Degradation in water

Solvents spilled onto the surface of soil may volatihze into the atmosphere. The Dow Method was used in this section to estimate half-hfe values of each solvent if spilled on the surface of a dry soil. The Dow Method is a simple relationship that was derived for the evaporation of pesticides from bare soil  

The resulting estimated half-life is inversely proportional to vapor pressure the greater the vapor pressure, the greater the extent of volatilization. Conversely, the rate of volatilization will be reduced if the solvent readily dissolves into water or is adsorbed by the soil. Organic carbon-water partition coefficients were compiled for each solvent (see 17.1.6.2.), and vapor pressure data (not shown) were collected from Howard. The resulting half-life estimates (Table 17.1.6) indicated that volatilization would be a major pathway if the liquid solvents were spilled on soil all of the half-life estimates were less than one hour. Thomas cautioned, however, that soil moisture, soil type, temperature, and wind conditions were not incorporated in the simple Dow Model. 

Organic carbon-water partition coefficients were compiled (Table 17.1.7) for each of the solvents in Table 17.1.1. A value is a measure of the affinity of a solvent to partition to 

The desorption of solvents from soil has not been extensively measured. In the application of advection-dispersion models to predict solute movement, it is generally assumed that adsorption is reversible. However, the adsorption of the solutes in T able 17.1.1 may not be reversible. For example, hysteresis is often observed in pesticide adsorption-desorption studies with soils. The measurement and interpretation of desorption data for solid-liquid systems is not well understood.Once adsorbed, some adsorbates may react further to become covalently and irreversibly bound, while others may become physically trapped in the soil matrix. The non-singularity of adsorption-desorption may sometimes result from experimental artifacts.  

Consequently, it appears likely that the alcohols, ketones, o-cresol, ethyl acetate, and pyridine will degrade rapidly in soil if rapidly is defined as having a half-life of 10 days or less. Most of the benzene derivatives, F-11, and the chlorinated aliphatic hydrocarbons may be relatively persistent in soil. Analogous information was not located for diethyl ether, hexane, decane, or tetrahydrofuran. ATSDR for example, found that there was little information available for the degradation of n-hexane in soil. It was suggested that n-hexane can degrade to alcohols, aldehydes, and fatty acids under aerobic conditions. 

F igure 17.1.1. The ranges in degiadatirai half-lives fiff the alcohols and benzene derivatives in surface water, groundwater, and soil (data from Howard et al. ). 

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J.D. Vargo, Determination of metolachlor and environmental degradates in water and soil by LC/MS/MS, Presented at the 219th ACS National Meeting, San Erancisco, CA, March 26-30, 2000. 

Reaction rate constants are postulated as shown in Table II for degradation in water (biolysis and photolysis), in bottom sediments (probably biolysis), and for permanent burial of sediment. The values were selected from a perusal of the literature and must be regarded as speculative. A factor of 20 reduction in reaction rate constant is assumed for addition of each chlorine. 

Weavers LK, Ling FH, Hoffmann MR (1998) Aromatic compound degradation in water using a combination of sonolysis and ozonolysis. Environ Sci Tech 32 2727-2733... 

Lurascu B, Siminiceanu I, Vione D, Vicente MA, Gil A (2009) Phenol degradation in water through a heterogeneous photo-Fenton process catalyzed by Fe-treated laponite. Water Res 43 1313-1322... 

Synthetic pyrethroids now account for at least 30% of the world insecticide market and are rapidly replacing other agricultural chemicals for control of insect pests. Fenvalerate is one of the more widely used synthetic pyrethroid insecticides. It is derived from a combination of a-cyano-3-phenoxybenzyl alcohol and a-isopropyl phenylacetate ester. Technical fenvalerate is a mixture of four optical isomers, each occurring in equal amounts but with different efficacies against insect pests. Fenvalerate does not usually persist in the environment for >10 weeks, and it does not accumulate readily in the biosphere. Time for 50% loss (Tb 1/2) in fenvalerate-exposed amphibians, birds, and mammals was 6 to 14 h for reptiles, terrestrial insects, aquatic snails, and fish it was >14 h to <2 days and for various species of crop plants, it was 2 to 28 days. Fenvalerate degradation in water is due primarily to photoactivity, and in soils to microbial activity. Half-time persistence in nonbiological materials is variable, but may range up to 6 days in freshwater, 34 days in seawater, 6 weeks in estuarine sediments, and 9 weeks in soils. 

Analysis of calculation results has shown profound reconstruction of links between interacting centers that occurred in the chosen model. The most significant changes are observed in the first coordination sphere of central atom. In the process of interaction of Zn(CN)42" complex with IT and OH" particles, there is a tendency to destruction of the first coordination sphere of Zn atom with subsequent forming Zn(OH)2 complex and four molecules of HCN. Further HCN degradation in water solution under plasma action is running in accordance with the pattern below ... 

Figure 6. Postulated pathway of trifluralin degradation in water from a model...

Ollis DF. 1985. Contaminant degradation in water Heterogeneous photocatalysis degrades halogenated hydrocarbon contaminants. Environ Sci Technol 19 480-484. 

At 87 °C and pH 2.5, malathion degraded in water to malathion a-monoacid and malathion P-monoacid. From the extrapolated acid degradation constant at 27 °C, the half-life was calculated to be >4 yr (Wolfe et al., 1977a). Under alkaline conditions (pH 8 and 27 °C), malathion degraded in water to malathion monoacid, diethyl fumarate, ethyl hydrogen fumarate, and QO-dimethyl phosphorodithioic acid. At pH 8, the reported half-lives at 0, 27, and 40 °C are 40 d, 36 h, and 1 h, respectively. However, under acidic conditions, it was reported that malathion degraded into diethyl thiomalate and 0,0-dimethyl phosphorothionic acid (Wolfe et al, 1977a). 

Ollis, D.F. Contaminant degradation in water, Environ. Sci Technol, 19(6) 480-484, 1985. 

Aeration, effect, degradation In water-soil system, 59t Aerial pesticide applicators, volume and characteristics of wastewater, 154t,196 Aerobic pathway, trlfluralln degradation, 39... 

Neamtu M., I. Siminiceanu, and A. Kettrup (2000). Kinetics of nitromusk compounds degradation in water by ultraviolet radiation and hydrogen peroxide. Chemosphere 40 1407-1410. 

Radium may be transported in the atmosphere in association with particulate matter. It exists primarily as a divalent ion in water, and its concentration is usually controlled by adsorption-desorption mechanisms at solid-liquid interfaces and by the solubility of radium-containing minerals. Radium does not degrade in water other than by radioactive decay at rates that are specific to each isotope. Radium may be readily adsorbed by earth materials consequently, it is usually not a mobile constituent in the environment. It may be bioconcentrated and bioaccumulated by plants and animals, and it is transferred in food chains from lower trophic levels to humans. 

Cai, Z., R. Cemy, and R. Spalding (1996). Microbore liquid chromatographic-mass spectrometric determination of atrazine and its major hydroxylate degradate in water at the part-per-trillion level using electrospray. J. Chromatogr. A, 753(2) 243-251. 

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