UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON D.C., 20460

Chemical: Chlorpyrifos-methyl

PC Code: 059102

              DP Barcode: 370120

DATE: November 23, 2009

MEMORANDUM

SUBJECT:  Registration Review – Problem Formulation for
Chlorpyrifos-methyl

FROM:		Donna Judkins, Biologist

				Mark Corbin, Senior Environmental Scientist

THROUGH: 	Dana Spatz, Branch Chief

				Environmental Risk Branch 3

		            Environmental Fate and Effects Division

		            Office of Pesticide Programs

TO:				Veronique LaCapra, Chemical Review Manager

				Reregistration Branch 2

				Pesticide Re-Evaluation Division

				Office of Pesticide Programs

Attached is the preliminary problem formulation, a part of the
registration review, for the insecticide Chlorpyrifos-methyl.

REGISTRATION REVIEW

PROBLEM FORMULATION FOR:

CHLORPYRIFOS-METHYL

Chlorpyrifos-methyl (CAS 5598-13-0)

PREPARED BY:   

Donna Judkins, Ph.D., Biologist

Mark Corbin, Senior Environmental Scientist 

APPROVED BY: 

Dana Spatz, Branch Chief

Environmental Risk Branch 3

Environmental Fate and Effects Division

Office of Pesticide Programs

STRESSOR SOURCE AND DISTRIBUTION

Chlorpyrifos-methyl is an insecticide used to target and kill a variety
of insects including beetles, weevils, moths, and grain borers.
Chlorpyrifos-methyl has two current registrations (EPA Reg # 264-992 and
62719-42) for treatment of grains in storage bins and warehouses. 
Chlorpyrifos- methyl is applied indoors with one application per year by
sprayer or automatic sprayer at a rate of 0.0253 lbs ai/1,000 square
feet.   Based on the most recent usage data provided by BEAD
chlorpyrifos-methyl has been applied predominantly on stored grains with
approximately 110,000 lbs applied annually.  

Table 1. Chemical Registration Data Summary

Common name		Chlorpyrifos-methyl 

Chemical name	Chlorpyrifos-methyl [C7H7Cl3NO3PS]

CAS number	5598-13-0

Pesticide type	Insecticide

PC Code	059120

EPA Registration Numbers	264-992 (Bayer Crop Science STORCIDE II (21.6%
active)) & 62719-42 (Dow AgroSciences Reldan* F Insecticidal Chemical
(97% active)) 



INTEGRATION OF AVAILABLE INFORMATION

The documents available in the Office of Pesticide Programs Regulatory
Docket and which serve as the basis for this problem formulation include
the following:

1980 Ecological Risk Assessment

December 2000 Tolerance Reassessment

October 2000 Pesticide Fact Sheet

December 2007 Product Cancellation Order

ECOLOGICAL EFFECTS

No ecotoxicological data have been required by EPA in past assessments
of chlorpyrifos-methyl since all uses were indoor.  However, according
to product labels, all end-use products are toxic to extremely toxic to
fish, birds and other wildlife; therefore, it is not allowed to be used
on or near water or on seed to be fed to birds or wildlife.  Data from
earlier risk assessments indicate that chlorpyrifos-methyl is
practically nontoxic to moderately toxic to avian wildlife based on
dosing studies (LD50, 100->2000 mg/Kg); practically nontoxic to slightly
toxic to avian wildlife based on dietary studies (LC50, 1835->5000
mg/L); moderately toxic to very highly toxic to fish based on acute data
(LC50, 0.014-4.58 mg/L); and slightly toxic to very highly toxic to
aquatic invertebrates based on acute tests (LC50, 0.00017-45.8 mg/L);
and very highly toxic to honeybees based on acute studies (LD50,
0.088-0.383 µg/bee).  



EXPOSURE CHARACTERISTICS

No acceptable environmental fate data have been submitted to EPA for
chlorpyrifos-methyl.  The environmental fate and metabolism of
chlorpyrifos-methyl are expected to be similar to the environmental fate
and metabolism for chlorpyrifos.  Previously, data summaries were
prepared by EFED that present overviews of the environmental fate as
captured in open literature.  These data suggest that
chlorpyrifos-methyl is relatively non-persistent under biotic (aerobic
soil metabolism and field dissipation studies) and abiotic conditions
(hydrolysis) based on both laboratory and field data with half lives
generally less than 30 days.  An exception to this is that hydrolysis
half lives are longer (i.e., up to 76 days) at colder temperatures
(i.e., 15 degrees Celsius) and is more stable under acidic conditions.  
Finally, chlorpyrifos-methyl is relatively immobile with Koc’s between
3,000 and 4,500.  

Chlorpyrifos-methyl does not appear in any of the surface or groundwater
monitoring data sets reviewed, however, this could be due to the fact
that most monitoring programs are not analyzing for it.  

Table 2.  Physical and Chemical Properties of Chlorpyrifos-methyl

Empirical formula	C7H7Cl3NO3PS

Molecular mass (g/mol)	322.6

Vapor pressure	4.22 x 10-5 mm Hg at 25 oC

Solubility in water 	4 mg/L

Kow 	4.3

pKa	NA

Hydrolysis half-life	3 days to 76 days



ANALYSIS PLAN 

Chlorpyrifos-methyl is used as an indoor treatment for small grains in
storage bins and warehouses.  The product is applied by manual and
automatic sprayer in self-contained units applied in discrete locations
with a spatial extent limited to building size areas with negligible
potential for offsite transport.  The application method does not allow
for drift to terrestrial areas or to water bodies.  The units are not
intended for moist areas and do not contain amounts of active ingredient
sufficient for runoff to be a concern.  Direct or indirect exposure to
humans or ecological receptors is not expected.  If used as directed on
the product label, then the likelihood of exposure to non-target
wildlife is minimal. Therefore, ecological exposure and effects are not
expected from this use.  In addition, the use pattern is unlikely to
result in exposure in aquatic resources or groundwater and thus drinking
water is unlikely to be impacted by this use.

According to 40 CFR Part 158, avian oral toxicity, freshwater fish acute
toxicity and freshwater invertebrate acute toxicity data are
conditionally required for the indoor use pattern, depending on whether
or not there is a potential for environmental exposure.  Since the use
of the currently registered products containing chlorpyrifos-methyl is
not expected to result in environmental exposure, no additional
ecological effects data are required.

The Agency anticipates that no quantitative ecological risk assessment
or drinking water assessment will be needed. Because these uses are
indoors, it is unlikely that listed species will be impacted and thus a
quantitative endangered species assessment will not be conducted. 

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