United States
Environmental Protection
Agency
Prevention, Pesticides
And Toxic Substances
(7508W)
EPA 738-R-95-036
September 1995
SERA R.E.D. FACTS
Pesticide
Reregistration
Tetrachlorvinphos
All pesticides sold or distributed in the United States must be
registered by EPA, based on scientific studies showing that they can be used
without posing unreasonable risks to people or the environment. Because of
advances in scientific knowledge, the law requires that pesticides which
were first registered before November 1, 1984, be reregistered to ensure
that they meet today's more stringent standards.
In evaluating pesticides for reregistration, EPA obtains and reviews a
complete set of studies from pesticide producers, describing the human
health and environmental effects of each pesticide. The Agency develops
any mitigation measures or regulatory controls needed to effectively reduce
each pesticide's risks. EPA then reregisters pesticides that can be used
without posing unreasonable risks to human health or the environment.
When a pesticide is eligible for reregistration, EPA explains the basis
for its decision in a Reregistration Eligibility Decision (RED) document.
This fact sheet summarizes the information in the RED document for
reregistration case 0321, tetrachlorvinphos.
Use Profile
Tetrachlorvinphos is an organophosphate insecticide. It is currently
used as a dermal and feed-through (oral) larvicide in cattle, hogs, goats and
horses; in cattle ear tags to control flies in cattle feedlots; in poultry dust
boxes to control poultry mites. Tetrachlorvinphos is also used in pet
sleeping areas and pet flea collars. It is used to control nuisance and public
health pests (flies) in and around refuse sites, recreational areas, and for
general outdoor treatment. Formulations include wettable powders, dusts,
granules, mineral blocks for livestock, impregnated materials (pet collars,
cattle ear tags), ready-to-use liquids, pressurized liquids, and emulsifiable
concentrates. Products containing tetrachlorvinphos are applied by hand,
pressurized aerosol, hand and power sprayers and dusters, and as free-
choice mineral blocks, livestock feed supplements, poultry dust boxes, pet
collars, and cattle ear tags.
Regulatory Tetrachlorvinphos (commonly referred to by the trade names Rabonฎ
History anc^ Gardona^) was initially registered for use in the United States in 1966
by the U.S. Department of Agriculture. Tetrachlorvinphos was originally
registered for use on various food crops, livestock, pet animals, and in or
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around buildings. The crop uses were voluntarily canceled from product
registrations in 1987.
In October 1988, EPA issued a Registration Standard. In the Standard
the Agency summarized its assessment of the supporting scientific data
available at that time, and identified and required the submission of
additional data to support the continued registration of tetrachlorvinphos
products.
Human Health Toxicity
Assessment In studies using laboratory animals, tetrachlorvinphos has been shown
to be practically non-toxic to slightly toxic in acute toxicity studies.
Tetrachlorvinphos did not cause delayed neurotoxicity in hens in two
neurotoxicity studies. In an acute neurotoxicity study, rats exhibited signs
consistent with cholinesterase inhibition but there was no indication of any
permanent behavioral changes or of any adverse neuropathological effects.
Cholinesterase inhibition was also observed at higher doses in two
subchronic studies (one dermal, one oral) conducted on rats.
Decreased plasma cholinesterase activity and increased kidney and
liver weights were noted in several chronic toxicity studies conducted on
dogs and rats.
Tetrachlorvinphos produced effects in three carcinogenicity studies
involving rats and mice as test animals. Effects included increased
incidences of adrenal cortical adenomas and thyroid C-cell adenomas, high
incidences of thyroid C-cell hyperplasia, hepatocellular carcinoma,
hepatocellular adenomas, and granulomatous lesions of the liver.
No indications of developmental toxicity were seen at the highest dose
tested in two developmental toxicity studies conducted on pregnant rats.
However, some clinical signs were noted in the mothers. A similar
developmental toxicity study conducted on rabbits noted developmental
toxicity at the mid-dose level. The signs of developmental toxicity included
abortions, red vaginal fluid, and reduced weight gain.
Two reproductive toxicity studies conducted using rats were
submitted. The two-generation reproductive toxicity study resulted in
reduced weight gains and increases in adrenal gland weights. The no
observed effects level (NOEL) was the highest dose tested. The three-
generation reproductive toxicity study produced an increase in liver weights
in the third generation rats. The livers and other organs exhibited no effects
when examined microscopically, however.
While two mutagenicity studies returned negative results, a third
study returned a positive result in the absence of metabolic activation and
negative result in the presence of metabolic activation.
Very little unmetabolized tetrachlorvinphos was found 48 hours after
dosing in a metabolism study conducted on rats. Metabolites found (mostly
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in urine and feces) included trichlorophenylethandiol and trichloromandelic
acid.
After 10 hours duration (longest test period), 84% of the total applied
tetrachlorvinphos remained unabsorbed in a dermal absorption study in rats.
The percent absorption increased with the duration of the exposure and
generally decreased with increasing dose. The actual quantity of
tetrachlorvinphos absorbed increased with increasing dose.
Tetrachlorvinphos has been classified as a group C (possible human)
carcinogen by the Carcinogenicity Peer Review Committee of EPA's Office
of Pesticide Programs based on the results of 3 studies using rats and mice
in which liver tumors were observed.
Dietary Exposure
Although no food or feed crop uses currently are registered, the
livestock uses of tetrachlorvinphos result in human dietary exposure. Since
people may be exposed to residues of tetrachlorvinphos through the diet., a
tolerance reassessment was conducted.
Tolerances or maximum residue limits have been established for
alfalfa, apples, cattle, cherries, corn, cranberries, eggs, goats, hogs, horses,
milk, peaches, pears, poultry, sheep, and tomatoes (please see 40 CFR
180.252). EPA has reassessed the fenthion tolerances and found that for use
on cattle, eggs, goats, hogs, milk, and poultry the tolerances must be
reassessed after additional data has been submitted to the Agency. The
tolerance for use on horses has been proposed for revocation due to the label
requirement precluding use on horses destined for slaughter.
While there are established tolerances for tetrachlorvinphos on certain
crops (as listed above), no currently registered tetrachlorvinphos end-use
product is labeled for use on any plant commodity. The Agency has
proposed revocation of the associated tolerances.
EPA has assessed the dietary risk posed by tetrachlorvinphos. The
Anticipated Residue Concentration (ARC) for the overall U.S. population
represents 1% of the Reference Dose (RfD), or amount believed not to
cause adverse effects if consumed daily over a 70-year lifetime. The most
highly exposed subgroup, children (1-6 years), has an ARC which
represents 3% of the RfD. This low fraction of the allowable RfD is
considered to be an acceptable dietary exposure risk.
For the U.S. population, the upperbound carcinogenic risk was
calculated using anticipated residues for meat, milk, poultry, and eggs, and
was refined using percent livestock treated estimates. The carcinogenic risk
for all published and supported uses was 4.3 x 10"5. This assumes that
100% of the fruit and vegetable commodities consumed are imported and
contain tetrachlorvinphos at tolerance levels. However, only meat, milk,
poultry, and eggs are supported for reregistration. When only these
commodities are considered, the dietary cancer risk is 1 x 10"6, a degree of
risk considered acceptable.
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Occupational and Residential Exposure
Based on current use patterns, handlers (mixers, loaders, and
applicators) may be exposed to tetrachlorvinphos during and after normal
use. Increased cancer risks to tetrachlorvinphos handlers wearing full
protective clothing range from 5.7 x 10"8 to 1.3 x 10~5, which the Agency
considers to be acceptable.
Risk estimates for occupational/residential uses of tetrachlorvinphos
were calculated using the upper bound carcinogenic risk for
mixers/loaders/applicators from ten different use scenarios. The highest
calculated risk (1.3 x 10~5) is for the low pressure handwand scenario. This
risk is less than the Agency's 10~4 level of concern for worker exposure.
Since risks to workers under this worst-case scenario do not exceed the
Agency's level of concern, it is not likely that exposures resulting from
applications of dusts, pellets, or impregnating materials will exceed the
Agency's level of concern.
To minimize worker exposure and reduce the risk to handlers,
baseline PPE are set through the RED document, including: long-sleeved
shirt, long pants, socks and shoes, and chemical-resistant gloves. The
Agency expects that this PPE will adequately protect workers from
exposures to tetrachlorvinphos. The use of chemical-resistant gloves by
applicators using low pressure handwands should further reduce the
potential carcinogenic risk.
Although there is the potential for homeowner exposure to
tetrachlorvinphos, it is unlikely that homeowners would experience
significant exposure resulting from typical household uses.
Human Risk Assessment
Tetrachlorvinphos has been shown to be practically non-toxic to
slightly toxic in all acute toxicity studies but causes reduced weight gain and
increased organ weights in certain studies.
Tetrachlorvinphos has been classified as a group C (possible human)
carcinogen by the Carcinogenicity Peer Review Committee of the EPA's
Office of Pesticide Programs.
Both chronic systemic and carcinogenic dietary risks were calculated.
These risks appear to be minimal when only uses supported for
reregistration are included in the assessment.
When dietary risk from chronic systemic effects was assessed, the
calculated exposure for the U.S. population was 59% of the RfD.
However, when only the anticipated residues from supported uses were
included, the estimated exposure for the U.S. population was only 1% of the
RfD.
In addition to revoking the food crop tolerances for tetrachlorvinphos,
the Agency is also proceeding to revoke the feed additive tolerances, as
required by the Delaney clause. When these tolerances are revoked and the
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Environmental
Assessment
Risk Mitigation
uses are removed from labeling, the dietary risk will change. It is not
possible to estimate the amount that the risk will be reduced or increased,
however, since it is possible that some users of tetrachlorvinphos would
switch from a feed-through application to a dermal application.
Based on current use patterns, handlers (mixers, loaders, and
applicators) may be exposed to tetrachlorvinphos during and after normal
use. Increased cancer risks to tetrachlorvinphos handlers wearing full
protective clothing range from 5.7 x 10"8 to 1.3 x 10~5, which the Agency
considers to be acceptable. Although there is the potential for homeowner
exposures to tetrachlorvinphos, it is unlikely that homeowners would
experience significant exposure resulting from such uses.
Environmental Fate
In the environment, tetrachlorvinphos is not persistent but its mobility
increases as soil texture becomes coarse and the organic matter content
decreases. The primary route of dissipation is through bio tic degradation.
Under alkaline conditions, abiotic processes (e.g., hydrolysis) are somewhat
effective. Parent tetrachlorvinphos is not available from the manure of
treated animals and is therefore not available to the environment from the
feed-through (oral) larvicide uses. Based on current product labeling, it is
unlikely that serious detrimental impacts to ground or surface water will
occur from the use of tetrachlorvinphos. Confirmatory data describing the
hydrolysis of tetrachlorvinphos have been submitted and are in review. The
results of this review are not likely to change the environmental assessment
for this pesticide.
Ecological Effects
Tetrachlorvinphos is practically non-toxic to birds, and moderately to
very highly toxic to freshwater and estuarine/marine organisms.
Ecological Effects Risk Assessment
Under the use patterns described in the RED document,
tetrachlorvinphos poses little acute or chronic risk to wildlife. Exposure to
the environment is expected to be minimal, especially exposures to aquatic
species because of the use patterns. Although the acute levels of concern
are exceeded for fresh water invertebrates and endangered fish and
invertebrates, significant risk is unlikely due to low exposure. Chronic
exposures and risks are unlikely because of the use patterns.
To lessen the potential human health risks posed by tetrachlorvinphos,
EPA is requiring the following risk mitigation measures:
Personal Protection Equipment (PPE) Requirements for Handlers
Entry Restrictions
Product Specific Labeling Changes
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Additional Data Because of the feed additive tolerance issue associated with the
Required Delaney clause, the requirement for livestock residue data for the feed-
through use is deferred. Data are required to upgrade the existing
Mixer/Loader/Applicator exposure study.
Product Labeling All tetrachlorvinphos end-use products must comply with EPA's
Changes Required current pesticide product labeling requirements and with the following.
All Products
Because tetrachlorvinphos is classified as a skin sensitizer, the Agency
requires that the following statement appear on all tetrachlorvinphos
labels in the "Hazards to Humans (and Domestic Animals)" section of
the Precautionary Statements:
"This product may cause skin sensitization reactions in certain
individuals."
Products Intended Primarily for Occupational Use
The Agency is requiring the following labeling statements to be
located on all end-use products containing tetrachlorvinphos that are
intended primarily for occupational use:
4 Application Restrictions:
"Do not apply this product in a way that will contact workers or
other persons, either directly or through drift. Only protected
handlers may be in the area during application."
4 User Safety Requirements:
"Follow manufacturer's instructions for cleaning/maintaining
PPE. If no such instructions for washables, use detergent and
hot water. Keep and wash PPE separately from other laundry."
4 User Safety Recommendations:
"Users should wash hands before eating, drinking, chewing
gum, using tobacco, or using the toilet."
"Users should remove clothing immediately if pesticide gets
inside. Then wash thoroughly and put on clean clothing."
"Users should remove PPE immediately after handling this
product. Wash the outside of gloves before removing. As
soon as possible, wash thoroughly and change into clean
clothing."
Occupational Products Used in Recreational Areas
The following entry restriction must be added to the labels of all
products used occupationally in recreational areas:
"For Liquid Application:
Do not enter or allow others to enter the treated area until
sprays have dried."
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Products with Feed-Through Uses
All products labeled for use on horses must have the following
restriction:
"This product is not to be used on horses destined for
slaughter."
Labels of all products with directions for use as a feed-through for
livestock must be clarified so that weights of pesticide to be added to
feed refer to weights of active ingredient and not weights of product.
Regulatory
Conclusion
For a comprehensive list of labeling requirements, please see the
Tetrachlorvinphos RED document.
The Agency has determined that all uses of tetrachlorvinphos, with the
exception of oral feed-through larvicide treatment to livestock intended for
food use, will not cause unreasonable risk to humans or the environment and
these uses are eligible for reregistration. The Agency has determined that
the dermal application to livestock, non-food animal, general outdoor
treatment, and pet uses of tetrachlorvinphos, specified in the RED
document, will not cause unreasonable risk to humans or the environment
and these uses are eligible for reregistration. However, the Agency cannot
make a determination regarding the reregistration eligibility of the feed-
through (oral) livestock use at this time.
Tetrachlorvinphos products will be reregistered once the required
product-specific data, generic data, revised Confidential Statements of
Formula, and revised labeling are received and accepted by EPA.
For More
Information
EPA is requesting public comments on the Reregistration Eligibility
Decision (RED) document for tetrachlorvinphos during a 60-day time
period, as announced in a Notice of Availability published in the Federal
Register. To obtain a copy of the RED document or to submit written
comments, please contact the Pesticide Docket, Public Response and
Program Resources Branch, Field Operations Division (7506C), Office of
Pesticide Programs (OPP), US EPA, Washington, DC 20460, telephone
703-305-5805.
Electronic copies of the RED and this fact sheet can be downloaded
from the Pesticide Special Review and Reregistration Information System at
703-308-7224. They also are available on the Internet on EPA's gopher
server, GOPHER.EPA.GOV, or using ftp on FTP.EPA.GOV, or using
WWW (World Wide Web) on WWW.EPA.GOV.
Printed copies of the RED and fact sheet can be obtained from EPA's
National Center for Environmental Publications and Information
(EPA/NCEPI), PO Box 42419, Cincinnati, OH 45242-0419, telephone 513-
489-8190, fax 513-489-8695.
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Following the comment period, the Tetrachlorvinphos RED document
also will be available from the National Technical Information Service
(NTIS), 5285 Port Royal Road, Springfield, VA 22161, telephone 703-487-
4650.
For more information about EPA's pesticide reregistration program,
the Tetrachlorvinphos RED, or reregistration of individual products
containing tetrachlorvinphos, please contact the Special Review and
Reregistration Division (7508W), OPP, US EPA, Washington, DC 20460,
telephone 703-308-8000.
For information about the health effects of pesticides, or for assistance
in recognizing and managing pesticide poisoning symptoms, please contact
the National Pesticides Telecommunications Network (NPTN). Call toll-
free 1-800-858-7378, between 9:30 am and 7:30 pm Eastern Standard Time,
Monday through Friday.
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