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isoxaben (Gallery, Snapshot) Application to Register Withdrawn 2/94

New York State Department of Environmental Conservation
50 Wolf Road, Albany, New York 12233
                                    FEB 11 1994
Mr. Steve A. McMaster
Manager, State Regulatory Affairs
308, 3E
9330 Zionsville Road
Indianapolis, Indiana  46268-1054
Dear Mr. McMaster:
Re:  Applications to Register the Pesticide Products:
     Gallery Technical 91~      (EPA Reg. No. 62719-144)
     Gallery 75 Dry Flowable    (EPA Reg. No. 62719-145)
     Snapshot 80 Dry Flowable   (EPA Reg. No. 62719-174)
     Snapshot 2.5 TG            (EPA Reg. No. 62719-175)
     Pursuant to your January 10, 1994 correspondence to this -office, 
the New York State Department of Environmental Conservation (NYSDEC) 
acknowledges DowElanco's decision to withdraw the applications to 
register the referenced pesticide products containing the new active 
ingredient isoxaben.
     The data package submitted by DowElanco on April 23, 1991 to the 
NYSDEC for the new active ingredient isoxaben was reviewed by the 
NYSDEC's Pesticide Product Registration Section, Division of Fish and 
Wildlife (DF&W), and Division of Water (DOW), and by the New York State 
Department of Health (NYSDOH).
     On September 29, 1993, representatives of DowElanco met with 
Department staff in order to address the remaining environmental fate 
issues surrounding their application to register the referenced products 
in New York State. The Department reviewed the following two additional 
isoxaben environmental fate studies listed below, received on September 
21, 1993, in preparation for the September 29, 1993 technical meeting:
     Volume 1 Study entitled "Investigation of the Leaching
              Characteristics of Isoxaben in an Agricultural
              Soil under Field Conditions: A Lysimeter Study"
              (T4A/SC 50/ESLEACH/EU/1-116) - conducted at the
              NATEC Institute in Hamburg, Germany
     Volume 2 Study entitled "Field Dissipation of Isoxaben
              Following Application of Snapshot D.F. to Bare
              Soil" (F P8A/DF/ESDSSP/US/1-37) - conducted in
              Fresno, California
     At the conclusion of this September 29, 1993 meeting, DowElanco 
agreed to provide written documentation to the NYSDEC which addressed 
the questions and issues raised at the meeting.  DowElanco subsequently 
submitted the following technical response dated November 19, 1993:
     Title:  Response to Questions and Technical Issues on Isoxaben,
             New York State Department of Environmental Conservation
     Authors: E.W. Day, Jr., I.W. Butler, and D.P. Rainey
     On November 23, 1993, DowElanco waived the December 1, 1993 
decision date for 60 days to enable the Department to fully consider the 
November 19, 1993 technical response.
     After full consideration of DowElanco's technical response received 
on November 22, 1993, the Department continues to have concern for the 
potential impacts of the referenced products on groundwater/drinking 
water in New York State.
     On pages 5 to 7 of the technical response, DowElanco uses total 
soil residue data from field dissipation studies to estimate isoxaben 
Metabolite II soil pore water concentrations.  Theoretical calculations, 
which assume that Metabolite II is present in soil pore water at the 
limit of detection (5 ppb) of the field dissipation studies, estimate 
Metabolite II soil solution concentrations ranging from 9 to 45 ppb and 
corresponding saturated zone (i.e., groundwater) concentrations of 5 to 
9 ppb.  These calculations assume a soil porosity of fifty percent, 
equilibrium sorption, no degradation, and the recovery of all 
contaminated pore water.  These assumptions are not conservative 
assumptions.  The estimates cause added concern in view of the flaws in 
the design and conduct of the field dissipation studies.
     The more recent German lysimeter study provides some additional 
insight into the mechanisms of dissipation, although interpretation of 
the results is limited by several factors: the duration of the study was 
limited; the study used only a single application at application rates 
ranging between 0.13 and- 0.55 lb /acre, which are all less than the 
maximum label application rate of up to 3 lb/acre (three applications 
per year of one pound per acre each); and the study was conducted under 
climatic conditions different than are prevalent in New York State 
(particularly, Long Island).
     Our evaluation of the lysimeter data leads us to conclude that the 
study may have been ended prematurely, just as solute breakthrough was 
beginning to be observed. Higher leachate concentrations could be 
expected had the study been continued. In addition, since the soils in 
the lysimeter were not analyzed during or after the test, the extent of 
vertical migration of isoxaben and metabolites and the magnitude of 
residual contamination are uncertain.
     Nevertheless, the lysimeter study does indicate that during high-
velocity flow events (e.g., as would occur in a sandy soil following a 
storm event or during the spring thaw) both the principal metabolite and 
the isoxaben could be mobilized and transported through the soil to a 
shallow groundwater table. With repeated use at label-recommended rates, 
it is possible that such periodic impacts could increase in frequency 
and significance. For example, extrapolating from the isoxaben Ieachate 
result of 0.5 ppb from lysimeter 2 of the German lysimeter study to an 
application rate of 3 lb/acre, results in an estimated isoxaben leachate 
concentration of 11 ppb under the same study conditions.
     DowElanco estimated the effect of multiple applications of isoxaben 
on carry-over and leaching using the GLEAMS model (pages 8 and-9 of the 
technical response). The model uses a solubility input parameter of 100 
ppm for metabolite II, while all that is known about this compound is 
that the solubility is greater than 100 ppm. The model was run assuming 
that the parent compound and metabolite II share a 73 day half-life, 
even though the degradation of metabolite II has not been characterized 
in any of the studies submitted in support of the registration.
     In addition, the modeling used an average Koc of the parent of 350, 
although a measured value of 190 for a loamy sand soil is known. While 
the GLEAMS output indicates that the model evaluated 20 soils from 
various parts of the country, it appears that none of the soil and 
climatic conditions evaluated are comparable to those in New York State. 
The model output also indicates that 16 of the 20 soils were assessed 
assuming "dryland pasture" conditions without irrigation, and many 
locations had very low rainfall in comparison to New York State. The 
remaining four soils (from four western states) were evaluated assuming 
irrigated pasture conditions, and the output data summary appears to 
indicate that no water percolates to recharge groundwater in these 
     DowElanco's use of the model primarily evaluated conditions which 
are not similar to the conditions of interest in New York State.
     Despite the above-noted shortcomings, the 15-year GLEAMS simulation 
(Cecil sandy loam, Henrico County, Virginia) predicts maximum daily 
concentrations of isoxaben in percolating water ranging from 6 to 28 ppb 
(Appendix B, Figure B). Metabolite II pore water concentrations for the 
same site were in the range of 8 to 30 ppb (Appendix B, Figure C).  In 
sandy soils, we could expect pore water concentrations in excess of 
these levels.
     The Department also simulated isoxaben leaching potential using the 
SESOIL and LEACHM models. The SESOIL model estimated isoxaben leachate 
concentrations at a depth of three feet in a sandy soil (with an organic 
carbon content of one percent in the upper twelve inches and 0.1 percent 
in the rest of the profile) may reach steady-state concentrations of 70 
ppb. This estimate assumed a Koc of 1000, a half-life of 350 days, and 
climatic and meteorological parameters from La Guardia Airport. The Koc 
of 1000 was developed using a regression equation because of the 
apparent inconsistency between the reported values for Koc and 
solubility (1 ppm) of isoxaben.
     The relatively high solubilities of other benzamides suggests that 
the solubility of isoxaben may be higher than the reported value of 1 
ppm, and that the lower estimates of Koc are appropriate. Using the 
measured Koc of 190 for a loamy sand soil, the SESOIL model would yield 
a significantly higher estimate.
     LEACHM simulations (input parameters: parent Koc= 190, metabolite 
II Koc= 21, half-life of 318 days, and sandy soil with one percent 
organic matter in the upper 200 mm, decreasing by 0.1 percent per 100 mm 
depth to a minimum of 0.1 percent) were conducted from 01/01/65 to 
12/31/89 using Kennedy Airport rainfall data from the same 25 year 
period. Assuming one annual application at 1 lb/acre isoxaben, the model 
estimated steady- state leachate concentrations of 30-60 ppb for 
isoxaben and 40- 240 ppb for metabolite II at a depth of 3.6 feet. Use 
at maximum label-recommended rates would significantly increase these 
     Based on the above observations, the Department has determined that 
use of the referenced products in conformance with the label directions 
may result in deterioration of groundwater resources in New York State. 
The laboratory and field data submitted to date do not adequately define 
the leaching characteristics of isoxaben and its metabolites. Modeling 
results and theoretical calculations based on field dissipation data 
support concerns for groundwater impacts. These concerns are heightened 
by the oncogenic potential of isoxaben.
     There are no federal or State ambient groundwater quality standards 
for isoxaben or its degradates. In existing New York State rules and 
regulations there are procedures for deriving ambient water quality 
standards. Using the procedures for oncogenic effects (1ONYCRR Part 
701), a value for isoxaben associated with a one-in-a-million increased 
lifetime cancer risk is 9 ug/L based on the mouse oncogenicity data. 
There are no federal or State chemical specific drinking water standards 
for isoxaben or its degradates. Based on their chemical structures, 
isoxaben and its major degradate fall under the 50 ug/L general New York 
State drinking water standard for an "unspecified organic contaminant" 
(1ONYCRR Part 5 - Public Water Systems). However, if it were necessary 
to develop a drinking water standard for isoxaben or its degradate, 
isoxaben's oncogenic potential would have to be considered and a 
standard less than 50 ug/L would be likely both at the federal and State 
    The Department considered DowElanco's proposal to limit the total 
amount of isoxaben applied annually to 1.5 lb/acre (2 applications at 
0.75 lb/acre) and evaluated the use of this lower application rate on 
various soil types in New York State.
     However, this proposed application rate limit is already within the 
range of current recommended label-use and would not reduce the isoxaben 
application rate sufficiently to alleviate concerns for the degradation 
of groundwater resources in New York State.
     Should DowElanco consider resubmitting an application to register 
isoxaben products in New York State, a properly conducted lysimeter 
study would assist in defining the leaching behavior of isoxaben and its 
     Please call Maureen Serafini, of my staff, at (518) 457-7446 if you 
have any questions.
                             Norman H. Nosenchuck, P.E.
                             Division of Hazardous Substances
cc:  N. Kim - NYS Dept. of Health
     D. Rapp - NYS Dept. of Agriculture and Markets
     D. Rutz - Cornell University