Subscriber access provided by - Access paid by the | UCSB Libraries
Environmental Processes
Atmospheric oxidation of a thiocarbamate herbicide used in winter cereals Amalia Munoz, Esther Borras, Milagros Ródenas, Teresa Vera, and Hans Albert Pedersen Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.8b02157 • Publication Date (Web): 11 Jul 2018 Downloaded from http://pubs.acs.org on July 16, 2018
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 37
Environmental Science & Technology
1
Atmospheric oxidation of a thiocarbamate herbicide used in
2
winter cereals
3 4
Amalia Muñoz*(1), Esther Borrás (1), Milagros Ródenas(1), Teresa Vera(1),
5
Hans Albert Pedersen (2)
6 7
(1)
8
Fundación CEAM. C/Charles R. Darwin, 14. Parque Tecnológico 46980 Paterna (Valencia), Spain.
9 10
(2)
Dept. of Agroecology. Aarhus University
11 12 13 14
*Corresponding author:
15 16
Amalia Muñoz
17
Fundación Centro de Estudios Ambientales del Mediterráneo (Fundación CEAM)
18
C/Charles R. Darwin, 14 46980 Paterna – Valencia - Spain
19
Corresponding author’s e-mail:
[email protected] 20
Phone: +0034 609644051
21
ACS Paragon Plus Environment
Environmental Science & Technology
Page 2 of 37
22
Abstract
23
The gas-phase atmospheric degradation of prosulfocarb (a widely used thiocarbamate
24
herbicide in winter cereals) at different NOx concentrations was investigated at the large
25
outdoor European Photoreactor (EUPHORE) in Valencia, Spain. Photolysis under sunlight
26
conditions and reaction with ozone were shown as unimportant. The rate constant for the
27
reaction of prosulfocarb with OH radicals was determined as k = (2.9±0.5) × 10-11 cm3
28
molecule-1 s-1 at 288±10 K and atmospheric pressure by a conventional relative rate
29
method. Significant ozone and aerosol formation was observed following the reaction of
30
prosulfocarb with OH radicals, and the main detected carbon-containing gas phase
31
products
32
benzylpropanoyl(propyl)carbamo-thioate.
were
benzaldehyde,
S-benzylformyl(propyl)carbamothioate,
and
S-
33 34 35 36
Key Words
37
Prosulfocarb, atmospheric degradation, photodegradation, atmospheric fate, rate constant,
38
products formation
39 40
ACS Paragon Plus Environment
Page 3 of 37
Environmental Science & Technology
41
42
1. Introduction
43
Pesticides are among the more extensively used chemicals worldwide. Their intensive use
44
has led to the contamination of not only water and soil, but also the atmosphere, in both
45
exposed and remote areas.1, 2, 3 In 2016, about 234 000 tons of pesticide active ingredients
46
were used in Europe (EU-28).4 The potentially adverse effects of exposure to pesticides in
47
the general population are of much concern.5 Once a plant protection product is applied to
48
the field, the active ingredient can be partitioned into soil, water, biota and the atmosphere.
49
In the atmosphere, pesticides are distributed among gas, particle and aqueous phases,
50
depending on their physicochemical properties and the environmental conditions.6, 7
51
Prosulfocarb
52
(C3H7)2NC(O)SCH2C6H5, is a thiocarbamate herbicide used in both pre- and post-
53
emergence stages in winter cereals. It can be released to the atmosphere directly while
54
being sprayed. It has been detected in air, with an average concentration
55
over 4 years at levels higher than 1 ng m−3: in France reaching even week average
56
concentration around 14–15 ng m−3.,8 and was also detected in the largest quantities in wet
57
deposition studies at two different sampling locations.9 Various vapor pressures are
58
reported in the literature, which range from 0.7 mPa at 20ºC 10 to 5-7 mPa at 25ºC 11-13. A
59
vapor pressure of 6.4 mPa at 20°C, which was theoretically estimated
60
that prosulfocarb could exist in both the gas and particulate phases in the atmosphere.
61
Concentrations up to 3.6 µg/L have also been detected in rainwater in Sweden from 2002-
62
2012 15. Prosulfocarb is often applied to winter crops early in autumn. In recent years the
63
herbicide has been detected in several batches of organically and conventionally grown
64
apples harvested near the prosulfocarb application time. This has led to its rejection at a
65
significant cost to apple growers, and is also a matter of concern for consumers.
(CAS:
52888-80-9,
S-benzyl
ACS Paragon Plus Environment
dipropylcarbamothioate,
14
, would indicate
Environmental Science & Technology
66
Like other organic compounds, the main pathways for the tropospheric degradation of
67
prosulfocarb could involve photolysis and reactions with ozone, hydroxyl and nitrate
68
radicals, although no previous studies on the degradation of prosulfocarb in air have been
69
found in the literature. Kwok et al.
70
several thiocarbamates, including S-ethyl N,N-dipropylthiocarbamate, which has several
71
similar structural features to prosulfocarb. They calculated the atmospheric lifetime of S-
72
ethyl N,N-dipropylthiocarbamate in relation to the reaction with OH radicals to be close to
73
6 h using an OH concentration of 1.5 x 106 molecules cm-1, for a 12-h-average daytime.
74
. In that study the main detected metabolite was S-ethyl N-formyl-N-propylthiocarbamate.
75
Photodegradation of prosulfocarb has been previously studied in the liquid phase and on
76
soil and leaf surfaces of barley. Dipropylaimne and propylamine have been detected in
77
studies carried out in methanol
78
and sulfonic acid have also been detected in other studies
79
systems, prosulfocarb sulfoxide and the complete transformation into CO2 have been
80
observed 19.
81
The present series of experiments was carried out to determine the major reaction
82
pathways of prosulfocarb degradation in the troposphere. Studies were performed at
83
EUPHORE (European PHOto-Reactor). The results provided information on the
84
atmospheric lifetime of prosulfocarb. The main primary products of the OH radical
85
initiated oxidation of prosulfocarb were also determined, and mechanisms for their
86
formation were proposed. To the best of our knowledge, the experimental determination of
87
the rate constant of OH with prosulfocarb in the gas phase at ambient temperature and the
88
identification of the main degradation products have not been previously published in the
89
peer-reviewed literature.
16
investigated the gas-phase atmospheric chemistry of
17
, while sulfoxide, despropyl prosulfocarb, benzoic acid 18
ACS Paragon Plus Environment
. In soil and sediment-water
Page 4 of 37
Page 5 of 37
Environmental Science & Technology
90
2. Experimental Section
91
2.1 Photoreactor and online instruments.
92
The experiments were carried out in the EUPHORE high-volume outdoor smog chamber
93
(Valencia, Spain) late in autumn. This simulation chamber enables reactions to be carried
94
out using natural sunlight and by minimizing losses and wall-interaction effects by
95
following similar procedures to those previously employed in this laboratory to investigate
96
the atmospheric fate of a number of pesticides 20-23.
97
The chamber consists of a half spherical fluoropolymeric bag (200 m3 volume) with
98
integrated measuring systems for different compounds and parameters. Humidity and
99
temperature were measured with a dew point hydrometer (TS-2, Walz, Effeltrich,
100
Germany). A TAPI NOx monitor (T200UP, Teledyne, San Diego, USA) was used to
101
measure NO, NO2 and NOx. Ozone was measured with a Serius 10 ozone analyzer
102
(Echotec, Knoxfield, Victoria, Australia). A White-type multi-reflection mirror system
103
(path length 553.5 m), coupled to a Fourier transform infrared (FTIR) spectrometer
104
equipped with an MCT detector (NICOLET Magna 6700, Thermo Scientific, Waltham,
105
MA, USA), was used to record the concentrations of prosulfocarb (1073-1196 cm-1),
106
nitrous acid (762-956 cm-1), SF6 (762-956 cm-1) and benzaldehyde (725-1220 cm-1). The
107
IR region analysis bands are shown in parentheses. Concentration profiles were calculated
108
by a specific software
109
products were also experimentally determined and validated by automated online SPME-
110
GC-MS (solid-phase microextraction, gas chromatography-mass spectrometry) and by
111
offline SPME-GC-FID (gas-chromatograph with a flame ionization detector). In the on-
112
line active sampling, the air was forced through the fiber, by means of a pump, through a
113
sampling cell for 5 min, while the off-line
114
that compounds are retained in the fiber by direct exposition to EUPHORE chamber due to
24
. The concentrations of prosulfocarb and other degradation
technique was passive sampling, that means
ACS Paragon Plus Environment
Environmental Science & Technology
115
diffusion processes. The optimization of exposure time was made in previous separate
116
experiments where known quantities of prosulfocarb were introduced at EUPHORE
117
photoreactor. The automatic online SPME-GC-MS consisted of a robot with an SPME
118
adapted to air sampling. Air from the chamber was sampled through an inert Silconert-
119
coated steel tube heated to 80ºC and connected to a sampling cell, where the SPME fiber -
120
coated with polydimethylsiloxane/divinylbenzene (PDMS/DVB) from Supelco (Madrid,
121
Spain)- was exposed. Air was passed through a cell at 10 L min-1 for 5 min. Finally, the
122
sample was thermally desorbed at 250ºC in the injection port of an Agilent GC-MS (Santa
123
Clara, CA, USA) equipped with an HP-5MS (Agilent) column of 30 m × 0.25 mm i.d. ×
124
0.25 mm film thickness. The chromatograph was programmed at 170ºC for 1 min, then
125
ramped at 25 ºC min-1 to 280 ºC, and held for 2 min. Samples were injected into the
126
splitless mode using helium as a carrier gas at a flow of 1 mL min-1. The EI voltage was 70
127
eV and the full-scan mode was used (m/z 45-650).
128
J(NO2) was measured with a calibrated JAZ Spectroradiometer (Ocean Optics Inc., Largo,
129
FL, USA). J(NO2) represents light intensity and is defined as the photolysis rate coefficient
130
for NO2 calculated from the actinic flux measurements of the spectroradiometer and the
131
recommended values for the absorption cross-section and quantum yield 25,26.
132
A proton transfer reaction mass spectrometer (PTR-MS) instrument for monitoring organic
133
compounds in the gas phase was used (Ionicon Analytik GmbH, Innsbruck, Austria).
134
Reagent ions, H3O+, were produced from a pure water vapor flow in a hollow cathode
135
discharge ion source. Data were continuously recorded in the PTR-MS instrument’s scan
136
mode (m/z 21-140 with 500 ms data collection in each step). A 1/4” sulfinert© tube (4.0
137
mm ID, 1m length), covered by a warming blanket set at 80ºC, was used as a sampling
138
line.
ACS Paragon Plus Environment
Page 6 of 37
Page 7 of 37
Environmental Science & Technology
139
The aerosol mass concentration was measured with a scanning mobility particle sizer
140
(SMPS), model 3080 (TSI, Shoreview, MN, USA). This system measured the size
141
distributions within the 11-789 nm diameter range in real time at a 5-minute scan rate, and
142
provided aerosol concentrations by assuming spherical shapes and multi-charge correction
143
for the condensed organic material. The sheath and aerosol sampling flows were 3 L min-1
144
and 0.3 L min-1, respectively.
145
2.2 Offline analysis: SPME and filters.
146
Manual SPME was also used to monitor reactants and products. The SPME device
147
consisted of a holder assembly with 65-µm fibers. The SPME fiber was introduced into the
148
chamber through a septum in the chamber floor. The methodology for prosulfocarb was
149
validated by a comparison with FTIR in the dark. Samples were taken for 10 min at a time
150
and were analyzed by GC-FID by inserting the fiber directly into the GC injector. A
151
Hewlett-Packard 6890 Gas Chromatograph, equipped with an HP-5MS column of 30 m ×
152
0.25 mm i.d. × 0.25 mm film thickness, was used. The chromatograph was programmed at
153
150ºC for 2.5 min, then ramped at 15ºC min-1 to 235ºC and held for 2.5 min.
154
For the fingerprint analysis, particles were collected at maximum aerosol formation at a
155
flow rate of 23 L min-1 for 1 h on quartz fiber filters, which had been pre-baked at 500oC
156
for 12 h. The analysis of the multi-oxygenated compounds was carried out by GC-MS after
157
derivatization following the methodology described in Borrás and Tortajada-Genaro 27. O-
158
(2,3,4,5,6-pentafluorobenzyl)hydroxylamine hydrochloride (PFBHA) (Sigma-Aldrich,
159
Barcelona, Spain) was used as the derivatization agent to determine carbonyl compounds.
160
N-methyl-N-trimethylsilyltrifluoroacetamide (MSTFA) (Sigma-Aldrich, Barcelona, Spain)
161
was used as the derivatization reagent to analyze the compounds with OH groups (See
162
Supporting Information S.1 for more details)
ACS Paragon Plus Environment
Environmental Science & Technology
163
2.3 Experiments.
164
Prosulfocarb (99%, Sigma Aldrich quimica, Spain, address) was injected into the
165
EUPHORE chamber via a heated air stream (flow rate, 10 L min-1).
166
The oxidation experiments, which were carried out in duplicate, consisted of photolysis,
167
ozonolysis under dry conditions (
