Dietary Exposure

What is the Dietary Module in CARES NG?

The CARES NG dietary module estimates dietary exposure from pesticide residues in food or drinking water using algorithms consistent with EPA/OPP guidance. Dietary exposure is estimated from the consumption of food or water (grams commodity / body weight) multiplied by the amount of residues in food or drinking water (mg a.i. / kg of commodity). The dietary module estimates exposure for different populations and different time frames (acute, multi-day, chronic), including cancer risk.

What data are used in the dietary module?

The CARES NG dietary module relies on publically available data on food consumption (i.e., WWEIA/NHANES) and user entered residue data (i.e., tolerances or field trial data) or user selected residue monitoring data (i.e., PDP). The user enters other information specific to their product including hazard endpoints, processing factors, and percent crop treated.

What is the WWEIA/NHANES?

What We Eat In America (WWEIA) is a national 2-day food consumption survey that is part of the National Health and Nutrition Examination Survey (NHANES). The WWEIA/NHANES data provide extensive, statistically representative information on food consumption for approximately 10,000 surveyed individuals for each 2-year survey cycle.  The U.S. EPA’s Office of Pesticide Programs (OPP) developed a food commodity intake database (FCID) to translate foods “as eaten” to a food commodity basis. FCID uses recipe files to break down all foods into their raw agricultural commodity (RAC) equivalents. WWEIA is expressed as grams of food commodity consumed per kg body weight per day for over 500 commodities derived from more than 7,000 different foods and beverages based on survey data from 2005 to 2010.

What is PDP?

The Pesticide Data Program (United States Department of Agriculture) is an American national pesticide residue database program.  PDP manages the collection, analysis, data entry, and reporting of pesticide residues on agricultural commodities in the U.S. food supply with an emphasis on those commodities highly consumed by infants and children. The PDP database is specifically designed to be a monitoring data set for dietary assessment. Samples are collected close to the point of consumption (e.g., distribution centers), analyzed every year, and published in the PDP electronic database, which is available on the PDP Website. The data captured and stored in the PDP database includes active ingredient information, residue findings, and process control recoveries for each sample collected and analyzed, plus fortification results for each set of samples.   The PDP electronic database from 1994 to 2013 is included in the CARES NG software in order to give the user the option of including these pesticide residue values in an exposure assessment. The PDP database within CARES NG will be updated when new data is released each year. The co-exposure information for each sample within the PDP monitoring data should be preserved and used in the cumulative assessment for multiple chemicals.

What are methods used in the dietary module?

The dietary module uses WWEIA food consumption data for individuals that have completed 2 days of survey. There are four statistical methods for simulating food consumption diaries to estimate acute and chronic dietary exposure:

  • Acute (Non-temporal) Approach: Each day of the 2-day food consumption diaries are assigned by commodities to a single residue value or a randomly selected value from a distribution of residue values (i.e., field or monitoring).
  • Acute (temporal – repeating diet) Approach: The 2-day food consumption diaries for the same person will be randomly selected as many times as necessary to cover the exposure period of 365 days. This will be a runtime process which will generate a new diary for each assessment.
  • Acute (temporal – match diet) Approach: The diary of each subject contains his/her 2-day food consumption data recorded in the WWEIA surveys and the 2-day data of other WWEIA neighbours. Each food consumption day, coming from both the subject and one of his/her neighbors, can be used more than once to fill the whole 365-day diary. The number of times each day must be used is fixed, but the order changes at each run of the model.
  • Chronic Approach:  For each population, the average residue value for each commodity is combined with average per-capita consumption to represent life-time exposure.

What are the rules for determining the number of zeroes?

The dietary module automatically incorporates the EPA guidance for adjusting residue values based on commodity blending status and residue type. The user can select from three sources for residue data: tolerance level, field trial study, or monitoring study (i.e., PDP). Information on percent crop treated and up to three different processing factors can be entered into the module. If field and monitoring data are used as empirical distributions, the dietary module automatically adjusts non-detects to ½ LOD or LOQ and adds the correct number of zeroes depending on following rules:

Residue Type Blending Residue Calculation Percent Crop Treated (PCT) Non-Detects
Field Partially Blended/Not Blended Distribution Incorporate zeroes

NZ = (N/PCT) -N

Blended Average Use as multiplier ½ LOD/LOQ

Partially Blended/Not Blended

D < PCT x N

Distribution ½ LOD = (PCT´N)-D

NZ = N – (PCT ´ N)


Partially Blended/Not Blended

D ≥ PCT x  N

Distribution NZ = N – D ½ LOD/LOQ
Blended Distribution Not Used ½ LOD/LOQ

Where: NZ = Number of Zeroes; PCT = Percent Crop Treated, D = Detects; N = Number of samples;

How is drinking water exposure determined?

The dietary module treats drinking water as a raw agricultural commodity, the WWEIA estimates direct drinking water consumption from either bottled water or tap water and indirect drinking water consumption from the preparation of foods. Estimated Drinking Water Concentrations (EDWC) are determined by different mathematical models developed by EPA/OPP based on use patterns and agricultural scenarios. The CARES NG dietary module allows user to enter single point values (i.e., EDWC), empirical distributions of data, and time series outputs from water models (i.e,. PRZM-EXAMS) or groundwater monitoring studies.