Half-lives environmental fate

The Environmental Fate Rate Constants refer to specific degradation processes rather than media. As far as possible the original numerical quantities are given and thus there is a variety of time units with some expressions being rate constants and others half-lives. The conversion is that the rate constant k is 0.693/t1/2 where t,A is the half-life. 

The Half-life in the Environment and Environmental Fate Rate Constants are medium-specific degradation reaction half-lives selected for use in Level II and Level III calculations. As discussed earlier, emphasis was based on the fastest and the most plausible degradation process for each of the environmental compartments considered. 

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. 

Endrin ketone may react with photochemically generated hydroxyl radicals in the atmosphere, with an estimated half-life of 1.5 days (SRC 1995a). Available estimated physical/chemical properties of endrin ketone indicate that this compound will not volatilize from water however, significant bioconcentration in aquatic organisms may occur. In soils and sediments, endrin ketone is predicted to be virtually immobile however, detection of endrin ketone in groundwater and leachate samples at some hazardous waste sites suggests limited mobility of endrin ketone in certain soils (HazDat 1996). No other information could be found in the available literature on the environmental fate of endrin ketone in water, sediment, or soil. 

Environmental Fate. Di-/ -oct Iphthalate partitions primarily to soils and sediment upon release to the environment. The compound is expected to be strongly sorbed to soil and sediment particulates therefore, it should have limited mobility (EPA 1979, 1992c). Biodegradation half-lives of 1-4 weeks have been estimated for aerobic surface waters and soils. Biodegradation also takes place in sediments half-lives under anaerobic conditions have been estimated to range from of 6 months to 1 year (Howard et al. 1991). The compound may also undergo photolysis in surface waters (estimated half-life of 144 days) and photooxidation in the atmosphere (estimated half-life of about 5-45 hours) (Howard et al. 1991). Di-n-octylphthalate may persist in sediments as a result of its limited rate of biotransformation and preferential partitioning to this medium. 

Thorium occurs in nature in four isotopic forms, thorium-228, thorium-230, thorium-232, and thorium-234. Of these, thorium-228 is the decay product of naturally-occurring thorium-232, and both thorium-234 and thorium-230 are decay products of natural uranium-238. To assess the environmental fate of thorium, these isotopes of thorium with the exception of thorium-234 which has short half- life (24.1 days), should be considered. 

Environmental Fate. Little experimental data on the resonance time and half-life of chlorine dioxide and chlorite (ions or salts) in the atmosphere are available. Additional information on the transport of chlorine dioxide in the atmosphere may be useful, considering that over 900,000 pounds are released annually to air (TRIOO 2002). Additional information about the mechanism of reformation of chlorine dioxide in water distribution systems from chlorite ion is needed (Hoehn et al. 1990). Additional information concerning the transport and partitioning of chlorite (ions or salts) is also needed. 

A colleague of yours who investigates the fate of benzene sulfonates and benzene sulfonate esters in natural waters is interested in the stability of methyl-3,4-dichlorobenzene sulfonate (MDCBS) in aqueous solution. Because he has not read Chapter 13 of Environmental Organic Chemistry he asks you to help him to estimate the hydrolysis half-life of this compound in water at 25 °C and at 5°C. In the literature you find rate constants for the neutral hydrolysis of some substituted methyl benzene sulfonates at... 

Sinkkonen, S., Passivirta, J. (2000) Degradation half-life times of PCDDs. PCDFs and PCBs for environmental fate modeling. Chemosphere 40, 943-949. 

Dibutyl ether s production and use as an extracting agent and as a solvent may result in its release to the environment through various waste streams. If released to air, a vapor pressure of h.OmmHg at 25 °C indicates dibutyl ether will exist solely as a vapor in the ambient atmosphere. Vapor-phase dibutyl ether will be degraded in the atmosphere by reaction with photochemically produced hydroxyl radicals the half-life for this reaction in air is estimated to be 13 h. Direct photolysis is not expected to be an important removal process since aliphatic ethers do not absorb light in the environmental spectrum. If released to soil, dibutyl ether is expected to have high mobility based upon an estimated Koc of 51. Volatilization from moist soil surfaces may be an important fate process based upon a Henry s law constant of 6.0 x lO atmm moH. Dibutyl ether is expected to volatilize from dry soil surfaces based... 

Aquatic fate If released to water, 2-heptanone is expected to rapidly volatalize to the atmosphere. The half-life for volatilization from a model river Im deep, flowing at Ims with a wind speed of 3ms is 8.4 h. The calculated bioconcentration factors ranging from 5.5 to 19 indicate that 2-heptanone is not expected to bioconcentrate in fish and aquatic organisms. The calculated soil adsorption coefficients ranging from 44 to 285 indicate that adsorption to sediment and suspended organic matter is not an environmentally important process. Screening... 

Hydrolysis is an important environmental fate process. Hydrolysis rate is characterized by a half-life of 17.5 and 11.9 days at pH 7 and 9, respectively. TOTM is not readily biodegradable. Bioconcentration factors are measured up to 2.7 which is considered low if released into surface water. TOTM is expected to absorb to suspended solids and the sediment. Because of the major use in electric wire and cable TOTM is fixed in the matrix and no substantial exposure is expected. 

The primary environmental fate mechanism followed by stored or buried HD is hydrolysis. Although HD is rapidly hydrolyzed (a half-life of 4 to 8 min at 25° C in distilled water has been reported [Bartlett and Swain, 1949]), the overall process of hydrolytic destruction is limited by the very low water solubility of HD. Intermediate hydrolysis products and/or water-insoluble thickeners that can coat or encapsulate droplets of mustard retard hydrolysis. Because of low water solubility and formation of intermediate products, bulk amounts of HD may persist undispersed under water for some time. However, HD dispersed as droplets or mist, as in the case of an aerial attack, is expected to hydrolyze rapidly in humid air. 

Water quality parameters, such as pH, temperature, hardness, and salinity, can influence the effects of contaminants on aquatic life. The toxicity of TNT decreases slightly with increasing pH and temperature, but is not significantly affected by hardness [39], The persistence of TNT in the environment is limited, and several biological and physical processes (photolysis, hydrolysis) influence its environmental fate [39], The photolysis half-life of TNT appears to be season and latitude dependent, as it ranged from 14 h at latitude 20 in summer to 84 h at latitude 50 in winter in the northern hemisphere [40], The aquatic toxicity of several photo- and biodegradation products of TNT has been studied. Pink water obtained by constant illumination of a TNT solution was more toxic than the TNT solution to P. promelas using... 

Fig. 2 Review of MTBE behavior and fate in the environment diffuse and point sources, degradation products and its reported half-life times (ti/2) at the different environmental...

In soil, ammonia may either volatilize to the atmosphere, adsorb to soil, or undergo microbial transformation to nitrate or nitrite anions. Uptake by plants can also be a significant fate process. Ammonia at natural concentrations in soil is not believed to have a very long half-life. If ammonia is distributed to soil in large concentrations, the natural biological transformation processes can be overwhelmed, and the environmental fate of ammonia will become dependent upon the physical and chemical properties of ammonia, until the ammonia concentration returns to background levels. 

PROBABLE FATE photolysis-, direct photolysis is probably not important, if released to atmosphere, will degrade by reaction with photochemically produced hydroxyl radicals (estimated half-life 1.15 days) oxidation photooxidation in atmosphere can occur, photooxidation half-life in air 4.61-46.1 hrs hydrolysis slow hydrolysis of carbon-chlorine bond, may be important fate mechanism volatilization if released to water, volatilization is expected to be the principle removal process, but may be slow, volatilization half-lives for a model river (1 m deep) and a model environmental pond 13.9 hr, and 6.6 days respectively sorption adsorption on organic matter is possible biological processes no data on bioaccumulation or biodegradation... 

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... 

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