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Assessing intermittent pesticide exposure from flea control collars containing the organophosphorus insecticide tetrachlorvinphos

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Fleas are a persistent problem for pets that require implementation of control measures. Consequently, pesticide use by homeowners for flea control is common and may increase pesticide exposure for adults and children. Fifty-five pet dogs (23 in study 1; 22 in study 2) of different breeds and weights were treated with over-the-counter flea collars containing tetrachlorvinphos (TCVP). During study 1, fur of treated dogs was monitored for transferable TCVP residues using cotton gloves to pet the dogs during 5-min rubbings post-collar application. Plasma cholinesterase (ChE) activity was also measured in treated dogs. Average amounts of TCVP transferred from the fur of the neck (rubbing over the collar) and from the back to gloves at 3 days post-collar application were 23,700+/-2100 and 260+/-50 microg/glove, respectively. No inhibition of plasma ChE was observed. During study 2, transferable TCVP residues to cotton gloves were monitored during 5-min rubbings post-collar application. Transferable residues were also monitored on cotton tee shirts worn by children and in the first morning urine samples obtained from adults and children. Average amounts of TCVP transferred to gloves at 5 days post-collar application from the neck (over the collar) and from the back were 22,400+/-2900 and 80+/-20 microg/glove, respectively. Tee shirts worn by children on days 7-11 contained 1.8+/-0.8 microg TCVP/g shirt. No significant differences were observed between adults and children in urinary 2,4,5-trichloromandelic acid (TCMA) levels; however, all TCMA residues (adults and children) were significantly greater than pretreatment concentrations (alpha=0.05). The lack of ChE inhibition in dogs and the low acute toxicity level of TCVP (rat oral LD(50) of 4-5 g/kg) strongly suggest that TCVP is rapidly detoxified and excreted and therefore poses a very low toxicological risk, despite these high residues.
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Assessing intermittent pesticide exposure from flea control collars
containing the organophosphorus insecticide tetrachlorvinphos
M. KEITH DAVIS, J. SCOTT BOONE
1
, JOHN E. MORAN, JOHN W. TYLER
2
AND JANICE E. CHAMBERS
Center for Environmental Health Sciences, College of Veterinary Medicine, Mississippi State University, Mississippi State, Mississippi, USA
Fleas are a persistent problem for pets that require implementation of control measures. Consequently, pesticide use by homeowners for flea control is
common and may increase pesticide exposure for adults and children. Fifty-five pet dogs (23 in study 1; 22 in study 2) of different breeds and weights were
treated with over-the-counter flea collars containing tetrachlorvinphos (TCVP). During study 1, fur of treated dogs was monitored for transferable TCVP
residues using cotton gloves to pet the dogs during 5-min rubbings post-collar application. Plasma cholinesterase (ChE) activity was also measured in
treated dogs. Average amounts of TCVP transferred from the fur of the neck (rubbing over the collar) and from the back to gloves at 3 days post-collar
application were 23,700
±
2100 and 260
±
50 mg/glove, respectively. No inhibition of plasma ChE was observed. During study 2, transferable TCVP
residues to cotton gloves were monitored during 5-min rubbings post-collar application. Transferable residues were also monitored on cotton tee shirts
worn by children and in the first morning urine samples obtained from adults and children. Average amounts of TCVP transferred to gloves at 5 days
post-collar application from the neck (over the collar) and from the back were 22,400
±
2900 and 80
±
20 mg/glove, respectively. Tee shirts worn by
children on days 7–11 contained 1.8
±
0.8 mg TCVP/g shirt. No significant differences were observed between adults and children in urinary 2,4,5-
trichloromandelic acid (TCMA) levels; however, all TCMA residues (adults and children) were significantly greater than pretreatment concentrations
(a ¼ 0.05). The lack of ChE inhibition in dogs and the low acute toxicity level of TCVP (rat oral LD
50
of 4–5 g/kg) strongly suggest that TCVP is rapidly
detoxified and excreted and therefore poses a very low toxicological risk, despite these high residues.
Journal of Exposure Science and Environmental Epidemiology (2008) 18, 564–570; doi:10.1038/sj.jes.7500647; published online 2 January 2008
Keywords: tetrachlorvinphos, human pesticide exposure, flea control, transferable residues.
Introduction
Pesticide exposures to infants and children from food, water,
and residential sources have been well documented (Woody,
1984; Zwiener and Ginsburg, 1988; Fenske et al., 1990;
Morgan et al., 2001; Castorina et al., 2003; Colt et al., 2003;
Rohrer et al., 2003; Hore et al., 2005; Boone et al., 2006;
Chambers et al., 2007). However, one area that does not
seem to have been appreciably explored is the possibility that
residues of insecticides remaining on pet fur from ea control
treatments could be a significant source of pesticide exposure
in children. Fleas are a continuous and persistent problem for
pets throughout the United States, especially in warmer
regions such as the South, where fleas are present most of the
year. To be efficacious, flea control insecticides must have
a residual effect on treated animals for several days, weeks,
or even longer. Collars impregnated with insecticides are
commonly used for flea control by homeowners, and may
serve as direct sources of exposure to children who pet or
hug treated animals. Thus, children are likely to have dermal
contact with these insecticides, a portion of which may
become an oral exposure because of their hand-to-mouth
behaviors. In warmer climates, an even greater risk of
exposure to these insecticides exists because children generally
wear less clothing and have less protection from contact with
treated animals.
Demographic studies indicate that more than 30% of all
US households own one or more pet dogs, a number that has
essentially been the same since 1987. This translates into an
average of approximately 1.6 dogs per dog-owning house-
hold or about 52 million dogs in the United States.
Furthermore, it has been shown that 59% of dog-owning
households have at least one child living in them (American
Veterinary Medical Association, 1997), which yields a
population of millions of children who could be in direct
contact with flea control insecticides from dogs alone.
Tetrachlorvinphos (2-chloro-1-(2,4,5-trichlorophenyl)vinyl
dimethyl phosphate (TCVP)) is one of a group of organo-
phosphorus (OP) insecticides that have been widely used for
Received 5 March 2007; revised 5 October 2007; accepted 5 November
2007; published online 2 January 2008
1. Address all correspondence to: Dr. J.E. Chambers, Center for
Environmental Health Sciences, College of Veterinary Medicine, Mississippi
State University, P.O. Box 6100, Mississippi State, MS 39762, USA.
Tel.: þ 662 325 1255. Fax: þ 662 325 1031.
E-mail: chambers@cvm.msstate.edu
1
Current address: United States Environmental Protection Agency,
Environmental Chemistry Branch, John C. Stennis Space Center,
Mississippi, USA.
2
Current address: Western University of Health Sciences, College of
Veterinary Medicine, Pomona, California, USA.
Journal of Exposure Science and Environmental Epidemiology (2008) 18, 564–570
r
2008 Nature Publishing Group All rights reserved 1559-0631/08/$30.00
www.nature.com/jes
flea control and numerous other agricultural and domestic
applications. TCVP (commonly referred to by the trade
names Rabon
s
and Gardona
s
) is a class III OP insecticide
with rat oral and rabbit dermal LD
50
s of 4–5 g/kg and 2.5 g/
kg, respectively. It has a half-life of 48 h (38% to 56% in
feces and 46% to 60% in urine), and its major metabolites
are trichlorophenylethanol (feces) and trichloromandelic acid
(urine) (USEPA, 1995).
All agricultural (crop) uses of TCVP were voluntarily
cancelled in 1987. Consequently, it is now mostly applied
dermally in poultry for the control of mites and flies and as
an oral feed-through larvicide for fly control in horses, cattle,
goats, and swine (USEPA, 1995; Berger et al., 2007). It is
also used for the control of nuisance and public health pests
(flies), as well as in the form of powder, aerosol, spray, or
shampoo for the dermal treatment of pets (USEPA, 1995).
Because TCVP is an organophosphate insecticide, its
primary mechanism of toxicity is the inhibition of the
nervous system enzyme, acetylcholinesterase (Ecobichon,
1996).
Because TCVP has been used in flea collars, the amount of
exposure to TCVP that could occur in children and adults
from the use of a TCVP-containing collar on a pet dog was
assessed. A long study (about 4 months) was conducted first
to determine the time course of transferable residue peak
and dissipation as assessed by transferable residues of TCVP
from the fur of dogs to white cotton gloves used to rub the
dogs. This was followed by a shorter study conducted over
3 weeks to include human biomonitoring of the TCVP
metabolite 2,4,5-trichloromandelic acid (TCMA) in urine of
children and adults. TCVP residues transferred to tee shirts
worn by children by contact with the dog were also quantified
to determine whether tee shirts might serve as a surrogate of
exposure.
Methods
Study Design
These experiments were designed to determine the levels of
transferable TCVP residues to white cotton gloves from
rubbing the back of a dog at three locations: near the base of
the tail, at the neck with the collar removed, and at the neck
with the collar in place. Children’s potential exposure to and
absorption of TCVP were estimated by TCVP residues on tee
shirts worn by children for average 4-h periods at selected
times after pesticide application, as well as the metabolite
trichloromandelic acid (TCMA) levels in the first morning
urine sample, the morning following wearing the tee shirt.
Urinary TCMA was also monitored from an adult in the
household on the same sampling days.
Studies were conducted in Oktibbeha County, Mississippi
(USA), with volunteer households having pet dogs. Study 1
was a longer term study conducted over 112 days (September
to December 1998) because the collar used was recom-
mended by the manufacturer for 6-month use. Twenty-three
dogs from different households were used, and petting
samples from fur and dog plasma cholinesterase (ChE)
measurements were obtained. On the basis of the results from
the first study, which indicated that residues peaked and then
dropped substantially within 3 weeks of collar placement,
study 2 was performed over 21 days (September and October
2002) with 22 pet dogs from different households. Study 2
quantified residues of TCVP from petting and tee shirt
samples, and urinary metabolite TCMA in children and
adults.
Chemicals
In each of the two studies, flea collars (Hartz Control
Ultimate Flea Collar F 14.55% TCVP) were purchased
from a local department store. All collars were of the same
manufacturer’s lot number. Optima grade solvents (suitable
for gas chromatography) were obtained from Fisher
Scientific. The TCVP standard was obtained from Chem
Service (West Chester, PA, USA) and was greater than 99%
pure.
A commercial analytical chemistry laboratory (PTRL
West Inc., Hercules, CA, USA) was contracted to analyze
the human urine samples for the presence of TCMA, the
primary urinary metabolite of TCVP (USEPA, 1995). Since
TCMA cannot be readily prepared due to a lack of
commercial starting material, the structurally similar 2,3,6-
trichloromandelic acid analog was synthesized from 2,3,6-
trichlorobenzaldehyde and used as an internal standard. The
2,3,6-trichloromandelic acid was purified by re-crystallization
and was shown to have a purity of 488% by UV
spectrophotometric analysis (averaged result from two
wavelengths, 240 and 254 nm) and was characterized by
mass spectrometry with a purity of 97% (total ion current).
It is our assumption that the relative ion efficiency of the
internal standard (2,3,6-trichloromandelic acid) is similar to
the target analyte (TCMA).
Animals
The selection and care of pet dogs used in these studies were
in accordance with our earlier studies (Chambers et al.,
2007). Dogs were of a variety of breeds (including both short
and long hair breeds) and sizes (range 8–85 lb). All dogs were
healthy adults and were of both genders; no pregnant females
were used. All procedures were approved by the Mississippi
State University Animal Care and Use Committee.
Human Test Subjects
Participating families were volunteers who routinely used flea
control products on their pet dogs. One child and one adult
were selected from each participating family (study 2 only) as
previously described by Chambers et al. (2007). A copy of
the protocol was distributed to each participating household
Pesticide exposure from flea collars Davis et al.
Journal of Exposure Science and Environmental Epidemiology (2008) 18(6) 565
and informed consent was obtained from the adults. Children
were informed verbally of the procedures and oral or written
assent was obtained from them. The Institutional Review
Board for Research on Human Subjects at Mississippi State
University approved all sampling protocols and informed
consent forms.
Plasma Cholinesterase Assay
During study 1, plasma ChE activity was determined
spectrophotometrically from blood samples taken from each
dog at the same time as rubbing samples (Chambers et al.,
2007).
Rubbing Protocol
Dogs were petted in a marked 10 4inchareawithclean,
white, cotton gloves for a continuous 5-min period as
previously described (Boone et al., 2001). Samplers utilized
during both studies were students enrolled in the veterinary
medicine curriculum at the College of Veterinary Medicine,
Mississippi State University. Preparation of gloves and
sampling procedures described by Chambers et al. (2007)
were employed. Rubbing samples were obtained prior to
collar placement (day 0) and at 4 h, and 3, 7, 14, 28, 56, 84,
and 112 days post-collar application during study 1 and prior
to collar placement (0), and again at 5 and 12 days following
collar placement in study 2.
Tee Shirt Protocol
In study 2, child participants were supplied with a new,
laundered, white cotton tee shirt to wear on the day before
the treatment (pretreatment) and on each of days 7–11 post-
collar placement. Tee shirts were worn, stored, and prepared
for extraction as previously described (Chambers et al.,
2007).
Urine Sampling Protocol
During study 2, first morning urine samples (entire void)
were collected from the child wearing the tee shirt and from
one adult in the same household on the day prior to the
treatment and then again on each of days 8–12 post-collar
placement. Although the collection of 24-h urine samples
would be preferred due to the short half-life of TCMA
(USEPA, 1995), rst morning voids were more practical
to obtain because of the ages of the child participants (range
3–13). Furthermore, rst morning voids have been used in
many biological monitoring studies to evaluate the concen-
tration of environmental chemicals in human urine (Barr and
Angerer, 2006), and they have been shown to be the best
predictors of weighted-average daily metabolite concentra-
tions in the absence of a 24-h sample (Kissel et al., 2005).
Following collection, urine samples were brought to our
laboratories where a subsample consisting of 3 ml was
removed from each sample. Both the original samples and
the subsamples were placed in an upright freezer and held at
201C. The subsamples were shipped frozen to PTRL West
Inc. for analysis.
Determination of TCVP on Gloves and Tee Shirts
The gloves used to obtain rubbing samples were stored,
extracted, and analyzed as described earlier (Boone et al.,
2001). TCVP residues on tee shirts were determined using
the same procedures described for the gloves, except for a
methylene chloride preextraction step that was used to reduce
the loose cotton fiber content in the glove extracts. The
extractions and analyses used were modifications of the
methods of Zweig and Sherma (1977), Luke and Dahl
(1976), and EPA Test Methods 8141A, 8081, and 3540
(USEPA, 1993).
All samples were analyzed on an HP5890 gas chromato-
graphequippedwithanelectroncapturedetector(ECD).
Separation of the analyte was achieved by using an RTX-5
Amine column (30 m 0.53 mm inside diameter/1.0 m lm
thickness Restek, Bellefonte, PA, USA). The oven tempera-
ture was ramped at a rate of 31C/min from 2051C to 2251C
and held for 5 min, followed by a second ramp of 51C/min to
a final temperature of 2901C. The ECD injector and detector
temperatures were set at 2901C and 3251C, respectively.
The limit of detection (LOD) was 2 p.p.b. and the limit of
quantification (LOQ) was 6 p.p.b. Various concentrations
(0.5–2500 mg) of TCVP were applied to different gloves and
tee shirts to determine recovery rates and extraction
parameters. The percent recovery obtained during these tests
ranged from 85% to 102%, with a mean of 95%.
Determination of TCMA in Urine
These analyses were conducted under contract to PTRL West
Inc. Urine samples were thawed at ambient room tempera-
ture, vortexed, and aliquoted (1.0 ml) to 1.8 ml glass auto-
sampler vials, and fortified with the 2,3,6-trichloromandelic
acid internal standard. Sufficient volume of concentrated
(12 N) hydrochloric acid (typically 0.1 ml) was then added to
each sample to achieve a final volume dilution of 1 N. Each
vial was then sealed with a PTFE/rubber-lined aluminum
crimp cap, vortexed to mix, and placed in a water bath
maintained at 801C for a period of 1 h, after which they were
allowed to cool to ambient temperature before being
analyzed.
Samples were analyzed by reverse-phase liquid chromato-
graphy mass spectroscopy using an Applied Biosystems/
MDS SCIEX API 3000 triple quadrupole mass spectrometer
and Analystt version 1.4 software. Analyses were performed
in the negative ionization mode using Turbo Ionsprayt
ionization. Two MS/MS transitions were monitored: 253-
209 and 255-211, which are associated with a loss of
CO
2
from the corresponding molecular ions [M-H] at
253
AMU (
35
Cl) and its associated
37
Cl at 255 AMU.Quantita-
tion was by integration of peak area for the single fragment
ion at m/z 209.
Pesticide exposure from flea collarsDavis et al.
566 Journal of Exposure Science and Environmental Epidemiology (2008) 18(6)
Separation of the two analytes (TCMA and 2,3,6-
trichloromandelic acid) from each other was achieved by
reverse-phase C-18 liquid chromatography. The target
analyte, TCMA, was identified by monitoring the two
MS/MS transitions previously mentioned and observing the
presence of a similar ion-intensity ratio of approximately 1:1
(for the fragment masses 209:211) as observed for the
internal standard. Because of an interfering, co-eluting
component detected in a large number of urine hydrolysates,
further identification of TCMA at the retention time of
13.9 min was conrmed by its anticipated longer retention
time relative to that of the 2,3,6-trichloromandelic acid
internal standard, which eluted at 12.4 min. The longer
retention of TCMA can be attributed to the differences in
polarity (TCMA is less polar than the 2,3,6-trichloroman-
delic standard).
A typical injection sequence for sample analysis involved
an initial acetonitrile solvent blank followed by a 20 ng/ml
internal standard quality control (prepared in acetonitrile)
and 10 experimental samples. This sequence was then
repeated until all samples were analyzed. The linear response
of the instrument was verified by sequential injections of
calibrants prepared in acetonitrile at nominal concentrations.
Quantitation of the target analyte (TCMA) was done by
comparing the peak areas of the internal standard (2,3,6-
trichloromandelic acid) and TCMA. LOD was 0.63 p.p.b.
and LOQ was 2 p.p.b. Samples that were below the LOQ
were assigned the value of the LOQ for the purpose of sample
analysis. Two percent of the adult samples were below the
LOQ, and 10% of the children’s samples were below the
LOQ. Except for pretreatment samples, none of the samples
were below the LOD. The accuracy of the method was
evaluated by examining the relative error of triplicate
concentrations for a selected analysis (family no. 110).
Relative error was calculated as (experimentally determined
concentrationtheoretical concentration) 100Ctheoretical
concentration. Magnitudes of relative errors were less than
17% at the lowest concentration, less than 12% at the mid-
level concentration, and less than 5% at the highest
concentration. The percent recoveries were in the range of
88.5% to 116.3%, with a mean of 102.1%.
With spot samples such as first morning voids, there is
variability in the volume of urine and the concentrations of
endogenous and exogenous chemicals from void to void that
must be considered. Urinary TCMA levels were adjusted
for urinary creatinine concentration for both adults and
children (Barr et al., 2005). Creatinine content of urine was
determined by colorimetric determination at 500 nm using a
creatinine kit (Creatinine-S Assay Kit; Diagnostic Chemicals
Limited, Oxford, CT, USA).
Statistical Analyses
Analysis of variance calculations for glove and tee shirt
residues were performed with the GLM procedure of the
SAS
s
System for Windows, Version 9.1, using the 0.05 level
of significance as described earlier (Chambers et al., 2007).
The glove and tee shirt data were also examined for
the presence of statistically significant correlations using
Spearman’s correlation coefficient. The calculation was
performed using the CORR procedure of the SAS System
for Windows, Version 9.1 (SAS Institute Inc., Cary, NC,
USA) at 0.05 level of significance.
Urinary TCMA data were statistically analyzed to
compare the amount of TCMA between adults and children.
The analyses were implemented in SAS System for Windows,
Version 9.1.3 using PROC MIXED with the REPEATED
statement and the autoregressive order one (AR 1)
covariance structure. The AR 1 was a covariance structure
with the desired property of correlations being larger for
nearby time than for far-apart times, which was a better fit in
this statistical model than the compound symmetric or
unstructured covariance.
Results
No significant changes in dog plasma ChE activities from
pretreatment levels were observed except for one increase
of 10% at 84 days post-collar application; this statistical
difference was not viewed as biologically significant.
Significant increases in transferable TCVP residues were
observed from cotton gloves used to pet dogs compared to
pretreatment concentrations. In study 1, transferable residues
from all three sampling locations decreased throughout the
112 days following a peak at day 7 (Figure 1). Mean glove
residues for all sampling times were 14,300 mg/glove over the
collar, 4300 mg/glove on the neck with the collar removed,
and 130 mg/glove in the tail region. In study 2, residues
obtained over the collar and around the neck without the
collar in place decreased from 5 to 12 days post-collar
application, while pesticide residues obtained from the tail
0
5000
10000
15000
20000
25000
TCVP ( µg/glove)
0 20 40 60 80 100 120
Days
Collar
Neck
Back
Figure 1. Mean transferable tetrachlorvinphos residues from 23
treated dogs to cotton gloves
±
SE (study 1).
Pesticide exposure from flea collars Davis et al.
Journal of Exposure Science and Environmental Epidemiology (2008) 18(6) 567
region remained fairly constant (Figure 2). Mean residues
(for all gloves) post-collar application were 19,000 mg/glove
over the collar, 8000 mg/glove on the neck with the collar
removed, and 80 mg/glove in the tail region.
Transferable TCVP residues peaked at 7 days post-collar
application (24,000
±
4000 mg/glove over the collar) in study
1 and then steadily declined until the end of the study (86%
decline). Similar trends were also observed in detectable
TCVP residues around the neck without the collar in place
and in the tail region where there were 94% and 71%
decreases, respectively. During study 2, the peak transferable
residues were collected over the collar at 5 days post-collar
application and were of a similar magnitude to those
observed in study 1. From 5 days post-collar application
until 12 days post-collar application, there was a 30% decline
in detectable TCVP residues obtained over the collar while
residues obtained from the tail region remained fairly
constant (81 mg/glove at 5 days and 82 mg/glove at 12 days
post-collar application).
The average amount of TCVP detected on children’s tee
shirts on sampling days 7–11 post-collar application was
1.8
±
0.8 mg/g shirt (mean
±
SE), with no significant differ-
ences among the sampling days (Figure 3). Transferable
TCVP residues were significantly greater than the mean
pretreatment residue of 0.03
±
0.006 mg/g shirt (mean
±
SE).
Urine samples obtained from children generally contained
more TCMA than that from the adults with significant
differences between the ages occurring on only one of the five
sampling days. Samples collected on day 11 from children
contained significantly greater TCMA residues than that
from adults. No significant differences in urinary TCMA
concentrations were observed among the adults or among
the children throughout the study. The ranges in urinary
TCMA concentrations were very large. For adults, the range
was 1.4–582 ng/ml urine, and for children the range was 2.1–
1558 ng/ml urine. As previously stated, the urinary TCMA
concentrations for adults and children were adjusted for
creatinine content. However, only unadjusted values are
reported here because there were no differences in the
outcome when urinary TCMA concentrations were adjusted
for creatinine content.
No significant correlations were present among transfer-
able TCVP tee shirt residues, the amount of time tee shirts
were worn, the amount of time spent with treated dogs,
and urinary TCMA concentrations. At the 0.05 level of
significance, mean Spearman’s correlation coefficients for all
variables examined were between 0.4 and 0.2, which
indicate the presence of very weak (low) associations among
the variables tested.
Discussion
To reect the diversity among pet dogs and the diversity
within dog and human activity, we used different breeds and
sizes of dogs from 55 different families (23 in study 1 and 22
in study 2). Approximately half of the children and adults
were male and half were female. This variability should be
similar to that encountered with the normal use of flea
control collars among pet owners.
The results of the previous studies from our laboratory
using flea collars containing chlorpyrifos (CP) showed that
the greatest level of potential human exposure to CP from
flea collars, as assessed by the glove residues, occurred within
2 weeks of collar application and was greatest in the areas
on/near sites of application (Chambers et al., 2007). The
results obtained in the present studies yielded similar
patterns, with transferable TCVP residues to cotton gloves
highest over the collar and lowest in the tail region with a
peak at 1 week (Figures 1 and 2).
However, the overall magnitude of transferable residues
from the TCVP collars was much greater than was observed
Da
y
0246810121
4
30000
25000
20000
15000
10000
5000
0
TCVP (µg/Glove)
Back
Neck
Collar
Figure 2. Mean transferable tetrachlorvinphos residues from 22
treated dogs to cotton gloves
±
SE (study 2).
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
TCVP (µg/g Shirt)
078
Day
910111
2
Treatment Samples
Pre-treatment Samples
Figure 3. Mean tetrachlorvinphos residues
±
SE on cotton tee shirts
worn by children at selected times post-application in study 2.
Pesticide exposure from flea collarsDavis et al.
568 Journal of Exposure Science and Environmental Epidemiology (2008) 18(6)
in our previous study with a CP-containing collar (Chambers
et al., 2007). The grand means
±
SEs (from both studies) for
samples taken from the collar were 16,600
±
1300 mg/glove
for TCVP and 370
±
60 mg/glove for CP. This very large
difference in magnitude, about 45-fold, could be attributed in
part to the concentration of the insecticides in the collars
(14.55% (4.8 g) active ingredient in the TCVP collar and 8%
(2.54 g) active ingredient in the CP collar). The differences
among the TCVP and CP studies may also be attributed to
different samplers, differences in dog fur composition from
one breed to another, and in all likelihood, different
formulation matrices between the two types of collars leading
to greater release of TCVP (for a 4-month collar) than CP
(for a 6 month collar).
Significant TCVP residues in cotton tee shirts indicate that
clothing could be a potential source of exposure for children.
All of the observed tee shirt residues were significantly greater
than pretreatment levels (which were essentially nil), but were
not significantly different from one treatment day to another.
The higher mean TCVP tee shirt residues on days 9 and 11
result from one very-high residue (17.9 and 17.3 mg/g shirt)
obtained from one tee shirt on each of these two sampling
days. When the aforementioned residues are excluded from
the analysis, the mean tee shirt residues
±
SE on days 9 and
11 are 1.2
±
0.5 and 0.800
±
0.5 mg/g shirt, respectively,
which are similar to the residues obtained from the tee shirts
of other children on those days. We believe these higher
residues are related to the amount of time these two children
spent in direct contact with their pet dogs on those two
occasions.
Children generally had greater urinary concentrations of
TCMA than adults, similar to the higher levels of the CP
metabolite trichloropyridinol observed in our earlier study
(Chambers et al., 2007). Maximum TCMA concentrations
were observed on post-treatment day 11 (199
±
74 ng/ml
urine) for children and on post-treatment day 12 for adults
(103
±
38 ng/ml urine). TCMA residues in all samples were
significantly greater than pretreatment levels (which were
essentially nil), indicating that some TCVP is absorbed by
both adults and children. The grand means for adults and
children’s urinary TCMA concentrations were 65
±
22 and
174
±
56 ng/ml urine, respectively. At the 0.05 significance
level, these concentrations represent 6- and 16-fold increases
above pretreatment levels, respectively. Even though we
expected significant correlations among time spent with dogs,
transferable TCVP residues, and urinary TCMA concentra-
tions, there were no such correlations present at the 0.05 level
of significance. Although disappointing, the lack of signifi-
cant correlations is consistent with other studies utilizing
passive dosimeters and biomonitoring of urinary metabolites
(Honeycutt et al., 2000; Geer et al., 2004; Fenske and Day,
2005). Pretreatment values for TCVP on gloves or tee shirts
and for TCMA in urine were essentially zero, reflecting the
very limited usages of TCVP, and, therefore, little wide-
spread environmental contamination. These results are in
contrast to CP that was present prior to collar placement,
reflecting the wider usage of CP.
In summary, significantly greater residues of TCVP were
detected in both glove and tee shirt samples obtained post-
collar application than in pretreatment samples. Further-
more, TCMA, a urinary metabolite of TCVP, was also
detected in urine samples from both adults and children,
indicating that some of the TCVP may be absorbed.
However, since there are very few published data quantifying
human exposures to TCVP, these results should be
interpreted with caution because the toxicological significance
of these residues is presently unknown. The lack of ChE
inhibition in dogs and the low acute toxicity level of TCVP
(rat oral LD
50
of 4–5 g/kg) strongly suggest that TCVP is
rapidly detoxified and excreted and therefore poses a very low
toxicological risk, despite these high residues. It should also
be noted that these data may not be representative of other
flea control formulations, as indicated by the differences in
magnitude of residues between this study and our previous
study on CP. However, caution should be observed when
applying flea control insecticides to pets, especially those in
direct contact with children, and especially for the rst few
days after applying the collar.
Acknowledgements
This research was supported by grants from the US
Environmental Protection Agency’s Science to Achieve
Results (STAR) grant program (Grant nos. R825170 and
R828017). Although the research described herein has been
funded wholly or in part by the US Environmental
Protection Agency STAR program, it has not been subjected
to any governmental review and therefore does not reflect the
views of the agency. No official endorsements should be
inferred. We thank Ms. Nicole Holield, Ms. Susan
Waldrop, and Mr. Collin Zumwalt for residue analyses, as
well as creatinine and cholinesterase assays, Drs. Carolyn
Boyle and Sumalee Givaruangwawat for statistical advice,
and Dr. Louis Ruzo and Curtis Hatton (PTRL West Inc.)
for the analysis of urine for TCMA. This research was
also supported by the Mississippi Agriculture and
Forestry Experiment Station (MAFES) and the College
of Veterinary Medicine, Mississippi State University.
This article is MAFES publication number J11104 and the
Center of Environmental Health Sciences publication
number 113.
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Chapter
IntroductionPesticide CategoriesPesticide HandlersStudy Design ConsiderationsProtection of Human SubjectsPesticide Exposure Monitoring Methods Validation of Passive DosimetryUse of Pharmacokinetic DataExposure Mitigation MeasuresExposure Studies Supporting Registration DecisionsConclusions and RecommendationsAcknowledgementsReferences