Dispersal from soil surface

Sorbed pesticides are not available for transport, but if water having lower pesticide concentration moves through the soil layer, pesticide is desorbed from the soil surface until a new equiUbrium is reached. Thus, the kinetics of sorption and desorption relative to the water conductivity rates determine the actual rate of pesticide transport. At high rates of water flow, chances are greater that sorption and desorption reactions may not reach equihbrium (64). NonequiUbrium models may describe sorption and desorption better under these circumstances. The prediction of herbicide concentration in the soil solution is further compHcated by hysteresis in the sorption—desorption isotherms. Both sorption and dispersion contribute to the substantial retention of herbicide found behind the initial front in typical breakthrough curves and to the depth distribution of residues. 

Secondary air contamination is caused because pesticides on plant and soil surfaces convert into steam, or disperse by adsorbing on dust particles. Under certain conditions, up to 50% of such OCRs (organochlorine pesticides) as DDT, aldrin, and dieldrin move into the air during the week after a field is treated. DDT evaporates from a treated field at a rate of 10-50 kg/ha a year, depending on temperature, humidity, and air movement [3]. On the second or third day after treatment, OPP concentrations can be higher than on the first day as a result of pesticides converting into steam [22]. 

The cationic surfactant hexadecyltrimethylammonium bromide (HDTMA) induced dispersion of goethite in a column of material from a surface soil and a aquifer substrate, possibly because the HDTMA reduced the negative charge of the clay particles and thereby desorbed the goethite (Seaman and Bertsch, 2000). 

They prevent redeposilion of soils removed from a surface back onto ihe surface through a dispersing action associated with chelating and charge-distribution effects. 

Hewitt found that volatile organic compounds are readily lost from soil samples unless care is taken to limit surface area exposure and to ensure subsample isolation [338]. Volatile organic carbon losses were found to be most abundant during field collection and storage. Hewitt reported that fortified soils held in sealed glass ampoules at 4 °C, or dispersed in methanol and held at 22 °C, showed no significant losses over 20 and 98 days, respectively [339]. 

For removal of insoluble and/or water-immiscible inorganics by emulsification with detergent solutions For removal of ester and amide-based organics and inorganic salts by chemical hydrolysis with alkaline solutions For removal of metal ions from solutions and surfaces by chelation or complexation reactions For wetting and dispersion of soils with surfactants, suspension of soil residues in order to prevent resedimentation and recontamination on metal surface For removal of surface contaminations, rust scale, mill scale, and other bound moieties (including surface layers of metal itself) by chemical dissolution with acids or alkaline deoxidation with or without the application of an electric current... 

Heavy rainfall combined with local conditions to create pockets ( hot spots ) of exceptionally high surface radioactivity levels resulting in external dose rates that were as much as five thousand times the dose rate due to the natural background. Once releases had been halted, changes in contamination patterns resulted from radioactive decay (primarily of which decays almost totally within three months) and normal weathering processes which caused the migration of contamination into the soil and the dispersion of soil particles through the runoff of surface waters. 

With few exceptions, most blind U deposits and other potential sources of He are situated below the water table, so that He must be released into the groundwater prior to its escape to the soil gas and the atmosphere. In consequence, groundwater, or at least groundwater as represented by water in drill holes and wells, has been sampled extensively as a means of determining the dispersion of He. Surface waters, however, tend to be equilibrated with the atmosphere and are unsuitable as sample media, except when collected from springs and at depth from lakes. 

The clean-up of contaminated ground water poses problems that are different from contaminated surface waters, particularly because ground water is not easily accessible. Due to the typical slow movement of pollutants in the aquifer and the relatively low degree of dispersion, concentrations of contaminants can remain high and detection can be difficult. In the case of pesticides, some of the factors that may contribute to ground water contamination include physical and chemical properties of the pesticide, application methods used for their application, and characteristics of the soil and site. Once an aquifer is contaminated, its restoration as a usable... 

Air and water transport of technical chlordane has resulted in the detection of chlordane and its metabolites in nonbiological samples worldwide. Chlordane enters the atmosphere mainly through aerial applications of dust and spray formulations, soil erosion by wind, and volatilization from soil and water. In aquatic systems, chlordane enters by way of surface runoff and rainfall chlordane is rapidly adsorbed onto bottom sediments, where it persists. Atmospheric transport of chlordanes is considered the major route of global dissemination. Levels of chlordane compounds in the marine atmosphere of the southern hemisphere are nearly the same as those of DDT and its metabolites this strongly suggests that chlordane compounds are globally distributed and dispersed. The yearly input of m-chlordane to the Arctic Ocean from atmospheric sources is... 

Soil in itself is not a cause of cross-infection. But soils serve as a refuge for disease-causing bacteria. Detergents are needed to break down the soils and permit the disinfectants to contact and kill the organisms. When a disinfectant is combined with a detergent, it is the role of the detergent to disperse and remove soil from a surface, and thereby enable the detergent to reach and destroy any microbial contamination that may lie beneath the dirt barrier. 

The detached soil is removed from the surface by solubilizing or dispersing the soil in the cleaning medium, that is, water. For this again, suitable solvents are used in the detergent formulations. 

Once the detergent is used, the soil on the surface needs to be detached from the surface, dissolved, or dispersed in the cleaning medium, and then has to be removed from the system. 

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