dimethenamid (Frontier) NYS DEC Letter - Acceptance of Registration 5/97
New York State of Environmental Conservation
Division of Solid & Hazardous Materials
50 Wolf Road, Albany, New York 12233-7250
Phone 518-457-6934 FAX 518-457-0629
May 15, 1997
RETURN RECEIPT REQUESTED
Ms. Sonia R. White
PO Box 13528
Research Triangle Park, NC 27709
Dear Ms. White:
Re: Acceptance of Registration of FRONTIER Herbicide - EPA Reg. No. 55947-140 (Sandoz),
FRONTIER 6.0 Herbicide - EPA Reg. No. 7969-147 (BASF) and FRONTIER 6.0 Herbicide - EPA Reg.
No. 55947-159 (Sandoz) Containing the New Active Ingredient, Dimethenamid
The New York State Department of Environmental Conservation (Department) has completed the
technical review of the applications for the referenced products and hereby accepts them
for registration subject to the conditions discussed later in this letter. The acceptance
of this registration is for the basic label covering field corn, seed corn, popcorn and
The application for FRONTIER Herbicide - EPA Reg. No. 55947-140 (Sandoz) was received
May 14, 1996 from Sandoz Agro, Inc. An additional application for FRONTIER 6.0 Herbicide -
EPA Reg. No. 7969-147 (BASF) and FRONTIER 6.0 Herbicide - EPA Reg. No. 55947-159 (Sandoz)
was received April 16, 1997 from BASF Corporation. Ownership of FRONTIER products has
recently been acquired by BASF Corporation from Sandoz Agro, Inc. On February 25, 1997, the
United States Environmental Protection Agency (EPA) transferred the registrations and data
from Sandoz Agro, Inc. to BASF Corporation. The application is a resubmission of a previous
application which was denied on June 9, 1995.
FRONTIER Herbicide and FRONTIER 6.0 Herbicide are federally registered to control most
annual grasses, certain annual broadleaf weeds and sedges in field corn, seed corn,
popcorn and soybeans. Additionally, these products are federally registered on sweet corn,
grain sorghum, dry beans and peanuts and the uses appear on supplemental labeling. At
BASF's request, the registration approval is for the basic label registered on field
corn, seed corn, popcorn and soybeans only. Use on sweet corn, grain sorghum and dry
beans will be the subject of a separate registration decision.
In the Department's review of the previous application which resulted in a denial of
registration, there were concerns about the levels of dimethenamid and the significant
degradate, oxalamide, that were expected to reach groundwater. Review of that application
concluded, based on the information submitted that:
- Dimethenamid has some oncogenic potential and is classified by the 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 five gg/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 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 the EPA in
their groundwater reviews, label statements, and conditional registration requirements
for FRONTIER use on soybeans.
These concerns still hold true. However, review of additional information submitted with
the most recent application leads us to conclude the following:
- A lysimeter study, submitted with the most recent application, was conducted in a
sandy loam soil consistent with the Riverhead series. Rainfall was consistent with
upstate New York. No dimethenamid was found in the leachate and very low levels (< 1.0 ug/l)
of the oxalamide degradate were found. However, because these levels of dimethenamid and
oxalamide degradate were determined by radiocarbon content only, the values are in need of
- With review of the additional information submitted in the current application and
rerunning the LEACHM model incorporating changes made by the model's author, these
groundwater issues have been resolved for areas other than sandy soil conditions such
as exist on long Island. In soils typical of upstate New York, it is not expected that
either dimethenamid, or the significant degradate, oxalamide will reach groundwater at
levels of concern. However, as discussed in our letter dated November 7, 1996, participation
in the Department's corn herbicide groundwater monitoring program would still be required
as a condition of any registration.
Toxicity to Aquatic Plants
In the Department's review of the previous application, aquatic plant toxicity concerns
were raised. Based on the information submitted with the most recent application, the
Department continued to have concerns that dimethenamid would be toxic to aquatic plants.
- Aquatic modeling conducted by the Department's Division of Fish, Wildlife & Marine
Resources (DFW&MR) predicts estimated environmental concentrations of dimethenamid
sufficient to cause toxicity to representative aquatic plants. The Department's aquatic
modeling predicts estimated environmental concentrations resulting from a two 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 gibba.
- Based on amounts of rain that are realistic for New York State, we believe a 2%
runoff value to be typical. According to EXAMS modeling conducted by Sandoz, 2% runoff
would result in the Lemna EC50 being exceeded for one to two days in three- and one-foot
ponds, respectively. Lemna LOEL values, as approximated by EC50/3, would be exceeded for
five to seven days in ponds one-, three- and six-feet deep. The DFW&MR incorporated
lower Lemna EC50 values reported by the EPA in the original data package for FRONTIER.
These lower values would result in EC50 and LOEL values being exceeded for three to four
days and seven to 11 days, respectively, in the aforementioned pond depths. Therefore,
the EXAMS modeling submitted by Sandoz corroborates DFW&MR concerns.
Responding to these concerns, BASF agreed to perform a microcosm study in an attempt
to determine actual impacts. The results of the study show that Frontier Herbicide
is not likely to harm aquatic plant populations when applied as labeled.
The study showed that the most significant impact of dimethenamid on non-target
plants was a 22% inhibition of stem growth. This impact was temporary, and plant growth
resumed as soon as the dimethenamid concentration had dissipated. The microcosm study
showed that by day 19, the dimethenamid in all three test concentrations had decreased
to an average of about 30% of what was originally applied into the closed test chambers.
This showed that dimethenamid was removed from the water column much more quickly than
laboratory environmental fate studies predicted, probably through aerobic metabolism,
sediment sorption, or plant uptake and metabolism.
The plants exposed to the highest concentrations during the microcosm test showed no
visible impact other than shorter length. The growth rates had resumed by the middle
of the recovery period, and the comparison of dry weights at the end of the test showed
no differences at all. Unless a rainfall event was unusually heavy, it is not likely
that enough dimethenamid would be removed from a treated field to cause any measurable
growth inhibition at all. If it were, the growth inhibition has been shown to be temporary.
The application for registration is hereby accepted with the following conditions:
1. BASF must ensure that no supplemental label is distributed in
New York State listing uses on sweet corn, grain sorghum or dry beans. At BASF's
request, a registration decision on these uses is reserved, pending approval by EPA
of an amendment to existing supplemental labeling prohibiting use on Long Island, New
2. BASF must participate in the corn herbicide management for New York State plan in
cooperation with this Department. This participation will involve developing a grower
education program including, for example, brochures and training sessions. A brochure
which will be provided by BASF at grower training sessions must be provided to this
Department within 90 days of receipt of this letter;
3. BASF must submit within 30 days of receipt of this letter the analytical methodology
for determining both dimethenamid and the oxalamide degradate in water;
4. BASF must agree to provide sales records through to the retail level for all sales
of FRONTIER in New York State for four years from 1997 through 2000. This information
will be used to locate areas of the existing monitoring network to look for dimethenamid
and the oxalamide degradate. This requirement will be revisited during the renewal process
in preparation for BASF's March 31, 2001 renewal;
5. BASF must agree to provide analysis of the oxalamide degradate on water samples
collected as part of the Department's overall groundwater monitoring program. The
Department is investigating the possibility of performing dimethenamid analysis as
part of our State monitoring program. If this is not possible, analysis of parent
dimethenamid may also be required. While it is not possible to provide an exact
number of samples, the number would not exceed 40 per year. This requirement may begin
with the 1998 season and continue until the Department approves discontinuance;
6. BASF must submit analytical standards for both dimethenamid and the oxalamide
degradate within 30 days of receipt of this letter. Both standards should be sent to:
U. S. Geological Survey
Attn. Mark Sandstrom
5293 Ward Road Arvada, CO 80002
In addition, the Department may in the future request that both these standards
be submitted to this Department for methods validation; and
7. BASF must submit information on any detections of dimethenamid or the oxalamide
degradate resulting from all monitoring programs nationwide.
Enclosed are the stamped acceptable labels and the Certificate of Registration.
If you have further questions, please contact Frank Hegener, of my staff, at (518) 457-7446.
Norman H. Nosenchuck, P.E.
Division of Solid & Hazardous Materials
cc: w/enc. - N. Kim/A. Grey - NYS Dept. of Health
N. Rudgers/R. Mungari -NYS Dept. Of Ag. & Markets
D. Rutz/W. Smith - Cornell PMEP