Human Health
                         United States
                         Environmental Protection
                         Prevention, Pesticides
                         and Toxic Substances
October 6, 2005
      All pesticides sold or distributed in the United States must be registered by
EPA (the Agency), based on scientific studies showing that they can be used without
posing unreasonable risks to people or the environment. Because of advances in
scientific knowledge, the law requires that pesticides, which were first registered
before November 1, 1984, be reregistered to ensure that they meet today's more
stringent standards.

      In evaluating pesticides for reregi strati on, EPA obtains and reviews a
complete set of studies from pesticide producers, describing the human health and
environmental effects  of each pesticide. To implement provisions of the Food
Quality Protection Act (FQPA) of 1996, EPA considers the special sensitivity of
infants and children to pesticides, as well as aggregate exposure of the public to
pesticide residues from all sources, and the cumulative effects of pesticides and other
compounds with common mechanisms of toxicity.  The Agency develops any
mitigation measures or regulatory controls needed to effectively reduce each
pesticide's risks. EPA then registers pesticides that meet current health and safety
standards and can be used without posing unreasonable risks to human health or the

      When a pesticide is eligible for reregi strati on, EPA explains the basis for its
decision with the Reregi strati on Eligibility Decision (RED) document. This fact
sheet summarizes the information in the RED document.
Use Profile
      Pyrazon [5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone], also known as
chloridazon, is an herbicide belonging to the pyridazinone class of pesticides.  It
works as an herbicide by blocking electron transport in photosystem II in green
plants, thereby inhibiting photosynthesis.  Pyrazon is registered for pre-plant, pre-
emergence, and early post-emergence use on sugar beets and red table beets to control
certain weeds. Approximately 10% of the U.S. sugar beet crop and 50% of the U.S.
table beet crop are treated with pyrazon annually. Pyrazon is also registered for
commercial use on ornamentals, including bulb crops and roses.

       Pyrazon is considered to be of low toxicity without highly specific responses
in mammals.  Pyrazon has low (category III/IV) acute toxicity via the oral, dermal,
and inhalation routes of exposure. It is not an eye or skin irritant (category IV) and
does not cause dermal  sensitization.  In longer-term studies, reduced body weight
associated with reduced food consumption appears to be the most significant effect of
pyrazon exposure in laboratory animals. At higher doses, conditions such as poor
general appearance and some motor effects considered to be associated with poor
nutrition are noted in rats. No systemic effects resulted from  dermal exposure to
pyrazon.  Pyrazon is classified as "not likely to be a carcinogen in humans."

Dietary Risks
       EPA determined that there is reasonable certainty that no harm to any
population subgroup will result from aggregate exposure to pyrazon when
considering dietary (food and water) exposure.

       An acute dietary assessment was not conducted because an endpoint of
concern attributable to a single dose was not identified.  Therefore, only a chronic
dietary assessment was conducted. According to the assessment, estimated exposures
from pyrazon residues in food represent less than 0.1% of the cPAD for all population

       The drinking water assessment for pyrazon and desphenyl pyrazon, the major
degradate, showed that estimated  exposures from drinking water are well below the
Agency's level of concern, representing 25% or less of the cPAD for all population

Residential and Other Non-Occupational Risks
       There are currently no pyrazon products registered for homeowner use, and no
residential exposure is expected from commercial uses of pyrazon; therefore, a
residential risk assessment was not conducted.

FQPA Considerations
       The FQPA Safety Factor (as required by the Food Quality Protection Act of
1996) is intended to provide up to an additional 10-fold safety factor (10X), to protect
for special sensitivity in infants and children to specific pesticide residues in food,
drinking water, or residential exposures. EPA chose to waive the FQPA safety factor
(i.e., reduce it to IX) based on a conclusion of no increased pre- and/or post-natal
susceptibility and no residual uncertainty for pre- and/or post-natal toxicity.

       EPA did not perform a cumulative risk assessment for pyrazon because
unlike other pesticides for which EPA has followed a cumulative risk approach based
on a common mechanism of toxicity, EPA has not made a common mechanism of
toxicity finding for pyrazon and any other substances, and pyrazon does not appear to
produce a toxic metabolite produced by other substances.

                           Worker Risks
                                  Occupational workers can be exposed to a pesticide through mixing, loading,
                           and/or applying a pesticide, or re-entering treated sites.  Nine occupational scenarios
                           were assessed for mixers, loaders, applicators, and flaggers supporting applications of
                           pyrazon via aerial, groundboom, low pressure handwand sprayer, and backpack
                           sprayer equipment. Dermal toxicity endpoints were not identified in existing studies;
                           therefore, only inhalation risks to workers were assessed.  Long-term exposures
                           (greater than 6 months) are not expected from use of pyrazon.  There were no risks of
                           concern identified for handlers when baseline PPE is worn.

                                  Post-application exposure was not assessed because there is no dermal
                           endpoint of concern and post-application inhalation exposure is expected to be
                           negligible. However, the Worker Protection Standard requires a 12-hour restricted
                           entry interval (REI) for chemicals classified as Toxicity Category III or IV. Pyrazon
                           is classified in Toxicity Category III for acute oral and dermal Toxicity Category IV
                           for acute inhalation and primary eye and skin irritation; therefore, the current REI  of
                           12 hours is appropriate and will remain on labels.
Environmental Fate
       Available fate date indicate that pyrazon is mobile in a variety of soil types
and is persistent in soil and in aquatic environments.  On soil, the photolysis half-life
is 69 days, with an aerobic soil metabolism half-life of 90-152 days, and an anaerobic
soil metabolism half-life of 307 to 607 days, depending on the soil texture tested.
The most significant route of degradation of pyrazon in water appears to be
photolysis, with  a half-life of 12.5 days.  Pyrazon is stable to hydrolysis at pH 5, 7
and 9.

Ecological Risks
       The screening level ecological risk assessment for aquatic organisms resulted
in no acute risks of concern for freshwater fish and invertebrates. Chronic risks to
freshwater fish and invertebrates could not be assessed, due to the lack of available
data.  Some pyrazon may be used in coastal areas in California; thus, estuarine/marine
organisms may be exposed.  However, due to the lack of available toxicity data
estuarine and marine organisms, risks to these organisms could not be assessed.  Also,
there are no risks of concern for non-listed aquatic plants, but are several RQs that
exceed the level  of concern (LOG) for listed threatened or endangered species.

The screening level assessment for terrestrial organisms resulted exceedances of the
Agency's endangered species acute LOG for birds and mammals.  Chronic risks were
not assessed for birds, because chronic toxicity data were not available.  EPA does
not expect pyrazon to pose chronic risks of concern to mammals.

       Based on modeled EECs and the available toxicity data, RQ values for all uses
of pyrazon and all application scenarios exceed the LOG for listed and non-listed
non-target terrestrial plants and terrestrial plants in semi-aquatic areas.

Risk Mitigation
       As with most herbicides, risks of concern associated with pyrazon were
identified for listed and non-target terrestrial and semi-aquatic plants, and in some
scenarios, endangered aquatic plants. Additionally, acute risks of concern, if
exposures occur, were identified for endangered species of birds and mammals.
Given that the pyrazon ecological risk assessment is a screening level analysis, EPA
is not imposing any mitigation at this time. Should EPA's endangered species
specific assessment indicate that use of pyrazon "may affect" listed species, the
registered uses of pyrazon may need to be modified (see section on "Endangered
Species Concerns)".

       Pyrazon is persistent and mobile in many types of soil, and therefore, has the
potential to enter surface and  ground water.  Label statements regarding drift,  runoff,
and leaching, as well as chemigation prohibitions and plant-back restrictions are to be
added to the labels.
Additional  Data
       The generic database supporting the reregi strati on of pyrazon has been
reviewed and determined to be substantially complete. However, the following
additional data requirements have been identified by the Agency as confirmatory and
are listed below.


       870.5550 - Unscheduled DNA Synthesis in Mammalian Cells in Culture

Residue Chemistry:

       860.1340 - Independent Laboratory Validation (ILV) study for Method A9202

      860.1900 - Field Accumulation in Rotational Crops Study

Ecological effects:

      None (72-3A) - Estuarine/marine Fish Acute Toxicity Test
      850.1020 - Gammarid Acute Toxicity Test
      850.1025 - Estuarine/marine Mollusk (Oyster) Acute Toxicity Test (Shell
      None (72-3F) - Estuarine/marine Myside Acute Toxicity Test
      850.1045 - Penaeid Acute Toxicity Test
       850.1300 - Daphnid Chronic Toxicity Test
       850.1350 - Mysid Chronic Toxicity Test
       850.1400 - Early-life Stage, Freshwater Fish
       850.1450 - Early-life Stage Estuarine Fish
       850.1500 - Fish Life Cycle Study

                                 850.2300 - Avian Reproduction Test, Bobwhite Quail
                                 850.2300 - Avian Reproduction Test, Mallard Duck
       The use of currently registered products containing pyrazon in accordance
with approved labeling will not pose unreasonable risks or adverse effects to humans
or the environment if the label changes outlined in the RED are implemented.
Therefore, all uses of these products are eligible for reregi strati on.  These products
will be reregistered once the required product specific data, confidential statements of
formula (CSFs), and revised labeling are received and accepted by EPA. Products
that contain ingredients in addition to pyrazon will be reregistered when all of their
other active ingredients also are reregistered.
For More
       To obtain a copy of the pyrazon RED document, please contact the OPP
Public Docket (7502C), US EPA, Ariel Rios Building, 1200 Pennsylvania Avenue,
NW, Washington, DC 20460-0001, telephone: (703) 305-5805. Electronic copies of
the pyrazon RED and all supporting documents are also available on the Agency's
electronic docket at

       For more information about EPA's pesticide reregi strati on program or the
pyrazon RED, please contact the U.S. EPA,  OPP, Special Review and Reregistration
Division (7508C), 1200 Pennsylvania Avenue, NW, Washington, DC 20460,
telephone (703) 308-8000.

       For more information about the health effects of pesticides, or for assistance
in recognizing and managing pesticide poisoning symptoms, please contact the
National Pesticide Information Center (NPIC).  Call toll-free (800) 858-7378, from
6:30 am to 4:30 pm Pacific Time, or 9:30 am to 7:30 pm Eastern Standard Time,
seven days a week. The NPIC internet address is http://www/