Exposure Assessment Tools by Media - Food

Overview

Contaminated media to which people might be exposed include air, water and sediment, soil and dust, food, aquatic biota, and consumer products. Food products (e.g., grains, fruits, vegetables) can become contaminated as a result of ambient pollutants in the air being deposited on plants, adsorbed onto or absorbed by the plants, or dissolved in rainfall or irrigation waters that contact the plants.

Plants growing in contaminated soil can take up the chemicals from soil pore water through their roots, and the chemicals could then be transported into plant tissues. Meat and dairy products from animals used as sources of food can become contaminated if grazing or foraging animals consume contaminated soil, water, or feed crops and bioaccumulate the contaminants in their tissues.

Pesticides, soil additives, and fertilizers that are applied to agricultural areas or gardens can also contaminate food products (see Pesticides Module of the Chemical Classes Tool Set in EPA ExpoBox). Another potential type of food is human milk, relevant for one population life stage—nursing infants (see the module on Lifestages in the Lifestages and Populations Tool Set of EPA ExpoBox).

Human exposure to contaminants in food occurs by direct ingestion. Various tools are available for evaluating sources and releases of food contaminants, fate and transport processes, and potential exposure concentrations. Exposure factors, calculation tools, and guidance for assessing exposure to contaminants in food are also discussed in this module.

For additional information related to the consumption of contaminated fish and shellfish, refer to the Aquatic Biota Module of the Media Tool Set in EPA ExpoBox.

Sources

Food crops can be exposed to pollutants that are present in ambient air. Pollutants that end up in food might also originate from contaminated soil and water. For additional information on the sources of contaminants for these media, see the Air, Soil and Dust, and Water and Sediment Modules in the Media Tool Set of EPA ExpoBox.

Food crops can become contaminated with chemicals in ambient air that are deposited on plants and become distributed in plant tissues after they are absorbed by the leaves (or other aerial parts of the plant). If present in soil or groundwater, contaminants can contact plant roots and become transported into plant tissues.

Other sources of chemical contaminants in food crops include agricultural applications to control pests or enhance growth. These chemicals may include pesticides (e.g., insecticides, herbicides, rodenticides) and fertilizers (see Pesticides Module of the Chemical Classes Tool Set).

Contaminants in vegetation or soil may be consumed by grazing or foraging animals that bioaccumulate the contaminants in their tissues. Thus contaminating animal food products including meats, dairy, and fats.

Other sources of contaminants in animal food products can include veterinary drugs and growth hormones. In addition to these agricultural food products being exposed to contamination during the growing process, these commodities may also be exposed to contamination while being harvested, transported, stored, packaged, processed, and prepared.

For lactating mothers who have been exposed to contaminants in food or other media, their breast milk may be a source of exposure to toxic substances for nursing infants (see the module on Lifestages in the Lifestages and Populations Tool Set of EPA ExpoBox).

Information on potential sources of agricultural contaminants in food is provided in the table below.

Fate and Transport

Fate and transport processes “link” the release of contaminants at a source with the resultant environmental concentrations to which receptors can be exposed. When a contaminant is released from a source, it is subject to transporttransportMovement within a medium or between media. and transformationtransformationChange in a chemical or physical state. in the environment.

Compounds can also transfer from an environmental medium (e.g., air, soil) to foods (e.g., plant, animal) - a process referred to as bioconcentration or bioaccumulation.

Migration Process	Examples Relevant to Food
Transport	Migration of a contaminant through soil used to grow crops; dispersion of contaminant through ambient air within agricultural areas (transport within a medium) Chemicals in soil that leach to groundwater used to irrigate crops; deposition of a contaminant from air to soil used to grow crops (transport between media)
Transformation	Organic breakdown or biodegradation of a compound in agricultural soil by soil microbes (chemical change) Inorganic metals that dissolve in pore water of agricultural soil (physical change)
Transfer - Environment to Food	Airborne contaminants that attach to plant leaves and become translocated to different tissues of a fruit or vegetable crop Soil contaminants that contact plant roots and become transported into edible plant tissues Grazing or foraging animals used as a source of food consume contaminated soil, water, or plants and bioaccumulate the contaminants in their tissues

For additional information related to the environmental fate and transport of chemical contaminants from water and sediment to fish and shellfish, refer to the Aquatic Biota Module of the Media Tool Set.

Bioconcentration refers to direct transfers of the chemical from the surrounding environmental medium into the plant or animal. An example is  a chemical that is transferred from soil into a plant through its roots. For animals, bioconcentration does not account for uptake by ingestion.

Bioaccumulation is the uptake of a substance from an environmental medium through all routes, including food chain transfers. For example, accumulation of substances can occur through ingestion of contaminated plants or animals.

Biotransformation refers to the alteration of a contaminant in the body. In addition, some chemicals can biomagnify as they move up the food chain.

Bioconcentration factors (BCFs) and biotransfer factors (BTFs) are sometimes used to estimate contaminant concentrations in plants or animals. BCFs and BTFs are derived from information on the concentrations in the food and the amount of chemical that is taken up by the plant or animal or is present in the surrounding environmental media.

BCFs represent the relationship between the concentration of contaminant in the vegetation and the corresponding soil, water, or air concentration.

A soil-plant BCF measures a chemical’s ability to accumulate in plant tissue and is the ratio of contaminant concentration in plants to the concentration in soil. An air-plant BCF is defined as the ratio of contaminant concentration in aboveground plant parts to the contaminant concentration in air (see below).

The BTF is an empirical ratio relating the chemical concentration in biota, such as produce, livestock, or animal products, to the amount of chemical to which the plant or animal is exposed in soil or feed (or other media). For example, an animal BTF for milk or beef represents the ratio of the concentration in the food to the rate of chemical intake by the animal (e.g., mass of chemical per day) as shown below.

BCFs and BTFs are sometimes estimated based on the physicochemical properties of the contaminants. For example, Travis and Arms (1988) published a methodology that uses the octanol-water partition coefficient (K_ow) as a predictor of BTFs in beef cattle.

The following tools provide information on the fate and transport of contaminants in the food chain and information on BCFs and BTFs. Additional information on estimating concentrations of contaminants through the use of models may be found in the Concentrations tab of this module.

Concentrations

• Measuring Concentrations
• Modeling Concentrations
• Available Data

Information on contaminant concentrations in food is needed to assess exposure via the food ingestion route. Characterizing contaminant concentrations for an exposure scenario is typically accomplished using some combination of the following approaches:

• Sampling the bulk foods that the receptor is expected to ingest and analyzing them to measure contaminant concentrations
• Modeling the contaminant concentrations based on environmental media concentrations and bioconcentration or biotransfer factors
• Using existing, available measured concentration data collected for related analysis or compiled in databases

EPA ExpoBox provides information on measuring or modeling contaminant concentrations in food and on available food measurement data that might be useful in estimating exposures. The concentrations of contaminants in food may be measured using sampling and analytical methods designed to support such measurements (see Measuring Concentrations below). In the absence of monitoring data, a variety of models can be used to estimate contaminant concentrations in food.

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Measuring Concentrations

Methods for measuring concentrations of chemical contaminants in food may include methods required for specific chemicals or groups of chemicals that are regulated by EPA or methods for unregulated chemicals or groups of chemicals of interest.

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Modeling Concentrations

In the absence of measurement data, the concentrations of contaminants in food may be estimated based on modeling. Typically, concentrations in foods are modeled using BCFs or BTFs as described in the Fate and Transport pages of this module. A number of resources are available to assist in these modeling efforts.

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Available Data

The U.S. Department of Agriculture and U.S. Food and Drug Administration have established food safety programs to monitor for potential contaminants in the food supply. EPA also conducts sampling and analysis of milk and other media to monitor for radiation. Food products have also been analyzed as part of special studies conducted by EPA (e.g., Total Exposure Assessment Methodology [TEAM] studies). Resources for obtaining available measurement data are summarized in the table below.

Exposure Scenarios

Exposure to contaminants in food can be estimated by first defining the exposure scenarioexposure scenarioA set of facts, assumptions, and inferences about how exposure takes place that aids the exposure assessor in evaluating or quantifying exposure. of interest. Exposure scenarios typically include information on the sources and pathways of exposure, contaminants of concern, and receptor populations. They may also describe a receptor population’s activities that may affect exposure and the timeframe over which exposure occurs.

For a food ingestion scenario, concentrations of the contaminants in food (modeled or measured) are needed to estimate exposure dose. Information about the receptor population(s) is also important. Any member of the general population could be consuming contaminated food, although the percentage of contaminated food consumed might be diluted if food from a variety of sources is consumed.

Because nursing infants obtain most – if not all – of their dietary intake from human milk, they are especially vulnerable to exposures to compounds in breast milk (see the module on Lifestages in the Lifestages and Populations Tool Set in EPA ExpoBox).

After characterizing the exposed population and identifying exposure concentrations, it is important to define all appropriate exposure factor inputs to estimate potential exposures and risks. These inputs (e.g., intake rates, body weights, and relevant patterns of behavior such as timeframe of exposure) can be obtained from the Exposure Factors Handbook: 2011 Edition (see Exposure Factors tab in the Indirect Estimation Module of Approaches Tool Set).

Ingestion of contaminated foods could occur over short durations (e.g., breastfeeding infant) or longer time periods (e.g., residence time for a receptor consuming homegrown food).

The table below provides some examples of scenarios involving contaminants in food. The list of examples is not meant to be exhaustive; there are numerous other food ingestion scenarios that may be constructed based on the specific needs of the assessment. There are also many variations of the examples provided in the table.

Additional information on exposure scenarios involving contaminated food may be found in the Indirect Estimation Module of the Approaches Tool Set in EPA ExpoBox.

Examples of Exposure Scenarios Involving Food and Related
Exposure Factors Handbook: 2011 Edition Tables

Medium	Receptor Population	Activity/Timeframe	Intake Rate	Exposure Period
Fruits	General population; consumer-only adults	Ingestion of fruits; short term	Total fruit intake rate [Table 9-1]	Subchronic
Meat products	General population; per capita adults	Ingestion of meat; long term	Total meat intake rate [Table 11-1]	Chronic
Dairy products	General population; children ages 1 - 6 years	Ingestion of milk; long term over 5 years	Total diary intake [Table 11-1]	Subchronic
Homegrown vegetables	Home gardeners	Ingestion of home-produced vegetables; long term	Intake of home-produced vegetables [Table 13-1]	Chronic
Grain products	General population, consumer-only adults	Ingestion of grain	Intake of total grains [Table 12-2]	Chronic
Human milk	Infants	Nursing during birth to 12 months	Intake of human milk [Table 15-1]	Subchronic

Several resources are available that illustrate food exposure scenarios.

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. These categories could be age group/lifestage; gender (if appropriate); population subgroup (e.g. 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)

Calculation Tools

A variety of tools are available for quantifying exposures (dose) and risks associated with contaminants in food. These calculation tools have typically been developed for specific situations or EPA Program Offices but may be tailored to meet the needs of the user.

Guidance

A number of guidance documents are available to support various aspects of food safety programs at EPA and other agencies.

References

• Travis, CC; Arms, AD. (1988). Bioconcentration of Organics in Beef, Milk, and Vegetation . Environ Sci Technol 22: 271-274.
• Travis, CC; Hattemer-Frey, HA; Arms, AD. (1988). Relationship between dietary intake of organic chemicals and their concentrations in human adipose tissue and breast milk [Review]. Arch Environ Contam Toxicol 17: 473-478.