r/EPA
United States
Environmental Protection
Agency
Office of Prevention, Pesticides
and Toxic Substances
(7501C)
Pesticide
Fact Sheet
Name of Chemical:
Reason for Issuance:
Date Issued:
Penoxsulam
Conditional Registration
September 27, 2004
DESCRIPTION OF CHEMICAL
Generic Name:
Common Name:
2-(Z2-difluoroethoxy)--6-(irifluoromethyl-N-(^,8-dimethoxy[l,2,4]
triazolo[l,5-c]pyrimidin-2-yn)benzenesulfonamide
Penoxsulam
Other Names Used: DE-638, XDE-638, XR-638
Trade Names:
Penoxsulam Technical
EPA Chemical Code: 119031
Chemical Abstracts
Service (CAS)
Number: 219714-96-2
Year of Initial
Registration:
Pesticide Type:
U.S. and Foreign
Producers:
2004
Herbicide
Dow AgroSciences LLC
9330 Zionsville Road
Indianapolis, Indiana 46268-1054
USE PATTERNS AND FORMULATIONS
Penoxsulam is a new post-emergence, acetolactate synthase (ALS) inhibitor herbicide developed
by Dow AgroSciences to be used as a foliar spray on dry-seeded rice crops, or as either a foliar
spray or a granular formulation on water-seeded rice crops in order to control broadleaf weeds,
aquatic plants, and certain grasses. Penoxsulam will be used on rice crops in the main rice
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growing regions of the United States - the Gulf Coast, the lower Mississippi Valley, and central
California. Penoxsulam comes in liquid and granular formulations. Foliar application is
recommended for use of the liquid formulation of penoxsulam on both dry- and water-seeded
crops. For water-seeded rice, the application practice is to lower the paddy water depth
sufficiently to expose at least 50% of the target plant before spraying. The granular formulation
of penoxsulam is only recommended for use on flooded paddies. Although rice paddies are
typically constructed to limit the amount of water escaping into the open environment,
penoxsulam can reach surface waters through spray drift and particulate drift during application,
or by subsequent release of paddy water.
SUMMARY
HUMAN HEALTH RISK: The Agency has concluded, based on the supporting data, that there
are no risks of concern from the use of penoxsulam. An appropriate endpoint attributable to a
single dose was not identified. Therefore, penoxsulam is not expected to pose an acute risk. No
dermal sensitive was detected with Grasp or Granite liquid or granule herbicides. The risk due
to exposure to residues in food and water was calculated below the Agency's level of concern for
all population subgroups, including infants and children. The FQPA safety factor for
penoxsulam has been reduced to IX when assessing acute and chronic dietary exposures to
infants and children for all exposure durations (acute and chronic). A residential risk assessment
was not performed, because there are no residential uses registered (or pending) for this
chemical. The tolerance expression is for penoxsulam, per. se., in or on rice grain and straw.
ENVIRONMENTAL RISK: Penoxsulam is expected to be very mobile, but not very persistent,
in either aqueous or terrestrial environments. Penoxsulam degrades by two different
transformation mechanisms, producing thirteen different identified transformation products,
eleven of which meet the criteria to be classified as major degradates1. Six of these
transformation products reached peak concentrations at study termination, indicating a greater
degree of persistence than penoxsulam and a potential to reach concentrations even greater than
those reported at study termination.
As a condition of registration the following data gaps must be filled:
- Seed germination/seeding emergence studies, vegetative vigor studies, and an aquatic plant
growth study using Duckweed with the degradates, BSA, 2-amino-TP, TPSA, BSTCA
methyl, BSTCA, 2-amino-TCA, 5-OH-penoxsulam, SFA, sulfonamide, 5,8-di-OH and 5-
OH, 2 amino TP.
- For any future food uses, submission and acceptance of the final ongoing storage stability
study in rice.
Penoxsulam application at proposed maximum levels does pose a potential risk to aquatic and
terrestrial plants. Specifically, seedling emergence risk quotients for terrestrial plants exceeded
Levels of Concern for eight out often crops studied, although half of those exceedances resulted
from a failure to test at a sufficiently high rate. The peak RQ for monocots was 44 for non-
endangered species and 120 for endangered terrestrial plants based on studies with onions. The
, 2-amino-TP, TPSA, BSTCA methyl, BSTCA, 2-amino-TCA,
5-OH-penoxsulam, SFA, sulfonamide, 5,8-di-OH and 5-OH, 2 amino
TP.
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peak RQ for dicots was 15 for non-endangered species and 41 for endangered species, both
based on studies with sugar beets. These endpoints are applicable to the Tier 1 estimate for
terrestrial plants in terrestrial and semi-aquatic settings from application of either the liquid or
granular formulation.
Any concern for endangered plants will be mitigated by the addition of buffer zones and drift
control strategies to product labels.
SCIENTIFIC FINDINGS
EPA reviewed the submitted product chemistry, toxicology, residue chemistry, occupational
exposure, ecological effects and environmental fate data. A summary of these assessments
follows:
Health Effects Division's Review - Hazard Identification
In subchronic and chronic feeding studies in rats and dogs, the most sensitive target organ was
the urothelium of the urinary system. Due to limited solubility in urine, penoxsulam (and/or its
metabolites) formed crystals/calculi, which were regularly observed in the pelvis of the kidney
and the lumen of the urinary bladder. These crystals/calculi apparently irritated the urothelium
in these organs and following repeated dosing lead to numerous secondary effects which resulted
in significant damage to the urinary system. In various studies, these secondary effects were
manifested as altered clinical chemistry parameters (increased blood urea nitrogen), altered
urinalyses parameters (increased urine volume, decreased urine specific gravity), increased
absolute and relative kidney weights, gross pathological findings in the kidneys (calculi and
roughened surface), and a variety of histopathological findings in the kidney and urinary bladder,
particularly hyperplasia, inflammation and mineralization in the pelvic epithelium of the kidney
and hyperplasia in the mucosa of the urinary bladder. Renal tubular degeneration was also
sometimes observed. Although a treatment-related increased severity of chronic progressive
glomerulonephropathy was observed in male rats, kidney damage observed in shorter-term
studies was generally not exacerbated in longer-term studies. At similar and/or somewhat higher
dose levels, mildly decreased body weight/body weight gain, often accompanied by decreased
food consumption, were often observed in feeding studies in rats and dogs. In addition, in male
rats, slightly decreased erythrocyte parameters (erythrocyte count, hemoglobin and hematocrit)
were occasionally observed.
In subchronic and chronic feeding studies in mice, no effects of toxicological significance were
observed in the 4-week, 13-week or 18-month feeding studies. In these studies, the only
treatment-related effects observed at the dose levels tested were increased liver weights,
increased hepatocellular hypertrophy, and related observations indicating stimulation of the liver
microsomal enzyme system. These effects were considered to be an adaptive response to
administration of the test material and not lexicologically significant adverse effects.
In a developmental toxicity study in rats, decreased body weight gain, decreased food
consumption and increased kidney weights were observed in the dams. No developmental
toxicity was observed. There was no increased quantitative or qualitative susceptibility of
fetuses, as compared to dams, in this study. In a developmental toxicity study in rabbits,
decreased body weight gain, decreased food consumption and clinical signs of toxicity
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(decreased/absent feces, or mucoid, soft, or abnormally colored feces) were observed in dams at
the highest dose tested. One high dose doe died late in the study after exhibiting signs of clinical
toxicity for several days. No developmental toxicity was observed. There was no increased
quantitative or qualitative susceptibility of fetuses, as compared to dams, in this study. In a 2-
generation reproduction study in rats, microscopic lesions in the kidney were observed in the
parental females at the mid and high dose levels. Preputial separation, an indicator of sexual
maturation, was significantly (p<0.05) delayed in mid and high dose Fx males. The mean age at
which preputial separation was attained for the control, low, mid, and high dose groups was 43.6,
44.0, 45.5, and 46.0 days, respectively. In addition, at the mid dose, 1 animal did not separate
and at the high dose, 3 animals did not separate whereas all animals at the control and low doses
did separate. The delay in preputial separation at the mid and high doses was considered to be a
treatment-related effect. No other endpoints of reproductive toxicity or offspring growth and
survival were affected by treatment. There was no increased quantitative or qualitative
susceptibility of fetuses or offspring, as compared to adults, in this study.
No treatment-related neurotoxicity was observed in acute or chronic neurotoxicity studies in rats,
or in any of the other available studies on penoxsulam. No systemic or dermal toxicity was
noted in a 28-day dermal toxicity study in rats.
In a carcinogenicity study in rats, male and female rats were given penoxsulam in the diet for
two years at dose levels of 0, 5, 50 or 250 mg/kg/day. In this study, there was a statistically
significant increased incidence of malignant large granular lymphocyte (LGL) leukemia in each
of the male treatment groups. The incidence was 24%, 60%, 58% and 60% in the control, low,
mid and high dose level groups respectively. There was no dose response with all treated male
groups having an approximately 2.5 fold increase over control animals. The incidence in the
male treatment groups exceeded the conducting laboratory's historical control mean (28.5%) and
range (16-40%), but fell within the National Toxicology Program (NTP) historical control data
base of mean (50.5%) and range (32-74 %). There was also an increased severity (Stage 3) of
LGL leukemia in all the treated male groups compared to the control group. There was no
increase in incidence or severity of LGL leukemia for the treated female rats in this study. The
dose levels in this study were considered to be adequate in male rats and marginally adequate in
female rats to assess the carcinogenicity of penoxsulam. In a carcinogenicity study in mice,
penoxsulam was administered in the diet for 18-months at dose levels up to 375 mg/kg/day in
male mice and up to 750 mg/kg/day in female mice. An increased incidence of treatment-related
tumors of any kind was not observed in the male or female mice. However, in males, the highest
dose tested (375 mg/kg/day) was considered to be inadequate for carcinogenicity testing because
no lexicologically significant adverse effects were observed at this dose (or in subchronic studies
at doses up to 1000 mg/kg/day). In females, the highest dose tested (750 mg/kg/day) was
considered adequate for carcinogenicity testing, but only because it was sufficiently close to the
limit dose of 1000 mg/kg/day. Like males, no lexicologically significant adverse effects were
observed in females at this dose (or in subchronic studies at doses up to 1000 mg/kg/day). The
Cancer Assessment Review Committee (CARC) determined that although dosing in the males
was not considered to be adequate, an additional mouse carcinogenicity study was not required
because a repeat of the male mouse cancer study would have no impact on the regulation of
penoxsulam. Penoxsulam was classified as "Suggestive Evidence of Carcinogenicity, but Not
Sufficient to Assess Human Carcinogenic Potential" and, therefore, quantification of human
cancer risk is not required.
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Technical grade penoxsulam did not demonstrate any mutagenic potential in a battery of four
mutagenicity studies. There is not a concern for mutagenicity resulting from exposure to
penoxsulam.
In a metabolism study in rats, 14C-penoxsulam was rapidly and nearly completely absorbed at the
low dose of 5.0 mg/kg, but at the high dose of 250 mg/kg, there was evidence that absorption
was largely incomplete (i.e. absorption was saturated). Both gender and dose affected the
excretion pattern. At the low dose, the major route of excretion of radioactivity was via the feces
in males and via the urine in females. At the high dose, radioactivity was predominantly
excreted via the feces in both sexes. A significant enterohepatic circulation was observed,
particularly in males. Most (>90%) of the administered dose was excreted within 36-48 hours.
There was negligible radioactivity in tissues at 7 days and no evidence of accumulation in any
tissue/organ. Although numerous metabolites were revealed in the urine, feces and bile, nearly
all were <1% of the administered dose. Parent compound and a 2-hydroxyphenyl derivative
were the major compounds in urine and feces.
HED concluded that the toxicology database for penoxsulam is complete for FQPA purposes,
and a database uncertainty factor is not needed for penoxsulam (i.e., removed or Ix). HED also
concluded that there is not a concern for neurotoxicity resulting from exposure to penoxsulam.
No evidence of neurotoxicity was observed in the acute or chronic neurotoxicity studies in rats
or in any of the subchronic or chronic feeding studies in rats, mice or dogs. HED determined
that no Special FQPA Safety Factor is needed (i.e. Ix) since there are no residual uncertainties
for pre- and/or post-natal toxicity.
Endpoints were selected for acute and chronic dietary exposure, short- and intermediate-term
incidental oral exposure and short-, intermediate- and long-term dermal and inhalation exposure.
There were no treatment-related effects observed in any of the available toxicity studies on
penoxsulam that could be considered to have resulted from a single dose of the test material,
therefore no acute endpoint was established for penoxsulam. The chronic dietary endpoint is
based on multifocal hyperplasia of the pelvic epithelium of the kidney in a 1-year chronic
feeding study in dogs (chronic PAD = 0.147 mg/kg/day). The incidental oral exposure short- (1-
30 days) and intermediate- (1-6 months) term endpoint is based on histopathologic changes in
kidneys in a 13-week feeding study in dogs (NOAEL= 17.8 mg/kg/day, MOE = 100). The
dermal absorption factor was estimated to be 50% as an upper bound estimate for all dermal
exposure scenarios. The absence of dermal, systemic, neuro or developmental toxicity concerns
resulted in there being no selection of a dermal short-term (1-30 days) endpoint. The dermal
intermediate-term (1-6 mo) endpoint is based on histopathologic changes in kidneys in a 13-
week feeding study in dogs (NOAEL= 17.8 mg/kg/day, MOE = 100). The dermal long-term (>6
mo) endpoint based on multifocal hyperplasia of the pelvic epithelium of the kidney in a 1-year
chronic feeding study in dogs (NOAEL= 14.7 mg/kg/day, MOE = 100). The inhalation exposure
short- (1-30 days) and intermediate- (1-6 months) term endpoint is based on histopathologic
changes in kidneys in a 13-week feeding study in dogs (NOAEL= 17.8 mg/kg/day, MOE = 100).
The inhalation long-term (>6 mo) endpoint is based on multifocal hyperplasia of the pelvic
epithelium of the kidney in a 1-year chronic feeding study in dogs (NOAEL= 14.7 mg/kg/day,
MOE =100).
FQPA Decision
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HED concluded that no Special FQPA Safety Factor is needed (i.e. Ix) since there are no
residual uncertainties for pre- and/or post-natal toxicity. The penoxsulam risk assessment team
evaluated the quality of the hazard and exposure data; and, based on these data, recommended
that the special FQPA SF be reduced to Ix. The recommendation is based on the following:
There was no lexicologically significant evidence observed of neurotoxicity in either the acute or
chronic neurotoxicity study.
No definitive quantitative or qualitative susceptibility was observed in either of the
developmental rat or rabbit studies
Significant dose-related effects in the two-generation reproduction study were limited to the
delay in preputial separation. No other endpoints of reproductive toxicity or offspring growth
and survival were affected by treatment.
The chronic dietary food exposure assessment utilizes proposed tolerance level residues and
100% CT information for all commodities. By using these conservative assessments, actual and
chronic exposures/risks will not be underestimated.
The dietary drinking water assessment (Tier 1 estimates) utilizes values generated by model and
associated modeling parameters which are designed to provide conservative, health protective,
high-end estimates of water concentrations.
Chronic Dietary Exposure
The chronic dietary analysis for penoxsulam was conducted using the Lifeline™ Model Version
2.0, which uses food consumption data from the United States Department of Agriculture's
Continuing Surveys of Food Intakes by Individuals (CFSII) from 1994-1996 and 1998. The
assessment was based on tolerance level residues and 100 %CT for the requested use on rice.
This conservative (Tier 1) analysis indicates that chronic risk from the dietary exposure to
penoxsulam from the requested use did not exceed HED's level of concern for the U.S.
population or any population subgroup. All exposures were determined to be <1% cPAD for the
U.S. population and all sub populations of interest.
Drinking Water Exposure
EFED determined Tier 1 Estimated Drinking Water Concentrations (EDWCs) for ground and
surface water for the postemergence herbicide, penoxsulam, when used on rice crops. The
degradates which are to be included in the risk assessment are BSTCA, 2-amino TCA, 5-OH-
XDE-638, SFA, sulfonamide, and 5,8-diOH. Applying the method outlined in the current EFED
interim policy for calculating both the Tier I estimated ecological effects concentrations (EECs)
and EDWCs resulting from the use of pesticides on rice crops produced an upper bound
screening estimation, using the lowest Kd value (0.13) for a non-sand soil, of 45 ppb (ug/L) in
paddy waters. The estimated EEC calculated in accordance with the EFED interim policy should
be used for both acute and chronic EECs, as well as for both aquatic ecological risk assessments
and for EDWCs in human health risk assessments. Modeling ground water concentrations using
the standard Tier 1 model, SCI-GROW, estimated combined residue EDWCs of 5.86 ppb (ug/L).
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Ground water concentrations were estimated for parent-only at 0.67 ppb (ug/L). However,
EFED does not regard ground water contamination from a pesticide applied to rice to be a
significant route of dissipation. The calculated chronic Drinking Water Level of Comparison
(DWLOC) for infants and children (ages 1-12 years old) is 1.5 ppm, for youths (ages 13 - 19
years old) and adults (20 - 50+ years old) it is 5.1 ppm, and females (ages 13-49 years old) it is
4.4 ppm.
Endocrine Disruption
For penoxsulam, effects which indicate potential endocrine disruption include kidney lesions
(crystals) in female rats and delay in preputial separation in male rats. When the appropriate
screening and/or testing protocols being considered under the Agency's EDSP have been
developed, penoxsulam may be subjected to additional screening and/or testing to better
characterize effects related to endocrine disruption.
Risks to Pesticide Applicators and Handlers
Besides a technical product, Penoxsulam Technical (EPA File Symbol 62719-UOO), and a
manufacturing use product, GF-881 MUP (EPA File Symbol 62719-LNE), Dow has requested
registration of four end-use products, two liquid formulations and two granular formulations, for
selective postemergence weed control in rice. The proposed labels for the Grasp SC (GF-443 SC
SF) liquid (EPA File Symbol 62719-LNN) and Grasp GR (GF-947 GRANULE SF) granular
(EPA File Symbol a62719-LNG) formulations indicates use in Arkansas, Florida, Louisiana,
Mississippi, Missouri, and Texas. The proposed labels for the Granite GR (GF-947 GRANULE
CA) granular (EPA File Symbol 62719-LNR) formulation and Granite SC liquid (EPA File
Symbol 62719-LRU) formulations indicate use in California only.
The end-use products as liquid formulations (EPA File Symbol 62719 - LNN and 62719-LRU)
are 21.7% active ingredient (ai) or 2.0 Ib ai per gallon. They may be applied one time per year
by aerial or ground equipment at a maximum rate of 0.044 Ib a.i./A. It may not be applied
through any type of irrigation equipment. It may be applied to water seeded rice or dry seeded
rice. The application is to be made between the 1 leaf stage of crop growth and 60 days before
harvest. The label requires the use of an agriculturally approved crop oil concentrate at a rate of
1 quart per acre or 2.5 % (Granite SC label) per application. Depending upon cropping
practices, the label includes specific water management directions relative to an application of
penoxsulam.
The granule products (EPA File Symbol 62719 - LNG and 62719-LNR) are used for selective
weed control in water-seeded rice. It is a 0.24 % granular formulation. The proposed products
are designated for use at a rate of 18.5 Ib (0.044 Ib a.i.) per acre. They may be applied one time
per year in ground or aerial equipment. The application should occur between the 1 leaf stage of
rice growth and 60 days prior to harvest. For optimum performance, fields should be flooded to
a depth of 2 to 4 inches prior to application and water maintained at 2 to 4 inches in depth for 10
days following application.
All four end-use products have a 12 hour restricted entry interval (REI). All proposed labels
require pesticide handlers to wear long sleeved shirt, long pants and shoes plus socks.
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A MOE of 100 is adequate to protect occupational pesticide handlers. All estimated MOE's are
> 100 except for intermediate-term exposures to mixer/loaders not using gloves with liquid,
open-pour loading in support of aerial operations (at either 1200 acres per day or 350 acres per
day). Loaders using liquid open-pour in support of aerial operations (and who may experience
intermediate-term exposures) should wear protective gloves. Generally speaking, HED advises
the use of protective gloves for mixer/loaders. Otherwise, the proposed uses do not exceed
HED's level of concern.
Environmental Fate and Effects Division's Review
Ecotox
The results of the screening-level risk assessment suggest that penoxsulam will not pose a threat
to aquatic or terrestrial animals, however, this conclusion must be tempered by the fact that
testing has not been conducted on several major degradates. Because penoxsulam is an ALS
inhibitor, it is not anticipated that it would pose a threat. Nevertheless, penoxsulam is a member
of the sulfonamide family which includes antimicrobial agents.
Penoxsulam application at proposed maximum levels does pose a potential risk to aquatic and
terrestrial plants. Specifically, seedling emergence risk quotients for terrestrial plants exceeded
Levels of Concern for eight out often crops studied, although half of those exceedances resulted
from a failure to test at a sufficiently high rate. That is the calculation of the RQ's defaulted to
using the highest dose tested, even when the dose indicated no adverse effects. The peak RQ for
monocots was 44 for non-endangered species and 120 for endangered terrestrial plants based on
studies with onions. The peak RQ for dicots was 15 for non-endangered species and 41 for
endangered species, both based on studies with sugar beets. These endpoints are applicable to the
Tier 1 estimate for terrestrial plants in terrestrial and semi-aquatic settings from application of
either the liquid or granular formulation.
Vegetative vigor risk quotients for terrestrial plants resulted in exceedances for eight out often
crops for endangered species and six out often crops for non-endangered species. The peak RQ
for dicots was 13 for non-endangered plants based on studies with the soybean and of 41 for
endangered species based on studies with the soybean, sugar beet, and tomato. The peak RQ for
monocots was 2.9 for non-endangered species and 120 for endangered plants, both based on
studies with ryegrass. Shoot weight was the sensitive endpoint for all of these risk quotients.
These endpoints form the Tier 1 estimates for non-target, terrestrial plant exposure due to spray
drift.
For aquatic plants, the vascular plant RQs are based on the response of Duckweed (Lemna
gibba). It generates an RQ of 15 for non-endangered species and of >45 of endangered species.
For non-target, non-vascular aquatic plants, the green alga ( Selenastrum capricornutum) had an
RQ of 9 for endangered species when stressed with technical grade penoxsulam and an RQ of 5
for endangered species when stressed with the end-use product GF-443. risk quotients (RQs) for
the following taxonomic groups exceed levels of concern for the screening-level risk assessment.
These estimates apply to all application practices.
Any concern for endangered plants will be mitigated by the addition of buffer zones and drift
control strategies to product labels.
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Environmental Fate
Penoxsulam is expected to be very mobile, but not persistent, in either aqueous or terrestrial
environments. Penoxsulam exists almost exclusively in a disassociated state at pH values
normally found in rice paddy water, but not in terrestrial environments where lower pH values
may be found. Penoxsulam degrades by two different transformation mechanisms, producing
thirteen different identified transformation products, for photolytic and biotic degradation. Six
of these transformation products reached peak concentrations at study termination, indicating a
greater degree of persistence than penoxsulam and a potential to reach concentrations even
greater than those reported at study termination.
Persistence- Penoxsulam is not expected to be persistent in the environment. Aqueous
photolysis and aerobic degradation are expected to be the major routes of dissipation. In
aqueous environments, penoxsulam is expected to be stable to hydrolysis, but to dissipate rapidly
through aqueous photolysis in clear shallow waters, and more slowly through biotic degradation
when sunlight has a limited ability to penetrate turbid waters, or when waters are shaded by
trees, riparian vegetation, and/or crop canopies. In terrestrial environments, penoxsulam is
expected to dissipate through soil photolysis and biotic degradation. Considering its low vapor
pressure and Henry's Law constant, volatilization form soil and water is not expected to
contribute significantly to the dissipation of penoxsulam the environment. Penoxsulam also has
low potential to bioaccumulate in fish.
Mobility- Penoxsulam is expected to be very mobile in both aqueous and terrestrial
environments, not binding strongly to either soil or sediment. Submitted mobility data for three
penoxsulam degradation products (3-[[[2-(2,2-Difluoroethoxy)-6-(trifluoromethyl)phenyl]-
sulfonyl]amino]-lH-l,2,4-triazole-5-carboxylic acid (BSTCA), 5-OH-penoxsulam, and 2-(2,2-
Difluoroethoxy) -N-lH-l,2,4-triazole-3-yl-6-(trifluoromethyl) benzenesulfonamide (BST))
indicate environmental mobility roughly equivalent to the parent compound. However, there are
no data regarding the mobility of the remaining transformation products or of combined
parent/degradate residues. Penoxsulam has low volatility indicating that atmospheric transport
is, at best, a very minor route of transportation.
Aquatic Concentrations- Surface water contamination by penoxsulam is assumed to occur
through drift or designed release to a stream or pond. Unlike terrestrial row crops, the major
growth and development phases for a rice crop take place in a flooded field, or paddy. A paddy
is typically designed to capture and maintain a uniform depth of irrigation (flood) water. This
design minimizes aquatic transport to ground water via levee overflow, breaching, and leaching
(also known as deep percolation).
Transformation Products- Data are not available to fully characterize the complex, potential
degradation pathways of penoxsulam. Submitted laboratory studies demonstrate that
penoxsulam transforms by competing mechanisms, through several generations of degradation
products. Examination of the specific transformation products formed in the submitted
laboratory studies, suggests that the more rapid photolytic transformation proceeds primarily
through cleavage of the parent molecule on, or adjacent to, the sulfonamide bridge. The slower
biotic degradation pathway proceeds primarily through fragmentation of the pyrimidine ring or
its residues.
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Six of the thirteen identified transformation products reached peak concentrations at study
termination. These six compounds are potentially more persistent than the parent compound,
and would probably have reached even greater concentrations with time. Only limited fate data
are available for the penoxsulam transformation products, including the six penoxsulam
degradates which the Health Effects Division determined to be of human toxicological concern:
BSTCA, 2-amino-l,2,4-triazole carboxylic acid (2-amino TCA), 5-OH-penoxsulam, 2-2,2-
Difluoroethoxy)-N-(iminomethyl-6-(trifluoromethyl)-benzenesulfonamide (SFA), 2-(2,2-
Difluoroethoxy) -6-(trifluoromethyl)-benzenesulfonamide (sulfonamide), and 5,8-di-OH-
penoxsulam.
OUTSTANDING DATA
Residue Chemistry
The final report of the ongoing storage stability study must be submitted in support of any future
food uses. Storage stability data for future uses will require the receipt and acceptance of the
final rice report as well as any data required for the additional use.
Physical Chemistry
One year storage stability (830.6317) and corrosion characteristic (830.6320) studies on the
technical chemical.
Environmental Fate
Seed germination/seeding emergence studies, vegetative vigor studies, and an aquatic plant
growth study using Duckweed with the degradates, BSA, 2-amino-TP, TPSA, BSTCA methyl,
BSTCA, 2-amino-TCA, 5-OH-penoxsulam, SFA, sulfonamide, 5,8-di-OH and 5-OH, 2 amino
TP.
The registrant submitted a large set of studies, including studies on penoxsulam's large number
of degradates. There are two studies that have been identified as outstanding. In addition
several of the studies with degradates need to be repeated or done for additional organisms.
EFED cannot determine which degradates or which organisms until the Health Effects Division
completes its analysis of the effects of these chemicals. EFED is concerned that certain
degradates that remain in the environment at relatively high concentrations will increase the
effect of the parent. Some of these degradates resemble the parent and may be the active moiety.
PUBLIC INTEREST FINDING
Penoxsulam use on rice was determined to be a reduced risk pesticide due to its favorable human
health risk profile when compared to registered ACCase alternatives and a similar or favorable
ecotoxicity profile when compared to other ALS-inhibitors registered for use on rice.
GOVERNMENT PERFORMANCE AND RESULTS ACT OF 1993 (GPRA)
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GPRA activities associated with this action are Registration of Safer Chemicals and Other
Registration Actions (Subobjectives 3.1.1, 3.1.3, and 4.1.1, ).
CONTACT PERSON AT EPA
Joanne I. Miller
Product Manager (23)
Herbicide Branch
Registration Division (7505C)
E-Mail Address:
Miller.Joanne@epa.gov
Mailing Address:
U.S. Environmental Protection Agency
1200 Pennsylvania Ave. N.W.
Washington DC 20460
Office Location and Telephone Number
Room 241, Crystal Mall Building #2
1801 South Bell Street
Arlington, VA 22209
(703)305-6224
DISCLAIMER: The information presented in this Pesticide Fact Sheet is for informational
purposes only and may not be used to fill data requirements for pesticide registration and
reregi strati on.
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