Atrazine photolysis: Mechanistic investigations of direct and nitrate- mediated hydroxy radical processes and the influence of dissolved organic carbon from the Chesapeake Bay

Article abstract of DOI:10.1021/es9607289

Direct and nitrate-mediated hydroxy radical photoprocesses were examined with respect to atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) transformation. Irradiation (λ > 290 nm) of aqueous solutions of atrazine in the presence of nitrate, which generates ·OH, yielded 20% of 6-amino-2- chloro-4-isopropylamino-s-triazine (CIAT), 10% of 6-amino-2-chloro-4- ethylamino-s-triazine (CEAT), 6% of 4-acetamide-2-chloro-6-isopropylamino-s- triazine (CDIT), 3% of 4-acetamide-2-chloro-6-ethylamino-s-triazine (CDET), 16% of chlorodiamino-s-triazine (CAAT), and 3% of hydroxy atrazine (OIET, 4- ethylamino-6-isopropylamino-2-hydroxy-s-triazine) at 87% atrazine conversion. Direct photolysis of atrazine was much slower and at 23% atrazine conversion gave rise to 14% OIET and ca. 9% of chloroalkyloxidized or chlorodealkylated compounds with the ratio of the reaction rate constants equal to 0.14 (κ(direct)/κ(indirect)). Results also suggest that DIET was not the product of a hydroxy radical process. The efficiency of the hydroxy radical process decreased more than 85%, with increasing DOC obtained from the surface layer of the Chesapeake Bay. However, only a slight decrease (<15%) in efficiency was observed for direct photolysis, suggesting that in the presence of surface layer DOC direct photolysis may become more important relative to the ·OH processes.

Full text of DOI:10.1021/es9607289

Environ. Sci. Technol. 1997, 31, 1476-1482
whereas during indirect photolysis a species other than the
Atrazine Photolysis: Mechanistic
Investigations of Direct and
Nitrate-Mediated Hydroxy Radical
Processes and the Influence of
Dissolved Organic Carbon from the
Chesapeake Bay
substrate absorbs the light. The excited species can then
transfer the energy directly to the substrate (sensitization),
undergo electron transfer with the substrate, or cause a series
of reactions with the subsequent formation of oxidants such
as singlet oxygen, hydroxy radical, and alkylperoxy radicals
(4-9).
Irradiation of nitrate, which is present in many natural
•
waters, has been shown to give rise to OH (6, 9-11). The
concentrations of nitrate in the Chesapeake Bay (located in
the Mid-Atlantic region of the United States) fluctuate
seasonally and spatially and are moderated by biological and
chemical processes with influences from anthropogenic
activities. For example, in the Wye River, an Eastern Shore
tributary of the Chesapeake Bay, nitrate levels range from
<14 µM NO3 during May through August up to 100 µM NO3
in January (12, 13). Nitrate concentrations at midbay were
observed at 36 µM NO3 in January 1991 and 0.3 µM NO3 in
August 1991 (14).
A L B A T O R R E N T S , †
B R E N T G . A N D E R S O N , † , ‡
S U S A N N A B I L B O U L I A N , † , ‡
W . E D W A R D J O H N S O N , ‡ A N D
C A T H L E E N J . H A P E M A N * , ‡
Environmental Engineering Program, Department
of Civil Engineering, University of Maryland,
College Park, Maryland 20742, and Environmental
Chemistry Laboratory, Natural Resources Institute,
Agricultural Research Service, U.S. Department of Agriculture,
Beltsville, Maryland 20705
Atrazine (CIET, Table 1) is a widely used herbicide in many
regions of the United States and is commonly found
throughout the entire hydrological cycle. Concentrations of
atrazine in the Chesapeake Bay and its 3000 square miles of
watershed have at times exceeded the U.S. EPA maximum
contaminant level of 0.01 µM during the spring and early
summer (15). Atrazine has also been observed in other surface
waters. For example, average levels of 0.02 µM have been
found during post-planting season in streams of the mid-
western United States (16) and up to 0.002 µM in a Swiss lake
(17).
Direct and nitrate-mediated hydroxy radical photoprocesses
were examined with respect to atrazine
(2-chloro-4-ethylamino-6-isopropylamino-s-triazine) transfor-
mation. Irradiation (λ > 290 nm) of aqueous solutions
•
of atrazine in the presence of nitrate, which generates OH,
Many reports have been published describing the pho-
tolysis of atrazine (18-23). Dechlorination, dealkylation, and
alkyl chain oxidation have all been observed in these studies.
The resulting products OIET, OEAT, OIAT, CEAT, CIAT, and
CDIT have also been observed in surface waters and rainwater
(24-28). However, the differences in direct versus photo-
initiated hydroxy radical processes have not been thoroughly
described. This lack of mechanistic understanding has led
to some confusion in describing the processes causing the
appearance of these products in the environment. For
example, the appearance of the dechlorination product OIET
has recently been attributed to a hydroxy radical process (24,
25) but in a non-photolytic hydroxy radical system, OIET was
not observed (29, 30).
yielded 20% of 6-amino-2-chloro-4-isopropylamino-s-triazine
(CIAT), 10% of 6-amino-2-chloro-4-ethylamino-s-triazine
(CEAT), 6% of 4-acetamide-2-chloro-6-isopropylamino-s-
triazine (CDIT), 3% of 4-acetamide-2-chloro-6-ethylamino-
s-triazine (CDET), 16% of chlorodiamino-s-triazine (CAAT),
and 3% of hydroxy atrazine (OIET, 4-ethylamino-6-isopro-
pylamino-2-hydroxy-s-triazine) at 87% atrazine conversion.
Direct photolysis of atrazine was much slower and at 23%
atrazine conversion gave rise to 14% OIET and ca. 9%
of chloroalkyloxidized or chlorodealkylated compounds with
the ratio of the reaction rate constants equal to 0.14 (kdirect
kindirect). Results also suggest that OIET was not the
/
product of a hydroxy radical process. The efficiency of
the hydroxy radical process decreased more than 85%, with
increasing DOC obtained from the surface layer of the
Chesapeake Bay. However, only a slight decrease (<15%)
in efficiency was observed for direct photolysis, suggesting
that in the presence of surface layer DOC direct
The aim of this work is to evaluate and discern the
mechanisms involved in the photolytic fate of atrazine. Direct
and indirect photolysis, using nitrate as a precursor for •OH,
and the products of these processes will be elucidated and
compared to other hydroxy radical processes. The relative
rates of the different mechanisms will be determined so as
to more accurately evaluate the impact of each on the overall
fate. In addition, dissolved organic carbon (DOC) not only
can serve as a hydroxy radical scavenger but also can absorb
UV light (5-9). The influence of DOC on the various processes
will also be examined. The DOC used in this study was
obtained from the surface layer of the Chesapeake Bay since
•
photolysis may become more important relative to the OH
processes.
Introduction
•
The environmental fate of pesticides is determined by various
transport and transformation processes. Solar irradiation can
initiate important transformation pathways in the atmosphere
and at the soil and water surfaces via direct or indirect
processes (1-3). In direct photolysis, the substrate absorbs
UV-visible light energy and undergoes transformation,
phototransformation and photoinitiated OH processes are
most likely to occur in the upper portion of surface waters.
Materials and Methods
Standards and Reagents. Atrazine, CEAT, CIAT, OAAT, OEAT,
OIAT, OIET, and OOAT were obtained gratis from Ciba, Plant
Protection Division (Greensboro, NC). CAAT and OOOT were
purchased from Aldrich (Milwaukee, WI). CDIT, CDET,
CDDT, and CDAT were synthesized according to procedures
discussed previously (29). Ultra-purified water (18 MΩ/ cm,
* Corresponding author e-mail: chapeman@asrr.arsusda.gov;
fax: (301)504-5048.
† University of Maryland.
‡ U.S. Department of Agriculture.
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1 4 7 6 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 31, NO. 5, 1997
S0013-936X(96)00728-6 CCC: $14.00
1997 Am erican Chem ical Society

TABLE 1. List of Triazine Compounds
acronym
compound
CAAT chlorodiam ino-s-triazine
CDAT 6-am ino-4-acetam ido-2-chloro-s-triazine
CDDT 2-chloro-4,6-diacetam ido-s-triazine
CDET 4-acetam ido-2-chloro-6-ethylam ino-s-triazine
CDIT 4-acetam ido-2-chloro-6-isopropylam ino-s-triazine
CEAT 6-am ino-2-chloro-4-ethylam ino-s-triazine
CIAT 6-am ino-2-chloro-4-isopropylam ino-s-triazine
CIET
atrazine (2-chloro-4-ethylam ino-6-isopropylam ino-s-
triazine)
OAAT am m eline (diam inohydroxy-s-triazine)
OEAT 4-ethylam ino-6-am ino-2-hydroxy-s-triazine
OIAT 6-am ino-4-isopropylam ino-2-hydroxy-s-triazine
OIET hydroxy atrazine (4-ethylam ino-2-hydroxy-6-
isopropylam ino-s-triazine)
OOAT am m elide (am inodihydroxy-s-triazine)
OOOT cyanuric acid (trihydroxy-s-triazine)
FIGURE 1. Product profile of direct photolysis of 30 µM atrazine.
Each data point represents an average of three experiments with
duplicates; standard deviations are <0.2 µM.
SCHEME 1. Products of Direct Atrazine Photolysis
FIGURE 2. Comparison of atrazine (30 µM) degradation: (1) direct
photolysis (no nitrate or t-butanol), (2) indirect photolysis (804 µM
•
nitrate, no t-butanol), (3) direct photolysis with OH quenched (30
mM t-butanol, no nitrate), (4) indirect photolysis with •OH quenched
(804 µM nitrate and 30 mM t-butanol).
Station, TX) using the persulfate oxidation method (32).
Several different samples were analyzed in triplicate, and the
sample with the highest concentration (5.3 ppm DOC) was
used in all experiments. UV spectra of the isolated DOC as
well as atrazine and atrazine with nitrate were obtained on
a Shimadzu UV160 UV/ vis recording spectrophotometer
(Columbia, MD). The UV spectrum of DOC (5 ppm) showed
a typical maximum at 205 nm (0.8 au) which rapidly decayed
to 225 nm (0.08 au) with some tailing to 350 nm (<0.01 au).
General Procedure for Photolytic Experim ents. Pho-
tolytic studies were conducted using a Suntest CPS machine
(Heraeus DSET Laboratories, Inc., Phoenix, AZ) equipped with
a xenon lamp and special glass filters restricting the trans-
mission of wavelengths below 290 nm. An average irradiation
intensity of ca. 450 W/ m2 was maintained throughout the
experiments and was measured by internal radiometer, which
was calibrated annually by the manufacturer. Chamber and
black panel temperature were monitored using thermo-
couples supplied by the manufacturer; the temperature of
samples was maintained at room temperature. Solutions
were irradiated in identical 15-mL quartz tubes sealed with
Teflon caps. Initial pH was ca. 6.5 and did not change over
the course of the reaction. (The pH of the Chesapeake Bay
ranged from 6.5 to 7.2.) In some experiments, samples were
Modulab, Type I HPLC, Continental Water System Corp., San
Antonio, TX) was used in all dilutions except as indicated.
Collection and Analysis of DOC. Samples of DOC were
obtained near the mouth of Patapsco River in the upper bay
from the bow of the R/ V Aquarius, University of Maryland,
in September 1993 using 47 cm2 stainless steel wire screens
attached to nylon lines. This technique generally collects
the top 100-450 µm (31). The screens were lowered to the
water surface, retrieved, and drained into a 4-L stainless steel
pressure filtration can (Millipore, Milford, MA). The 4-L can
was subsequently pressurized with nitrogen gas (10 psi),
forcing the contents through a 90-mm-diameter stainless steel
filter head (Millipore) containing three stacked filters in the
following order: Whatman GF/ D (nominal 1.7 µm pore size
pre-combusted at 450 °C, glass fiber), Whatman GF/ F
(nominal 0.7 µm pore size pre-combusted glass fiber), and
a 0.45-µm pore size silver membrane filter (Hytrex Filter
Division, Osmonics, Inc., Minnetonka, MN). The filtrate was
collected in a 4-L brown glass bottle, stored on ice, and
transported back to the laboratory for analysis.
DOC concentrations were measured on an Oceanographic
International Model 700 total organic carbon analyzer (College
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VOL. 31, NO. 5, 1997 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 1 4 7 7

SCHEME 2. Products of Indirect Atrazine Photolysis (•OH Process)
amended with 85.7 mg of NaNO3. These two stock solutions
and a third stock solution of 5.3 ppm DOC were used to
prepare samples for irradiation. Final concentrations were
30 µM atrazine, 0 or 800 µM NaNO3, and 0-4.2 ppm DOC.
Duplicate samples were irradiated, and each experiment was
conducted several times. In some experiments, final solutions
contained 30 µM atrazine, 0 or 800 µM NaNO3, 3 or 30 mmol
•
of tert-butanol to serve as a OH scavenger, and no DOC.
Photolytic Experim ents with CEAT and CIAT. Stock
solutions of CEAT, CIAT, and NaNO3 were prepared by adding
4.8, 6.2, and 66.1 mg, respectively, to 500 mL of deionized
water. Dilutions were prepared, affording samples that
contained 33 µM CIAT; 33 µM CIAT with 800 µM NaNO3; 28
µM CEAT; and 28 µM CEAT with 800 µM NaNO3. Duplicate
samples of all four dilutions were irradiated. In another set
of experiments, dilutions resulted in two solutions: the first
containing 26 µM CIAT and 28 µM CEAT and the second
containing 26 µM CIAT, 28 µM CEAT, and 800 µM NaNO3.
Duplicate samples were irradiated.
FIGURE 3. Product profile of indirect photolysis of 30 µM atrazine
(804 µM nitrate present). Each data point represents an average of
three experiments with duplicates; standard deviation are <0.2 µM.
To make the figure clearer, OEAT and OIAT have been excluded as
they were formed and did not accumulate to quantities more than
0.02 µM.
HPLC Analysis. Irradiated samples were analyzed directly
by HPLC employing two Gilson Model 303 HPLC pumps
(Middleton, WI) equipped with a Gilson Model 116 UV
detector (210, 225, and 235 nm monitored). Separations were
achieved using a sequence of linear gradients, 0% (4 min),
0-12% (3 min), 12-60% (5 min), and 60% (7 min) acetonitrile
in phosphoric acid buffer (pH 2) at a flow rate of 1.5 mL/ min
on a Beckman C-18 (ODS, 5 µm), end-capped, 4.6 mm × 25
cm steel-jacketed column. Identification was established by
comparison of the retention times and the UV spectra
obtained using the above gradient and a second LC system:
two Waters 510 pumps (Milford, MA) equipped with a Waters
996 photodiode array detector, a 712 autosampler, and Waters
Millennium software.
purged prior to irradiation with argon for ca. 15 min to remove
oxygen. Approximately 200 µL of each solution were removed
at selected intervals and analyzed by HPLC. Irradiations were
carried out for ca. 60 h.
Photolytic Experim ents with Atrazine. Concentrations
of nitrate and atrazine in the mainstem of the Chesapeake
Bay range from 0.3 to 100 µM and from 0.005 to 0.01 µM,
respectively (12-15). This is very near the limit of detection
by HPLC for the triazines, which is the preferred analysis
method for many of the transformation products. Therefore,
experiments were conducted at higher than normal levels
while maintaining an excess of nitrate to triazine and at similar
ratios to that found in the Chesapeake Bay. A stock solution
of atrazine was prepared by adding 32.4 mg of atrazine to 1
L of ultra-pure water. A total of 250 mL was removed and
Results
Direct Photolysis of Atrazine. Direct photolysis of atrazine
has been shown previously to proceed via excitation of the
triazine followed by dechlorination and hydroxylation.
Dealkylation of OIET was also observed (Scheme 1) (18-20).
Excitation of atrazine in ultra-pure water under simulated
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1 4 7 8 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 31, NO. 5, 1997

FIGURE 4. Product profile of (a) direct photolysis (no nitrate present) and (b) indirect photolysis (804 µM nitrate present) of CIAT. Note different
y-axis scales. Each data point represents an average of three experiments with duplicates; standard deviation are <0.2 µM.
solar irradiation afforded 14% OIET, 4% CDIT, 1% CIAT, 4%
CDET, and <1% CEAT with 76% atrazine remaining (reaction
time ) 60 h); no hydroxy dealkylated products (OEAT, OIAT,
and OAAT) were detected (Figure 1). A solution of 20 µM
OIET was irradiated under the exact same conditions as
atrazine, and no detectable loss of OIET was observed over
a 60-h period.
concentrations of CDIT and CDET, i.e., ([CIAT] + [CEAT])/
([CDIT] + [CDET]). Attack on the ethyl group was 1.7 times
as likely to occur as attack on the isopropyl as determined
from the ratio ([CIAT] + [CDIT])/ ([CEAT] + [CDET]).
While several groups observed the formation of OIET in
other hydroxy radical systems such as TiO2 and Fenton’s
reagent (23, 33), OIET was not observed in non-photo-
•
The appearance of the chlorodealkylated (CEAT and CIAT)
and chloroalkyloxidized (CDET and CDIT) products was
somewhat unexpected since these compounds were the
lytic ozonation systems (29, 30). To determine if OH was
involved in the formation of OIET, atrazine solutions con-
taining nitrate and t-butanol were irradiated and compared
to atrazine solutions containing nitrate only (indirect pho-
tolysis), t-butanol only (direct photolysis), and neither nitrate
nor t-butanol (direct photolysis). Interestingly, as Figure 2
indicates, the rate of atrazine degradation in the nitrate/ t-
butanol system was the same as the rate of direct photolysis.
Furthermore, the product profile of the nitrate/ t-butanol
system was very similar to the product profile for direct
photolysis as presented in Figure 1 (data not shown). This
strongly suggests that OIET is the result of a direct photolytic
process (i.e., excitation of the triazine) rather than a •OH
product.
Relative Rates and Reactivity. Simultaneous irradiation
of atrazine with and without nitrate was carried out. The
observed rate constants calculated from first-order rate plots
were 0.0040 ( 0.0006 and 0.029 ( 0.002 h-1 (x ) 7) for direct
and indirect photolysis, respectively, with the ratio of rate
constants (kdirect/ kindirect) equal to 0.14 ( 0.02 (Figure 2).
To obtain additional mechanistic information, CIAT and
CEAT were irradiated with and without nitrate, separately
and together. Essentially no differences in the rates of
degradation or the product ratios were observed between
the reactions conducted in separate tubes and those in the
same reaction vessel. Direct photolysis of CIAT at 24%
conversion afforded 10% OIAT, 1% CDAT, and 5% CAAT while
•
principle products of OH systems (20, 22, 23, 29, 30, 33),
although CIAT and CEAT were observed when using acetone
•
as a photosensitizer (21). To eliminate OH as a possible
reactant, t-butanol, a •OH scavenger, was added to the system.
No differences in the product ratio or the rate of atrazine loss
were observed between the t-butanol system and the system
without t-butanol (Figure 2). Another possible oxidant is
singlet oxygen (22); however, no changes in the rate or the
product ratios were found when irradiation was conducted
on argon-purged solutions.
Photoinitiated Nitrate-Mediated Hydroxy Radical Proc-
ess. Irradiation of aqueous atrazine solutions containing
nitrate, in which •OH is readily generated, afforded alkyl
oxidation and/ or removal of the alkyl moiety. At 87% atrazine
conversion (60-h irradiation), the reaction gave rise to 6%
CDIT, 20% CIAT, 3% CDET, 10% CEAT, 1% CDAT, and 16%
CAAT (Scheme 2 and Figure 3). Also formed were the
dechlorinated compounds OIET, OEAT, and OIAT at 3%,
<0.1%, and <0.1%, respectively. During the initial stages of
the reaction (i.e., less than 24 h), the products CDIT, CIAT,
CDET, and CEAT accounted for over 95% of the atrazine
degraded. Over this time period, dealkylation was favored
by 1.4 over alkyl oxidation as determined by the ratio of the
concentrations of CIAT and CEAT divided by the sum of the
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VOL. 31, NO. 5, 1997 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 1 4 7 9

FIGURE 5. Product profile of (a) direct photolysis (no nitrate present) and (b) indirect photolysis (804 µM nitrate present) of CEAT. Note
different y-axis scales. Each data point represents an average of three experiments with duplicates; standard deviation are <0.2 µM.
of DOC. In the nitrate and DOC system, alkyl oxidation was
favored over dealkylation, and the relative ratio of dechlo-
rination byproduct (OIET) to all other products increased.
For example, in the presence of nitrate and 3.2 ppm DOC, the
ratio of dealkylation to alkyl oxidation was 0.67 at 24-h
irradiation versus 1.4 in the absence of DOC. At this same
point, the ratio dechlorination/ (dealkylation + alkyl oxidation)
was 0.15 as compared to 0.029 in the absence of DOC. This
provides further evidence that OIET formation is not a hydroxy
radical process.
A plot of ln k versus ln [DOC], where k is the observed rate
constant from first-order rate plots, clearly indicated the
dependence of indirect photolysis on the [DOC]; k4.2 ppm DOC
/
kno DOC ) 0.20 (Figure 7). Direct photolysis was affected less
by the increase in concentration of surface layer DOC; k4.2 ppm
DOC/ kno
) 0.83.
DOC
FIGURE 6. CEAT versus CIAT degradation without (direct photolysis)
and with nitrate (indirect photolysis).
Discussion
The ratio of products formed upon direct and indirect
irradiation are significantly different. Results from this study
strongly suggest that the formation of OIET is not a hydroxy
radical process. This further implies that the observation of
OIET in surface waters is due to the absorption of light energy
by atrazine itself (direct photolysis), photosensitization, metal-
assisted hydrolysis or biotic processes. In addition, since no
effect was observed on direct photolysis degradation rate
relative to ethyl or isopropyl substitution, the rate-determining
step must not involve the alkyl group, further supporting that
dechlorination is the major degradation pathway in direct
photolysis. And, the rate-determining step in the photo-
initiated nitrate-mediated hydroxy radical system must
therefore involve the alkyl group for exactly the opposite
direct photolysis of CEAT at 24% conversion gave rise to 5%
OEAT, 1% CDAT, and 5% CAAT. Photolysis of CIAT in the
presence of nitrate gave rise to 2% CDAT, 43% CAAT, and 5%
OIAT at 60% conversion, while irradiation of CEAT in the
presence of nitrate at 77% conversion afforded 7% CDAT,
55% CAAT, and 2% OEAT (Figures 4 and 5). The observable
rate constants were calculated from first-order rate plots: kCEAT,
direct ) kCIAT, direct ) 0.004 h -1, kCEAT, indirect ) 0.026 h -1 , and kCIAT,
indirect ) 0.016 h -1 (Figure 6). Again, attack at the ethyl carbon
was favored 1.6 over the isopropyl.
Effect of DOC. The effect of surface layer DOC on direct
and indirect atrazine photolysis was examined using various
concentrations of DOC. The product profile of direct
photolysis was very similar to that obtained in the absence
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1 4 8 0 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 31, NO. 5, 1997

Acknowledgments
The authors extend their sincere appreciation to Dr. Glenn
C. Miller, University of Nevada, Reno, for his insightful
comments. This work was funded in part by a Cooperative
Agreement (Contract T-5-1270-0090) from the U.S. Depart-
ment of Agriculture. Mention of specific products or suppliers
is for identification and does not imply endorsement by U.S.
Department of Agriculture to the exclusion of other suitable
products or suppliers.
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FIGURE 7. Effect of DOC concentration (ppm) on atrazine degradation
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between CEAT and CIAT. These data also suggest that a
•
sterically controlled mechanism is operational in the OH
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•
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In the current study, indirect photolysis decreased sub-
stantially whereas only a slight decrease was observed in the
direct photolysis reactions with increasing DOC concentra-
tion. These data, in contrast with the earlier studies, indicate
that the DOC in this study does not effectively compete with
atrazine for UV light but does efficiently scavenge •OH.
Indeed, the UV spectrum shows that DOC from the surface
layer does not effectively absorb UV light, indicating low
aromatic or conjugated character. This further suggests that
a significant concentration of structural components sus-
ceptible to hydroxy radical attack, such as alkyl hydrogens,
maybe present in this DOC.
This study demonstrates that much knowledge can be
obtained by determining degradation products, their relative
ratios, and the mechanisms that lead to their formation. DOC
concentration and presumably the type of functional groups
and aromaticity present in the DOC will also influence the
photoprocesses differently. Clearly, in this study direct
photolysis becomes more important while •OH processes
contribute less to the photolytic fate of atrazine as surface
layer DOC concentrations increase, but this was not the case
for all types of DOC. Thus, to predict accurately the photolytic
fate of atrazine and other organic pollutants in surface water,
the differences in direct versus indirect processes should be
delineated as well as the influence of diverse structural
properties of DOC.
9
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Received for review August 22, 1996. Revised manuscript
received December 12, 1996. Accepted December 16, 1996.X
ES9607289
X Abstract published in Advance ACS Abstracts, February 15, 1997.
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