Bruno Yaron

Stochastic analysis of water flow and pesticides transport in a field experiment

Abstract Analysis of water flow and transport of one conservative (Bromide) and two reactive [Bromacil (BMC) and Terbuthylazine (TBA)] solutes in a field experiment at Bet Dagan site, Israel is carried out. The study is based on the early developed column model of flow and transport in unsaturated soil which is expanded here to incorporate the redistribution stage. The transport of reactive solute is modeled by assuming three mechanisms: advection by water flow, equilibrium sorption and linear decay. The solutions of flow and transport equations are derived for a infiltration–redistribution cycle and averaged further by regarding the soil properties (saturated conductivity, saturated and residual water contents) and the rate of water application by irrigation on the soil surface as independent random values. The most extensive experimental data are concentration measurements in 20 vertical profiles at a few depths and times. These data are used in order to evaluate the spatially averaged concentration as function of time and depth. Flow parameters are identified by a best fit between the model and measured mean concentration of the conservative solute. The same procedure is used to identify the reactive properties (partition coefficient, half life) of the reactive solutes.

Soil pollution by petroleum products. III: Kerosene stability in soil columns as affected by volatilization

Abstract The stability of kerosene in soils as affected by volatization was determined in a laboratory column experiment by following the losses in the total concentration and the change in composition of the residuals in a dune sand, a loamy sand, and a silty loam soil during a 50-day period. Seven major compounds ranging between C 9 and C 15 were selected from a large variety of hydrocarbons forming kerosene and their presence in the remaining petroleum product was determined. The change in composition of kerosene during the experimental period was determined by gas chromatography and related to the seven major compounds selected. The experimental conditions — air-dairy soil and no subsequent addition of water—excluded both biodegradative and leaching. losses. The losses of kerosene in air-dried soil columns during the 50-day experimental period and the changes in the composition of the remaining residues due to volatilization are reported. The volatilization of all the components determined was greater from the dune sand and loamy sand soils than from the silty loam soil. It was assumed that the reason for this behavior was that the dune sand and the loamy sand soils contain a greater proportion of large pores (>4.5 μ m) than the silty loam soil, even though the total porosity of the loamy sand and the silty loam is similar. In all the soils in the experiment, the components with a high carbon number formed the main fraction of the kerosene residues after 50 days of incubation.

Soil-parathion surface interactions

There are three groups of factors which are considered in soil-pesticides interaction studies: the properties of pesticides, the properties of the soil, and the environmental factors which may affect these interactions. As is generally known, the soil is a very complex and nonhomogeneous medium and the soil environment is determined by climatic conditions and agricultural technology. Soil-pesticides interactions are, therefore, complex processes governed not only by each of the mentioned groups of factors but also by the integrated effects and interrelations.

Retention and volatilisation of kerosene: Laboratory experiments on glacial and post-glacial soils

Abstract The influence of environmental conditions and soil characteristics on the retention and volatilisation of kerosene hydrocarbons in soils is investigated through laboratory experiments in six different glacial and post-glacial soils. The soils ranged between 0.55 and 1.80 g cm −3 in density, 29% and 70% in porosity, 0.4% and 28% in organic matter content, and 0% and 51% in clay content. The water retention capacity (WRC) could be estimated on basis of the bulk density and the sand, silt, clay and organic matter contents for many of the soils; for these soils a simple linear relation was identified between WRC and the kerosene retention capacity (KRC). Furthermore, the combined effects of soil porosity and soil moisture content on the KRC were found to be significant and could be quantified by a linear relationship. For moisture contents that can be expected in humid climate zones, the KRC will be relatively low and exhibit small variations between different soils. The effect of temperature on KRC was found to be small. The kerosene volatilisation flux was quantified as a function of time by a power law relationship, based on the initial surface density of kerosene in the soil and the prevailing temperature. The C 9 –C 11 components of the kerosene had selectivities above zero and were thus removed preferentially, while the C 14 and C 15 components were characterised by negative selectivities. The selective volatilisation alters the composition of the kerosene that remains in the soil by increasing the concentration of the C 14 and C 15 components. The results for the different soil types indicate that the organic matter content of the soil affects the selective volatilisation, possibly through hydrophobic adsorption on surfaces, whereas the clay content appears to be less influential.

Soil pollution by petroleum products, II. Adsorption-desorption of “kerosene” vapors on soils

Abstract Adsorption and desorption of vapor hydrocarbons from a synthetic “kerosene” source on different soils was studied. The “kerosene” used consisted of a mixture containing 20% aromatic components (m-xylene, n-butylbenzene, ps-cumene) and 80% aliphatic components (n-decane, n-dodecane). Three different types of soils were used: Mediterranean red sandy clays, arid brown loessial silty loam and Evesham clay. The most influential parameter in the adsorption-desorption processes was the moisture content, which was examined over a range from oven dry to −1 bar water pressure (70% field capacity). The highest adsorption values were on the arid brown loessial silty loam soil, having the following order of adsorption: n-decane > m-xylene > ps-cumene > n-butylbenzene > n-dodecane. From the “kerosene” components the fastest desorption rate was exhibited by m-xylene and the slowest by n-dodecane, in all the soil studied.

General principles of pesticide movement to groundwater

Abstract The processes governing pesticide behavior in porous media during their movement are emphasized. Discussions on retention (adsorption, desorption, phase distribution) and transformations (biological and chemical degradation) include data from the literature as well as from the authors own research work. Pesticide movement by diffusion, mass flow, volatilization and transport on adsorbed particles is described with regard to the potential contamination of the groundwater. Factors affecting pesticide movement through the unsaturated zone, such as soil heterogeneity, leaching regime, and fluctuation of environmental conditions, are discussed.

Numerical analysis of field-scale transport of bromacil

Abstract Field-scale transport of bromacil (5-bromo-3-sec-butyl-6-methyluracil) was analyzed using two different model processes for local description of the transport. The first was the classical, one-region convection dispersion equation (CDE) model while the second was the two-region, mobile-immobile (MIM) model. The analyses were performed by means of detailed three-dimensional, numerical simulations of the flow and the transport [Russo, D., Zaidel, J. and Laufer, A., Numerical analysis of flow and transport in a three-dimensional partially saturated heterogeneous soil. Water Resour. Res., 1998, in press], employing local soil hydraulic properties parameters from field measurements and local adsorption/desorption coefficients and the first-order degradation rate coefficient from laboratory measurements. Results of the analyses suggest that for a given flow regime, mass exchange between the mobile and the immobile regions retards the bromacil degradation, considerably affects the distribution of the bromacil resident concentration, c, at relatively large travel times, slightly affects the spatial moments of the distribution of c, and increases the skewing of the bromacil breakthrough and the uncertainty in its prediction, compared with the case in which the soil contained only a single (mobile) region. Mean and standard deviation of the simulated concentration profiles at various elapsed times were compared with measurements from a field-scale transport experiment [Tauber-Yasur, I., Hadas, A., Russo, D. and Yaron, B., Leaching of terbuthylazine and bromacil through field soils. Water, Air Soil Poln., 1998, in press] conducted at the Bet Dagan site. Given the limitations of the present study (e.g. the lack of detailed field data on the spatial variability of the soil chemical properties) the main conclusion of the present study is that the field-scale transport of bromacil at the Bet Dagan site is better quantified with the MIM model than the CDE model.

On the relation between viscosity and hydraulic conductivity for volatile organic liquid mixtures in soils

Abstract Changes in the volatile organic liquid mixture (VOLM) hydraulic conductivity in different soils are compared with corresponding changes in VOLM viscosity through an extended analysis of results from three previous experimental studies. The conductivity with regard to four different kerosene mixtures, corresponding to different degrees of volatilisation of the original kerosene, was determined in one set of soils; an increasing degree of volatilisation implies less lighter kerosene compounds, changing both kerosene viscosity and its chemical composition. In another set of soils, kerosene conductivity measurements were conducted at two temperatures, which provided two different viscosities but did not affect the kerosene chemical composition. Both volatilisation- and temperature-induced changes in kerosene viscosity and conductivity were studied in two of the soils. In all the soils that were used in the temperature experiments, the changes in kerosene conductivity could be successfully predicted by scaling the original kerosene conductivity value based on the observed viscosity ratio. For the chemically different kerosene mixtures, the changes in conductivity agreed with the corresponding viscosity changes only in inert sands. For a montmorillonitic loam, a montmorillonitic clay and a peat soil, considerable deviations were found between the conductivity ratio and the viscosity ratio; for the peat, which was also used in temperature experiments, no such deviations were observed at different temperatures. The deviations between the conductivity ratio and the viscosity ratio were also found to increase with increasing differences in kerosene chemical composition. These results indicate that chemical composition may be of major importance for VOLM hydraulic conductivity in interacting soils, apart from the effect that the composition has on viscosity. The viscosity ratios were shown to deviate more than 300% from observed conductivity ratios for the chemically most different kerosene mixtures.

Attapulgite-pesticide interactions

As most pesticides are either insoluble or only slightly soluble in water and must be applied in relatively small amounts over large areas, they are formulated in such a way that a highly concentrated organic chemical can be put into a convenient-to-use and effective form for field use by blending it with additives and inert carriers. The formulation must be easy and economical to use, do the job it is meant for, have an adequate shelf-life, and have no undesirable side effects. In solid-based formulations, the inert materials used, called diluents or carriers, can be either botanicals (e.g., ground corn cobs, walnut shells), synthetics (both organic and inorganic), or minerals (carbonates, oxides, and clays). In 1976 nearly 300,000 tons of various clays were delivered to pesticide manufacturers in the United States alone for use in pesticide formulations (U.S. Department of Agriculture 1976). Of this amount, over 65% was attapulgite. The predominance of attapulgite in the formulation of pesticides in preference to more common clay minerals such as kaolinite and montmorillonite stems from the fact that it is not easily flocculated by electrolytes and does not cake at high relative humidities but remains free-flowing (HADEN and SCHWINT1967).