Atrazine photolysis

Torrents A, BG Anderson, S Bilboulian, WE Johnson, CJ Hapeman (1997) Atrazine photolysis mechanistic investigations of direct and nitrate-mediated hydroxyl radical processes and the influence of dissolved organic carbon from the Chesapeake Bay. Environ Sci Technol 31 1476-1482. 

Schmitt, Ph., D. Freitag, Y. Sanlaville, J. Lintelmann, and A. Kettrup (1995). Capillary electrophoretic study of atrazine photolysis. J. Chromatogr. A, 709 215-225. 

Torrents, A. Anderson, B. G. Bilboulian, S. Johnson, W. E. Hapeman, C. J. Atrazine Photolysis Mechanistic Investigations of Direct and Nitrate-Mediated Hydroxy Radical Processes and the Influence of Dissolved Organic Carbon from the Chesapeake Bay, Environ. Sci. Technol. 1997, 31, 1476-1482. 

Atrazine is successively transformed to 2,4,6-trihydroxy-l,3,5-triazine (Pelizzetti et al. 1990) by dealkylation of the alkylamine side chains and hydrolytic displacement of the ring chlorine and amino groups (Figure 1.3). A comparison has been made between direct photolysis and nitrate-mediated hydroxyl radical reactions (Torrents et al. 1997) the rates of the latter were much greater under the conditions of this experiment, and the major difference in the products was the absence of ring hydroxylation with loss of chloride. 

An aqueous solution (15 °C) of atrazine (10 mg/L) containing acetone (1% by volume) as a photosensitizer was exposed to UV light (). = 290 nm). The reported photolysis half-lives with and without the sensitizer were 25 and 4.9 h, respectively (Burkhard and Guth, 1976). Photoproducts formed were hydroxytriazines, two de-A-alkyls, and the de-A/A -dialkyl analogs. 

Illustrative Example 16.2 Estimating the Indirect Photolysis Half-Life of Atrazine in a Shallow Pond Reactions with Singlet Oxygen ( 02)... 

The indirect photolysis half-life of atrazine (assuming that reaction with HO is the dominant process) is then given by (Eq. 16-7) ... 

Estimating the Indirect Photolysis Half-Life of Atrazine in a Shallow Pond... 

Deethylatrazine, deisopropylatrazine, and acetamido-s-triazines are the primary oxidation by-products of atrazine by UV/Q3. UV photolysis of atrazine... 

Prosen, H., and Zupancic-Kralj, L. (2004). Evaluation of photolysis and hydrolysis of atrazine and its first degradation products in the presence of humic acids. Environ. Pollut. 133, 517-529. 

Garbin et al. (2007) investigated the direct and indirect photolysis of pesticide residues atrazine, imazaquin, and iprodione (3-(3,5-dichlorophenyl)-/V-(l-methylethyl)2,4-dioxo-l-imidazoline-carboxamide) in aqueous solutions in the presence and absence of HS and under ultraviolet and visible radiation (280-480 nm) (Figure 16.29). All pesticides showed a fast direct photolysis following a first-order kinetics. HS were added to the pesticide solutions in concentrations from 1 to 100 mg liter1 by means of HS mixture and pesticide stock solutions. HS only exhibited photocatalytic effect within specific concentration ranges—that is, about 30 mg liter-1 for atrazine and below 10 mg liter-1 for iprodione. For imazaquin, only a decrease was observed in the photolysis rate with HS addition. 

Current information on the photochemical dissipation of the triazine herbicides in the atmosphere is very limited. No studies concerning the vapor-phase photolysis of these herbicides have been reported, and only two studies have investigated the phototransformation of triazine herbicides when associated with atmospheric aerosols. Photodegradation of atrazine and terbuthylazine was observed in these studies, but the significance of photodegradation in the dissipation of atmospheric concentrations of these herbicides has yet to be established. 

Nearly all thin film photolysis studies involving triazine herbicides have utilized model surfaces such as filter paper (Jordan et al., 1964 Morita et al., 1988), aluminum (Jordan et al., 1965), glass (Pape and Zabik, 1972 Chen et al., 1984 Hubbs and Lavy, 1990), and silica gel (Lotz et al., 1983). A shortcoming of the use of model surfaces is that herbicide dissipation due to volatility losses is often not accounted for (Hubbs and Lavy, 1990). Konstantinou et al. (2001) studied the sunlight photolysis of atrazine, propazine, and prometryn on soil (sandy clay loam, clay loam, and... 

Direct photolysis of aqueous solutions of the 2-chloro-.v-iriaz.ine herbicides (atrazine, simazine, propazine) proceeds via excitation of the triazine molecule, followed mainly by dechlorination and hydroxylation to form the corresponding hydroxytriazine (Pape and Zabik, 1970 Khan and Schnitzer, 1978 Chan et al, 1992 Lai et al, 1995 Schmitt et al, 1995 Sanlaville et al, 1997 Torrents et al, 1997 Texier et al, 1999b Hequet et al, 2001). This observation - plus the fact that when 2-chloro-v-triazine herbicides are photolyzed in methanol, ethanol, and n-butanol, the respective 2-alkoxy derivatives are formed - indicates a mechanism involving photochemical solvolysis rather than the involvement of hydroxyl radicals. This conclusion is supported by the fact that the rate of oxidation of atrazine was unaffected by the presence of either bicarbonate ion (Beltran et al, 1993) or ferf-butanol (Torrents et al, 1997), both strong hydroxyl radical scavengers. 

Figure 23.1 Direct photolysis of atrazine in aqueous solution.

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... 

Figure 23.2 Photoproducts resulting from the photolysis (>290 nm) of an aqueous solution of atrazine in the presence of nitrate.

When irradiated with UV light in aqueous solution, hydrated ferric ions are photoreduced to ferrous ions with the production of hydroxyl radicals. Thus, the photolysis (>290nm) of aqueous solutions of atrazine, ametryn, prometryn, and prometon in the presence of ferric perchlorate or ferric sulfate was greatly enhanced in comparison to direct photolysis (Larson et al., 1991). In the absence of oxygen or in stream water, photoreaction rates were... 

CAAT, the didealkylated product. No hydroxyl analogs were formed. Penuela and Barcelo (2000) reported that the rates of photolysis (sunlight, >286 nm) of aqueous solutions of atrazine or desethylatrazine (CAfT) were greater in the presence of ferric ion compared to Ti02. 

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). 

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