Hydrolytic half-life

This property of organophosphate esters may be of environmental importance since phosphoric acid diesters are much more soluble and very little is known concerning the environmental toxicity of these compounds. The available data do not provide sufficient descriptions of the experimental methods to determine if the rates are reliable (Barnard et al. 1961 Ciba-Geigy 1984e, 1986 Howard and Deo 1979 Mayer et al. 1981 Wolfe 1980). The majority of reports provide only a minimum of information and exclude important facts such as the duration of the experiments and the concentration of buffers. Despite the lack of experimental detail, published rate constants for base-catalyzed hydrolysis appear to be reasonably consistent and suggest that the hydrolytic half-life of triphenyl phosphate will vary from... 

Biotic and abiotic degradation of 1,2-dibromoethane in surface waters is slow relative to volatilization of the compound to the atmosphere (ERA 1987b). 1,2- Dibromoethane is resistant to hydrolysis (Jaber et al. 1984) the hydrolytic half-life of the compound has been reported to range from 2.5 years (Vogel and Reinhard 1982) to 13.2 years (HSDB 1989). As a result of its hydrolytic stability and the limited biological activity in subsurface soils, 1,2- dibromoethane leached to groundwater is expected to persist for years. 

Chemical/Physical. Eighty-eight percent of endosulfan sulfate was recovered from an aqueous solution after 33 d. Based on this data, a hydrolytic half-life of 178 d was reported (Ali, 1978). 

In solution buffered at pH 5, the hydrolytic half-life decreased from 12 weeks to 6 weeks as the temperature increased from 20° to 30° C, Hydrolysis at pH 7 and greater proceeded with a half-life >200 days (52). In buffered solutions and in the presence of fulvlc acid at a concentration of 0.5 mg/ml and at 25°C, the hydrolytic half-lives of atrazlne were found to Increase from 35 days to 742 days as the pH was Increased from 2.9 to 7.0 (53). However, the half-lives decreased to about 10% of those values when the fulvlc acid concentration was Increased to 5 mg/ml. 

Based on the half-lives of one and two carbon chloroall-phatlcs, the hydrolytic half-life of DCP Is expected to be 6 months to several years (86). Vapor phase photolysis under simulated sunlight did not occur after prolonged exposure (87). 

At this point in our discussion about chemical bonds and structural formulas, we should stress that structural isomers may exhibit very different properties and reactivities. For example, the rates of hydrolysis (reaction with water, see Chapter 13) of the four butyl chlorides shown in Fig. 2.1 are quite different. While the hydrolytic half-life (time required for the concentration to drop by a factor of 2) of the first and third compound is about 1 year at 25°C, it is approximately 1 month for the second compound, and only 30 seconds for the fourth compound. When we compare the two possible structural isomers with the molecular formula C2H60, we can again find distinct differences in that the well-known ethanol (CH3CH2OH) is a liquid at ambient conditions while dimethylether (CH3OCH3) is a gas. These examples should remind us that differences in the arrangement of a single collection of atoms may mean very different environmental behavior thus we must learn what it is about compound structure that dictates such differences. 

P 13.3 Why Do DDT and Methoxychlor Exhibit Such DifferentpH-Hydrolytic Half-Life Profiles What Is(Are) the Major Transformation Products ... 

Mills and Hoffmann (1992) investigated ultrasonic degradation of parathion. Parathion (0,0-diethyl O-p-nitrophenyl triphosphate) is a major pesticide used in large quantities worldwide. Organophosphate esters such as parathion have been used as alternatives to DDT and other chlorinated hydrocarbon pesticides however, the organophosphate esters are not rapidly degraded in natural waters. At 20°C and pH 7.4, parathion has a hydrolytic half-life of 108 days and its toxic metabolite, paraoxon, has a similar half-life of 144 days. Ultrasonic irradiation of 25 mL of parathion-saturated, deionized water solution was conducted in a water-jacketed, stainless-steel cell with a Branson 200 sonifier operating at 20 kHz and 75 W/cm2. The temperature of the sonicated solution was kept constant at 30°C. All sonolytic reactions were carried out in air-saturated solution. The concentration of the parathion hydrolysis product p-nitrophenol (PNP) was determined in alkaline solution with a Shimadzu MPS-2000 UV /visible spectrophotometer. 

Dichloroethane in surface water is expected to be lost to the atmosphere through volatilization before undergoing any significant chemical or biological degradation. The hydrolytic half-life of... 

The in human blood half-life of esmolol is around 25-27 min (50, 51). As a nice confirmation of the soft drug design principles, the presence of other ester-containing drugs, such as acetylcholine, succinylcholine, procaine, or chloroprocaine, have been shovm to have no effect on this hydrolytic half-life, and consequently no metabolic interactions are to be expected (50). 

PROBABLE FATE photolysis . C-Cl bond photolysis can occur, not important in aquatic organisms, photooxidation half-life in air 9,24-92.4 hrs, reported to photodegrade in water in spite of the lack of a photoreactive center oxidation-, not an important process hydrolysis . very slow, not important, first-order hydrolytic half-life 207 days, reaction with hydroxyl radicals in atmosphere has a half-life of 2.3 days volatilization may be an important process, however, information is contradictory, volatilization half-life from a model river 6 days, half-life from a model pond considering effects of adsorption 500 days, slow volatilization from water is expected with a rate dependent upon the rate of diffusion through air sorption important for transport to anaerobic sediments biological processes biodegradation is important occurs slowly in aerobic conditions, occurs quickly and extensively in anaerobic conditions... 

PROBABLE FATE photolysis C-CI photolysis can occur, not important in aquatic systems, photooxidation half-life in air 9.24 hrs-3.85 days oxidation not an important process hydrolysis very slow, not important, first-order hydrolytic half-life 207 days volatilization information is contradictory as to how important process is sorption important for transport to anaerobic sediments biological processes biodegradation could be important... 

PROBABLE FATE photolysis C-C bond photolysis can occur, not important in aquatic systems, photooxidation by U.V. light in aqueous medium 90-95°C, time for the formation of CO2 (% theoretical) 24% 3 hr, 50% 17.4 hr, 75% 45.8 hr, photooxidation in air 9.24 hrs-3.85 days oxidation probably not an important process hydrolysis very slow, not important, first-order hydrolytic half-life 207 days volatilization not an important process, calculated half-life in water 4590 hr 25°C and 1 m depth, based on an evaporation rate of 1.5x10 m/hr sorption important for transport to anaerobic sludges, 30-40% adsorbed on aquifer sand 5°C after 3-100 hr equilibrium time, 75-100% disappearance from soils 3-10 yrs biological processes biotransformation is the most important process other reac-tions/interactions electrochemical reduction with products of benzene and gamma-TCCH has been studied... 

PROBABLE FATE photolysis-, aqueous photolysis is not expected to be important, reaction with photochemically produced hydroxyl radicals has a half-life of 13.44 hr, direct photolysis is not expected to be important since it should not adsorb wavelengths >290 nm oxidation photooxidation is not expected to be important, photooxidation only in atmosphere, photooxidation half-life in air 9.65 hrs-4.02 days hydrolysis very slow, maybe significant, hydrolysis of carbon-chloride bonds, release to water results in hydrolysis with a half-life of 40 days when released to soil, it may hydrolyze hydrolyzed slowly in aqueous dimethylformamide at pH 7, first-order hydrolytic half-life 22yrs volatilization expected to volatilize if released to water, volatilization half-lives from lakes, rivers, and streams 3.5, 4.4, and 180.5 days respectively sorption not an important process biological processes biodegrades in water after several weeks of acclimation, biodegradation not important under natural conditions, no bioaccumulation noted... 

PROBABLE FATE photolysis could be important, photooxidation half-life in water 54.1-541 days, direct photolysis in the stratosphere may occur, but is insignificant in the troposphere, reaction with photochemically produced hydroxyl radicals yields a half-life of 1.45 yrs oxidation atmospheric photooxidation by hydroxyl radicals to COBT2 is relatively rapid hydrolysis too slow to be important, first-order hydrolytic half-life 687 yrs volatilization volatilization has been demonstrated, could be an important transport process, volatilization from moist soil surfaces expected to occur sorption no information is available biological processes slight potential for bioaccumulation/metabolization is known to occur in some organisms other reactionsAnteractions possibly produced by halogen reaction... 

PROBABLE FATE photolysis could be important in aqueous environment, in the stratosphere, photodissociation occurs to eventually form phosgene as the principal product oxidation no information available, in troposphere it exhibits an extremely slow rate of reaction with hydroxyl radicals, photooxidation half-life in air 1.8-18.3 yrs hydrolysis first-order hydrolytic half-life 7000 yrs based on a rate constant of 4.8xl0 mol s pH 7 and 25°C vola-... 

PROBABLE FATE photolysis, sensitized process may be important, reacts in the vapor phase with photochemically produced hydroxyl radicals at an estimated half-life of 6.2 hr, suggesting that this reaction is the predominate chemical removal process oxidation photooxidation half-life in air 5.2-51.7 hrs hydrolysis not an important process, first-order hydrolytic half-life >197,000 yrs volatilization probably an important process, can volatilize significantly from soil surfaces from which it is sprayed, particularly moist soil surfaces, volatilization half-life from a model pond, river, and lake is 18-26,3.6-5.2, and 14.4-20.6 days respectively sorption probably an important process biological processes bioaccumulation is an important process... 

PROBABLE FATE photolysis, could be important, only identifiable transformation process if released to air is reaction with hydroxyl radicals with an estimated half-life of 8.4 months oxidation, has a possibility of occurring, photooxidation half-life in air 42.7 days-1.2 yrs hydroiysis too slow to be important, first-order hydrolytic half-life 275 yrs voiatilization likely to be a significant transport process, if released to water or soil, volatilization will be the dominant environmental fate process, volatilization half-life from rivers and streams 43 min-16.6 days with a typical half-life being 46 hrs sorption adsorption onto activated carbon has been demonstrated bioiogicai processes moderate potential for bioaccumulation, biodegradation occurs in some organisms, in aquatic media where volatilization is not possible, anaerobic degradation may be the major removal process other reactions/interactions may be formed from haloform reaction after chlorination of water if sufficient bromide is present... 

PROBABLE FATE photolysis information is lacking, probably unimportant, appreciable photodissociation may occur in stratosphere, photooxidation half-life in air 61.3-613 days oxidation information lacking, probably unimportant, in troposphere oxidation by hydroxyl radicals for formyl chloride and other products is an important fate hydrolysis slow hydrolysis, unimportant in comparison to volatilization, first-order hydrolytic half-life 292 days at pH 7 volatilization volatilization to the atmosphere is rapid and is a major transport process for removal of methyl chloride, evaporation from water 25°C of 1 ppm solution 50% after 27 min, 90% after 91 min volatilization half-life in a typical river 2-1 hr sorption no data is available, sorption onto sediments and suspended particulates probably unimportant biological processes data is lacking, biodegradation and bioaccumulation are not expected to be important fates... 

PROBABLE FATE photolysis photooxidation to DDE occurs slowly, indirect photolysis may be important oxidation photoxidation occurs, photooxidation half-life in water 7-350 days, photoxidation half-life in air 7.4 days hydrolysis may be an important process under certain conditions, first-order hydrolytic half-life 22 yrs volatilization is an important process, some will evaporate from soil and surface water into the air sorption is an important process, will adsorb very strongly to soil if released to the soil, will adsorb very strongly to sediments if released to water biological processes biotransformation and bioaccumulation are important processes, may be subject to biodegradation in flooded soils or under anaerobic conditions, may be significant in sediments... 

PROBABLE FATE photolysis no direct photolysis, indirect photolysis too slow to be environmentally important, photooxidation half-life in water 2.4-12.2 yrs, photooxidation half-life in air 7.4 hrs-2.5 days oxidation not important, reaction with photochemically produced hydroxyl radicals gives a half-life of 18 hrs hydrolysis hydrolysis (only in surface waters) believed to be too slow to be important, first-order hydrolytic half-life 10 yrs volatilization not expected to be an important transport process sorption sorption onto particulates and com-plexation with organics are dominant transport processes biological processes bioaccumulated in many organisms, biodegraded rapidly in natural soil, some biotransformation, all biological processes are important fates... 

PROBABLE FATE photolysis, expected to oecur slowly oxidation no data available on aqueous oxidation, oxidized by hydroxyl radicals in atmosphere hydrolysis not important process first-order hydrolytic half-life >879 yrs volatilization volatilizes at a relatively rapid rate, half-life is about 10 hr volatilization from soil surfaces is expected to be a signifieant transport mechanism sorption sorbed by organic materials adsorption to sediment expected to be a major environmental fate process based on research in the Great Lakes area biological processes bioaccumulates more than chlorobenzene, biodegradation is not as significant as volatilization slightly persistent in water, half-life 2-20 days approximately 98.5% of 1,3-dichlorobenzene ends up in air 1% ends up in water the rest is divided equally between terrestrial soils and aquatic sediments. 

PROBABLE FATE photolysis-, direct photolysis is not significant, photodissociation in stratosphere to chloroacetyl chloride oxidation photooxidation in water expected to be slow primarily removed in air by photooxidation degraded in atmosphere by reaction with hydroxyl radicals, half-life of 1 month and 1.9% loss/12 hr sunlit day products of photooxidation CO and HCl oxidation half-life 1.5 weeks-4 months hydrolysis not significant first-order hydrolytic half-life 1.1 yr volatilization high vapor pressure causes rapid volatilization, major transport process, half-life 30 min 25°C evaporation primary removal from water half-life from 1 ppm solution 25°C, still air, and an avg. depth of 6.5 cm 28 min., evaporation from water 25 °C of 1 ppm solution 50% after 29 min. and 90% after 96 min. 

PROBABLE FATE photolysis, possible, but cannot compete with microbial biodegradation oxidation, any oxidation which occurs is too slow to be important hydrolysis not an important process, first-order hydrolytic half-life 3.4 yrs volatilization not expected to be an important process sorption sorption will not remove significant amounts biological processes rapid microbial degradation is the principal fate of 2,4-DCP other reactions/interactions chlorination of water may produce further chlorination of 2,4-DCP... 

PROBABLE FATE photolysis can occur in atmosphere, in air reacts with photochemi-cally generated hydroxyl radicals, half-life >23 days oxidation photooxidation in troposphere is probably important hydrolysis not expected to compete with volatilization, first-order hydrolytic half-life 15.8 yr volatilization probable important transport process, if injected to soil, primarily lost by volatilization, volatilization from surface water half-life 6hr and 10 days for a river and a lake respectively biological processes compound can be used as a carbon source by several soil bacteria washed out of air by rain... 

PROBABLE FATE photolysis direct photolysis in water expected to be slow oxidation photooxidation in the troposphere is probably the predominant fate process hydrolysis slow hydrolysis to 3-cloroallyl alcohol occurs, may be important process, first order hydrolytic half-life 5.5 days-11.3 days volatilization volatilization to the atmosphere should be a major transport process biological processes biodegradation is possible evaporation from water 25°C of 1 ppm solution is 50% after 31 min., and 90% after 98 min about 95% ends up in air the rest ends up in water... 

PROBABLE FATE photolysis direct photolysis may be important oxidation probably not important, photooxidation by u.v. light in aqueous medium 90-95°C, formation of CO2 25% took 2.9 hr, 50% took 4.8 hr, 75% took 12.5 hr, photooxidation half-life in air 4 hrs-1.7 days hydrolysis hydrolysis of epoxide, too slow to be important, first-order hydrolytic half-life 10.5 yrs volatilization volatilization is an important process, volatilization 25°C from soils in lab sandy loam 8.9% after 60 days, sand 34.2% after 60 days, calculated half-life in water based on an evaporation rate of 5.33x10m/hr 12,940 hr sorption probably an important process, will adsorb strongly to sediments once it reaches surface water biological processes moderate bioaccumulation... 

PROBABLE FATE photolysis no direct photolysis, half-life from surface waters 3500 hr, indirect photolysis is too slow to be important, photodegradation by hydroxyl radicals will occur with a half-life of 23.8 hrs oxidation not an important process, photooxidation half-life in air 4.7 days-46.6 days hydrolysis too slow to be important under natural conditions, first-order hydrolytic half-life 1163 days volatilization possible, but not important sorption sorption onto particles and biota and complexation with humic substances principal transport mechanism, little adsorption to soil or sediment is expected to occur biological processes bioaccumulation, biodegradation, and biotransformation by many organisms (including humans) are very significant fates... 

PROBABLE FATE photolysis . C-Cl bond photolysis is possible, could be important, may photolyze on the soil surface, when released to the atmosphere, it will react with photo-chemically produced hydroxyl radicals with an estimated half-life of 1.23 hr, adsorption onto atmospheric particles will increase this half-life oxidation , probably not important, photooxida-tion by u.v, light in aqueous medium 90-95°C, 25% CO2 formation 5.0 hr, 50% 9.5 hr, 75% 31.0 hr, oxidation rate constant 9.7x10 at pH 7, half-life 71.4 days hydrolysis , hydrolysis of sulfite group may be rapid, probably important above pH 7, hydrolyzed rapidly by alkalies, when released to water, hydrolytic half-life 37.5 and 187.3 days for pH 7 and 5.5 respectively, in the presence of ferric hydroxide, a higher rate of hydrolysis was observed at pH 7 and 20°C, in a solution of ferric oxide, hydrolysis half-life was 9.4 days volatilization could be important sorption sorption is an important process biological processes not important... 

PROBABLE FATE photolysis photoisomeraization occurs, rate undetermined, photooxidation half-life in air 59 minutes-9.8 hrs, vapor phase hepatchlor in air will react with photo-chemically produced hydroxy radicals, half-life 36 min., direct photolysis may occur oxidation information is not available hydrolysis rapid hydrolysis for heptachlor in solution, first-order hydrolytic half-life 23.1 hrs or 129.4 hrs, significant in moist soils volatilization expected to be an important process, evaporates slowly, release to soil will result in volatilization from the surface, especially in moist soils sorption probably an important process, but no reliable data is available, sticks strongly to soil particles biological processes will bioaccumulate if not hydrolyzed, biodegradation is significant... 

PROBABLE FATE photolysis not subject to considerable direct photolysis, occurs slowly, sunlight photolysis in surface water at 40 deg latitude in summer has a reported half-life of 450 years oxidation oxidized by hydroxy radicals after volatilization hydrolysis not important process, first-order hydrolytic half-life 3.4 years volatilization very rapid volatilization can be hindered by adsorption if organics are present sorption high potential for adsorption by organic materials biological processes high potential for bioaccumulation very little, if any biodegradation due to volatilization and adsorption evaporation half-life from 5.4m deep seawater 11-22 days half-life from a model river 4.2 hr predicted in atmosphere, reacts with photochemically produced hydroxyl radicals with an approximate vapor phase half-life of 18.5 days. 

PROBABLE FATE photolysis, tropospheric photooxidation of volatilized trichloroethylene by hydroxyl radicals to phosgene and dichloroacetyl chloride is very rapid, C-Cl bond can photolyze slowly oxidation not important except for photooxidation, photooxidation half-life in air 1.1-11.3 days hydrolysis not important under environmental conditions, first-order hydrolytic half-life 10.7 months volatilization rapid volatilization is the major transport process, evaporation from water 25°C of 1 ppm solution 50% after 19-24 min, 90% after 63-80 min ... 

PROBABLE FATE photolysis reported in experiments, but environmental significance is unknown, aqueous photolytic half-life 4 days, release to the environment can decrease due to photolysis and reaction with hydroxyl radicals oxidation too slow to be an important process, photooxidation half-life in water 84.5 days, in air 5.1-51.4 days hydrolysis not an important process first-order hydrolytic half-life >8x10 yrs volatilization not an important process, may contribute to losses at the surface of the soil sorption high potential for sorption by organic materials, rate is unknown biological processes biodegradation very important, but exact rate uncertain due to variations between data photomineralization may contribute to losses at the surface of the soil... 

Bromomethanes. Hydrolysis (hydrolytic half-life = 20 days) and volatilization are the important processes in the fate of bromomethanes in water. Once volatilized, photooxidation yielding bromine atoms and inorganic bromides and diffusion to stratosphere with subsequent photodissociation will probably determine the fate of bromomethanes. At present, the importance of sorption and biotransformation processes in the fate of these compounds in the aquatic environment is not known. 

Chloroethanes. Based on the results obtained on compounds analogous to chloroethanes, it could be concluded with reasonable confidence that volatilization is an important transport step in moving chloroethanes from the hydrosphere to the atmosphere. In addition, hydrolysis and photooxidation also significantly influence the fate of chloroethanes in the environment. The former largely reflects the high solubility and the relatively short hydrolytic half-life of monochloroethane. 

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