Silvex
Position Document 1/2/3
(U.S.) Environmental Protection Agency
Arlington, VA
9 Jul 79
IX
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112ZLJ2L
RCORT DOCUMENTATION
PAGE
1. RCPOffT NO.
EFVSPRD-80/52
4. Title and Subtitle
Sllvex: Position Document 1/2/3
7. AuthorU)
t. Performing Om*nltatl«n Nam* and Addratl
Special Pesticide Review Division
Environmental Protection Agency
Crystal Hall #2
Arlington, VA
II. Sponsoring Organization Nam* and Addrm
Environmental Protection Agency
401 M St. S.W.
Washington, U.C. 20460
II. Supplementary Not**
J. Roclptan:'* Aec***l*n No.
.__Ea.8flHl.iM5_
«. Itapoit Oat*
7/9/79
•. Mormloi Organliatlr.n ftept. No.
10. Pro(*ct/T*»l
(G)
II. Typ* of Report A Period Covered
U
It. Abstract (Limit- IOO Mr4t)
Preliminary Risk Assessment: Examination of possible unreasonable
risks aswociated with uses of pesticide and a gathering of all available
information to determine whether or not this or any other risk does
exist. Initiates literature search and evaluates risk data. Limited
information on exposure to forecast extent, of risk.
Risk/benefit analysis: qualitative & quantitative risks of a pesticide,
value of crop uses, availability of alternative pesticides, exposure to
man and environment. Identification of risk reducing regulatory options
and proposed Agency action.
II. Oo.um*M Analytlt a. Deecrtptor*
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It. Availability tt*t*m**i
Release Unlimited
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(»** ANtl-XM.lt)
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(formally NTIt-IM
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PRELIMINARY DETERMINATION CONCERNING
A REBUTTABLE PRESUMPTION AGAINST REGISTRATION
OF PESTICIDE PRODUCTS CONTAINING
2-< 2 ,4,5-TRICHLOROPHENOXY PROPIONIC ACID (SILVEX)
NOTICE OP INTENT TO HOLD A HEARING TO
DETERMINE WHETHER OR NOT CERTAIN USES OP
SII*VEX SHOULD BE CANCELLED
NOTICE OF AVAILABILITt 0f POSITION DOCUMENT
SILVER: POSITION DOCUMENT 1/2/3
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
EPa/s/>*2) - go/so.
Of tie* of Pttiieidt Protrtat
July t, it?f
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ENVIRONMENTAL PROTECTION AGENCY
[FRL- OPP- 1
PRELIMINARY DETERMINATION CONCERNING
A REBUTTABLE PRESUMPTION AGAINST REGISTRATION
OP PESTICIDE PRODUCTS CONTAINING
2-(2,4,5-TRICHLOROPHENOXY PROPIONIC ACID (SILVEX)
NOTICE OF INTRNT TO HOLD A HEARING
TO DETERMINE WHETHER OR NOT CERTAIN USES OF
SILVEX SHOULD BE CANCELLED
NOTICE OF AVAILABILITY OF POSITION DOCUMENT
I. INTRODUCTION
On February 28, 1979 the Administrator of the
Environmental Protection Agency (EPA) ordered the
emergency suspension of the use of two phenoxy herbicides,
2,4,5-trichlorophenoxyacetic acid (2,4,5-T) and 2-
(2,4.5-trichlorophenoxy) propionic acid (silvex) on forests,
rights-of-way and pastures, and the home and garden,
aquatic ditch bank/weed control, and commercial/ornamental
turf uses of silvex (suspended uses). (44 FR 15897,
1/
March 15, 1979).
The emergency suspension orders were based in part
on data and information developed for and through the
Agency's rebuttable presumption against registration
1/ Suspension hearings commenced on April 19, 1979,
Eut were discontinued on May 15, 1979 after all regis-
trants withdrew from the hearings. The first pre-
hearing conference for the related cancellation
proceedings was held on June 5, 1979; the formal
evidentiary hearing will probably begin in the fall.
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(RPAR) for pesticide products containing one of these
chemicals, 2,4.5-T (43 FR 17116, April 21, 1978). Silvex
was included in the suspension orders in part because
2,4,5-T and silvex both contain the contaminant 2,3,7,8-
tetrachlorodibenzo-p-dioxin (TCDD), a highly toxic chemical,
have comparable uses and correspondingly comparable
exposure potential, and pose risk concerns which are
similar in many ways.
At the time the suspension orders were Issued, silvex
was a candidate for a rebuttable presumption against
registration (RPAR), but an RPAR had not been Issued.
However, the RPAR review of 2,4,5-T and the suspension
action prompted the Agency to expedite its RPAR review of
the use of silvex on rangeland, rice, sugarcane, orchards
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and non-crop areas (non-suspended uses). As a result of
this expedited review, the; Agency has determined that the
non-suspended uses of silvex meet the risk criteria for
issuance of a rebuttable presumption against registration
based on the oncogenic and other chronic or delayed toxic
effects risk criteria for issuance of a rebuttable
presumption against registration. (40 CFR 162.11(a)(3)).
2/ The non-crop uses of silvex include use on or
around non-crop sites, including fencerows, hedgerows,
fences (not otherwise included in suspended uses, e.g,
rights of way. pasture); industrial sites or buildings
(not otherwise Included in suspended uses, e.g., rights-
of-way, commercial/ornamental tjrfh storage arets, waste
areas, vacant lots, parking areas.
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The Agency has also determined that the criteria for
rebutting the presumptions of risks do not appear to be
satisfied, and that the risks appear to be greater than
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the benefits.
Accordingly, the Agency is announcing its determi-
nation to initiate proceedings to determine whether or
not to cancel or modify the terms and conditions of
registration of the non-suspended uses of silvex,
pursuant to FIFRA section 6(b)(2) of the Federal Insect-
icide, Fungicide, and Rodenticide Act, as amended, 7 U.S.C.
SS136 et. seq. (FIFRA). As explained in this
3/ Ordinarily, the public phase of the RPAR review of
a chemical begins with issuance of a notice of rebut-
table presumption in which the Agency presents the data
and other Information which indicate that the chemical
meets or exceeds the risk criteria set out at 40 CFR
162.11(a)(3). The Agency Invites registrants and other
Interested parties to comment on the data and information,
and to present information on the benefits of the chemical.
The rebuttals to the presumption and the information on
benefits are reviewed and a Position Document 2/3
presenting the Agency's review of data relating to risks
and benefits is Issued to the public, and submitted to
the U.S. Department of Agriculture and the Scientific
Advisory Panel for review (see section II of this Notice).
In the present case, the Agency has collapsed these
procedures into a single action because the data and
information indicating that the non-suspended uses of
silvex appear to present unreasonable risks to the
environment indicate that a decision on these chemicals
should be reached as expeditiously as possible. It is
in the public Interest to consolidate decisionmaking on
all uses of 2,4,5-T and silvex in a single legal proceed-
ing. Moreover, since the action is at this point
preliminary and subject to revision after consideration of
the views and recommendations of the United States Department
of Agriculture, pesticide registrants, the Scientific Advisory
Panel, and other interested parties, the public review and
comment function of the RPAR process is fully satisfied by the
procedures outlined in this notice.
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notice, this action is a preliminary determination at
this point, pending external review through submission
to ar.d review by tne United States Department of
Agriculture and the Scientific Advisory Panel, pursuant
to FIFRA sections 6(b) and 25(d). The action does not
become final until the Agency has reviewed the comments
of these reviewer a and issued final notices based in
part on consideration of these comments.
In broad summary, the Agency has determined ~•.hat
the non-suspended uses of silvex meet or exceed the risk
criteria for issuance of an RPAR set out at 40 CFR 162.11
(a)(3), and that applicable data and information submitted
in response to TCDO issues in the 2,4,5-T RPAR do not
rebut the presumptions. Therefore, the risks to humans
of oncogenic, fetotoxic, and teratogenic effects are of
sufficient concern to require the Agency to consider
whether offsetting economic, social or environmental
benefits exist.
The Agency has considered benefits information which
pesticide registrants, the U.S. Department of Agriculture,
and other interested parties have provided to the Agency,
and has analyzed the economic benefits of the non-suspended
uses of silvex. The Agency has weighed risks and benefits
together in order to determine whether the risks of each
use are warranted by the benefits of the use.
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With respect to the non-suspended uses of silvex,
the Agency has determined: (1) that these uses appear
generally to cause unreasonable adverse effects on the
environment, (2) that there are uncertainties in the data
relating to the risks and benefits of these uses, (3) that
additional data on the risks and benefits of the non-
suspended uses of silvex will permit the Agency to
determine whether or not to cancel the registrations
,!or these uses, and {4} that such information can best
be acquired through a public hearing pursuant to FIFRA
Section 6(b) (2).
The remainder of this Notice and the accompanying
Position Document set forth in detail the Agency's
analysis of data and information relating to the risks
and benefits of the non-suspended uses of silvex and
the Agency's reasons and factual base? for the regulatory
action it is initiating. The Notice is organized into
four sections. Section I is this introduction. Section
II sets forth a general discussion of the regulatory
framework within which this action is taken. Section III
sets forth the Agency's preliminary determinations
relating to the risks and benefits associated with
the non-suspended uses of silvex and initiating the
regulatory actions which flow from these determinations.
Section IV provides a brief discussion of the procedures
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which will br followed in implementing the regulatory
actions which the Agency is initiating in this Notice.
II. Legal Background
A. General
In order to obtain a registration for a
pesticide under FIFRA, a manufacturer must demonstrate th.it
the pesticide satisfies the statutory standard for registra-
tion. That standard requires (among other things) that the
pesticide perform its intended function without causing
"unreasonable adverse effects on the environment" (FIFRA,
section 3(c)(5)). "Unreasonable adverse effects on the
environment" is defined to mean "any unreasonable risk
to man or the environment, taking into account the
economic, social and environmental costs and benefits of
the use of any pesticide" (FIFRA, section 2(bb)). In
effect, this standard requires a findinq that the benefits
of each use of the pesticide exceew the risks of use,
when the pesticide is used in accordance with the terms
and conditions of registration, or in accordance with
commonly recognized practice. The burden of proving
that a pesticide satisfies the registration standard
is on the proponents of registration (e.g., registrants,
users), and continues as long as the registration remains
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in effect. Under section 6 of FIFRA, the Administrator
is required to cancel the registration of a pesticide or
nodify the terms and conditions of registration whenever
he determines that the pesticide no longer satisfies the
statutory standard for registration.
B. The RPAR Process
The Agency created rebuttable presumption
against registration (RPAR) process to facilitate the
identification of pesticide uses which may not satisfy
the statutory standard for registration and to provide
a public, informal procedure for the gathering and
evaluation of information about the risks and benefits
of these uses. The regulations governing the RPAR process
are set forth in the Agency's regulations at 40 CFR 162.11.
This section provides that a rebuttable presumption shall
arise if a pesticide meets or exceeds any of the risk
criteria set out in the regulations. The Agency generally
announces that an RPAR has arisen by publishing a notice
in the Federal Register. After an RPAR is issued, regis-
trants and other interested persons are invited to review
the data upon which the presumption is based rind to submit
data and Information to rebut the presumption. Respond-
ents may rebut the presumption of risk by showing that
the Agency's initial determination of risk was in error,
or by showing that use of the pesticide is not likely
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to result in any significant exposure to nan or to
animals or plants of concern with regard to the adverse
effect in question. Further, in addition to suomltting
evidence to rebut the risk presumption, respondents may
submit evidence as to whether the economic, social and
environmental benefits of the use of the pesticide subject
to the presumption outweigh the risks of use.
The regulations require the Agency to conclude an
RPAR by issuing a Notice of Determination in which the
Agency states and explains its position on the question
of whether the RPAR risk presumptions have been rebutted.
If the Agency determines that the presumption is not
rebutted, it will then consider information relating to
the social, economic and environmental costs and benefits
which registrants and other interested persons submitted
to the Agency and other benefits information known to the
Agency. After weighing of the risks and the benefits
of a pesticide's use, the Agency may conclude the RPAR
process either by issuing a notice of intent to cancel or
deny registrations), pursuant to PIFRA section 6(b)(1)
and 3(d)(1) or by issuing a notice of intent to hold a
hearing pursuant to section 6(b)(2) of FZFRA to determine
whether the registrations) should be cancelled or appli-
cations for registration s) denied.
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C. Notices of Intent to Cancel or to Hold
a Hearing
FIFRA provides two mechanisms for instituting
proceedings to cancel pesticides. The Administrator may
issue a notice of intent to cancel a pesticide and offer
registrants and other affected persons an opportunity to
request a hearing. (FIFRA, 56(b)(1)!. Alternatively,
the Administrator may issue a notice of intent to hold a
hearing to determine whether or not the pesticide should
be cancelled. (FIFRA, 56(b)(2)).
The judgment of whether to issue a §6(b)(l) or a
S6(b)(2) notice is within the sole discretion of the
Administrator or his duly designated delegatee. If the
Administrator determines that the risks of a pesticide's
use appear to outweigh its benefits, he may issue a
notice of intent to cancel pursuant to FIFRA section
6(b)(1). If, however, the Administrator's judgment
concerning the risks and benefits of a pesticide's use is
only tentative, the Administrator may issue a notice
under section 6(b)(2) declaring his intention to hold a
hearing '¦to determine whether or not its registration
should be cancelled."
D. External Review
FIFRA requires the Agency to submit notices
issued pursuant to section 6 to the Secretary of Agricul-
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appropriate steps are taken to make copies of
the Position Document available to registrants a/id other
interested persons at the time the decision documents are
transmitted for formal external review, through publi-
cation of a notice of availability in the Federal
Register, and by other means. Registrants and other
interested persons will be allowed the same period of
tine to comment—30 days—that the statute provides for
receipt of comments from the Secretary of Agriculture
and the Scientific Advisory Panel.
E. Pinal Notices
The determination to issue a FIFRA section 6
notice is a preliminary determination, pending external
review and Agency analysis of comments received. On the
basis of these comments, the Agency nay withdraw the
notice, issue a final notice without modification, or
modify the notice, as appropriate.
After complying with these external review require-
ments and if the notice is not withdrawn, accomplishing
any changes in the contemplated action which are deemed
appropriate as a result of any comments received, the
Agency Implemer s the desired regulatory action by
sending and making public a notice of Intent to cancel
under FIFRA soction 6(b)(1) or a notice of intent to
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ture with an analysis of the impact of the proposed
action on the agricultural economy (FIFRA, Section 6(b)).
The Agency is required to submit these documents to the
Secretary of Agriculture at least 60 days jefore making
the notice effective by sending it to registrants or
making it public. If the Secretary of Agriculture
comments, in writing, within 30 days after receiving the
notice, the Agency is required to publish the comments
and th' Administrator's responses to them along with
publication of the notice. FIFRA also requires the
Administrator to submit section 6 notices, at the same
time and under the same procedures as those described
above for review by the Secretary of Agriculture, to the
Scientific Advisory Panel for comment on the impact of the
proposed action on health and the environment. (FIFRA,
S2i(d)).
Although not required to do so under the statute,
the Agency has dstermined that it is consistent with the
general theme of tne RPAR process and the Agency's overall
policy of open decisionmaking to afford registrants and
other interested persons an opportunity to comment on the
bases for the proposed action during the time that the
proposed action is under review by the Secretary of Agri-
culture and the Scientific Advisory Panel. Accordingly,
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hold a hearing under FIFRA section 6(b)(2). If related
hearings are in progress, the Agency may move to consoli-
date proposed FIFRA section 6(b) proceedings with such
ongoing FIFRA proceedings. Hearings are governed by the
Agency's rules of practice for hearings under FIFRA section
6 [40 CFR 164]. At the end of the hearing, the Adminis-
strator issues his final decision regarding cancellation,
which may include an irder cancelling some or all uses.
III. Determinations and Initiation of Regulatory Action
The Agency has considered information on the risks
associated with the non-suspended uses of silvex,
including information submitted by registrants and other
interested persons in rebuttal of the 2,4,5-T RPAR. The
Agency has also considered information on the social,
economic, and environmental benefits of the non-suspended
uses of silvex, including information submitted by
the United States Department of Agriculture. The Agency's
assessment of the risks and benefits of the no.n-suspended
uses of silvex, and its conclusions and determinations as to
whether any use of silvex appears to cause unreasonable
adverse effects on the environment, are set forth in
detail in the Position Document accompanying this Notice.
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This Position Document is hereby adopted by the Agency as
its statement of reasons for the determinations and actions
announced in this Notice. For the reasons summarised
below and developed in detail in the Position Dor isnt,
the principal determinations of the Agency with L«..,pect
to silvex are as follows:
A. Determination on Risks
Data and information summarized in the Position
Document indicate that silvex and/or its TCDD contaminant
meet or exceed the oncogenic, and other chronic and
delayed toxic effects risk criteria at 40 CFR 162.11(a)(3),
and that the rangeland, rice, sugarcane, orchard and non-
crop area uses of silvex pose risks of these adverse effects
to human populations. As the Position Document explains,
the Agency has determined that information available to the
Agency (including information submitted to rebut these risk
criteria for the 2,4,5-T RPAR) is insufficient to lay to
rest the Agency's concerns that silvex and/or TCDD pose risks
of fetotoxic and teratogenic effects in unborn chilcren, and
that TCDD and silvex containing TCDD pose risks of cancer
among exposed populations- The Agency has determined that
the uses of silvex create opportunities for human exposure
to these chemicals and that such exposure appears generally
to cause adverse human effects. The Agency has therefore
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concluded that the oncogenic, Cetotoxic and teratogenic
risks associated with the non-suspended uses of silvex
are of sufficient magnitude to require the Anency to
determine whether the non-suspended uses of silvex offer
social, economic, or environmental benefits which offset
these risks.
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B. Determination of Benefits
The uses of silvex which are subject to this notice
fall into five categories: range, rice, sugarcane, orchard
and non-crop areas. For each of these use categories an
estimate of the economic impact of cancellation of silvex
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was made. These estimates are intended only as approxi-
y
nations based on available Information. The Agency's
analysis of this available information leads to the
conclusion that the benefits of silvex for the five
categories of uses are approximately as set forth below.
1. Rangeland
a. Fest Infestation and Damage
Approximately 900 million acres of rangeland exist
in the United States. Rangeland is used as grazing land
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for livestock, principally cattle. A wide variety of
4/ It is assumed that 2,4,5-T also would be canceled
and unavailable as a substitute for silvex. In view of
the virtually Identical toxicologleal characteristics of
the two compounds and the similarity of their benefits,
it is unlikely that only one of them would be canceled
for the uses for which they are alternatives for each
other.
5/ The Agency is continuing to collect and review data
Felating to the benefits of silvex for range, rice,
sugarcane, orchard, and non-crop areas.
6/ "Rangeland" Is defined as land producing forage for
animal consumption, harvested by grazing, which Is not
cultivated, seeded, fertilized, Irrigated or treated with
pesticides or other such similar practices on an annual
basis. Fencerows enclosing range areas are Included as
part of the range.
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herbaceous and woody plant* infest rangeland and
compete with the desired forage species for nutrients,
water, space and light. The most serious problems occur
on rangeland in the southwestern U.S.
b. Use of Sllvex and Alternatives
(i) Current Use of Sllvex
Each year, approximately 150,000 acres of rangeland
in the United States are treated with silvex. Sllvex is
used almost exclusively in the Southwest. The principal
pest species which silvex is applied to control are
various oak species.
(II) Non-Chemical Alternatives
Prior to the introduction and wide-scale use of
chemical herbicides, various hand and mechanical methods
*ere the exclusive tools for range weed control. These
methods have not been entirely replaced by chemical
herbicides. However, while hand and mechanical operations
can effectively control many of the pests in a reasonably
efficient manner, .hey do not substitute efficiently for
aerial chemical treatments when large tracts of Infested
acreage are Involved.
(III) Chemical Alternatives
Several registered chemical alternatives as well as
non-chemical controls not analyzed here are effective
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against one or more of the various range weeds controlled
by silvex. However, these chemicals are either not
registered Cor aerial application or are not as effective
as silvex for aerial application. 2,4-0 and dlcamba can
be applied aerially to rangeland, but they are relatively
ineffective as foliar sprays. The USDA Assessment Team
concluded that there is no effective alternative to silvex
for aerial control of oaks.
Since there are no effective alternatives to aerially
applied silvex for oak control, the yield effects
resulting from cancellation of silvex for range use could
be severe on acreage currently treated with silvex.
Cancellation would leave users with no aerially applied
alternative control or. tnese acres. In some areas, beef
yields could fall substantially.
c• economic Impact of Cancellation of
Silvex for Rangeland
User impacts developed by the USDA Assessment Team
members are used in this analysis. These estimates were
based on available information (both empirical and
opinion) and form approximate measures of potsntial
impacts.
Current silvex use is limited primarily to control
of various oak species by aerial application of the
herbicide. If silvex is canceled for this use, most
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users probably will choose not to treat large areas
formerly treated with silvex because no comparably-
effective alternatives are available. These users will
save front $4.60 to $13.00 per acre in control costs.
These savings, however, will be offset by lower revenues
from reduced production. Those silvex users who need
only spot treatments on smaller tracts will be able to
obtain soae degree of control with one or more of the
alternatives now available, since aerial application
would be unnecessary. The aggregate impact on users will
be small because few acres are treated with silvex now.
The economic impact of cancelling silvex for range
would be negligible at consumer and national levels
because silvex is now used on so few acres of rangeland
(approximately 0.2% of U.S. rangeland).
2. Rice
•• Pest Infestation andDamage
Weeds reduce the yield and quality of rice in the
U.S. on approximately 2.5 million acres. Herbicides are
used on about 98% of commercial U.S. rice acreage. Fields
are frequently treated more than once per year. Moot
treatments are made by custom aerial applicators. It
has been estimated that the total cost of weed control
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and direct 1 ises froa weeds Is several hundred a 11 lion
dollars per year.
Conditions favor ">le for growing rice also favor the
growth and reproduction of aany terrestrial, aquatic, and
seai-aquatic weeds. Rice weeds reduce yields by direct
coapetition and reduce quality through contamination of
the harvested grain with weed seeds. Weeds in rice
produce an abundance of seed. Once these Infest the land,
they are difficult to reaove and aay remain viable in the
soil for aany years.
Silvex is used annually on only 2000 rice-growing
acres in the United States. The principal weed pests
for which silvex is used include hemp sesbania, northern
jointvetch, aornlngglory, ducksalad and redstea. With-
out weed control, significant yield and quality reductions
on rice in the silvex use area could occur.
b. Pse ofSllvex and Alternatives
(1) Corrent Use of Silvex
andAlternatlves
Silvex use on rice is confined to the lower
Mississippi Valley region (Arkansas, Northern Louisiana,
Mississippi and Missouri). Silvex Is used annually on
2,000 acres out of approxiaately 2.5 alllion rice-growing
acres in the U.S. that receive soae herbicide treatment.
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Various herbicides and cultural practices are
commonly employed to control rice weeds. Current practices
generally combine chemical and cultural controls. There
is no information which suggests that cultural controls
would provide adequate control of rice weeds in the
absence of any chemical controls. Thus, it is likely
that chemical alternatives to silvex would be used in
conjunction with cultural controls if silvex were canceled
for use on rice.
Herbicides most frequently used on rice include
propanil and molinate, which together account for 73% of all
herbicide acre-applications to rice. These two herbicides
are used principally to control grass weeds; however,
propanil controls certain broadleaf and aquatic weeds
that are controlled by silvex. 2,4-D is the only other
herbicide used in appreciable quantities in the four-
state silvex use area. Other herbicides, MCPA, fcifencx,
bentazon and oxadiazon may also be used in place of silvex.
They are currently used in other states.
c. Comparative Efficacy and Cost of Silvex
and Alternatives of Use on Rice
Silvex controls most broadleaf, aquatic and sedge
weeds. Silvex, however, injures soybeans, a crop commonly
grown in rotation with rice. Silvex also damages cotton,
a crop connonly grown in areas adjacent to rice-growing
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acreage. These phytotoxic properties of silvex explain
why silvex in used on few acres; rice growers prefer to
use 2,4,5-T, which is less phytotoxic.
Propanil is currently applied to about 95 percent
of the southern rice-producing area for early sec&on
control of grasses. Propanil selectively kills barnyard
grass and aany other grasses, aquatic, broadleaf and sedge
weeds. Propanil controls henp sesbania as effectively as
silvex; however, propanil is less effective than silvex
for controlling northern jointvetch, ducksalad, and
redstem. If propanil were substituted on acres treated
with silvex, yield and quality losses could occur.
2,4-0 is applied for control of nany broadleaf,
aquatic, and sedge weeds. Its use, however, is
curtailed in the lower Mississippi Valley because it Is
highly injurious to cotton. Most rlce-growlng states
regulate the aerial application of 2,4-0 to reduce
damage from spray drift to nearby cotton fields. There-
fore, 2,4-D nay not be a viable alternative on all of
the acreage now treated with silvex. 2,4-D is applied
applied at midseason and apparently provides control of
¦any broadleaf weeds as effectively as silvex. 2,4-0
does not control northern jointvetch as effectively as
silvex and is Ineffective on grass weeds.
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Several other herbicides used for control of rice
weeds include mrlinate, MCPA, bifenox, bentazon and
oxadiazon. Molinate may not effectively control hemp
sesbania, northern jointvetch, ducksalad, morningglory or
redstem. MCPA is not used in the silvex use area since
it is thought to be relatively ineffective on hemp
sesbania, northern jointvetch and Indian jointvetch.
Bifenox, bentazon and oxadiazon are three new herbicides
which are currently used to a limited extent; they do not
appear to be as effective as silvex on most broadleaf and
aquatic weeds.
Effective weed control systems in rice combine
preventive, cultural, mechanical and biological methods
with chemical control methods. Cultural/mechanical weed
control practices include planting weed-free seed, summer
fallowing, crop iotation, land leveling, seedbed
preparation, special seeding methods, proper management
of water, cultivation and hand weeding (in sparse weed
infestations or in small areas). Although some of these
methods are effective alone on some rice weeds, they are
usually combined with chemical herbicide treatments.
d. Economic•Impact of Cancellation
of Silvex UseonRice
If Silvex is cancelled for use on rice, current
silvex users probably would use alternative chemical
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controls. 2,4-D and t>copanil would be the most likely
alternatives. Use of these alternatives would cost
$7.40 per acre-treatment (for 2,4-D) or $12.90 per acre-
treatment (for propanil), compare.! with $9.50 per acre-
treatment for silvex. Use of pronanil may necessitate
a second treatment, brinying the annual cost of control
with this herbicide to $21.80 per acre. Other possible
alternatives are somewhat more expensive than silvex or
these alternatives.
The economic impact of cancelling silvex for control
of rice weeds would be negligible at consumer, user and
national levels. This is due to the very limited use of
silvex (less than 0.1% of all treated acres) and the
availability of effective alternatives.
3. Sugarcane
a. Pest Infestation and Damager Ose and
Efficacy of Silvex and Alternatives
for~Sugarcane Use
Silvex is used in Louisiana and Florida on sugarcane
to control a variety of weeds that are resistant to 2,4-D.
If uncontrolled, pest weeds would compete wit-h sugarcane
for nutrients, water, space and sunlight and would reduce
crop yield.
Silvex is used on about 15% of all sugarcane
harvested acres. Use of silvex has decreased in recent
-23-
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years; in 1976, approximately 331 or acres used for growing
sugarcane were treated with silvex. The primary alter-
natives to silvex are a combination of dicamba apd ,*-D
and 2,4-D alone.
Neither the combination of dicamba and 2,4-D nor
2,4-D alone is as effective as silvex. Therefore, some
production losses, in some instances significant, may be
expected from replacement of silvex by either of these
alternatives.
b. Economic-Impact of Cancellation
of Silvex for Sogarcane Use
User level production value losses, in a worst-case
situation, could amount tc $4.0 million in Florida and
$6.3 million in Louisiana if jilvex were canceled and the
combination of dicamba and 2,4-D or 2,4-D alone substituted
for it. Th? maximum estimated yield losses would amount
to only about 2% of total U.S. sugarcane production.
Total U.S. sugarcane production accounts for only 18! of
tne U.S. sugar supply. Therefore, the cancellation of
silvex would not result in measurable sugar price changes
at the market or consumer level.
4. Orchard
a. Use of Silvex and A1 t.ernatives
on Orchards
Silvex is registered for use in preventing 4rples
and prunes from dropoinq fi.»m trees prior to harvest and
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for increasing fruit set on pears. Premature drops cause
a complete economic loss of prune crops and a substantial
loss in apple crops. Apples that have dropped prematurely
may be sold for low-return uses such as cider. Prunes
that have dropped early cannot be put to any commercial
use.
In addition to minimizing preharvest apple drop and
thus increasing aggregate production, silvex also acts
to increase the quality of treated fruit by enhancing
the coloring of red varieties. Use of silvex adds two to
three weeks t" apple trees' retention of fruit for on-tree
ripening. The extra one to two weeks of on-tree ripening
of fruit improves the color, sugar content and flavor of
the sprayed fruit. These factors are particularly
important for fresh-market growers who strive to maximize
the percentage of their crops which gr de out in the
fresh-quality categories. The grade impacts of silvex
are important to users in all areas, including the
southernmost apple states (Georgia, North Carolina, South
Carolina, Virginia), where growers attempt to produce
high-color fresh quality apples for the highly-profitable
early-season market.
Little quantitative data are available indicating
the specific location or extent of silvex use on apples,
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prunes, or pears. A proprietary pesticide usage survey
indicates that silvex use on apples in 1976 was limited
to a few thousand acres as was silvex use on prunes.
This survey data contrasts with information provided by
horticultural personnel, who believed that use was sub-
stantially higher than that indicated by the survey data.
Apparently, little silvex is applied to pears.
Currently, two alternatives to silvex are available
for use on apples to control preharvest drop. NAA
(1-Napthaleneacetic acid) is registered for apples bo*.h
<18 an early season thinning agent and as a late season
drop control agent. Alar (succinic acid 2,2-dimethyl
hydrazide) is registered for premature apple drop control
as well as for other growth regulating functions.
Neither NAA nor Alar is considered to be as effective
as silvex for premature drop control. NAA is less
effective than silvex in the southern apple states and is
best suited for varieties other than Red Delicious, the
apple cultivar on which silvex is principally used. Use
of NAA also may require a second annual application in
some cases, whereas silvex is applied only once a year.
Alar is a major alternative to silvex on apples
since it is suitable for use on red Delicious. Alar seems
to be less effective tnan silvex for preharvest drop
-------
control and also may reduce fruit size. Alar will also
adversely affect fruit shape the following year if applied
within 60 days of harvest.
There are currently no registered alternatives to
silvex for premature drop control on prunes. However,
2,4-DP, which is currently registered for some non-crop
applications, has reportedly provided good prune drop
control in Held tests, and may be registered for this
use in the future. There are no registered alternatives
for silv»x use on pears.
(b) Economic Impact•of•Cancellation•of•311 vex
for Orchard Use
Substitution of Alar and NAA for silvex could increase
apple production costs by as much as $1 million per year.
Prune growers could incur revenue reductions of approxi-
mately $1.8 million per year if silvex were cancelled,
assuming no suitable alternative becomes available.
If the Increased apple production costs ace absorbed
by the growers, no impact will be felt by consumers.
Bven if the costs are passed on to the consumer, the
retail price effect on apples would be negligible.
Although some adverse impact on consumer prices would
occur as a result of a cancellation of silvex for use on
prunes, it is not possible to as&ess the magnitude of
such an increase. Cancellation of silvex use on pears
-------
is unlikely to have any effect on consumer supply or the
quality or price of pears because little silvex is
applied for this use.
y
5. Non-crop Areas
a. Pse of Silvex-and Alternatives
on Non-crop Areli
Silvex is registered for control of many broadleaved
£/
and herbaceous weeds in a variety of urban and rural non-
crop areas. Silvex is used because of its relatively low
cost, the broad spectrum of wr.eds it controls and its
selectivity for control of undesirable plant species.
Generally, the weed control achieved on these sites does
not ccnfer significant economic benefits.
Recent data on the usage of silvex for non-crop
areas is not available. However, a 1974 publication
reported that 60,000 lbs. a.e., of silvex were used for
general maintenance on 30,000 acres of grounds at
industrial, commercial and institutional sites. This
7/ "Non-crop areas" include: fencerows, hedgerows, fences
(not otherwise included in suspended uses, e.g., rights-
of-way, pasture); industrial sites or buildings (not
otherwise included in suspended uses, e.g., rights-of-way,
commercial/ornamental turf); storage areas, waste areas,
vacant lots, parking areas.
8/ The weeds are numerous; they include the following
Broadleaved plants—pigweed, ragweed, lambsquarters,
horsenettle, cocxlebur, morningglory—and woody plants—
poplar, Cottonwood, wild cherry, maple, blackberry,
honeysuckle, poison ivy, and wild grape.
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area is a snail proportion (1.7%) of the 1.8 Billion acres
treated with herbicides for grounds maintenance.
Numerous chemical and non-chemical controls are
available as alternatives to silvex. Chemical alter-
natives include herbicides, such as 2,4-D, picloram,
dicamba, AMS, or amit al?. The most comparable alter-
natives are combination products, such as 2,4-0 and
picloram or 2,4-D and dicamba. Soil sterHants, such as
sodium borate or sodium chlorate, control weeds that
silvex controls but are effective primarily as preventive
controls. Subsequent infestations sometimes may require
follow-up treatments with conventional herbicides.
Mechanical methods of control, such as mowing or
shearing, or manual methods could also serves as alter-
natives to silvex.
The efficacy of the alternatives compared with that
of silvex is not known. The spectrum of weeds controlled
will differ from that of silvex for the individual active
ingredients. However, silvex's weed spectrum may be
approximately fairly closely by using a combination
product or by using multiple applications of different
herbicides. It can be assumed that products listing
weed species controlled by silvex on their labels are
as effective as silvex at controlling those weeds.
-------
Generally, no more than one treatment with silvex
is needed annually to achieve control of the problea
weeds. Zn some circumstances, one treatment will give
comparable length of control of silvex, but other
herbicides, such as 2,4-D alone or amitrole, may require
more than one treatment annually. The length of control
with mechanical or manual means is unknown.
b. Economic Impact"of Cancellation
of Sllvex for won-crop Oses
In general, effective alternatives to silvex exist
for non-crop sites. Effective alternative combination
products which provide equally long-term control at a
comparable price are registered and available. Impacts
on users of silvex will be felt in the form of increased
control costs for the combination alternatives.
Little if any impact is expected at market and
consumer levels because effective alternatives are
available and because the economic value of weed control
on non-crop sites is very small.
30-
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C, Determinations-on-Apparent treasonable
Adverse Effects
For the reasons set forth in detail in the
Position Document, the Agency has made the following
determinations relating to the apparent unreasonable
adverse effects on the non-suspended uses of silvex:
1. Determinations•on Rangeland Bse
The Agency has determined that the use of silvex on
rangeland appears to pose risks which are greater than
the social, economic, and environmental benefits of the
use. The Agency has further determined thac the available
data on the exposure potential and benefits of use on
rangeland are to some extent uncertain and/or incomplete,
and that the necessary information may be developed
through a public hearing for the review of these questions.
Accordingly, the Agency has determined that Ih? use of
silvex on rangeland appears generally to cause unreasonable
adverse effects on the environment when used in accordance
with widespread commonly recognized practice.
Determinations•on Rice Oae
The Agency has determined that the use of silvex on
rice appears to pose risks which are greater than
the social, economic and environmental benefits of the
use. The Agency has further determined that the available
data on the exposure potential and benefits of the rice use
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are to some extent uncertain and/or incomplete, and
that the necessary information may be developed through
a public hearing for the review of these questions.
Accordingly, the Agency has determined that the use of
silvex on rice appears generally to cause unreason-
able adverse effects on the environment when used in
accordance with widespread and commonly recognized
pr act ice.
3. Determinations on Sugarcane•Pse
The Agency has determined that the use of silvex on
sugarcane appears to pose risks which are greater than
the social, economic, and environmental benefits of the
use. The Agency has further determined that the available
data on the exposure potential and benefits of use on
sugarcane are to soiae extent uncertain and/or incomplete,
and that the necessary information may be developed
through a public hearing for the review of these questions.
Accordingly, the Agency has determined that the use of
silvex on sugarcane appears generally to cause unrea-
sonable adverse effects on the environment when used in
accordance with widespread and commonly recognized
pr act ice.
4. Petermlnations on Orchard Pse
The Agency has determined that the use of silvex on
orchards appears to pose risks which are greater than
-------
the social, economic and environmental benefits of the
use. The Agency has further determined that the avail-
able data on the exposure potential and benefits of the
orchard use are to some extent uncertain and/or
incomplete, and that the necessary information may b^
developed through a public hearing for the review of
these questions. Accordingly, the Agency has determined
that the use of silvex on orchards appears generally to
cause unreasonable adverse effects on the environment
when used in accordance with widespread and commonly
recognized practice.
5. Determinations on Hon-*frop Kses
Th* Agency has determined that the use of silvex on
fences, lumber yards, refineries, non-food crop areas,
storage areas, wastelands, vacant lots, tank farms, industrial
sites and other non-crop areas, not subject to the emergency
suspension orders (i.e., the suspension orders applied to
forests, rights-of-way, pastures, home and garden, aquatic weed
control/ditch bank and commercial/ornamental turf) appears
to pose risks which are greater than the social, economic
and environmental benefits of che use. The Agency has
further determined that the available data on the exposure
potential and benefits of the non-crop uses ate to some
extent uncertain and/or incomplete, and th.it the necessary
-------
information may be developed through a public hearing
for the review of these questions. Accordingly, the
Agency has determined that the non-crop uses of silvex
appear generally to cause unreasonable adverse effects
on the environment when used in accordance with
widespread i.nd commonly recognized practice.
D. Initiation of Reqolatory Actions
Based on the determinations summarized above
and developed in detail in the Position Document, the
Agency is initiating the following regulatory actions
and this document shall constitute its notice of intent
to initiate these actions:
(1) issuance of a notice of intent to hold a
hearing pursuant to FIFRA $6(b)(2) to
determine whether or not to cancel the
use of silvex on rangeland;
(2) issuance of a notice of intent to hold a
hearing pursuant to FIFRA 56(b)(2) to
determine whether or not to cancel the
use on rice;
(3) issuance of a notice of intent to hold a
hearing pursuant to FIFRA $6(b)(2) to
determine whether or not to cancel the
use of silvex on sugarcane;
34-
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(4) Issuance of a notice of intent to hold a
hearing pursuant to PIFRA 56(b)(2) to
deternine whether or not to cancel the
orchard uses of silvex;
(5) issuance of a notice of intent to hold a
hearing pursuant to PIFRA S6(b)(2) to
deternine whether or not to cancel the
non-crop use of silvex.
B. Statement of Issues
In accordance with S164.23 of the Agency's
Rules of Practice (40 CFR 164) , this part of the
notice states the questions on which evidence relative
to the non-suspended uses of silvex shall be taken at
the $6(b)(2) hearing.
With respect to the use of silvex on rice, range-
land, sugarcane, orchards, and non-crop areas, evidence
V
-will be taken as to the following questions:
(1) Whether the use of silvex on rangeland
generally causes unreasonabi adverse
57 Because the Agency plans to propose that this FIFRA
7(b)(2) hearing on the non-suspended uses of silvex be
consolidated with a proposed FIFRA 6(b)(2) hearing on
the non-suspended uses 2,4,5-T and the FIFRA 6(b)(1)
hearing, already in progress, for the suspended uses of
2,4,S-T and silvex, the consolidated hearing would review
uses of both silvex and 2,4,5-T. The statement of issues
refers only to those issues which are specific to the non-
suspended uses of silvex. It is important to emphasize that
this Notice is specific to the non-suspendrd uses, and th t
other issues would be addressed in the hearing as a whole.
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effects on the environment when used in
accordance with* widespread and
commonly recognized practice;
(2) Whether the use of silvex on rice
generally causes unreasonable adverse
effects on the environment when used in
accordance with widespread and commonly
recognized practice;
(3) Whether the use of silvex on sugarcane
generally causes unreasonable adverse
effects on the environment when used in
accordance with widespread and commonly
recognized practice;
(4) Whether the use of silvex on orchards
generally causes unreasonable adverse
effects on the environment when used in
accordance with widespread and commonly
recognized practice; and
(5) Whether the use of silvex on non-crop areas
generally causes unreasonable adverse
effects on the environment when used in
accordance with widespread and commonly
recognized practice.
(6) Whether the use of silvex on rangeland,
-------
rfce, sugarcane, orchards, and non-crop
areas will generally cause unreasonable
adverse effects on the environment when
used in accordance with widespread and
commonly recognized practice unless
modifications more restrictive than those
currently employed are accomplished; and
(7) Whether, if modifications to the terms and
conditions of registration arc accomplished,
the labeling of silvex products for these
uses will comply with the provisions of FIFRA.
In considering these issues and whether or not to
participate in a hearing on these issues, it should be
clearly understood that these ind other uses of silvex
may be cancelled as a result of evidence presented and
actions taken in the Section 6(b)(2) hearing.
IV. Procedural Matters
This Notice of Determination notifies the United
States Department of Agriculture, the Scientific Advisory
Panel, pesticide registrants and users, and other
interested parties of the Agency's preliminary determi-
nations relating tc the risks and benefits of the
non-suspended uses of silvex, and provides these entities
and individuals with opportunity to comment on these
determinations.
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As discussed in section XI of this notice, the
Agency's decision to initiate the regulatory actions
described in section III ruust be referred for review by
the Secretary of Agriculture and the Scientific Advisory
Panel. I.i accordance with FIFRA, the EPA position
document setting jEorth in detail the reasons &nd factual
bases for the regulatory actions which the Agency proposes
and this notice of determination are being transmitted
immediately to the Secretary of Agriculture and to the
10/
Scientific Advisory Panel for comment.
The Agency also is transmitting copies of these
documents to pilvex registrants, and is offering
registrants and other interested parties an oppor-
tunity to comment on the bases for the Agency's action
by making copies of the Position Document available
upon request. Interested persons may rece copies of
10/ FIFRA Section 6(b) also provides that upon a finding
5y the Administrator that suspension of a pesticide
registration is necessary under S6(c) of FIFRA to prevent
an imminent hazard to human health, he may waive these
external review requirements. In his Emergency Suspension
Orders Regarding Registrations of Pesticide Products
Containing Silvex, the Administrator made such findings
(44 FR 15901, March 15, 1979). Accordingly, in the
Notices of Intent to Cancel the Registrations or Change
the Classifications of Pesticide Products Containing
Silvex and the Statement of Reasons (44 FR 15919,
March 15, 1979), the Administrator specifically invoked
that authority and waited the external review require-
ments for the actions .nitiated by the Suspension Orders.
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the documents by communicating their requests to
Michael Dellarce, Project Manager, Special Pesticide
Review Division (TS-791), EPA, Room 447, 401 M St. S.W.,
9
Washington, D.C. 20460. Registrants and other interested
persons will be given the same period of time to submit
comments —30 days—that FIFRA provides for comments
from the Secretary of Agriculture and the Scientific
Advisory Panel.
After completion of these review procedures, the
Agency will consider the comments received and publish
an analysis of them, together with any changes in the
regulatory actions announced in this notice which it
determines are appropriate.
Die Agency's analysis of the comments received during
the external review period may lead to withdrawal or
modification of the section 6(b)(2) notice of intent to
hold a hearing. Alternatively, if the Notice is not
Withdrawn, the Agency intends to petition the Adminis-
trative Law Judge to consolidate the FIFRA section
6(b)(2) hearing on the suspended uses of silvex with
the FIFRA section 6(b)(1) hearing on the suspended uses
of silvex.
Until this external review phase is concluded and
the Agency Issues final notices, it is unnecessary for
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registrants or other interested persons to request
a hearing to contest any regulatory actions resulting
from issuance of this notice.
All comments on the proposed actions should be sent
to the Federal Register Section, Proaram Support Division
(TS-791), Office of Pesticide Programs, EPA, Room 447,
East Tow^r, 401 N Street, S.W., Washington, D.C. 20460.
In order to facilitate the work of the Agency and of
others interested in inspecting the comments, registrants
and other interested persons should submit three copies
of their comments. The comments should bear the
identifying notation QPP/30000/ -, and should be submitted
on or bef
Dated:
\ V_/»teven D. JeUIinek
Assistant Administrator
Xpr Toxic Substances
40-
I
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SILV1I: POSITION DOCUMEMT 1/2/3
U.S. ENVIRONMENTAL PROTECTION AGENCY
PROJECT MANACER: MICHAEL DELLARCO
9
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Silvex: Position Docuaent
CONTENTS
Pai
I. Introduction
A. Legal Authority: Statutory Provision*..
1) Statutory Provisicss
2) The IPAft Process
B. Background Information Relating to
ilvex
1) Cheaical/Physical Charactariatica.
2) Manufacturing Procaaa and Contam-
inants
3) Registered Uses and Production.... 10
4) Environmental Fate 1
a) Degradation 1
b) Persistence: Soil 1
c) Persistence: Water 1
d) Tranaport. 1
e) Pish and Wildlife 1
£) Bioaccuaulation 1
(3) Reeiduea in Man and Aniaala 1
(6) Residues in Food Products 2
C. Regulatory History 2
(1) Tolerances 2
(2) Other Regulatory Action 2
II. Risk Analysis 28
A. Toxicity Tests in Aniaals 30
(1) Adverse Reproduction Effects...... 30
(a) Exposure of Test Aniaals to
TCDD 31
(i) Fetotoxic and Eabryo-
lethal Effects 31
(ii) Skeletal Anoaalies 37
(iii) Injury to Internal
Organs 38
(b) Exposure of Test Aniaals to
Silvex 40
(c) Risk of Adverse Reproduction
Effects 42
(2) Oncogenic Effects in Test Aniaals. 44
(a) Exposure of Test Aniaals to
TCDD 44
(b) Effects ot' Silvex 46
(c) Risk of Oncogenic Effects.... 47
(3) Conclusion 47
B. Exposure Resulting froa the Use of
Silvex 48
» -i-
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Put
(1) Expoaure Due co Silvex Use on
Rice 46
(a) Direct Expoaure froa Atrial
Drift 49
(b) Contaaination of Surface
Water 50
(2) Expoaure Due to Silvex Oae on
Rangeland 51
(a) Dae Practicea and Popula-
tiona Expoaed... 51
(b) Hater and Soil Reaiduea...... 53
(3) Expoaure Due Co Silvex Oae on
Applea 56
(4) Expoaure Due to Silvex Oae on
Peara 57
(5) Expoaure Due to Silvex Oae on
Pruoea 58A
(6) Expoaure Due to Silvex Oae on
Sugarcane 5SB
(7) Expoaure Due to Silvex Oae on
Non-crop Sitea 60
C. Ep ideai o logi ca 1 Da:a 61
111. Preliainary Benefita Analytia of Silvex
Oae on Range, Rice, Orcharde, Sugarcane,
and Non-crop Areaa 64
A. Introduction 64
B. Suaaary of Findinga 66
(1) Rangeland 66
(2) Riee 67
(3) Orch arda 68
(4) Sugarcane 70
(5) Non-crop * 70
C. General Production and Oae Pattern 71
D. Preliainary Benefita Analyaia of
Silvex Oae on Rangeland 72
(1) Current Oae 72
(2) Evaluation of Silvex and Alter-
native 7 3
(3) Econoaic Xapact. 74
E. Preliainary Benefita Analytia of
Silvex Oat on Rice. 75
(1) Currtnt Oat 75
(2) Evaluation of Silvtx and Alttr-
na t iv t a 7 7
(3) Econoaic lapact 71
F. Prtliainary Btntfita Analytia of
Silvtx Oat on Orcharde 79
(1) Currtnt Oat 79
-ii-
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f ata
(2) Iva luac ioa of Silvas and A1car-
aa c £>¥ aa*#«»*«»*..•»•**••••*«•••••» Si
(3) tcoaoaie lap ace.... S3
(•) Caaara I Coaaidaratioaa 83
(b) Baar Iaptcci.. S3
(e) Coaauaar Xapaeca I?
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Silvas : Position Docuaant
I. IWHODOCTIOW
During eha pace two yaara, eha Environaaneal Protection
Agancy (EPA) has b««n gathering inforaaeion about eha closely
ralatad phanoxy herbicides, 2-< 2 ,4 ,5-t rich lorophaaoxy )
propionic acid (aiivas) and 2,4,5-t richlorophenoxy acetic
acid (2,4,5*1), a* pare of ies Rebuttable Presuaption
Against Kagiatration (ftPAt) orocati in order to daearaina
whether tha ragirtraeiona of tha«a paaeieidaa ahouid b«
coneinued. Th is review was pr rap ted in pare by a tud iaa
ah owing that silvex, 2,4,5-T, and/or fCDO (2,3,7,8-taerachlor-
diban.-o-p-dioxin), eba dioxin contaainaat of both 2,4,3*7
and aiivas cauaad reproductive and oncoganie affacea in
Caac an iaa 1*.
On April 11, 19 78, tha Agency iaauad a noc ica of rebu ee-
abla pr eauape ion againae all regiaeraeiona of tha harbicida
2,4,3-erichIorophenoxyacetic acid (2,4,3-T) [43 Ft 17116,
21 April 1978). Subaaquanely, on fabruary 28 , 1979, reaponding
in pare to information developed through tha 2,4,5-T
KtAK, tha Adainiaeraeor ordered eba aaarganey suspension of
silvex for foresery, vights-of-way, pastura, aquatic weed
control/diecbbanka, boaa and gardan, and coaaa rcial/ornaaantal
eurf uaaa ("auapandad uaaa"} (44 Ft 13897 , 1 3 March 1979).
At eha aaaa eiaa, eha Adainiaeraeor also iaauad noeicaa of
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iataac to cancal chaaa ui«i. Thaaa accioaa initiatad public
haariofa on iaauaa ralating to cba riaka and baaafica of cbaaa
Bacauaa cba data raviawad and aaalyxaw for cba
auapaaaioa accioo indicacad chat cba auapaadad uaaa of
ailvax eraacad an iaaiaaac bacard for huaaa haalth, cba
Agaecy accalaraCad ica raviaw of cba uaa of ailvax on
•« /
raagalaad, rica, augarcana, orebarda and non-crop— araaa
(aoa-auapaadad uaaa). Thaaa uaaa vira aaaaaaad in caraa
of Cba IPAt riak critaria (40 CFt 162'.ll(a)), uaiag data
praaaacad ia cba Eaargaacy Daciaioa aad Ordar auapaadiag
carcaia uaaa of ailvax (44 Ft 13(97, 13 Marcb 1979), daca
aad iaforaacioa oa TCDD aubaitcad ia rabuttal to cba 2,4,3-1
KPAK, aad ocbar ralavaac iaforaacioa. Froa cbia raviaw, cba
Aganey baa coacludad cbac whaa uaad ia accordaaca wich
widaapraad aad coaaoaly racogaiaad praccica, cha aoa-auapaadad
uaaa of lilvu appaar Co cauaa uaraaaoaabla advaraa affacca
oa cba aaviroaaaac. Aa a raaulc, cba Agaacy ia iaauiag a
aocica of iacaac to bold a haariag co dataraiaa wbathar cha
aoa-auapaadad uaaa of ailvaz abould ba caacallad.
»/
w tuapaaaioa procaadiaga coaaaaead oa April 19 , 1979 ,
buc wara diacoacinuad oa Hay 13, 1979 afcar all ragiacraaca
withdraw froa cha haariaga. Tha firat pra-haariag
ccafaraaca for cha caarallatioa procaadiaga vai hald oa
Juaa 3, 1979; cba foraal haariag will probably bagia ia
##.cha fall.
— Tha aoa-erop uaaa of ailvas iacluda uaa oa faacarowa,
hadgarowa, faacaa (aoc otharwiaa iacludad in auapaadad
uaaa, a.g., righta-of-way, paatura); induatrial aicaa or
buildiaga (aoc ocharviaa iacludad ia auapaadad uaaa,
a.g., righca-of-way , coaaarcial/oraaaaacal turf);
acoraga araaa, waata araaa, vacant lota, parkiag araaa,
aad cba ocbar aicaa for which ailvas uaa ia ragiacarad.
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This Potieioa Docuaaac rtfitwi cha Agaacy'• ••¦•••¦•He
of Cte* ricks aad baaafies of eh« noa-s uspaadad ua«3 of
silvax, p«re icularly ua« oo rie«, raagalaad , ?ugare aaa. aad
orchards, aad asp 1 aias eha b«sas for Cha Agaacy'a dacisioa
Co coavaaa • baariag Co daearaiaa vhaehar Co caaeoL Chasa
uati.
Th is Foaicioa Docuaaac coacaiaa four parca. Part 1,
ehis iac roduc c ioa , suaaarixaa cha lagal proviaioaa ral ac iag
co cha ragiscraeioa aad caaeallacioa of pas cicidas, aad
backgrouad iaforaaeioa oa cha chaaisery aad usas of silvax.
Pare II ia aa avaluaeioa of cha da ca aad iaforaacioa ralaciag
Co Cha risks assoelacad wich cha aoa-sus paadad usas of
•iIvax. This pare iaeludas Cha Agaacy's ana ly•is of Laboratory
daca oa silvax aad TCDD, iaforaacioa oa TCDD davalopad
chrough cha 2,4,5-T tfAK raviav, iaforaacioa oa axposura
pocacial of cha usas of silvax, aad ochar risk coca idaracioas.
Pare III raviavs Cha baaafies as aoei scad wich cha aoa-suspaadad
usas of silvax oa a usa-by-usa basis. Pare IV discussas aad
axplaiaa cha basas for Cha dacaraiaacioa Co hold a haariag
oa cha risks aad baaafies of cha orchard, sugarcaaa, rica,
raagalaad aad cha aoacrop araa usas of silvax.
A. Latal AuChority
(I) SeaeuCorv Provisions
Tha Padaral tasaceicida, Puagicida, aad Kodaacicida
Ace, as aaaadad ("PXFftA") {? U.S.C. 136 ac sag.1 raqui ras
cha Kavi roaaa tic a I Proeac c ioa Agaacy (CPA) co ragu 1 a ea
all pasCicida produces chrough raviav of Cha risks aad
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banafita of tha uses of theae cheaicala. A key proviaiou ia
Section 12(a)(1)(A) of FIFEA which apeci'.iea that «11
peaticide producta auat be regiatered by ch« Adainiatrator
bafora they aay ba aold or diatributed. Bafora a peaticide
aay ba ragiatarad, hovtvtr, tha Adaiaiatrator auat deteraine
that ica uaa will not raault in "uarmoDibla adverae
affacta on tha •nviroaatnt," defined in Saetion 2(bb) of
FXFftA aa "any unraaaonabla riak to aan or tha environaent,
taking into account tha econoaic, aocial, and anvironaantal
coata and banafita of tha uaa of any paaticida." In othar
worda, any daciaion on paaticida ragiatration auat taka into
account both riaka and banafita froa tha peaticide'a uaa.
Under Section 6(b) of FXFK.A the Adainia trator aay
cancel the regiatration of a peaticide or change ita
teraa and conditiona of regiatration if it appeara that the
peaticide "when uaed in accordance with wideapread and
coaaonly recognised practice, generally caue-ea unraaaonabla
advaraa effecta on the environaent." For exaaple, the
Adainiatrator aay cancel the regiatration of a peaticide, or
change ita teraa and conditiona of regiatration, if ita
labeling doea not coaply with the aiabranding proviaiona of
F1FKA which require the labeling to contain the language "adequate
to protect health and the environaent" (FIFKA 2(q) ]. The
Adainiatrator aay alao change the elaaaification of any uaa
of a paaticida if ha deterainea that auch a change "ia
neceaaary to prevent unreaaonable adverae effecta on the
environaent" (FIFHA 3(d)(2)].
-4-
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Tvo typea of proceedings are available under section
6(b) of FIFRA Co cancel a pesticide registration, or aodify
Cha taraa and coadicioaa of a paacieida regiaeration:
FIFRA Saccion 6(b)(1) proceedings and FIFRA Section 6(b)(2)
proceedinga. Ia general, FIFRA section 6(b)(1) proceedinga
begin with a notice specifying the regulatory action which
the Adainistrator is proposing. This action cakes
effect autoaatically, without hearings, at the expiration of
a notice period prescribed by statute, unless the registrant
or a person adveraely affected by the notice requests a
hearing within that period. If a hearing is requested, the
regulatory action propoaed by the Adainistrator does not
cake effect; however, at the conclusion of the hearing, the
Adainistrator aay iaplaaent the proposed action, if he
deterainea that it ia appropriate to do ao baaad on the
record developed ia the hearing.
Section 6(b)(2) proceedings, on the other hand,
begin with a general notice specifying the issues which
the Adainistrator deairaa to have explored at a hearing.
Onlike section 6(b)(1) proceedings, Section 6(b)(2)
proceedings do not include an initial proposed regulatory
solution which would take effect autoaatically if a hearing
ia not requested. Interested persona way participate
ia the hearing; at the concluaion of the hearing, the
Adainistrator aay take whatever action ha daeas appropriate,
baaed upon the record developed in the hearing, including
cancellation of a pesticide registration or aodifieation of
the teraa and conditions of registration.
-5-
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(2) The RPAR ProctM
Th« Rebuttable Presuaption Against Registration
(RPAR) proem provides a aechanisa through which tht
Agency gathers risk aod benefit information about pesticides
which appear to pose risks of adverse effects to huian
health or the environaent which aay be unreasonable.
Through this process, the Agency invites pesticide registrants,
environaenta1 ists, and other interested persons to participate
in the Agency's review of suspect pesticides and in reaching
an op#n and balanced decision on the continued use of the
pe stic ides.
The RPAR regulations at 40 CFR 162.11 (a)(5)
prescribe regulatory criteria for the Agency's preliainary
assessaent of a pesticide's health and environaenta1 affects
and provide that an RPAR shall arisvv if the Agency deteraines
that any of the risk criteria have been aet. The Agency
generally announces that an RPAR has arisen by publishing a
Notice in the Federal Register. Once a rebuttable presuaption
has arisen, registrants, applicants, and interested persons
aay subait evidence in rebuttal or in support of the presuaption.
Inforaation on the econoaic, social, and environaental
benefits of any use of the pesticide aay *lso be subaitted.
If the presuaptions of risk are not rebutted,
the benefits evidence subaitted and that gathered hy the
Agency aust be evaluated and considered in light oi' the
risk inforaation. If the Agency deteraines that the risks
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appear co oucweigh cha benefits, Che Agency can ioiciace
accion under FIFRA secCioa 6(b)(1) Co cancel Che registration
for a use or to modify Che terma tad condiciona of regietracion
for Che uii. FIFRA Section 6(b)(2) proceeding! are appropriate
(aaoag other situations) whare a peacicide us* appears co
poae unreasonable adverse effects, and additional information
oo riaka or benefica voulu aaaiac the Agency in making a
deciaion oo Che ultimata face of Che peacicide use.
B. Background Information Relatin co Silvex
(1) Chemical/Physical Characceriacica
The herbicide ccamooly known aa silvex, 2-(2,4,3-
Tr ichlorophenoxy) Propionic Acid—haa ao empirical
formula of CqH^CL^O^ and a molecular weight of
269.33, wieh a melting poinC of 181.6°C. Ac 25°C,
ic ia essentially insoluble in wacet- (0.0141) but is relatively
soluble ia organic solveocs such as acecooe (13.22), methanol
(10.3X), echer (7.131), and Sensane (0.16X) (R*v, 1970).
;he eacera of ailvex are formulaCed co be emu 1 s i.i i ab le in
vaCer aod soluble ia moac o'ls, while its smine salts are
soluble io water buc ioaoluble ia petroleum oila (Packer,
1973). A water aoluble silt with criechaoolamine, called
ailveramine, ia alao produced.
Also called 2-(2 ,4,3-Crichlorophenoxy) propanoic acid,
Tylvex, 2,4,3-TP or feooprop.
-7-
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(2) Manufacturing Proceaa and Contwininti
Silvex it produced coaatrcially by hydrolyaia of
1,2,4,5-tetracM.orobenzene uaiag methanol and aodiua hydroxide
co yield the aodiua tale of 2,4,5-Crich1 oropheno 1 (2,4,5-TCP).—^
Thia produce ia reacted with 2-chloroproponic acid in hoc
aqueoua aodiua hydroxide to form che aodiua aalc of aiivex,
which ia converted co aiivex bv che addicion of acid. The acid
form of aiivex can be reacced readily wich a variety of
alcohola Co produce a large aelection of eateri, and wich
aninea Co produce aaine aalta (Packer, 1975).
During the firat acep in the aanufacturing proceaa
of aiivex, if teaperature and preaaure are not carefully
controlled, condenaation rtactiona can occur to produce
large guantitiea of highly toxic polych1 orinated dibenio-p-
dioxin sontaainanta. The tera dioxin doea not apply to any
one coapound but to a group of related aubatancea, which are
diatinguiahed by the nuaber and orientation of chlorine atoaa
they contain. The particular dioxin foraed ia dependent on
the ch1orophenola preaent (Poland and Kende, 1 976). Dioxin
toxicity variea with the poaition and nuabera of chlorinea
attached to th« phenol ringa.
2,4,3-TCP ia the aubject of a aeparate Rebuttable
Preauaption Againat Regiatration (RPAR) Poaition Docuaent.
It ia diacuaaed in thia docuaent becauae both it and ita
contaainant 2,3,7,8-tetrachlorodiben«o-p-dioxin (TCDD) aay
be preaent in aoae coaaercial aiivex and in aiivex aaaplea
uaed in aniaal experiuenta.
-8-
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In the silvex manufacturing process an especially
toxic dioxin, 2 , 3 , 7 ,8-tatrachlorodibenzo-p-dioxin (TCDD), is
formed whan the reaction temperature is excessive (Fike and
Seaton, 1962), most commonly at temperatures above 160°C.
Halognns at th«i 2, 3, and 7 positions are known to produce
the moat toxic dioxins (Burger, 1973). In tne case of TCDD,
the chlorine atoms are Attached at the 2, 3, 7, and 8
positions which are considered the most toxic positions
possible (Schwetz et al., 1973). The dioxin contaminant
in silvex is of particular concern because of its extremely
high toxicity, and because of the apparent inability of
manufacturers to produce silvex without the contaminant,
• /
TCDD.-'
TCDD occurs as a white crystalline solid. It is
99.3X decomposed at 800°C. TCDD has the following solubility
in various solvents at 25°C (Harvey, 1973):
Solvent Solubility (wt. per cent)
Acetone 0.011
Bensene 0.057
Dime thy Isulfoxide <0.01
Methanol 0.001
Water 0.00000002 (0.2 ppb)
Current methods for manufacturing silvex produce
TCDD as a by-product of the manufacturing process.
Although silvex manufacturers attempt to remove
this contaminant, TCDD cannot be completely removed.
An EPA contract laboratory haa measured the TCDD con-
cent in 8 recently produced commercial samples of technical
grade silvex from two different manufacturers. The contrac-
tor reported that the TCDD content in these samples ranged
from 0.012 to 0.024 ppm (limit of detection 0.01 ppm)
Therefore, because TCDD is present as a low-level coritaminant
in commercial samples of silvex, references in this document
to "silvex" or the "pesticide product" mean silvex that is
contaminated with TCDD.
9
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Siuct 1950, doic of the chemical industry has known
chat large quantities of TCDO nay b« formed as a byproduct
of the 2,4,5-TCP manufacturing process if the procedures are
not carefully controlled. After concern arose in 1969 about
the extremely toxic effects of TCDD, manufacturing methods
were changed end carefully controlled by manufacturers. By
1971 industry had reduced TCDD content in commercial pheooxy
herbicides to less than 1 ppm (Milnes, 19*1; Crieg et si., 19 73 ;
Hussein et el., 1972). Current U.S. manufacturing specifications
require silvex presently being sr,ld to contain lass than 0.1
ppm TCDD.—' (Dow Chemical Co., FIFRA Docket No. 295).
(3) Reiistered Uses and Production
Silvex is a selective herbicide for control of
woody plants, broadleaf herbaceous weeds, and aquatic weeds.
Registered uses include selective weed control in rice,
sugarcane, pastures, rangeland, rights-of-way, forest site
preparation, conifer release, industrial areas, fence
rows, highways, commercial turf, home lawns, uncultivated
agricultural land, waste land, aquatic sites (still water,
lekes, and ponds) and ditch banks. At sub-herbicid a 1 concen-
trations, silvex is used as a plant regulator to retard
preharvest fruit drop on plums (prunes), pears, and apples.
Silvex is effective against a number of weed species
resistent to 2,4-dichlorophenoxy acetic acid (2,4-D) and
2,4,5-T. Among the silvex target species ere wild lettuce,
* / See footnote, page 9.
-10
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chicory, aighcabada Ciaviaa. «11 igacorvaad , pose oak,
blackjack oak, sand sbinnary oak, yucca, sale eadar, chickvaada,
apurgaa, black asdic, and poiaoa ivy.
Silvax ia commonly applied poacaaargaaca is watar,
oil, o il-waear, aad granular carriara uaiag coavaacioaal
aarial aad grouad «qui paaae. Th« aosC coaaoaly uaad
foraulacioaa ara eha low to la c ila aa cara for brush, rica ,
augi»rcana aad aixeuraa with 2,4-D, or 3 ,6-d ichloro-o-
aniaie acid (dicaaba), for lawn aad turf vaad coacrol
(Tboapaoa, 1973 ). Silvax alao occura ia foraulac ioaa aixad
with criachaaolaaiaa (ailvaramioa) or 2,4,5-T. Applicacioo
ratal vary froa 0.73 to 4 pouada acid aquiva laae (a.a.)/acra,
6 co 16 pouada a.a./ABG aud 6 co 8 pouada a.a./acri f c.
dapaadiag upon ea rga e apacias aad uaa ai ca.
Silvax has baaa producad aa a ragiacarad paa eicida ia
cha Unicad Seaeaa aiaca 1933. Accordiag co EPA racorda,
apprsxiaataly 100 coapaaiaa hold Fada ral rag i a cr ac ioaa aad
foraulaea 247 ragiacarad producea; 14 coapaaiaa hava foraac
acaca ragiacracioaa aad foraulaca 23 producea (Maao, 1979a).
(4) lovlroaaaacal Fata
Ca) Dagra<*ac ioo
Thara ia lieela data available ragardiag
cha paraiacaaca of ailvas; however, aeveral actadiaa of cba
dagradafcioa of pheaylaIkaaoie acida, a group Chat iacludea
ailvas, iadicaCa Chat cartaia of chaaa chaaicala caa ba
dagradad phocochaaica I ly or biologically (Croaby aad TuCaaa,
-11-
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196S) have found degradation is liaited when a halogen aeoa
occurs ac Che acta position of an alkylated aromatic ring
coapound, or vhen the aroaatic ring is linked to the alkyl
ether side chain at the alpha position, independent of the
halogen orientation. Both of these conditions exist in the
silvex aolecule. A likely degredation product of silvex
would be 2,4,5-trich1orophenol. However, efforts to produce
2,4,5-trich1oropheno 1 by treating saturated solutions of
silvex with different concentrations of hydrochloric acid or
sodiua hydroxide at rooa teaperature have not been successful
(Bailey, et.al., 1970). Also, silvex was stable to irradi-
ation in the dry state, and could be photolysed to 2,4,5-TCP
only when irradiated as th» soaiua salt in water (Crosby,
19 69).
Fig. 1. Silvex aolecule illustrating the alpha carbon
atoa on the alkyl chain and the aeta position of the
chlorine atra at position 5 of the aroaatic ring:
HCOOH
(b) Persistence: Soils
Silvex has a relatively short half-life and appears to
have an affinity for soil particles. Wiese and Davis (1964)
•stiaated silvex aoveaent through soil to range froa 3 to 6
-12-
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iacbaa, uaiag Fullua ailey clay Lota. Alcoa ( 197 3) datar-
aiaad chat eba balf-lifa of ailvax ia graaalaad aoil via 14
daya. Siaitar raaulea vara raporcad by Laag aftar applicaeioa
of ailvas co graaaaa.
Vbaa coaaidariag cba paraiataaea of ailvax, tha paraia-
caaea of ica eoacaaiaaac, TCOO, auae alao ba coaaidarad.
lalliag ac al. (1973) fouad ebac TCOO via aoe pbocodaeoapoaad oa
aoil. TCOO via £ouad Co ba iaaobila ia Norfolk aad Lakalaad
aaady loaaa, lagaraeova ailey clay loaa, laraaa elay loaa, aad
Calaryvilla auek, aad vaa aoc laaebad furcbar iato aoil by
raiafall or irrigaeioa. Tb» iavcatigatora obaarvad ebae TCOO'a
paraiataaea via pradictabla aiaea it ia iaaolubla ia vicar.
Dariag aurfaca aroaioa of aoil, bovavar, lacaral craaaporc of
TC8D could occur. Tha paraiataaea of TCDD ia Lakalaad loaay
ac al. (1972). Aftar oaa yaar ebaaa raaaarebara racovarad 56 aad
til of eba origiaally appliad TCDD ia lagaraeova aad Lakalaad
aoila, raapactivaly.
(«) Paraiataaea. Vaeat
Fhatosy cbaaica.a aaeariag vicar aay ba loae by
~olatiliiatioa, dagradatioa, adaorpeioa oa aadiaaae, adaorp-
tioa by biota, aad dilatioa aa additioaal atraaa vaear
paaaaa tbrougb eba aita. Alaoae all autboriciaa agraa cbae
ebara ia adaorpeioa oa boesoa «adiaaae (Bailay ae a 1 ., 1 9 7 0 ;
Fraak aad Coaaa, 1967).
13
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In October 1963, th«. D.S. ecological Survey initiated
a limited prograa of pesticide aonitoring of 11 waterways
is tha vcicarc United Scacaa (Brown aad Nishioka, 1967)
vhirt cba probability of observing pesticide residues would
be greatest. Pesticide* choaea for analysis included the
insecticides aldria, ODD, ODE, DDT, dieldrin, eadria,
heptachlor, heptachlor epoxide, and lindane, aad tbe
herbicides 2,4-D, 2,4,3-T, aad ailvex. Tha auehors reported
that ao herbicide was found at any tiae at any station
during the firat year of the saapling prograa (liait of
detection: 3ppt). Hanigold aad Schulae (1969), reporting oa
the results for October 1966 to Septeaber 1961, observed
that begianing ia August 1967, 2,4-D, silve*. aad 2,4,3-T
had beea detected frequently. Silvex was found in 10 of tbe
233 aaaples at concentrationa ranging froa 0.01 to 0.21
ppb.
The Rational Interiua Priaary Drinking Water Regulations
(EPA, 1977) allow up to 10 ppb of silvex ia drinking
water. lowever, these regulations are aeant to apply ia the
event silvex is found in water. Deliberate addition of
silvex to driakiag water sources is aot sanctioaed by
these standards.
Kearney et al. (1972) concluded tnat contaaination
of underground water supplies with TCDD seeaed very unlikely,
since vertical aoveaent of TCDD did not occur in a wide
range of soil types. The fact that no leaching occurred,
however, would not preclude runoff contaainetion when aoil
eroaion is significant (Balling et el., 1973).
14
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(4) Tr£M£or£
Thara ara f«« published acudiaa tagarding cha
craaslocacioa of ailvax aad ica TCOO coacaaiaaac is plaaea.
laaaaaa aad Joaaa (1971) aaaaurad upcaka of TCDO fro* aoil
by evo crop ipaeiaa. Oaca (Avaaa aativa) aad aoybaaaa
(Clrciaa aax) vara grows ia Lakalaad aaady loaa toil craacad
with 0.06 ppa TCDD. Tba Copa of ebaaa plaaea vara harvaacad
ac iatarrala Co aacuricy. Macura oaca aad aoybaaa copa
eoacaiaad laaa cbaa 1 pare par bilLioa (ppb) TCDO. TCOO vaa
datarcad (dacactioa liaic: 1 ppb) ia aatura oat graia, wbila
ao TCDD vaa fouad ia cba baaa of aoybaaaa. Tba auebora
coacludad ebae aoil upcaka of TCOO by plaata vaa highly
ualikaly, aiaea liccla or ao TCDO via cakaa up by oaca or
aoybaaaa uadar cba eoadiciooa of cbia axpariaaac.
(a) Flab aad Wildlifa
ttaaarally, ailvax aacara ara coaaidarad co ba
aora coxic Co flab aad aquacic lavarcabracaa cbaa cha
ailvax aalea. Tba eoaeaacracioa of auvat chat killa SOS of
Cha auabar of fiah axpoaad (LCjQ) ia 48 hoar or 96 hour
laboracory acudiaa raagaa froa 0.14 co 70 ppa for ailvax
aacara la eoacraac co 14 co 340 ppa for ailvax aalca
(Svahay aad Schaaala, 1943; lilcibraa, 1967; luclar, 1963).
rurcharaora, Cha daea iadleaea that Cha bucoxyachaaol aatar
(III) ia eha aoac cosie ailvax foraultcloa co fiah (laiaarc,
1973). Siailarly, 48-hour aad 96-hour L&jg aaciaacaa for
aquacic iavarcabracaa raaga froa 0.2 co graacar Chan 100 ppa
-13-
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dapeadiag os tbe a il vex formulation used aad eh« spec in
tiatid (Burtler, 1 963 ; Crosby tad Tucker, 1966; Saaders,
1970).
Id concrnt, bantbic feuaa were observed to increase
ia direct proportion eo tbe aaouat of lilvtx applied co a
Mi ssouri pond (Barp aad Caapbell, 1964). Tba poad chat was
pareieioaed aad craacad with 0, 2.8, aad 4.6 ppa of a ilvex
potaa ai ua talc. Tha aoae abuadaac invertebrates aaaplad
throughout tha count of tba 13-aoath atudy vara oligochaata
worms, odonatai, laacbas aad aaaila. Only tba Chrvsopa
(grove flias) populations wara raducad by tba ailvex traataaat,
Coaparat ive data regarding tba toxic affacts of
ailvax foraulatioas ia wild aaaaala or aviaas ia iiaitad
To data, thara have aot baaa any fiald studiaa coaductad oo
tba toxic affacta of a ilvax oa wildlifa; p 'liahed raporta
hava baaa liatad to studiaa of laboratory aad doaastic
aaiaals. Available avidaaca froa aviaa studiaa iadicaca
tbat silvex astars ara aora toxic to youag birds tbaa silvex
acid (Stickel, 1964; Tuckar aad Crabtraa, 1970 aad Heath at
al. , 1972).
Studies by Moffett aad co-workers suggest tbat
silvax is relatively aoa-toxic to boaey bees. Ia separata
experiaeat s, silvex propyleae glycol butyl atbar aster
(PGIEE) was tasted for its effect oa brood production, aad
aortality ia botb aew bora worker bees aad adult bees. The
authors coacluded tbat silvex ia aot toxic to bees aad tbat
-16-
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advara* affacta co hivaa could ba aetributad eo eha usa of
ailvaa with diaaal oil as eha earriar(Moffact ac al., 1972;
Mortoa aad Noffacc, 1972; aad Morcoo at al., 1972).
«
(f ) i-ioaeicu«uliatijO£
Suggaaciwa awidaaca axiats which iadieataa that
•lira* raaiduaa aay paraiat ia wildlifa. la a study of
watar fowl eollaccad whara silvaa had baaa appliad at 20 lba
ai/acra tavaa aoaths aarliar, 36X (5 of 14) of birda aaaplad
eoataiaad silvaa raaiduaa raagiag froa 0.06 to 0.20 ppa.
Siailarly, ia fiald trials of ailvas aa aa aquatic harbieida
by tha O.S. Aray Eagiaaara, ailvas raaiduaa of 0.053 ppa
wara fouad la fiah 33 days aftar silwaa traataaat at 8 lbs.
ai./ac*3.
Voolson at al. (1973) coaductad a study to dataraiaa
if TCDD raaiduaa could ba datactad ia tissua axtracti of tha
bald aagla (lal iaactas laucocaphalua) as a raprasaatativa of
tha top of a food cbaia. Niaataaa bald aagla carcaasas froa
fifcaaa aeataa wara aaaaiaad batv*aa 1966 aad 1971. No
dioaia raaiduaa wara datactad at « Laval of 0.03 ppa TCSD,
tha Howar liait of detactioa. Tba authors stacad chat eha
aaa-dataeeioa of diomia raaiduaa could iaply that thara was
aa diosia build-up ia tha food chaia; that cha build-up was
lata thaa tha datactabla laval of thair analytical aquipaaat;
that tha aaglas aaaaiaad wara aot coataaiaatad although
other saaplaa aight ba; or that othar apacias could faad oa
a diffaraat food chaia to aceuautata dioaiaa.
-17
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Iseasee and Jones (1975) exposed tivtrtl orgaaiaaa in
14
• aodel aquatic ecosysCea Co C-label«d TCDO for up Co 31
daya Co daceraiae cha diaCribuCioa and bioaccuaulacioa
poCancial in an aquacic invironaint. Soil wich 0.0001 Co
14
7.45 ppa adaorbad C-TCDD vaa placad in aquaria coaCaiaing
anaila (Phyaa ap.), a fav acranda of algae (Oedogoniua
£ard_iacua), and old aquariua vaCir eoncaining various
diacoaa, proCoioa, and rocifera. Duckveed (Laana aiaor)
planes vara also addad Co ona aquariua. Saaplaa of daphnida
vara cakaa for analyais ac 30 days, and aoaquico fiah
(Caabuaia affinia) vara addad co aach cank. Thraa days
lacer all of Che organisas wara reaoved for aaalyeia, and
cvo fingarling chaaoal catfish (IcCalurua puaccacua) vara
addad co aach cank and expoaed for aix days.
Tba aucbora acacad chac all organi-ta in bocb craac-
aanc and control Canka proaparad during cbis axpoaura
pariod, indicacing chac TCDO vaa noc toxic ar cna concaoCra-
Cioaa uaad. TCDD aeeuaulacad in all organi»aa. ac Cha
highaac TCOD coacaacracioa (7.45 ppa) algaa aeeuaulacad
6,690 2. '60 PPb TCDD; snails, 1 ,820 ^ 170 ppb; daphnida ,
10,400 2. ppb; and Gaabuaia, 1 ,380 _~ 220 ppb. Cacfiah
vara ooc analysed for TCDD raaiduaa. Ac cha saeond highaac
TCDD eoaeancracion (3.17 ppa), hovever, catfish aeeuaulacad
720 ^ 130 ppb TCDD. Tha authors stated thac accuaultcion in
all of cha case organiaas froa soil eoncaining 0.1 ppb TCDD
is iaportanc ainea chia eoneancracion approaehes che concen-
tration vhieh vould occur uader aoraal field ui, of 2,4,5-7.
-18
-------
certain cireus*cancea (e.g., diacharge of atora runoff froa
recently created rangeland into a aaall pond), water-eroded
•urface soil or debria nay contain enough TCDD for aeaaurable
reaiduea to accumulate in fiah or other aquatic organiaaa.
However, Che author* speculated that TCDO, orginating froa
2,4,5-T applicationa, diacharged into large lake*, atreaai ,
or eatuariea woui.
-------
of 4.0M.9 hr in the firat phase and 16.5^7.3 hr in ch«
second phase. Total recovery of silvex and ies conjugates
in urine and feces ranged from 66.6X to 95.IX of the admin-
istered done vitb a scan value of 80. 31. No trictalcloph*no1
conjugates vere found in the urine. Only small amounts of
silvex and silvex conjugates vert found in feces. The
authors concluded that this aay represent unaLsorbed
compound excreted in bile and eliminated from the body in
feces.
The National Human Monitoring Program for Pesticides,
through its cooperative arrangement with the Health and
Nutritional Examination Survey II (Hanes II project), is
currently analyzing human urine samples for silvex. 2,4.5-T.
and 2.4.5-TCP (Memo.1977). The survey is scheduled for completion
in 1V79; however, preliminary results on 864 samples show
measurable amounts of silvex in 3 samples, at levels as
high as 33 ppm. and trace amounts in 10 samples.
Pheuoxy acetic acids are relatively strong acids.
and animals rapidly excrete them unchanged in their urine
In their study of the fate of atrazine, kuron. silvex. and
2.4,3-T in the dairy cow, St. John et al. (1976) found that
dairy cows given 2.4,3-T and silvex in their feed at S ppm
for four days, completely eliminated both 2.4,3-T and silvex
as soluble salts in the urine two days after dosing stopped.
Sauerhoff at al. (1976) fad rats a single oral dose of 5
1 4
mg/kg C silvex and recovered 77.54^5.05X of the radio-
activity in urine and 16.5W.74X of the radioactivity in
20-
-------
material wn silvex or ailvex ae tabo L i te ( s ) va» aoc conducted
in Che study.
•
Experimental result# suggeat that liver and kidney
are the main aitea for ailvex clearence activity. Sauerhoff
et al. ( 1977) treated rata with a aingle intravenoua injection
of 3 ag/kg or SO ag/kg of ailvex in an aqueoua aolution.
They aacrificed the aniaala at 8 houra and 216 hour* after
injection abd analysed aeveral tiaauea for ailvex. The
14
highest C levela were recorded in the liver and the
kidney at both doaea. Theae findinga were confiraed by
aeparace experiaenta aeaauring the half-life of silvex
clearance froa plaaaa and bile which iadit^«.ed that ailvex
ia rapidly reaoved froa the circulatory ayscea t. the liver
and then rapidly excreted froa the body in urine. Similar
reaulta were obtained in a prelirinary report froa a
two-year chronic toxicity feedir.g atudy with TCOO by uov
Cheaical USA (1977) (reported). Feaale ra*s ingesting 220 ppt
TCDD/day or 2,200 ppt TCOD/day were noted to !ave high TCOD
reaiduea in liver and in fat at both treatment levels. The
preliainary report givea no reaidue data for treated aalea,
or for controla of eithet sex.
Zitko (1972) a. 'ayed chlorinated dibentodio*in reaiduea
in aquatic aniaala, but waa unable to detect theae coapounda
(detection liait: 0.04 ppa for TCD0) in any of aeveral
aquatic aniaala froa Canadian locationa. The author had
aelected apecies froa high trophic levels of the aquatic
-2 1-
-------
food web to measure cumulative pesticide contamination.
More recently, using improved analytical methods for detection
of di?xin at ppt levels, Baughman and Meselson (1973) found
mean TCDD levels ranging from 18 ppt to 810 ppt in fish and
crustaceans taken from Vietnamese rivers in August and
September, 1970. TCDD levels tended to be higher in fish
from interior rivers than in those from seacoast locations.
In comparison, Baughman and Meselson (1973) found less than
3 ppt TCDD in fish obtained in a market in Cape Cod. Massachusetts.
In another study. Matsumura and Benezet (1973) placed TCDD-
coated sand directly in an aquarium containing brine shrimp,
mosquito larvae, and fish (si1verside) . TCDD pickup was low
in fish (2 ppb) and brine shrimp (157 ppb) under the experi-
mental conditions. But mosquito larvae, which are bottom
feeders, showed a surprisingly high rate of accumulation
(4.150 ppb). The authors concluded that TCDD was not likely
to accumulate in as many biological systems as DDT because
of TCDD's low solubility in water and lipids, as well as its
low partition coefficient in lipids.
(6) Residues in Food Products
Available data indicate that silvex residues may occur
in foods. When sprayed on oranges, a silvex ester was
hydrolyted to the free acid, conjugated in the peel and
pe-sisted for several months (Hendrickson. 1969 ). Leidy
¦t al. (1975) did not detect silvex in harvested apples
29 to 91 days after the application of silvex to the ground
-------
cover under apple trees. Bov«v«r, Cochran* at al. (1976)
reported chat direct application of a 20 ppo solution of
silvex to apple tree* (to prevent fruit drop) resulted in
residues in unwashed fruit of 0.097 ppa initially. 0.046 ppa
at harvest (day 10) and 0.036 ppa after 4 months in storage.
Also after storage, washed fruit contained 0.015 ppa; washed
and waxed fruit contained 0.014 ppa.
Studies where cattle and sheep were fed rations
containing silvex for several weeks and than iaaediate ly
slaughtered, indicate that silvex residues ranging froa 0.6
to IS.O ppa can be found in auscle, fat, liver, and kidney.
However, when aniaals were allowed to withdraw froa the
treated feed, residue levels decreased aarkedly, often below
0.03ppa the liait of detection in these studies (Leng, 1972;
Clark, 1 97 3 ), Although Duggan at al. ( 1 96 7 ) reported that
silvnx residues of 0.018 and 0.929 ppa ware found in two
coaposite saaples of dairy product in 1 965- 1966 , silvex
residues have not been detected in total diet studies
since that tine (Martin sad Duggan, 1968; Co rne 1 iuss en.
1970, 1972; Manilas and Corneliussen, 1974),
-23-
-------
(1) Tolerances
A tolerance of 0.05 ppm has been established for
ailvex in or on pears (the raw agricultural commodity"
resulting from post harvest application of the triethanolamine
salt of silvex to pear trees. (40 CFR, 180.340). There are
also interim tolerances of 0.1 ppm for silvex on sugarcane
and pre-harvest application to apples and plums for prunes
(40 CFK 180.319). No tolerances have been set specifically
for TCDD in or on food crops. However, 40 CFR 180.302
establishes a tolerance of 0.0S ppm for hexachlorophene on
cotton seed, with a stated limitation that the technical
grade fungicide shall not contain more than 0.1 ppm TCDD.
The limitation does not constitute a tolerance.
(2) Other
Regulatory Action
Silvex was developed and registered as a
herbicide on brash shortly after Vorld War II.
Since then, it, along with 2,4,3-T, has been the subject of
several Federtl regulatory actions.
Initially, silvex was classified as a non residue,
sero tolerance chemical. However, on April 13, 1966, the
United States Department of Agriculture (USDA) and the Food
and Drug Administration (FDA) published an announcement in
the Federal Register abolishing the "No Residue and Zero
".'o 1 erance" concepts. Future registrations would be granted
-24-
-------
on the basis of either "Negligible Residue" or "Peraissible
Residue." Industry was given until Deceaber 31, 1967, to
comply by obtaining tolerances for residues of silvex in all
treated food, feed products, and byproducts. In addition none of
the old registrations would be continued beyond December 31, 1970.
Following this action, a series of Pesticide
Registration (PR) Notices were issued over several years,
extending certain "no residue" and "zero tolerance"
registrations beyond the Deceaber 31, 1967, deadline for
obtaining residue tolerances. Aaong uses of silvex extended
beyond the deadline were uses on pasture grasses and rangeland;
on apples, pears, pluas, rice, and sugarcane; and in lakes
and ponds.
PR Notice 70-22. published by the USDA on Septeaber
28. 1970. addressed the pretence of chlorodioxin ccntaainants
*- ¦ ' poisons. This notice stated that the USDA had
determined that certain toxic ch lorodioxins (such as TCDD)
¦ay be present as contaainants in the besic Materials used
in foraulating 2,4,3-T and silvex. The notice also stated
that the presence of such ch lorodioxins constituted a
possible hasard to aan since they had been found to be
extreaely toxic to laboratory aniaals. and that appropriate
regulatory action would be taken under provisions of FIFRA
since products containing ch lorodinxins are considered to be
in violation of FIFRA.
-23-
-------
On July 20. 1973. a notice of intent to hold public
hearings on all uses of 2.4.5-T vaa filad with tha EPA
Haaring Clark under Section 6(b)(2) of FIFRA. as aaended
1972. All federally approved uaea of 2,4.5-T were to be
explored in a public hearing scheduled for April 1974,
following completion of an intensive monitoring prograa for
detecting dioxin in the ppt range (38 FR 19869, July 29.
1973). On Hay 10. 1974. the FIFRA Section 6(b)(2) hearing
was expanded to include all insecticides and herbicides
having 2,4.5-TCP in their aanufacturing process. These
included silvex, erbon, and ronnel, as veil as 2,4.5-T and
2.4.5-TCP, all of which aay contain TCDD.
On June 24. 1974. EPA halted the FIFRA Section
6(b)(1) and 6(b)(2) proceedings initiated againat 2.4.5-T
and related compounds because of its inability to monitor
food for TCDD reaidues with the necessary analytical precision.
Although the hearing was terainated. the Agency
stated that it "will continue its TCDD residue aonitoring
prograa and will take such further action as it deeas
appropriate once the results of the aonitoring project are
available" (39 FR 24050 June 28. 1974).
In 1976. 2.4,5-T. silvex and related cheaicale-^
were placed on the original list of cheaicals scheduled for
• /
— The related cheaicals were ronnel, erbon.
and 2,4,5-trichlorophenol.
26
-------
pra-KPAK rivitv, baeauaa of advaraa affacca chat v«r«
obaarvad in taac aniaala axpoaad co 2,4,5-T. Much of cha
eotearo eistirid irouad TCDO, eha axeraaaly toxic eoaetaiaiBC
found in chaaa chaaicals.
On April LI, 1978, EPA iaauad an KPAR vich raapace co
pateicida produces coneaiaiag 2,4,3-T. Tha RPA& rivitv
for aoaa uaaa of 2,4,3-T vn earaiaacad on Fabruary 28,
1979, vbto thi Adaiaiacritor auapandad cha uaa of 2,4,3-T oa
foraaea, righea-of-vay, anl paaeuraa bacauaa ho found ehae
Chaaa uaaa praaancad an iaainane hasard co huaan haaleh.
foraacry, righea-of-vay, paatura, aquaeic vaad eoaerol/
ditch bank, hoaa and gardan, and eoaaarcia1/ornaaaat a 1 turf
uaaa of ailvax bacauaa ha found ehae Chaaa uaaa praaaaead an
iaainane ha;ard co huaan haaleh. Tha Adainiaera cor'a
ace ion ragardiag ailvax vaa baaad oa daca and information
about TCDD praaancad in eha 2,4,3-T RFAR Poaieion Oocuaanc
I, oa* inforaaeion davalopad ehrough eha RPAR procaai, and
aeudiaa raporeing advaraa affaeea in eaac aniaala axpoaad to
ailvax. An axpadicad haariag oa eha auapaaaioa ordara
waa convanad on April 19, 1979; oa May 13, 1979, cha haaring
vaa diaconeinuad.
-27-
-------
In addicion, shortly after the suspension order# vara
issued. Dow and other affactad parties filad suit on March
6, 1979 in cha United States District Court. Eastern District
of Michigan. Northern Division for judicial raviaw of this
decision requesting an iaaadiate stay of the emergency
suspension orders. The court denied plaintiffs' request*, for
an iaaadiate stay of the suspension order, and a hearing
for a preliainary injunction was held on April 5, 6. 7. and
9. 1979. On April 12. 1979. the Court denied plaintiffs
request for an injunction against the Agency's suspen-
sion orders.
II. RISK ANALYSIS
There are two key coaponents to the assessaent of
any chemica1-ra 1 ated risk: (1) assessaent of the toxicolo-
gical properties of the cheaical. and 2) assessaent of
exposure to the cheaical. The risk assassaent itself is a
suaaation of the conclusions in each of these areas. For
axaapla, a highly toxic cheaical aay pose low risks if
exposure is low; conversely s compound of low to aoderata
toxicity aay pose high risks if exposure is high. In the
present instance, TCDD, is an extreaely toxic cheaical,
whereas silvex is significantly less toxic to teat
aniaals. However, beeause commercial saaples of silvex
contain TCDD, pesticide products containing silvex aay have
adverse effects on huaan health.
-28
-------
Lam *1" a» bu« «|«m.7 «-« •»»«»• vn«
riak potential of a pesticide ia ctrii of the risk criteria
••C out at 40 CFR 162.11(a). Sp«cifically, 40 CFR 162.11(a)
(3)(ii)(A) provide* chat a rebuttable preauaption shall
irise "if a pesticide's ingrediaot(•)...(i)oducaa oncogenic
•ffaeea ia experiaental aiaaalita apacias or ia man as a
result of oral, inhalation or daraal upoiuri..." Section
162.3(bb) dafinaa tba tara oncoganie aa "the property
of a substance or a aixture of substances to produce or
induce benign or aalignant tuaor foraation in Living aniaals."
40 CFR 162.11(a)(3)(ii)(B) provides
that "a rebuttable presuaption shall arise if a pesticide's
ingredient(s)...(p)roduces any other chronic or delayed
toxic effect in test aniaals at any dosage up to a Isvel,
ea deterained by the Adainistrator, which is substantially
higher than that to which huaans can reasonably be anticipate''
to be expoaed, taking into Account aaple aargins of safety."
This section reflects concern that chronic exposure eo
cheaicsls aay result,aaoog ether things, in injury to the
reproductive systea and/or the fetus and provides that a
rebuttable presuaption shall arise if chtonic cheaical
exposure in test aniaals produces such results.
The following data and Information on toxic effects
and exposure indicate that silvex and/or TCDO exceed the
oncogenic effects and other chronic or delayed toxic sffacts
risk criteria for Issuance of a rebuttable presuaption
against registration. This deta also indicatns that these
cheaicals aay pose risks of adverae effects on huaan haaleh.
-29-
-------
A. Toxicity in Teat Aniaala
Studiea have deaonatrated that TCDD and/or ailvex
contaainated with TCDD can produce fetotozic, teratogenic,
•ad carcinogenic «ff«ct> io experiaentel aniaala which
have been ezpoaed to theae cheaicala.—' The oceurr«aci of
theae effecta in teat aniaala indieatea that huaaaa who are
ezpoaed to TCDD and/or ailvez may axparianea coaparable
effecta. Tha Agency haa extracted key data from tha ouaeroua
atudiaa for praaancation in ehia docuaant.
(1) Adver^^l^fcrodue^ijre^^fee^
TCDD and ailvez with TCDD produca fetotozic and
teratogenic affacta aueh aa daath and ?*d*jced fatal aisa;
akalatal daforaieiaa aueh aa elafe palaca; injury to inearnal
organa aueh aa incaacinal blaading, inteatinal leaiona,
and abnonaal kidnaya; and poat-par:ua affaeta aueh aa
raduead aurvival. Tbaaa affacta appear in aeveral diffarant
aaaaalian atraina and apeciea, oeeur in all of the littera
in aoaa doaa groupe, and oeeur in rata at doaaa «a low aa
0.001 ug/kg of TCDD and SO ag/kg of ailvez.
— Othar atudiaa hava attributed additional adverae affaeta
to ailvas and/or TCDD ezpoeura. Tha Ageney ia currently
analysing theae atudiaa to eaaeaa the aerioua iaplicationa
auggeated by their reaulta.
30-
-------
( •) Expoaura of Taat Aniaala to TCDD —^
( i) Fatoto'xic and Eabryolathal E f fac t a
Fatotoxic and aabryolathal affacta hava baan raportad
for at laaat thraa diffarant aouii itniti, two diffarant
rat •trains, aad on* atraio of aubhus.an priaataa axpoaad to
daily doaagaa of TCDD during tha pariod of aajor organoganaa is
in gaatatioo. For axaapla, in atudiaa uaing ganarally
low-doaa ragiaana of TCDD. Naubart and Dillaann ( 1972)
raportad that raaorption aitaa (raaorbad or daad aabryos)
occurrad in 34Z (7/13) of tba littara at 0.3 ug/kg and in
100Z (3/3) of tha littara at 9.0 ug/kg for NMftl taica,
coaparad to 24-32Z (23/95 and 21/63) of littara axhibiting
raaorptiona in control aniaals which had not baan axpoaad to
TCDD (Tabla I). Sparachu at al. (1971) raportad raaorption
of 100Z (110/110) of tha fatuaaa in Spragua-Dawlay rata
xpoaad to 8 ug/kg of TCDD, coaparad to 20Z raaorption
(63/309) of tha fatuaaa froa tha control aniaala. Khara and
Ruddick (1973) raportad 100Z (77/77) raaorption of fatuaaa
at 4 ug/kg and 36Z (36/133) at axpoauraa of 1 ug/kg in
Vlatar rata, coaparad to 7Z (3/132) in tha control aniaala.
—^ Sxcapt aa otharviaa apacifiad, all raproductlva data
wara darivad froa atudiaa in which pragnant rodanta
vara orally axpoaad to TCDD and/or ailvax with TCDD
during tha aacond ona-third of gaatation by daily gavaga
or in which priaataa wara chronically axpoaad bafora
aating and during gaatation. Tha pragnant rodanta wara
sacrificad shortly bafora tha achadulad birth of tha
offspring, and tha fatuaaa wara axaainad for abnoraalitiaa.
Pragnant priaataa dalivtrad offapring at tara.
31-
-------
Table 1. Eabryotoxic and Teratogenic
Iffecta of TCPD on WM»I Mice"
«/
r
IT
ittera
Affected/Viable
Liettrsl
i
b/t
1
i
1
Doae
1
Reaorp tions
1
Cleft
Palate 1
1(
ux/kt)1
# 1
W
A
1
# 1
Z 1
1
0
1
23/931
24
1
6/93 1
6 1
1
oil
1
21/631
32
1
4/63 1
6 1
1
0.3
1
7/131
34
1
0/13 1
0 1
1
3.0
1
16/241
67
1
7/24 1
29 1
1
4. v
1
3/121
42
1
6/12 1
30 1
1
9.0
«
3/3 1
100
1
3/3 1
100 1
1
9.0
1
3/6 1
30
1
5/6 1
83 1
£/ All doaea administered on daya 6 to IS,
except ••coad 9.0 ug/kg dot* which wee
edainiatered on daya 9 to 13.
Siailar effecta have been reported «t higher doaagea
of TCOO. Iteubert and Dillaann (1972) reported that a aingla
doaa of 43 ug/kg to NMKX aiea on day 6 produced raaorptiona
in 1001 (3/3) of the viable littera, coapared co raaorptiona
in 24Z (23/93) of the control littera. Courtney (1977)
reported an average of S7Z aortality in 6 littera of CD-I
aice orally expoaed to 200 ug/kg, coapared to an average
aortality of 6Z in 13 vehiele contro> littera (Tabl 2).
; iia inveatigator alao reported an average of ?6X aortality
littera of CD-I aice expoaed aubcutaneoua ly to 200 ug/kg
t TCDD, coapared to 14Z in the aix littera of control aniaala.
Soaa of theae atudiea alao deacribe a tatiatical ly aignificant
weight depreaaion in the aurviving eabryoa (e.g., Sparachu
at al. 1971).
32-
-------
These and other atudiea also reported that TCDD bid
ao measurable idvtri* effects at aooa dose levels in soae
atraiaa. For ix»pl«, Khar* cad Ruddiek ( 1973 ) reported ao
fetotoxic affacta at 0.125 ug/kg in Wiacar rata, and Neubert
aad D i1laaaa (1972) raportad ao taratogaaic a £ tacts at 0.3
ug/kg ia NMRX aice. Courtney end Moon (1971) raportad that
TCOD had ao effect oa fetal weight or eabryooic aortality at
0.S ug/kg ia CD rats, and Sparachu at al. (1971) reported
ao effect at 0.03 ug/kg ia Sprague-Davley rats. However,
subaequeat experiaeate ia the itae species have deaoastrated
adverse fetal effecti at eveo lover doae levels.
a/
Table 2. Fetotoxic and Teratogenic Effects of TCDD ia CD-I Mice
!
1
{Average # 1
Aooaalies/Toeal
Fetuaesl
1 Doae
1
1
lAbnoraal
Cleft
1 Kidney
Club 1
1(ug/kg 1Rouc« of Ad-IX Average Fetal IFetuaaa
Iper day)1ainistratioa1Mortality/Litter1per Littec
Palate
I
1 Aaoaaliaa
i :
Foot 1
X 1
1 25
1
Oral
1
6
1
4.6
3
1 34
3 1
1 50
t
Oral
1
13
1
8.1
19 •
1 72
7 1
1 100
1
Oral
1
14
1
8.3
66
1 71
13 1
1 200
1
Oral
1
87
1
1.5
100
1 100
14 1
1 400
1
Oral
1
97
1
0.4
100
1 50
50 1
1 25
ISubcuCanaoual
36
i
6.7
82
< ii
11 1
1 50
ISubcutaneoual
56
i
5.0
79
1 58
17 1
1 100
ISubcutaenoual
72
i
3.5
85
1 95
0 1
1 200
ISubcutaenoual
76
*
3.1
100
1 38
18 1
ill
1
Oral
1
6
1
0.8
0
1 I
4 1
lanisole
1
1
1
1
1
Icon oill
1(0.1 al)1
1
1
i
i
1
1
1
1
1 b/ 1
1
1
1
1
1 DHSO
ISubcutaneousI
14
1
0.2
0
1 0
1 1
a/ Data froa Courtney,
b/ DHSO • diaethylsulfoxide.
-33-
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Dow Cheaical Coapany haa recently coaplatad a acudy
oI the effects of TCOD on reproduction in Sprague-Dawley
rata expoaed Co lov doae lavala of thia chaaical for chraa
ganarationa. Dow concludad that "iapairaant of raproduction
vaa cleanly evident aaong raca ingaacing 0.01 or 0.1 ug/kg/dey
of TCDD. Significant dacraaaaa vara obaarvad in fertility,
littar size, gaatation aurvival, poat-nacal aurvival and
poatnatal body weight." In addition, expoaure to 0.001 ug /kg/day -
of TCDD, the loweat level teated in thia atudy, reaulted in
atatiatica 1ly aignificant increaaea in the percentage of
pupa dead at birth aad/or dying before the end of three
weeka of life and in the incidence of dilatau venal pelvia
in aoaa generational'
— Dow Cheaical Coapany haa claiaed that the raw data
and/or reaulta of certain of ita atudiea are "trade aecrac"
or "confidential." An injunction iaaued on April 4, 1978,
in the caae of Dow Cbeaical Co. v. Coacle. Civil Action Mo.
76-10087, U.S. Diatrict Court for the Eaatern Diatrict of
Michigan (Northern Division), arguably pracludea CPA froa
diacloaing thia inforaation at the preaent tiae. Although
the relevant proviaiona of FXFKA have ainca been aaended to
allow diacloauve of data auch aa thia [aee, e.g., FXFKA
Sectiona 10(d) and 10(g)], the iujunction haa not yet been
aodified. EPA haa requeatad the Court to aodify the injunc-
tion, but until thia haa been done the Agency will not
publicly diacloae the data froa the atudy. The auaaary
praaented in the test of thia Poaition Docuaent doea not, in
EPA'a opinion, eonatituta diacloaure of the allegedly "trade
aecret" data aubaittad by Dow and would not cauae any hara
to Dow'a legitiaata coapetitive intereata. The data froa
the atudy aay be aade available to any party in a cancellation
proceeding under an appropriate protective arrangeaeae.
-34-
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Recent reproductive studies in rhesus aonkeys indicate
that aaternal exposure co TCDD results in en increased
incidence of early ipoat. •. i ¦. . lults ia aoahuetn
priaates should aot be underestiaated .'-.ruse of the close
siailaritias between the reproductive of huaeas and
aonkeys. Long-tera exposure to even ainute quantities of
TCDD resulted ia e aerked increase in spontaneous abortions
in the first third of the gestational period, even where there
was no evidence of aaternal toxicity by clinical observati-*a
or bioaedical testing. Honkeys exposed to 50 ppt TCDD (2..
ng/kg per day) before and during pregnancy had a total fetal
loss of 67Z (50X by abortion and 172 as stillbirth) and
fertility rate of 75X, coapared with OS and 100X, respectively,
in the controls. Atteapts to re-breed one of the aborceri
resulted in an additional early abortion (Schantz 1979;
Spencer. 1979). When aniaals were treated with a higher
dose, the fertility rate dropped to 23X. with ine of rhe two
gravid aniaals aborting in the first third of gestation.
Irregularities in aenstrual cycles, anovulation, «nd reduction
in the reproductive horoones, progesterone and estrogen,
ware aaon^ the toxic effects seen at the higher dose. The
investigators concluded that the reproductive abnoraa1ities
were aost probably the result of horaone iabalance. and were
apparently cue result of the TCDD treataent. rather than
general toxicity, because the horaonal alterations were
observed before the aniaals becaae obviously ill (Allen
et si.. 1977; Barsotti 1979).
33
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Early abortion! have also been obnrvtd in monkeys
whjre ixpoiun haa only been for a shore period of the
pregnancy. An accumulated doaa of 1 ug/kg (1,000 >pc) of
TCDD ovtr a three-week period resulted in a 73* abortion
race, compared with 0Z in the controls. All abortions in
the treated aniaals ware during the first third of the
gestational period, and the only evidence of aaternal
toxicity was slight acnegenic response in one animal,
observed months later. l.e viable offspring produced at
this dose had abnormal palate development, and three of the
four at a lover dose had debatable abnormal development ia
the same orofacial region (Mcltulty, 1979).
Although the experimental protocols and animal strains
differ for the several studies cited, in each case TCDD
significantly increased the incidence of resorbed embryoe or
stillborn animals relative to the rate observed ia control
anisals not exposed to TCDD. The regular occurrence of
embryonic death in studies by different investigators ia
primates and in different rodent strains iadicates that
exposure to TCDD duriag mammalian gastacioa may result ia
the death of the embryos aad related maternal reproductive
failure.
36-
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(ii) SkalaCal Anoaaliaa
Skalacal dafacCi appaar in aiz aCudiaa involving
four diffaranc sous* aeraina. Courcnay and Koora (1971)
raporc cha following ineidancaa of elafc palata in eha
indicaCad acraina aspoaad Co 3 ug/kg TCOO: 71Z (3/7)
of liccara of C37BL/6 aica, coaparad co nona (0/23) in
eha eoncrola; 22Z (2/9) in liccara of DBA/2 aica
coaparad co nona (0/23) in cha eoncrola; and 302 (3/10)
for CD-I aica, coaparad Co nona (0/9) in cha eoncrola
(Tabla 3). ttaubarc and CilJaann (1972), alao uaing 3 ug/kg
of TCDD, raportad 29X (7/24) of cha viabla liccara had
facuaaa vieh elafc palaca for NMftI aica coaparad co 6Z
(10/160) of Cha conCrol liccara (Tabla I). Saich ac
al. (1976) raporcad elafc palaCa in 71Z (10/14) of CT-l aouia
liccara ac 3 ug/kg, coaparad co nona (0/34) in e:ia
eoncrola (Tabla 4).
In axpoauraa of ahorcar duraeion, Moora ac al.
(1973) raporcad elafc palaca in 86Z (12/14) of C37BL/6 aouat
liccara aspoaad on daya 10-13 co 3 ug/kg, coaparad co nona
(0/27) in eha concrol liccara. Naubarc and Dillaann (1972)
raporcad c la fpalaca in 7 IS (10/14) of liccara of NM1X aica
aspoaad co a aiagla 43 ug/kg doaa on day 11, coaparad co 61
(6/93) of liccara in cha eoncrola.
-37-
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any of eh* littara in CD rata azpoaad co 0.5 ug/kg. Siailarly,
Khar a aad Ruddick ( 1973), uaing Viacar rata, raporcad chat eha
occurraaca of tha akalatal anoaaliaa ia tha fatuaaa azpoaad
to 2.0 ug/kg via coaparabla to tha rata for tha untraatad
an inala.
(iii) Injury to Intarnal Ortana
Ezpoaura to TCDD producad injury to tha kidnaya and
intaatinal traeta of at laaat fiva diffarant aouia and rat
atraina. Smith at. al. (1976) raportad 282 (4/14) of
lictara with kidnay anoaaLiaa ae 3 ug/kg in CF-1 aica,
eoaparad to nona (0/34) in tha conerola (labia 4). Moora at
al. (1973) raportad 100Z (14/14) of littara with kidnay
anoaaliaa in C37BL/6 aica azpoaad to 3 ug/kg on daya 10*13,
eoaparad to nona (0/27) in tha control littara. Courtnay
and Noora (1971) raportud kidnay anoaaliaa in 1002 (10/10)
of tha littara of CD-I aica at 3 ug/kg, eoaparad to 332
(3/9) in tha conerola, and 672 (4/6) littara with abnoraal
kidnaya in tha CD rat at 0*3 ug/kg aa eoaparad to nona (0/9)
in tha control littara (Tabla 3). Sparachu at al. (1971)
raportad haaorrhagaa or laaiona in tha intaatiaa of 362
(36/99) of tha azaainad fatuaaa of Spragua-Davlay rata
azpoaad to 0.5 ug/kg, eoaparad to nona (0/246) in tha
control fatuaaa.
-38-
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labia 3. TiriCOHttic EffacCa of TCDD ia Mica and Uci
IStrainlDoaa ILietara Affacead/Liva Lieearal
1 1(ug/kf)1C lafe Palacaltidnay Aaoaaliaal
1
1 1
#
Z
1
#
X 1
iMouaa
1 1
i
1CD-1
10(PMSO) 1
0/9
0
1
3/9
33 1
1
1 1 *
1/5
11
1
5/9
56 1
1
1 3 1
3/10
30
510/10
100 1
1DBA/2
10(DHSO)1
0/23
0
1
3/23
13 1
1
1 3 1
2/9
22
1
8/9
89 1
1C57BL/10(DKS0)1
0/23
6
i
2/23
9 1
16
1 3 1
5/7
71
1
7/7
100 1
1 lac
1 1
1
1
1 CD
n0(JMS0)1
0/9
0
1
0/9
0 1
1
1 0.5 1
0/6
0
1
4/6
67 1
a/ Data froa Coureaay aad Moora.
3J
Tabla 4. Faeoeoxie aad Taraeotaaic Efface* of TCDD la CF-l Mica ""
i ,i /-t-j-j.'* ...'IZ i. '
r
11ae idaaea
of C la
f e1Li e ear a
Wi eh
ii
ietara Wi eh
D i laeadl
i
IPalaea
ia
Lieeara IRaaorbad
FaeuaaalRaaal Palvia
pa r 1
1
i
Doaa
Ipar Lira
Lieeara
Ipar Liva
LieearalLiva Lieeara
i <
ut/kt) 1 *
1
S
1 # 1
z
1
P 1
! i
i
0
1 0/34
1
0
1 25/34 1
74
i
0/34 1
0 1
1
0.001
1 2/41
1
3
1 30/41 1
73
i
0/41 1
0 1
5
0 .01
1 0/19
1
0
1 17/19 1
89
1
0/19 1
0 1
1
0.1
1 1/17
1
6
1 16/17 1
94
i
0/17 1
0 1
1
1
1
b/
1 1
i
1
1
1 .0
1 4/19
1
21
1 18/19 1
95
i
1/19 1
5 1
1
1
1
b/
1 1
i
1
b/ 1
1
3.0
110/14
1
71
1 11/14 1
78
1
4/14 1
28 1
a/ Daea froa Sa\el> at al. ""
b_/ S cati * r. ical ly diffaraae froa coacrola by tha Fiateara met
probability caac (p < O.Oj).
39
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(b) Iipo«ur« of Tut Animals to Silvax
Silvax haa baan above to produca fatotoxic affaeca
•ucb aa fatal mortality, raducad body waight, akalacal
anoaalita, and injury to intarnal organs. Tha affaeta
hava baan obaarvad ia taat rodaat apaciaa ac aataraal
doaaa aa low aa 50 ag/kg (TCDO < 0.05 ppa). Thaaa raaulta
claarly iadieata that ailvax ia fatotoxic aad taratogaaie
in aaaaala.
Courtaay (1977) raportad aignificant iacidancaa of
iacraaaad fatal mortality aad raduead fatal waight ia CD-I
aica which had racaivad praaaeal axpoaura to silvax.
Hataraal aubeutaaaoua axpoaura to 405 ag/kg silvax CTCDD <
0.1 ppa) raaulead ia 25Z (33/132) fatal mortality aad aa
avaraga fatal waight of 0.87 g, eoaparad with control valuas
of 1?X (19/171) aad 1.03 g, raapactiva ly. Oral axpoaura to
tba aaaa doaa raaultad in an avaraga fatal waight of 0.83 g,
eoaparad with 1.J1 g in tha controls. An incraaaad incidanca
of claft palata waa also obsarvad aaong tha traatad fatusaa.
Oral axpoaura rasultad in an incidanca of 7Z (7/95); aubcuta-
naoua axpoaura raaultad in 3Z (3/99). No claft palatas
(0/260) wara obsarvad aong tha control aniaala.
-AO-
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affacta of ailvax tod tha propylana glycol butyl athar aatar
of ailvax (ailvax-PGBE), aach containing lata than 0.03 ppa
TCDD. Spragua~Dawlay rata war* axpoaad co 23 co 100 ag/kg of
ailvax oa daya 6 through 13 of gaatation. Significant
•ffacta on fatal aortality and birth waight vara obaarvad in
tha littara of traatad daaa. Skalatal .noaaliaa, aueh aa
claft palata, ratardad oaaification, and axtra carvical riba
vara obaarrad aaong tha axpoaad fatuaaa. Micropchalaia
(abnoraal aaallnaaa of tha ayaball) and cardiovaacular
abnoraalitiaa vara aiao aaan. Siailar affacta vara obaarvad
whan aniaala vara doaad with ailvax-PGBE, or whan doaad for
thraa-day intanrala during tha pariod of aarly organoganaaia.
In aaeh of th etudiaa eitad abova, soaa aatarnal
toxic affacta vara obaarvad. Courtnay found aoaa incraaaad
aatarnal waight gaina and incraaaaa in livar to body waight
ratioa aaong tha traatad groupa; Oow notad baldnaaa (alopacia),
lack of appatita and vaginal blaading. Kowavar, tha axiatanca
of aatarnal toxic affacta doaa not nagata tha iapact of tha
obaarvad injury co and daath of tha fatua.
In auaaar/, TCOO producaa Ototoxic affacta in taac
aniaala at tha lowaat doaaa taatad. For axaapla, aataraal
doaaa aa low aa 0.001 ug/kg in rata and 30 ppt in aonkaya
hava incraaaad lattiality to fatuaaa. To data, a no-obaarvad
affact laval haa not baan aatabliahad far TCDD-ralatad
—1' Dow Chaaical Co. haa alao raquaatad confidantialiey
for tha raaulta of thia atudy. Th* diacuaaion in eha
footnota in Saction 1I.A.(I)(a)(i) of thia docuaane
appliaa to thaaa data.
-41-
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effecta on reproduction in any apeciea teatad. Exposure to
ailvex containing leas than 0.05 ppa TCLD reaulted in
increaaed fetotoxicity at 400 ag/kg in mica and at 50 mg/kg
in rata. No aignificant effecta vara obaarvad below t; •
lava la .
(c) Riak of Advtrae Reproductive Effacta
Generally. a no-effect laval ia viewed aa a
toxico1ogica1 andpoinc. aarking a laval of axpoaura in
aniaala which ia "aafa" bacauaa ehara ara no obaarvabla
advaraa affacca. Toxicologiaca generally aaauae that
cha aniaal no-affact laval can aarva aa a baaa for
aatiaating axpoaura lavala which would ba "aafa" for
huaana. Tha "aafa" laval for huaaaa ia aat at aoaa
laval lower than tha aniaal no-affact laval to provida
a "margin of aafaty" that takaa into account diffarancaa
in aanaitivitiaa batwaan aniaala and huaana, and
diffarancaa in aanaitivitiaa aaorg huaana. Thia
"aargin of aafaty" doaa not rapraaant an *.nfallibla
indica sr of potantial hatard to huaana. Error could
ba introduced bacauaa huaana ara aora -naitiva than
tha taat apaciaa by a graatar factor than noraally
allowed, or by the incorrect choice of a no-affact
1 aval.
42
-------
Tha lowaae level ae which TCDD haa no obaarvabla
affatca in eaae aoiaala ia crucial Co cha Agancy'a dacaraina-
eion of eh* riak pocancial of ailvax. TCDD ia praaane ia
ebia paaeiciia aa low-laval concaainanc and chua will ba
praaane in tha anvironaant ae low lavaia whanavat and
wherever ailvax ia uaad. If ehere truly wtra a no-efface
laval in aniaala, it would ba reaaonaole Co ae laaae bagin
Co aatiaaca a poaaibla "safa" laval for huaana and Co aaaaaa
tha poaaibla ti«k Co husana by ralacing chia aaauaed "aafa"
laval co cha laval of eha paacicida ehac aay ba in eha
environaene, if ehac laval w«ra known. Howavar, if ehara
wara no no-effect laval, any uaa of. ailvax would raaule in
pocancially aignificane expoaure Co TCDD, becauaa ehara
would ba no ainiaua laval upon which ro aaeiaaca a aargin of
aafaey. Ic ia cha Agancy'a poaicion ehac n_o no-affacc
laval haa bean found for fecoeoxic affacet raaulcing froa
TCDD axpoaura. Tharafora, any axpoaura eo TCDD or ailvax
containing TCDD auac ba conaidarad pocancially dangaroua Co
cha huaan faeua.
43
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(2) Oncoitnic Effect* in Tut Animals
Chronic exposure studies have shown that TCDD
induces oicogenic responses in mice and rats at exceedingly
low dose levels. These effects, together with data
showing that TCDD is autagenic. constitute substantial
evidence that TCDD is likely to be a human carcinogen.
(a) Effects of TCDD
The Agency's Carcinogen Assessaent Croup (CAC)
has concluded there is a sufficient evidence froa
aniaal studies to indicate that TCDD is likely to be a
t.uaan carcinogen (Meao, 1979). Carcinogenic responses have been
observed at doses as low as 210 ppt in rats.
Dow Cheaical Coapany. a silvex registrant, studied
the effects of TCDD on aale and feaale Sprague-Dawley
rats exposed to 22, 210 or 2200 ppt TCDD and reported
that there were statistically significant increases in
the incidence of hepatocellu r carcinoaa in feaale rats
exposed to 2200 ^pt TCDD (Dow Cheaical U.S.A.. 1977). After
analysing the raw data froa this study, the CAC has concluded
that the coabined increase
-44-
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in the incidence of hepatocellular hyperplastic nodules tad
hepatocellular carcinoaa in rati exposed to both th« 2,200
ppc and 210 ppt levels it •ignificant^ In another study
using Sprague-Dewley rats, Van Millar at al. (1977) repotted
tbac 1000 ppc and 5000 ppt TCDD produced a carcinogenic
response in aale Sprague-Dawley rata. These observations
tend to confirm the registrant's observations that TCDD
produces an oncogenic response in the livers of aale Sprague-
**/
Dawley rats.—
Further, a preliainary report of a not-yet-coaplet«d
National Cancer Iaatitute study tends to confira these
observations of a carcinogenic response in rets. A contractor
for the National Cancer Institute has reported that TCDD is
carcinogenic in the rats and aice used in that study.
CAG also eaphasized chat, at low levels. TCDD
is a potent inducer of arylhydrocarbon hydroxylase, an
eniyae systea chat concains an entyae chat is known to
aediate the foraation of epoxidea. compounds which are
*/ Dow Cheeical Coapany has alto requested confidentiality
for raw data supporting this finding. The discussion in
the footnote in Section IIA (I) (a) of this docuaenc
applies to these data.
•*/ The CAG and an E?A auiit found that this study had
aajor shortcoaingt in design and conduct thac limited the
reliability of che dace developed ac dote Levels lower Chan
1000 ppc .
45 -
-------
potentially active carcinogenic aetabolitea. Zn
addition, CAC raportad chat TCDD ia autagenic in tha
Asa a taat without tha aetabolic activation ayatea. Ita
autaganic activity ia exhibited by fraaaahift autationa
cauaad by intercalation batwaan baae-paira of DNA (EPA,
1979).
Finally, CAC a.- athera hava coaparad tha carcinoganic
potancy of TCDD with othar known carcinogana (EPA, 1979)
Baaad on thaaa caleu 1 ationa, TCDD appaara to ba cha aoat
potant chaaical earcinogan known (javaral tiaea aora potant
than aflatoxin).
(b) Effacta of S i1 vex
Thava ia littla dafinitiva inforaation regarding
tha oncogenic potential of ailvex. Innea at al. (1969)
raportad no aignificant differencea in the incidence of
tuaora between control aniaala and aice fed a diet containing
121 ppa ailvex £ or 18 aoaeha. Siailar reaulLa were obtained
by Mulliaon (1966) who fed Kuroaol, S.L., containing 33.3Z
ailvex acid to rata at 10, 30, 100, and 300 ppa for two
yeara. However, when beagle doga were fed 190 ppa ailvex
potaaaiua aalt for two yeara and 360 ppa for one year,
necroaia aod fibroplaatic proliferation in the liver were
reported (Mulliaon, 1966).
-4 6-
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(c) Ri»k of Oncogenic Effecte
The Agency haa examined the data ahoving that
TCDO ia carcinogenic ac vary low txpoaurt levela in light of
other inforiation indicacing that tha uae and diacribution
of ailvex co eh« environment craacaa opporcunieiaa for
huaan axpoiura to cbaaa chaaicala. In view of Che non-chreahoId
concapc upon vhich Agency Caacar Policy ia baaad (Albert
at al., 1977), any expoaure co TCDD poaaa a aignificanc riak
of oocoganic affacca occuring in che expoaed population.
(3) Coneluaion
In auaaary, available inforaacion aupporca
Cha concluaion chat chara ia a vary raal poconeial for
huaan .iaka dua to expoaure to ailvex and/or TCDD. Thaaa
riaka primarily ralata to tha oncogenic and fecocoxic
affacta of TCDD. Bacauaa TCDD ia invariably praaant aa
a contaainant of coaaarcial ailvax, any expoaur* to ailvax
rapraaanta a aignificant potential riak to the axpoaad
human population.
47-
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B. Exposure Resulting from th« Use of Silvex
The uit of silvex results in the distribution
of th« pesticide to air, water, non-target vegetation,
soil, and other environmental coaponanti in araas where
paopla liva and work. As a rasult, people and their food
and water supplies may ba exposed directly or indirectly to
silvex and its dioxin contaminant, TCDD. This section of
the Position Document details information on the exposure
potential resulting from the non-suapended uses of silvex,
particularly uae on orchards, sugarcane, rice, and rangelend.
In some cases, information on exposure potential from these
uses is derived from data on use practices, and in other
cases this information is based on chemical residue data.
(1) Exposure due to Silvex Use on Rice
About 2,000 acres (1!) of the annual rice crop are
treated with silvex to control broadleaf and aquatic weeds.
The major use areas «re in Mississippi, Arkansas, Louisiana,
and Missouri.
Greater taao 99Z of all application of silvex for
rice production is by fixed-wing aircraft which fly at
speeds of 8} to 120 mph, 3 to 10 feet above the rice
cvop, when winds do not exceed 5 mph.
48-
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(a) Direct Iipoiun froa Aerial Drift
The total rural population of th« Delta region rice-growing
counting i» about 633,000 with «n c.tiaated 272,000 people
residing within 1/2 milt of rice fields.
The ivirigt rural population density is 40 paopla/iquari
¦ila. When the use of the peaticide results in drift to
these areas of huaan work and habitation, people who live
and work in the path of the drift Bay be directly exposed to
the pesticide by inhalation and/or by deraal exposure to
pesticide droplets in the airborn drift.
Cotton faraers who live in the Delta rice-growing
region have reported drifr onto their cropland and related
crop daaage ( 30 ,000 / 26 : #302 . #1888). These report* indicate
that the pesticide has drifted beyoad the t-ray area of the
rice fields and into non-target areas. Such reports are
consistent with studies showing that aerial application of
other pesticides aay result in drift for seversl
ailes away froa the site of the spray operation (Akesson
and Yates, undated; Maybank et al., 1978).
„ -49
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(b) Contamination of Surface Witen
Application of silvex to rice fields a«7 mult in
contamination of rivcra and streama. Rice fielda are
flooded with well water 2 to 4 inches deep and maintained
at thia level until harvest, except when producers drain
their fields for an application of fertiliser in the
middle of the growing season. Abort two weeks before
harveit, the water is diverted from the fields to ditches
which eventually enter streams and rivers. Silvex
contamination of these waters is demonstrated by data
retrieved from the STORET system which indicate that silvex
residues are present in surfa- iters throughout the Delta
region. It is noted, however, •. the monitoring programs
do not distinquish between silvex residues originating from
rice, pasture ant*, rights-of-way uaea in these areas.
In the Delta Region, surface water* are a source of
commercial and sport fishing. Although w». 11 water is recommended
for catfish confinement operations, surface water is sometimes
impounded. As a result, some of the fish harveated annually
in this region may be cultivated in water contaminated
with silvex. This piactice creates an opportunity for
expoaure to the local population which consumes much of
the catfish harvested each year. Estimate* indicate that
the average person in the Delta Region consumes 2.8 kilograms
of freshwater catfish, mostly from local sources, each
year.
50
-------
Because surface waters in this area are used for
local fish cultivation, the Agency has considered these
waters as a possible source of human exposure to ailvex.
However, in rice-growing areas of Mississippi and Arkansas,
the majority of the population obtain drinking water froa
deep wells and the exposure of these populations would be
greater if the ground water also is contaminated. However,
because silvex has a half-life in water of about 2 weeks,
and TCDD residues, though stable, are relatively immobile in
soil, the Agency assumes that contamination of ground water
from the rice use is generally unlikely.
(2) Exposure due to Silvex Use on Rangeland
(a) Use Practices and Populations Exposed
Silvex is used on rangeland throughout the country
but major usage occurs in Arizona, Arkansas, Kansas,
Missouri, New Mexico, Oklahoma, and Texas where about 1.6
million acres of rangeland are treated annually with 2,4,5-T
and/or silvex. Estimates indicate that 47,000 people reside
within 1/4 mile of the treated areas. Rural population
density is generally 3 to 4 people/sq mi with one exception
of 16 people/sq mi. in central Missouri.
31
-------
Generally, silvex is applied by fixed-wing aircraft
which fly at speeds of 85 Co 105 mph, 10 ft above vegetation
in winds that do not exceed 10 mph. The average spray
droplet size is 300 microns, and drift control agents are
used to reduce spray drift in 50Z of the«appiicationc.
Ground rigs and backpack spray units are used to treat
snail areas or especially troublesome areas. Applicators
set their equipment to deliver droplet sizes ranging from
200 to 300 microns. Estimates indicate that up to 6Z
of the spray wo-ild be 100 "icrons or less, the particle size
most likely to drift significant distances from the target
area when these methods are used to apply silvex (Akesson
and Yates, Undated).
The amount and formulation of silvex used depends on
the kind of vegetation being treated and the density
of the growth in the area (see Table 5). Both amiue
and low volatile ester formulations of 2,4,5-T and silvex
are used, frequently in emulsions of water and oil during
the spring and summer.
Rates of 0.5 to 2.0 pounds a.i./acre, in 1 to 4 ga)/icre
volumes are used, but 2 gal/acre volumes are used by 501 of
the applicators. Average droplet size is 300 microns, and
half of the apolications are made with drift control agents.
Treatment schedules vary from 1 to 3 consecutive years,
depending on the severity of the problem, followed by
retreatment 5 or more years later depending on the need.
-52-
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( b) Water and Sail Residue s
The STORET system contains data which show silvex
residues in water and sediment in the major rangeland use
areas, and residues of silvex have been reported in several
Wastern streams during monthly monitoring for chemical
residues at USGS stations. However, because silvex may also
ha^e been used on rights-of-way, ditch banks, pastures or
aquati-. sites in the localities where the residues were
detected, it has not been determined if rangeland use of
silvex is the source of these residues. The National
Surface Water Monitoring Program for Pesticides has not
detected levels of silvex in surface water in rangeland use
Studies by Leng (1972) indicate that silvex residues
in rangeland decllue during the fir*t f«w months after
application. For example, residues of silvex on soil or
grasjes immediately after epplication of 0.5 to 1.3 a.i./acre
range from 27 ppm to 199 ppm but decline to 3 after 16
weeks. The hydrolytic half-life for silvex has been estimated
to be about 14 days (Altom, 1973). The half-life of TCDD
residues is estimated to be one year in soil, but TCDD
residues were not found deeper than 6 inches below the soil
surface (Isensee and Jones, 1971).
33-
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Tabla 5. 2,4,5-T/Silv«x Application Rataa on Rangaland by Diffarant
Traat—nt Mathod*
^Application application
Ragion
Application
Huabar of 1
ISita Method
Appliad
Rata
Application* 1
IMaaquita Aarial
South Tazaa
0.67 pound*
3 conaacutiva 1
PI aim
acid aquivalant
•aaaoaa; ratr«anant1
par acra
in 16 yaara 1
Rolling
0.5 pounda
ona application; 1
Plain* of
a.a./acra
ratraataant is 1
Taxaa and
8 jraara 1
Oklahoma
Rolling
0.3 pounda
ona application; 1
Plaina of
a.a./acra
ratraataant is 1
Taxaa and
10 ]raar* 1
Ntv Maxico
Calf Coaat
1 pound
ona application; 1
and Caaatal
a.a./acra
ratraataant in 1
Prairia
5 7a art 1
South Taxaa
1 pound
ona application; 1
Plaina
a.a./acra
ratraataant in 1
5 yaar* 1
2 pounda
ona application; 1
a.a./acr* of
ratraataant in 1
2,4,5-T ~
5 7«ara 1
picloraa
(50:30)
Soutbvaat
0.5 pounda
ona application; 1
a.a./acra
ratraataant in 1
10 raara 1
1Poat and Aarial
2 pounda
ona application; 1
1Blackjack
a.a./acr«
ratraataant in 1
lOak
5 jraara 1
IScaimah
2 pounda
ona application; 1
a.a/acra
ratrtataant in 1
lat yaar 4
10 jaara 1
1.5 to 2
pounda a.a.
par acra
2nd yaar
-54-
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Tab la 3. Coneimiad Machoda
lApplicacion Applicaeisn tagi^a Applicaeion
1Sica Mathod Appliad Rata
Nuabar )i
ApplicaCiona
1 Hardwoods Aariul
Ivichia
1PoaC and
IBlackjack
lOak
ISavanaaa*
1
5 Sand Shi ana ry
lOak
1
1
1
1
1
ICactua
1
1
ITucea
1
IMaaquica
land Oak
1
1
1
ITucca
1
1
2 pounda
a.a./acre
0.3 pounda
a.a./acra
0.3 pounda
a.a./»c?a
2 pounda
a.a./acra
0.67 pounda
a.a./acr<
for 2 aaaaons;
racraacaaac ia
10 yaara
for 2 aaaaoaa;
rarraafiaanc ia
10 yaara
ooa application;
racraacaane ia
3 7«ari
racraacaane ia
20 ?«ara
racraacaane ia
10 eo 13 raara
IMaaquica,
lOaka, aad
locbar
lapaciaa
1
1
1
1
1
Broadcaac
Ground
Applicacioa
2 pounda
a.a./acra
0.67 pounda
a.a./acra
oaa application;
racraacaane ffra-
qnancy variaa frc
3 Co 10 jaara
oaa applieacion;
racraaeaanc ia
10 co 13 vaara
•pot
Traacaanc
8 to 16
pounda aah«
oil for bark
craacaanc, oc
6 co 8 pounda
aahc vacar-oil
aaalaiona for
baaal-acaa
craacaanca
-33-
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(3) Exposure due to Silvax Pae on Applaa
Approxiaately 52,000 icru (10S) of applaa are treated
manually with ailvex to control preharvest fruit drop and to
eahaace fruit eo lor (Me la te r, 1977). An aatiaatad 2,500
pouada of silvex active iagradiaat (ai) ia uaad aaialy to
traat tad Dalieioua applaa. Tbia aceouata for 35Z of the
520,000 aeraa of apple productioa ia tba Oaited Statea. Tha
¦ajor araaa produeiag tbia variety of appla are Vaabiactoa
(55Z), North Caroliaia C 6 Z) , Raw York (4Z), Virginia (41),
Oragon (32), aad Michigan (3D All otbar atataa produeiag
tbia variety of appla aeeouat for 21Z ot tba aaaual crop.
Silveraaiae, tha trieebaaolaaiae aalt of ailvex
ia tha foraulatioa uaad oa applaa. Tba application rata
gaaarally uaad ia 3/4 piat/acra ia 300 galloaa of vatar (0.8
ai./aera) appliad aerially aad by grouad riga.
Tha iapaet of apray drift oa tha populatioa that
raaidaa Lb tba viciaity of appla orebarda baa aot baaa
datarainad but tba iapaet of tha exteat of poaaible apray
drift eaa ba aatiaatad froa othar atudies. Spray drift
during aaribl application baa baaa above to ba dapaadaat oa
tba apray aquipaaat uaad, bydrolie praaaura, air turbulaaca,
aad cba preveiliag vied apaad. Spray droplets caa drift aaay
ailaa avay froa the aita of applicatioa (Akaaaoa aad Yataa,
uadated). Drift eatiaatas for grouad rig appieatioa of
2,4-D have baaa calculated experiaeeta 1 ly. Eatiaataa iadiea
it'
-------
that thara it a potantial for up to 8.0Z of eha spray Co
drifc ac laaat aa far aa 5 aatara away from cha target aita
dapanding on tha apray aquipaant uaad, hydrolic priaiura,
and tha pravailing wind spaad (Maybank at al., L978).
Tha nuabar of paopla who raaida or work in tha vicinity
of orcharda who aay ba aubjactad to apray drift has aot baaa
asaassad. Moraovar, applaa ara harvaatad by hand which aay
raaul: in axpoaura to fara workara during tha harvaat
aaaaon. Thara ia littLa inforaation ragarding tha paraiataaca
of ailvax and TCDD raaiduaa on thia food aourca, and tha
ralatad quaation of axpoaura to paraona who harvaat and
handla tha crop. Howavar, tha naad for partinant data
ragardiag potantial axpoaura to ailvax and TCDD ia undaracorad
by tha finding of an avaraga 0 .036 ppa ailvax raaiduaa ,;.a
unwaahad appla* tavaral aontha aftar harvaat (Cochrana
at al.. 1976).
(4) Expoaura dua to Silvax U»a on Paara
Silvax ia ragiatarad for uaa on Anjou paar traaa
iaaadiataly aftar harvaat to iaprova fruit tat for tha
following yaar. It ia uaad on an aatiaatad 6C0 to 700 acraa
annually, priaarily in Oragon and Waahington.
-37-
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The triethano iaaine silvex formulation is applied
at a rate of one ounct silvex [11.4 great (a.i.)J in 70
gallons of vattr/acri by (round rigs.
The ixcttt of ispoiuri Co fara workers and eh«
population in the vicinity of th«s« orchards has not been
assessed, but a study conaucted with a ground rig application
of 2,4-D indicates that aa auch as 8.OX of the spray aay
drift at least as far as 5 alters away froa the site of
application (Maybank et el., 1 978 ). Measureaents to deteraine
drift beyond 3 asters were not aade. The iapact of this
potential spray drift has not been deterained.
(5) Exposure froa Silvex Use on i .las
Approxiaately 8,300 acres (92) of the 93,638 acres
of pluas (for use as prunes) are cultivated annually are
treated with silvex. Most of r.he usage, e»tiaated at 400
pounds active ingredients (a.i), occurs in Oregon (7,407
acres), Washington (1,940 acres), and Idaho (978 acres)
where the Italian and Early Italian varieties coaprise the
greatest percentage of plua acreage in the United States.aud
account for approxiaate1y 111 of the annual prune harvest
Cround rigs are used to apply silvex to virtually all
of the pluas that are cultivated in these three states.
The triethanolaaine salt is the only foraulation used
to prevent fruit drop in pluas. The Agency estiaacas
that silvex is applied at the rate of 0.8 ounces (a.i.)/acre
-58 A-
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of ailvex trietanolaaine salt. While information regarding
Che iapact of ailvex drife away froa ehia uae sice ia
lacking, drift eatiaates for ground rig application of 2,4-0
have been calculated experimentally. Eatiaatea indicate
chat there is a potential aa auch as 8.0 of the spray to
drife S meters away froa the target aite defending on the
apray equipaent used, hydrolic pressure, and the prevailing
wind speed (Kayba^k et al., 1978).
There ia • substantial need for data regarding the
extent of silvex and TC00 exposure due to the use of silv*x
on pluas. The population in the vicinity of che major uae
areaa that aay be aubjected to apray drift froa gt r»und rigs
haa not been eaciaaced. Moreover, neicher che excenc of
exposure Co applicacors or fa**a workers during spraying or
harveacing nor Che persistence of silvex and TCDD residues
on pluaa haa been investigated.
(6) Exposure due to Silvex Uae on Sugarcane
Silvex is used annually on approximately 113,000 to
230,000 acrea of augarcane primarily for contol of weeds
that are reaistaot to 2,*-D on an eatiaated 30,000 acres
(10Z) in Florida and on approximately 85,000 to 200,000 (30
eo 632) acrea (63Z) of the augarcane grown in Louisiana.
Silvex ia applied mainly by aerial application when the cane
38 B-
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is lets than 3 1/2 feet call in Louisiana. In contrast,
silvex is usually applied by ground rigs in Florida for
prt-taergiot weed control when seeds are expected to germinate
or iaaediately after the crop bed has been shaped.
The aost cooaon silvex foraulations used are the lov
volatile esters which are applied at the rate of 0.75 to 1.0
povnds active ingredients (a.i.)/acre in 10 to 15 gallons of
vater/acre for both pre-eaergent and post-eaergent weed
control.
The iapact of spray drift on the. population that resides
in the vicinity of sugarcane fielJs has not been determined
but the iapact of the extent of possible spray drift can be
estimated froa other studies. Spray drift during cerial appli-
cation his been shown to be dependent on the spray equipaent
used, hydrolic pressure, air turbulence, and the prevailing
wind speed. Spray droplets can drift aany miles away froa
the site of application (Akeason and Yates, undated). Drift
estiaetes for ground rig appication of 2,4-D have been
calculated experiaentally. Estimates indicate that there is
a potential for up to 8.0Z of the spray to drift at least
5 aeters away froa the target site depending on the spray
equipaent used, hydrolic pressure, and the prevailing wind
spaed (Maybank at al., 1978). Therefore, when the use of
the pesticide results in drift in these areas of huaan work
and habitation, people who live and work in the path of the
-59-
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drift nay be directly exposed to the pesticide by inhalation
and/or by deraei exposure to pesticide droplets ia the
ai, /cm drift. Moreover, there is little information
regarding the persistence of silvex sad TCDD residues on
this food source, end the delated question of exposure to
persons who harvest and handle the crop.
Data retrieved from nhe STORET System for both of
''hese sugarcane growing areas indicates the presence of
silvex residues in both surface water and sediment. However,
because silvex was used on other sites in the sugarcane
growing areas, it has not been determined whether these
residues orginated from uilvex sugarcane us« .
(7) Exposure due to Silvex Use on Hon-crop Sites
Silvex is used to treat many broadleaf, herbaceous,
and that may be present in a variety of urban and rural
non-crop areas such as hedgerows, storage areas, and
vacant lots. Recent data regarding the extent of silvex
used for these purposes is unavailable. However, data is
available from a 1974 report which indicated that approxi-
mately 60,000 pounds active ingredient (a.i.) of silvex was
used annually for general Maintenance of grounds at industrial .
commercial and inatitutiona I sites. Presently, the Agency
has no better estimate of how much silvex is used for
non-crop areas (EPA, 1978).
-60-
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Silvex is used throughout the country for t h * i kind
cf weed control. The most comnon formulations are the low
volatile silvex esters which are frequently formulated with
2,4-D or Dicanba for a broad spectrum of weed control
action. Ground rigs are used to treat large areas but hand
held application devices are frequently used for spot
treatment* in sm*ll areas. The Agency has no estimate of
the number of people that use silvex or the number of people
in the immediate vicinity of these spray sites because of
their heterogeneous nature.
Exposure for this kind cf usage appears to be
confined to the applicator and those people residing or
working in the immediate vicinity of the spray area.
Information from studies of forest workers who apply phenoxy-
herbicldes with backpack sprayers indicates that it may be
possible for the applicator to contact 0.8 ppb of the
chemical spray due to dermal exposre and 0.3 ppb due to
inhalation exposure (Lavy, 1976). Therefore, the Agency is
concerned about thr exposure that may result due to direct,
coutact aa weil us drift.
C. Epidemiologic Data
The risk assessment for silvex is based in
part on data showing th*t exposure to silvex and/or TCDD
results in tumors, and dead and deformed offspring in test
animals, and that the uses of the pesticide create opportunities
for exposure to humans. Together these facts suggest that
61
-------
if the an of eh* pesticide results is huatn exposure,
haaans who live end work ia ireti of use nay experience Che
kinds of adverse health effects observed iu test eoiaels.
This reasoning is borne out by the results of •
recent epidemiological study which reported that woaen
living in the vicinity of Alsea, Oregon have a stat istica 11y
significant higher incidence of spontaneous abortions
(miscarriages) than woaen living in a control area. Alsea
is an area in which two dioxin-containing pesticides,
2,4,5-T and silvex are used extensively for forest aanagenent and
on right* of way. Additional analyses of the data indicate
that there is a significant correlation between the use of 2,4,3-T
in the study area and the subsequent increase in the rate
# /
of sponta eous abortions in the study area.—
# j
—The Alsea study sas analysed using only 2,4.5-T data.
However, the serious iaplications of this study are as
applicable to silvex as to 2,4,5-T, because TCDD, the
contaainant contained in both herbicides, is a potent
aaaaalian fetotoxin and teratogen at very low doses.
Conversely, silvex and 2,4,5-T are fe totoxic and teratogenic
at coaparat ively higher doses. It is reasonable to
assuae that the adverse huaan reproductive effects
observed in Alsea, which have been attributed to low-level
exposure to 2,4,5-T, are due priaar ily, or at least in
part, to the TCDD in the 2,4,5-T. Therefore, since
silvex also contains TCDD, it is prudent to conclude that
the Alsea data are applicable to silvex use whan evaluating
potential reproductive risk to huaans. See 44 FR 15904.
»
-62-
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Thi« relationabip b«cv««a ixpoiurt to TCDD-containing
phenoxy herbicidea tod 4a increeaed incidence of aiacerriagea
in huaana ia not aurpriaing. Thia ia ch« aeae relationahip
Chat hea been deaonatreted co exiat irf teat aniaela through
nuaeroua eniael ntudiea. Vhile there ere uncertaintiea
concerning the eaount of phenoxy herbicide end/or TCDD
to which the Alaee aree woaen aey have been expoaed end
concerning the preciae route (or routea) of huaen expoaure,
the atetiatically aignificent incidence of aiacerriagea
deacribed above, coupled with the unconteatable data froa
the eniael atudiea, aekea it reeaonable to conclude that
woaen in the Alaee atu«*y «rei aey be expoaed to, end edveraely
effected by 2,4,5-T, ailvex end/or TCDD. Moreover, it ia
alao reeaoneble to laiuae thet the aaae type of efftcta
aey occur wherever end whenever 2,4,3-7 or ailvex containing
TCDD ia uaed.
Further, the Alaea experience any net be en iaolated
incident. Heporta of people edveraely effected by exposure
to phenoxy herbicidea end/or TCDD have frequently appeared
in aedical end acientific journela. Recent tuaaariea eppeer
in IARC , NRCC, and U.S. Air force docuaenta on phenoxy
herbicidea and dioxina. In eddition, aa a reault of the
2,A,3-T RPAR, the Agency haa received nuaeroua accounta of
adverae huaan health effecta which the reportera ettributed
to phenoxy herbicidea and/or TCDD. The cuaulative effect of
theae reported incidenta auggeata that people who live
and/or work in areaa of ailvex uae aey experience adverae
he elth ef feet a .
-63-
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III. Preliminary Beavfita Analy»i* of S ilvex uae on Range,
R~i.ce. Orchard*""'Sugarcane and Non-crop Areaa.
A. Introduction
Thia preliminary an«lyaia ia an aneiiaeac of the
econoaic impact of the cancellation of ailvex for uae on
range, rice, orcharda, augarcane, and non-crop areaa. Tht
analyaia aaauaea that 2,4,5-T alao vill be cancelled
for theae uaea. In view of the virtually identical toxi-
cological characteriatica of the two coapounds and the aiai-
larity of the benefita of both, it ia unlikely that only one
of thea would be cancelled.
The inforaation, relating to the benefita of ailvex,
uaed in thia report waa derived principally froa a aingle
aource - The Biologic and Ecnnoaic Aaaeaaaent of 2,4,5-T
("tJSDA Aaaeaaaent Report").—^ Alao under thia aeaorandua,
a joint USDA-Statea-EPA Silvex Aaaeaaaent Teaa waa foratd
to provide benefita inforaation on ailvex. The econoaic
analyaea for the augarcane and orchard uaea of ailvex are
baaed on preliainary inforaation partially provided by
aeabera of the Silvex Aaaeaaaent Tea*:.
• /
— Thia report waa prepared jointly by the USDA-Statea-EPA
2,4,3-T Aaaeaaaent Teaa, eatabliahed purauant to a aeaorandua
of underatanding between OSDA and E?A.
-64-
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There are disadvantages to the heavy reliance of
this analysis upon the 2,4,5-T Assessaent Report for the
range and rice information. As is coaaonly the case in
assessing benefits of pesticides, the available information
reported in the 0SDA Assessaent Report was a mixture of
eapirical data and expert opinion and did net lend itself to
precise statistical analysis. thus, the est iaates reported
in this analysis represent rough predictions of the iapact
of cancellation. The lack of confidence intervals or error
teras does not iaply exact precision. The estiaates are
aerely approxiaations of the projected iapacts within the
## /
liaitations of the data and analyses.—'
The general approach of this analysis is to evaluate
the econoaic impacts arising froa t •ri' shifting to alterna-
tives to silvex (other than 2,4,5-T) where alternatives are
available and, where no alternatives are available, econoaic
iapact s on users and at th* coaaodity and consuae r levels
are projected based on crop yield reduction and possible
user shifts to other crops then projecting these iapacts at
the coaaodity and consuaer levels where appropriate.
Iapacts oa users arc considered on a per-unit, per-establ ian-
aent basis and at the state, regional, and national levels.
*»/ The Agency is continuing to collect and review data
relating to the benefits of silvex use for range, rice,
orchards, sugarcane and non-crop areas.
65-
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( B) Suaaary of Findinia
(1) Rameland***^
There are an estiaated on* Million icru of range ioi*
paature land suitable for grazing in Che coneiguoua 48
itatei, plus 331 aillion acrei in Alaaka and 3 aillion acre*
in Hawaii. About 90 percent of this total acreage ia
rangeland. Of this total, approxiaate1y one percent ia
treated with herbicides, priaarily 2,4-0. Only about
150,000 acres, or less than 0.1Z of range acres, are
treated with silvex.
Silver is used to control various woody and herbaceous
plants found in rangeland. Host silvex use is directed
at control of various oak species which coapete with
desirable forage plants for water, nutrients, sunlight and
space. Treataent is generally directed at acreage with
severe infestation which, if left uncontrolled, would reduce
forage available for livestock grasijg.
A nuaber of cheaical and non-cheaical alternatives to
silvex are available to control the varioua weeds now
~~»/ "tar«eland" is defined as land producing forage for aniaal
consuaptioj, harvested by grating, which ia not cultivated,
seeded, fertilised, irrigated or treated with pesticides
or other such siailar practices on an annual basis. Fencerows
enclosing range areaa are included as part of the range.
-66-
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ia effective against oaks when applied aerially. Thus,
effective aubatitute treataeata for silvex au«t be applied
by ground techniques which are aore expensive and leaa
convenient. The availability of alternativea and the very
saall quantity of acreage involved indicate that no signifi-
cint econoaic iapacts will be felt at either the conauaer or
aarket level# if ailvex ia cancelled for thia uae. At the
uaer level, aoae inereaaed control coata and decreaaed
production aay be experienced by a aaall nuaber of uaera. In
aoae locationa, the iapact on uaera aay be significant.
(2) tice
Although about 962 of all D.S. rice areaa are treated
with one or aore herbicidea, ailvex ia uaed on only 2,000
acrea annually, or leaa than 0.1Z of all U.S. rice acrea.
In those areaa where silvex is used, it is taployed to
coutrol various broadleaf, aquatic and sedge weeds. These
weeds, it not controlled, reduce yield and lower the quality
of the rice by c ont aai na t ing the harvested grain with weed
seeds.
there are several ?heaical alternatives which are
likely to be eaployed as substitutes for silvex uie on rice.
These coapounds aay be soaewhat less effective and/or aore
expensive thau silvex for use on soae weeds. Therefore,
soae degree of increased control costs and reduced production
-67-
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aay be experienced on aoae icrei aa a reault of the aub-
atitution of cheat aateriala for lilfti. However, bcciuae
liUii ia uaed oo ao little rice-growing acreage, ehe *conoaic
iapact ac ehe uier, conauaer and aarkec levela will t>e qu*te
aaall if ailvex jere cancelled for thia uae.
(3) Orchard
Silvex ia uaed oo applea and prunea Co control preharveat
f-uit drop and on peara Co increaae fruic aec. Preaature dropa
cauie a coaplece econoaic loaa of prunea and a aubacancial loaa
of apple cropa. Approxiaately 30,000 acrea of applea (10Z of
U.S. crop) are created annually with about 2,300 pounda of
ailvkx. Mo«e of the treated applea are Red Delicioua, grown
in Waehington and aeveral other atatea, which are aold for
freah conauapcion. About 8,300 acrea of Italian prunea (9X
of O.S. acrea) grown in Oregon, Vaahingtoo, and Idaho are
treated with about 400 pounda of ailvex annually. Treated
prunea are believed to be aold priaarily for freah conauaption.
The extent of ailvex uaage on pear* ia unknown.
NAA ( 1-napthaleneacetic acid) and Alar (auccinic acid 2,2*
diaethyl hydraclne) probably would be uaed by apple growera
aa cheaical alternativea to ailvex. Soae acrea would
require two annual treataenta with theae aateriala for
effective control, whereaa uae of ailvex require* only one
-6a
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treacaent. The econoaic iapact it likely co conaiat of
higher coata co «pple growers, totaling approxiaately $1
aillion per year or 920 per av«rage affected acre, reaulting
froa the uae of theae alternativea. The higher drop eoatrol
coata will increaae production coata by 2-31 per year.
Apple production and quality ahould not be aignificantly
affected.
Prune growers currently uaing silvex would auffer
aignificant incoae reductiona if ailvex ia unavailable.
Italian and early Italian prunea in the Northwest atatea
drop an average of 35X of the fruit if ailvex ia not applied
in aid-June to control auaaer drop. Since there art no
regiatered alternativea to ailvex fo«- thia uae, production
and revenuea would decline aharply on the affected acrea.
Revenue reductiona totaling $1.8 aillion annually, or about
$222 per affected acre, are projected to occur, askuaing no
alternativea to ailvex are developed to prevest preharveat
drop. Continued loaaea of thia aagnitude would eventually
cauae growers to grow alternative cropa on the eatiaated
8,300 acrea of prunes for which preharveat drop probleaa are
aignificant.
The retail price of applea and peara would probably be
unaffected by cancellation cf ailvex for orchard uae. The
retail price vf prunea would increaae by an undeterained
aaount.
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(«~) Sun at
Silvex is used on sugarcane fields Co cooerol weeds aoc
controlled by 2,A Failure Co control these weeds can result
in reduced yields. About X (115,000 acres) of all O.S.
sugarcane acres (7S2,000 ac 4) were created with silvex in
1978. This reflects a significant decrease in silvex use over
previous y*ars, probably resulting froa increased use of an
alternative dicaaba /2,4-D aixture. The dicaaba / 2,4-D
coabioation alternative is likely to be the aost coaaonly used
substitute if silvex is canceled for use on sugarcane. Iconoaic
iapacts arising froa a cancellation of silvex would result froa
reduced yield, which would occur because the alternative is
less efffective than silvex . A worst-case esciaate indicates
a 21 loss of overall O.S. sugarcane production could be experi-
enced. Since O.S. - prod-iced cane sugar coaprises only 18Z of
the total O.S. sugar supply, no aeasurable sugar price changes
are likely to occur at either the aarket or consuaer levels.
( 3) lion-Crop Oses—^
Silvex is registered for control of aany broadleaved
and herbaceous weeds in a variety of urban and rural non-crop
areas such as fencerows, storage areas and parking lots.
Only a very saall percentage of non-crop areas
is treated with silvex each year.
•/"ion -crop areas" includes: fencerows, hedgerows, fences
Tnot otherwise included aaong previously suspended uses,
e.g. rights-of-way, pasture); industrial sites or buildings
(not other wise included aaong previously suspended uses,
e.g. rights-of-way, coaaercial/ornaaental turf); storsge
areas, waate areas, vacant and parking lots.
-------
Both cheaical and non-cheaical controls are available
a« alternatives Co silvex for uae on non-crop areas. The
cheaieal alternative# include 2,4-D, picloraa, dicaaba, AMS ,
aaierole. Non-cheaical controls include aechanical aeChods
such as aowing, shearing, and aanual aethoda. The relative
efficacy of che alternatives in coaparsion to silvex is
unknown. However, it is believed that one or a coabination
of the cheaical alternatives will be widely substituted for
silvex and will provide equivalent control.
The cconoaic iapact of cancelling silvex for non-crop
uses is not likely to be significant at user, consuaer
or aarket levels because little acreage is treated with
silvex and effective alternatives are readily available.
(C) Ceneral Production and Dse Pattert.
Silvex is produced doaestically by Th» Dow Cheaical
Coapany, Thoapson-Hayward Cheaical Coapany, Transvaal Inc.,
and Vertac Inc. Doaestic use of silvex is estiaated to be
about 3.0 aillion pounds acid equivalent (a.e.) annually.
The use of silvex on raoge and rice coaprises alaost T.ciZ
(202,000 pounds a.e.) of the estiaated 3.0 aillion pounds
a.e. used annually. Rangeland usage accounts for 6.7X
(200,300 pounds a.e.) of this aaount, and use on rice accounts
for 0.1Z (2,000 pounds a.e.). Reliable use inforaation for
71
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orchard uses is aoe available. Silvex is used on approxiaate ly
100,000 acres of rangeland and 2,000 acres of rice annually.
This acreage aaounes Co about 0.01 percent of che total U.S.
range acreage and 0.08Z of total U.S. rice acreage.
(0) Preliminary Benefits Analysis of Silver Pse on Range
land—
(1) Current Pse
A wide variety of herbaceous and woody plants grow
on rangelands. Several weed species controlled with lilvex
such as yucca, salt cedar and various oak species, coapete
with the desired forage species for nutrients, water, space
and light. Serious infestations of range weeds can signifi-
cantly reduce forage available for grazing and thus reduce
livestock production on the infested acres.
Silvex ie not a aajor range weed herbicide. Its use
has been liaited because 2,4,5-T is slightly less expeisive
and controls a broader apectrua of weeds. Of the 700
aillion acres of range in the U.S., only about 130,000
acres are treated with silvex annually. Silvex is used
priaarily to control several oak species, alaost exclusively
in Texas, Rew Mexico, Arkansas, Oklahoaa, Kansas, and
Missouri.
~/ "lame I and" is defined as land producing forage for aniaal
consuaption, harvested jy grating, which is not cultivated,
seeded, fertilised, irrigated or treated with pesticides
or other such siailar practices on an annual basis. Feneerows
enclosing range areas are included as part of the range.
-72
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This analysis evaluates only aerial application for the
control of oak apeciea; such applications are believed to
account for the aajerity of silvex range treataeoti.
(2) Evaluation of Silvex and alternativei
Silvex provides good control of several oak species for
periods of 5-10 years per application. Several registered
cheaical alternatives as veil as non-cheaical controls not
analyzed hrre are effective against one or aore of the
various range weeds controlled by silvex. However, these
cheaicals are either not registered for aerial application
or are not as effective as silvex for aerial application.
For exaaple, 2,4-D and dicaaba can be applied aerially, to
rangeland, as foliar sprays, but they are relatively
ineffective .is foliar sprays. The DSDA Assessaent Teaa
concluded that there is no effective alternative for aerial
spray control of oaks. ('or situations where ground applica-
tions, especially spot rreitaent, are practical the cheaical
alternatives aay provide effective control, depending on
che nature and coaplexit? of the weed problea.
Assuaing there are no alternatives to aerially applied
silvex for oak costrol, the yield effects could be severe on
acreage currently treated with silvex. Cancellation would
leave users with no aerially applied alternative control for
oak on these acres. In the post-blackjack oak area, beef
-73
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yields could fall from about 28 pounds of bee£ (live
weight) per sere with silvex control to 11 pounds of beef
(live weight) per acre for calf production and from about
84 to 45 pounds per acre for steer production. In the
sand-shinnery oak area beef yield could <«»cline from about
27 to 14 pounds per acre following a shift from silvex to
no-coatro1.
(3) Economic Iapact
Current silvex use appears to be liaited primarily to
control of various oak species by aerial application. If
silvex is cancelled for this use most users will probably
choose not to treat large areas formerly treated with silvex
because of the absence of a practical md efficacious
aerially applied control agent. These use'i will save from
$4.60 to $13.00 per acre ii control coiti . However, this
savings will be offset by lower revenues from lower beef
production. Those silvex u^ers who need only spot treatments
will be able to obtain at least some control with one or
¦ore of the various alternatives now available.—^ The
tggregaze iapact on users will be saall because of the small
acreage involved.
*/ In addition to the cheaical alternatives now registered
Tor range use, several promising herbicides are under
review; this analysis does not atteapt to estimate the
iapact of these or other possible new alternatives.
7 4
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The cancellation of silvex for range weed control
will not have significant econoaic impacts at either the
consumer or market levels, since few vangeland acres are
currently treated.
E• Preliminary Benefits Analysis of Silvex Use on Rice
(1) Current Use
Conditions favorable for growing rice also favor the
growth and reproduction of many terrestrial, aquatic, and
aemi-aquatic weeda. Weeds in rice-growing areaa produce an
abundance of seed. Once these infest the land, they are
difficult to remove and say remain viable in the soil for
many years. Rice weeds reduce yields by direct competition
and reduce quality through contamination of tne harvested
rice with weed seeds.
Th* total estimated direct losses and expenditures
for weed control in U.S. rice acreage were $295 million
annually for the 1975-1977 period. Weeds reduce the yield and
quality of rice in the U.S. by an estimated 15 percent each
year on approximately 2.5 million acres. The average loss
was valued at about $165 million annually during the 1975-1977
period. The cost of using all herbicides on rice acreage
was about $60 million each year during the same period. The
-------
cose of cultural practice* (including rotation, land preparation,
irrigation, and fertilization) during this period vas
estiaated at $70 aillion.
Silvex is useful for controlling certain weed pests,
but it is injurious to soybeans, an iaportant crop grown ia
rotation wi ;h rice. Silvex is used annually on only Z,000
rice-growing acres, primarily in the lower Mississippi
Valley area. The average annual cost of silvex for
use on these 2,000 acres for 1975-1977 was approxiaately
$20,000.
Propanil and aolinate are the herbicides used aost heavily
on rice acre«Ae. Coabined, these cheaicals account for 73Z
of herbicide acre-applications to rice. Each of these coa-
pounds controls soae of the weeds controlled by silvex and
is likely to be used to rep'.ace silvex on soae acres now
treated with silvex* In addition, 2,4-0, MCPA, bifenox,
bentason aad oxadiazon are all currently used on rice and will
control various soabinations of weeds currently controlled by
silvex.
Cultural and aechanical weed control ethods used in rice
production include suaaer fallowing, seedbed preparation, crop
rotation, special seeding aethods, aanageaent of irrigation
water, cultivation and hand weeding (in sparse weed infesta-
tions or in saall isolated areas). Although soae of these
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methods are effective alone on lose rice weede, they are
usually combined with chemical herbicide treatments.
(2) Evaluation of Silvex and Alternatives
Silvez controls most broadleaf, aquatic and sedge weeds
more effectively than the registered chemical alternatives.
However, silvex is very injurious to ..o/oeans, a crop commonly
grown in rotation with ric*. In addition, silvex is also
damaging to cotton, a crop often grown aear rice fields.
Propanil is currently applied to tbout 95Z of the rice
acres in the lower Mississippi Valley ar*a for early season
control of grasses. Propanil selectively kills barnyard
grass and many other grass, agnatic, broadleaf and sedge
weeds. At maximum label rates (8 lbs/acre/season) propanil
alone is said to often fail to provide adequate control of
the total weed population. fropanil controls hemp sesbaoia
as effectively as silvex. However, northern jointvetch,
ducksalad, and redstem are only partially controlled by
propanil. 2,4-D is tho
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Molin«te does not effectively control heap sesbania,northern
jointvetch, ducksalad, aorningglory or redstea. MCPA ia not
used ia the silvex use are* since it is relatively ineffective
on heap sesbania, northern jointvetch, and Indian jointvetch.
Bifenox, bentaxon, and oxadiazon are three nev herbicides which
arc currently used to a limited extent. They are not as
eftective as silvex on aost broadleaf and aquatic weeds.
If silvex were canceled for use on rice, current silvex
users probably tould turn to alternative cheaical controls.
2,4-D and propauil would be the aost likely alternatives. Us*
of these alternatives would cost $7.40 per -~re-treata*»nt for
2,4-D and 912.90 per acre-treataent for propanil coapared with
)9.30 per acre-treataent for silvex. (Jse of propanil aay
require a second treataent, thus raising the annual cost of
control to 921.80 per acre.
(3) Econoaic Iapact
Silvex is used on only 2,000 rice-growing acres in the
U.S. There are sev*r*l alternative controls available which
will function adequately as substitutes for silvex. For
these reasons, econoaic iapacts are not expected to be
significant at us*r, consumer or a«rk*t levels.
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F. Preliminary Benefits Analysis of Silvex Use in
Orchard!
(1) Current Die
Silvex ia registered for uae in preventing preharvest
fruit drop of applea and prunes and to increase the yield of
pears.
Prunes that drop froa trees prematurely cannot be put to any
commercial use; applea that drop prematurely can, in some
cases, be sold for low-return uses, such as cider.
On apples, silvex applications are generally made using
ground equipment a few days before preharvest drop would
normally occur. Ordinarily, the application takes place one
to two weeks prior to the expected peak of harvest for a
given apple variety, and one application controls drop for
several weeks (through harvest). Both the timing and
application rate of the silvex spray vary according to the
cultivar involved.
In addition to minimising preharvest apple drop and
thus increasing aggregate production, silvex alsa acts
to increase the quality of treated fruit. The extra one ro
two weeks of on-tree ripening of fruit facilitated by the
use of silvex tends to improve the color, sugar content and
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flavor of ebc aprayed fruit. Theae chacC•riatica arc
particularly iaportaat for freah-aarket growera—
Silvex uac on certain prune varietiea in th« Northwest
ia of aajor iaportauce. Silvex ia uacd in the production of
Italian and Early Italian prunes in Oragon, tfaahington and
Idaho. It ia believed that i;lvex applicationa prevene an
average 30Z drop rat* which would otherwise occur. Silvex
ia alao used on about 700 acraa of Anjou pears in Oragon and
Washington to increase fruit act in the year following
application. The uac of silvex for this purpoac ia not
recoaaended by either atate.
Very little quantitative data are available indicating
the apecific location and/or extent of ailvex uae on applea
or Information for thia analyaia waa developed
through diacuaaiona with horticultural apecialiata. Baaed on
theae diacuaaiona, it it eatiaated that approxiaatcly 30,000
*/ The aajority of the ailvex uaed on applea is probably
applied to led Delicioua, the leading apple variety which
accounted for 33X of U.S. apple production in 1977. The
aajor ted Delicioua producing atatea, ranked in order of 1977
productioe, are aa follows: Waahington (33X of O.S. ftrd
Delicioua ere?), North Carolina (3X), California (3X),
lew York (41), Virginia (4X), Oregon (3X), Michigan (3X),
all other atatea (212). Saall quantitiea of ailvex are
alao applied to other apple cultivars auaceptible to pre-
harveat drop, including Jonathan, toae Bc
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acres of U.S. apples (10% of U.S. apple acreage) are created
annually with silvex —^
Silvex use od prunes if probably res trie ted Co Italian
and Early Icalian varietiea in che Northwest •tacea (Oregon,
Washington, Idaho).— Recent estiaates indicate chac abouc
801 and 100%, respectively, of Washington and Idaho prunes are
treated annually with silvex. The extent of silvex use on
pears ia not known.
v 2) Evaluation of Silvex and Alternatives
Currently, two alternatives to silvex are available
for use on apples to control preharvest drop. NAA (1-naptba-
leneacetic acid) is registered for apples both as an early
season thinning agent and as a late season drop control
agent. NAA aay be applied at the race of 35 grass of active
The quantity of silvex required to treat SO,000 acres
~ot apples per year was derived based on the following
aaauaptions:
aaterial used: triethanolaaine salt of silvex 9.61
equivalent to 6.2X silvex by weighc
or 8.5 ounces a.i. per gallon,
applicacion race: 1/4 pint/100 gallona water, 300
gallons water/acre; 3/4 pint/acre
x 1.063 ounces a.i./pint • .8
ounces a.i./acre,
quantity a.i. used: 50,000 acrea treated x .8 ounces
a.i./acre * 2,500 pounds silvex
tf • % •
**/ Prune acreage in the affected states is as follows:
Oregon
Washington
Idaho
7,40? acres
1 ,940 acres
978 acres
acres
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ingredient per icr« via air or ground to control preaature
drop; Application is aade 7 to 14 days before harrest. Alar
(succinic acid 2,2-diaethyl hydraside) ia registered for
preaature drop control at the rate of 6.8 pounds of active
ingredient per acre.
Silves is believed to be effective in preventing
apples froa dropping preaaturely. lovever, quantitative
data indicating the aaount of drop actually prevented are
not available. Zt ia believed that silves is a preferable
drop control agent in aany areas because of its relatively
long period of effectiveness (3 to 4 weeks in the last, up
to 5 to 6 weeks ia the Vest).
¦AA and Alar would have increased usage on apples if
silves were unavailable, but they are thought to be soaewhat
less effective than silves. MAA is less effective in the
southern apple states and is best suited for varieties other
than Red Delicious. RAA's period of effectiveness is
shorter than silves's; a second application aay be needed in
soae eases. Alar is a aajor alternative to silves on apples
since it is suitable for use on led Delicious. lovever, Alar
is believed to be less effective than silves for preharvest
drop control and aay reduce fruit site. Alar aay also cause
undesirable changes in fruit shape the following year if
applied within 60 days of harvest. Alar aay be applied froa
10 to 70 days after full blooa but is usually applied froa SO
to 70 days following blooa to ainiaise the adverse fruit site
82
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eczecEi. inui, uae or axar aa a iutii aittrnaiiTt wouia
neceaaitate a carefully ciaed apray achedule aod would
reaulc in aoaewhae lover preharveac drop effecciveaeaa.
Silvex ereataent of pruaea ia believed Co reaulc in
recencioo of approxiaacely 95X of che fruic uncil hanreac.
Silvex uae on prunea ia particularly uaeful during yeara
vhen cool but noc froacy conditiona occur in che apring,
reaulcing in a particularly light fruit act. Without ailvex,
aa auch aa SOZ of the Early Italian prunea and about 22.51
of the atandard Italian prunea in the northveac acatea would
be loat due to preaature fruit drop.
There arc currently no regiatered alternativea to
ailvex for preaature drop control on prunea. However,
2,4-DP (currently regiatered for aoae non-crop applicationa)
reportedly haa provided good prune drop control in field
ceata. There are no regiatered alternativea for ailvex uae
on peara.
There ia no indicatioa that non-cheaical controla are
effective in preventing prehanreet drop of applea or pruaea.
(3) Econoaic Iapact
(a) General Coneiderationa
Since applea and prunea are peraanent, capital-inteaaive
cropa, the loaa of ailvex would aot cauae a ahift to other
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aa eeriala (ia the caaa of applea). Pruaa grow* ra would ba la fc
without: a regiatered preharveat drop conero 1 agaac «ad would
likely incur aoaic idvirat ec oaoai c iapac t a. Thaaa ef fect a
eould eauae « long-term ahift fro* pruaea Co other cropa.
For applaa, ic ia aaauaed chac all of cha eatiaated
acraaga curreatly tre ated with ailvax will ba eraaead w i eh
alearaa tivea (Alar and BAA) . Sua Co NAA* a ihorear e f fee t iv e-
s«ai period relative Co ailvex'a aad the disrupeioa ia
harveae iag aoaa MAA-treited orcharda which aey ba axpaccad eo
occur bacauaa of poor wtathcr, labor ahort'gea, aad other
factor a, it ia aaauaad that aa aucb aa 2S1 of tha R AA-cra«ted
acraaga aay requi ra as addieioaal ap piica t'oa. la addition,
a iaca Alar aay aoe provide a lava I of pr eh arv e at drop control
equal to that provided by NAA or ailvex, aa aaauaptioa waa
aade that aa additional preharveat applieacioa of NAA aay be
required oa aa aueh aa 23Z of the Alar-treated acreage to
provide a level of preharveat drop control equal to that
provide by ailvex.
Although Alar ia aigaificaatly aore expeaaive to uae Chan
IAA, iea beaefieial effect a other chaa drop control would tend
* /
to encourage uaage.- Ia the aba eac e of a precise at thod co
—' Alar proaotea iateaaificatioa of color ia red eultivara,
reducea iacideace of water core aad vegetative growth,
aad proaotea flower bed foraation.
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deteraine the relative substitution ratio of Alar and RAA for
silvex, thia analysis aisusts aa equal distribution of the tvo
alternatives.
For prunes, the analysis assuaes that, as a vorst case,
the unavailability of silvex will result in an inereaental
loss in annual production of 30Z of the Italian prune crop in
Oregon, Vashingtoo, and Idaho. This assuaption is based on a
"noraal" (with silvex) preharvest drop of 5X and an "abnoraal"
(without silvex) loss rate of 3SZ due to unchecked aid-June
drop.
(b) Dser Iapacts
The unavailability of silvex will increase grower
preharvest drop control costs for apple growers by about
fi.OO (using NAA) or $33.00 (using Alar) per acre-treataent.
Although the use of Alar significantly increases preharvest
drop control costs, it also provides additional benefits:
Alar, like silvex, enhances the quality of the fruit and
proaotes early-season aarketabiIity. Thus, it is reasonable
to conclude that Alar would be used by growers as a silvex
alternative.
• 3-
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The uit of Alar and NAA aa ailvex aleernativea aay
increaae tpple grower production coata by aa such as about
$1 aillioa per year or an average of $20 per affected
acre. Since apple production (growing ~ harvesting) coats
range froa about $700 - $930 per acre, the projected increaae
in drop control coata would iucreaae total production coata
by froa 2-3X per year on the affected acrea. Aaauaing that
50,000 acrea of applea are currently treated with ailvex per
year, the coat iapact would occur on about 10Z of U.S. a' pie
producera.
Growera of Italian-variety prunea would incur aajor
adverae incoae iapacta if ailvex ia unavailable. Prune
grower iapacta were derived aa follows:—''
~/Thia analyaia ia baaed on a 3-year (1973-1977) average
price for freah prunea grown in Oregon. Production
averagea and coata are baaed on a 1974 budget for Italian
pru. a grown in the Hillaaette Valley of Oregon. Costa
wert tdjuated upward by 3Z per year to account for
inflation during the 1974-1979 period. Coata without
ailvex were reduced by $10 per acre to account for the
lack of treataent expenae if ailvex ia unavailable (treat-
aent coata uaing ailvex on prunea aaauaed to be the saae
aa thoae for applea).
with ailvex:
average production per acre:
aarket:
grower price per ton:
average groaa revenue per acre:
average production coata per acre:
nec revenue per acre:
freah
$155
$775
$504
$271
5 tona
-•6-
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average production per acre: 3.5 Com
¦arkec: freah
grower price per ton: $155
average groat revenue per acre: $543
average production coata per acre: $494
net revenue per acre: $49
4
Seduction in per acre net revenues (from $271 to
$49) of thia magnitude (822) due to the lack of preharveat
drop control amounta to an aggregate revenue loaa of about
$1.8 aillion per year. Revenue loaaea of thia magnitude
(aaauning the continuing lack of an alternative for ailvex)
would probably lead growera gradually to replace the Italian
prune cultivara with other cropi; completion of thia proceaa
would take aeveral yeara following ca*»allation of ailvex.
Asauming growera would replant the affected acrea with other
tree fruits, they would incur establishment coata ranging
froa about $3,000 to $5,000 per acre in curTtnt dollars.
Sufficient information to evaluate producer the impact
of a cancellation of ailvex for uae on peara ia not available.
(c) Conaumer Impacts
The coat increaaes projected for affected apple growers
($1 mi 11ion/ year) may be absorbed at the grower level since
only about 10X of U.S. growers would be directly affected by
a restriction on silvex. If the coats "ere paaaed on to
conaumera, the retail price effects would be negligible.
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Retail price* for prune* would be expected Co increase
as supplier dropped, but Che extent of such an increase
cannoc be reliably determined with available data. The
estimated 30Z reduction in production of Italian prune
cultivars in the Northwest would result in production
losses of 12,390 ens (8,260 affected acres X l.S ton loss
per acre), as auch as 40Z of U.S. fresh prune production
(30,700 tons in 1977) and 6Z of total U.S. prune production
(fresh, processed, and dried prunes; 215,^00 tons).
Sufficient information to evaluate Che consumer impact
of cancellation of silvex for use on pears is noc available.
(d) Limicationa of Analysis
The foregoing analysis has the following limitations
in addition to the limitations common to the economic
analysis of the range, rice, non-crop and sugarcane uses of
silvex:
(1) Extremely little data are available concerning
the ffxtent of silvex use on apples, prunes or pears; and
(2) Information provided by horticultural specialists
was used in lieu of quantitative data concerning extent of
silvex use and crop yields withouc silvex.
88-
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G• Preliminary Benefits Analysis of Silvex
Use on Sugn cine
(!) Current Use of Silvex and
A1ternatives
Silvex is used in Louisiana and Florida sugarcane
fields to control various weeds which have developed
resistance to 2,4-D. In Louisiana, these weeds include
goldenrod, aster, alligator weed, and various winter annual
broadleaves. In Florida, the priaary target weed pests are
dogfennel, ground cherry, nightshade, and ragweed.
In Louisiana, the principal alternative to silvex is
a combination product, consisting of dicaaba (1 pound
per gallon) and 2,4-D (1 pounds per gallon). Florida does
not now have a registration for this combination product.
Therefore, 2,4-D is the only currently available alternative
to silvex in Florida.
Silvex use has decreaird markedly in Louisiana in recent
years (Table 1). The decreased levels of silvex in Louisiana
have been attributed to shortages of silvex and the lower
application costs of the 2,4-D-dicaaba coabination product.
Soae of the Louisiana cane growers are likely to shift back
froa the 2,4-D-dicaaba coabination product to eilvex
because of yield losses reportedly experienced with the
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combination produce. In addition, »ome sugarcane acreage is
shifting to soybean production in Louisiana. The 2,4-D-dicamba
combination product cannot be used on sugarcane adjacent to
soybean fields because it is phytotoxic to soybeans. This
is expected to further increase siivex use.
Table 1. Siivex Use on Sugarcane Grown for Sugar and Seed, 1978
1 1976 1977 1978 1
5Location Harvested Treated Harvested Treated Harvested Treatedl
1 — -1,000 acres— 1
IFlorida 298.0 30.0 300.0 30.0 310.0 30.0 1
1Hawaii 106.7 0 103.5 0 108.3 0 1
^Louisiana 313 . 0 200 . 0 32 2.0 1 70 . 0 300 . 0 85 . 0 1
1 Texas 27.3 0 33.9 0 34.1 0 1
1U.S.* 747.0 230.0 739.4 200.0 752.4 115.0 1
*7 Puerto Rico is not included, but siivex use in that location is negligible.
Exp« -t opinion suggests that sugarcane yield loss of
less rhan 10Z would occur in Louisiana if the 2,4-D-dicamba
combination product were substituted for siivex. In Florida,
yield losses of up to a maximum of 30Z could occur if 2,4-0
were substituted for siivex.
(2> Economic Impact
(a) User Impacts
The economic impacts of the cancellation of «ilvex to
sugarcane producers include changes in weed control costs
4nd potential yield losses in Louisiana and Florida.
Berbicide costs would decline in both Louisiana and Florida.
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la Louisiana, Che substitution of the 2 ,4-D-dicamba combi-
nation product for ailvex would reduce chemical coats from
$5.00 to $3.50 per acre. In Florida, the aubatitution of
2,4-D for silvex would reduce chemical coats from about
$5.00 to $4.00 per acre. The aggregate decrease in weed
control coses .s estimated at approximately $260,000 annually
(aaaumes the 1976-1978 average of silvex treated acre*).
This raving in herbicide costs will be offset by yield
losses and therefore gross revenue losses to sugarcane
producers. Yield losses of 252 are expected to result in
a loss in value of production of approximately $4.0 million
in Florida. Yield loaaea ranging from 0 to 10 percent could
result in losses in value of production as high as $6.3
million in Louisiana.
Aggregate economic impacts to the users of silvex
are estimated at approximately $3.8-10.1 million annually.
Aggregate losses of $4.0 million ($130 per silvex treated
acre) are expected in Florida. In Louisiana, estimated
economic impacts range from gaina of $0.2 million to loases
of $6.1 million (economic impacta ranging from a gain of
approximately $1.50 per acre to loases of $40 per silvex
treated acre), depending on the level of yield loaa (0~10Z).
(b) Market and Consumer Impacts
The 1976-197C average annual sugarcane production
exceeded 26 million tons. Production losses of 596,580
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com following a ailvex cancellation (aaauaing a 25Z yield
loaa and a 10Z yield loaa on ailvex treated acreage in
Florida and Louiaiana, respectively) ia approximately 2Z of
Che total U.S. cane production. 1978 U.S. - produced cane
augar repreaented leaa than 18Z of the U.S. augar supply.
Therefore, the cancellation of ailvex ia not anticipated to
reault in aeaaurable augar price changes at the aarket or
conauaer level. Since cane can be aold for either augar or
seed at approxiaately the aaae price, aeaaurable price
changea are not anticipated in the aeed cane aarket.
H. Freliainary Benefita Analysis of Silvex uae on
# /
Non-crop Areaa—
(I) Current Pae
Silvex ia registered for control of aany broadleaved and
herbaceoua weeda^^in a variety of urban and rural non-crop
areaa auch aa fencerowa, storage areas and parking lots.
Silvex is used becauae of ita relatively low cost, the broad
apectrua of weeds it controls and ita aelectivity for control
of undesirable plant speciea. Generally, the weed control
achieved on theae sites does not involve aajor econoaic
benefits.
•/"Hon-crop areaa" includes: fencerows, hedgerows, fences
Tnot otherwise included aaong previoualy suspended uses,
e.g. rights-of-way, paature); industrial sites or buildings
(not other wise included aaong previoualy suspended uses,
e.g. rights-of-way, coaaercial/ornaaenta I turf); storage
|f*as, waate artaa , vacant aod parking lots.
— Pest weeds include the following broadleaved planta--
pigwesd , t.^gweed, laabsquarter s horsenettle, cocklebur,
aorningglory--and woody pi ants--oaks , poplar, cottonwood,
wild cherry, blackberry, honeysuckle, poison ivy, and
wild grape.
92
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Recent data on Che usage of silvex for noocrop areas
ia not available. However, a 1974 publication reported that
60,000 lba. a.e. of silvex were uaed for general aaintenance
on 30,000 acres of grounds at industrial, coaaercial and
institutional sites. This area is a saall proportion (1.7Z)
of the 1.8 aillion acres treated with herbicides for
grounds aaintenance.
Both che-rical and non-cheaical controls are available
as alternatives to silvex. Cheaical alternatives include
herbicides, such as 2,4-D, picloraa, dicaaba, AMS, or
aaitrole. Probably the aost coaparable alternatives are
coabination products, such as 2,4-D ~ picloraa or 2,4-D
~ dicaaba. Soil sterilants, such as sodiua borate or sodiua
chlorate, control weeds that silvex controls but are effective
priaarily as preventive controls. Subsequent infestations
soaetiaes aay require follow-up treatments with conventioual
herb icides.
Mechanical aethods of control, such as aowing or shearing,
or aanual aethods could also serve as alternatives to silvex.
(2) Evaluation of Silvex and Alternatives
The efficacy of the alternatives coapared with that of
silvex is not Known. The spectrua of weeds controlled will
differ froa that of silvex for the individual active ingredients.
91
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However, ailvex'a weed apectrua aay be approximated fairly
cloaely by uaing a coabination product or by uaiag aultiple
applicatioaa of different herbici'ea.
Generally, so aore than one treataent with aiUei ia
aeeded aaaually to achieve control of the problea weeda.
In aoae circuaatancea, one treataent will give control
for up to four yeara. Coabination producta with 2,4-D and
picloraa 11 give control for a length of tiae coaparable
to that provided by ailvex, but other herbicidea, auch aa
2,4-D alone or aaitrole, aay require aore than one treataent
annually. The length of control with aechanical or aanual
aeana ia unknown.
(3) Econoaic lapact
Xn general, effective alternativea to ailvex exiat for
non-crop aitea. Effective alternative coabination producta
which provide equally long tera control are regiatered.
lapacta on uaeri of ailvex will be felt in the fora of
increaaed control coeta for the coabination alternativea.
Cancellation for the non-crop uae of ailvex ia likely
to cauae little,
-------
IV. REGULATORY DETIRMIHATIOW
Section 6(b) of FIFRA provide* that the Agency
¦•7 aove Co cancel the registration of a pesticide H[i]f it
appears to the Adainistrator that a peaticide... when uaed
in accordance with widespread and coaaonly recognised
practice, generally causes unreasonable adverse effects on
the environaent." Zn effect, this "unreasonable adverse
effects" standard requires a finding that the risks of each
use of the pesticide exceed the benefits of use, when
the pesticide is used in accordance with the teras and
conditions of registration or in accordance with widespread
and coaaonly recognised practice.
Upon concluding the RPAR review of a pesticide, if
the Adainistrator deteraines that the risks of use outweigh
the benefits of use, he Bay issue a notice of intent to
cancel or deny registratioa , pursuant to section 6(b)(1)
or Section 3(c)(6). If on the other hand, the Adainistrato
deteraines that the use of the pesticide appears to cause
unreasonable adverse effects on the environaent, that there
benefits will assist the Agency in deteraining whether or
not to cancel the pesticide, he aay issue a notice of intent
-93-
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Co hold a hearing pursuant to section 6(b)(2) of FIF1A to
deteraine whether the registration should be cancelled or
applications for registration denied. In the present
instance, relative to the orchard, sugarcane, rice, rangeland,
and other non-suspended uses of rilvex, a determination to
issue a notice of intent to hold a hearing pursuant to
section 6 (b) (2) is the prudent course of action.
The foregoing review indicates that exposure to
silvex and/or TCDO nay result in significant adverse effects
on exposed populations. Agency analysis shows that the
rice, sugarcane, orchard, rangeland and non-crop
uses of bilvex create opportunities for direct and indirect
exposure to huaana through aerial drift and/or relate*
cootaaination of water, food, and environaenta 1 aedia.
Even without quantitative data^ on levels and routes
of exposure, it is clear that any exposure, particularly in
the case of TCOD, whether froa a single source or cuaulative
sources, appears to pose risks of oncogenic, fetotoxic
and/or teratogenic effects in the exposed populations.
Additional data on routes of exposure, relative contribution
froa the several uses of the pesticide in areas of aultiple
use, and aechanisas for reducing exposure would assist the
Agency in assessing with greater precision the degree of
haiard associated with the non-suspended usee of silvex.
*/ Because of the aany varied and widespread uses of silvex
Tilvex, it is often difficult, or iapossible, to ascribe
residue to any one particular use.
-»6-
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The Agency estiaates that cancelling the use of
silvex on range would have only a flight iapact on fara
m
incoae and beef price*. A nuaber of cheaical and non-
cheaical alternative* to silvex are available to control the
varioui weed* not treated with silvex. The availability of
alternative! and the very saall quantity of acreage involved
indicate that no unreasonable econoaic iapact* will be felt
at either the coniuacr or aarket level* if silvex i* cancelled
for thi* u*e. At the user level, *oae increased coetrcl
cost* and decreased production aay be experienced by a saall
auabc of users. Zn soae locations, the iapact on users aay
be significant.
There are several cheaical alternatives which are
likely to be eaployed as substitutes for silvex use on rice.
These coapounds aay be aoaewhat less effective and/or aore
expensive than silvex for use on soae weeds. Therefore,
soae degree of increased control costs and reduced production
aay be experienced on soae acres as a result of the sub-
stitution of these aaterials for silvex. At the user level
the increased costs and reduced production will not be
large. However, beeause silvex is used on little rice-growing
acreage, the econoaic iapact at the uaer, the conauaer and
aarket levels will be quite saall if silvex were cancelled
for this use.
97
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diaeChyl hydrazine) probably would be uaed by apple growers
as cheaical alternatives Co silvex. Soae acre# would require
cwo annual treacaenci wieh these aaceriala for effective
control, whereaa uae of silvex requires only one creacaenc.
The eeonoaic iapace ia likely Co conaiac of higher eoici Co apple
growers reauleing froa Che uae of cheae alternatives equivalenc
Co - 'ocal of approxiaately 91 aillion per year or $20 per
a**i«ge affecced acre. The higher drop concrol costs will
increaae production coata by 2-3X per year. Apple production
and quality should not be significantly affected. Prune
growera currently uaiog silvex would auffer significant incoae
reductions if ailvex ia unavailable. Italian and early
Italian prunea in the Northwest atates drop an average of 35*
of the fruit if ailvex ia not applied in aid-June to control
auaaer drop. Since there are no regiatered alternativea to
ailvex, production and revenuea would decline aharply on the
affected acrea. levenue reductiona totaling 91.8 aillion
annually, or 9222 per affectsd acre, are projected to occur,
aaauaing no alternativea to ailvex are developed to prevent
preharveat drop. Continued loaaea of this aagnitude would
eventually cause growers to push out the estiaated 8,300 acrea
of prunea for which preharveat drop probleaa are aignificant.
The retail price of applea and pears would be unaffected
by cancellation of ailvex for orchard uae. The retail price
of prunes would increaae by an undeterained aaount.
-98-
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The dicaaba - 2,4-D coabination ilternicivc it likely
co be Che ioic coaaonly used aubaticute if ailvex ia cancelled
for uae on augarcane. Econoaic iapacca ariaing froa a
cancellacion of ailvex would resulc froa reduced yield,
which would occur becauae che alternative ia leaa effective
ehan ailvex. k worit-caie eaeiaace indicate a 2Z loaa of
overall U.S. augarcane production could be experi-
enced. Since O.S. produced cane augar coapriaea only 18Z of
che cocal D.S. augar aupply, no aeaaurable augar price changea
are likely to occur ac either che aarkec or conauaer level*.
Both cheaical at>d non-cheaical controla are available
aa alternatives to ailvax for uae on non-crop artaa. The
cheaical alternativea include 2,4-D, picloraa, dicaaba, AMS,
aaitrole. Non-cheaical controla include aechanical aethoda
such aa aowing, ahearing, and aanual aethoda. The relative
efficacy of the alternativea in coaparaion to ailvex ia
unknown. However, it ia believed that one or a coabination
of the cheaical alternativea will be widely aubatituted for
ailvex and will provide equivalent control.
The econoaic iapact of cancelling ailvex for non-crop
uaea ia not likely to be aignificant at uaer, conauaer or
aarket levela; little acreage ia treated with ailvex, and
effective alternativea are readily available. In addition,
weed control on theae acrea doea not confer aignificant
econoaic benefita.
99
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While eh* benefice of silvex use on rangeland, rice,
iu|trc«ae, orchards and aon-crop artai are in some respects
not insubscaneial, ehese benefits do noe, in ehe Ageacy'j
judgement, appear Co offaec Che risks which these uses pose
Co aaa aad che environment. Accordingly, Che rangeland,
rice, sugarcane, orchard and noo-crop uses of silvex appear
generally Co cause unreasonable adverse effeccs on che
env ironaene.
Because of uncercaineies and incaapl4Ce data relating
Co soae of che factors which enter inco Che risk-benefic
analysis, che Agency is seeking addicional daca on chese
silvex uses before aaking a final regulacory decerainacion.
FirtA provides for ehe resolucion of such quescions through
public hearings held pursuanc Co scceion 6 (b)(2). Through
che hearing process, Che uncercain areas becoae subject co
public debaee, new inforaaeion is colleceed, and che Agency
is able Co arrive ac an inforaed decision.
Moreover, in Chis case, a section 6(b)(2) hearing is
parcicularly appropriaee because seccion 6(b)(1) hearings on
che suspended uses of silvex are currencly in progress.
Because aany of ehe issues eo be reviewed and resolved are
generic Co boch Che suspended and ehe non-suspended silvex
uses, inforaaeion and approaches developed for one cacegory
aay shed addieional lighe on che ocher cacegory. Thus, a
section 6(b)(2) hearing aerged with ehe ongoing 6(b)( 1 >
hearing would allow consolidaced debaee and disposieion
regarding all silvex uses.
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Allen, J.R., D.A. Barsotti, J.P. Van Miller, L.J.
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101
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Burger, E.J., Jr. 1973. luoaary: conference on
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Dow Chemical USA. 1977 . Preliainary ¦ueiiaeac of chronic
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-104-
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106
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Meao. 1979c. Carcinogen Aa•caiatnt Group's risk aa aeasaent
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