dimethenamid (Frontier) NYSDEC Denial to Register Frontier 1995
New York State Department of Environmental Conservation
50 Wolf Road, Albany, New York 12233-7250
518-457-6934 FAX 518-457-0629
RETURN RECEIPT REOUESTED
Mr. Charles W. Boyd
Sandoz Agro, Incorporated
1300 East Touhy Avenue
Des Plains, IL 60018
Dear Mr. Boyd:
Re: Application for Registration of FRONTIER Herbicide EPA Reg. No.
55947-140 Containing the New Active Ingredient Dimethenamid
The New York State Department of Environmental Conservation has
completed the technical review of the referenced application received
August 15, 1994 together with supplemental information submitted
November 17, 1994. We have also reviewed the facsimile of your letter
dated May 31, 1995 in which you address the issues we raised in our
letter of May 23, 1995.
Based on all the information submitted, we are hereby denying your
The mission of the Department of Environmental Conservation (DEC) of
the State of New York is to conserve, improve, and protect its natural
resources and environment and control water, land and air pollution, in
order to enhance the health, safety and welfare of the people of the
state and their overall economic and social well being.
In carrying out this mission with regard to pesticide use, DEC
evaluates all pesticides used in the State to assure that they will
perform their intended function without causing unreasonable risk to
the environment. DEC performs these reviews in conformance with the
New York State Environmental Conservation Law Article 33 (copy
enclosed). In the case of dimethenamid, it has been determined that
there is potentially an unreasonable risk of groundwater contamination
from either the parent compound itself, or its metabolites/degradation
products, and unreasonable risk of toxicity to aquatic plants.
FRONTIER Herbicide contains the new active ingredient, dimethenamid.
FRONTIER Herbicide is federally registered for selective control of
certain annual grasses and broadleaf weeds on field corn, seed corn,
popcorn and soybeans. It is federally registered for both ground and
aerial application. Application was submitted to DEC to register all
these uses in New York State.
The data package submitted was also reviewed by the New York State
Department of Health (DOH) and the DEC's Division of Fish and Wildlife
(DFW) and DEC's Division of Water (DOW).
Several concerns with the data you submitted to date for the referenced
herbicide in the area of groundwater contamination and toxicity to
aquatic plants have been identified during the review, which have led
to the decision to deny registration. The following discussion
highlights those concerns:
- Dimethenamid has some oncogenic potential and is classified by the
United States Environmental Protection Agency (EPA) as a Category C
(possible human carcinogen) chemical.
- In accordance with 6NYCRR Part 702.4 procedures for deriving ambient
water quality standards and guidelines based on oncogenic effects, the
ambient water quality value for dimethenamid is 5 ug/L (ppb), based on
the dose-response data for combined benign and malignant liver tumors
from the two-year rat feeding study. This level is a guidance value
and a potential standard. It is a level that may not be exceeded in
any groundwater since all groundwater in New York State is considered a
potential source of drinking water.
In accordance with these same procedures for deriving ambient water
quality standards and guidelines for unspecified organic chemicals, the
ambient water quality value for the oxalamide or any other metabolite
of dimethenamid is 50 ug/L.
The Koc of dimethenamid is low (72-184), suggesting that it would be
very mobile in coarse, textured soils.
- The concern for potential groundwater contamination was also
reflected by EPA in their groundwater reviews, label statements and
conditional registration requirements for FRONTIER use on soybeans.
Field dissipation studies conducted in several states are the sole
support that you provided to show that dimethenamid will not pose a
risk to groundwater. The DEC review did not rely on the field
dissipation studies alone, but also on the registration package, the
physicochemical properties, such as the Koc and half-life, and on
vadose zone transport modeling.
No data from groundwater or Lysimeter studies have been submitted to
the DEC for review.
In response to groundwater issues raised in our letter dated May 23,
1995, you contend that field dissipation studies, particularly the
Indiana study, should be taken as proof that dimethenamid will not pose
a risk to groundwater.
Field dissipation studies alone do not address all questions regarding
the leaching behavior of compounds. They measure dissipation from
surface soils but generally do not account for the mechanisms of
dissipation. Soil concentrations at or near the method detection limit
(in this case 10 ug/Kg or 10ppb) do not necessarily indicate that
leaching did not take place, sincenon-detects can be associated with
elevated (above 5 ug/L or 5ppb) equilibrium pore water concentrations,
especially when Koc's are low. Because these studies rely on periodic
soil sampling alone and do not isolate soil pore water, analytes of
interest may migrate through surface soils to lower depths in the
profile, or to groundwater, without ever appearing in field dissipation
DEC previously discussed its position regarding field dissipation data
vs. groundwater contamination with Sandoz in a technical meeting for
another registration application, SENTINEL, on January 20, 1995. You
were present at this January 20 meeting.
Three items are useful to note concerning the protocols of the field
dissipation studies and the results:
- The limit of quantitation for soils in these studies was 10 ug/Kg (10
ppb). Given the low Koc's of these compounds, pore water
concentrations could exceed the drinking water guideline of 5 ug/L (5
In the Indiana and Minnesota field dissipation studies, evaporation and
transpiration were probably equivalent to precipitation (supplemental
irrigation supplied only as needed). The result would be no net
downward movement of water, a condition highly unlikely in New York
State in the spring when the product is used.
There were some detections of dimethenamid and the oxalamide metabolite
below 10 cm soil depth including one oxalamide detection below 20 cm in
Indiana and one parent dimethenamid detection below 20 cm in Minnesota.
DEC also conducted modeling using the LEACHM model for two typical
scenarios in New York State. The following supports our concern for
potential groundwater contamination from the use of FRONTIER:
On soils approximating those found on Long Island (Riverhead sand),
pore water concentrations of dimethenamid at a depth of three feet
would exceed 25 ppb within two years. During the third year,
concentrations would increase significantly, approaching 100 ppb.
On soils approximating those found in upstate New York and where corn
is grown (Howard gravelly loam), pore water concentrations of
dimethenamid at a depth of six feet may reach 1 ppb within five years
and 6 ppb within eight years. LEACHM results are probably
underestimates because LEACHM cannot account for the significant gravel
fraction in Howard gravelly loam.
The oxalamide metabolite concentrations increase in the Howard gravelly
loam continuously, reaching 100 ppb at the end of the fourth year and
rising above 420 ppb by the end of ten years. This prediction uses the
assumptions that 1.) that the oxalamide metabolite does not further
degrade; and 2.) that the Koc of the parent and the metabolite are the
same, although it is expected that the Koc for the oxalamide
metabolite would be even lower than the Koc for the parent compound.
No Koc or metabolism half-life data were submitted for the oxalamide
In your response to the modeling predictions, you asserted that we
should have used the PRZM model instead of the LEACHM model because EPA
uses the PRZM model and because Sandoz validated the primary PRZM model
by calibrating to the Indiana field study.
LEACHM uses a more rigorous technique to simulate water flow through
the soil profile than other models and is capable of simulating most
significant physical, chemical and biological processes controlling
water flow and pesticide greater detail. For example, LEACHM simulates
the fate of degradates and metabolites as well as the parent compound.
Our concerns about pesticide fate modeling are generally not related to
the algorithms themselves (model selection) as long as they address the
relevant mass loss mechanisms. Our main concern is the misuse of input
parameters that do not reflect the conditions of interest. DEC has
used the LEACHM model to evaluate all other new active ingredients
submitted for review by DEC. It is also our understanding that many
other pesticide product registrants accept modeling information
generated from the LEACHM model.
We are aware that the label prohibits use on soils classified as sands
if the organic matter is less than 3% and less than 30 feet to
groundwater, and that this would preclude the use on most of Long
However, this restriction is difficult to enforce since soil
classifications are imprecise. Other potentially vulnerable soil types
are not restricted by the label language. For example, sandy loams
regardless of the percent organic matter can be treated.
Toxicity to Aquatic Plants
- Dimethenamid is highly toxic to non-target aquatic plants.
Aquatic exposure is likely due to the persistence of dimethenamid on
land and in water, and its tendency to remain in the water column. It
is stable to hydrolysis, has an anaerobic aquatic metabolism half-life
of 36 days at 25°C and 292 days at 5°C, and an aquatic photolysis half-
life of 23.9 days. These numbers indicate dimethenamid could be
present in the water for a sufficient period to cause toxicity to
- Based on the low Kow, dimethenamid is not likely to bind to
sediment, thereby prolonging its presence in water.
- Aquatic modeling conducted by DEC predicts estimated
environmental concentrations of dimethenamid sufficient to cause
toxicity to representative aquatic plants. DEC's aquatic modeling
predicts estimated environmental concentrations resulting from a 2
cm/hour rain event of one hour duration falling on a ten acre treated
field, which drains into a one acre pond. Runoffs of 1%, 3% and 5% are
estimated and environmental concentrations are determined for one,
three, and six foot ponds. According to this model, dimethenamid is
extremely toxic to the following aquatic plants: Scenedesmus
subspicatus, Skeletonema costatum, Selanastrum capricornutum, and Lemna
You stated in your May 31, 1995 letter that it would be more
appropriate to use 0.5% and 2% runoff levels for modeling purposes,
rather than 1%, 3% and 5% levels which we use in the model.
In your May 31, 1995 response, you contend that any issues concerning
groundwater should be covered under DEC's Generic Corn Herbicide
Management Plan. It is not DEC's responsibility to establish or create
a data base upon which we will then make a management decision for the
potential use of this product; nor do we intend to register or include
products into our Corn Herbicide Management Plan when we do not know
the complete impact of theproduct.
The ECL Section 33-0704 states that a registration decision must be
made within 150 days of the completeness determination of that product.
The law does not imply that a favorable decision must be made. DEC
issued a completeness determination for FRONTIER on January 10, 1995.
We, in fact, have enough information to issue a decision.
However, when it appears that a denial is forthcoming, we allow all
registrants an opportunity to rebut our technical position.
In our letter of May 23, 1995, we offered Sandoz an opportunity to
respond to our concerns, submit any additional information that might
bear on these concerns and then to come in and meet with our technical
staff to discuss the Department's position. In your May 31, 1995 response,
Sandoz declined this opportunity. Minimal information was provided to
DEC to review with no substantiating data or results provided as backup
material. Therefore you leave DEC no alternative but to deny your
New York State Environmental Conservation Law Section 33-0711 provides
that whenever an application for registration is denied, the applicant,
within 30 days after service of notice, may file a petition requesting
that the matter be referred to an advisory committee or file objections
and request a public hearing.
Should Sandoz choose to re-submit an application for registration of
FRONTIER, you must provide the following items to us:
1. EXAMS modeling (including input parameters, procedures,
and results) referred to in your May 31, 1995 letter;
2. Specific information on the physicochemical properties
of the oxalamide metabolite;
3. PRZM modeling inputs and results referred to in your
May 31, 1995 letter;
4. Proposed groundwater monitoring program with analytical
method which provides appropriate detection limits for
the parent and metabolite;
5. Application fee of $300.
If you have any questions, contact Maureen P. Serafini of my staff, at
Norman H. Nosenchuck, P.E.
Division of Hazardous Substances Regulation
W. Lapinski - NYS Dept of Ag. and Mkts.
R. Mungari - NYS Dept of Ag. and Mkts.
D. Rutz - Cornell University
A. Grey - Department of Health