Photolysis in distilled water

The photodegradation of an aqueous solution of terbuthylazine was not only accelerated, but was also more extensive in the presence of humic acids isolated from soil (Mansour et al., 1997). In the absence of humic acids, only hydroxyterbuthylazine (OBET) was formed (Sanlaville et al., 1996), whereas in the presence of humic acids, dealkylated products (CBAT, CBDT, CEAT, CAAT, OAAT) were formed (Table 23.2) (Sanlaville et al., 1996 Mansour et al., 1997). In contrast, fulvic acids isolated from stream water slowed the photolysis of terbuthylazine, most likely reflecting differences in structure between the soil- and stream-derived materials. The photodegradation of atrazine and its initial photoproduct OEIT (Table 23.2) in artificial sea water containing humic acids was also accelerated compared to photolysis in distilled water (Durand et al., 1990,1991). 

Surface water t,/2 = 0.025 - 0.075 h, based on direct photolysis in distilled water in midday summer sunlight (Banerjee et al. 1978 Sikka et al. 1978 quoted, Howard et al. 1991) and approximate winter sunlight direct photolysis half-life (Banerjee et al. 1978 Sikka et al. 1978 Lyman et al. 1982 quoted, Howard et al. 1991). 

Photolysis In Distilled Water. The six test compounds were exposed to sunlight Individually In distilled water to study their photo-lytic behavior In the absence of an organic matrix. These results were then compared with those obtained In aqueous CRM-1 to evaluate the effect of the presence of the matrix. 

Figure 5. Oxidant concentrations during ozone photolysis in distilled water.

Saunders and Nosier studied the photolysis of NDPA by sunlight in lake water and by sunlamps in distilled water. They found fairly rapid NDPA decomposition in both cases, and in contrast to published work with other nitrosodialkyl amines, did not observe any pH effects in the range pH 3-9. The primary product in water was 1-ami nopropane dipropylamine was also observed. 

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). 

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. 

Photolytic. Photolysis of 2,4-D in distilled water using mercury arc lamps (A, = 254 nm) or by natural sunlight yielded 2,4-dichlorophenol, 4-chlorocatechol, 2-hydroxy-4-chlorophenoxyacetic acid, 1,2,4-benzenetriol, and polymeric humic acids. The half-life for this reaction is 50 min (Crosby and Tutass, 1966). A half-life of 2 to 4 d was reported for 2,4-D in water irradiated at 356 nm (Baur and Bovey, 1974). 

Photolytic. Distilled water irradiated with UV light (X = 290 nm) yielded the following photolysis products 2-chloro-l-propanol, allyl chloride, allyl alcohol, and acetone. The photolysis half-life in distilled water is 50 min, but in distilled water containing hydrogen peroxide, the half-life decreased to <30 min (Milano et al, 1988). 

Photolytic. The major photolysis and hydrolysis products identified in distilled water were pentachlorocyclopentenone and hexachlorocyclopentenone. In mineralized water, the products identified include cis- and /ra/3s-pentachlorobutadiene, tetrachlorobutenyne, and pentachloro-pentadienoic acid (Chou and Griffin, 1983). In a similar experiment, irradiation of hexachlorocyclopentadiene in water by mercury-vapor lamps resulted in the formation of 2,3,4,4,5-pentachloro-2-cyclopentenone. This compound hydrolyzed partially to hexachloroindenone (Butz et ah, 1982). Other photodegradation products identified include hexachloro-2-cyclopentenone and hexachloro-3-cyclopentenone as major products. Secondary photodegradation products reported include pentachloro-as-2,4-pentadienoic acid, Z- and A-pentachlorobutadiene, and tetrachloro-butyne (Chou et ah, 1987). In natural surface waters, direct photolysis of hexachlorobutadiene via sunlight results in a half-life of 10.7 min (Wolfe et al, 1982). 

In sterile water and river water, photolytlc half-lives of 41.25 d and 16 h were reported, respectively (Archer, 1971). Zepp and Schlotzhauer (1983) found photolysis of malathion in water containing algae to occur at a rate more than 25 times faster than in distilled water. 

Fukuda et al. (1988) studied the photolysis of naphthalene in distilled water using a high pressure mercury lamp. After 96 h of irradiation, a rate constant of 0.028/h with a half-life of 25 h was determined. When the experiment was replicated in the presence of various NaCl concentrations, they found that the rate of photolysis increased proportionately to the concentration of NaCl. The photolysis rates of naphthalene at NaCl concentrations of 0.2, 0.3, 0.4, and 0.5 M following 3 h of irradiation were 33.3, 50.6, 91.6, and 99.2%, respectively. It appeared that the presence of NaCl, the main component in seawater, is the cause for the increased rate of degradation. Schwarz and Wasik (1976) reported a fluorescence quantum yield of 0.16 for naphthalene in water. 

When an aqueous solution containing pentachlorophenol (45 pM) and a suspension of titanium dioxide (2 g/L) was irradiated with UV light, carbon dioxide and HCl formed in quantitative amounts. The half-life for this reaction at 45-50 °C is 8 min (Barbeni et al, 1985). When an aqueous solution containing pentachlorophenol was photooxidized by UV light at 90-95 °C, 25, 50, and 75% degraded to carbon dioxide after 31.7, 66.0, and 180.7 h, respectively (Knoevenagel and Himmelreich, 1976). The photolysis half-lives of pentachlorophenol under sunlight irradiation in distilled water and river water were 27 and 53 h, respectively (Mansour et al., 1989). 

Photolytic. The reported photolysis half-lives of chlorsulfuron in distilled water, methanol, and natural creek water at 1 >290 nm were 18, 92, and 18 h, respectively. In all cases, 2-chlorobenzenesulfonamide, 2-methoxy-4-methyl-6-amino-l,3,5-triazine, and trace amounts of the tentatively... 

When prometryn in aqueous solution was exposed to UV light for 3 h, the herbicide was completely converted to hydroxypropazine. Irradiation of soil suspensions containing prometryn was found to be more resistant to photodecomposition. About 75% of the applied amount was converted to hydroxypropazine after 72 h of exposure (Khan, 1982). The UV (A = 253.7 nm) photolysis of prometryn in water, methanol, ethanol, /i-butanol, and benzene yielded 2-methylthio-4,6-bis(isopropylamino)-s-triazine. At wavelengths >300 nm, photodegradation was not observed (Pape and Zabik, 1970). Khan and Gamble (1983) also studied the UV irradiation (A = 253.7 nm) of prometryn in distilled water and dissolved humic substances. In distilled water, 2-hydroxy-4,6-bis(isopropylamino)-5-triazine and 4,6-bis(isopropylamino)-5-triazine formed as major products. 

If released to water, 1,3-DNB and 1,3,5-TNB may be subject to direct photolysis when exposed to sunlight because both compounds can absorb light at wavelengths greater than 290 nm (ERA 1976 Mill and Mabey 1985). However, no data were located regarding the photolysis of 1,3,5-TNB in water. The photolytic half-life of 1,3-DNB in pure water was calculated to be 23 days (Simmons and Zepp 1986). A three-to four-fold increase in the rate of photoreaction of 1,3-DNB was observed in ambient waters containing natural humic substances or in distilled water containing dissolved humic materials compared to reaction without humic substances (Simmons and Zepp 1986). This enhancement of the reaction rate has been attributed to catalysis of the photoreaction by photosensitization effects of humic substances. 

Distilled rather than natural water is often used as the solvent for determination of quantum yields for two major reasons. First, the total absorbance of the solution at the wavelength of irradiation should not exceed 0.02. Second, and more important, the presence of natural water constituents (e.g., humic material, nitrate) could enhance the total photolytic transformation rate by indirect photolytic processes as described in Chapter 16. Zepp and Baughman (1978) have argued that for many chemicals d>,r obtained in distilled water is nearly the same as that observed in natural waters (at least in uncontaminated freshwaters), because concentrations of natural water constituents that could undergo reactions with or quench photolysis of excited pollutants are generally very low. Furthermore, the effects of molecular oxygen, which may act as a quencher, can also be studied in distilled water. 

Rates of photolysis for atrazine (Mansour et al., 1988) and other pesticides (Mansour et al., 1997) have been reported to be greater in natural river waters than in distilled water. These enhanced photolysis rates in natural waters are most... 

Photolysis aqueous photolysis tA = 67-200 d, based on measured photolysis rate constant in distilled water under midday sun at 40°N latitude (Simmons Zepp 1986 Howard 1989 Howard et al. 1991) atmospheric photolysis tA = 67-200 d, based on measured photolysis rate constant in distilled water under midday sun at 40°N latitude (Simmons Zepp 1986 quoted, Howard 1989 Howard et al. 1991) rate constant k = 2.37 x 10-3 Ir1 with H202 under photolysis at 25°C in F-l 13 solution and with HO- in the gas (Dilling et al. 1988). 

Photolysis t,/2 = 2.25 h in distilled water (Tanaka et al. 1981 quoted, Cessna Muir 1991) 640 ppb contaminated water in the presence of Ti02 and H202 photodegraded to 3.5 ppb by 15 h solar irradiation with complete degradation after 75 h (Muszkat et al. 1992). 

Photolysis t,/2 = 6 h for 206 pg/ml, to degrade in distilled water under sunlight (Sheets 1963 quoted, Cessna Muir 1991) ... 

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