In 1996, Dr. Barbara Petersen
left Technical Assessment Systems to start
a new consulting practice, Novigen Sciences,
Inc. At this same time Steve Petersen retired
from NBS (by then renamed the National Institute
of Standards and Technology) and founded
an independent software development company,
Durango Software, LLC, in order to allow
him to work full time as a private software
developer and to provide faster response
to the needs of his software users. His
first project was to redesign his dietary
exposure programs for the “Windows”
operating environment, allowing significant
improvements to the user interface and for
all practical purposes ending the memory
constraints inherent in the older MS-DOS-based
programs. Microsoft Visual Basic was used
as the programming language for these new
programs. Entirely new and improved “recipe”
files for converting foods as eaten to RACS
and FFs were developed by the staff of Novigen
Sciences for the 1989-91 CSFII and provided
to Durango Software. Durango Software used
these recipes to translate the dietary intake
data in the 1989-92 CSFII to RACs and foodforms
and generated an entirely new database of
dietary intake data for use in the new dietary
exposure program. The new program was called
the “Dietary Exposure Evaluation Model”
(DEEM), copyrighted by Durango Software
LLC and licensed to Novigen Sciences, Inc.,
with the trademark “DEEM” owned
by Novigen Sciences.
DEEM was licensed to EPA and,
after significant amounts of QA, it became
their de facto standard for dietary exposure
analyses. DEEM was installed on approximately
50 EPA computers in order to support their
tolerance assessment activities. Steve Petersen
and scientists at Novigen Sciences worked
closely with scientists at EPA to assist
them in their QA and to determine the kind
of improvements that would improve the productivity
of their analysts and increase the usefulness
of the program.
Durango Software LLC,
working closely with Novigen Sciences, Inc.,
continued to make important enhancements
to the DEEM program over the following years.
Improved Monte Carlo analysis capabilities
were built into the Acute module and the
format of the residue distribution file
(RDF) with empirical residue distribution
data was formalized (now the de facto standard
for such data at EPA). The Critical Exposure
Contribution (“CEC”) analysis
and reporting capability was developed and
incorporated into the acute model, so that
the contribution of each RAC and FF toward
the total exposure within a user-specified
band of the exposure distribution (e.g.,
the 95th through 99th percentile in the
target subpopulation) could be determined.
In addition, the CEC report provides the
actual exposure calculation basis for every
individual in the designated distribution
band, including intake amounts by RAC and
FF and the residue amounts used with those
intake amounts to arrive at a total daily
exposure amount for that individual. (This
CEC analysis reporting capability of DEEM
has been extensively used by EPA.)
The DEEM dietary residue
file format was expanded so that an internal
list of RDF files can be included with reference
“pointers” assigned to specific
RACs and FFs. Intake data from the 1994-96,
1998 CSFII were processed with updated “recipes”
from Novigen Sciences and incorporated into
both the chronic and acute modules of DEEM.
A methodology for conducting and reporting
cumulative exposure assessments, which allows
the analysis of multiple chemicals used
on the same foods, was developed and incorporated
into the DEEM Acute module so that a CEC
analysis can not only report the contribution
of each RAC and FF to the exposure in any
given band of the exposure distribution,
but identify the source of exposure by chemical
as well. The capability of breaking out
daily food intake amounts by discrete intake
events, with a new draw of a residue amount
from the residue distribution at each event,
was developed and incorporated into the
acute module.
The RDFgen program,
developed at Novigen Sciences and accessed
through DEEM, provides the capability of
extracting chemical- and food-specific residue
data from the USDA Pesticide Data Program
(PDP) in order to automatically generate
RAC-specific RDF files that can be used
with DEEM. The RDFdoc program was developed
by Durango Software to provide QA and documentation
reporting for the large numbers of RDF files
used in DEEM (and, later, Calendex) exposure
assessments. The RDFdoc program, and a similar
utility within the DEEM residue file editor
itself, allows the user to view any residue
distribution in 1% increments from 0 to
100%, in order to provide the analyst with
a better understanding of the residue data
being included in a DEEM Monte Carlo assessment.
