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Laboratory-scale Assessment of Chemical Sprays using Dynamic Olfactometry.

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Dev. Chem. Eng. Mineral Process. 12(5/6)8pp. 559-572, 2004.
Laboratory-scale Assessment of Chemical
Sprays using Dynamic Olfactometry
N. Hudson* and D. Duperouzel
Intensive Livestock System Unit (ILSU), Agency for Food and Fibre
Sciences, Queensland Department of Primary Industries (DPI),
PO Box 102, Toowoomba, Queensland 4350, Australia
Dynamic olfactometry enables odour quantitation. Presentation of odorous air to
human panellists necessitates a comprehensive risk assessment to ensure that panellist
health and safety is not compromised. Assessment of odour of samples derived from
sprayed pesticideformulations required a three-stage process:
i. Review of information for all product components to identifl health risks;
ii. Identi3cation and quantification of volatile chemicals in samples destined for
olfactometry,
iii. Determination of odour concentration by dynamic olfactometry.
The odour strength of air samples derived from commercially available pesticide
materials was assessed following spray application in a spray chamber. Measured
odour concentrations were combined with application rates and flushing rates to
derive specific odour emission rates, thus enabling comparison of odour strength on
the basis of the amount of active ingredient in each material sprayed.
*Authorfor correspondence (neale.hudson@dpi.qld.gov.au).
559
N.Hudson and D.Duperouzel
Introduction
Many agrochemicals generate strong odours when applied by ground or aerial
spraying methods. Some persons who detect odours arising from agrochemicals
erroneously conclude that they have been exposed to toxic chemicals in harmful
amounts [ 1, 10, 181, as cited in [2]. The odours associated with the agrochemical may
arise from the active ingredient itself, contaminants present in technical grade
material, and/or solvents used in formulating the material actually applied in the field.
Methods for reducing the odour produced by sprayed materials could include:
Increasing the purity of technical grade material through reduction of
contaminant concentrations,
Modifying the formulation of the sprayed material
Reducing the impact of odorous chemicals by incorporation of chemical
scavenging agents, which selectively target odorants, etc.
Evaluating the efficacy of these and other methods that could potentially reduce odour
emission rates necessitates measuring odour concentrations and quantifying odour
emission rates.
ILSU was approached by Syngenta Crop Protection Pty. Ltd. (Syngenta) to assess
the impact of formulation on the odour characteristics of profenofos formulations.
Profenofos is the active ingredient (a.i.) in a number of agrochemicals, including
Curacron 500 Pro, Curacron 250 Flexi and Kestrel. Profenofos is used extensively on
the Queensland and New South Wales cotton crop. Use of the chemical has led to
numerous odour complaints.
Dynamic olfactometry is the method of choice for odour assessment. It uses the
human olfactory sense (which actually detects the malodour in the field) to assess the
strength of the odour under controlled conditions. A comprehensive health risk
assessment is a prerequisite to any olfactometry process because the technique
involves presentation of odour samples to a panel of human subjects. In addition, the
pesticide active ingredients were Schedule 6 poisons.
The project involved developing :
A laboratory-scale chamber that would mimic conditions under which aerial
spray application takes place, along with
560
Laboratory-scale Assessment of Chemical Sprays using Dynamic Olfactometry
A sampling and analytical program that would enable collection and analysis
of gaseous materials, including olfactometry.
Materials and Methods
(0 Spray chamber and sampling apparatus
A spray chamber was constructed from a lOOOt high-density polyethylene bulk
chemical tank. The air d e t system comprised a 200 mm diameter centrifugal fan,
directly coupled to the tank via PVC waste pipe (900 mm x 150 mm). The delivery
pipe was slotted axially within the chamber to produce a diffuser. Air was exhausted
from the chamber via PVC waste pipe (1500 mm x 150 mm) into a laboratory fume
hood, where waste gases were continuously scrubbed with water prior to discharge.
The air flushing rate in the tank was maintained at 137Plsec during sprayng. The
elements of the spray chamber are shown schematically in Figure 1.
ULV applicator,
I
I
Active ingredient as
formulated spray
(11-21 mUmin)
A
I
1 m3 dynamic mixing chamber
Figure 1. Schematic showing components of spray chamber.
N. Hudson and D.Duperouzel
Mixed spray material was gravity fed to an ultra-low volume application (ULVA)
device. The liquid delivery rate was regulated using a 6 mm SwagelokTMfine
metering valve. The rotation speed of the spray head was adjusted using a custombuilt variable pulse-width power supply. All materials in contact with the spray
mixture were glass, stainless steel or Teflon to minimize odour contributions and
unwanted reaction with the spray materials.
Air samples were collected from the exhaust duct via a 6 mm stainless steel tube
connected to a four-stage Greenberg-Smith glass impinger train. All vessels in the
impinger train were empty, ensuring that only droplets were eliminated from the
sampled air. Air sampling rates were regulated using rotameters, while the total
volume of air sampled was measured using a dry gas meter.
Pesticide and chemical residues were retained on SupelcoTM OrboTM-43and
OrboTM-49Qsorbent traps, as specified in various OSHA [9, 14, 151, NIOSH [7, 81
and USEPA [ 16, 171 semi-volatile organic chemical (SVOC) residue determination
methods. Retained material was recovered with acetone (2 x 2 ma). US OSHA
Method 12 was used for benzene residue determination [13].
Air samples (approximately loll) were drawn through activated carbon filters
(SupelcoTMOrboTM-32,large and small) at between 0.5 and 1.0 Umin. Trapped
aromatic hydrocarbon material was desorbed from the charcoal sorbent material using
carbon disulphide (2 x 5 mll aliquots). Odour samples were collected using the “lung”
method according to standard DPI procedures [6].
(ii) Agrocheniicals trialed
Syngenta Crop Protection Pty Ltd provided sealed 411 containers of the following
commercial products for the spray trial:
Curacron 500 Pro (500 gl11 Q-grade profenofos),
Curacron 250 Flexi (250 glll Q-grade profenofos),
Kestrel (250 g/11 standard grade profenofos),
Predator 300 EC (300 glll chlorpyrifos),
DC-Tron, an oil used to prepare ULV sprays.
5 62
Laboratory-scale Assessment of Chemical Sprays using Dynamic O[factometry
All pesticide products were mixed in a 1:2 ratio with DC-Tron immediately prior to
spraying.
(iii) Chemical residue analysis
An HP 5890 Series 2 GC was used for all quantitative analyses. The instrument was
equipped with a splitlsplitless inlet system, 0.32 mm x 25 m SPB 5 capillary column
and flame-ionisation detector. Data were captured and integrated using an HP 3392
integrator or DeltaTM5 chromatography data system.
An HP6890 GC with quadrupole mass selective detector was used to confirm the
identity of the profenofos peak, as well as identify other materials in the air samples.
Standard operating conditions used by the Department of Natural Resources and
Mines for pesticide residue determinations were used for all samples [12]. Data were
collected in scan and selected ion mode.
(iv) Dynamic olfactometty
Odour concentrations were determined using the eight-panellist, triangular, forcedchoice dynamic olfactometer developed by ILSU. This device was constructed and
operated in compliance with the requirements of the AustraliadNew Zealand
Standard for Dynamic Olfactometry [ 111. Operation of the olfactometer has been
described previously [4,51. In brief, odour assessment was performed as follows:
Each panellist was first screened with the reference gas (n-butanol)
according to the Australian standard [ 111 to ensure their detection
thresholds for the reference gas was between 20 and 80 parts per billion.
Odorous air was diluted and presented to the olfactometer panellists in
one of three ports, while the other two ports emitted clean odour-free
air. The panellists were prompted to sniff from the ports and determine
whether they could detect a difference between the three ports. Each
panellist was allowed a maximum of 15 seconds to detect a difference.
The panellists were then asked to answer whether they were certain,
uncertain or guessing from which port the odour (if any) was emitted.
563
N . Hudson and D. Duperouzel
This process was repeated by doubling the strength of the previous
presentation until all panellists had responded with certainty and
correctly for two consecutive presentations. The panellists’ individual
threshold estimate (ZITE) were then determined by calculating the
geometric mean of the dilution at which the panellists did not respond
with certainty and correctly and the first of the two dilutions where the
panellists responded with certainty and correctly. This dilution series is
defined as a round. Three rounds were undertaken for each sample
where sufficient sample was available [4].
Odour concentrations were expressed in terms of Odour Units (OU) as a nondimensional ratio. Some practitioners use a form analogous to conventional
concentration, namely OU/m3. Either form is recognised [lo].
The odour concentration values were combined with the chamber volumetric
flushing rate measurements to provide an odour flux. The odour flux values were
normalised to provide an estimate of the odour formation potential of each product,
correcting for variations in active ingredient application rate. The calculations were
of the form:
Odour flux (OU I s ) = Odour conc. (OU / m’)x Flushing rate (m’ I s )
(1)
SOER (OU I pg) = 0dourflu.x(ou I S) x
Application rate ( p g active ingredient I s )
(v)
Health-risk assessment
A comprehensive health risk assessment was undertaken as a separate component of
the project.
The assessment was based on information supplied by the product
manufacturer, including information contained in product Material Safety Data
Sheets. A number of chemicals with a potential for adverse health impacts were
identified [3].
564
Laboratory-scale Assessment of Chemical Sprays using Dynamic Olfactometry
Results and Discussion
(i)
Chemical residue analyses
Components of the spray materials are shown in typical chromatograms such as in
Figures 2 , 3 and 4.
-
t
Figure 2. Chromatogram of Curacron 500 Pro material (96 mg/9.
n
‘g
I
Figure 3. Chromatogram of DC-tron oil (440 mg/d.
S6S
N. Hudson and D. Duperouzel
Figure 4. Typical chromatogram of material recovered from sorbent trap.
Preliminary analysis of sprayed material indicated that significant amounts of
solvents were trapped from the spray material (as shown in Figure 4), while
profenofos appeared to be absent. Trials indicated that profenofos would be recovered
from the trap if present (mean recovery of profenofos from the sorbent materials used
was 77%, number of tests
=
6 ) . It was concluded that the profenofos was retained
almost quantitatively in the high boiling oil used in mixing the spray material, with
very little profenofos present in the vapour phase under the experimental conditions
that prevailed.
The materials retained on the trap were investigated using mass spectrometry to
identify individual components.
Most of the peaks present were aromatic and
aliphatic hydrocarbons. The majority of these were substituted benzene and
naphthalene compounds.
Benzene (B) was specifically identified in this mixture.
It was the only
component for which an exposure limit could be identified [13].
Three other
components were also selected for specific concentration measurement - naphthalene
(N), 2-methylnaphthalene (MN) and 1,3,5-trimethylbenzene (TMB).
While an
exposure limit could not be identified for these compounds, they were identified as
the most abundant constituents of the materials retained on the traps. Results of
recovery tests are shown in Table 1. While the recovery tests indicate that the
recovery of benzene is lower than optimal, it still complies with the US OSHA
method [ 131.
566
Laboratory-scale Assessment of Chemical Sprays using Dynamic Olfactometry
Table 1. Summary statistics for recovery tests.
Test compound
Test statistic
B
TMB
N
3MN
Mean recovery @)
79.8
98.7
45.2
41.9
Standard Deviation
7.6
9.7
4.3
5.0
Number of replicates
4
4
4
4
(ii) Benzene exposure assessment
Time-weighted average (TWA) exposures are calculated in terms of the average fullshift exposure level for an employee. This is done by the US OSHA method in terms
of an 8-hour day, weighting the various concentrations to which the employee is
exposed.
TWA =
where C
=
C,T,+C,T, +C,T-,.....C,T,
8hr
(3)
concentration of contaminant during an incremental exposure time; and
T = duration of incremental exposure time (expressed in terms of hours).
Currently, the US OHA TWA standard or recommended maximum concentration
level for exposure to benzene in the workplace is 1.O ppm [ 131.
For the current trial, an incremental exposure time of 30 minutes was chosen for
each sample. Thls was a conservative value as olfactometric assessment of a typical
odour sample takes about 30 minutes, during which time the panellist is actually
exposed to the sample for 6-8 discrete periods of 15 seconds duration. This creates a
cumulative exposure period of about 2 minutes per sample during which time actual
inhalation takes place.
The 30-minute exposure period chosen for the TWA estimate therefore provides a
safety factor of at least 15 when assessing exposure risk.
Measured benzene concentrations ranged from 0.02-0.14 ppm for all olfactometry
samples (undiluted samples). During olfactometry, samples were diluted by a factor
S67
N. Hudson and D. Duperouzel
of 8 to 1024, with most samples diluted at least 256 times. Inclusion of dilutions due
to olfactometry increases the safety factor to 320. This means that panellists were
exposed to concentrations of benzene at least 320 times lower than the level permitted
by the US OSHA. These samples posed no danger to the panellists on the basis of
identified components of the pesticide spray mixture.
(ii0 Olfactometry results
The odour concentration of each product was analysed in duplicate. Two different
batches of one of the products were analysed, providing a total of ten results.
Combining the odour concentration values with the active ingredient application
rate data for each pesticide enabled the “odour forming potential” of each pesticide to
be compared on the basis of a Specific Odour Emission Rate (SOER).
The SOER was calculated for each product by combiniiig the measured
application rate values for each product with the odour emission rate value for each
product, as shown in Equations (1) and (2). These data are summarized in Figure 5
and Table 2.
m
i
5 0.8
0.6
0.4
O 0.2
%
g o
i
v)
Product & Replicate Number
Figure 5. Comparison of specific odour emission rates.
568
Laboratory-scale Assessment of Chemical Sprays using Dynamic Olfactometry
Table 2. Relationship between active ingredient concentration, odour concentrations
and specific odour emission rates.
Product
ai conc.
Sample
(rcs/m3)
660
Rep. 1
Kestrel
~-
Curacron 500
-_
SOER
(OU/pg a.i)
Odour conc.
(0wm3)
3,444
0.52
--
-.
Rep. 2
660
6,086
0.92
Rep. 1
5 65
1,248
0.22
~
Rep. 2
Pro I
207
Rep. 1
Predator
-
Curacron 250
_
_
~
~
_ _
2,376
1.14
-
-~
Rep. 2
207
1,367
Rep. 1
69 1
1,448
--
0.65
0.2 1
_
_
.
Flexr
Rep. 2
69 1
1,188
0.17
Curacron 500
Rep. 1
565
1,680
0.29
Pro 2
Rep. 2
565
2,048
0.36
_
(iii) Statistical comparison of SOER values
The SOER data presented in Table 2 was subjected to a series of statistical tests,
differing in treatment of the additional set of replicates for one of the samples. The
results of an ANOVA test are summarized in Table 3 .
Table 3. Statistical comparison of SOER values.
Treatment
Mean SOER value for
commercial product
Difference (at 12%
confidence leveI) *
-
(0U/pg a.i.)
_-
Curacron'250 Flexi -
-- 0.190
A
Curacron 500 Pro A
0.245
A
Curacron 500 Pro B
0.325
A
Kestrel
0.720
-
LSD Value
*
B
B
0.895
Predator
~-
-
-
~~_
0.448
- _ ..
Treatments-with the-same letter are not significantly diferent.
569
~
N.Hudson und D. Duperouzel
The ANOVA test indicates that the Curacron 250 Flexi and Curacron 500 Pro
sample SOER’s were not significantly different. The SOER’s of these products were
however different to both the Kestrel and Predator products, which were not
statistically different to each other.
Examination of the odour concentration data alone (see Table 2) does not provide
any useful information in terms of the odour formation potential of the various
products trialed. When the active ingredient application rate is included as well
however, it becomes possible to compare the odour concentration data.
The SOER information generated is representative of the material immediately
after spraying. The elevated odour concentrations are almost certainly due to the high
concentrations of solvents present. It has been shown in this work and the literature
confirms [2] that most solvent constituents are considerably more volatile than
agrochemical active ingredients.
As such, these results do not provide specific
insights regarding the contribution of the active ingredient or breakdown products of
active ingredient to the measured odour. This is relevant when considering the
emission of odour following field application of agrochemicals containing active
ingredients such as profenofos. Anecdotal evidence suggests that odour continues to
be emitted from crops following profenofos application for periods of days to weeks.
It is likely that solvents associated with the original spray mix would have evaporated
in the first few hours of application. This would indicate that the residual odour
detected is probably due to other source materials, including breakdown of the
pesticide active ingredient.
Impurities originally present in the technical grade
materials potentially take on increased importance when addressing the odour
problem. The contribution of these trace impurities to the total odour emitted by the
material sprayed may be masked initially, but become more significant once more
volatile odorants have evaporated. The impact of hydrolysis and/or photochemical
degradation on components of the original spray mix should also be considered.
Investigation of delayed effects such as these were specifically excluded from this
study, but are probably very significant in the context of total odour emission from
agrochemical sprays.
570
Laboratory-scale Assessment of Chemical Sprays using Dynamic Olfactometry
While the current methodology has focused on measuring odour emission rates for
agrochemicals immediately after spraying, the methodology could be modified to
estimate post-spraying odour emission rates as well. This objective would necessitate
performing the spray operation as described in this study. The spray chamber would
be drained to ensure that residual liquid was removed. The fan would be left running
to continue ventilation of the spray chamber but at a lower flushing rate. Conditions
in the spray chamber would be managed to achieve temperature and humidity
conditions similar to those observed under field conditions. Artificial lighting could
be included to simulate the effect of solar radiation. Air samples could be collected at
intervals to track the formation and emission of various breakdown products, while
odour samples could be collected periodically to determine trends in odour formation
and emission rate. This procedure would allow for convenient assessment of factors
creating odour problems associated with the application of agrochemicals.
Conclusions
The odour forming potential of agrochemicals can be assessed at laboratory scale by
using a customized spray chamber to generate odour samples. Specialized sampling
procedures are required to avoid contamination of air samples with oil droplets.
Dynamic olfactometry can be used to quantify odour strength and thereby determine
odour emission rates for various agrochemicals. The requirements of a human health
risk assessment process must be carefully considered, and as a minimum requirement
the composition of gaseous materials comprising the odour samples should be
determined.
The process could potentially be used to assess any agrochemical. It was used in
this study to compare the immediate specific odour emission rates of four commercial
products. With limited modification, the process could also be adapted to investigate
longer-term odour emission issues. Combined chemical and olfactometric assessment
could become an important tool in the future management of odour issues associated
with agricultural and industrial processes
N. Hudson and D. Duperouzel
References
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Baker, P., and
Selvey. D. 1992. Malathion-induced epidemic hysteria in an elementary school.
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5 72
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