UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
Inorganic Chlorates Facts
EPA 738-F-08-001
February 2008
Pesticide Reregistration
All pesticides sold or distributed in the United States must be registered by EPA
based on scientific studies showing they do not pose unreasonable risks to people or the
environment. Because of advances in scientific knowledge, the law requires that
pesticide products 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 reregisters
pesticide products meeting current human health and safety standards that can be used
without posing unreasonable risks to human health and the environment.
When a pesticide active ingredient is eligible for reregi strati on, EPA explains the
basis for its decision in a Reregistration Eligibility Decision (RED) document. This fact
sheet summarizes the information in the RED document for the pesticide inorganic
chlorates (case no. 4049). The Agency has determined that sodium chlorate-containing
products are eligible for reregi strati on provided that the risk mitigation measures outlined
in the RED are adopted, label amendments are made to reflect these measures, and a
safety finding can be made for sodium chlorite.
Use Profile and Regulatory History
Sodium chlorate (073301), calcium chlorate (073302), potassium chlorate
(073303), and magnesium chlorate (530200) are the four inorganic chlorates listed as
active ingredients. However, only one, sodium chlorate, is used as an active ingredient in
currently registered products. For that reason, sodium chlorate is the primary focus of the
RED. Sodium chlorate, calcium chlorate, and potassium chlorate are present as inert
ingredients in other currently registered products.
Sodium chlorate is an inorganic salt herbicide that was first registered in 1966. It
is a defoliant and a desiccant primarily used on cotton, but it also has other agricultural
and non-agricultural uses. Other agricultural uses include rice, corn, soybeans, dry beans,
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potatoes, sunflowers, flax, safflower, chili peppers, grain sorghum, and wheat. As a non-
selective herbicide, it is used to kill grasses and weeds in industrial and non-agricultural
sites such as driveways, tennis courts, and recreational areas. Products formulated as
soluble concentrates can be applied using aerial, ground boom, or handheld equipment.
Products formulated as granules or pellets can be applied using belly grinders, push-type
spreaders, tractor-drawn spreaders, or by hand. There are 56 active product registrations
containing sodium chlorate as an active ingredient.
In agriculture, application rates range from 6 to 12.5 pounds active ingredient per
acre (Ib ai/A). Industrial and other non-crop site rates range from 132 to 1032 Ib ai/A,
based on current labels. Sodium chlorate can be applied multiple times per year, and
according to Agency data, approximately 2.8 million pounds are applied annually to
agricultural, residential, and commercial use sites.
Human Health Exposure and Risk
No acute dietary (food and drinking water) endpoint was selected for sodium
chlorate because effects attributable to a single dose were not seen in the available data.
Therefore, acute dietary (food and drinking water) risk is not of concern to the Agency,
and no mitigation measures are required. However, sodium chlorate is a thyroid toxicant
producing thyroid gland follicular cell hypertrophy in rats and mice following chronic
exposures. Sodium chlorate is classified, in accordance with EPA policy, as not likely to
be carcinogenic to humans at doses that do not alter thyroid hormone homeostasis.
The chronic dietary risk assessment for food only is below the Agency's level of
concern (LOG) for the general US population and all population subgroups. The most
highly exposed subgroup, children 1 to 2 years of age, was at 28% of the chronic
Population Adjusted Dose (cPAD). Since this is less than 100% of the cPAD, no
mitigation is needed.
The chronic dietary risk assessment for chlorate in drinking water, calculated
using the highest annual average concentration derived from the Information Collection
Rule (ICR) Database (estimated at 0.69 mg/L), is below 100% of the cPAD and,
therefore, below the Agency's LOG for the general US population and all population
subgroups except for infants. Exposure to infants, the highest exposed subgroup, was
159% of the cPAD based on the highest annual average concentration of chlorate.
However, using the 90th percentile annual average concentration (estimated at 0.24 mg/L)
the chronic dietary (water only) risk for infants was 55% of the cPAD. Also for infants,
using the median annual average concentration (estimated at 0.1 Img/L) the risk was 25%
of the cPAD. The ICR Database was considered the most appropriate source for
estimating exposure averages from individual water treatment plants because it was the
most robust set of data.
All residential (non-occupational) handler and post-application risk estimates for
inorganic chlorates, as active or inert ingredients in conventional pesticide products used
in residential environments, are below the Agency's LOG (i.e., margins of exposure or
MOEs are greater than the LOG of 100). The handler inhalation MOEs ranged from 370
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to 710,000. The post-application combined MOE (for inert ingredients) was 23,000 for
all potential routes of exposure to children. Therefore, no residential mitigation is
necessary.
Aggregate assessments combine food, drinking water, and any residential or other
non-occupational exposures. Short term aggregate risks, assessed for adults only using
the highest exposure scenario, are all below the LOG. Chronic aggregate risks, however,
are above the LOG for both infants and children ages 1 to 2, when calculated using the
estimated highest annual average drinking water concentration (0.69 mg/L). When the
90th percentile and median annual average water concentrations are used (0.24 or 0.11
mg/L, respectively), all population subgroups are below the LOG. The Agency believes
that sodium chlorate does not constitute a risk of concern to the general population or any
population subgroups, since the LOG exceedances are associated with a small number of
water treatment facilities and inappropriate treatment practices. Furthermore, the Agency
anticipates that the community water system outreach strategy discussed in the RED will
greatly reduce potential drinking water byproduct exposure.
Most risk scenarios for occupational handlers of sodium chlorate did not exceed
the Agency's LOG, but several did. However, by enacting the mitigation measures
outlined in the RED, to include engineering controls and application restrictions, all
scenarios are below the LOG (i.e. MOEs are greater than the LOG of 100). Post-
application occupational exposure was not assessed because dermal and inhalation
exposures are negligible due to the chemical's physical and chemical characteristics as an
inorganic salt.
Environmental Exposure and Risk
Sodium chlorate is not a naturally occurring chemical. Physical properties
indicate that it is not expected to volatilize from soil or water and has low potential to
bioaccumulate. Sodium chlorate is highly soluble and is expected to be very mobile and
partition predominately into water. In the environment, extensive redox reactions are
expected to reduce the concentration of chlorate in the water column. Key findings from
the ecological risk assessment are summarized below.
There appears to be no acute risk to fish at the Agency's LOCs. However, some
data suggest that brown trout could be substantially more sensitive than other fish species
tested to chlorate's toxicity. No toxicity studies are available to quantify the chronic risk
to fish. For freshwater and saltwater invertebrates acute risks for both agricultural and
non-agricultural uses of sodium chlorate are below the LOG of 0.5. Chronic risk to
invertebrates was not assessed since treatment-related effects were not observed at any
concentration in available studies. For non-endangered aquatic plants, the Agency's LOG
of 1.0 was not exceeded for either the agricultural or non-agricultural uses of sodium
chlorate (highest risk quotient or RQ was 0.91).
No mortality occurred in the submitted avian subacute toxicity studies at the
highest concentration tested, representative of chlorate's agricultural use pattern.
However, acute risk to birds cannot be precluded for chlorate's non-agricultural uses
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because estimated environmental concentrations (EECs) from these higher application
rates are significantly greater than those estimated for agricultural use patterns. However,
mitigation measures enacted in the RED will limit avian exposure to sodium chlorate and
reduce these risks. For chronic risks to birds, LOCs were exceeded for agricultural uses,
and the highest calculated RQ was 11 (LOG is an RQ above 1.0). Chronic RQs were not
calculated for sodium chlorate's non-agricultural uses, but based on the higher
application rates and resulting EECs, RQs would exceed those calculated from
agricultural uses. Risks to birds will be reduced through mitigation measures, including
limiting applications to spot treatments and decreasing application rates.
For mammals, acute toxicity was not calculated because of inability to classify the
dose response curve. Instead, high-end acute risk ratios were calculated and indicate that
sodium chlorate's agricultural uses will not exceed the LOG of 1.0 except in one scenario
(small mammals eating short grass). However, acute risks to mammals from sodium
chlorate's non-agricultural uses are likely above the LOG due to higher application rates
and resulting EECs. Considering these ratios are over-estimates and that mitigation
measures will impose application restrictions, the likelihood of a risk of concern will be
reduced. A conservative estimate of chronic toxicity to mammals for agricultural sites
was calculated, and RQs exceeded the LOG of 1.0 (highest RQ was 2.6). Chronic
toxicity was not calculated for non-agricultural use sites, but risk estimates would likely
be considerably higher than those calculated for agricultural uses for the reasons stated
previously. Mitigation measures outlined in the RED and the possibility that risk ratios
are overstated reduce the likelihood of a risk of concern.
Adequate data are not available to allow for derivation of RQs for terrestrial
plants. However, risk to plants is presumably higher than the Agency's concern level
based on chlorate's non-selective mode of action as an herbicide.
The preliminary risk assessment for endangered species indicates that RQs
exceed endangered species LOCs for chronic risks to birds (RQs up to 11 for agricultural
uses and greater for non-agricultural uses); acute risks to mammals (RQs up to 33);
chronic risks to mammals (RQs up to 1.2 for agricultural uses and greater for non-
agricultural uses); and risks to aquatic plants (RQs up to 13). Risks could not be
calculated for terrestrial plants and for chronic risks to fish. Potential indirect effects to
any endangered species dependent upon a species that experiences effects from use of
sodium chlorate can not be precluded based on the screening level ecological risk
assessment. These findings are based solely on EPA's screening-level assessment and do
not constitute "may affect" findings under the Endangered Species Act.
Risk Mitigation
The following mitigation measures are necessary to address identified risks for
products containing sodium chlorate to be eligible for reregi strati on.
Agricultural use mitigation:
• Engineering controls (enclosed cockpits) for aerial applications on agricultural
crops.
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• For cotton, the maximum application rate will be reduced from 7.5 Ibs ai/A to 6
Ibs ai/A, and applications will be limited to a single application in all states except
California, where a second application will be allowed.
Non-agricultural use mitigation:
• All non-agricultural uses will be limited to spot treatments only (with the
exception of the granular formulation for use under asphalt, although this use will
be limited to an 8000 ft2 treatment area). The uses limited to spot treatments
include, but are not limited to: building perimeters, driveways, parking lots, fence
rows, military installations, pipelines, railroads, lumberyards, industrial sites,
tennis court perimeters, picnic areas, bleachers, cemeteries, fuel tanks, airport
runways, helicopter pads, wood decks, guard rails, highway medians, sidewalks/
walkways, vacant lots, fire hydrants, recreational areas, and other similar areas.
• Use on rights-of-way and ditch banks will be cancelled.
• The label will specify a maximum application rate of 0.9 Ib ai/100 ft2.
Data Requirements
The generic database supporting the reregi strati on of sodium chlorate has been
reviewed and determined to be substantially complete. However, some data gaps remain,
and the data requirements listed below must be submitted to EPA. The OPPTS Guideline
Numbers are noted in parenthesis. Note that the list below varies slightly from what is
shown in the RED due to post-RED consultations and determinations within the Agency.
• UV/Visible Light Absorption (830.7050)
• Avian reproduction test (1-generation mallard duck) (850.2300)
• Honey bee acute contact toxicity (850.3020)
• Seedling emergence, Tier II (850.4100)
• Vegetative vigor, Tier II (850.4150)
• Submittal of analytical reference standards (860.1650)
Product Labeling Changes
All sodium chlorate products must comply with EPA's current pesticide product
labeling requirements and with the labeling changes set forth in Section V of the
Inorganic Chlorates RED document. All labels must be amended to incorporate the risk
mitigation measures outlined in the RED. The Agency may require changes to the
language of the sodium chlorate label in the future if deemed necessary under the
Endangered Species Protection Program.
For More Information
Electronic copies of the Inorganic Chlorates RED and this fact sheet are available
at http://www.epa.gov/pesticides/reregistration/status.htm. All supporting documents are
available through the public docket EPA-HQ-OPP-2005-0507 located on-line through the
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website above or in the Federal Docket Management System at
http://www.regulations.gov.
For more information about EPA's pesticide reregi strati on program, the Inorganic
Chlorates RED, or reregi strati on of individual products containing inorganic chlorates,
please contact the Special Review and Reregi strati on Division (Mailcode 7508P), Office
of Pesticide Programs, U.S. EPA, Washington D.C. 20460, telephone (703) 308-8000.
For information about the health affects of pesticides, or for assistance in
recognizing and managing pesticide poisoning symptoms, please contact the National
Pesticide Information Center (NPIC). Call toll-free 1-800-858-7378, 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://npic.orst.edu.
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