Remediation of s-triazines contaminated water in a laboratory scale apparatus using zero-valent iron powder

Article abstract of DOI:10.1016/S0045-6535(00)00133-8

Atrazine, propazine and simazine were tested separately and in mixture by batch procedure in a laboratory-constructed apparatus. 3.751 of a buffered s-triazines pesticide solution was treated at room temperature by 325-mesh zero-valent iron powder (ZVIP) (20 g/l). High performance liquid chromatography was used to separate by-products and study the decline in the pesticide's concentrations. Results obtained show that the order of degradation was simazine, atrazine and then propazine. The half-lives (t(1/2)) of the s-triazines pesticides are, respectively, 7.4, 9.0 and 10.6 min when they are treated separately, and 9.8, 11.2 and 13.7 min when they are treated together under the same conditions. The final by-product obtained after 50 min of contact of simazine with ZVIP shows a shift to longer wavelength in its UV spectrum. A similar phenomenon is shown for atrazine and propazine. Identical primary by-products are produced and subsequently degraded to 4,6-(diamino)-s-triazine, which seems to be the major by-product of the reductive treatment process. Pathways for the degradation of the studied s-triazines by ZVIP are proposed. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0045-6535(00)00133-8

Chemosphere 41 (2000) 1835±1843
Remediation of s-triazines contaminated water in a laboratory
scale apparatus using zero-valent iron powder
*
Antoine Ghauch , Joel Suptil
ESIGEC-Laboratory of Chemistry and Environmental Engineering LCIE, University of Savoie, Scienti®c Campus, Savoie Technolac,
7
3376 le Bourget du Lac Cedex, France
Received 28 February 2000; accepted 6 April 2000
Abstract
Atrazine, propazine and simazine were tested separately and in mixture by batch procedure in a laboratory-con-
structed apparatus. 3.75 l of a bu€ered s-triazines pesticide solution was treated at room temperature by 325-mesh zero-
valent iron powder (ZVIP) (20 g/l). High performance liquid chromatography was used to separate by-products and
study the decline in the pesticideÕs concentrations. Results obtained show that the order of degradation was simazine,
atrazine and then propazine. The half-lives (t1=2) of the s-triazines pesticides are, respectively, 7.4, 9.0 and 10.6 min when
they are treated separately, and 9.8, 11.2 and 13.7 min when they are treated together under the same conditions. The
®nal by-product obtained after 50 min of contact of simazine with ZVIP shows a shift to longer wavelength in its UV
spectrum. A similar phenomenon is shown for atrazine and propazine. Identical primary by-products are produced and
subsequently degraded to 4,6-(diamino)-s-triazine, which seems to be the major by-product of the reductive treatment
process. Pathways for the degradation of the studied s-triazines by ZVIP are proposed. Ó 2000 Elsevier Science Ltd.
All rights reserved.
Keywords: Iron; Pesticides; Reduction; Treatment
1
. Introduction
and sorghum acres are treated with atrazine annually
for weed control, which accounts for most of the sev-
eral million pounds used per year. In 1994, for exam-
ple, about 21±34 million pounds of cyanazine were
applied annually (US), with about 85±90% used to
control weeds on ®eld corn. After December 2002,
cyanazine cannot be used. Roughly 5±7 million pounds
of simazine are used per year. About one-third of that
amount is applied to ®eld corn, one-third to orchard
fruits and nuts, and the remainder is applied to non-
crop sites such as lawns (EPA, 1999). Approximately,
20±40 thousand pounds of propazine are used per year
on sorghum. The EPA has received and reviewed many
studies on triazines, most which were required of the
registrants as a condition of initial and continued reg-
istration. Based on the results of these studies, the
Agency is concerned about potential cancer risks
The ubiquitous use of triazine pesticides in agricul-
ture applications has resulted in extensive groundwater
contamination. The triazines are a group of chemically
similar herbicides including atrazine, cyanazine, prop-
azine and simazine primarily used to control broadleaf
weeds. Triazines are characterized by a symmetrical
six-membered ring consisting of alternating carbon and
nitrogen atoms. Atrazine currently is one of the two
most widely used agriculture pesticides in the US and
Europe (EPA, 1999). About three-fourths of ®eld corn
*
Tel.: +33-4-7975-8844; fax: +33-4-7975-8843.
E-mail address: antoine.ghauch@univ-savoie.fr (A. Ghauch).
0045-6535/00/$ - see front matter Ó 2000 Elsevier Science Ltd. All rights reserved.
PII: S 0 0 4 5 - 6 5 3 5 ( 0 0 ) 0 0 1 3 3 - 8

1
836
A. Ghauch, J. Suptil / Chemosphere 41 (2000) 1835±1843
Fig. 1. Structure of the triazine compounds.
Fig. 2. Schematic representation of the cylindro-conical pilot treatment process. Capacity: 3.75 l, material: clear Poly-Vinyl Chloride
PVC), weight: 1 kg.
(
resulting from exposure to the triazines. Because of
their persistent in water and mobile soil, triazines are
among the most frequently detected pesticides in
groundwater (EPA, 1999).
In order to remediate pesticides from water, several
researchers have studied elimination of these contam-
inants using di€erent method of treatment. With the
exception of granular activated carbon (Duguet et al.,
1
992) and oxidation processes (De Laat et al., 1995),
neither of which is easily adaptable at low cost ap-
plications, relatively little attention has been focussed
on reductive degradation processes (Sweeny, 1981;
Vogel et al., 1987; Je€ers et al., 1989; Matheson and
Tratnyek, 1994; Roberts et al., 1996; Siantar et al.,
1
996) using zero-valent iron powder (ZVIP). Cao et al.
1999) have investigated the reducing degradation of
(
Fig. 3. UV-Vis absorption spectra of simazine (1.25 mg/l, 22°C,
phosphate bu€ered solution pH ˆ 6.6) during treatment with
acidic pretreated ZVIP (20 g/l). (1) 0 min; (2) 5 min; (3) 10 min;
(4) 20 min; (5) 30 min.
azo dye by zero-valent iron in aqueous solution and
have shown an e€ective treatment with half-lives of
several minutes for all studied organic compounds.

A. Ghauch, J. Suptil / Chemosphere 41 (2000) 1835±1843
1837
Recently, Ghauch et al. (1999) investigated the treat-
ment of water contaminated with atrazine and para-
thion using ZVIP. They found that a rapid decreasing
in pesticides concentration from 1 ppm (atrazine) and
temperature phosphorescence and liquid chromatog-
raphy (Ghauch, 2000; Ghauch et al., 2000b,c). They
found that the half-life of carbaryl being close to
several minutes, and the degradation device with
acidic pre-treated ZVIP stills better than with unpre-
0
.1 ppm (parathion) to undetectable quantities re-
3
‡
quires 30 min. They also carried out reductive treat-
ment of an industrial e‚uent contaminated by
pesticides without the identi®cation of by-products.
More recently, Ghauch et al. (2000a) studied for the
treated iron. The concentration of iron cations ꢀFe †
in the treated solution was determined by di€use re-
¯ectance spectroscopy (Ghauch et al., 2000d).
As a consequence of the previous highly encouraging
tests, the present study was undertaken to evaluate the
rate of degradation of the triazine pesticides (Fig. 1) in
®rst time the degradation of carbaryl insecticide (car-
bamate group) using ZVIP by solid surface room
Fig. 4. (a) S
nm. S -HPLC chromatogram and UV absorption spectra of by-product at 60 min of treatment with ZVIP (20 g/l). (b) A
chromatogram and UV absorption spectrum of atrazine. Rt ˆ 7.19 min. Maximum absorption peak is at 223.8 nm. A
chromatogram and UV absorption spectra of by-products at 60 min of treatment with ZVIP (20 g/l). (c) P
1
-HPLC chromatogram and UV absorption spectrum of simazine. Rt ˆ 4.9 min. Maximum absorption peak is at 223.8
2
1
-HPLC
-HPLC
2
1
-HPLC chromatogram and
2
-HPLC chromatogram and UV
UV absorption spectrum of propazine. Rt ˆ 11.4 min. Maximum absorption peak is at 223.8 nm. P
absorption spectra of by-products at 60 min of treatment with ZVIP (20 g/l).

1
838
A. Ghauch, J. Suptil / Chemosphere 41 (2000) 1835±1843
the presence of ZVIP in water. Tests were conducted to
con®rm the feasibility of the process, and to understand
the mechanism of reduction device. Though not exhaus-
tive, reduction pathways were examined to determine
the breakdown products of the degradation process.
Table 1
The half-lives (t1=2) of simazine (1.25 mg/l), atrazine (1.25 mg/l)
and propazine (1.25 mg/l) transformation using 20 g/l of ZVIP
(
325 mesh) in phosphate bu€ered solution (pH ˆ 6.6) and at
a;b
room temperature (22°C)
Half-lives
(
Simazine
Atrazine
Propazine
min)
c
t
t
1=2
7.41 ‹ 0.39
9.82 ‹ 0.49
9.04 ‹ 0.48
11.21 ‹ 0.56
10.62 ‹ 0.54
13.71 ‹ 0.68
2
. Experimental
d
1=2
a
b
c
Errors are 95% con®dence intervals.
1=2 was calculated by plotting (C/C
2
.1. Instrument
t
0
) versus (time of reaction).
Separately.
In mixture.
A Hewlett Packard UV-VIS diode array spectro-
d
photometer was used to record the evolution of the UV
spectra throughout the experiments. HPLC analysis of
pesticides was performed by a Diode Array Controller
2
.3. Reagents
(
Waters TM 996), equipped with a diode array detector,
and supplemented with a programmable multiwave-
length UV/VIS detector. Twenty ll samples taken from
the reaction bottles were injected automatically via a
Iron powder (purity > 99%, 325-mesh nitrogen ¯u-
shed) was purchased from Acros (Geel, Belgium), and
KH PO and Na HPO .12H O from Prolabo (France).
The triazines were obtained from Riedel-de-Ha e n
Germany) at the highest purity available. Acetonitrile
2
4
2
4
2
C18
50  4:6 mm, porosity ˆ 5 lm). The mobile phase was
a mixture of acetonitrile/water (60:40, v/v).
nonpolar
column
(Supelco,
Discovery
2
(
was spectroscopic grade and purchased from Acros.
Deionised water was used throughout the experiments.
2
.2. Pilot
A laboratory-constructed pilot (Fig. 2) was devel-
2.4. Experimental procedures
oped in order to study the degradation of the triazine
pesticides using ZVIP as reductive agent. ZVIP was
treated for 10 min with acidic solution (HCl 1M), wa-
shed several times with distilled water, and then manu-
ally introduced into the pilot. The processing pilot is
equipped with a propeller located at middle height, al-
lowing the aspiration of ZVIP through a 5-mm diameter
tube, from the bottom to the top surface, for ZVIP to be
propagated in the whole reactive zone. Once settled, the
ZVIP is aspirated again continuously. The pilot was
built to be used in batch, semi-batch, or in continuous
mode.
All experiments were carried out at room tempera-
ture ꢀ22°C Æ 1°C† in phosphate bu€ered solutions (0.025
M; pH ˆ 6.6). The ZVIP was pretreated with 200 ml 1M
HCl for 10 min, then washed with distilled water (400
2
‡
ml) for four times to remove the residual HCl and Fe
.
Pesticide stock solutions were prepared in aqueous
phosphate bu€ered solution as follow: atrazine 20 mg/l,
simazine 5 mg/l, propazine 5 mg/l. Working solutions
were prepared by an appropriate dilution giving 1.25
mg/l for atrazine, simazine and propazine. 75 g of
acid-washed ZVIP were manually added to the pilot
Fig. 5. Comparison of the s-triazines transformation when treated separately (a) and in a mixture (b) at the same concentration of
ZVIP (20 g/l), 0.025 M phosphate bu€ered deionised water (pH 6.6) at 22°C.

A. Ghauch, J. Suptil / Chemosphere 41 (2000) 1835±1843
1839
Fig. 6. HPLC chromatogram and UV absorption spectra of the triazine solutions treated with 20 g/l ZVIP in 0.025 M phosphate
bu€ered deionised water (pH 6.5) at 22°C. (a) SAP -siamzine (1.25 mg/l), atrazine (1.25 mg/l) and propazine (1.25 mg/l). Rt of the three
pesticides are, respectively, 4.79, 7.07 and 11.4 min. Maximum absorption peaks are at 223.8 nm. (b) SAP -treated triazines solution at
0 min of contact with ZVIP. Appearance of all by-products, which represent a maximum absorbency at 223.8 nm, 228.5 nm, 214.5 nm
1
2
3
3
and 219.2 nm, respectively. (c) SAP -treated triazines solution at 60 min of contact with ZVIP. All by-products present retention times
between 2 and 4 min and a maximum of absorbency at 214.5, 219.2, 223.8 and 228.5 nm, respectively.
containing 3.75 l of triazine solution. At intervals, 3 ml
were taken with a syringe in order to record the UV-Vis
spectra of the treated solution and carry out HPLC
chromatography during the reductive process.
Table 2
The rate constant of simazine, atrazine and propazine trans-
formation using 20 g/l of ZVIP (325 mesh) in phosphate buf-
a;b
fered solution (pH ˆ 6.6) and at room temperature (22°C)
c
� 1
d
� 1
Pesticides
K
obs (min
)
K
obs (min )
3
. Results and discussion
Simazine
Atrazine
Propazine
0.093 ‹ 0.004
0.077 ‹ 0.004
0.065 ‹ 0.003
0.070 ‹ 0.003
0.061 ‹ 0.003
0.050 ‹ 0.002
3.1. Evolution of the UV absorption spectra of the triazine
pesticides
a
Errors are 95% con®dence intervals.
The observed transformation rate constant Kobs of the triazine
b
The UV absorption spectra of the triazine solutions
pesticides were calculated by plotting Ln [% (C/C
of reaction).
0
)] versus (time
under our experimental conditions show a maximum at
223.8 nm. Fig. 3 shows the evolution of the UV spectra
of simazine during the reducing degradation using
c
Separately.
In mixture.
d

1
840
A. Ghauch, J. Suptil / Chemosphere 41 (2000) 1835±1843
ZVIP, with a shift in the maximum wavelength to 228
nm that correlates with the appearance of new by-
products. The same phenomenon was observed for the
UV evolution spectra of atrazine and propazine, which
are not presented in this paper.
reduced by ZVIP within a few minutes of half-lives (Fig.
5 and Table 1). The e€ect of dissolved oxygen (DO) is
not studied here, but the consequence of the DO on the
®rst-order rate of the triazines transformation should be
non-negligible. This phenomenon was studied by Siantar
et al. (1996) who found that increasing the amount of
In order to understand the global reductive reaction,
we proceeded to study the degradation of each of the
triazine pesticides by using HPLC to separate by-prod-
ucts and to monitor the disappearance of the starting
compounds and the appearance of new by-products.
The estimated reductive degradation pathway presented
at the end of this paper is based on the basic reductive
reaction in organic chemistry coupled with information
given by the retention time of by-products and their UV-
Vis absorption spectra.
DO from 0 to 41.6 mg/l (saturation concentration of O
2
in water at 22°C) decreases linearly the pseudo-®rst-or-
der rate reduction of 1,2-dibromo-3-chloropropane
(DBCP) to propane from 0.28 ‹ 0.03 to 0.07 ‹ 0.02 min.
They concluded that this observation may indicate
that the DBCP competes with O
sites and/or that the O deactivates the surface by
forming non-reactive iron oxide coatings. In the O
2
for iron surface active
2
2
concentration range relevant for deionised water (under
the conditions of the current experiment, 8 mg/l), the
decrease in s-triazines transformation rate constant
should match with that obtained for DBCP by a maxi-
mum of 17%.
3
.2. Evolution of the s-triazine pesticides chromatograms
Fig. 4 shows chromatograms of simazine, atrazine
and propazine at the same concentration (1.25 mg/l)
before and after treatment with ZVIP.
Increasing the s-triazines concentration in the same
reactive media (Fig. 6) has a small e€ect on the constant
degradation rate of the reductive treatment. Table 2
As can be seen, after 60 min of contact with ZVIP, a
complete disappearance of the triazines is observed. For
example, simazine, which has a retention time of 4.9
min, shows the appearance of four by-products. Three
of them disappear completely at the end of the treat-
ment. However the by-product exhibiting a retention
time of 2.4 min and a maximum absorption band at
shows that
K
obs decreased from 0:093 Æ 0:004 to
0:070 Æ 0:003
for simazine, to
0:077 Æ 0:004
0:061 Æ 0:003 for atrazine and 0:065 Æ 0:003 to
0:050 Æ 0:002 for propazine when the s-triazines are
treated together under the same conditions or when
treated separately. The concentration evolution of all
by-products when the reductive degradation treatment is
carried out in a solution containing simazine (1.25 mg/l)
or atrazine (1.25 mg/l) is presented in Fig. 7. (The evo-
lution of the propazine by-products is not presented in
this paper.) The number of the intermediate by-products
pending from simazine and propazine is less than those
from atrazine. This fact can be explained by the sym-
metrical position of the two ethyl±amino groups on the
2
28.5 nm seems to be the ®nal by-product. (Fig. 4(a)).
For atrazine (Rt ˆ 7.2 min), we observe the appearance
of two by-products at Rt ˆ 2.4 and 3.3 min presenting a
maximum peak at 228.5 nm (Fig. 4(b)). For propazine
(
Rt ˆ 11.4 min), we perceive the appearance of three by-
products at Rt ˆ 2.4, 3.2 and 3.74 min presenting max-
ima peaks at 228.5, 214.5 and 228.5 nm, respectively
Fig. 4(c)). Under aerobic conditions, the triazines were
(
Fig. 7. (a) Product distribution of simazine (1.25 mg/l) transformation into 100% 4,6-(amino)-s-triazine via products shown in the
estimated simazine pathway map (see Fig. 8(a)). (b) Product distribution of atrazine (1.25 mg/l) transformation into 100% 4,6-(amino)-
s-triazine via products shown in the estimated atrazine pathway map (see Fig. 8(b)).

A. Ghauch, J. Suptil / Chemosphere 41 (2000) 1835±1843
1841
Fig. 8. Reductive degradation pathway map for simazine (a) and for atrazine (b). The pathway map of propazine is similar. Chemical
nomenclature: a-4,6-diethyl-amino-s-triazine; b-4-ethyl amino 6-deethyl amino simazine; c-4-deethyl amino 6-diethyl-amino simazine;
d-4-ethyl amino-6-deethyl amino-s-triazine; e-4,6-deethyl-amino simazine; f-4-isopropyl amino 6-deethyl amino propazine; g-4-iso-
propyl amino 6-ethyl-amino propazine; h-4-isopropyl amino-6-deethyl amino-s-triazine; i-4-deisopropyl amino 6-ethyl amino-s-tri-
azine; j-4,6-diamino-s-triazine.
simazine molecule and the two isopropyl±amino groups
on the propazine molecule.
can be explained by the elimination of the chlorine atom
followed by the elimination of the alkyl group and the
formation of the corresponding alkane.
On the other hand, atrazine has one ethyl±amino
group and one isopropyl±amino group that makes
possible the reductive dealkylation from both sides of
the molecule. The appearance of 2-deethylamino or 4-
deethylamino, and 2-deisopropylamino or 4-deisopro-
pylamino triazine, occurs by increasing the number of
intermediate products. For all compounds studied, the
by-product that appeared at Rt ˆ 2.4 min seems to be
the major one. It corresponds to the reduced triazine
pesticides obtained by the contact with ZVIP. One hy-
pothesis can be envisaged and should correspond to the
reductive dechlorination of the triazine ring followed by
the reductive dealkylation of the secondary amines. This
In order to fully understand the reductive pathway of
the s-triazines pesticides, we investigated the potential
presence of compounds recognized as natural by-prod-
ucts obtained by microorganism reductive degradation
in soil. For example, comparisons made between a
standard solution of hydroxyatrazine and a sample
taken from the pilot at di€erent reaction times shows an
absence of hydroxyatrazine (HPLC chromatograms and
UV-Vis spectra analyses). The later is also a by-product
obtained when the oxidation process is used to remove
atrazine from water (Duguet et al., 1992; De Laat et al.
1995). Added tests were carried out with the intention of

1
842
A. Ghauch, J. Suptil / Chemosphere 41 (2000) 1835±1843
studying the possibility of establishing breakdown
products such as deisopropylatrazine or deethylatrazine,
but results shows no evidence of these molecules. This
fact can be explained by the rapid dechlorination of the
s-triazines molecules followed by the reductive dealky-
lation reactions.
Acknowledgements
The author would like to thank Prof. Rima of the
Lebanese University, Prof. Martin-Bouyer of the LCIE
laboratory, and Dr. Gallet of the laboratory of Dy-
namics of Altitude Ecosystems, University of Savoie, for
their helpful cooperation.
For all studied s-triazines, we did not observe any by-
product that is obtained through an oxidation process.
This can be explained by the fact that the chlorine atoms
in the s-triazines pesticide molecules are reduced to hy-
drogen atoms. Thus, all the intermediate breakdown
products do not have a chlorine atom in their structure.
Fig. 8 shows the reduction pathway of simazine and
atrazine by ZVIP. The reductive pathway of propazine is
not presented but is similar to the simazine map by re-
placing the ethyl±amino group by the isopropyl±amino
group.
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