Residential/ Non- occupational Exposure Assessment Jeff Evans Biologist Health Effects Division Office of Pesticide Programs Purpose To present our use of a calendar based model (Calendex™), to address the temporal aspects of OP pesticide use
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Non- occupational Exposure Assessment
Health Effects Division
Office of Pesticide Programs
MOE = POD (mg/kg/day)
Source: USDA ERS
Range of residues that deposit onto lawns is based on a percent of public health use application rate (3.8 to ~30%) using values presented in Tietze et al., 1994 and the Spray drift model, AgDrift
(Collins et al., 1973)
(Gold et al., 1983)
1 person from each of 4 seasons
1 person from each of 2 day categories (weekend and weekday)
Fix 5 weekday diaries and 2 weekend diaries
Repeat 7 day activity patterns within each season
Day of Year
Historically, the Agency has relied on means (primarily arithmetic or geometric) from residue and exposure studies for key input variables in exposure assessments. The recent development of calendar based models and others having features to incorporate distributions of exposure values has presented the Agency an opportunity to consider using all available data points from existing exposure and residue studies. In the Cumulative Risk Assessment Case study presented to the FIFRA Scientific Advisory Panel in September, 2000, most of the exposure variables were presented as uniform distributions. The exceptions were for variables that are reasonably well established , such as exposure durations taken from the Agency’s Exposure Factors Handbook. The data used in the Case Study and in the preliminary CRA, are believed to be from well conducted studies of generally high quality. However, these data sets tend to be small (e.g., n = 10 - 30) and are being used to address wide variety of exposure situations. The uniform distribution appears to be most appropriate for these relatively small data sets because it relies on easily established values such as the minimum and maximum and provides the most conservative estimate of the standard deviation ([email protected]).
The use of calendar based models also allows exposure assessors to consider exposure from a variety of sources from the same or from different chemicals. Longitudinal survey data such as the National Human Activity Pattern Survey (NHAPS) are available for consideration by HED for use in future assessments. In addition, from a practical standpoint, the use of such survey data ensures combinations of exposure do not come from unrealistic random combinations that current models may produce (e.g., activities adding up more than 24 hours in a day).
The use of calendar based models provides an opportunity to explore the potential for the co-occurrence of multiple sources of exposures from residential pathways. In the cumulative assessment, OPP used summary statistics from sources such as the Exposure Factors Handbook (EFH) regarding the time spent indoors, time spent on lawns and time spent at other outdoor locations. In the preliminary assessment, we assumed these activities were stochastically independent. OPP is currently evaluating data in the EFH such as data from the National Human Activity Pattern Survey (NHAPS) to determine if it can directly incorporate (i.e., empirically) information on an individual’s activity patterns over a full day from this database to account for the likelihood and duration that an individual might be exposed to a pesticide through various activities over the course of a day.