- [Show abstract] [Hide abstract] ABSTRACT: Spatial heterogeneity in the chemical concentration of interstitial water in the vadose zone was previously observed under apparently homogeneous surface conditions on two leveled fields sprinkler irrigated with treated sewage effluents on the phreatic Coastal Plain aquifer of Israel. This phenomenon greatly hampers the monitoring of groundwater quality. In this study we report on the presence of puddles of different size and shape that were sporadically observed in these fields. Temporal variability noted in the concentration of treated sewage effluents components in the puddles were considered to be related to evapotranspiration and degradation. For example: increases in the electrical conductivity (up to 1.32mS/cm), and in the concentrations of chloride (up to 521mg/L), dissolved organic carbon (up to 28.4mg/L), and carbamazepine (up to 780ng/L) and decreases in the concentrations of nitrate (up to 20.1mg/L) and caffeine (3396ng/L). Variable trends in concentration were observed for sulfamethoxazole, venlafaxine, 10-hydroxy-10,11-dihydrocarbamazepine and o-desmethylvenlafaxine. The presence of puddles was not necessarily related to areas with high irrigation water input. It is postulated that the continuous chemical variability in the puddles, whose location and size are also variable, determine a heterogeneous influx of solutes into the soil and subsequently into the vadose zone. Copyright © 2015 Elsevier Ltd. All rights reserved.
- [Show abstract] [Hide abstract] ABSTRACT: Six boreholes were drilled during the course of a year to a depth of 2 m beneath the water table, located at a depth of about 28 m, under agricultural land sprinkler irrigated with treated sewage effluents in the Coastal Plain aquifer of Israel to determine the extent of penetration of 20 pharmaceuticals and personal care products (PPCPs) into the unsaturated zone. The fields were planted to turf and had different histories of effluent irrigation. From each borehole, 7 to 21 samples were taken for analysis of PPCPs, as was the underlying groundwater. Nine PPCPs (carbamazepine and its metabolite 10-hydroxy-10,11-dihydrocarbamazepine, acridone and acridine, venlafaxine, sulfamethoxazole, oxcarbazepine, O-desmethylvenlafaxine, and caffeine) were detected in the vadose zone of the study area to a depth of 27 m. For example, the detected concentrations of carbamazepine were up to 109 ng/kg, of caffeine up to 36,700 ng/kg, and of venlafaxine up to 50 ng/kg. Only five of the compounds (carbamazepine, acridone, venlafaxine, sulfamethoxazole, and caffeine) were found in the underlying groundwater with concentrations in the nanogram per liter range. The results of this work show that significant amounts of PPCPs can penetrate even a thick vadose zone of 27 m with sections containing up to 50% clay and up to 0.40% soil organic C. Venlafaxine, for example, penetrated the vadose zone at an average velocity of 2.8 to 4 m/yr. Irrigation with treated sewage effluents or contaminated water should be carefully considered if the penetration of PPCPs into groundwater is undesirable.
- [Show abstract] [Hide abstract] ABSTRACT: Field-scale transport of conservative and reactive solutes through a deep vadose zone was analyzed by means of two different model processes for the local description of the transport. The first is the advection dispersion equation (ADE) model, and the second is the mobile-immobile (MIM) model. The analyses were performed by means of three-dimensional (3-D), numerical simulations of flow and transport considering realistic features of the flow system, pertinent to a turf field irrigated with treated sewage effluents (TSE). Simulated water content and concentration profiles were compared with available measurements of their counterparts. Results of the analyses suggest that the behavior of both solutes in the deep vadose zone of the Glil Yam site is better quantified by the MIM model than by the ADE model. Reconstruction of the shape of the measured solute concentration profiles using the MIM model required relatively small mass transfer coefficient, γ, and relatively large volume fraction of the immobile water, θim. This implies that for an initially non-zero solute concentration profile, as compared with the MIM model, the ADE model may significantly overestimate the rate at which solutes are loaded in the groundwater. On the contrary, for an initially zero solute concentration profile, as compared with the MIM model, the ADE model may significantly underestimate solute velocities and early arrival times to the water table. These findings stem from the combination of relatively small γ and relatively large θim taken into account in the MIM model. In the first case, this combination forces a considerable portion of the solute mass to reside in the immobile region of the water-filled pore space, while the opposite is true in the second case.
- [Show abstract] [Hide abstract] ABSTRACT: The use of treated effluents in agriculture for irrigation has become the mainstay in Israel and other parts of the world due to increasing population and the limited amount of high-quality water. While effluent irrigation has immediate benefits, such as mitigating water shortages and providing plant nutrients, the disadvantages and potential risks associated with its long-term use need to be evaluated if it is to be considered a sustainable practice. Among the potential risks associated with effluent irrigation is the presence of anthropogenic chemicals in the effluents (e. g., hormones, pharmaceuticals, and pesticides), enhanced transport of these chemicals out of the root zone due to their interaction with effluent-borne dissolved organic matter (DOM), and the possible uptake of these anthropogenic chemicals by plants and crops. DOM may reduce the sorption of organic pollutants through stable DOM-pollutant interactions in solution or by competing with the pollutant molecules for the sorption sites on the soil surface. The extent and nature of the interactions of dissolved organic matter with organic pollutants depend on factors such as the nature of the organic compound and the size, polarity, and molecular configuration of the DOM. In addition to the potential risks associated with effluent-borne DOM, contaminants present in treated wastewater may leach into groundwater used as a drinking water source or enter aquatic ecosystems through irrigation runoff. There are also concerns about whether these organic micro-contaminants can be taken up by plants and crops. A large number of potentially problematic organic micropollutants have been identified in treated wastewater and in streams receiving treated effluent. Classes of pollutants identified or potentially present in treated wastewater include pharmaceuticals, personal care product ingredients, nutraceuticals/herbal remedies, flame retardant chemicals, plasticizers, and disinfection byproducts. In this paper we review some of the potential risks posed by irrigation with treated effluent (wastewater), with a specific emphasis on organic chemicals present in the wastewater and soil-applied pesticides.
- [Show abstract] [Hide abstract] ABSTRACT: Background and Aims Amendment of soil by biochar may reduce efficacy of soil-applied herbicides due to sorption. Methods Bioassays with Green Foxtail (Setaria viridis) tested the influence of two biochars on phytoavailability of S-metolachlor and sulfentrazone under biochar amendment of 0, 13, 26 and 52 Mg ha-1. Results Adsorption of both herbicides was an order of magnitude greater on a high specific surface area (SSA) biochar (EUC-800; SSA 242 m2 g-1) than on a low SSA biochar (BC-1; SSA 3.6 m2 g-1). Herbicide doses near the lowest recommended label rates controlled the weed at 13 and 26 Mg ha-1 of BC-1; sulfentrazone was also effective at 52 Mg BC-1 ha-1. These same herbicide doses controlled weed germination and development only at 13 Mg ha-1 of EUC-800; at herbicide doses near the highest label rates, weed control was also achieved at 26 Mg EUC-800 ha-1, but not at 52 Mg EUC-800 ha-1. Conclusions Increased doses of soil-applied herbicides cannot necessarily offset decreases in herbicide phytoavailability in biochar-amended soils, particularly if the biochar has a high SSA. Considering the long half-life of biochar in soil, pest control needs will be best served by low SSA biochars.
- [Show abstract] [Hide abstract] ABSTRACT: Use of genetically modified cultivars resistant to the herbicide glyphosate (N-phosphonomethylglycine) is strongly associated with conservation-tillage (CsT) management for maize ( Zea mays L.), soybean ( Glycine max L.), and cotton ( Gossypium hirsutum L.) cultivation. Due to the emergence of glyphosate-resistant weed biotypes, alternate weed management practices are needed to sustain CsT use. This work focused on metolachlor use (2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide) in a CsT system. The fate and efficacy of granular and emulsifiable concentrate (EC) formulations or an EC surrogate were compared for CsT cotton production in the Atlantic Coastal Plain region of southern Georgia (USA). The granular formulation, a clay-alginate polymer, was produced in the authors' laboratory; EC was a commercial product. In field and laboratory dissipations the granular metolachlor exhibited 8-fold greater soil persistence. Rainfall simulation runoff assessments indicated that use of the granular formulation in a common CsT system, strip-tillage (ST), may reduce metolachlor runoff loss when compared to conventional tillage (CT) management or when EC formulations are used in the ST system. Metolachlor leaching assessments using field-deployed lysimeters showed some tillage (ST > CT) and formulation (EC > granular) differences. Overall leaching was generally small when compared to runoff loss. Finally, greenhouse bioassays showed control of two weed species with the granular was greater than or equal to that of the EC formulation; however, the granular formulation suppressed cotton growth to a greater extent. In sum, this metolachlor granular formulation has advantages for CsT cotton production; however, additional research is needed to assess impacts on crop injury.
- [Show abstract] [Hide abstract] ABSTRACT: Sudden wilt (vine decline) of melon caused by Monosporascus cannonballus is a problem in arid and semiarid regions worldwide. Preplanting soil disinfestation with methyl bromide, a common treatment for disease management, has been banned in many countries, raising the need for alternative disease-control measures. Soil fungicide application during the growing season is one possible treatment. Twelve fungicides were evaluated in vitro for M. cannonballus suppression, seven of those were evaluated under field conditions. The fungicides azoxistrobin, prochloraz and pyraclostrobin + boscalid exhibited high and similar efficacies in controlling sudden wilt disease under field conditions. Fludioxonil applied at high rates was also effective but was phytotoxic. Fluazinam, the first fungicide found capable of suppressing sudden wilt and one which has been used in Israel since 2000, was less effective. The results indicate that two applications of a fungicide during the short fall season should be sufficient for effective control of the disease. In the long spring season, at least three applications are needed to protect the melon crop. Melon fruits were examined for fungicide residues and only boscalid residues were found. This fungicide was therefore limited to the first application before fruit set. KeywordsAzoxystrobin-Melon- Monosporascus cannonballus -Prochloraz
- [Show abstract] [Hide abstract] ABSTRACT: The use of quantitative structure-activity relationships (QSARs) based on linear free-energy relationships (LFERs), molecular connectivity (MC) indices, and on more sophisticated quantum mechanical approaches, for predicting soil sorption coefficients is reviewed. The nature and energetics of sorption of organic chemicals by soils are also briefly reviewed.On the basis of the data presented we may conclude that from the large body of physicochemical parameters, the n-octanol/water partition coefficient (Kow) has been most successful in modeling sorption data of organic chemicals. From the large set of nonempirical parameters that are defined in terms of a compound's 2- or 3-dimensional structure and can be derived for any chemical without experimental efforts, the MC indices have proven the most reliable and easily available.
- [Show abstract] [Hide abstract] ABSTRACT: The assemblages of soil organic matter (SOM) and mineral components present in soils are considerably more heterogeneous than are organoclays and hence the latter cannot directly serve as models for the complex systems that are soils. Yet, comparison between the behavior of soils and of organoclays vis a vis organic sorbates may shed light on the nature of the interaction of organic sorbates with SOM and the architecture of this key environmental sorbent. This presentation provides a comparative examination of recently published data on the effect of sorbent hydration on sorption interactions of selected probe organic compounds with a model organoclay (Na-montmorillonite exchanged with n-hexadecyltrimethylammonium) and model SOM. Effect of the sorbent hydration has been established by comparing the sorption isotherms of a probe organic compound measured on a (dried) sorbent from water and from inert, non-aqueous medium (n-hexadecane). To eliminate differences in compound-bulk solvent interactions, a comparison of sorption isotherms was carried out using the compound activities instead of compound concentrations in a solution phase. A different effect of sorbent hydration on the interactions of organic compounds with organoclays and with SOM is observed. While sorbent hydration may significantly enhance the sorbate's interactions with SOM, in the case of the organoclays it strengthened interactions to a much lesser extent or even weakened them. This difference may be associated with a large number of functional groups present in SOM and the non-covalent, intra- as well as inter-molecular links they form. Such links block sorbate access but are broken in the presence of water. This effect is not present in organoclays which lack functional groups in the quasi-organic layer. This contrast supports the previously proposed idea that the presence and disruption of non-covalent linkages formed between functional groups in the SOM structure as well as a direct involvement of the SOM-sorbed water in the sorption process have an important role in the interactions between organic compounds and SOM.
- [Show abstract] [Hide abstract] ABSTRACT: The potential role of mechanochemical processes in enhancing degradation of imazaquin by soil components is demonstrated. The investigated components include montmorillonite saturated with Na(+), Ca(2+), Cu(2+)and Al(3+), Agsorb (a commercial clay mix), birnessite and hematite. The mechanical force applied was manual grinding of mixtures of imazaquin and the minerals, using mortar and pestle. The degradation rates of imazaquin in these mixtures were examined as a function of the following parameters: time of grinding, herbicide load (3.9, 8.9, 16.7 and 26.6 mg imazaquin per g mineral), temperature (10, 25, 40 and 70 degrees C), acidic/basic conditions, and dry or wet grinding. Dry grinding of imazaquin for 5 min with Al-montmorillonite or with hematite resulted in 56% and 71% degradation of the imazaquin, respectively. Wet grinding slightly reduced the degradation rate with hematite and entirely cancelled the enhancing effect of grinding with Al-montmorillonite. Wet grinding in the presence of the transition metals: Ni(2+), Cu(2+), Fe(3+) added as chlorides was carried out. Addition of Cu(2+) to Na-montmorillonite loaded with imazaquin was the most effective treatment in degrading imazaquin (more than 90% of the imazaquin degraded after 5 min of grinding). In this treatment, Cu-montmorillonite formation during the grinding process was confirmed by XRD and accordingly, grinding with Cu-montmorillonite gave similar degradation values. LC-MS analysis revealed that the mechanochemical transformation of imazaquin resulted in the formation of a dimer and several breakdown products. The reported results demonstrate once again that mechanochemical procedures offer a remediation avenue applicable to soils polluted with organic contaminants.
- [Show abstract] [Hide abstract] ABSTRACT: Spilled or leaked petroleum products often contaminate groundwater and subsequently evaporate through the soil to the atmosphere by gaseous diffusion. This study developed and tested a model that can predict the rate of diffusion through a dry soil column of the individual components in a liquid mixture when they are of low or intermediate volatility. We derived equations that relate the vapor pressures of the components to their sorption from the gaseous phase by the soil. We also provided for slow sorption. Three cases of increasing complexity were treated: evaporation of a mixture directly into the atmosphere; evaporation of a mixture through a soil column without significant sorption; and finally, evaporation through a highly sorbing soil column, for which a computer program was written. The model has been tested by comparing the evaporation of m-xylene and n-dodecane mixtures through sand, and air-and oven-dry Evesham clay soil (Aquic Eutrochrept or orthic grumsquert) in the laboratory. The equilibrium sorption isotherms and sorption kinetics for these soils and compounds were determined in separate experiments, and other parameters were obtained from the literature, so that the model contained no adjustable fitting parameters. There was fair agreement between the model predictions and the experimental results. 23 refs., 9 figs., 5 tabs.
- [Show abstract] [Hide abstract] ABSTRACT: Sorption of nitrobenzene, phenol, and m-nitrophenol from water and n-hexadecane was measured on Na-montmorillonite and organoclays in which 41 and 90% of the exchange capacity of the Na-clay was occupied by hexadecyltrimethylammonium. The strength of sorbate-sorbent interactions in n-hexadecane for all three sorbents was in the following order: nitrobenzene < phenol < m-nitrophenol. The magnitude of the distribution coefficients suggests that the contribution to solute uptake of partitioning between n-hexadecane and the organic pseudophase of the dried organoclays is minor, whereas the major contribution is from adsorptive sorbate-sorbent interactions. Sorption isotherms obtained in different solvents were compared using a sorbate activity scale. In the organoclays, the stronger the tendency of a sorbate to interact with sorption sites, the less pronounced is the reduction in the activity-based sorption due to competition with water. The order of this reduction for the different sorbates is nitrobenzene > phenol > m-nitrophenol. The weakening of sorbate-sorbent interactions resulting from water-sorbate competition might be mitigated by interaction between the organic sorbate and sorbed water molecules. Since the more strongly interacting organic compounds are less susceptible to suppression of sorption in the presence of water, hydrating organoclays may result in an increased differentiation between "weakly" and "strongly" interacting ("nonpolar" and "polar") compounds in the organoclay phase.
- [Show abstract] [Hide abstract] ABSTRACT: The release of alachlor from controlled-release formulations (CRFs) based on alginate-montmorillonite matrices into aqueous polyethylene glycol (PEG) solutions of different concentrations and into a soil at different moisture contents was studied. In distilled water and in PEG-containing solutions displaying -0.1 MPa potential and up, the beads imbibe water and swell. The ensuing increase in weight is about 5%, and the increase in the bead's diameter is about 10%. At water potentials of -0.5 MPa and lower, loss of weight and shrinkage of the beads were observed. The changes in weight and diameter of the alginate-clay beads incubated in a Hamra loamy sand soil at 26.5% moisture content (w/w; -0.18 MPa) were similar to those observed in PEG solutions of >-0.5 MPa moisture potential. The weight and diameter losses observed in the drier soils (12.0 and 7.1% water content; -0.49 and -1.11 MPa) were similar to those in the more concentrated PEG solutions. A decrease in the rate of release of the active ingredient from the beads into soil was observed as the water potential decreased (drier soils). The release of the active ingredient from the investigated CRFs displayed a linear relationship to the square root of time, suggesting a diffusion-controlled-release rate. Data extracted from this relationship enabled the formulation of a mathematical model that correlates rate of release to water content.
- [Show abstract] [Hide abstract] ABSTRACT: We tested the possibility of using tree cores to detect unknown subsurface contamination by chlorinated volatile organic compounds (Cl-VOCs) and petroleum hydrocarbons, a method we term "phytoscreening". The scope and limitations of the method include the following: (i) a number of widespread Cl-VOC contaminants are readily found in tree cores, although those with very high vapor pressures or low boiling points may be absent; (ii) volatile petroleum hydrocarbons were notwell-expressed in tree cores; (iii) trees should be sampled during active evapotranspiration and from directions that are well exposed to sunlight; (iv) there is not necessarily a direct correlation between concentrations measured in tree cores and those in the subsurface; (v) detection of a contaminant in a tree core indicates that the subsurface is contaminated with the pollutant; (vi) many possible causes of false negatives may be predicted and avoided. We sampled trees at 13 random locations in the Tel Aviv metropolitan area and identified Cl-VOCs in tree coresfromthree locations. Subsequently, subsurface contamination at all three sites was confirmed. Phytoscreening is a simple, fast, noninvasive, and inexpensive screening method for detecting subsurface contamination, and is particularly useful in urban settings where conventional methods are difficult and expensive to employ.
- [Show abstract] [Hide abstract] ABSTRACT: The mechanism for the hydrolysis of methyl parathion (MP) by a bifunctional quaternary-ammonium based long-chained organclay(LCOC) containing an alkylamine (-CH2CH2-NH2) headgroup was elucidated. The pathway of the catalytic hydrolysis of methyl parathion by the LCOC was defined by following the effect of replacing H20 with D20, by replacing the primary amino headgroup by a tertiary amino group, and by a detailed mathematical analysis of the proposed reaction scheme. A phosphorothioate isomer of MP was formed in the presence of the LCOC as an intermediate reaction product, initially increasing in concentration and then disappearing. The isotope effect was minimal and substituting a tertiary amine in the LCOC increased the rate of MP hydrolysis. A mechanism is proposed in which hydrolysis of MP can proceed via both a direct route (specific base hydrolysis) and through the formation of the isomer which then undergoes specific base hydrolysis more rapidly than the parent MP. The relative importance of each pathway is a function of pH with the direct hydrolysis of MP being predominant at higher pH values (pH > 10) and the isomer intermediate pathway predominating at lower pH values (pH approximately 8-10).
- [Show abstract] [Hide abstract] ABSTRACT: Organoclays are clays whose surfaces are rendered organophilic by the exchange of inorganic cations with various organic cations. The sorption of six compounds with a range of log Kow values from 2.5 to 6 was studied on shortand long-chain organoclays. Compounds with low or medium hydrophobicities were more strongly sorbed on the short-chain organoclay, whereas the more hydrophobic compounds were better sorbed on the long-chain organoclay. It was found that both types of organoclays were able to remove organic pollutants from the effluent of a pesticide producing plant, but solute uptake by short-chain organoclays was strongly depressed by competition, while long-chain organoclays were only slightly affected by the presence of competing solutes in the industrial wastewater. A bifunctional organoclay that is able to sorb organophosphate pesticides, as well as to catalyze their hydrolysis, has been prepared. The detoxifying capacity of this organoclay for methyl parathion and tetrachlorvinphos, was demonstrated. The half-life for the hydrolysis of the investigated pesticides in the presence of the bifunctional organoclay is about 12 times less than for their spontaneous hydrolysis. The mechanism of the catalytic hydrolysis of methyl parathion by the bifunctional organoclay was studied by following the effect of replacing H2O with D2O, by replacing the primary amino headgroup of the organic cation in the bifunctional clay by a tertiary amino group and by a detailed mathematical analysis of the reaction kinetics. An isomer of MP was formed in the presence of the bifunctional organoclay, initially increasing in concentration and then disappearing, the effect of the isotope replacement was minimal and the tertiary amine substitution increased the rate of MP hydrolysis. Based on these findings we propose a mechanism in which hydrolysis of MP proceeds both via a direct route (specific base hydrolysis) and via the formation of the isomer which then undergoes specific base hydrolysis more rapidly than the parent MP. The relative importance of each pathway is a function of pH with the direct hydrolysis of MP predominant at higher pH values (pH>10) and the isomer pathway predominating at intermediate pH values (pH-8-10).
- [Show abstract] [Hide abstract] ABSTRACT: SUMMARYA study was undertaken to define the dissolution kinetics of gypsum in the presence of ion exchange resins and to study sodic soil reclamation in laboratory soil columns.Gypsum pellets were prepared at 1.5 MPa pressure and the time course of their dissolution followed by measuring the electrical conductivity of the solution. Dissolution experiments were carried out in distilled water with and without Na- and Cl-saturated exchange resins or a combination of the two. The results indicate that in the presence of resin the reaction is first order as calcium and/or sulphate are removed from solution by the resin driving the reaction to completion. In water alone the reaction follows second-order kinetics and depends on the rate of mixing as the reaction is transport controlled.The effect of gypsum placement (uniformly mixed with the entire soil, mixed with the top third of the soil, applied to the soil surface or applied as a saturated gypsum solution) on the efficiency of exchangeable sodium removal, leaching of soluble salts and soil hydraulic conductivity was studied. In addition, the effect of various flow rates on reclamation efficiency was investigated.The amount of leachate required for reclamation was found to be dependent on gypsum placement, tending to decrease in the order mixed < top third mixed < saturated gypsum solution < gypsum surface application < water. Soil hydraulic conductivity was much higher in the mixed gypsum column than in the gypsum applied on the surface; a result of the higher effective gypsum solubility. Sodic soil electrical conductivity in the presence of solid-phase gypsum is linearly related to the total amount of exchangeable sodium expressed in mol dm−3.
- [Show abstract] [Hide abstract] ABSTRACT: The transport of polycyclic aromatic hydrocarbons (PAH) in porous media in the presence of dissolved organic matter (DOM) was predicted with a transport bicontinuum model using independently obtained relationships to derive transport parameters for describing the effect of PAH binding to the DOM. The sorption constants of PAHs to soil and their binding constants to DOM were derived from basic correlations with K(ow) (indicator of hydrophobicity). The kinetic (rate) constants were derived from previously published correlations with K(p) (sorption constant). The independently obtained sorption and rate constants were corrected for binding to DOM and were used to predict the breakthrough curves (BTC) of contaminants in the presence and the absence of DOM. Column results confirmed the independently predicted BTC of PAHs in the presence of DOM that did not sorb to the solid phase, as well as the effect of DOM on the rate of the sorption and desorption processes. These findings confirm the ability to quantitatively describe how DOM facilitates transport of contaminants in the subsurface using independently derived parameters.
Agricultural Research Organization ARO
Beit Dajan, Central District, Israel
- Institute of Soil, Water and Environmental Sciences