Document ID: EPA-HQ-OPP-2012-0384-0002
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2012-07-25T04:00Z

EPA REGISTRATION DIVISION COMPANY NOTICE OF FILING FOR PESTICIDE PETITIONS PUBLISHED IN THE FEDERAL REGISTER  

EPA Registration Division contact: Kable Bo Davis (703)306-0415

BASF Corporation

2E8021

	EPA has received a pesticide petition (2E8021) from BASF Corporation, 26 Davis Drive, Research Triangle Park, NC 27709 proposing, pursuant to section 408(d) of the Federal Food, Drug, and Cosmetic Act (FFDCA), 21 U.S.C. 346a(d), to amend 40 CFR part 180.490 by establishing a tolerance for residues of imazapic (+-)-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1-H-imidazol-2-yl]-5-methyl-3-pyridinecarboxylic acid in or on the raw agricultural commodity sugarcane at 0.01 parts per million (ppm).  EPA has determined that the petition contains data or information regarding the elements set forth in section 408(d)(2) of FDDCA; however, EPA has not fully evaluated the sufficiency of the submitted data at this time or whether the data supports granting of the petition. Additional data may be needed before EPA rules on the petition.

A. Residue Chemistry

	1. Plant metabolism. The metabolic pathway of imazapic is understood and is similar in a range of different crops including Bermuda grass, sugarcane and peanuts (a legume). Parent imazapic and the hydroxymethyl metabolite M715H001 (CL 263,284) were identified as major components of the total residue. Imazapic is metabolized via oxidative hydroxylation of the 5-methyl substituent to form the 5-hydroxymethyl metabolite M715H001 (CL263, 284), which in immature plants and mature leaves is subsequently conjugated with glucose to form metabolite M715H002 (CL189, 215).

	2. Analytical method. The proposed analytical method for detecting residues of imazapic and the metabolites M715H001 (CL 263,284) and M715H002 (CL 189,215) in sugarcane is an LC-MS/MS method.  This validated method has an LOQ of 0.01 mg/kg.

Enforcement methods for analysis of residues of imazapic and metabolite M715H001 (CL 263,284) in animal commodities have been previously submitted.  The analytical method for analysis in meat and meat by-products is based on capillary electrophoreses with confirmation by LC/MS.  The method LOQ is 0.05 mg/kg for meat and meat by-products.  The analytical method for analysis in milk and fat is based on determination by LC/MS with confirmation by LC/MS/MS.  The method LOQ is 0.01 mg/kg for milk and 0.05 mg/kg for fat.  Both methods were successfully validated by an independent laboratory validation.

	3. Magnitude of residues. i. Sugarcane.  Imazapic was applied at labeled rates in 9 field trials.  Residues of imazapic were below the limit of quantitation (<0.01 mg/kg) in all treated and control samples, 148 to 365 days after treatment.  

In two residue trials, a separate pre-emergence application was made at a rate of 5x maximum proposed label rate, for the purposes of providing cane for processing.  Processed commodities were not analyzed since residues of imazapic in the cane stalks treated at five times the proposed application rate were below the limit of quantitation (<0.01 mg/kg) for each analyte and parent. Processing studies showed no concentration of residues from sugarcane into sugar or molasses.

ii.  Ruminants. Not relevant to import tolerances since imported crops would not be used for animal feed.

iii.  Poultry. Not relevant to import tolerances since imported crops would not be used for poultry feed.

B. Toxicological Profile

	1. Acute toxicity. Imazapic technical is considered to be non-toxic (toxicity category IV) to the rat by the oral route of exposure. In an acute oral toxicity study in rats, the LD50 value of imazapic technical was greater than 5,000 milligrams/ kilograms body weight (mg/kg bw) for males and females. The results from an acute dermal toxicity study in rabbits indicate that imazapic is slightly toxic (toxicity category III) to rabbits by the dermal route of exposure. The dermal LD50 value of imazapic technical was greater than 2,000 mg/kg bw for both male and female rabbits. Imazapic technical is considered to be nontoxic (toxicity category IV) to the rat by the respiratory route of exposure.  The 4-hour LC50 value was greater than 5.52 mg/L (analytical) for both males and females. Imazapic technical was shown to be non-irritating to rabbit skin (toxicity category IV) and minimally irritating to the rabbit eye (toxicity category III). Based on the results of a dermal sensitization study, imazapic technical is not considered a sensitizer in guinea pigs.

	2. Genotoxicity. Imazapic technical was tested in a battery of in vitro and in vivo genotoxicity assays measuring several different endpoints of potential genotoxicity. Collective results from these studies indicate that imazapic does not pose a mutagenic or genotoxic risk.

	3. Reproductive and developmental toxicity. i. The developmental toxicity study in Sprague Dawley rats conducted with imazapic technical showed no evidence of teratogenic effects in fetuses and no evidence of developmental toxicity. Thus, imazapic is neither a developmental toxicant nor a teratogen in the rat. In the rat developmental toxicity study with imazapic technical, the no observed adverse effect level (NOAEL) for maternal toxicity and developmental toxicity was 1,000 mg/kg bw/day, the highest dose tested.

ii. Results from a developmental toxicity study in New Zealand White rabbits with imazapic technical also indicated no evidence of teratogenicity or developmental toxicity. Thus, imazapic technical is neither a developmental toxicant nor a teratogen in the rabbit. In the rabbit developmental toxicity study, the NOAEL for maternal toxicity was 350 mg/kg bw/day, based on decreased food consumption and body weight gain at 500 mg/kg bw/day, the next highest dose tested. The NOAEL for developmental toxicity was determined by EPA to be 500 mg/kg bw/day; the excessive mortality in dams at 700 mg/kg bw/day (the highest dose tested) resulted in too few fetuses that were available for evaluation. 

iii. The results from the two-generation reproduction toxicity study in rats with imazapic technical support a NOAEL for parental toxicity of 20,000 ppm (or approximately 1,205 mg/kg bw/day in males and 1,484 mg/kg bw/day in females, calculated from food consumption data), the highest concentration tested. The NOAEL for growth and development of the offspring is also 20,000 ppm, or approximately 1,205 mg/kg bw/day in males and 1,484 mg/kg bw/day in females. Results from the reproduction study and the developmental toxicity studies conducted with imazapic technical show no increased sensitivity to developing offspring as compared to parental animals, because the NOAELs for growth and development of offspring were equal to or greater than the NOAELs for parental toxicity.

	4. Subchronic toxicity. i. A short-term (21-day) dermal toxicity study in rabbits was conducted with imazapic technical. No dermal irritation or abnormal clinical signs were observed at dose levels up to and including 1,000 mg/kg bw/day (highest dose tested), supporting a NOAEL for dermal irritation and systemic toxicity of 1,000 mg/kg bw/day. 

ii. In a subchronic (13-week) dietary toxicity study in rats with imazapic technical, no signs of systemic toxicity were noted, supporting a NOAEL of 20,000 ppm (or approximately 1,552 mg/kg/day for males and 1,728 mg/kg/day for females, calculated from food consumption data), the highest concentration tested. The requirement for a subchronic dietary toxicity study in non-rodents is satisfied by the one-year dietary toxicity study in dogs.

	5. Chronic toxicity. i. A one-year dietary toxicity study was conducted with imazapic technical in Beagle dogs at dietary concentrations of 0, 5,000, 20,000, and 40,000 ppm. In this study, the NOAEL for systemic toxicity was less than 5,000 ppm or approximately 158 mg/kg bw/day (137 mg/kg bw/day for males and 180 mg/kg bw/day for females), calculated from food consumption data, based on a slight skeletal myopathy, characterized by degeneration/necrosis of single fibers (minimal severity) and lymphocyte/macrophage infiltration in skeletal muscle, in males and females, and slightly decreased serum creatinine in females at 5,000 ppm (lowest concentration tested).

The skeletal myopathy observed at 5,000 ppm was considered of minimal toxicological significance because the limited presence and the minimal severity of skeletal myopathy were evident in only a few fibers out of hundreds evaluated per section per animal. Further, these focal myopathies of minimal severity were not consistently diagnosed in all skeletal muscles sites examined per dog (i.e., vastus and abdominal muscles, diaphragm and esophagus). Moreover, no clinical observations indicative of muscle dysfunction were noted in any animal in the study. Finally, although the skeletal myopathy noted at 40,000 ppm (highest concentration tested) was associated with increases in creatine kinase, aspartate aminotransferase and lactate dehydrogenase, no statistically or biologically significant increases in these serum enzymes were noted during the study period for animals in the 5,000 ppm group. As such, the minimal myopathy diagnosed microscopically at 5,000 ppm was not considered to impair or adversely affect the functional capacity of the affected skeletal muscles. 

ii. In a 2-year chronic dietary oncogenicity and toxicity study in rats conducted with imazapic technical, the NOAEL for oncogenicity and chronic systemic toxicity was 20,000 ppm (approximately 1,029 mg/kg bw/day in males, 1,237 mg/kg bw/day in females, calculated from food consumption data), the highest concentration tested. 

iii. An 18-month chronic dietary oncogenicity and toxicity study in mice with imazapic technical supports a NOAEL for oncogenicity and for chronic systemic toxicity of 7,000 ppm (or approximately 1,134 mg/kg bw/day in males, 1,422 mg/kg bw/day in females, calculated from food consumption data), the highest concentration tested. 

The EPA has classified imazapic as a group E carcinogen (evidence of noncarcinogenicity for humans) based on the absence of treatment-related tumors in acceptable carcinogenicity studies in both rats and mice.

	6. Animal metabolism. The rat, goat and hen metabolism studies indicate that the qualitative nature of the residues of imazapic in animals is adequately understood.

In the rat metabolism study conducted with radiolabeled imazapic (BAS 715 H, CL 263,222), urinary excretion was the primary elimination route with 94% to 102% of the radioactivity excreted in the urine.  The major component in the urine and feces was the unchanged parent compound.  

Lactating goats were orally treated using radiolabeled imazapic.  Imazapic was mainly eliminated from the goat through urine and feces.  HPLC of goat urine showed essentially unchanged imazapic, while residues in feces were comprised of imazapic and low levels of hydroxymethyl metabolites M715H001 (CL 263,284).  There were no detectable radiolabeled imazapic-derived residues in milk during or after treatment, nor in tissues except kidney 20 hours after the last dose.  The [14]C-residue in the high-dose kidney (0.05 mg/kg) was predominantly parent imazapic with low levels of metabolite M715H001 (CL 263,284, 8% TRR, <0.01 mg/kg) and two unknowns, each <=0.02 mg/kg.

A ruminant metabolism study was also conducted with the radiolabeled imazapic hydroxymethyl metabolite M715H001 (CL 263,284).  During treatment, TRR in the daily blood and milk samples were less than 0.01 mg/kg, regardless of the treatment dose levels. The TRR in liver, muscle, and omental fat were less than 0.01 mg/kg, regardless of the dose level. Analysis of the kidney extract showed that 9% (<0.01 mg/kg) of the extractable TRR was CL 263,284.

A metabolism study was performed on hens using radiolabeled imazapic.  Total recovery of radioactivity in urine and feces was 90.6% and 95.2% for the low and high doses, respectively.  Residues in all tissues (liver, kidney, muscle, skin with adhering fat), blood and eggs were <0.01 mg/kg, the validated detection limit.

A poultry metabolism study was also conducted with the radiolabeled imazapic hydroxymethyl metabolite M715H001 (CL 263,284).  Total recovery of radioactivity in urine and feces was 85.3% and 88.6% for the low and high doses, respectively.  Residues in all tissues, liver, kidney, muscle, skin with adhering fat, blood and eggs, were less than 0.01 mg/kg, the validated detection limit.

	7. Metabolite toxicology. Metabolism studies in grass, peanuts and sugarcane indicate that the only significant metabolites are the hydroxymethyl resulting from hydroxylation of the methyl group at the 5-position of the pyridine ring, (+-)-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-hydroxymethyl-3-pyridinecaroxylic acid, and the conjugate resulting from glucosylation at the hydroxyl group. The hydroxymethyl metabolite was also identified in minor quantities in the rat metabolism study and in the goat metabolism study. No additional toxicologically significant metabolites were detected in the plant or animal metabolism studies.

	8. Endocrine disruption. Collective organ weight data and histopathological findings from the two-generation rat reproductive study, as well as from the subchronic and chronic toxicity studies in three different animal species, demonstrate no apparent estrogenic effects or treatment-related effects of imazapic on the endocrine system.

C. Aggregate Exposure

	1. Dietary exposure. 

	i. Food. 

a. Acute Dietary Exposure.  An acute dietary assessment is not necessary because no acute dietary endpoint was selected based on the absence of an appropriate endpoint attributable to a single dose of imazapic.

b. Chronic Dietary Exposure.  A Tier 1 assessment of potential chronic dietary exposure was performed for the proposed import tolerance for use of imazapic on sugarcane.  The assessment was done using DEEM(TM), incorporating the current tolerances as listed in 40 CFR 180.490 on peanut, tissues of cattle, sheep, goats, and horses, and milk and the proposed tolerance for sugarcane.  For this Tier 1 analysis, tolerance values were used for sugarcane at 0.01 mg/kg ; peanut at 0.1 mg/kg; fat of cattle, sheep, goats, and horses at 0.1 mg/kg; kidney of cattle, sheep, goats, and horses at 1.0 mg/kg; meat byproducts, except kidney of cattle, sheep, goats, and horses at 0.1 mg/kg; meat of cattle, sheep, goats, and horses at 0.1 mg/kg; and milk at 0.1 mg/kg.  Chronic dietary exposures for the overall U.S. population and population subgroups, including infants and children were compared to the chronic Reference Dose (RfD) of 0.46 mg/kg/day (based on a LOAEL of 137 mg/kg bw/day from the chronic dog toxicology study and a safety factor of 300).  Results of the chronic dietary analyses for all population subgroups examined were below 1.0% of the chronic RfD.  Exposure estimates for children 1-2 years old, the most highly exposed subpopulation, were only 0.003876 mg/kg bw/day (or 0.8% of the RfD).  Therefore, the results of the chronic dietary assessment demonstrate a reasonable certainty of no harm from the proposed and existing uses of imazapic.

      ii. Drinking water.  Drinking water residues at an estimated drinking water concentration (EDWC) of 14 μg/L, i.e., the maximum level estimated by EPA, as reported in the 2001 Federal Register notice (66 FR 66325) were included in a dietary assessment using DEEM(TM).  A proposed tolerance for an imported commodity would have no impact on the exposure due to drinking water. The exposure estimates for all population subgroups when compared to the RfD of 0.46 mg/kg bw/day were at or below 0.3% (non-nursing infants) of the chronic RfD.

      iii. Aggregate dietary.  The aggregate exposure estimate due to food and water in the diet for children 1-2 years old, the most highly exposed subpopulation, was 0.004314 mg/kg bw/day or less than 1% of the chronic RfD.

	2. Non-dietary exposure.  Residential aggregate exposure assessments are not required because the only source of potential imazapic exposure in the U.S. is via the diet and drinking water.

D. Cumulative Effects.  

      Imazapic belongs to the imidazolinone class of compounds a class comprised of a number of registered herbicides.  The herbicidal activity of the imidazolinones is due to the inhibition of acetohydroxyacid synthase (AHAS), an enzyme only found in plants.  AHAS is part of the biosynthetic pathway leading to the formation of branched chain amino acids.  Animals lack AHAS and this biosynthetic pathway.  This lack of AHAS contributes to the low toxicity of the imidazolinone compounds in animals.  We are aware of no information to indicate or suggest that imazapic has any toxic effects on mammals that would be cumulative with those of any other chemical.

E. Safety Determination

	1. U.S. population. Based on the chronic RfD of 0.46 mg/kg bw/day, the proposed sugarcane application, in addition to the existing uses, will utilize a maximum of approximately 1.0% of the RfD.  Exposure estimates for the general U.S. population were only 0.001066 mg/kg/day or 0.23% of the RfD.  Exposure estimates for children 1-2 years old, the most highly exposed subpopulation, were only 0.004314 mg/kg/day or 0.94% of the RfD.  EPA generally has no concern for exposure below 100% of the RfD, which represents the level at or below which daily aggregate dietary exposure over a lifetime will pose no appreciable risks to human health.  The complete and reliable toxicity data, indicating low potential mammalian toxicity and the conservative chronic exposure assumptions support the conclusion that there is a "reasonable certainty of no harm" from aggregate exposure to imazapic residues.

	2. Infants and children. The conservative dietary exposure estimates presented above will utilize 0.50% of the RfD for all infants and 0.94% of the RfD for children 1-2 years old, the most highly exposed population subgroup.  Results from the two-generation reproduction study in rats and the developmental toxicity studies in rabbits and rats indicate no increased sensitivity to developing offspring when compared to parental toxicity.  These results also indicate that imazapic is neither a developmental toxicant nor a teratogen in either the rat or rabbit.  Therefore, an additional safety factor is not warranted, and the RfD of 0.46 mg/kg/day, which utilizes a 300-fold safety factor is appropriate to ensure a reasonable certainty of no harm to infants and children.

F. International Tolerances

	EFSA in its reasoned opinion has recommended 0.01 mg/kg for imported sugarcane treated with Imazapic. There are no Codex tolerances established for imazapic on sugarcane.