Environmental Fate of the Herbicide Fluazifop-P-butyl and Its

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Environmental Science & Technology

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Environmental fate of the herbicide fluazifop-P-butyl

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and its degradation products in two loamy agricultural

3

soils – a combined laboratory and field study

4 5

Nora Badawi†, Annette E. Rosenbom†, Preben Olsen‡, Sebastian R. Sørensen†*

6 7 8 9

† Department of Geochemistry, Geological Survey of Denmark and Greenland (GEUS), Øster

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Voldgade 10, 1350 Copenhagen K, Denmark

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‡ Department of Agroecology, Aarhus University, Blichers Allé 20, DK-8830 Tjele, Denmark

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*Corresponding author

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Tel: +45 91333583

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Fax: +45 38142050

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Email: [email protected]

18 19 20

1

ACS Paragon Plus Environment


21

ABSTRACT

22

The herbicide fluazifop-P-butyl (FPB) is used against grasses in agricultural crops

23

such as potato, oilseed rape and sugar beet. Limited information is available in scientific

24

literature on its environmental fate, therefore extensive monitoring at two agricultural test

25

fields was combined with laboratory studies to determine leaching and the underlying

26

degradation and sorption processes. Water samples from drains, suction cups, and

27

groundwater wells showed leaching of the degradation products fluazifop-P (FP) and 2-

28

hydroxy-5-trifluoromethyl-pyridin (TFMP) following FPB treatment. Laboratory experiments

29

with soil from each field revealed a rapid degradation of FPB to FP. The degradation was

30

almost exclusively microbial, and further biodegradation to TFMP occurred at a slower rate.

31

Both degradation products were sorbed to the two soils to a small extent and were fairly

32

persistent to degradation during the two-month incubation period. Together, the field and

33

laboratory results from this study showed that the biodegradation of FPB in loamy soils gave

34

rise to the production of two major degradation products that sorbed to a small extent. In this

35

study, both degradation products leached to drainage and groundwater during precipitation. It

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is therefore recommended that these degradation products be included in programs monitoring

37

water quality in areas with FPB use.

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INTRODUCTION

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The selective post-emergence phenoxy herbicide fluazifop-P-butyl (FPB) is used

44

against annual and perennial grasses, for example in fruits, broadleaf crops, trees, and

45

ornamental nurseries.1 FPB is in use around the world in a variety of different products – for

46

example there are 22 different products containing FPB registered in the state of New York

47

alone.2 In northern European countries, however, FPB is primarily used in agricultural crops,

48

such as potato, oilseed rape, sugar beet, and pea.3 There is very limited information available

49

in scientific literature on the fate and behavior of FPB in the environment. Recent risk

50

assessments of FPB carried out by the European Food Safety Authority,3 the Canadian

51

Management Regulatory Agency,4 and the United States Environmental Protection Agency1

52

have taken several studies on the environmental fate of FPB into consideration. The vast

53

majority of these studies, however, have not been published in peer-reviewed journals, which

54

means that the technical approaches and data are unavailable to the scientific community.

55

Degradation of FPB in agricultural soils has been described as a combination of

56

abiotic hydrolysis and microbial activity.5 The degradation of hydrophobic and low water-

57

soluble FPB in soil is rapid, according to a recent EFSA report, with reported times for the

58

dissipation of 50% of the added amount (DT50 values) ranging from 0.3 to 2.9 days at 20°C.3

59

The initial steps of the pathway may involve degradation of FPB to fluazifop-P (FP), and

60

subsequently to the highly water-soluble 2-hydroxy-5-trifluoromethyl-pyridin (TFMP)

61

(Scheme 1).6 Degradation rates reported for the first degradation product FP are slightly

62

longer, with reported DT50 values from a field study of nine arable soils ranging from 6 to 17

63

days.7 There is a lack of data on the fate of TFMP in soil, although the degradation product is

64

mentioned in several reports (sometimes noted as compound X), that suggest that it should be

65

classified as moderate to medium persistent in soil.3 Mineralization of FPB in soil

66

experiments has been reported in studies using

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the rate appears to be slow, with a maximum of 9 – 30% mineralized to

14

C-pyridyl or

3


14

C-phenyl-labelled FPB, but 14

CO2 within 168


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days.3 Bewick8 looked at the R- and S-enantiomeric degradation and mineralization of

69

fluazifop-butyl (FB; a 1:1 racemic mixture of the S- and R-enantiomers) and fluazifop in soil,

70

and found that FPB (R-FB) was rapidly degraded to FP, in contrast to the S-enantiomer (S-

71

FB), which degraded more slowly. However, no difference in the mineralization potentials of

72

the two enantiomers of fluazifop was found, and a total of 4.5%

73

mineralized to 14CO2 within one week.8

14

C-phenyl-fluazifop was

74

In many northern European countries, a high proportion of drinking water originates

75

from groundwater. In Denmark, for example, groundwater accounts for 100% of drinking

76

water, which places an emphasis on the quality of this resource. FP and TFMP are classified

77

as “relevant metabolites” by the European Commission, as defined in the Guidance document

78

on the assessment of the relevance of metabolites in groundwater of substances regulated

79

under Council Directive 91/414/EEC.9 As a consequence, they are restricted to a maximum

80

allowable concentration of 0.1 µg L-1 in drinking water.10 Knowledge about the fate and

81

possible risk of leaching of FPB, FP, and TFMP from agricultural soils through the variably-

82

saturated zone into groundwater under field conditions is therefore of great importance and

83

calls for combined laboratory and field studies.

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The aim of this study was two-fold: i) to monitor closely the leaching of degradation

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products to drainage and groundwater following multiple FPB applications on different crops

86

during exposure to natural climatic conditions in two loamy agricultural fields included in the

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Danish Pesticide Risk Assessment Program (PLAP),11,12 and ii) to determine the underlying

88

sorption and degradation processes of FPB, FP, and TFMP in plow layer soils sampled from

89

the two PLAP fields using controlled laboratory experiments.

90 91 92 93

MATERIALS AND METHODS Chemicals.

Analytical-grade

fluazifop-P-butyl

(FPB;

butyl

(R)-2-[4-(5-

trifluoromethyl-2-pyridyloxy)phenoxy]propionate; CAS RN 79241-46-6, > 96% purity), 4


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fluazifop-P (FP; (R)-2-(4-[5-(trifluoromethyl)-2-pyridyloxy]phenoxy)-propionic acid; CAS

95

RN 83066-88-0, > 98% purity), and TFMP (2-hydroxy-5-trifluoromethylpyridin; CAS RN

96

33252-63-0, > 97% purity) were purchased from Sigma Aldrich. The commercial FPB

97

products, Fusilade X-tra (250 g FPB L-1) and Fusilade Max (125 g FPB L-1), used in the field

98

study were purchased from Syngenta Crop Protection A/S, Denmark (formerly Zeneca Agro).

99

Fields, treatment, and monitoring. The two PLAP fields at Silstrup (1.7 ha) and

100

Faardrup (2.3 ha) are situated on flat or slightly sloping glacial tills with a shallow

101

groundwater table. During the monitoring period, the groundwater table was located 1.0 –

102

3.0 m below ground surface (b.g.s.) at Faardrup and 0.5 – 3.7 m b.g.s. at Silstrup. Tile drains

103

were installed more than five decades ago at a depth of approximately 1 m in both fields. The

104

drainage systems were modified prior to PLAP monitoring by cutting off and blocking any

105

drainpipes transporting water from upstream fields, thereby ensuring that the sampled

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drainage water only came from the PLAP field.13 These loamy soils are characterized by

107

preferential transport through macropores such as wormholes and fractures and further details

108

on the characteristics of these two sites are available in Rosenbom et al. 12

109

The leaching of FPB, FP, and TFMP has been monitored for several years in the two

110

fields. Throughout that time, changes have been made to the monitoring program. Details on

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this are summarized in Table 1. FPB was originally included in the monitoring at Faardrup,

112

but the lack of detections combined with knowledge from literature meant that it was

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excluded from the monitoring program after three years. Initially, TFMP was not included in

114

the monitoring program, but it was subsequently suspected of being an important degradation

115

product and therefore included in the analysis program at Silstrup in July 2008 and at

116

Faardrup in April 2011.

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In accordance with conventional agricultural practice in the area, the two fields are

118

cultivated with crop rotations in which FPB was applied in red fescue grass, fodder and sugar 5



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beet.12 FPB was applied against weeds five times at Silstrup and twice at Faardrup, at the

120

maximum permitted dose of the active ingredient (Table 1). The water balance including

121

precipitation and leaching have been monitored continuously in the two fields since May

122

2000. Additional climatic data are obtained from automatic climate stations located 0.5 – 3.0

123

km from the fields. To avoid an artificial bypass of the soil layer and direct leaching of

124

pesticides into the groundwater, all sampling equipment was installed from or within the

125

buffer strips surrounding the treated area. Furthermore, all soil sampling was restricted to the

126

upper 20 cm (the plow layer) in order to keep the subsoil intact.

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Water samples were collected from the tile drain system and the vertical and

128

horizontal groundwater screens. The drainage was sampled flow proportionally, with

129

subsamples collected for every 3000 L of flow during winter (September – May) and for

130

every 1500 L during summer (June – August) each week. All the collected subsamples were

131

pooled weekly and sent to the accredited commercial laboratory for analysis. The detection

132

limits for the accredited analyses were 0.01 µg L-1 for FPB and FP, and 0.02 µg L-1 for

133

TFMP. As the samples were pooled, they do not represent the peak concentrations that may

134

have occurred during the week. Samples were refrigerated at all times. The vertical

135

groundwater wells consisted of four 1-m screens covering approximately the upper four

136

meters of the saturated zone. Two horizontal wells were installed 3.5 m b.g.s., consisting of an

137

18-m screen, providing integrated water samples that represented the groundwater directly

138

beneath the field. Additional information about sampling methods and monitoring design is

139

available.13-17

140

Laboratory degradation studies. Soil from the two loamy PLAP fields were sampled

141

from the plow layer (0 – 20 cm b.g.s.) in March 2014 and transported back to the laboratory

142

and stored in the dark at 10°C until the start of the experiments. Degradation of FPB (3 µmol

143

kg-1 soil) and the occurrence of the degradation products FP and TFMP were measured in the

144

two soils, in addition to the degradation of FP (4 µmol kg-1 soil) and TFMP (9 µmol kg-1 soil) 6


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individually. 0.5-g subsamples (wet weight; soil water content in Faardrup was 20% and in

146

Silstrup 30%) were transferred to sterile 20 ml Pyrex glass tubes with PTFE sealed screw

147

caps. Stock solutions of the three compounds were prepared in acetonitrile and spiked (50 µl)

148

individually to the 0.5-g subsamples (in triplicates). Samples were left for four hours to

149

evaporate the acetonitrile before adding a further 2 g of soil to each subsample. The soil in

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each tube was mixed, 500 µl sterile milliQ water was added, and then the samples were

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incubated in the dark at 15°C. Samples were set up in parallel, and triplicate samples were

152

terminated at each sampling time point. Abiotic degradation of FPB, FP, and TFMP was

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studied in autoclaved soil and the experiment was set up in parallel, similar to the degradation

154

experiment. The two soils were autoclaved four times before spiking with FPB, FP, and

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TFMP. Extraction of FPB, FP, and TFMP from all soil samples was performed as described

156

in Negre et al.,18 with slight modifications. In brief, 2.5 ml extraction solution consisting of

157

methanol:1M HCL (9:1, v/v) was added to each sample and agitated at 150 rpm overnight.

158

The following day, samples were centrifuged at 1,500 g (20 min), the supernatant was

159

transferred to 2 ml safe-seal tubes, and then centrifuged again at 10,000 g (15 min). 500-µl

160

aliquots of the supernatant were then filtered (PTFE filters, 0.22 µm, Titan Filtration Systems;

161

Sun SRi, Wilmington, NC, USA) directly into HPLC vials and diluted 1:1 with acidified

162

milliQ water (pH 2.2).

163

The diluted soil extracts were analyzed by a gradient liquid chromatography method

164

using a UPLC system (ACQUITY UPLCTM; Waters, Milford, MA, USA) with a photodiode

165

array detector scanning the interval of 210 – 300 nm. Chromatography was performed on a

166

Waters ACQUITY UPLC BEH C18 (1.7 µm, 2.1 × 50 mm) column with a mobile phase

167

consisting of acetonitrile and acidified milliQ water (pH 2.2), a column temperature of 40°C

168

and a flow rate of 0.7 ml min-1. The retention times and photodiode array spectra of the

169

analytical-grade standards were used to identify the compounds. MassLynxTM software

170

version 4.1 (Waters, Milford, MA, USA) was used for data acquisition and processing. The 7



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UPLC quantification limits for FPB, FP, and TFMP in the soil extracts were 0.07, 0.06, and

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0.3 µmol kg-1 soil, respectively. The recoveries of the three compounds from the soils were in

173

the range of 93-97%.

174

The degradation curves were fitted to a simple first order decay equation, and the first

175

order degradation rate constant (k) and DT50 value (the time to 50% degradation of the initial

176

content of the compound) were determined using the following equations:

177 178

t = 0 ×

179

DT50 =

(1)

(2)

180 181

where Ct is the concentration (µmol kg-1) of pesticide remaining in the soil at time t (days), C0

182

is the initial concentration (µmol kg-1) of pesticide in the sample, and k is the degradation rate

183

(days-1).

184

Soil sorption experiments. The batch equilibrium technique described in OECD

185

Guideline 10619 was used to determine the soil sorption coefficients Kd (mL g-1) for FP and

186

TFMP in four replicates. Sorption of FPB was not tested since it is reported that FPB is

187

rapidly hydrolyzed in soil.3, 5 Solutions of FP and TFMP were prepared in 0.01 M CaCl2 and

188

the final concentration in the samples was similar to the laboratory degradation study.

189

Following standard batch equilibrium technique procedures, 2 grams of air-dried soil

190

were pre-equilibrated with 3.6 ml 0.01 M CaCl2 (containing 0.01 M NaN3 to avoid microbial

191

degradation during incubation) in glass tubes and rotated overnight in the dark to establish

192

equilibrium before being combined with each degradation product solution (400 µl) to

193

provide a final soildry-weight:solutionCaCl2 ratio of 1:2 (w/v). Samples were rotated for 96 hours

194

before being centrifuged for 20 min at 1,500 g. 1.5-mL subsamples of the supernatants were

195

then transferred to 2 ml Eppendorf tubes, centrifuged at 10,000 g (15 min), and filtered (PTFE 8


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filters, 0.22 µm) into HPLC vials. Samples were analyzed by UPLC to measure Ce (µmol L-1),

197

the concentration of pesticide remaining in solution after adsorption. Four replicates per

198

degradation product only containing the 0.01 M CaCl2 (and 0.01 M NaN3) solution (no soil)

199

were included and used as the reference for Ci, the initial sample concentration (mg L-1).

200

Triplicate blank samples of soil and CaCl2 (0.01 M NaN3) solution (no degradation products)

201

were used as background references for the UPLC analysis.

202

The amount of degradation product adsorbed to the soil was calculated as the

203

difference between the concentration of degradation product initially present in the solution

204

(Ci, µmol L-1) and the concentration remaining at the end of the incubation (Ce, µmol L-1).

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Since NaN3 (a strong antimicrobial agent) was added to all samples in the sorption

206

experiment, it was assumed that removal of the degradation products from the solution was

207

due solely to sorption to the soil. The amount of the degradation product adsorbed in the solid

208

phase, Cs (µmol kg-1), was then calculated as:

209 210

s =

(ie)

(3)

s

211 212 213

where V (mL) is the volume of the solution in the samples and ms is the mass of the soil (g). The soil sorption coefficient Kd (mL g-1) was then calculated as:

214 215

s

d =

(4)

e

216 217

RESULTS

218

Leaching of FPB and its degradation products from the PLAP fields. The data

219

from the field experiments are summarized in Table 1. FPB was monitored in water from a

220

depth of 1 meter in the variably-saturated zone (tile drains and suction cups) and in the 9



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saturated zone (groundwater wells) in the first two years of the field experiments at Faardrup

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following the first treatment in 2001 (Table 1). After this period, the suction cups were

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removed from the monitoring program. No FPB was detected in 120 water analyses from the

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drains (98 samples) and suction cups (22 samples) or 199 analyses of groundwater (Table 1)

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during this period, and it was therefore decided that the herbicide itself would be excluded

226

from the remaining monitoring campaign.

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After the first treatment with FPB in the year 2000 – 2001, the degradation product FP

228

could be detected in groundwater in both fields. At Silstrup, FP was not detected in the

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variably-saturated zone, and was only detected in 1 out of 95 groundwater samples collected

230

from the saturated zone (Table 1) at a concentration of 0.07 µg L-1. At Faardrup, FP was

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detected six times in the groundwater, with a maximum concentration of 0.17 µg L-1.

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Furthermore, FP was detected 13 times in water from the drainage and suction cups, with five

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detections at or above the threshold limit of 0.1 µg L-1, with the highest concentration (3.80

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µg L-1) measured in drainage (Table 1). Following the herbicide treatments in 2008 and 2010

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at Silstrup, FP was not detected (analyses of 40 samples of drainage and 169 samples from

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groundwater) and was consequently excluded from the monitoring program at Silstrup. The

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change to the monitoring program was introduced in December 2010, half way through the

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2010-2011 monitoring period. However, FP was monitored in the drainage at Faardrup in the

239

period 2011-2012, but was not detected in the drainage (25 samples) following the treatment

240

in 2011 (Table 1).

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During the last four field treatments at Silstrup (2008 – 2012) and the last treatment at

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Faardrup (2011), the degradation product TFMP was included in the monitoring program.

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This revealed a leaching of this compound to the drainage at maximum concentrations during

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the hydrological year, ranging from 0.03 µg L-1 to 0.64 µg L-1 at Silstrup. TFMP was also

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detected in the groundwater at Silstrup during this period in maximum concentrations during 10


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the hydrological year from 0.03-0.29 µg L-1, with 28% out of a total of 312 samples

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containing this degradation product (Table 1). In contrast, no TFMP was detected in samples

248

collected at Faardrup (58 in the variably-saturated zone and 122 in the saturated zone).

249

Following the FPB treatment in the Silstrup field in 2008 and 2012, a high frequency of

250

TFMP detection in both drainage and groundwater was evident. In drainage, for example, the

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degradation product was detected in 100% of the samples taken in the year following the 2008

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application (17 out of 17), all at concentrations above 0.1 µg L-1 (Table 1). In the same period,

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TFMP was detected in 48% of the groundwater samples (46 out of 95), with a maximum

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concentration of 0.29 µg L-1 (nine samples had detections above 0.1 µg L-1). A similar pattern

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with a high detection frequency of TFMP was apparent following the 2012 application. Both

256

time periods were influenced by a high amount of precipitation at Silstrup during the month

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after application, with 105 mm in July 2008 and 127 mm in April-May 2012. In contrast, the

258

lack of TFMP detection at Faardrup after the 2011 application coincided with less

259

precipitation (59 mm) and, compared to Silstrup, Faardrup received less yearly precipitation

260

in general and therefore yielded less percolation to the tile drains and groundwater (Table 1).

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Degradation and sorption experiments. With the aim of determining the potential

262

for degradation and sorption of FPB and its two degradation products FP and TFMP in

263

agricultural soils, soil samples were obtained from the plow layers in each of the two fields

264

and used for controlled laboratory experiments. The degradation experiments are presented in

265

Figures 1 and 2 and the calculated DT50-values are summarized in Table 2, together with the

266

sorption data.

267

FPB was rapidly degraded to almost equivalent amounts of the degradation product FP

268

in soils from both Silstrup (DT50 = 17 hours) and Faardrup (DT50 = 26 hours) (Table 2).

269

TFMP was also produced, but at a much slower rate and later in the incubation period in both

270

soils (Figure 1 A, B). In contrast to the rapid biodegradation of FPB, further degradation of

271

the two degradation products FP and TFMP was slow. The degradation of FP and the 11



272

formation of TFMP were not observed until day ten in the Silstrup soil and day 20 in the

273

Faardrup soil (Figure 1 C, D) in samples where FP was initially added. Samples where TFMP

274

had been added showed a degradation slower than that of FPB and approximately similar to

275

that of FP (Figure 1 E, F). FPB was primarily biodegraded in both soils, and only a negligible

276

abiotic transformation to FP was apparent in the sterilized soils within the first few days of

277

incubation (Figure 2 A, B). No abiotic transformation of FP and TFMP was observed in the

278

two soils within the two-month incubation period (Figure 2 C-F).

279

Sorption of the two degradation products to the soil was evaluated using OECD

280

Guideline 106.18 Sorption of FPB was not included due to its rapid biodegradation to FP

281

within a matter of hours. Both soils had very low sorption capacities of the degradation

282

products. Slightly lower sorption was observed in the Faardrup soil compared to the Silstrup

283

soil, with FP having a Kd of 0.14 and 0.49 mL g-1, and TFMP having Kd-values of 0.18 and

284

0.39 mL g-1 (Table 2).

285 286

DISCUSSION

287

Keeping up with the constant flow of new pesticide products being launched on the

288

international market is a major task for environmental scientists, especially when most of the

289

studies conducted for regulatory purposes are unavailable to the scientific community. A

290

further challenge is presented by degradation products that are found to be relevant for

291

groundwater: in many countries, degradation products deemed relevant are those that leach

292

into the groundwater in concentrations above 0.1 µg L-1.20 The PLAP project was designed to

293

serve as an early warning system for testing pesticides already on the market.12 It has been

294

used to evaluate the leaching risk of 50 pesticides and 50 degradation products at five

295

agricultural fields monitored in Denmark, and new compounds are added to the program

296

every year. Even though methods for evaluating pesticide degradation in the environment are 12


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being developed and tested,20-22 assessing the field behavior of the ever-increasing range of

298

new pesticide products under realistic conditions is a challenge. Upcoming analytical

299

techniques such as compound-specific isotope analysis21 and enantiomer fractionation

300

analysis22 can, for example, be used to demonstrate biodegradation potential, differentiate

301

between abiotic and biotic degradation and even indicate which microbial degradation

302

pathway is the most active one for specific pesticides, without measuring degradation

303

products. However, these analytical techniques require time-consuming method development

304

for each compound separately. At present, this is not a realistic approach for determining

305

leaching and the underlying processes for the large number of pesticide products on the

306

market.

307

Even with FPB-based products being used on a wide variety of different crops around

308

the world, several recent regional or national evaluations of FPB have highlighted the lack of

309

available data on the fate and behavior of this herbicide in the environment.1, 3, 4 Based on

310

massive field monitoring experiments (> 1800 analyses of FPB, FP, or TFMP in water

311

samples) at the two PLAP fields, leaching of the two degradation products FP and TFMP was

312

observed in the months following application of FPB in concentrations above the European

313

Commission’s (EC) maximum allowable concentration of 0.1 µg L-1. This is in contrast to an

314

earlier study by Mills and Simmons,6 where a groundwater monitoring survey in northern

315

Italy and Germany was used to conclude that agricultural use of FPB posed a negligible risk

316

of groundwater contamination with FP and TFMP. In a similar study focusing on fluazifop-

317

butyl, there were detections above the EC threshold concentration in both river water and

318

groundwater in an agricultural area in Spain.23 However, this study did not include any of the

319

degradation products. Prior to the introduction of FPB, fluazifop-butyl was used instead,

320

which is a racemic mixture of both the R- and S-enantiomer of the compound.8 The R-

321

enantiomer has a higher herbicidal activity and at present only the R-isomer (FPB) is used.

322

Another strong indication of the potential for leaching of degradation products after the 13



323

addition of FPB is reported in a study of 21 pesticides in a full-scale model biobed.24 The

324

degradation product FP was the only degradation product from FPB that was included, and it

325

was among the four most frequently detected pesticide residues in effluent from the biobed

326

system.

327

Soils sampled from the two PLAP fields showed a potential for rapid biodegradation

328

of FPB, with DT50-values of 17 and 26 hours, and no or only minor abiotic transformation

329

during the laboratory experiments. These degradation rates are in the same range as

330

previously reported values.3, 5, 7, 8 However, the observed degradation of FP was much slower,

331

with DT50 values greater than two months in both Silstrup and Faardrup soil. This slow

332

degradation of FP was in contrast to previously reported DT50 values ranging from only 6 to

333

23 days.7, 25 The main degradation product was FP and the sequence in the detection of the

334

degradation products could suggest a further degradation of this compound to TFMP (as

335

shown in Scheme 1). Although only minor degradation of FP to TFMP was seen within the

336

incubation period, the field study confirmed that TFMP is produced under field conditions.

337

The slow production of TFMP observed in the laboratory could suggest that TFMP is formed

338

through an intermediate degradation product. In Scheme 1 the theoretical degradation of FP

339

via compound IV to TFMP is proposed. This pathway is suggested by the European Food

340

Safety Authority.3 Compound IV is mentioned as a major degradation product in soil at 10°C,

341

and might be classified as moderate to highly persistent (a study based on one soil and data

342

not published in peer-reviewed literature).3 Since compound IV is not included in the present

343

degradation studies or in the PLAP program, this pathway could not be confirmed in these

344

agricultural soils. A fourth degradation product, designated compound III (Scheme 1), is also

345

mentioned by the European Food Safety Authority,3 but the degradation product was only

346

observed in plant material at low concentrations after spraying with FPB.

14


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347

The slow production of TFMP and its persistence in soil (DT50 > 68 days) observed in

348

both PLAP fields, combined with a reported minor extent of complete FPB mineralization (9 -

349

30%)3 could suggest a production of other intermediate degradation products in soil. Based on

350

the mass balance established in the laboratory study (Figure 1), it appears that the PLAP

351

monitoring program at Silstrup and Faardrup covers the major degradation products produced

352

following initial degradation of FPB. Inclusion of compound IV in future degradation and

353

leaching studies might contribute to clarifying the complete pathway. The pathway covering

354

compound III and degradation products further down the complete degradation pathway

355

remains to be studied in detail.

356

The low soil sorption of the two degradation products could explain why they were

357

detected in drainage and groundwater below the PLAP fields. Furthermore, low sorption and

358

high water solubility could be reflected in the high detection frequency at Silstrup in the

359

month after the applications in 2008 and 2012 during high amounts of precipitation. Sorption

360

values (Kd) of 0.3 - 1.6 mL g-1have been reported for FP in previous peer-reviewed studies,7, 26

361

whereas the European Food Safety Authority reported a wider range of Kd values from 0.5 to

362

24.9 mL g-1. Sorption of TFMP (Kd) has been reported to be 0.3 - 1.4 mL g-1.3 An even lower

363

sorption capacity of FP was observed in the present study than the reported values from Kah

364

and Brown.26 A similar low sorption of TFMP was observed at Faardrup, whereas TFMP was

365

found to be even less sorbed than FP in Silstrup soil. No peer-reviewed studies are available

366

on the sorption of TFMP in soil, but from the present study it is evident that both TFMP and

367

FP have a low sorption capacity in plow layer soil and that they are fairly persistent to

368

degradation. This means that there is a high risk of both degradation products leaching.

369

Altogether, these results show that field application of FPB can give rise to leaching of

370

degradation products to groundwater in concentrations that exceed the threshold limit of 0.1

371

µg L-1. This observation is explained by a rapid microbial degradation of FPB to FP, and a 15



372

further slower degradation to TFMP. Both of these degradation products sorb to the soils to a

373

small extent, resulting in leaching following rain events. These results underline the

374

importance of including FP and TFMP in groundwater monitoring programs in areas where

375

the herbicide is used.

16


Page 16 of 28

Page 17 of 28

376


FIGURES

377 378

Figure 1. Degradation of fluazifop-P-butyl (FPB) (∆) (A, B) and the two degradation products

379

fluazifop-P (FP) (●) (C, D) and 2-hydroxy-5-trifluoromethyl-pyridin (TFMP) (□) (E, F) in

380

soil from Silstrup and Faardrup. The data are mean values (n = 3); bars indicate standard

381

deviations, with some being smaller than the symbol.

382 383 384

Figure 2. Abiotic transformation of fluazifop-P-butyl (FPB) (∆) (A, B) and the two

385

degradation products fluazifop-P (FP) (●) (C, D) and 2-hydroxy-5-trifluoromethyl-pyridine

386

(TFMP) (□) (E, F) in sterilized soil from Silstrup and Faardrup. The data are mean values (n =

387

3) and bars indicate the standard deviations, with some being smaller than the symbol.

388

17



389

ACKNOWLEDGMENTS

390

This study was funded by the National Geological Survey of Denmark and Greenland and the

391

Danish Pesticide Leaching Assessment Program. We would like to thank the many people

392

whose work within the program made the present study possible, especially Mai-Britt

393

Fruekilde (pesticide analysis), Lasse Gudmundsson and Jens Molbo (technical assistance in

394

the field), Spire M. Kiersgaard and Martin H. Engqvist for their help with the laboratory

395

studies of degradation and sorption, and Claire Tarring for revising the manuscript.

396 397 398

REFERENCES

399

(1) Report of the Food Quality Protection Act (FQPA) Tolerance Reassessment Progress and

400

Risk Management Decision (TRED) for Fluazifop-P-butyl; United states Environmental

401

Protection Agency: Washington, DC, 2005;

402

http://nepis.epa.gov/Exe/ZyPDF.cgi/P1002OAF.PDF?Dockey=P1002OAF.PDF.

403

(2) Registration of the Major Change in Labeling for the Product Fusilade DX Herbicide

404

(EPA Reg. No. 100-1070) Containing the Active Ingredient Fluazifop-p-Butyl (chemical code

405

122809); New York State Department of Environmental Conservation: New York, 2014;

406

http://pmep.cce.cornell.edu/profiles/herb-growthreg/fatty-alcohol-monuron/fluazifop-

407

butyl/fluazifop-p-butyl_mcl_0514.pdf.

408

(3) Conclusion on the peer review of the pesticide risk assessment of the active substance

409

fluazifop-P (evaluated variant fluazifop-P-butyl); European Food Safety Authority: Parma,

410

Italy, 2012; www.efsa.europa.eu/de/search/doc/2945.pdf.

411

(4) Fluazifop-P-butyl, Re-evaluation decision; Pest Management Regulatory Agency: Ontario,

412

Canada, 2012; www.hc-sc.gc.ca/cps-spc/alt_formats/pdf/pubs/pest/decisions/rvd2012-

413

05/rvd2012-05-eng.pdf.

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(5) Negre, M.; Gennari, M.; Cignetti, A.; Zanini, E. Degradation of fluzifop-butyl in soil and

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aqueous systems. J. Agric. Food Chem. 1988, 36, 1319-1322.

416

(6) Mills, M.S.; Simmons, N.D. Assessing the groundwater contamination potential of

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agricultural chemicals: a flexible approach to mobility and degradation studies. Pestic. Sci.

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1998, 54, 418-434.

419

(7) Kah, M.; Beulke, S.; Brown, C.D. Factors Influencing Degradation of Pesticides in Soil. J.

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Agric. Food Chem. 2007, 55, 4487-4492.

421

(8) Bewick, D.W. Stereochemistry of fluazifop-butyl transformations in soil. Pestic. Sci.

422

1986, 17, 349-356.

423

(9) Guidance document on the assessment of the relevance of metabolites in groundwater of

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substances regulated under Council Directive 91/414/EEC; European Commission: Brussels,

425

Belgium, 2003;

426

www.ec.europa.eu/food/plant/pesticides/approval_active_substances/docs/wrkdoc21_en.pdf.

427

(10) Council Directive 98/83/EC of 3 November 1998 on the quality of water intended for

428

human consumption; European Union: EUR-lex, 1998; http://eur-lex.europa.eu/legal-

429

content/EN/TXT/PDF/?uri=CELEX:31998L0083&from=EN.

430

(11) Danish Pesticide Leaching Assessment Programme (PLAP) Website;

431

http://pesticidvarsling.dk.

432

(12) Rosenbom, A.E.; Olsen, P; Plauborg, F.; Grant, R.; Juhler, R. K.; Brüsch, W.; Kjær, J.

433

Pesticide leaching through sandy and loamy fields – long-term lessons learnt from the Danish

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Pesticide Leaching Assessment Programme. Environ. Poll. 2015, 201, 75-90.

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(13) The Danish Pesticide Leaching Assessment Programme: Site characterization and

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monitoring design. Geological Survey of Denmark and Greenland: Copenhagen, Denmark,

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2001; http://pesticidvarsling.dk/publ_result/plap_site_char_2001.html.

438

(14) Ernsten, V.; Olsen, P; Rosenbom, A.E. Long-term monitoring of nitrate-N transport to

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drainage from three agricultural clayey till fields. Hydrol. Earth Syst. Sci. 2015, 19, 1-32. 19



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(15) Jørgensen, L.F.; Kjær, J.; Olsen, P.; Rosenbom, A.E. Leaching of azoxystrobin and its

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degradation product R234886 from Danish agricultural field sites. Chemosphere. 2012, 88,

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554-562.

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(16) Kjær, J.; Olsen, P.; Ullum, M.; Grant, R. Leaching of glyphosat and amino-

444

methylphosphonic acid from Danish agricultural field sites. J. Environ. Qual. 2005, 34, 608-

445

620.

446

(17) Kjær, J.; Olsen, P.; Bach, K.; Barlebo, H. C.; Ingerslev, F.; Hansen, M.; Sørensen, B. H.

447

Leaching of estrogenic hormones from manure-treated structured soils. Environ. Sci. Technol.

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2007, 41, 3911-3917.

449

(18) Negre, M.; Gennari, M.; Cignetti, A. High performance liquid chromatographic

450

determination of fluazifop-butyl and fluazifop in soil and water. J. Chromatogr. 1987, 387,

451

541-545.

452

(19) OECD Guidelines for the testing of chemicals Test No. 106: Adsorption - Desorption

453

Using a Batch Equilibrium Method. ©OECD Publishing, 2000; http://www.oecd-

454

ilibrary.org/docserver/download/9710601e.pdf?expires=1421851570&id=id&accname=guest

455

&checksum=8155A74BF71140C3E9930FB23D107BF0.

456

(20) Fenner, K.; Canonica, S.; Wackett, L. P.; Elsner, M. Evaluating pesticide degradation in

457

the environment: Blind spots and emerging opportunities. Science. 2013, 341, 752-758.

458

(21) Penning, H.; Sørensen, S. R.; Meyer, A. H.; Aamand, J.; Elsner, J. C, N, and H isotope

459

fraction of the herbicide isoproturon reflects different microbial transformation pathways.

460

Environ. Sci. Technol. 2010, 44, 2372-2378.

461

(22) Qiu, S.; Gözdereliler, E.; Weyrauch, P.; Magana Lopez, E. C.; Kohler, H-P. E.; Sørensen,

462

S. R.; Meckenstock, R. U.; Elsner, M. Small 13C/12C fractionation contrasts with large

463

enantiomer fractionation in aerobic biodegradation of phenoxy acids. Environ. Sci. Technol.

464

2014, 48, 5501-5511.

20


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(23) Martínez, R. C.; Gonzalo, E. R.; Laespada, M. E. F.; San Román F. J. S. Evaluation of

466

surface- and groundwater pollution due to pesticides in agricultural areas of Zamora and

467

Salamanca (Spain). J. Chromatogr. 2000, 866, 471-480.

468

(24) Spliid, N.H.; Helweg, A.; Heinrichson, K. Leaching and degradation of 21 pesticides in a

469

full-scale model biobed. Chemosphere. 2006, 65, 2223-2232.

470

(25) Smith, A.E. Persistence studies with the herbicide fluazifop-butyl in Saskatchewan soils

471

under laboratory and field conditions. Bull. Environ. Contam. Toxicol. 1987, 39, 150-155.

472

(26) Kah, M.; Brown, C.D. Prediction of the Adsorption of Ionizable Pesticides in Soils. J.

473

Agric. Food Chem. 2007, 55, 2312-2322.

474

(27) Allerup, P.; Madsen, H. Accuracy of the point of precipitation measurements. Nord.

475

Hydrol. 1980, 11, 57-70.

21



Page 22 of 28

Table 1. Fluazifop-P-butyl (FPB), fluazifop-P (FP), and TFMP detections and maximum concentrations of hydrological years (1 July – 30 June) in the period July 2000 to June 2013. Data were obtained from analyses of water samples collected from the variably-saturated (drainage and suction cups) and saturated zones (groundwater monitoring wells) at the loamy PLAP fields Silstrup and Faardrup. Gray areas indicate water samples with concentrations above the detection limit of 0.01 µg L-1 for FPB and FP, and 0.02 µg L-1 for TFMP. The yearly precipitation and measured drainage are presented for each hydrological year within the monitoring period. Furthermore, the first month’s precipitation after FPB application is presented together with the date and dose of the application.



203

2010-April 2011*,**

1027

172

53

02-052010

2011-April 2012*

995

218

26

26-042011

2012-13

1020

261

127

2001-02

810

197

56

2002-03

636

49

2011-12*

828

98

59

21-052011

Detections

Detections => 0.1 µg L-1

Analyses

Detections


Detections


Analyses

Detections

Detections


Analyses

Detections


-

32

0

0

0 -

-

-

-

-

-

-

32

0

0 -

-

-

-

144

0

0

0 -

-

-

-

-

-

-

42

0

0

0 -

-

-

-

-

-

-

19

0

0 -

-

-

-

95

1

0

0.07 -

-

-

-

-

-

-

17

0

0

0

17

17

17

0.52 -

-

-

-

-

-

-

-

-

-

94

0

0

0

95

46

9

0.29

-

-

-

14

0

0

0

14

3

0

0.03 -

-

-

-

-

-

-

-

-

-

46

0

0

0

46

2

0

0.03

0.2

-

-

-

9

0

0

0

17

1

0

0.06 -

-

-

-

-

-

-

-

-

-

29

0

0

0

49

0

0

0.00

0.2

-

-

-

-

-

-

-

21

8

3

0.64 -

-

-

-

-

-

-

-

-

-

-

-

-

-

63

7

4

0.22

0.2

-

-

-

-

-

-

-

22

22

4

0.41 -

-

-

-

-

-

-

-

-

-

-

-

-

-

59

32

3

0.12

0.4

Analyses

Dose [kg of FPB ha-1]

Time of FPB application 19-042012 21-062001

-

0.4

0.2

-

58

0

0

58

10

5

3.8 -

-

-

-

40

0

0

40

0

0

0 -

-

-

-

25

0

0

0

-

-

2012-13 569 62 * Monitoring period ended in April †† Monitoring of fluazifop-P (FP) ended in December 2010 *** Precipitation is corrected to soil surface according to the method of Allerup and Madsen.26

-

22

0

0

22

3

0

0.09

86

0

0

86

6

1

0

0 113

0

0 -

-

-

-

-

-

-

-

113

0.17 -

Cmax [µg L-1]

758

01-072008

-

0.4

Detections

2009-April 2010*

105

Total no. of:

Analyses

161

Total no. of:

Cmax [µg L-1]

985

Total no. of:

Analyses

2008-09

Total no. of:

Cmax [µg L-1]

227

FPB


1034

FP

Total no. of:

Analyses

2001-02

28-062000

Total no. of:

Cmax [µg L-1]

52

FPB


217

Total no. of:

TFMP

Detections

909

Total no. of:

Saturated zone Groundwater monitoring wells FP TFMP

Suction cups

Analyses

2000-01

FPB

Cmax [µg L-1]

First month of precipitation following application [mm] ***

Faardrup

Measured drainage [mm year-1]

Silstrup

Precipitation [mm year-1]***

Field

Monitoring period (from FPB application date or 1 July - 30 June following year)

Variably-saturated zone Drainage FP


Page 23 of 28

-

-

-

-

-

-

34

0

0

0 -

-

-

-

-

-

-

-

-

-

-

-

-

-

65

0

0

0

24

0

0

0 -

-

-

-

-

-

-

-

-

-

-

-

-

-

57

0

0

0



Page 24 of 28

Table 2. Measured pH, water content, half-life of fluazifop-P-butyl (FPB, DT50) and sorption coefficient (Kd) of the two degradation products fluazifop-P (FP) and 2-hydroxy-5-trifluoromethylpyridine (TFMP) in soil samples from the plow layer at Silstrup and Faardrup Soil Silstrup Faardrup

pH (CaCl2) 5.85 6.19

Water content [%] 29.3 19.4

DT50 FPB [hours (R2)] 17 (0.98) 26 (0.95)


Kd TFMP [mL g-1] 0.39 0.18

Kd FP [mL g-1] 0.49 0.14

Page 25 of 28


N

O

F O F

F

O

fluazifop-P-butyl (FPB)

CH3

H3C O

?

N

OH

F F N

O

? F TFMP

F O HO

?

F

F

OH

fluazifop-P (FP)

H3C N

O

O

?

?

?

O

F

OH

?

H3C

Compound III

OH F

O

F

Compound IV

Scheme 1. Proposed degradation pathway of fluazifop-P-butyl (FPB) in soil, including the main degradation products fluazifop-P (FP) and 2-hydroxy-5-trifluoromethyl-pyridin (TFMP). Solid lines represent observed microbial degradation steps in soil. Punctuated lines represent theoretical degradation steps not confirmed in this study



Silstrup

Faardrup

Degradation of FPB

Degradation of FPB

4

4

B

FPB FP TFMP

3

Concentration (µmol kg-1)


A

2

1

0

3

2

1

0 0

10

20

30

40

50

60

70

0

10

20

Days

Degradation of FP

40

50

60

70

60

70

Degradation of FP 5

C

D

FP TFMP

4



30

Days

5

3

2

1

0

4

3

2

1

0 0

10

20

30

40

50

60

70

0

10

20

Days

30

40

50

Days

Degradation of TFMP

Degradation of TFMP

12

12

F

E 10



Page 26 of 28

8 6 4 2

TFMP

0

10 8 6 4 2 0

0

10

20

30

40

50

60

70

0

10

20

Days

30

40

Days

Figure 1


50

60

70

Page 27 of 28


Silstrup

Faardrup

Abiotic controls - FPB

Abiotic controls - FPB

5

5

B



A 4

3

FPB FP

2

1

0

4

3

2

1

0 0

10

20

30

40

50

60

70

0

10

20

Days

Abiotic controls - FP

50

60

70

60

70

Abiotic controls - FP 5

D


C


40

Days

5

4

3

2

1

FP

0

4

3

2

1

0 0

10

20

30

40

50

60

70

0

10

20

Days

30

40

50

Days

Abiotic controls - TFMP

Abiotic controls - TFMP

12

12

F

E 10



30

8 6 4 2

TFMP

0

10 8 6 4 2 0

0

10

20

30

40

50

60

70

0

10

Days

20

30

40

Days

Figure 2


50

60

70



Page 28 of 28

Environmental Fate of the Herbicide Fluazifop-P-butyl and Its

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