Photolysis aquatic systems

No information was found on the transformation of diisopropyl methylphosphonate in the atmosphere. Based on the results of environmental fate studies of diisopropyl methylphosphonate in distilled water and natural water, photolysis (either direct or indirect) is not important in the transformation of diisopropyl methylphosphonate in aquatic systems (Spanggord et al. 1979). The ultraviolet and infrared laser-induced photodegradation of diisopropyl methylphosphonate in both the vapor or liquid phase has been demonstrated (Radziemski 1981). Light hydrocarbon gases were the principal decomposition products. Hydrogen, carbon monoxide (CO), carbon dioxide (C02), and water were also detected. 

Diisopropyl methylphosphonate does not undergo direct or indirect photolysis in aquatic systems, as demonstrated by the stability of the compound in distilled water or in a natural water sample after 232 hours of reaction time with the mercury lamp filtered to exclude all wavelengths below 290 nm (Spanggord et al. 1979). 

Methoxychlor. Methoxychlor is strongly adsorbed to the soil and does not leach, and volatilization is slow. There is no evidence for oxidation, and although photolysis is rapid in aquatic systems, it is assumed not to occur in the soil environment. The hydrolysis half-life is a year in aquatic systems (33) and probably longer in soil systems because of adsorption. Biodegradation does occur in soil systems, however, with a half-life of from 1 to 3 weeks (34). Methoxychlor would not persist in the soil environment. 

Monkiedje et al. [10] investigated the fate of niclosamide in aquatic system both under laboratory and field conditions. The octanol/watcr partition coefficient (Kaw) of niclosamide was 5.880 x 10 4. Adsorption isotherm studies indicated that the Freundlich parameters (K, n) for niclosamide were 0.02 and 4.93, respectively, for powder activated carbon (PAC), and 9.85 x 10 5 and 2.81, respectively, for silt loam soil. The adsorption coefficient (Aoc) for the drug was 0.02 for PAC, and 4.34 x 10-3 for the same soil. Hydrolysis of niclosamide occurred in distilled water buffer at pH above 7. No photolysis of the drug was observed in water after exposure to long-wave UV light for 4 h. Similarly, neither chemically volatilized from water following 5 h of sample aeration. Under field conditions, niclosamide persisted in ponds for over 14 days. The half-life of niclosamide was 3.40 days. 

Simmons, M.S. and Zepp, R.G. Influence of humic substances on photolysis of nitroaromatic compounds in aquatic systems. Water Res., 20(7) 899-904, 1986. 

Although the paths of dissipation of fenitrothion in aquatic systems are well known, their relative importance needs to be established at the pg/L concentrations observed in field studies. For example, volatilization has been suggested as a major path of loss from lakes (6) but has not been measured directly. The relative contribution of photolysis under shaded and unshaded conditions has also not been studied. 

Photolysis not important only by UV in the stratosphere (Robbins 1976) probably not significant in aquatic systems (Callahan et al. 1979) ... 

Equation 17.26 is directly involved in DOM photomineralization, and Equation 17.25 yields Fe2+. Complexation of Fe(III) by organic ligands is in competition with the precipitation of ferric oxide colloids [79], and the formation of ferrous iron on photolysis of Fe(III)-carboxylate complexes is an important factor in defining the bioavailability of iron in aquatic systems. Iron bioavailabihty, minimal for the oxides and maximal for Fe2+, is considerably enhanced by the formation of Fe(III)-organic complexes and their subsequent photolysis. Iron bioavailabihty plays a key role in phytoplankton productivity in oceans [80-82], while that of freshwater is mainly controlled by nitrogen and phosphoms. 

Hwang, H.-M., Hodson, R.E., Lee, R.F. (1987) Photolysis of phenol and chlorophenols in estuarine water. In Photochemistry of Environmental Aquatic Systems. American Chemical Society, Washington DC. 

Zepp, R.G., Schlotzhauer, P F. (1983) Influence of algae on photolysis rates of chemicals in water. Environ. Sci. Technol. 17,462-468. Zepp, R.G., Wolfe, N.L., Gordon, J.A., Fincher, R.C. (1976) Light-induced transformation of methoxychlor in aquatic systems. 

Biogeochemical interactions of UVR upon DOM in aquatic systems are also important, but poorly studied at the ecosystem level. Continued intensive study of natural dissolved organic substances in aquatic ecosystems is resulting in improved understanding of the many ways in which these diverse compounds, particularly humic compounds, can interact with other important metabolic components. Any of these processes will be altered by UV partial or complete photolysis of DOM. Examples are manifold ... 

Several possible mechanisms are available for UV-induced photoreactions of iron complexes. First, direct photoreactions involving ligand-to-metal charge transfer are likely to be one of the most important mechanisms for photoreaction [117,198,224]. Second, iron complexes can be reduced by photochemically-produced superoxide [207-209]. Superoxide ions are formed via the photoreduction of molecular oxygen by CDOM and it is one of the most concentrated radicals in seawater and is the precursor to hydrogen peroxide [Chapter 8]. Superoxide-induced reduction of Fe(iii) is an important mechanism in certain lakes [207]. However, the fact that Fe(ii) photoproduction can be more rapid in oxygen-free water than in air-saturated water in acidic estuaries [59] or model systems with well-defined organic acid complexes of Fe(iii) [117] indicates that direct photolysis of Fe(iii) is likely to be a dominant mechanism for Fe(ii) photoproduction in many aquatic systems. 

Factors that control the fate and transport of organic compounds in aquatic systems include photolysis, hydrolysis, sorption, hydrodynamics, and biodegradation. Biodegradation is the least well understood of these processes, primarily because it is difficult to predict the effects of adaptation, or acclimation, of microbial populations in response to specific compounds. 

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 photooxidation to chlorinated biphenyls and chlorinated benzophenones occurs, could be important in aquatic systems, atmospheric and aqueous photo-lytic half-life 6.1 days, photolytic half-life if released to ware 15-26 hrs oxidation photooxidation half-life in air 5.25-40.9 hrs, vapor phase half-life in the atmosphere 4.63 hrs from reaction with photochemical ly produced hydroxyl radicals hydroiysis not an important process ... 

PROBABLE FATE photolysis volatilized methyl bromide should photodissociate above the ocean layer, probably not significant in aquatic systems, reaction with photochemi-cally produced hydroxyl radicals has a half-life from 0.29-1.6 yrs, direct photolysis is the dominant fate in the stratosphere, but is not expected to be important in the troposphere oxidation atmospheric photooxidation by hydroxyl radicals releases inorganic bromide which is carried... 

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... 

Figure 6.10 Photolysis at 313 ntn of TNT (4.9 x 10 A/) in distilled and natural waters. [Reproduced from W. R. Mabey, D. Tse, A. Baraze, and T. MiU, Photolysis of nitroaromatics in aquatic systems, 1. 2,4,6-Trinitrotoluene , Chemosphere 12, 3. Copyright 1983, with permission from Elsevier]...

Fisher AM, Winterle JS, Mill T (1987) Primary photochemical processes in photolysis mediated by humic substances. In Zika RG, Cooper WJ (eds) Photochemistry of environmental aquatic systems. ACS Symposium Series 237, American Chemical Society, Washington DC, p 141... 

Photolysis by sunlight Is an Important environmental degradation process for many pollutants In aquatic systems. Photolytlc reactions In complex organic mixtures such as those found In natural waters, wastewaters, and other surface waters are likely to be enhanced by "sensitizers" or retarded by "quenchers" that may be present In complex organic matrices. 

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