Regulatory toxicology of alternative fumigants

Proceedings of the 7th International
Working Conference on Stored-product Protection - Volume 1
Regulatory toxicology of alternative fumigants
J. M. Desmarchehe?
V. S. Hantos'', Y. L. Ren and
Abstract
extensive
Carbonyl sulfide (COS), ethyl formate (HCCh~Hs,
carbon disulfide (C~)
the protection
At present
Glossary of terms
fumigants for
are potential alternative
of stored grams.
EF) and
use of C~ m the future.
EF
Amencan
ACGIH:
used as a
1S
and m a region of Australia.
are relevant
Two toxicological issues that
to the registration
safety to workers potentially
of these fumigants
of potential
health effects
exposed workers but there
literature
and
DRG:
Deutsche
EF:
IDLH:
Ethyl formate
Immediately Dangerous to Life or Health level
durmg
viscose
exposed to C~
effects,
exposures
an extensive
of workers
chronically
have shown neurotoxicological
and ocular
manufacture.
and increased mortality from cardiovascular
However,
to C~
Workers
rayon
LC50:
Lethal concentration
MAK:
Maximum
many of the studies lack accurate
level data and this has complicated
disease
study,
funugation
Values
in
the
Maximum Residue Level
NIOSH:
National Institute
for Occupational
Safety and
Health (USA)
National
NOHSC:
trials were conducted
with COS, EF or C~ on wheat to determme
for 50% of test animals
Concentration
MRL:
of safe
occupational exposure levels
In the present
(Federal
Workplace
C~ exposure
the settmg
Forschungsgemeinschaft
Republic of Germany)
of COS and EF m
by companson,
1S,
on the occupational
Governmental
Carbonyl sulfide
Carbon disulfide
the presence of residues m the commodity. There have been
few studies
of
C~:
COS:
are the
exposed to the fumigants,
Conference
Industrial Hygienists
fumigant of dried fruit, and C~ as a gram fumigant in Chma
Occupational
Heath
and
Safety
Commission (Australia)
the fate of
OSHSA:
Occupational Safety and Health Administration
PEL:
ppm:
Permissible
s110had been aerated for less than 2 h. The level of COS in
REL:
fumigated
STEL:
Recommended Exposure Limit
Short- Term Exposure Limit
TLV:
Threshold Limit Value
TWA:
Time Weighted Average
Wheat was treated With COS (24 g/t) ,
fumigant residues.
EF (90 g/t) or C~ (42 g/t)
farm silos.
On outloadmg
in sealed,
COS-treated
levels that were higher than untreated
wheat
fell
rapidly
wheat had residue
wheat,
durmg
The concentrations
however the
transport
conditionmg to reach levels indistinguishable
wheat
and
from untreated
of EF in wheat had decayed to
natural levels after a withholding period of 4 weeks.
present in untreated
(USA)
50 tonne-capacity
wheat at concentrations
and EF between O. 1 - 3 mg/kg,
Exposure Level
parts- per-million
COS is
of 0.05 mg/kg
and both substances
occur
naturally at higher levels in other foods. Wheat treated With
< 10
C~ had residues
wheat,
after 24 h aeration
Introduction
of the
higher than the natural level of C~ ( <
substantially
0.005-0.02
mg/kg
mg/kg)
m untreated
wheat.
The presence
New and safer fumigants
of
ever-present
COS and EF residues at background levels after fumigation of
wheat
favours
persistence
Ahmenuiriu«
occupational
their
of C~
registration
residues
maximum
health
as
and
residue
and safety
fumigants.
absence
limit,
of a
m
considerations,
are being sought because of the
of resistance developing
The
environment. Isolated cases of resistance to phosphine have
developed,
to
for example,
and methyl bromide is being phased
out because of its depletion
may hmit
of stratospheric
fumigants carbonyl sulfide (COS),
carbon disulfide (C~)
1
RMIT-Umverslty,
TOXicology Key
Centre,
GPO
Box
CSIRO Entomology,
GPO
Box 1700,
ozone.
ethyl formate
(EF)
The
and
have been proposed as alternatives
to
methyl bromide and phosphine for the fumigation of grain.
2476v,
COS has not been used previously as a gram fumigant and
Melbourne Victona 3001, Australia
2
to existing
fumigants and adverse effects of others on health and the
Codex
addition
prospect
Canberra,
ACf
has had limited
2601,
Austraha
solvent,
356
industrial
use
a flavouring m foodstuffs,
EF is widely
used as a
fragrance ingredient
and
Proceedings of the 7th Internatwnal
as a fumigant of dried fruits and tobacco.
C~ are m the manufacture
ingredient
Working Conference on Stored-product Protection - Volume 1
The main uses of
of VIScose rayon
Governmental
and as an
many
organisations
in the synthesis of, and as a solvent for numerous
pharmaceutical,
agricultural,
Registration of the alternative
chemicals
will be required
widespread
fumigants
prior
alternative
in
as agricultural
to their
use m the case of ~.
for workers
is mterestmg
chenucals are present naturally m wheat,
concentrations
(Desmarchelier
quantities
mglkg
in wheat.
fumigants IS given in Table 1. Most occupational
are based on an 8 h per d, 5 d per wk
which IS known as the time weighted
duration
Table 1.
Occupational
to the
alternative
Regulatory Agency
100
10[skin]a
is present
n.a
100
lO[skin]
TLV (ACGIH)
n.a.
100
lO[skin]
PEL (OSHA)
n..a.
100
4b[skin]
REL (NIOSH)
n.a.
100
Il skm]
STEL (NIOSH)
n.a.
n.a.
10
IDHL (NIOSH)
n.a
1,500
500
Germany
MAK (DGF)
in trace
U.S.A.
fumigants.
and pressure
whereas EF
and are
n.a
a
Flammability
not assigned
[skm]
notation
substantIal
gram funugation
however,
lower and upper flammable
substances
b
given the
their flammability
risk.
signifres
non-enforceable
route may lead to
Transitional
hrmt due to a US court decision.
TLV values are on a TWA
The
that this exposure
absorptIon
PEL of 20 ppm currently
some methods of their use in
may reduce
for
n.a.
Australia
TLV (NOHSC)
COS at
and C~ are liquids that have high vapour pressures
therefore readily volatilised.
optimal conditions,
ppm)
C~
albeit at different
of the alternative
are flammable
(in
EF
Occupational health and safety
of alternative fumigants
COS, EF and C~
standards
COS
ThIS paper discusses these Issues in the
COS IS a gas at room temperature
exposure
fumigants in different countries.
as all three
up to 3 mglkg,
while C~
context of possible registration
many
exposure
and Ren, unpublished data).
EF may be present in concentrations
levels up to 0.05
are
in different
average (TWA).
use or more
who may be exposed
The matter of fumigant residues
there
which produce exposure standards
exposure standards
and the presence of residues in fumigated wheat.
fumigants,
(ACGIH) and adopted by
However,
Two issues that are
critical to this process are the occupational health and safety
considerations
countries.
countries and a list of the vanous exposure standards for the
mining and rubber chemicals.
Currently there is some use of C~ as a grain fumigant
China and one region of Australia.
Industrial Hygienists
other
apphes
baSIS
See Glossary for explanatIon of acronyms
(explosive) hrruts (LFLIUFL)
Source of values ACGIH (1993)
for COS in air are 12 and 28.5 % (v /v ) (Sax and LeWIS,
1986) and are well above the concentration
control of insects.
Pure EF has LFLIUFL
required
for
An exposure standard has not been assigned for COS. ThIS
of 2.8 and 16%
may be due to the lirruted use of COS in industry or the lack
but the proposed formulation of EF for gram fumigation is a
of sufficient information on which to base a standard.
4% aqueous
of 10 ppm has been recommended
solution
substantially
reduces
of EF.
The dilute
the flammability
solution
risk.
of EF
C~ has LFLI
sheet for COS which
is also the exposure
UFL of 1.3 and 50% and as it apphed as a neat liquid for
grain fumigation it poses a flammability risk.
hydrogen sulfide (EOC, 1996).
Exposure standards
formation of hydrogen
is converted
to hydrogen
A TL V
in the material safety data
standard
for
It has been shown that COS
in rats,
sulfide
and It is the
sulfide that IS considered
to be the
tOXICaction of COS (Chengelis and Neal, 1980).
The health of workers exposed to chemicals durmg work
hours may be protected
air concentrations.
of a substance
by regulatory
standards
The occupational
Table I, and higher than methyl bromide and phosphine that
discomfort to most workers
effects of the substance.
which
are
(NOHSC,
breathmg
1995).
based on new information
widely recognised
for EF (TL V 100
The exposure standard is a concentration
m the air withm a worker's
as parts-per-million
standards
ppm) are much higher than those of the other fumigants in
zone,
have TLVs of 5 and 0.3 ppm, respectively
exposure to which should not cause adverse health effects or
may be altered
exposure
governing
The standard
about the health
Exposure standards
produced
by
the
limit values (TLV®
Amencan
Conference
standards
SImilar m different
are expressed
for
C~
countries
vary
(10
ppm),
bodies in the US, the National Institute
(ppm) on a volume baSIS, and the most
are the threshold
(ACGIH, 1993).
depending on the
regulatory body that has set them. While the TLV level IS
Exposure
Safety and Health
(NIOSH)
Health Admmistration
)
standard
of
357
for C~
and Occupational
(OSHA),
following
two regulatory
for Occupational
Safety and
have reduced the exposure
review
of the epidemiological
Proceedings of the 7th International
literature
of CSz-related effects in workers.
the Permissible
Exposure
Level (PEL)
Worktng Conference on Stored-product Protectwn - Volume 1
OSHA reduced
personahty
to 4 ppm (12 mg/
including excitability,
disturbances
confusion,
anger,
insomnia,
pSYChOSISand suicide
m") with a STEL of 12 ppm (36 mg/ m") but this level IS
These
symptoms
are expenenced
currently
above those of the present occupational exposure standards.
unenforceable
Issue is decided,
pending a court decision.
the transitional
Until that
Chronic exposure
PEL defaults to the original
value of 20 ppm, 30 ppm ceihng and a 100 ppm (30 rrun)
industry,
(Wood,
during
to CSz in workers
1981).
exposures
well
in the VISCose rayon
as detailed below, has led to effects on the eye and
maximum peak. NIOSH reduced the Recommended Exposure
to the
Limit (REL) to 1 ppm by attaching a lO-fold safety factor to
cardiovascular and reproductive effects. Other effects of CSz
the lowest concentration
thought to increase risk of coronary
exposure observed m exposed workers include hearing loss,
heart disease
1977).
(NIOSH,
The PEls
estabhshed
OSHA are the only exposure standards enforceable
the U. S.
by
irregulanties
by law in
miscarriages
some
Continuous
exposure
membranes
to
COS gas
will generally
cause
in addition to headache,
Exposure to concentrations
may lead to respiratory
(EOC, 1996).
at
15 -
Irritation
50
There have been few documented
1968).
a bunker
toxic
cases
of a worker
and
Neal,
1979;
Fmmsh
system,
muscle
sulfide m
of neuropathy
coordination may be observed.
eye protection
(Roe
and Salaman,
Adverse
effects
of
of the exposure
very high concentrations
poisonmg,
Acute exposure
penods
may
1983).
(WHO,
1979).
to
findings
monitoring
rapid coma formation
of time may result
in permanent
include
CSz
at
or tingling,
m the
up to 10 years
symptoms
headache,
loss
risk of coronary
of
of
sleep
libido
and
- 30 ppm).
to coronary
Although
were the main nsk factors
current
TLV.
disease
decreased
had
when
inadequate
was
et al. ,
CSz concentration
to ascertam
m coronary
exposure
to below 10 ppm.
heart
workers
the
disease
heart
measures
A recent
have found little
risk compared
with
(Drexler et al. , 1996).
of the effect
of CSz exposure
have shown significant
levels of endocrine
from coronary
occupational
endpoints such as decreased
358
exposure
studies on which these
The rate of mortahty
Some studies
reproduction
on the
CSz
heart disease,
has made it difficult
unexposed workers
central nervous system which are manifested by mood and
close to
age and
risk of coronary heart disease at levels near the
difference
short
advanced
to the overall risk (Beauchamp
based
which
disease has been
heart
exposed to CSz concentrations
study of low level CSz-exposed
and death.
effects
et al.,
m definite
The reported
fatigue,
lowered the air concentration
into
leads to
to 500 - 1000 ppm CSz for relatively
(10
were
increased
Inhalation of
of CSz ( > 3000 ppm)
were present
Many of the epidemiological
m
Rady et aI.,
categorised
different
to
resulted
such as numbness
damage
general
shown to contribute
1976; ZImmerman et
be
to
in workers exposed to CSz at levels generally
predisposing
acute, subacute and chronic by the duration and
concentration
hyperacute
CSz
1955;
from
Vanhoorne
20 years)
elevated diastolic blood pressure
skin and
EF was not carcinogenic
1981), nor was it mutagenic (NTIS,
al. , 1976).
hyperacute,
however,
system
m workers
the TLV
The proposed
should be worn as it IS good practice
minimise exposure to chemicals.
animal studies
1978),
1983,
to CSz ceased
nervous
reported
is unlikely to cause significant skin
irri tation or sensitisa tion (Anon,
exposed
or pam and loss of sensation
An increased
and loss of
formulation of grain fumigant EF IS an aqueous solution (4%
w /w) and this mixture
and
higher than the TLV (Beauchamp et ai, 1983).
The LC50 of EF in rats was
8000 ppm after a 4 h exposure (Anon, 1978).
been
the studies showed
in workers
The symptoms
disturbances,
depression of the central
fatigue,
workers
up to 70 ppm have
Parkinsonism
headache,
rayon
of effects
weakness
central
1968).
nausea,
possible
not
Additional studies of
However,
ca .
indications
1980).
EF is an Irritant to nose, throat and lungs at levels >300
nervous
damage
exposures
Chronic
1981) and the approximate
ppm. At higher concentrations,
and Dutch
et al.,
concentrations
in humans is 600 ppm for a 30 nun
lethal concentration
the
has
in eye structure
1983).
(Beauchamp
after exposure
exposure (Lefaux,
and
gases
m changes
et al.,
countries
concentrations.
et aI.,
workers,
spectra
extremities,
rats is 444 ppm (Tansy
m
different
Hydrogen sulfide is highly toxic and may be fatal at high
The 60 mm LC50 for hydrogen
in
1996) .
m rats to carbon dIOXIde and
CChengelis
agent
increase
and
lower levels of CSz for at least one year, showed early signs
hydrogen sulphide with the latter compound proposed to be
the
and to
exposure to CSz in relatively high doses (32 to
of ophthalmological
to COS (Thiess et al. ,
was attributed
COS IS metabohsed
systems,
cycle
With other
has resulted
Japanese,
to 50% of
and Lewis,
entering
effects
function (Beauchamp
in 35 mm was 1200 ppm (Sax
to COS but the death
menstrual
exposure
Long-term
coma and unconsciousness
(LC50)
of human exposures
the
these
128 ppm),
dizziness and nausea.
the test population
1986).
ppm
to mucous
In mice, the lethal concentration
of
nervous
addressed (WHO, 1979; Beauchamp et al. , 1983).
of COS between 200 - 300 ppm
arrest,
of
and penpheral
although there have been conflicting reports of
concomitant
Adverse health effects of a1temativefumigants
concentrations
central
hormones
on male
effects on reproductive
spermatogenesis,
and reduced
lower serum
libido, whereas
Proceedings of the 7th International
Working Conference on Stored-product Protection - Volume 1
other studies found no differences in semen quality compared
with unexposed controls (Schrag and DIxon, 1985). In a
recent study, libido and potency were significantly reduced
in workers occupationally exposed to CSzat levels above the
TLV, m companson with age-matched unexposed controls,
but the quality of the semen and the number of children of
the workers were not significantly different between the two
groups (Vanhoorne et at. , 1994).
It is not known how similar the exposure scenarios for
workers in rayon manufacture are to potential exposures of
workers during grain fumigation or how a different exposure
pattern may affect the risk of adverse effects with Its use.
There is a high risk of permanent damage to the nervous
system in gram fumigators using CSz without adequate skin
protection or suitable respirators. That is, unprotected
grain fumigators may be exposed to higher concentrations of
CSz than workers in rayon manufacture as they are more
likely to be handling liquid CSz concentrate. Most exposure
standards for CSz include a [skin] notation which signals
that dermal exposure can have an Important contribution to
overall exposure. Skin absorption of CSz can also result m
irritation or blistering and splashes m the eye can cause
immediate severe Irritation.
unpublished data) . Therefore the development of a
biomonitoring method for occupational COS exposure will
have to address background exposure from natural sources.
Alternative Fumigants Trialmonitoring Exposure,
Residues and Efficacy
Field-scale experiments of COS, EF and CSz fumigation of
wheat were conducted by CSIRODIvision of Entomology 0.
Desmarchelier, Chief Investigator) for the purpose of
obtaining efficacy and residue data that would support future
registration of the fumigants and monitonng worker
exposure.
Chemicals
COS was obtained from BOC, Australia, EF was a gift of
ICI Australasia and CSzwas purchased from Ajax Chemicals,
Australia. The purity of COS was determined to be 95%
prior to purification by passage of the gas through copper
sulfate solution to remove hydrogen sulfide contamination.
Fumigation protocols
Biomonitoring of occupational fumigant exposure
It IS possible to measure the absorbed dose of CSz in an
exposed worker, in addition to ambient air concentrations by
measuring the presence of CSzmetabolites m the urine. The
metabolite 2-thiothiawlidine-4-carboxylic acid (TTCA)
accounts for approximately 3% of the absorbed human dose
of CSz, and is used to monitor occupational exposures to CSz
(Van Doorn et at., 1981). In many studies, the level of
TTCA in unne has been correlated to the magnitude of
exposure to CSzby ambient monitoring during the workshift
(e. g. Meulin et at. , 1990, Drexler et at. , 1994).
The concept of biomonitoring for EF exposure has not
been reported. In the case of EF, biomonitoring may not be
feasible as EF is rapidly hydrolysed once it enters the body
to form ethanol and formate. Ethanol monitoring would be
subject to interference from other exposure sources and the
measurement of formate as a product of EF m blood or urme
of exposed workers IS complicated by the presence of
endogenously produced formate. The mean concentration of
formate in human serum is 13 mg/L in serum, and formate
is excreted at the rate of 0.5 mg/h in unne (d'Alessandro et
at. , 1994).
The implementation of biological monitoring of COS
exposure will require an understanding of the metabolic fate
of the fumigant in man, and the identification and ready
detection of a suitable product in saliva or urine. COS is a
naturally occurring substance both in the atmosphere and in
some foods, particularly vegetables of the Brassica genus
( broccoli, cabbage etc)
(DesmarchelIer and Ren,
359
Welded-steel cylindrical farm silos of 50 tonne capacity,
fitted with aeration ducts were sealed With silicone and
tested for air-tightness. Australian Standard White wheat
(36 t) of unspecified moisture content was loaded into the
silo and purified COS (400 L) was added to the headspace
above the wheat. The final application rate of COSwas 24.4
g/t wheat and the fumigation proceeded for 7 d. The silo
was aerated for up to 2 h until the mtra-silo concentration
reached the TLV (10 ppm) and then the wheat was
outloaded.
In a separate experiment, aqueous EF, 4% (w/w), was
dripped onto wheat (40 t) as it was loaded into the silo. The
final concentration of EF in wheat was 90 g/t and the
fumigated wheat was withheld for 4 wk prior to outloading.
In a further trial, CSzwas added as a neat liquid (1.2 L)
via an external funnel and tube to hessian sacking placed on
the surface of the wheat (36 t) in a sealed silo. The total
rate of CSz application was 41.6 g/t. The fumigation
proceeded for 6 d, the silo was aerated for 24 h until the
intra-silo concentration reached the TLV (10 ppm) and then
the wheat was outloaded Intra-silo concentrations of COS
and CSz were measured by sampling of gas via nylon lines
that were inserted mto the silo at multiple positions in the
wheat mass and analysis of the gas by gas chromatography.
The appropriate respirator and skin protection were used
during the handling of fumigant concentrates and mixtures.
Monitoring exposure tofumigants
Multiple measurements were taken of COS, EF and CSz
Proceedmqe of the 7th International
concentrations
Working Conference on Stored-product Protection - Volume 1
in the air around the silos under fumigation.
when sealed storage is used.
A radius of 3 m around each farm silo and a height of 1.5 to
1.9 m from the ground was determined
for potential exposure of workers to fumigants.
of air in the workspace
20 measurements
drawing
air into Tedlar'"
measured
concentrated
Around 10 -
(GC).
EF and C~
The analytical
(0.01 % of the respective
fumigant
concentrations
originating
dnp,
a
wheat held in 'dirty'
bags, at the bottom of the 'dirty'
the bin containing
conditioned
and skm protection.
bins into Tedlar"
(see
Analysis of Wheat and Milled Products
the sampling stages).
workers in the mill.
These
Sampling
for a descnption
SIteS were
of ~
bins containing
( 1) of outloaded wheat from the silo as it was loaded into
bags
route into the
these
were
commercial
grade
approximate
e. g. methanol
method
were
(Daft
1988)
Band
are given in Figure
mid-stream
samples
and Ren, unpublished
using
dechned
after
levels
than
2 h before
aeration
to natural
levels
COS-fumigated
the official analytical
were similar for untreated
into
analysis (Sharp et
COS,
EF
and
concentrations
during
This demonstrates
~
remain
can
an
be
carried
out
it is
wheat
at
and in the nulled
the concentrations
and EF-fumigated
of EF
wheat that had
age and storage
and Ren, unpublished data).
the
hmit (MRL)
of 10 mg/kg,
data ).
air
360
level of C~
wheat
The
transportation,
standards
of the wheat.
were below the Australian
untreated
the fumigation
and
in fumigated
C~ residues
than the natural
that fumigation With
well Within the exposure
and
Wheat fumigated with C~ had residues of 6.4 mg/kg on
0.01 % of the respective
TLV for COS, EF or ~
outloading
depending on the wheat variety,
conditions (Desmarchelier
area defined by a radius of 3 m from the silo at a height of
phase of the trials.
during
B). The natural level of EF in wheat ranges between 0.1 3 mg/kg
of fumigants in the workspace,
did not exceed
wheat
been withheld for 4 wk, during all sampling stages (Figure 1
Workspace exposure monitoring
current
The levels of
wheat had the same level of COS
outloading after 24 h aeration
m,
C,
time will result in COS
At the stage of conditioning
as the untreated wheat.
In wheat fumigated with EF,
Results and Discussion
1.5 - 1.9
data).
in the fumigated
that extendmg
falling
fractions,
sampling
and EF was extracted
for less
outloading.
for EF determmation,
methanol using a method for multi-residue
al. , 1988).
The air concentrations
1 (A,
.
anticipated
(10 g) were taken.
or milled fractions
analysed
1984,
milled fractions,
aerated
thereby initiating the analytical process as soon as possible.
COS and ~
to the
transport and processing (Figure lA). Fumigated wheat was
(60 g) or milled fractions
solvents
from the silos, after transport
and in the
of COS rapidly
of grain) at the mill
were added to wheat
and untreated
higher than the natural levels in wheat but the concentration
(18 h moistening
flour, pollard finished flour, pollard, germ and bran.
Extraction
in fumigated
COS in COS-fumigated wheat on outloading was substantially
container
At all sampling stages,
TL V of 10 ppm.
at the surface of the conditioned
flour mill and within the mill, after conditioning
(Desmarchelier
(4) of wheat after it was conditioned
of wheat
of ~
COS is naturally present in wheat at levels of 0.05 mg/kg
container
(5) of milled fractions,
the air
wheat but the value (0.62
below the current
of fumigant
respectively)
(3) at the flour mill, during transfer of the cleaned wheat
treatment
of the wheat,
The levels of COS, EF and C~ in untreated and fumigated
Sampling of wheat for fumigant analysis was carried out:
to the 'clean'
Also, during the application
C~-fumigated
wheat on outloading
from the receival
the
wheat
Sampling and analysis of wheat and milledprodncts
forfumigant levels
holding 'dirty'
to be
to
wheat was 0.15 ppm.
to
Levels
(2) at the flour null,
exposure
were highest at the bottom of 'dirty'
The air concentration
of
accessible
was
equipment is not used.
ppm) was substantially
and
air
ppm)
significant exposure above the TL V is
At the flour mill during processing
bins and at the surface of
wheat
the
the
was minimal as he was wearing an appropnate
concentrations
of ~-fumigated
during
workspace
of 4% EF solution
however,
likely where protective
Air samples were drawn from the surface
fumigated wheat.
of the container
as
the
the TL V (100
during refilhng
of C~ to the grain,
from C~-
circumstance
where
applied
respirator
At the flour mill, some sampling of air was carried out to
determine
trial
of EF exceeded
experimenter
TLVs).
One
fumigant
concentration
methods used were capable of detecting as low as 10 ppb EF
and 1 ppb for COS and ~
fumigants.
alternative
were sampled by
bags and COS,
by gas chromatography
Elevated exposure to fumigants may occur when handling
to be the workspace
highest
residues
(Figure
1 C).
residue
they were substantially
higher
«
(Desmarcheher
C~
residues
conditioning
of milled
Although the
maximum
0.005 - 0.02
and
Ren,
persisted
and milling
fractions
mg/kg)
in
unpublished
throughout
the
stages
the
found
with
in the
germ
Proceedings of the 7th International
Working Conference on Stored-product Protection - Volume 1
A
0.25
0.2
Carbonyl
0.15
sulfide
(mg/kg)
0.1
0.05
o
i'o..
h~""
&c¥ ~ft;
o~ 'f)~
tt- ~
e
~
.....
<:>
.II' ;..O~.#' ~ ~~ ~
J:~~
cf -~~ ~~ ~~
~ orq<$>~
!b~
C>
Fumigated
Untreated
~J>/
~~'b
Sampling stage <fS
B
0.75
Ethyl
formate
(mglkg)
0.5
0.25
Fumigated
Untreated
c
Fumigated
Untreated
Fig.l.
Levels of furrugant (and mterfenng substances) m wheat furrugated With (A)
natural levels m untreated wheat
361
ms (B)
EF or (C) ~
compared With
Proceedings of the 7th International
Working Conference on Stored-product Protection - Volume 1
Efficacy of fumigations
Conclusion
The applied levels of fumigant were efficacious in killing
Triboltum castaneum (adults and larvae), Rhyzopertha
dominica (mixed age cultures), Sitophilus oryzae (nuxed
age cultures) that were placed in traps in the silos prior to
COS and CSz fumigation, or after loading of EF~treated
wheat All insect stages were killed by the fumigation
regimes except in the EF fumigation where two adult S.
oryzae (0.26% of total S. oryzae) survived fumigation.
After incubation of the surviving adults for a further 28 d at
30'C, 31 progeny were produced.
Where sufficient aeration or withholding periods are used,
fumigation of wheat with COS and EF can result in levels of
these fumigants present that are indistinguishable from the
natural levels. The optimal aeration times and withholding
periods for other grains fumigated with the alternative
fumigants are currently being investigated. The moisture
content of grain may also affect the persistence of EF
residues. In this field trial, a 4 wk withholding period was
proposed for EF-fumigated wheat based on the slower decay
of EF in cool, dry grain. The natural levels of COS and EF
in commodities will need to be carefully identified to ensure
the levels are not exceeded after fumigation and appropriate
withholding periods. The registration process may be
simplified for fumigants whose residue levels in the
fumigated commodity is indistinguishable from the natural
level as there is less requirement for long term feeding
studies to assess the toxicity of persistent residues.
The benefits and disadvantages of potential alternatives to
methyl bromide and phosphine for grain fumigation have
been discussed by various researchers (e. g. Bond 1984;
Banks 1996). Among the perceived drawbacks of CSz as a
grain fumigant were its high flammability and the loss of
Codex Alimentarius • guidelme ' tolerance (full maximum
residue limit at Codex was never attained for CSz). To
obtain a Codex MRL for CSz full toxicological assessment of
the chemical, including long-term feeding studies in
rodents, would be required to ensure that CSz residues in
commodities were safe to consume, in addition to proof of
efficacy of CSz In field trials. Presently, the lack of
mammalian toxicological data on which to base an application
for international registration, and the cost of toxicology
studies, will limit the future use of CSz as a grain fumigant
The safety to workers potentially exposed to CSzwill need to
be carefully considered in the light of the extensive
knowledge of adverse effects from occupational exposure to
CSz. The revised 1989 PEL exposure standard for CSzin the
U. S. (4 ppm) is lower than the current TLV (10 ppm) and
signals the trend to reduce occupational exposures.
Industries where workers are exposed to CSz will need to
consider whether they can comply with the lower exposure
standard when they are introduced.
On the basis of occupational health, the presence of residues
at natural levels and efficacy it is worth pursumg
registration for COSand EF as grain fumigants, but for CSz,
persistent residues and occupational health and safety
considerations may limit extensive use of CSzIn the future.
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