  SEQ CHAPTER \h \r 1 

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C.  20460

OFFICE OF

PREVENTION, PESTICIDES, AND

TOXIC SUBSTANCES

PC Code:  081501

DP Barcode: 314394

Decision  #: 354829

	

April 5, 2007

MEMORANDUM								    

SUBJECT:	Response to Phase III Public Comments on the Draft
Environmental Fate and Ecological Risk Assessment Chapter in Support of
the Re-registration Eligibility Decision on Chloropicrin 

TO:		Nathan Mottl, Risk Manager Reviewer 

		Susan Lewis, Branch Chief

Special Review and Reregistration Division (7508P)

FROM:	Faruque Khan, Environmental Scientist

		James Felkel, Wildlife Biologist

		Environmental Risk Branch V		

Environmental Fate and Effects Division (7507P)

Approved	Mah Shamim, Branch Chief

 By:		Environmental Risk Branch V		

		Environmental Fate and Effects Division (7507P)

		

The Environmental Fate and Effects Division (EFED) has completed its
review of comments from the Chloropicrin Manufactures’ Task Force
(CMTF) (Data Package: EPA-HQ-OPP-2006-0661) received during the public
comment period (Phase III) on the draft environmental fate and
ecological risk assessment for chloropicrin. EFED did not receive any
other comments during the public comment period of the re-registration
process of chloropicrin. Specifically, EFED has reviewed the comments
relevant to the environmental fate and ecological risk assessment
chapter in support of the re-registration eligibility decision (RED) for
chloropicrin. This review paraphrases issues and concerns in order to
efficiently address common concerns.  After comments are summarized,
EFED then provides a response to the comments.  The intent of EFED’s
review is to address issues regarding the underlying science/data used
to estimate potential risk to the environment from the use of
chloropicrin. Comments regarding human health and worker exposure issues
will be addressed separately by the Health Effects Division. Overall,
none of the comments seem to warrant a refinement of EFED’s
Environmental Fate and Ecological Risk Assessment chapter at this time.
However, the ecological incidents data were updated in the attached
Phase IV Screening Level Environmental Fate and Ecological Risk
Assessment of Chloropicrin document.

III. ECOLOGICAL RISK ASSESSMENT

Aquatic exposure and Model 

Comment: A fundamental issue in the preliminary Ecological Risk
Assessment is the potential for substantial error introduced by improper
physical parameters that define the model. In modeling, EPA used
chemical-specific input parameters for chloropicrin and appears to have
used site specific meteorological data for the application sites. For
other than chemical-specific input values, PRZM/EXAMS modeling uses
generic scenarios created by EPA for all agricultural use pesticides.
Use of these generic values represents an important source of error
because chloropicrin is used (applied) in a manner different from
non-soil fumigant pesticides. The differences between chloropicrin
application methods and crop-use pesticide application methods do not
appear to have been taken into account in the site-specific physical
input parameters used in chloropicrin modeling. 

Response: As with earlier comments made by the CMTF in the error-only
comment phases (DP Barcode D305331), a large percentage of the comments
focused on the underlying assumptions used by EFED in modeling surface
water vales for ecological risk assessments and on the resulting
conservatism associated with the estimated surface water concentrations.
 EFED’s methods for estimated surface water concentrations use
standard modeling procedures and input parameter guidance that have been
subject to rigorous internal and external quality assurance review. 
These procedures and guidance are used in all modeling done by EFED. 
The screening-level process and underlying assumptions used by EFED to
estimate aquatic risks associated with the current uses of chloropicrin
is fully described in the Overview of the Ecological Risk Assessment
Process in Office of Pesticide Programs (OPP) document
(http://www.epa.gov/oppfead1/endanger/consultation/ecorisk-overview.pdf)
and has been subject to review by the Federal Insecticide, Fungicide and
Rodenticide Act Scientific Advisory Panel (FIFRA SAP). 

 Comment: The environmental fate values EPA used in its preliminary
freshwater aquatic risk modeling had some apparent deficiencies.
EFED’s selection of the aerobic soil metabolism and aerobic aquatic
metabolism values and their use in modeling erroneously overestimates
the environmental persistence of chloropicrin and its subsequent,
“predicted” ability to be mobilized into surface water. Without
evaluation of both the chemical-specific input parameters for modeling
(supplied by EPA in the preliminary risk assessment) and the
non-chemical-specific physical site parameters used by EPA, it is not
possible to establish reliability of the modeling output. The effects of
rain events on treated fields, tarped and non-tarped, are not well
established by EPA in the Risk Assessment and are not appropriately
accommodated in PRZM/EXAMS modeling.

Response: The ecological risk assessment process used by OPP is clearly
defined in the overview document cited previously and the process used
to evaluate the potential risks of chloropicrin is consistent with the
Overview Document. EFED performed the PRZM/EXAMS model using input
parameter according to PRZM/EXAMS input guidance document. EFED has
acknowledged in the chloropicrin document that there are some
limitations in the PRZM/EXAMS modeling of fumigants when tarps are used.
This is captured in the uncertainties and aquatic exposure modeling
sections of the document. There are a number of uncertainties associated
with any risk assessment and to the extent possible, the Agency attempts
to delineate those uncertainties.  However, just as the CMTF has
indicated that actual exposure may be lower than estimated exposure,
assessments may also underestimate exposure; that is the nature of
uncertainty.  It is the mandate of the EPA to preserve and protect human
health and the environment and when attempting to do so at a national
level, OPP’s approach, as outlined in the Overview Document, is to
gauge risk based on the most vulnerable areas using upper-bound exposure
values.  However, even using conservative assumptions for environmental
modeling and reliance on the most sensitive tested species may not fully
account for the range of environmental conditions or species
sensitivities that may exist in areas where a pesticide may legally be
applied. 

Terrestrial exposure and model

Comment: In terms of terrestrial animal exposure modeling, EFED not only
relied on modeling of off-site monitoring data (when on-site data are
available), EFED also used the model least able to incorporate realistic
meteorological conditions (ISCST3). , EFED stated that it relied on
off-site monitoring data to generate estimates of ground-level
concentrations of chloropicrin using the ISCST3 model. All of these
factors have led EPA to unrealistic results and conclusions. For a more
accurate and refined risk assessment, EFED needs to (1) use readily
available, direct measurement data taken on-site at various monitoring
heights across a broad array of application methods and/or locations (as
used by EPA’s Health Effects Division in the Human Health Risk
Assessment on Chloropicrin); and/or (2) use a modeling approach more
able to realistically incorporate the effects of fluctuating
meteorological conditions; and/or (3) develop a Level of Concern
interpretive context in which to evaluate inhalation exposure risks.
EFED’s current approach to modeling terrestrial animal exposure has
several compounding technical and conceptual flaws, and as such, a more
refined risk assessment is needed to properly characterize the potential
for terrestrial animal risk to chloropicrin. 

Response: The revised risk assessment used both deterministic and
ambient monitoring data to estimate exposures to terrestrial organisms
at the edge of treated fields which are the key concern. EFED did not
rely on off-site monitoring data to generate ground-level concentrations
of chloropicrin using the Industrial Source Complex: Short-Term Model
(ISCST3) model. The deterministic approach is based on Registrant’s
field monitoring data and the use of the EPA’s ISCST3 model. The basic
approaches to estimate air concentrations using ISCST3 model are
outlined in the Health Effects Division’s Draft Standard Operating
Procedures (SOPs) for Estimating Bystander Risk from Inhalation Exposure
to Soil Fumigant (USEPA,2004). Detailed input assumptions and model
results were described in the HED’s Draft Chapter on Non-Occupational
Risks Associated with Chloropicrin (USEPA, 2005). Since defining the
ISCST3 method, EFED is working with Health Effects Division (HED) and is
considering using additional modeling (e.g. PERFUM model) that allows
for the incorporation of actual meteorological data for future
assessment.  

Comment: Based on air monitoring data from seven studies with seven
different application methods and/or locations at a sufficiently low
sampling heights of 15, 33 and 55 cm to evaluate terrestrial animal
exposure risk, no LOCs are exceeded. The highest air concentrations of
chloropicrin were 1.470 ppm at the 15-cm height, 0.988 ppm at the 33-cm
height, and 0.565 ppm at the 55-cm height. When the highest air
concentration measured (1.470 ppm) is used along with an LC50 value of
17 ppm (as used by EFED), an RQ of 0.0865 (1.470/17) is derived, which
is below the acute risk LOC for endangered species (0.1).

Response: The CMTF’s calculated RQ was based on monitoring data at 60
feet away from the edge of the field. Reported RQ in the chloropicrin
chapter was based on the estimated air concentration at the edge of the
field. If RQs are calculated based on ISCTS3 estimated air concentration
values at 25 meters from the edge of the field (Table 5), they will be
comparable with CMTF’s RQs, and below the acute risk LOC for
endangered species. However, EFED is concerned with ground-level
residues at the edge of fields.

Risk Characterization

Comment: Three new freshwater animal (cold-water fish, warm-water fish,
and aquatic invertebrate) acute toxicity studies have been procured to
replace the three older studies deemed supplemental by EFED. These new
studies provide different toxicity reference values with which to
evaluate freshwater animal exposure risks.

Response: Once EFED receives and review these toxicity data for the
aquatic organisms, EFED will consider refining the aquatic exposure and
risk assessment. 

Comment: The CMTF claims that birds “will flee or avoid the treatment
area when the irritation effects are first experienced” resulting in
an acute exposure that is “self-limiting with no injurious health
effects” (p. 19).

Response:  CMTF clearly admits that chloropicrin would be highly
irritating to wildlife.  Nesting birds could experience substantial
disruption.  Adults fleeing their nests could leave nestlings exposed to
heat, cold, and predators, as well as to the toxic effects of
chloropicrin.

Comment: The CMTF claims that because of their above avoidance
prediction, chronic exposure of wildlife will also not occur, and that
animals unable to flee will have their exposure limited by the amount of
chloropicrin treatments that could occur in their vicinity.

Response:  The potential for repeat and/or continuous exposure of
wildlife may be similar to that identified by HED for humans.  The
exposure may not be negligible for wildlife.  

Data Requirements

Comment: The CMTF requests a waiver for chronic freshwater organism
studies, aquatic plant studies, terrestrial plant studies, marine
estuarine studies, and a honeybee study. 

Response:  Since available information indicates that nontarget
terrestrial and aquatic animals (vertebrate and invertebrate) and
nontarget terrestrial and aquatic plants could be exposed to
chloropicrin, the previously requested studies are still needed for risk
assessment.

Responses on deficiencies related to Submitted Fate Studies

CMTF provided additional explanation on the deficiencies related to the
following fate studies. EFED will review the response on the
deficiencies and upgrade the following fate studies accordingly. 

161-2	Aqueous photolysis (MRID# 429002-01)

162-1	Aerobic Soil Metabolism (MRID# 436139-01)

162-3	Anaerobic Soil Metabolism (MRID# 437593-01)

163-2	Laboratory Volatility (MRID# 437986-01)

164-1	Terrestrial Field Dissipation (MRID# 430851-01)

References:

U.S. EPA (United States Environmental Protection Agency). 2002. Guidance
for selecting input parameters in modeling the fate and transport of
pesticides. Version II. February 28, 2002.

U.S. EPA (United States Environmental Protection Agency). 2004. Health
Effects Division’s Draft Standard Operating Procedures (SOPs) for
Estimating Bystander Risk from Inhalation Exposure to Soil Fumigant.

U.S. EPA (United States Environmental Protection Agency). 2005c. Human
Health Risk Assessment: Chloropicrin. U.S. Environmental Protection
Agency, Office of Pesticide Programs, Draft Report.

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