Notes from PCNB Reregistration Meeting

Thursday, January 26, 2006, 1:30-3:30pm

Attendees:

Amvac:  Ian Chart, Jon Wood,   SEQ CHAPTER \h \r 1 Cliff Habig, Charles
Staples, Joe Conti

Chemtura:  Kevin Donovan,   SEQ CHAPTER \h \r 1 Betsy Katzman, Stuart
Cohen, Ray Cardona,

(Mark Schocken on the phone)

EPA:  Tara Chand-goyal, David Donaldson, Steve Bradbury, Betsy Behl, Tom
Steeger, Cheryl Sutton, Christopher Salice,   SEQ CHAPTER \h \r 1
Margaret Rice, Tom Myers, Jill Bloom, Arty Williams (for part of the
meeting)

The agenda for the meeting followed the approximate order of issues
discussed in registrants’ letters of December 21, 2005 and January 19,
2006.  The registrants provided hard copies of the slides presented
during the meeting (attached).  The purpose of the meeting was to air
residual risk issues (particularly those related to ecological risk,
persistence, bioaccumulation, and long-range transport).  The Agency has
addressed comments from the registrants on these topics previously and
extensively; these responses are available on the Public Docket for the
reregistration of PCNB.  Other issues raised by the registrants for the
first time are presented in the attachment.

PCNB and the POPs Criteria

Commenting on registrant statements, the Agency clarified that it is not
proposing PCNB should be a listed POP, but that PCNB and its metabolites
share characteristics with listed POPs chemicals, and meet or exceed
some criteria for POPs chemicals and PBTs.  The registrants are
concerned about the message the public might take away from the
PCNB/POPs discussion.  The Agency expressed a willingness to revise the
draft RED to clarify its characterization of PCNB with respect to the
POPs treaty.

Bioaccumulation

The registrants posit that PCNB does not bioaccumulate because it is
rapidly depurated in aquatic species.  The Agency considered more than
just bioconcentration in fish in its assessment, and believes that the
registrants argument concerning bioaccumulation and trophic levels is
not accurate.  The opportunity for depuration is limited because
exposures to PCNB and its PCA degradate would likely be continuous. 
Studies clearly indicate that BCF factors for PCNB range as high as
20,000X.

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Long-range transport

The registrants maintain that, with the large body of research conducted
on long-range transport to pristine areas, significant transport of PCNB
would have been, and has not been, reported.  The registrant believes
that infrequent citation of detects adds uncertainty to the Agency’s
assessment.  The Agency believes that most of the studies available in
the literature did not involve monitoring specifically for PCNB or its
metabolites, while studies targeting PCNB and PCA have demonstrated
movement to areas where there is no history of use.

Persistence

The registrants believe that PCNB may be persistent, but not as
persistent as the Agency has concluded based on half-life data,
particularly because of the way the Agency accounts for volatility in
its modeling.  The Agency has addressed this concern about the
contribution of volatiles extensively in several documents and meetings
with the registrants.  The Agency reiterated that one of the two aerobic
soil metabolism studies is not adequate for use in the risk assessment. 
The Agency also noted that conclusions about persistence are not based
solely on the characteristics of the parent PCNB, but also on the
characteristics of the metabolites.  The Agency believes that its
classification of PCNB as persistent in the environment is consistent
with international standards.  Additionally, residues of PCNB occur with
frequency in crops when PCNB has not been applied for several seasons,
substantiating the persistence of PCNB in certain environmental
compartments

Ecological Risk Assessment

The registrants believe that 1) wildlife exposures are overestimated by
the Agency’s reliance on the standard nomogram, 2) chronic exposures
should be based on mean exposures, 3) risks to mammals may be overstated
because the endpoint was taken from a gavage study, 4) the mammalian
NOEC should be an order of magnitude higher, so RQs should be lower.

The Agency believes that its assessments of exposure and effects of PCNB
closely adhere to the methods defined in the Overview of the Ecological
Risk Assessment Process in OPP.  The Agency acknowledged that the use of
maximum residues is intended to be protective; however, mean residues
would likely be exceeded 50% of the time.  

While the risk assessment identifies the uncertainties associated with
the use of hepatic and thyroidal effects for assessing chronic risk in
mammals, these endpoints are consistent with those used by the Health
Effects Division for estimating risks to humans. However, a more
sensitive endpoint, decreased pup growth, has also been measured.  Had
decreased pup growth been used to assess chronic risk, then mammalian RQ
values would have increased by an order of magnitude.

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Comparing conclusions from the other ecorisk assessments

The registrants cite ranges of RQs from three REDs (chlorothalonil,
dicofol, iprodione) to show that they are in many cases higher than the
RQs the Agency has calculated for PCNB, but the risk mitigation the
Agency desires for PCNB is much greater than that applied to the three
RED chemicals.

The Agency indicated it would look over the comparison, but noted that
its risk mitigation decisions for PCNB are based not just on risks but
also on benefits and non-quantified concerns (like persistence,
long-range transport, etc.).  No information was provided by the
registrants to support the relevance of its comparison to the issues
identified for PCNB in terms of persistence, toxicity, bioaccumulation
and possible alternatives.

Alternatives

The registrants mentioned potential constraints related to the use of
alternatives.  EPA requested further detail on these constraints as they
apply to specific alternative products so that the Agency could evaluate
them in a more systematic manner.

Follow-up

The Agency agreed to address the issue the registrants raised with
respect to PCNB and the REDs for chlorothalonil, dicofol, iprodione, and
evaluate the alternatives information to be submitted by the
registrants.  The Agency concluded that we have discussed the remaining
technical issues with the registrants, and that it would soon be time to
move the debate into the public environment.

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