Durango Software's Calendex
was the first computer program designed
specifically to conduct aggregate and cumulative
human exposure assessments from pesticides,
as required by the Food Quality Protection
Act (FQPA) of 1996. An aggregate exposure
assessment combines dietary exposure to
a specific pesticide with exposure to the
same pesticide resulting from non-dietary
uses (e.g., residential termite treatment,
turf treatment, etc.). A cumulative exposure
analysis expands the scope of dietary and
non-dietary analysis by including exposures
from other pesticides with similar operating
mechanisms. Without the probabilistic analytical
methods incorporated into the Calendex
program, aggregate and cumulative exposure
assessments will usually result in improbable,
worst case, estimates based on the compounding
of unlikely exposure events.
Calendex is based
on a “Calendar Model” which
sets up a schedule of dietary intake events
and pesticide applications and human contact
events in the residential environment over
a calendar year for a designated individual
using Monte Carlo analysis methods. It then
allows the user to assess the probable aggregate
and cumulative exposure for that individual
on a daily, weekly, multiple-week, or annual
basis. These exposure amounts are calculated
for many thousands of individuals in a user-specified
subpopulation (e.g., 1-2 year olds in the
Northeast), and distributions of exposure
amounts for that subpopulation are generated
and compared to benchmark risk measures
(e.g., RfD or NOEL). In addition, a critical
exposure contribution report is generated
for any given segment of this distribution
(e.g., 99-100th percentile of exposure),
showing the relative contribution of each
pesticide use by exposure route (dietary,
inhalation, dermal, and incidental ingestion).
Calendex uses the
database of population demographics and
dietary intake data from USDA’s CSFII
for 1994-96, 1998 to provide a representative
sample of the U.S. population and user-specified
subpopulations. Individual intake of specific
agricultural commodities (e.g. wheat, corn,
tomatoes) is derived from the foods-as-eaten
intake amounts in the CSFII using “recipe”
translation factors from the joint USDA/EPA
Food Commodity Intake Database (FCID). [Link
to information about the CSFII and FCID
in this same web site.] CSFII statistical
weighting factors for the individuals in
that survey assure that the exposure distributions
are representative of the entire U.S. population
and related subpopulations. The most prominent
advantage of using this CSFII database is
that EPA has been using this survey for
many years to conduct dietary exposure assessments
with its own DRES program and Durango Software’s
DEEM™ program. Thus there
is a great deal of continuity in the way
that exposure amounts are computed and reported
by Calendex.
There are over 20,000 2-day
participants in the current CSFII. Calendex
allows each individual to be repeatedly
sampled with different pesticide residue
amounts in their dietary intake and different
schedules of residential pesticide usage
and contact, so that literally millions
of combinations of exposure patterns can
be computed in a single analysis, providing
a statistically significant basis for estimating
the distribution of exposures in many user-defined
demographic groups.
Calendex uses DEEM
dietary residue files for conducting the
dietary exposure portion of the aggregate
and cumulative exposure analysis. Calendex
also provides an “AGX” file
editor to assist the user in setting up,
in probabilistic terms, the application
schedules, residue amounts, and contact
events associated with each pesticide use
over a given year of interest. Each AGX
file provides the data needed to conduct
an assessment of a single resident pesticide
use (e.g., lawn treatment, crack and crevice
treatment, garden treatment) over all three
exposure routes (inhalation, dermal, and
incidental ingestion). These AGX files can
be run through Calendex separately
or in combination, with or without the dietary
analysis and with or without relative potency
factors assigned to each treatment type
and exposure route. Calendex can
also include water intake analysis using
conventional residue data or residue data
from the EPA PRZM-EXAMS database, which
tracks residues in regional water supplies
through an entire year.
One of the shortcomings of
the CSFII database is that there are only
two days of dietary intake data available
for each individual. (In fact, there are
no databases that provide a statistically
significant sample of longitudinal dietary
intake in the United States.) Calendex
allows the user to use these two days of
dietary intake repeatedly throughout the
period of analysis (usually restricted to
the same season) or to use a “dietary
matching file” of individuals with
similar demographic characteristics (e.g.
age, ethnicity, body mass) to share dietary
records within the same season in order
to provide a mode diverse basis for estimating
the dietary portion of the aggregate and
cumulative exposure assessment over longer
periods of time (up to one year). More information
on DMFgen, a program developed by Durango
Software to allow the user to generate a
dietary matching file based on user-specified
demographic matching criteria, is available
on this web site.
Calendex requires
a significant amount of exposure-related
data to run successfully. However, the exposure
analysis can be built up in small steps
with the basic elements of the analysis
in order to provide the user with confidence
that the exposure assessment is being conducted
correctly and so that the user understands
how the model performs. A listing of all
user input data can be reported for inclusion
in the exposure analysis, along with an
analysis of all empirical distribution files
used in the analysis.
