Content uploaded by Samsuri A. W.
Author content
All content in this area was uploaded by Samsuri A. W. on Sep 22, 2015
Content may be subject to copyright.
African Journal of Agricultural Research Vol. 6(17), pp. 4010-4018, 5 September, 2011
Available online at http://www.academicjournals.org/AJAR
DOI: 10.5897/AJAR11.533
ISSN 1991-637X ©2011 Academic Journals
Full Length Research Paper
Determination of glyphosate through passive and
active sampling methods in a treated field atmosphere
Md. Mahbub Morshed1, Dzolkhifli Omar1*, Rosli B. Mohamad2 and Samsuri B. Abd. Wahed3
1Toxicology Laboratory, Department of Plant Protection, Faculty of Agriculture, University Putra Malaysia, 43400
Serdang, Selangor D. E., Malaysia.
2Department of Crop Sciences, Faculty of Agriculture, University Putra Malaysia, 43400 Serdang, Selangor D. E.,
Malaysia.
3Department of Land Management, Faculty of Agriculture, University Putra Malaysia, 43400 Serdang, Selangor D. E.,
Malaysia.
Accepted 30 May, 2011
The study was carried out to determine the atmospheric residues of glyphosate (N-
phosphonomethylglicine) using both passive and active sampling methods in Malaysia’s tropical
weather conditions. The field was treated with Roundup (Monsanto) @ 2L ha-1 using Mistblower (Solo
412). Glyphosate was sampled in 12 h day time pre and post-spray sampling events using three simple
and low-cost passive air samplers (cotton gauze, cellulose filter, and PUF) and active sampling using
PUF plug and quartz filter cartridges. In pre-spray sampling event, no glyphosate detection was shown
in both passive and active sampling. On the other hand, post-spray passive samples data revealed that
only cotton gauze among the three passive air samples showed detection in both post-spray events
during which the first post-spray (2.49 ng/cm2) showed significantly higher residue measurement than
that of second post-spray period (0.84 ng/cm2). In active sampling, however, no glyphosate residue was
detected in any of the PUF plug samples but detected only in quartz filter samples, revealing that
glyphosate is associated with particles rather than vapour in the air. The highest concentration of
glyphosate (42.96µg/m3) was measured in the air at operator’s breathing zone during the 25 min spray
application period. In the post-spray active sampling periods, glyphosate residue was significantly far
below compared to the spray period concentration. Furthermore, in paired comparison between active
and passive sampling methods in terms of residue uptake performance, passive sampling showed
significantly better performance than the active sampling method in this study.
Key words: Glyphosate, active sampling, passive sampling, atmospheric residue.
INTRODUCTION
Glyphosate (N-phosphonomethylglicine) is a broad-
spectrum, foliar-applied herbicide used to kill unwanted
plants in a wide variety of agricultural crops, lawn and
garden, aquatic, and forestry situations (Humphries et al.,
2005). Glyphosate is registered in more than 130
countries and is believed to be the world’s most heavily
used pesticide (Duke and Powles, 2008), with over 600
thousand tonnes used annually (CCM International,
2009). Based on the registration eligibility data on
toxicology and exposure study (USEPA, 1993), glyphosate
*Corresponding author. E-mail: zolkifli@agri.upm.edu.my.
is under toxicity category III (low toxicity). Moreover, poor
absorption through skin and rapid elimination of
glyphosate upon normal exposure (WHO, 1994) might
convince the occupational safety regulators not to set any
occupational exposure limits for glyphosate. However,
workers in a variety of occupations on exposure to
glyphosate, develops acute illness. It has been revealed
that glyphosate exposure was reported as the third most
commonly-reported cause of pesticide illness among
agricultural workers in California (Cox, 1995). In Malaysia,
glyphosate is the predominant herbicide used in different
cropping systems through motorised knapsack sprayers
in low volume spray (increased herbicide concentration)
for increased herbicide efficacy. This intensive use of
glyphosate has resulted into serious contamination of the
environment because substantial amount of applied
pesticides have been shown to become airborne during
and after application (Seiber et al., 1980). These airborne
residues present a potential exposure route for field
workers and other individuals dwelling close to
agricultural sites.
Unlike the sampling of solid and liquid matrices, air
sampling has always posed unusual challenges because
of the ever changing nature of the components in the
atmosphere. However, understanding the physical
properties of the pesticide (that is, primarily its vapour
pressure) and environmental conditions is the key to the
selection of an appropriate field sampler and its sampling
strategy (Woodrow et al., 2003). In the atmosphere,
pesticides are distributed between particle and vapor
phases based on the vapor pressure of the chemical,
ambient temperature, and concentration of suspended
particulate matter in the air (Gioia et al., 2005). To
determine the residue level in air, both passive and active
sampling methods are commonly used. Active sampling
enable the pesticides present in the air to be trapped by
pumping air through filter and solid adsorbent media
(Tadeo, 2008), whereas passive sampling methods are
conceptually simple. It is based on free flow of analyte
molecules from the sampled medium to a collecting
medium resulting from different physical principles
(Gorecki and Namiesnik, 2002). Numerous passive air
samplers are being used commercially and all of them
are designed to perform sampling keeping various factors
in mind, including, the matrix (air, water, soil), physico-
chemical properties of the target analytes, sampling
duration, environmental variability, cost and easy
availability (Seethapathy et al., 2007). Despite having
some limitations (possible environmental effects on
analyte uptake), passive samplers could be an attractive
alternative to more established sampling procedures due
to its simplicity and cost-effectiveness (Kot-Wasik et al.,
2007)
In Malaysia, several efforts have been made over the
years to determine glyphosate in the environmental
samples (soil and water) but the air compartment is still
overlooked. Moreover, very little information exists in the
literature on studies quantifying glyphosate residues in
the air following spray application. Therefore, the
objective of this study was to measure the airborne
residue present during and after glyphosate application in
the field.
MATERIALS AND METHODS
Experimental site
The study was conducted from February to April, 2009 at field 2
located inside the University Putra Malaysia (UPM), and the test
plot size was 1000 m2 which was a weedy harvested corn field. The
site is bit down compared to the surrounding area. It is completely
open to the west and south where prevailing winds originate, and is
Morshed et al. 4011
not adversely affected by natural trees or shelterbelts on this side.
North of the site is a hay field which extends for 0.2 km before the
start of the urban area. East of the site has office building and some
shed housing facilities for research studies. No fields in close
proximity to this site were treated with glyphosate for pre-seeding,
post-emergent or pre-harvest weed control.
Glyphosate application
Glyphosate herbicide 41% a.i. (Roundup, Monsanto Sdn. Bhd.,
Malaysia) was applied with a calibrated mist blower (Solo Master
412) set at a discharge rate of 0.64 L min-1. Glyphosate was applied
at a field dosage rate of 2 L ha-1 with a spray volume of 160 L.
Spray droplet diameter of this sprayer were measured using
microscope fitted with Porton G12 Graticule , as described by
Matthews (2000). The estimated VMD (volume median diameter)
and NMD (number median diameter) for spray droplet size were 67
and 35.5 µm respectively, and these droplets diameters are
considered as fine droplets (Matthews, 1999).
Air sampling procedures
Three types of passive air samplers with an exposed surface area
of roughly 16 cm2, namely Cotton gauze (Gasmed Sdn. Bhd.,
Malaysia) , Cellulose filter patches (Whatman grade 41, England),
and Polyurethrane Foam(PUF) (SKC Inc., USA) were used for
passive air sampling and each type of samplers was taped on five
surfaces of an identical dimensions foil-covered box (15x15x15cm)
– vertically on west (W), East (E), North (N),South (S), and
horizontally on Top (T). These boxes were placed 1 m above the
ground surface at three randomly selected points nearer to
downwind edges of the test plot.
Active sampling was done using field air sampling pump (Model
1067) supplied by Supelco, USA calibrated to a flow rate of 10L
min-1 using bubble flow meter. The sampling pump was connected
by tygon tube to polyurethane foam (PUF) plug cartridge (ORBOTM
1000, Supelco, USA) containing 0.022 g/cm3 density PUF plug in
the glass housing, fitted in front with a Quartz fibre filter cartridge
(Supelco, USA). The PUF plug will work mainly for the vapour and
the quartz filter for particulate phase of airborne glyphosate (Van
Dijk and Guicherit, 1999). After starting sampling, the pump
operation was observed for a short time to make sure that it is
operating correctly. The pump was powered by electricity through
long extension cable to avoid fluctuations in the pump flow rate that
have a significant effect on measurement accuracy when air is
sampled.
Personal air sampling is done to determine the concentration
level that a spray worker is exposed to during a full work shift or
task by measuring the breathing zone concentration of the worker.
Battery-operated personal air sampling pump (Model PAS-500,
Supelco Inc. USA) calibrated to a flow rate of 0.3 L min-1 was used
during spraying. The sampling pump was fixed at the sprayer’s
waist belt and the sampling head fitted with PUF plug and quartz
filter cartridges (Supelco, USA) was attached at sprayer’s collar
bone area in downward position to cover the breathing zone. The
duration of spraying was recorded using a stopwatch.
Sampling frequency and duration
Air sampling was carried out in 12 h day time from 6:30 am to 7 pm
at 4 h interval which was as follows: 4 h pre-spray, during spray (25
min), and post-spray periods (0 to 4 and 4 to 8 h). After sampling,
active samplers (PUF and Quartz filter cartridges) were caped and
passive samplers were collected in centrifuge falcon tubes. All
samples were put in ice box at reduced temperature for transport.
4012 Afr. J. Agric. Res.
Figure 1. Linear calibration curve for glyphosate (N = 9; Y = 7.94 e+6 x + 4.43 e+5 and correlation coefficient r2 = 0.999).
Micrometeorological measurements
Air temperature and wind velocity were recorded on ‘sampling data
sheet’ at every one hour during sampling period by using Thermo-
Anemometer (Extech Instruments, USA). Relative humidity was
also measured at same intervals using Humidity Indicator (Airguide
Instrument Co., USA). During the period wind directions, cloud
cover, and incidence of rain were also noted.
Chemical analysis
Preparation of standard solution and curve
Standard stock solution (400 ppm) was prepared by dissolving
0.004 g glyphosate standard (Sigma-Aldrich, USA. purity 99.7%) in
10 ml 0.025 M sodium borate buffer (pH 9) solution. Nine working
standards of 10.0, 5.0, 2.0, 1.0, 0.5, 0.1, 0.05, 0.01 and 0.005 ppm
were prepared taking the corresponding aliquots from the stock
solution followed by dilution with sodium borate buffer for the
preparation of standard curve to estimate the linearity and
sensitivity of response. Prior to HPLC injection, each working
solutions was pre-column derivatized with a derivatizing agent
(0.002M FMOC-Cl) as described in the pre-column derivatization
step. The lowest calibration level (LCL), which runs on an
instrument with acceptable response (area) is 0.005 ppm. Standard
curve (Figure 1) for glyphosate was found to be linear over the
above range through the evaluation of the correlation coefficient,
which was 0.999. Chromatogram of working standard solution of
glyphosate (10.00 ppm) was shown in Figure 2.
Sample preparation
The sample preparation method was done according to ‘Method
PV2067’ with some modification as proposed by Occupational
Safety and Health Administration (OSHA) analytical laboratory,
USA. Both active and passive samplers were carefully transferred
to 50 mL centrifuge tubes by clean tweezers. 10 ml borate buffer
was added to each tube and then the tubes were capped and
allowed to stand for 30 min to soak samples completely. The
centrifuge tubes were placed on an orbital shaker at 200 rpm for 1 h
followed by ultra sonication (Cole Parmer, USA) for 2 h to desorb
the analyte.
Pre-column derivatisation
The derivatizing agent (0.002M FMOC-Cl) was prepared by adding
0.1293g 9-florenylmethoxycarbonyl chloride (obtained from ACROS
Organics, USA; purity 98%) in 250 ml acetone. Before injecting into
HPLC, 1 mL aliquot of each sample extract was transferred in a
silanized vial and derivatized with 1 mL of derivatizing agent to
produce a highly florescent derivative. The vials were shaken to mix
for 30 sec on a mini-shaker and subsequently allowed them to sit at
room temperature in a dark place for 30 min. Then 1 mL of each
sample was transferred in HPLC vial and subsequently labeled and
injected to HPLC-FD for analysis.
HPLC systems
HPLC (High performance liquid chromatography) was consisted of
Morshed et al. 4013
Figure 2. Chromatogram of glyphosate obtained at 10 ppm standard concentration with the recommended HPLC-Florescence
conditions.
Waters 600 controller pump equipped with Waters 717 auto
sampler and a florescence detector (Waters 4174). The detector
was set with an emission wavelength of 320 nm and an excitation
wavelength of 206 nm that was operated in single channel mode
with photomultiplier gain at 1, attenuation at 64 and output data
sensitivity (EF) at 5000.. The stationary phase was 250 mm × 4.6
mm i.d 5µ A0 Hypersil NH2 column (APS-2) and the mobile phase
was comprised of 50% Acetonitrile and 50% Phosphate buffer
(0.05M Potassium phosphate monobasic KH2PO4 adjusted to pH
6.0 with 7N KOH). The mobile phase flow rate (isocratic) was 1
ml/min. All the solvents and solutions used in the mobile phase
were previously filtrated and degassed by ultrasonic application.
The injection volume was 25.0 µL. Total sample run time was 10
min and analyte retention time was 5.6 min.
Fortification and recovery studies
The percentage of analyte recovery from fortified samples generally
represents the extraction efficacy of the method. Fortification was
done in triplicates by applying 100µL of three spiking concentrations
(1.0, 5.0 and 10.0 ppm) over the surface of three fresh unused
samplers (cotton gauge, cellulose filter, and PUF). Then the fortified
(spiked) samples were capped and allowed to keep at 4°
C inside
freeze drawer overnight to equilibrate. The following day, the
fortified samples were extracted and analyzed to HPLC-FD as
same as field samples. Mean recovery percentages from fortified
samples were comprised between 88.8 to 97.2% with a relative
standard deviation (RSD) value of 4 to 6% (Table 1).
Chromatogram of glyphosate fortified at the concentration of 10.0
ppm showed the same peak retention time (5.6 min) as standard
peak (Figure 3).
Limit of Detection (LOD) and Limit of Quantitation (LOQ)
determination
The LOD and LOQ were determined via linear regression method
using linear calibration curve of glyphoshate established at 5
concentration levels with three replicates (ICH, 1996). The LOD for
this method was 0.015 ug ml-1 and the LOQ was determined to be
0.05 ug ml-1.
QC/QA considerations: Laboratory and solvent blanks were
prepared and extracted as same as the field samples which
showed no contamination in solvent and samplers. One field blank
sample for every 15 samples was used for analysis along with the
field samples. All field blank samples were below the analytical limit
of detection (LOD) for glyphosate tested.
Statistical analysis
The study was repeated three times in the same location. Data
collected were analyzed following analysis of variance (ANOVA)
technique under RCBD (factorial) experimental design and means
separation were done by Turkey’s Studentized range (HSD) using
statistical analysis system (SAS). Differences were considered
significant at p<0.05.
RESULTS AND DISCUSSIONS
During the entire sampling period, the weather was clear
and sunny. Temperatures were warm, ranging from 82 to
97°
F. Relative humidity ranging from 84 to 55% was
observed. However, relative humidity was high in the
morning and evening, and decreased as temperature
increased in the mid-day periods. Wind velocity was
almost same throughout the day blowing predominantly
from south and south-west direction, ranging between 2
to 5 mil/h. However, there was no incidence of rainfall on
the sampling days during the study period.
4014 Afr. J. Agric. Res.
Minutes
Fluorescence
Figure 3. Chromatogram of glyphosate obtained at 10 ppm fortification concentration with the recommended HPLC-Florescence
conditions.
Table 1. Percent recovery (mean± S.D.) and relative standard deviation (% RSD) for the glyphosate fortified samples (N = 27).
Compound
Fortification concentration (ppm) Fortification level (µg/sample) % mean recovery ± S.D. % RSD
Glyphosate
1.0 0.1 88.8 ± 5.75 6.61
5.0 0.5 98.7 ± 4.28 4.31
10.0 1.0 97.2 ± 4.50 4.66
Passive air samplers
The results for each passive air sampler showed very
little amount of glyphosate detection only on cotton gauge
samples as summarized in Table 2. Since glyphosate has
no significant vapour pressure and therefore, the loss of
glyphosate to the atmosphere via volatilization from
treated surfaces is nonexistent (Franz et al., 1997). The
main emission pathway for non-volatile particulate-
phased compounds like glyphosate into atmosphere
occurred through wind erosion process of dust particles
on treated surfaces loaded with pesticides (Van Dijk and
Guicherit, 1999). In this study, pre-spray air sampling
was taken for 4 h period prior to spraying and glyphosate
was not detected in any of the three samplers in this pre-
event sampling. The absence of detection at pre-spray
sampling in the morning could be due to the complete
removal of residual atmospheric glyphosate via wet
deposition mainly by night dew/fog, since glyphosates
low Henry’s Law Constant (4.6 × 10-10 Pa m3 mol-1)
indicates that it tends to partition in water versus air
(Franz et al., 1997) and thereby efficiently removed from
the air (Chang et al., 2011). On the other hand, post-
event sampling was carried out in 8 h periods with an
interval of 4 h that started immediately after completion of
spraying, and among the three passive samplers, very
little glyphosate was detected mainly on cotton gauge
passive samplers in both post-spray sampling periods.
However, glyphosate was also detected on the PUF
samples only in the first post-spray sampling event (0 to 4
h periods) that was found below the limit of quantitation
(LOQ) levels and in contrast, no glyphosate was detected
on cellulose filter samples in both post-spray sampling
periods. The amount of glyphosate deposition by cotton
Morshed et al. 4015
Table 2. Glyphosate residue amount mean ± S.D deposited on three passive air samplers before and after application in the treated
field air.
Passive air
samplers Samplers orientation
Deposition amount (ng/cm2)
Pre-spray Post-spray
4 h 0-4 h 4-8 h 8 h TWA
a
PUF
West ND <LOQ
b
ND -
East ND <LOQ ND -
North ND <LOQ ND -
South ND <LOQ ND -
Top ND <LOQ ND -
Average - - -
Cellulose filter
West ND ND ND -
East ND ND ND -
North ND ND ND -
South ND ND ND -
Top ND ND ND -
Average - - - -
Cotton gauge
West ND 3.42± 1.11ab 1.95± 0.24a 2.68±0.67a
East ND 1.79± 0.68ab <LOQb 0.89±0.34b
North ND 1.97 ± 0.65ab <LOQb 0.98±0.32b
South ND 4.16± 0.70a 2.25± 0.47a 3.20±0.58a
Top ND 1.12± 0.92b NDb 0.56±0.46b
Average - 2.49
± 1.12
0.84
± 1.03
1.66
± 1.07
a TWA, time-weighted average = sum of the products of concentration and time for each sampling period, divided by total sampling time. b
<LOQ = below limit of quantitation. Values followed by the same letter (s) column wise, are not significantly different at (P < 0.05). Samples that
produced undetected results have been assigned as ‘ND’.
gauze samplers could be explained by the findings of
OECD (1997) which recommended cotton fabrics for
trapping particles constructed with layers of cotton
surgical gauze as they are porous enough and have
uneven surfaces that help to retain the particles landing
on it. In first 0 to 4 h post-spray event, cotton gauze
samples yielded higher average glyphosate deposition
(2.49 ng/cm2) than that of second 4 to 8 h post spray
sampling event (0.84 ng/cm2). Obviously, the low levels
of glyphosate detection may account for its insignificant
post-application volatilization from treated surfaces.
Furthermore, once glyphosate had been sprayed, the
resulting fine pesticides particles tends to adsorbed onto
dust particles present in the air and subsequently
partitioned to particulate phase in the atmosphere.
Therefore, the nature and concentration of dust particles
in the air would determine the atmospheric loading as
glyphosate in the air is associated with particulate matter
(dust), assuming that this particulates are removed by
gravitational settling or wind erosion. But this atmospheric
loading into particles is dependent upon many factors in
which environmental factors (such as wind speed,
temperature and humidity) are of importance (Van Dijk
and Guicherit, 1999). However, in the tropical weather of
Malaysia, prevailing high temperature and humidity as
well as high precipitation plays very important role in
glyphosate atmospheric deposition. The amount of dust
particles in the air is reduced as a result of high
atmospheric humidity and frequent precipitation events
(UN-ECE, 1979). This resulted to lower levels of atmos-
pheric glyphosate deposition.
In addition to the above findings, the glyphosate
detection was showed in higher amount on cotton gauze
samplers oriented on south approach (4.16 and 3.42
ng/cm2) followed by west (2.24 and 1.95 ng/cm2) in post
sampling periods indicating the correlation of wind
movement with atmospheric deposition of glyphosate
during which wind was predominantly blown from south
and south-west direction across the face of samplers.
This wind movement might influence the gravitational
settling and inertial impaction of wind blown particulates
at the time of deposition on samplers. In agreement with
the effect of wind movement on airborne pesticides,
Thistle (2000) asserted that the dispersion of pesticide
droplets in the air is influenced by the droplet size,
atmospheric stability and wind movement (vertical and
4016 Afr. J. Agric. Res.
Table 3. Glyphosate residue amount mean ± S.D measured on active air samplers before, during and after application in the treated
field air.
Spray periods
Active sampling
Air volume (m3)
Air concentration (µg/m
3
)
Quartz filter PUF plug Total air concentration
Pre- spray (4 h) 0.24 ND ND ND
During spray(25 min) 0.0075 42.8 ND 42.96 ± 7.96a
Post- spray 0-4 h 0.24 0.10 ND 0.10 ± 0.013b
4-8 h 0.24 0.051 ND 0.051 ± 0.007b
Samples that produced undetected results have been assigned as ‘ND’. Values followed by the same letter (s) column wise, are not
significantly different at (P < 0.05).
horizontal components).
Active air samplers
The air concentrations of glyphosate measured by active
sampling were presented in Table 3. The result showed
that glyphosate was not detected in any of the air
samples collected with polyurethane foam (PUF) plug
samples but it was detected only in quartz filter samples.
The absence of glyphosate in the PUF plug indicates that
glyphosate is not released as the vapour into the
atmosphere but rather is carried by particulate matter
(Humphries et al., 2005). In the pre-spray sampling event,
no glyphosate was detected in both quartz filter and PUF
plugs, this indicates that glyphosate is no longer in the
atmosphere in the wet and high humid morning but have
been removed through wet deposition.
The highest air concentrations of glyphosate (42.96
µg/m3) occurred during 25 min spray application period
that was collected through personal air sampling pump
operated at operator’s breathing zone. The result was
within a range of 0.41 to 48 µg/m3 glyphosate residue
levels in the working air depending upon the method of
application and rate of applications which was revealed in
a study conducted in Ukraine (Chmil and Kuznetsova,
2009). The high concentration measured during spray
application period was due to fine droplets produced by
mist blower sprayer that remain in the surrounding air
due to their lower terminal velocity (Matthews, 1999).
Most importantly, a significant proportion of these fine
droplets are inhalable particles that pose serious risk of
health injury to spray operators. On the post spray
sampling done by field air sampling pump, glyphosate
was detected in small amounts in quartz filter samples
that were drastically lower than the spray period
concentration. However, glyphosate concentrations were
markedly higher during 0 to 4 h post spray (0.10 µg/m3)
and decline during 4 to 8 h period (0.051 µg/m3).
However, this post spray results were far below the
reported residue range of 10 to 17 µg/m3 during 24 h post
spray fine filter sampling to measure Alberta’s
atmospheric glyphosate deposition conducted by Water
research group of Alberta Environment (Humphries et al.,
2005). Concentration of glyphosate in air was found very
small at post-spray sampling, and this occurrence might
be because of negligible volatility after spray application.
Furthermore, this might be due to the total volume of air
sampled with the field air sampling pump.
Paired comparison of passive sampling method
performance with active sampling
In field situations, there is a considerable variability of the
concentrations of airborne residues during sampling
periods in which the performance of both active and
passive sampling methods also showed different
performance in terms of residue uptake. Active air
samplers have been widely accepted as the reference
method for the evaluation of the performance of passive
air samplers. Hence, both active and passive samplings
were done side-by-side in all sampling events in this
study to do the paired comparison between the active
and passive sampling methods. This paired comparison
is important for the performance evaluation of passive
samplers by assessing the magnitude and direction of
differences between passive and active air samplers.
However, current National Institute for Occupational
Safety and Health (NIOSH), Health and Safety Executive
(HSE), and European Committee for Standardization
(CEN) validation protocols have used Student’s t-tests,
paired sample Student’s t-tests, and linear regression as
the statistical methods for evaluating the performance of
passive samplers. In this context, linear regression
analysis would be preferable providing a measure of the
degree of association between the two methods (that is,
the correlation of coefficient) on the assumption that a
linear relationship exists between them, over the range of
conditions covered by the field tests. Basically, these
tests can only investigate whether in general the mean
concentrations measured by active and passive sampling
Morshed et al. 4017
GLYPHOSATE
Residue concentration found by active sampling
(ppm)
Residue concentration found by passive
sampling (ppm)
Residue concentration found by active sampling (ppm)
Figure 4. Paired relationship between the active and passive sampling methods -based on the results of airborne
glyphosate residue uptake concentration (ppm).
methods are statistically different from each other, but not
identify the source of the differences (Shih et al., 2000).
The linear relation determined by the regression analysis
is taken the following equation form:
y = a + bx
Where y and x are the residue concentrations measured
by the passive and active sampling methods respectively.
For perfect agreement between the two methods, the true
values of the intercept (a) and slope (b) parameters
should be respectively 0 and 1.
From the field performances of three passive samplers
in terms of glyphosate residue uptake, it was quite
evident in this study that only cotton gauze samplers
showed residue uptake in comparison to other two
passive samplers. Therefore, passive (cotton gauze) and
active (quartz fibre filter) air samplers (a total of 6 pairs of
residue concentrations in ppm) were used for determining
the agreement between passive and active sampling
methods.
In regression analysis (Figure 4), linear correlation was
found between pair-wise (n = 6) comparison of residue
concentrations measured by active and passive sampling
methods over the range of 0.001 – 0.004 ppm. The linear
regression line equation showed satisfactory correlation
coefficient (R2 = 0.98) with a moderate slope (b = 1.63)
and a negative intercept (a = -0.0006). It was also
observed that residue concentration found at the second
post-spray events (4 to 8 h) were very close to standard
line (y = x line). In contrast, the residue concentrations
found during the first post-spray sampling events (0 to 4 h)
were far above the standard line. Hence, it can be
inferred that residue uptake by passive sampling was
much higher than active sampling method in the first
post-spray sampling event immediately after spraying,
and with passage of time the performance of two
methods became almost similar in the second sampling
event.
Conclusion
The study of airborne glyphosate residue in post-spray
application showed that in the air, glyphosate is
associated with particles rather than vapour. It was also
noted that meteorological conditions play a significant
role in atmospheric sampling. Among the three passive
samplers used in this study, only cotton gauze passive
sampler showed atmospheric glyphosate detection in
both post-spray sampling events and could be suitably
used for non-volatile pesticides residue measurement in
the air. In paired comparison between active and passive
sampling methods, it was quite evident that passive
sampling showed significantly better performance than
the active sampling. Although occupational safety
organizations have not yet established any threshold
limits for glyphosate exposure, but the air concentration
during spray application at sprayer’s breathing zone was
substantially higher that suggesting the use of personal
protective equipments (PPEs) for persons in charge of
application.
REFRENCES
Cox C (1995). Glyphosate, part 2: Human Exposure and Ecological
Effects. J. Pesticide Reform., 15(4): 14-20.
4018 Afr. J. Agric. Res.
CCM International (2009). Glyphosate Competitive Analysis in China.
http://www.researchandmarkets.com/reportinfo.asp?report_id=64903
1.
Chang FC, Simcik MF, Capel PD (2011). Occurrence and Fate of the
Herbicide Glyphosate and Its Degradate Aminomethylphosphonic
Acid in the Atmosphere. Environ. Toxic Chem., 30(3): 548-555.
Chmil V, Kuznetsova E (2009). Glyphosate: Environmental Fate and
Levels of Residues. Medved’s Institute of Ecohygiene and Toxicology,
Kiev, Ukraine.
http://www.cipac.org/NEXT_Meeting/.../Vitaly_Chmil_GLYPHOSATE.
pdf.
Duke SO, Powles SB (2008). Glyphosate-resistant Weeds and Crops.
Pest Manage. Sci., 64: 317-318.
Franz JE, Mao MK, Sikorski JA (1997). Glyphosate: A Unique Global
Herbicide. Am. Chem. Soc., 4: 65-97.
Gioia R, Offenberg JH, Gigliotti CL, Totten LA, Du SY, Eisenreich SJ
(2005). Atmospheric Concentrations and Deposition of
Organochlorine Pesticides in the US Mid-Atlantic Region. Atmos.
Environ., 39: 2309-2322.
Gorecki T, Namiesnik J (2002). ‘Passive Sampling’. Trends Anal. Chem.,
21: 276-291.
http://alcor.concordia.ca/~raojw/crd/reference/reference002139.html.
Humphries D, Byrtus G, Anderson AM (2005). Glyphosate Residues in
Alberta’s Atmospheric Deposition, Soils, and Surface Waters. Pub No.
T/806, Alberta Environment, Edmonton.
http://environment.gov.ab.ca/info/library/6444.pdf.
ICH (1996). Q2B Validation of Analytical Procedures: Methodology,
International Conference on Harmonization of Technical
Requirements for Registration of Pharmaceuticals for Human Use.
U.S.FDA. http://www.fda.gov/Regulatoryinformation/guidance.
Kot-Wasik A, Zabiegala B, Urbanowicz M, Dominiak E, Wasik A,
Namiesnik J (2007). Advances in Passive Sampling in Environmental
Studies (review article). Anal. Chim. Acta, 602: 141-163.
http://www.elsevier.com/locate/aca.
Matthews GA (1999). Application of Pesticides to Crops, Imperial
College Press, London, United Kingdom, pp. 1-311. ISBN: 1-86094-
168-0
Matthews GA (2000). ‘Spray Droplets’ In: Pesticide Application Methods.
Third Edition, Blackwell Science Limited, Oxford, United Kingdom.
ISBN: 0-632-05473-5
OECD (1997). Environmental Health and Safety Publications Series on
Testing and assessment No.9: Guidance document for the Conduct
of Studies of Occupational Exposure to Pesticides during Agricultural
Application. OCDE/GD(97)148y. OECD, Paris.
OSHA Method Number PV2067: Glyphosate, Occupational Safety and
health Administration, U.S. Department of Labor. Carcinogen and
Pesticide Branch, OSHA Analytical Laboratory, Salt Lake City, Utah.
http://www.osha.gov/dts/sltc/methods/partial/t-pv2067-01-8911-ch/t-
pv2067-01-8911-ch.html.
Seethapathy S, Gorecki T, Li X (2007). Passive sampling in
environmental analysis – A review. J. Chromatogr. A, 1184(1-2): 234-
235. doi:10.1016/j.chroma.2007.07.070.
Seiber JN, Ferreira GA, Hermann B, Woodrow JE (1980). Analysis of
pesticidal residues in the air near agricultural treatment sites, In:
harvey Jr. J, Zweig G (eds). Pesticide analytical methodology, ACS
Symposium Series, Washington D.C., 136: 177.
Shih TS, Chen CY, Cheng RI (2000). Field evaluation of a passive
sampler for the exposure assessment of 2-methoxyethanol. Int. Arch.
Occup. Environ. Health, 73: 98-104.
Tadeo JL (2008). Analysis of Pesticides in Food and Environmental
Samples, CRC press, Boca Raton, FL, p. 257.
Thistle H (2000). The role of stability in fine pesticide droplet dispersion
in the atmosphere: A review of physical concepts. Trans. ASAE, 46:
1409-1413.
UN-ECE (1979). Removal of Fine Particulates From The Atmosphere.
In: Particulate Pollution – A report of the United Nations Economic
Commission for Europe. Pergamon Press ltd. Oxford, England, pp.
54-56. ISBN 0-08-023399-6.
USEPA (1993). EPA Reregistration Eligibility Document, Glyphosate.
EPA 738-R-93-014. Office of Prevention, Pesticides and Toxic
Substances, United States Environmental Protection Agency,
Washington, D.C.
Van Dijk HFG, Guicherit R (1999). Atmospheric dispersion of current-
use pesticides: A review of the evidence from monitoring studies.
Water, Air and Soil, 115: 21-70.
World Health Organization (WHO) (1994). Glyphosate. Environment
Health Criteria No. 159. World Health organization, Geneva,
Switzerland.http://www.inchem.org/documents/ehc/ehc159.htm.
Woodrow JE, Hebert V, LeNoir JS (2003). ‘Monitoring of agrochemical
residues in air’ In: ‘Handbook of Residue Analytical Methods for
Agrochemicals’ ed. Philip W. Lee, 1: 908-935. John Wiley & Sons Ltd.
USA. ISBN: 0-471- 49194-2.
