Evaporation rate half-life

Commercial condensed phosphoric acids are mixtures of linear polyphosphoric acids made by the thermal process either direcdy or as a by-product of heat recovery. Wet-process acid may also be concentrated to - 70% P2O5 by evaporation. Liaear phosphoric acids are strongly hygroscopic and undergo viscosity changes and hydrolysis to less complex forms when exposed to moist air. Upon dissolution ia excess water, hydrolytic degradation to phosphoric acid occurs the hydrolysis rate is highly temperature-dependent. At 25°C, the half-life for the formation of phosphoric acid from the condensed forms is several days, whereas at 100°C the half-life is a matter of minutes. 

Chloropromazine (8—34 wt% loading) has been microencapsulated in PCL-cellulose propionate blends by the emulsion solvent evaporation method (61). Phase separation for some ratios of the two polymers was detectable by SEM. The release rate from microcapsules in the size range of 180-250 pm in vitro (Fig. 11) was directly proportional to the PCL content of the blend, the half-life (50% drug release)... 

The Half-life in the Environment data reflect observations of the rate of disappearance of the chemical from a medium, without necessarily identifying the cause of mechanism of loss. For example, loss from water may be a combination of evaporation, biodegradation and photolysis. Clearly these times are highly variable and depend on factors such as temperature, meteorology and the nature of the media. Again, the reader is urged to consult the original references. 

If 1000 kg/h of benzene is discharged to water, as in the second row, there is predictably a much higher concentration in water (by a factor of over 2000). There is reaction of 546 kg/h in water, advective outflow of 134 kg/h and transfer to air of 320 kg/h with negligible loss to sediment. The amount in the water is 134000 kg thus the residence time in the water is 134 h and the overall environmental residence time is a longer 140 hours. The key processes are thus reaction in water (half-life 170 h), evaporation (half-life 290 h) and advective outflow (residence time 1000 h). The evaporation half-life can be calculated as (0.693 x mass in water)/rate of transfer, i.e., (0.693 x 133863)/320 = 290 h. Clearly, competition between reaction and evaporation in the water determines the overall fate. Ninety-five percent of the benzene discharged is now found in the water, and the concentration is a fairly high 6.7 x 10 g/m3, or 670 ng/L. 

Mackay and Wolkoff (1973) estimated an evaporation half-life of 10.1 d from a surface water body that is 25 °C and 1 m deep. Singmaster (1975) studied the rate of volatilization of aldrin (1 ng/L) in a flask filled with 0.9 L water obtained from California. The flask was gently stirred and an air stream was passed over the air-water interface. He reported volatilization half-lives of 0.38, 0.59, and 0.60 h from San Francisco Bay, American River, and Sacramento River, respectively. 

Plant Although no products were identified, the half-life of chlorpyrifos in Bermuda grasses was 2.9 d (Leuck et al., 1975). The concentration and the formulation of application of chlorpyrifos will determine the rate of evaporation from leaf surfaces. Reported foliar half-lives on tomato, orange, and cotton leaves were 15-139, 1.4-96, and 5.5-57 h, respectively (Veierov et al., 1988). 

Surface Water. The volatilization half-life of naphthalene from surface water (1 m deep, water velocity 0.5 m/sec, wind velocity 22.5 m/sec) using experimentally determined Henry s law constants is estimated to be 16 h (Southworth, 1979). The reported half-lives of naphthalene in an oil-contaminated estuarine stream, clean estuarine stream, coastal waters, and in the Gulf stream are 7, 24, 63, and 1,700 d, respectively (Lee, 1977). Mackay and Wolkoff (1973) estimated an evaporation half-life of 2.9 h from a surface water body that is 25 °C and 1 m deep. In a laboratory experiment, the average volatilization half-life of naphthalene in a stirred water vessel (outer dimensions 22 x 10 x 21 cm) at 23 °C and an air flow rate of 0.20 m/sec is 380 min. The half-life was independent of wind velocity or humidity but very dependent upon temperature (Klopffer et al., 1982). 

The experiments discussed above determined the rate of disappearance and the half-life of elemental phosphorus in water in open systems. The phosphorus in these experiments disappeared due to hydrolysis/oxidation and evaporation. Spanggord et al. (1985) studied the loss of elemental phosphorus in sealed reaction flasks. In a closed reaction flask with argon-saturated water, the loss of white phosphorus can only be due to hydrolysis. The estimated half-life for hydrolysis at ambient temperatures was 84 hours (Spanggord et al. 1985). The estimated half-lives of white phosphorus at ambient temperatures due to a... 

In the last year a new formulation of aminocarb has appeared on the insecticide market. It is finely ground aminocarb suspended in an oil and it has the advantage that it can be tank mixed to give either an oil or a water suspension. Studies (10) show that, like the oil solution, this product has a half life in the same range (3.2 to 6.0 days). There was an indication of a variation in the initial rate of loss due to the physical characteristics of the water emulsion spray (in a series of repeat studies the evaporation rate was not constant). The presence of the emulsifier inhibited evaporation resulting in a higher initial foliar deposit than with the oil base spray. The occurence of the lower rate of deposit of the oil spray can be attributed to the particular oil used in the Canadian budworm sprays. To meet the concerns of the health authorities the standard No. 2 and No. 4 fuel oils which had been used are now prohibited. The accepted product, known as Insecticide Diluent 585 is volatile with an evaporation rate approaching that of water. 

VX has a water solubility of 3 g per 100 g solvent at 25°C and 7.5 g per 100 g solvent at 15°C (DA, 1974). It s Henry s Law Constant has been estimated to be 3.5x10 atm m /mol, indicating a low potential for evaporation from water (MacNaughton and Brewer, 1994) its evaporation rate is about 1/1,500 that of water (Rosenblatt et al., 1995). The agent is relatively resistant to hydrolysis (Franke, 1982) reported half-lives in water at 25°C and pH 7 range from 400 to 1000 hours (Clark, 1989) half-life increases under acidic conditions [(100 days at pH 2-3 (DA, 1974)]. Although solubility is increased at lower temperatures, low temperatures decrease the rate of hydrolysis (Clark, 1989). VX in surface waters may sink and be adsorbed by sediment (Trapp, 1985). 

PROBABLE FATE photolysis direct photolysis is slow, indirect photolysis may be important, vapor phase aldrin residues expected to react with photochemically produced hydroxyl radicals with a half-life of 35.46 min oxidation reacts to form dieldrin, photooxidation by ultraviolet light in aqueous medium 90-95°C forms 25% CO2 in 14.1 hr, 50% CO2 in 28.2 hr, 75% CO2 in 109.7 hr, photooxidation half-life in air 0.9-9.1 hrs hydrolysis too slow to be an important process volatilization an important process, evaporation rate from water 3.72x10 m4ir, will volatilize from soil surfaces sorption an important process, adsorption to sediment is... 

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 very little specific data, but photolysis may claim some of the dissolved compound, atmospheric and aquatic photolytic half-life 4.4-13 hrs, subject to near surface, direct photolysis with a half-life of 4.4 hrs, if released to air, it will be subject to direct photolysis, although adsorption may affect the rate, reaction with photochemically produced hydroxyl radicals gives an estimated half-life of gas phase crysene of 1.25 hrs oxidation chlonne and/or ozone in sufficient quantities may oxidize chrysene, photooxidation half-life in air 0.802-8.02 hrs hydrolysis not an important process volatilization probably too slow to compete with adsorption as a transport process, will not appreciably evaporate sorption adsorption onto suspended solids and sediment is the dominant transport process if released to soil or to water, expected to adsorb very strongly to the soil biological processes short-term bioaccumulation, metabolization and biodegradation are the principal fates... 

BIOLOGICAL PROPERTIES BOD5 0.002 BOD,o 0.05 BCF 1.2 Koc 40 evaporation rate 11.6 biodegradability data is unavailable but may be possible aerobic half-life 32 days-22 weeks anaerobic half-life 128 days-88 weeks can be detected in water by EPA method 601 inert gas purge followed by gas chromatography with halide specific detection or EPA method 624 gas chromatography plus mass spectrometry... 

PROBABLE FATE photolysis-, information lacking, photodissociation to chloroacetyl chloride in stratosphere is predicted oxidation-, photooxidation in troposphere may be the predominant fate, photooxidation in aquatic environments probably occurs at a slow rate hydrolysis-. unimportant compared to volatilization volatilization due to high vapor pressure, volatilization to the atmosphere should be the major transport process, if released in water, will be removed by volatilization with a half-life of 6-9 days, 5-8 days, and 23-32 hr, in a typical pond, lake, or river respectively, will be removed quickly by volatilization if released on land biological processes data is lacking, bioaccumulation not expected, biodegradation may be possible evaporation from water 25°C of 1 ppm solution 50% after 22 min, 90% after 109 min. 

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 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 significant in aquatic environment, photodissoeia-tion in stratosphere probably a significant fate oxidation not important in aquatic environment, oxidation is rapid above 110°C, photooxidation in the troposphere probably important hydrolysis too slow to be consequential, rapid above 110°C, expected to hydrolyze under alkaline conditions first-order hydrolysis half-life 45 days volatilization probable primary transport process, release to water will primarily be lost by volatilization in days to weeks, volatilization half-life in a model river and pond is estimated to be 6.3 hr and 3.5 days respectively, volatilization from dry soil will be fairly rapid biological processes NA evaporation from water 25°C of 1 ppm solution is 50% after 56 min. and 90% after less than 120 min., evaporation rate 0.65 oxidative decomposition occurs by UV radiation... 

PROBABLE FATE photolysis-, no data for rate of photolysis in aquatic environment oxidation-, in aquatic systems not expected to be important fate, photooxidation in troposphere is probably the predominant fate hydrolysis expected to be slow, neutral aqueous hydrolysis half-life 25 °C >50 years, first-order hydrolysis half-life 37 years pH 7 volatUiz/ttion primary transport process, volatilization from soil will occur biological processes NA evaporation from water 25 °C of 1 ppm solution is 50% after 21 min and 90% after 102 min release to water primarily through evaporation (half-life days to weeks) rate of evaporation half-life from water 21 min photodegrades slowly by reaction with hydroxyl radicals, half-life 24-50 days in polluted atmosphere to a few days in unpolluted atmospheres will be removed in rain... 

The test times for oven aging at 200 °C are too long for practical application (20 days = 2.9 -10 minutes up to more than 400 days = 5.8 10 minutes). Attempting to reduce the experimental period by increasing the test temperature leads to increased overlap of evaporation and oxidation and does not supply any data which are useftil in practice. It is more worthwhile to use DSC at moderately elevated pressure to determine the coefficients of the Arrhenius equation for the oxidation reactions, because it is then possible to calculate the reaction rate constant k and the half life time to extrapolate... 

All of the 23 plasticizers in Table 18.1 occur as viscous or oily liquids that range from colorless to an amber color. If these liquids were spilled on soil or sediments, a portion of the liquid could volatilize into the air, depending on the specific compound, but most of the 23 plasticizers have vapor pressures that are less than 10 mm Hg at 25°C (Table 18.13). The vapor pressures of nine of the compounds have not been measured. For these plasticizers, vapor pressures were estimated using the Fragment Constant Method. As noted earlier, most of these chemicals will also be adsorbed by soil and sediments which would reduce the extent of volatiUzation. The rate of volatilization of plasticizers from soil has not been measured. For the purpose of illustration, the Dow Method was applied to estimate the half-life of each plasticizer if it was 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 ... 

DOCUMENT It is assumed that 1% of the amount in the eatchment may be lost per time unit due to evaporation, ehemieal transformations, transport to "geologieal" eompartments, ete. The rate of loss for Cs is defined from the physieal half-life (1/30.2 years). 

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