Chemical-soil interaction

The results (Table III) demonstrate that essentially identical values of K were determined in each case, indicating that for this chemi-ical the adsorption is independent of flow velocity. The value of K, representing aldicarb adsorption by Palmyra soil, was 0.05-0.07, indicating very slight chemical-soil interaction. This is consistent with other studies (8, 9, J 0) conducted in medium to coarse textured soils. No interaction (K =0) of aldicarb sulfoxide with the soil was detected, and the interaction of aldicarb sulfone, K =0.02, was even less than measured for aldicarb and also independent W flow velocity. 

Further progress may derive from a more accurate definition of the chemical and physical properties of the humic substances present at the rhizosphere and how they interact with the root-cell apoplast and the plasma membrane. An interaction with the plasma membrane H -ATPase has already been observed however this master enzyme may not be the sole molecular target of humic compounds. Both lipids and proteins (e.g., carriers) could be involved in the regulation of ion uptake. It therefore seems necessary to investigate the action of humic compounds with molecular approaches in order to understand the regulatory aspects of the process and therefore estimate the importance of these molecules as modulators of the root-soil interaction. 

In its simplest form a partitioning model evaluates the distribution of a chemical between environmental compartments based on the thermodynamics of the system. The chemical will interact with its environment and tend to reach an equilibrium state among compartments. Hamaker(l) first used such an approach in attempting to calculate the percent of a chemical in the soil air in an air, water, solids soil system. The relationships between compartments were chemical equilibrium constants between the water and soil (soil partition coefficient) and between the water and air (Henry s Law constant). This model, as is true with all models of this type, assumes that all compartments are well mixed, at equilibrium, and are homogeneous. At this level the rates of movement between compartments and degradation rates within compartments are not considered. 

In the vadose zone, liquid or dissolved contaminants exist in a complex environment that involves interaction among the chemicals, soil grains, water attached to soil grains (or between the soil pores), the atmosphere in void spaces, and numerous... 

Alkaloids from many plants are considered to be used as biological fertilizers in ecological cultivation. This is very important especially in cases when more attention is given to these plants, which play not only a role in production but also in the cyclical maintenance of a field, garden or forest ecosystems . Plants containing alkaloids, for example lupines, have the ability to establish complexes with the soil and with the rhizosphere. The excretion of many chemicals from roots to soil occurs in this complex. Plant mediation with the soil environment is the result. The alkaloids play a major role in this plant-soil interaction system. 

The mechanism and extent of adsorption are ascertained to depend on several factors, which include (a) the physical and chemical nature and properties of both HS and organic xenobiotic and (b) the conditions of the medium. Organic matter in organic amendments is relatively fresh or little humified, has composition and properties that differ substantially from native soil HS, and affects the composition and structure of native soil HS. Therefore, organic xenobiotics added to soils interact with a complex mixture of applied and native HS, which is expected to affect both quantitative and mechanistic aspects of adsorption phenomena. 

Dose estimates for soil contact include a great deal of uncertainty. This uncertainty arises because we must deal with the transport of chemicals within the skin layer the interaction of the soil layer on the skin with the skin surface the dynamic conditions always involved in scenarios addressing interaction of the skin surface with chemicals, soil, air, and water and addressing the level of protection provided by clothing. 

With the help of the concentration factor a balance of the chemical soil-water interactions may be established (Table IV) the negative values in column 3 indicate the amount of dissolved constituents which seem to be retained in the soil, positive values indicate the amount of dissolved constituents, which seem to be added to the initial concentration of throughfall water, when it percolates through the soil layer. In column 4 the percentages of each element in the soil, subtracted or added, have been calculated. 

Gillman, G. P. 1991. The chemical properties of acid soils with emphasis on soils of the humid tropics. In Wright et al. (eds.), Plant-Soil Interactions at Low pH, pp. 3-14. 

Pesticide and soil properties determine the mobility and degradation of applied chemicals. The interaction of the organic molecules with soil solids varies according to chemical structure, organic matter and clay content, soil pH, and in some cases concentration. Degradation rates are influenced by pH, substrate concentration,... 

Factors that must be considered in developing a remediation strategy include the chemical nature, quantity, and location of the contaminants the permeability of the soil and how soil interacts with contaminants and how various cleanup or containment methods may impact workers, the community, and remediation costs. 

A review paper covering forms of boron in soils, interactions between soil solution boron and adsorbed boron, adsorption-desorption processes, and relationships to plant nutrition is presented. Diagnostic criteria are given for chemical analysis of soils and irrigation waters in terms of boron status, i.e., deficient, adequate, or excessive, and specified according to crop species group. The potential boron hazard of municipal sewage effluents to water supplies is discussed. 

Soil has long been considered as a chemical system due to its semipermeability to chemicals, bioactivity, interactions with chemicals, and so on. As a result, soil has been idealized as a leaky semipermeable membrane in chemical osmosis to explain various abnormal transport phenomena of water and chemicals in soil (Hanshaw, 1972 Marine and Fritz, 1981 Fritz and Marine, 1983 Yeung, 1990 Keijzer, Kleingeld, and Loch, 1999) as a Donnan membrane (Donnan, 1924) to examine the influences of soil type, water content, electrolyte concentration, and the cation and anion distribution in pore fluid on electroosmotic flow of fluid in soil (Gray and Mitchell, 1967) as a bioreactor to evaluate the impact of oxygen transfer on efficiency of bioremediation (Woo and Park, 1997) and so on. 

Many factors affect the mechanisms and kinetics of sorption and transport processes. For instance, differences in the chemical stmcture and properties, ie, ionizahility, solubiUty in water, vapor pressure, and polarity, between pesticides affect their behavior in the environment through effects on sorption and transport processes. Differences in soil properties, ie, pH and percentage of organic carbon and clay contents, and soil conditions, ie, moisture content and landscape position climatic conditions, ie, temperature, precipitation, and radiation and cultural practices, ie, crop and tillage, can all modify the behavior of the pesticide in soils. Persistence of a pesticide in soil is a consequence of a complex interaction of processes. Because the persistence of a pesticide can govern its availabiUty and efficacy for pest control, as weU as its potential for adverse environmental impacts, knowledge of the basic processes is necessary if the benefits of the pesticide ate to be maximized. 

It appears that pesticides with solubiHties greater than 10 mg/L are mainly transported in the aqueous phase (48) as a result of the interaction of solution/sediment ratio in the mnoff and the pesticide sorption coefficient. For instance, on a silt loam soil with a steep slope (>12%), >80% of atra2ine transport occurs in the aqueous phase (49). In contrast, it has been found that total metolachlor losses in mnoff from plots with medium ground slopes (2—9%) were <1% of appHed chemical (50). Of the metolachlor in the mnoff, sediment carried 20 to 46% of the total transported pesticide over the monitoring period. 

D. L. Nofzigfer and A. G. Hornsby, CMES Interactive Simulation of Chemical Movement in Eayered Soils, Institute of Food and Agriculture Sciences, Circular 786, University of Florida, GaiuesviUe, FI., 1986. 

Some Physico-chemical Interactions of Paraquat with Soil Organic Materials and Model Compounds. I. Effects of Temperature, Time and Absorbate Degradation on Paraquat Adsorption, I. G. Bums, M. H. B. Hayes, and M. Stacey, Weed Res., 13 (1973) 67 -78. 

The combined influences of runoff generation mechanisms, runoff flowpaths, and soil properties together control runoff chemistry. In spite of the wide range of interactions that characterize terrestrial environments, a few broad generalities can be offered, as the chemical composition of streamflow typically contains... 

Fig. 9-3 Conceptual model to describe the interaction between chemical weathering of bedrock and down-slope transport of solid erosion products. It is assumed that chemical weathering is required to generate loose solid erosion products of the bedrock. Solid curve portrays a hypothetical relationship between soil thickness and rate of chemical weathering of bedrock. Dotted lines correspond to different potential transport capacities. Low potential transport capacity is expected on a flat terrain, whereas high transport is expected on steep terrain. For moderate capacity, C and F are equilibrium points. (Modified with permission from R. F. Stallard, River chemistry, geology, geomorphology, and soils in the Amazon and Orinoco basins. In J. I. Drever, ed. (1985), "The Chemistry of Weathering," D. Reidel Publishing Co., Dordrecht, The Netherlands.)...

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