Document ID: EPA-HQ-OPP-2005-0265-0027
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2006-11-08T05:00Z

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON D.C., 20460

							     

								   	PC Code: 031301			          	DP Barcode: D294451

          Date: October 17, 2006

MEMORANDUM	

SUBJECT:	Response to Phase 4 Comments on EFED’s Environmental Fate and
Ecological Risk Assessment for DCNA (Dicloran)

TO:		James Parker, Chemical Review Manager

		Special Review and Reregistration Division (7508C)

Kelly Sherman, Team Leader

Special Review and Reregistration Division (7508C)

FROM:	Cheryl Sutton, Ph.D., Environmental Scientist

		Christopher Salice, Ph.D., Biologist

		Environmental Risk Branch IV

		Environmental Fate and Effects Division (7507C)

REVIEWED

BY:		Thomas M. Steeger, Ph.D., Senior Biologist

		Environmental Risk Branch IV

		Environmental Fate and Effects Division (7507C)

		

APPROVED

BY:		Elizabeth Behl, Branch Chief

		Environmental Risk Branch IV

		Environmental Fate and Effects Division (7507C)

	

The Environmental Fate and Effects Division (EFED) has completed its
review of Phase 4 comments received from the technical registrant, Gowan
Company, on the final environmental fate and ecological risk assessment
for DCNA (dicloran).  This memo includes each of the registrant’s
comments and EFED’s response to each. 

The EFED responses indicate that the following data requirements have
already been fulfilled or may not be required:  1) Aerobic Aquatic
Metabolism (835.4300) – previously fulfilled; 2) Droplet Size Spectrum
(840.1100) – fulfilled; 3) Drift Field Evaluation (840.1200) –
fulfilled; 4) Aquatic Field Dissipation (835.6200) – no data
requirement established.  The following data requirements may be needed:
 1) Accumulation in Aquatic Non-Target Organisms (850.1950); 2) Mysid
Life Cycle (850.1450).

REGISTRANT COMMENT:

1.	Aerobic Aquatic Metabolism (835.4300)

An acceptable aerobic aquatic metabolism study was conducted in 2003 and
reviewed by EFED in November, 2005.  The DER was sent to Gowan Company
in February, 2006 [MRID 46657101;  EPA DP Barcode D313901].   Therefore,
no additional study is required.  Gowan Company does not think it is
necessary to request a waiver from this study because it appears that
this proposed data requirement is in error.

EFED RESPONSE:  

The registrant is correct that the data requirement is in error.  MRID
46657101 was reviewed by EPA and found acceptable.  Additional aerobic
aquatic metabolism data are not needed.  While the EFED environmental
fate and ecological effects chapter and the RED document both contain
estimated environmental concentrations (EEC) that were determined using
the newly submitted acceptable data, portions of the amended EFED
chapter text were inadvertently not included in the version of the text
used in the RED document.

REGISTRANT COMMENT:

2.	Aquatic Field Dissipation (835.6200)

Even EFED seems to have concluded that there is little indication of
risk to aquatic organisms [cf. RED pages 24 – 25] so Gowan Company
found this data requirement surprising. 

Gowan Company requests a waiver from this data requirement for three
reasons:

Criteria Not Met

First of all, OPPTS Harmonized Guideline 835.6200 does seem to not
exist.  It is not publicly available even in draft form.  We assume the
Agency intended to refer to the earlier OPP Guideline 164-2.  This brief
guideline in the 1982 Subdivision N Pesticide Assessment Guidelines
states when this study is required:  “…to support the registration
of an end-use product intended for 

aquatic food crops

aquatic non-crop uses (which include anti-fouling paints and other
outdoor protective uses where the pesticide-containing surface is in
contact with water, and also pesticide application to ditchbanks and
shorelines)

any aquatic impact uses involving direct discharge of treated water into
outdoor aquatic sites.”

No registered use of dicloran meets any of these criteria.  We conclude
that the requirement of this study is inappropriate and unjustified.

Perceived Persistence 

Secondly, we think that EFED perceives dicloran to be more persistent
than it actually is.  The first paragraph of the Environmental Risk
Assessment in the RED (page 20) states that “in aerobic mineral soils,
the half-life ranged from six to eighteen months.  In anaerobic sandy
soils, the half-life ranged from twenty-four to thirty-eight days.” 
That information was derived from a 1988 soil metabolism study in which
the microbiological health of the test soils was questionable [MRID
40894801].  Subsequent work has shown that dicloran is not nearly as
persistent as the 1988 study suggests:

In the 2002 aerobic aquatic metabolism study discussed above, the
half-life in two systems was calculated to be 2.6 – 2.9 days in water,
3.8 – 4.9 days in sediment and 3.4 – 3.5 days in the total systems. 

In a 1995 anaerobic aquatic soil metabolism study [MRID 43866501 and
45333301] the initial half-life was 0.45 day but “lengthened” to 3.0
days between Day 1 and Day 14.

 

In an acceptable 1997 California field soil dissipation study [MRID
44414201] the half-life was 32.8 days.

Therefore, dicloran is not persistent in soil and particularly not in
aquatic sites where anaerobicity in the sediment often occurs.

Perceived High Residues in Water 

Thirdly, we think that EFED may have felt this study necessary because
high residues in water were perceived.  EFED has predicted surface water
residues up to 42.3 ppb [cf. RED page 21].  This number is derived from
a Tier 0/Tier 1 screening model in which the default assumption is that
87% of the watershed is treated with the chemical in question.  

Real-world data always supplants default numbers used in screening
models, however.    Dicloran is a very specialized and geographically
limited product, and approximately 41% of all dicloran usage nationwide
is in Monterey County, California, where it is used mostly on celery. 
California Department of Pesticide Regulation records show that in 2004
(the latest year for which results have been tabulated), dicloran was
used on 50,805 acres in Monterey County.  This is equivalent to 79.4
square miles.  The area of Monterey County is 3322 square miles, so
dicloran was applied to 2.4% of the county.  This is approximately 37
times less than the Agency’s modeling program assumes, and so the
presumed concentration in water calculated by the Agency, 42.3 ppb, can
safely be reduced by a factor of 37 for Monterey County.  Obviously this
number can be reduced by a much larger factor for all other areas of the
United States.

Gowan Company conducted a groundwater study in Monterey County.  Our
groundwater study [MRID 45237401] can also be viewed as a very large
runoff study.  It was in fact difficult for us to find an acceptable
agricultural test site in the county that had not previously been
treated with dicloran.  The Salinas River, which runs through Monterey
County, was analyzed for dicloran 18 times over a 592-day period,
including during some flooding events.  Dicloran was detected only once,
at 0.3 ppb.  It can therefore be concluded that dicloran will not reach
surface water in appreciable quantities, and certainly not in
concentrations remotely as high as those envisioned by EFED.

For these reasons Gowan Company respectfully requests a waiver from this
data requirement.

EFED RESPONSE:  

No data requirement has been established for an Aquatic Field
Dissipation study, thus this waiver request is not technically accurate.
 Completion of the study is not likely to add significant information to
the body of environmental fate data already available for DCNA.  The
acceptable aquatic metabolism study data, both aerobic and anaerobic,
indicate that the persistence of DCNA is quite low in aquatic systems. 

Although a data requirement has not been established, there are a number
of statements in the registrant’s comment (Perceived High Residues in
Water) that are inaccurate.  These statements are listed below in
Italics.  

EFED has predicted surface water residues up to 42.3 ppb [cf. RED page
21].  This number is derived from a Tier 0/Tier 1 screening model in
which the default assumption is that 87% of the watershed is treated
with the chemical in question. 

Tier II modeling was conducted for this screening assessment. 
Additional data (such as monitoring data) may be useful in refining a
screening assessment, but do not replace the values predicted in the
screening level assessment which were determined using peer-reviewed
methods. 

Real-world data always supplants default numbers used in screening
models, however.  

EFED notes that simulation modeling and monitoring data are
complementary rather than a competitive source of information on the
concentrations of pesticides in water. Simulation modeling, as used in
the Office of Pesticide Programs, provides an upper bound estimate on
potential concentrations that can occur in the environment. With
modeling, it is possible to observe the effects of events that are
difficult to capture in monitoring. Monitoring provides a more direct
measurement of environmental concentration. However, infrequent
sampling, and sampling in places where there is little use of the
pesticide of concern or little vulnerability to runoff, tend to make
monitoring an underestimate of exposure in the environment, particularly
for acute exposure.  Monitoring data are often difficult to interpret
because the ancillary data on pesticide usage in the basin, and factors
that could make the location more or less vulnerable, are often not
available. Taken together, modeling and monitoring typically provide a
more complete picture of exposure than either alone. Because the
modeling is generally conservative, and the OPP ecological risk
assessments for DCNA are considered to be screening assessments, the
risk quotients are based on the modeling.

Dicloran is a very specialized and geographically limited product, and
approximately 41% of all dicloran usage nationwide is in Monterey
County, California, where it is used mostly on celery.  California
Department of Pesticide Regulation records show that in 2004 (the latest
year for which results have been tabulated), dicloran was used on 50,805
acres in Monterey County.  This is equivalent to 79.4 square miles.  The
area of Monterey County is 3322 square miles, so dicloran was applied to
2.4% of the county.  This is approximately 37 times less than the
Agency’s modeling program assumes, and so the presumed concentration
in water calculated by the Agency, 42.3 ppb, can safely be reduced by a
factor of 37 for Monterey County.  Obviously this number can be reduced
by a much larger factor for all other areas of the United States.

The method recommended by the registrant for assessing percentage
cropped area (PCA) does not accurately describe peer-reviewed EPA
methodologies.  The document describing PCAs can be found at   HYPERLINK
"http://www.epa.gov/oppefed1/models/water/regional_pca.htm" 
http://www.epa.gov/oppefed1/models/water/regional_pca.htm  

Gowan Company conducted a groundwater study in Monterey County.  Our
groundwater study [MRID 45237401] can also be viewed as a very large
runoff study.  It was in fact difficult for us to find an acceptable
agricultural test site in the county that had not previously been
treated with dicloran.  The Salinas River, which runs through Monterey
County, was analyzed for dicloran 18 times over a 592-day period,
including during some flooding events.  Dicloran was detected only once,
at 0.3 ppb.  It can therefore be concluded that dicloran will not reach
surface water in appreciable quantities, and certainly not in
concentrations remotely as high as those envisioned by EFED.

The criteria used to select a site for a ground water study are
inconsistent with those that would be used to select a site for surface
water monitoring.  This discussion is fundamentally scientifically
flawed.

REGISTRANT COMMENT:

3.	Accumulation in Aquatic Non-Target Organisms (850.1950)

Gowan Company vehemently objects to the imposition of this data
requirement.  

The correct title of OPPTS Guideline 850.1950 is “Field Testing for
Aquatic Organisms.”  This guideline primarily concerns mesocosm
studies, and field studies are mentioned only in passing.  

First we must emphatically state that the Agency is unjustified in
requiring a Tier 4 study when, as we have shown, Tier 1 evaluations of
dicloran give no cause for concern. 

Secondly, the Agency effectively rescinded the requirement for mesocosm
studies many years ago.  That was because the Agency itself concluded
that mesocosm studies were uninterpretable and of no value for risk
analysis.  Mesocosm studies today remain uninterpretable and of no value
for risk analysis.  This is because detailed protocols still have not
been validated and subjected to appropriate peer review.  We are aware
of the recommendation of SAP in 1997 for the Agency to reinstate
mesocosm studies.  However, if the Agency wishes to pursue the basic,
preliminary research and validation work on mesocosm studies that would
be required for mesocosm studies to be of regulatory value, then this
work should be funded by the Agency itself.  Gowan Company contends that
it is a breach of the Agency’s authority to demand funding of such
blue-sky research by the regulated community.

Furthermore, even if mesocosm data for dicloran were to exist today, and
if EFED were to attempt to use such data for regulatory purposes, Gowan
Company would charge that this would be a violation of the Agency’s
own Information Quality Guidelines, in contravention to the Office of
Management and Budget guideline of 2002 and in contravention to Section
515 of the Treasury and General Government Appropriations Act for FY2001
(Public Law 106-554).

Any concerns of EFED regarding the potential for bioaccumulation of
dicloran should have been answered by our acceptable bluegill
bioaccumulation study [MRID 43782001].  The RED concluded (page 20) that
dicloran has only a moderate 136X potential for bioconcentration, and
residues are eliminated quickly.  EFED has provided no rationale or
justification for requiring any further work on accumulation in
non-target species.  

For these reasons Gowan Company respectfully requests a waiver from this
data requirement.

EFED RESPONSE:  

No data requirement has been established for Field Testing for Aquatic
Organisms (OPPTS Guideline 850.1950), thus this waiver request is not
technically accurate.  EFED agrees that such data are not necessary at
this time, as an Accumulation in Aquatic Non-Target Organisms study is
not deemed likely to add significant information to the body of
environmental fate data already available for DCNA.  While properly
designed mesocosm studies have utility for more refined assessments,
such refinements are not presently planned for DCNA.

  

REGISTRANT COMMENT:

4.	Droplet Size Spectrum (840.1100)

5.	Drift Field Evaluation (840.1200)

This information has been developed by the Spray Drift Task Force. 
Gowan Company is a member of the SDTF and thereby references the studies
already on file with the Agency.  These data requirements are considered
to be fulfilled.

EFED RESPONSE:  

EFED concurs with the registrant.  The data requirements are fulfilled
by the registrant’s participation in the Spray Drift Task Force.

REGISTRANT COMMENT:

6.	Mallard Duck Reproduction (850.2300)

Gowan Company will conduct a reproduction study with the mallard duck. 
A recent study with bobwhite quail was acceptable [MRID 46218900;  EPA
DP Barcode D304580].

EFED RESPONSE: 

EFED will review the study following its submission to the Agency.

REGISTRANT COMMENT:

7.	Sheepshead Minnow Acute LC50 (850.1075)

8.	Mysid Acute LC50 (850.1025)

Gowan Company recognizes that toxicity data on estuarine/marine species
are incomplete.  We will conduct acute toxicity studies with the
sheepshead minnow and mysid shrimp.

EFED RESPONSE:  

EFED will review the studies following their submission to the Agency.

REGISTRANT COMMENT:

9.	Rainbow Trout Early Life-Stage (850.1300)

10.	Fathead Minnow Full Life Cycle (850.1500)

EFED has provided no credible justification for the requirement of these
Tier 2 and Tier 3 studies.  Even when EFED used a simple screening model
to evaluate risk to aquatic organisms, in only one scenario was the RQ
above the Level of Concern (LOC).  The RED on pages 24 and 25 states,

“No acute or chronic RQs exceeded the LOCs for freshwater fish or
invertebrates, with the exception of the use of DCNA on celery…in
which the RQ exceeded the listed-species acute risk LOC for freshwater
fish at the peak predicted EEC. “ 

In response to requirement No. 2 above, Gowan Company above demonstrated
that EFED’s screening model substantially overestimates aquatic
exposure and aquatic risk.  As we said earlier, real-world use data
always prevails over a default assumption of percent treated land in a
watershed (87% in this case).  When actual use data are considered, it
can safely be concluded that the use of dicloran will not exceed the LOC
in Monterey County and certainly not in any other region of the United
States.  Therefore EFED is without justification in requiring these
studies.  Since the LOC is in fact not exceeded, then these studies
would add no additional useful decision-making information regarding the
evaluation of risk to fish.  Gowan Company therefore respectfully
requests the Agency to waive these two data requirements.

EFED RESPONSE:  

Sufficient justification for fish chronic toxicity studies on DCNA is
based on the CFR 40 Part 158.490.  Specifically, for DCNA, a fish
chronic toxicity study is being requested because (1) the fish LC50 is
less than 1 mg/l, (2) the estimated EECs are greater than 0.01 of any
EC50/LC50 (RQ > 0.01) for several uses for both fish and invertebrates,
and (3) DCNA is persistent in water (>4 day half life; DCNA is stable to
hydrolysis).  According to the CFR, the toxicity and fate
characteristics of DCNA are such that a fish chronic toxicity study
would reduce uncertainties associated with potential risks to fish. 
Therefore, EFED has recommended a freshwater fish chronic toxicity
study, preferably a fish early life stage toxicity (850.1400).    

The registrant also commented that “EFED’s screening model
substantially overestimates aquatic exposure and aquatic risk.”  And
that “real-world use data always prevails over a default assumption of
percent treated land in a watershed”.  Similar comments by the
registrant were fully addressed above.  However, it is important to
stress that the Office of Pesticide Programs uses peer-reviewed
simulation models that provide upper bound estimates of potential
environmental concentrations.  Modeling and monitoring data are
complementary rather than competitive sources of information that, taken
together, can provide a more complete picture of exposure.  However,
because modeling results are generally considered more conservative and
given the potential for monitoring data to underestimate exposure, risk
quotients are based on modeling results for screening-level assessments.

REGISTRANT COMMENT:

11.	Mysid Life Cycle (850.1450)

It is entirely inappropriate for EFED to require this Tier 2 study
before the results of the Tier 1 acute toxicity study with mysids
(requirement No. 8 above) are completed.  Gowan Company requests the
Agency to hold this requirement in reserve pending a review of the
results of the mysid acute toxicity study.

EFED RESPONSE:  

EFED agrees, the mysid life cycle study requirement may not be needed
and a final determination will be made pending review of the mysid acute
toxicity study.

REGISTRANT COMMENT:

12.	Tier I Terrestrial Plant Toxicity (850.4025)

Gowan Company will conduct a Tier 1 terrestrial plant toxicity study
with dicloran.

EFED RESPONSE:  

EFED will review the study following its submission to the Agency.

 PAGE   

 PAGE   8 

OFFICE OF

PREVENTION, PESTICIDES AND

TOXIC SUBSTANCES