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EPA-Expo-Box (A Toolbox for Exposure Assessors)

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Exposure Factors

To estimate human exposure to contaminants in food, exposure factor information is needed. Exposure factors are human behaviors and characteristics that help determine an individual's exposure to an agent. Data on food ingestion rates are available in Chapters 9–15 of EPA’s Exposure Factors Handbook: 2011 Edition for the following food categories:

  • Fruits and Vegetables (Chapter 9)
  • Fish and Shellfish (Chapter 10) (see Aquatic Biota Module in the Media Tool Set)
  • Meats, Dairy Products, and Fats (Chapter 11)
  • Grain Products (Chapter 12)
  • Home-Produced Foods (Chapter 13)
  • Total Food Intake (Chapter 14)
  • Human Milk (Chapter 15)

Intake rates (except those for human milk) are provided in units of g/day or g/kg-day (normalized to body weight). Many of the study-specific intake rate summaries reflect the distribution in the target population, so mean, median, and other percentiles intake rates are often presented. Chapters 9–13 of the Handbook report per capita and consumer-only data on food ingestion rates for various food items and food categories. According to the Handbook:

Consumer-only intake is defined as the quantity of [food] consumed by individuals during the survey period. These data are generated by averaging intake across only the individuals in the survey who consumed these food items. Per capita intake rates are generated by averaging consumer-only intakes over the entire population (including those individuals that reported no intake). In general, per capita intake rates are appropriate for use in exposure assessments for which average dose estimates are of interest because they represent both individuals who ate the foods during the survey period and individuals who may eat the food items at some time, but did not consume them during the survey period.

Chapter 14 of the Handbook provides data on total food intake and diet composition using data from the USDA’s Continuing Survey of Food Intake by Individuals (CSFII) conducted in 1994−1996 and 1998.

When using exposure factor data with contaminant concentration data for food, it is important to be aware of the basis of the measured intake (i.e., whether the intake rate is expressed on the basis of the as-consumed, cooked or prepared weight or the uncooked or unprepared weight). Intake rate data should be chosen to “match” the concentration data that are being used (i.e., whether concentrations are based on cooked or uncooked food). EPA’s Exposure Factors Handbook: 2011 Edition states:

Intake rates may be expressed on the basis of the as-consumed weight (e.g., cooked or prepared) or on the uncooked or unprepared weight. As-consumed intake rates are based on the weight of the food in the form that it is consumed and should be used in assessments where the basis for the contaminant concentrations in foods is also indexed to the as-consumed weight … Other [data] are provided as uncooked weights based on analyses of survey data that account for weight changes that occur during cooking. This is of importance because concentration data to be used in the dose equation are often measured in uncooked food samples. It should be recognized that cooking can either increase or decrease food weight.

If the as-consumed ingestion rate and the uncooked concentration are used in a dose equation, dose may be underestimated or overestimated. Information on cooking losses and conversions necessary to account for such losses can be found in Chapter 13 (Intake of Home-Produced Foods) of the Handbook.

In addition, contaminant concentrations in food can be reported on a dry-weight, lipid-weight, or whole-weight basis.

  • Dry-weight food concentrations are based on the weight of the food consumed after the moisture content has been removed.
  • Lipid-weight concentrations are indexed to the fat content in the foods.
  • Whole-weight concentrations may also be referred to as wet weight or fresh weight.

Whole-weight intake rates should be used with whole-weight contaminant concentrations in food. Likewise, dry- or lipid-weight intake rates should be used with dry- or lipid-weight contaminant concentrations, respectively. Chapter 9 (Intake of Fruits and Vegetables), Chapter 11 (Intake of Meats, Dairy Products, and Fats), and Chapter 12 (Intake of Grain Products) of the Handbook provide the equations and moisture and lipid content data for various food that can be used to convert between whole weights and dry or lipid weights.

Chapter 15 of the Handbook provides human milk intake rates and lipid intake rates, and values are provided as mL/day or mL/kg-day (normalized to body weight). Information on the fat content of milk is needed for estimating dose from human milk residue concentrations that have been indexed to lipid content.

Ingestion rates should be selected to represent the appropriate food category; age group/lifestage; gender (if appropriate); population subgroup—which might defined by race, geographic region, urbanization, or other factors (if appropriate); and timeframe for the exposure scenario of interest.

Other exposure factors that might be needed for assessing ingestion exposures include:

  • Body weight (Chapter 8)
  • Life expectancy values, specifically when evaluating cancer risk (Chapter 18)

Exposure factor data may be accessed from the Exposure Factors Tab of the Indirect Estimation Module.

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