July 1999, Questions for Session 3
Questions for the Session 3:
Higher Tier Ecological Risk Assessment for Chlorfenapyr
- The following questions address EFED's presentation of the environmental
fate profile for chlorfenapyr.
A. Does this environmental fate profile raise any unique risk issues not adequately considered in EFED's assessment?
B. Is the 28-day exposure model used for birds adequate?
C. Does the SAP have any suggestions to enhance EFED's analysis of this type of data?
- In 1996, the SAP provided several comments and recommendations
for improvement of risk assessment methods and procedures that
would help the Agency move beyond a screening level assessment.
Among these was the recognized need for better characterization
of risks and use of environmental fate data in assessment of terrestrial
wildlife exposure. Has the progression of EFED chlorfenapyr risk
assessments, culminating in the Agency's most recent 1998 assessment,
demonstrated a consideration of environmental fate information
in the assessment of wildlife exposures?
A. Specific to the 1998 assessment, has EFED made appropriate use of residue data in wildlife food items for a deterministic assessment?
B. Given the design of the insect residue study (executive summary Attachment 3), was EFED's selection of residues for risk assessment appropriate?
C. Is EFED's use of mean or composite residues from the weed seed study (executive summary Attachment 4) appropriate for risk assessment purposes?
D. Given the types of wild plant fruits that may be considered to be typically consumed by birds, are the fruit and vegetable types monitored for residue by the registrant appropriate surrogates for this route of exposure? If not, is it appropriate to use seed weed head chlorfenapyr residues as surrogates for wild fruit components of the avian diet?
- Has EFED made appropriate use of allometric relationships and
registrant-supplied information on dietary selections in establishing
daily ingestion rates for food items?
- EFED has attempted to incorporate registrant-supplied avian
census information regarding avian use of cotton fields (executive
summaries Attachment 6) into the risk assessment through modification
of the proportion of diet originating from a treated field versus
surrounding buffer areas. EFED assumed that 100% diet from a treated
field was a reasonable worst case for short-term acute effects
considerations. However, the risk characterization also evaluated
avian risks for a 10% proportion of diet from treated fields,
along with no chlorfenapyr residues in buffer zone dietary items,
as a lower limit for exposure for longer-term effects.
A. Does the SAP find these assumptions to be reasonable?
B. Can the SAP make recommendations about how to better make assumptions for this type of data?
C. Since the avian census data were for the number of birds observed in cotton fields versus buffer areas, are the available data adequately representative of feeding behavior on cotton fields and buffer zones to allow for more in-depth evaluations?
- EFED converted LC50 and reproduction NOEC endpoints from dietary
concentrations to daily oral doses to facilitate more direct comparisons
with dietary exposure and to account for ingestion rate differences
between species as it affects actual ingested chlorfenapyr dose.
EFED relied on observed body weights and the caged group feed
consumption to make these conversions.
A. Is EFED's conversion approach for dietary concentration to oral dose reasonable? Lead Discussants:
B. Does the SAP have recommendations for additional methods to account for intra- and interspecies variability in sensitivity?
- EFED recognizes the limited ability of 120-day avian reproduction
effects protocol to elucidate reproduction and sublethal effects
associated with shorter exposure periods. However, EFED's risk
assessment suggests that dietary exposure levels of chlorfenapyr
exceed the NOEC established for the existing reproduction study
for multiple weeks. In addition, maternal effects (weight reductions)
were observed following the first two weeks of exposure of test
animals to chlorfenapyr in the reproduction study.
A. Does the SAP agree with EFED's conclusions with regard to reproduction effects in exposed individual birds?
B. Can the SAP provide guidance on potential ways for accounting for dose response characteristics for reproductive effects?
- EFED has based the risk assessment on parent chlorfenapyr alone.
A. Do the toxicity data for birds, mammals and aquatic organisms suggest that degradates should also be considered in the assessment of risks to wildlife and aquatic organisms?
B. Are there sufficient data to allow for the consideration of degradates with the same level of confidence as the parent compound?
C. Can SAP suggest how these can be quantitatively incorporated into the assessment, using the existing residue and fate information?
- Does the SAP have comments or concerns regarding the use of
the MUSCRAT model for evaluating aquatic exposures for pesticides
used on crops within widely distributed cultivation?
- Are the available toxicity data sufficient in scope to enable
EFED to succinctly characterize the risk to untested terrestrial
and aquatic phyla?
A. Does EFED need to incorporate interspecies extrapolation uncertainty in establishing toxicity thresholds? If so, can the SAP recommend appropriate methods for such extrapolation in avian, mammalian, amphibian, reptile, fish and aquatic invetebrate endpoints.
B. Are additional toxicity tests warranted in this case?
- EFED is seeking guidance of the assessment of risks to sediment-dwelling
organisms. The MUSCRAT model provided the Agency with dry-weight
sediment concentrations, which were used to compare with the data
from acute sediment toxicity tests.
A. Was this approach appropriate?
B. Does SAP have specific recommendations for improvement of the method?
Assisting EFED In Taking Steps Toward Probabilistic Risk Assessment With Chlorfenapyr
- In progressing from deterministic to probabilistic risk assessment
techniques for terrestrial organisms, EFED is concerned with accounting
for intra- and inter-species variability in reproduction toxicity
testing. Can the SAP recommend any approach for accounting for
these areas of uncertainty in a probabilistic assessment?
- Given the geographic, temporal, and measurement limitations
of the available chlorfenapyr residue data in insects, does the
SAP believe that a probabilistic risk assessment using these data
should incorporate an expression of extrapolation uncertainty
for the data's application to non-tested sites of potential chlorfenapyr
use? If yes, can the SAP suggest appropriate methods for capturing
this uncertainty in the probabilistic assessment?
- Can the SAP provide guidance on capturing uncertainty in extrapolating
from sampled fields to larger areas of chlorfenapyr treatment?
Can the SAP recommend other data sets from the literature that
would enhance a chemical-specific probabilistic risk assessment?
- EFED is concerned with the uncertainty associated with using
avian census data (number of observed birds in and out of fields)
to predict dietary proportions obtained from treated and untreated
A. Does the SAP have suggestions for ways to reduce such uncertainty?
B. Should EFED focus on mean values for censussed regions or consider the spectrum of species variability in observations in the data?
- All previous deterministic approaches for avian risk assessments
tend to focus on local effects(treated fields at the screening
levels followed by assessment of treated fields and surrounding
buffer areas at more data-intensive levels of assessment). Given
the available data for chlorfenapyr, at what geographical scales
should EFED concentrate a probabilistic assessment? How should
population concerns over larger scales be addressed?
- Probabilistic assessments for avian effects may involve assessing exposure and effects for generic birds (no species consideration), focal species levels, or for all species associated with the particular agro-environment treated with the pesticide. Can SAP provide guidance as to the level of avian species resolution that would be appropriate for assessing avian reproduction risks for chlorfenapyr use on cotton?