without HA, sorption of HAs and humate complexation of Tl(I) as a function of pH were investigated as well. In spite of the low complexation between Tl(I) and HAs, the presence of HAs results in obvious alterations of Tl(I) sorption onto pyrolusite and sediment. An influence on Tl(I) sorption onto goethite was not observed. Predictions of K_d (distribution coefficient) for Tl(I) on goethite in the presence of HAs, based on a linear additive model, agree well with the experimental data, while a notable disagreement occurs for the pyrolusite and sediment systems. Accordingly, it is suggested that HAs and goethite may act as a non-interacting sorbent mixture under the given conditions, but more complex interactions may take place between the HAs and the mineral phases of pyrolusite or sediment.     

Characteristic and mechanism of sorption and desorption of benzene on humic acid

Environmental Science and Pollution Research - The sorption/desorption behaviors of benzene, toluene, ethylbenzene, and xylene (BTEX) on soil organic matter (SOM) have a significant influence on...     

Time and pH-dependent sorption of the veterinary antimicrobial sulfathiazole to clay minerals and ferrihydrite

Substantial amounts of sulfonamides, ionizable, polar veterinary antimicrobials, may reach the environment by spreading of manure. Sorption to soils and sediments is a crucial but not sufficiently understood process influencing the environmental fate of sulfonamides. Therefore, we investigated sorption of sulfathiazole to clay minerals (montmorillonite, illite) and ferrihydrite for varying pH values and two contact times (1d, 14 d) under sterile conditions. Results were compared to sulfathiazole sorption to organic sorbents. Sulfathiazole sorption to inorganic sorbents exhibited pronounced pH dependence consistent with sorbate speciation and sorbent charge properties. While sulfathiazole cations were most important for sorption to clay minerals, followed by neutral species, ferrihydrite was a specific anion sorbent, showing significant sorption only between pH 5.5-7. Experiments revealed a substantial increase of sorption with time for ferrihydrite (pH 5.5-7) and illite (pH<5.5). Reasons may be disaggregation of clay minerals and, for ferrihydrite, diffusion and sorption of sulfathiazole in micropores. Independent of contact time and pH, sorption to inorganic sorbents was more than an order of magnitude lower than to organic sorbents. This implies that in many topsoils and sediments inorganic sorbents play a minor role. Our results highlight the need to account for contact time and speciation when predicting sulfonamide sorption in the environment.     

Influence of sorption to dissolved humic substances on transformation reactions of hydrophobic organic compounds in water. Part II: hydrolysis reactions

The effect of dissolved humic acid (HA) on two types of hydrolysis reactions was investigated: (I) dehydrochlorination of gamma-hexachlorocyclohexane (HCH) and 1,1,2,2-tetrachloroethane (TeCA) as a reaction involving hydroxide ions (OH(-)) and (II) hydrolysis of 1-octyl acetate (OA) which is catalyzed by H(+) at the applied pH value (pH 4.5). The rate of TeCA hydrolysis was not affected by addition of 2 g l(-1) of HA at pH 10 (k' = 0.33 h(-1)) but HCH hydrolysis was significantly inhibited (k' = 4.6 x 10(-3) h(-1) without HA and 2.8 x 10(-3)h(-1) at 2 g l(-1) HA). HCH is sorbed by 51% whereas TeCA sorption is insignificant at this HA concentration. Sorbed HCH molecules are effectively protected due to electrostatic repulsion of OH(-) by the net negative charge of the HA molecules. In contrast, OA hydrolysis at pH 4.5 (k' = 1.6 x 10(-5) h(-1)) was drastically accelerated after addition of 2 g l(-1) HA (k' = 1.1 x 10(-3) h(-1)). The ratio of the pseudo-first-order rate constants of the sorbed and the freely dissolved ester fraction is about 70. H(+) accumulation in the microenvironment of the negatively charged HA molecules was suggested to contribute to the higher reaction rate for the sorbed fraction in case of this H(+)-catalyzed reaction. Analogous effects from anionic surfactants are known as micellar catalysis.     

Effects of organic acids on adsorption of lead onto montmorillonite,goethite and humic acid

Adsorption isotherms for Pb onto six soil components (quartz, feldspar, kaolinite, montmorillonite, goethite and humic acid) were studied. The influence of pH, EDTA and citric acid on the adsorption of Pb onto montmorillonite, goethite and humic acid were considered. Results indicate that the experimental data fit the Langmuir Adsorption Isotherm. The adsorption capacity for Pb at pH 6 was found to be in the order: humic acid (22.7 mg g(-1)) > goethite (11.04 mg g(-1)) > montmorillonite (10.4 mg g(-1)) > kaolinite (0.91 mg g(-1)) > feldspar (0.503 mg g(-1)) > quartz (0.148 mg g(-1)). Generally, the amount of Pb adsorbed onto montmorillonite, goethite and humic acid decreased with increasing concentrations of EDTA and citric acid and with increases in alkality. However, there were two exceptions: (1) addition of citric acid increased the amount of Pb adsorbed onto humic acid; and (2) the amount of Pb adsorbed onto goethite decreased with increasing pH in the presence of EDTA. Some mechanisms involved in the adsorption reactions are discussed.