Assessing the Intake of Contaminants and Nutrients: An Overview of Methods

JOURNAL OF FOOD COMPOSITION AND ANALYSIS ARTICLE NO.

9, 243–254 (1996)

0030

Assessing the Intake of Contaminants and Nutrients: An Overview of Methods BARBARA J. PETERSEN AND LEILA M. BARRAJ1 TAS, Inc., The Flour Mill, 1000 Potomac Street NW, Washington, DC 20007 Received October 17, 1995, and in revised form April 9, 1996 The methods being applied to assess the intake of food contaminants or nutrients from one or more foods are reviewed and their advantages and disadvantages are discussed. Methods currently being used for estimating the joint intake of food contaminants or nutrients from several foods depend on the data and resources available. Ideally, the methods should account for the fact that individuals eat a variety of foods in a single day and do not necessarily consume the same foods every day. Similarly, the methods should adjust for the large variability that exists in the amount of food consumed by various individuals or on various days and in the food combinations consumed by different individuals or on different days. Finally, the methods should also adjust for the fact that food contaminants and nutrients are often present in more than one food and are usually present at varying concentrations. q 1996 Academic Press, Inc.

INTRODUCTION

Estimates of contaminant or nutrient intakes are needed in order to assess the potential health impact of these intakes. In the case of contaminants, intake levels exceeding some ‘‘safe acceptable limits’’ may be associated with adverse health effects. In the case of nutrients, intake levels below minimum daily requirements or above some acceptable levels may also result in adverse health effects. Depending on the toxicological profiles of the contaminants, for some contaminants, occasional intakes above the safe limits may not necessarily result in adverse health effects, while for others they may. Sometimes only a rough estimate of the average or of an upper percentile of the distribution of intakes is needed, while other instances require a more accurate estimate of the entire distribution of intakes. There may be instances where intake from a single food is desired (e.g., because it is the only food likely to contain the contaminant) and others where intake from several foods is of interest. The estimate of the intake of a particular population subgroup is needed in some instances, while other times, an estimate of the intake of the entire population is of interest. In the case of food contaminants, the toxicological profile of the contaminant guides the choice of the method used to estimate intake. For instance, for contaminants with acute effects, daily intake estimates or intakes per meal are more relevant than intakes over a period of time (Rees and Tennant, 1993). Intake of a food contaminant or nutrient is calculated as the product of the amount of food consumed and the contaminant or nutrient concentration in the food. The purpose of the assessment dictates the data needed and the method to be used to 1

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0889-1575/96 $18.00 Copyright q 1996 by Academic Press, Inc. All rights of reproduction in any form reserved.

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estimate intake. For example, when the interest is in estimating the actual contaminant or nutrient intake of a population subgroup at risk, knowledge of the actual diets of the individuals in that subgroup and of the actual concentration of the contaminant or nutrient is needed. On the other hand, national food consumption data or hypothetical diets can be used in combination with estimates of contaminant or nutrient concentrations derived from national monitoring programs to estimate the potential intake of larger population subgroups (Berry, 1992). The methods used to estimate intake can be classified into four major groups: 1. Duplicate Methods 2. Total Diet Study or Market Basket Methods 3. Hypothetical Diet Methods 4. Methods Combining Estimates From Food Consumption Surveys and Food Monitoring Programs, including: Methods using single-point estimates of the consumption of a food and concentration of nutrient or contaminant in that food Methods using a distribution of consumption values and a single-point estimate of the concentration of nutrient or contaminant in a food Methods using food frequency and serving size data Methods using distributional analyses Such classification, however, should not be interpreted to imply that the methods are not related and do not overlap. In fact, all the methods described here derive intake estimates as the product of food consumption data and concentration data. They differ in whether the consumption data used refer directly to a specific diet consumed by a specific group of individuals or to typical or hypothetical diets and whether the concentration data refer directly to the specific foods consumed or are obtained independently. The methods also differ in whether they aim at producing point or distributional estimates of intake. In this paper, we will describe each method and how it relates to the other methods, identify some of the advantages and limitations of each method, and present examples of situations where each method may be used. THE DUPLICATE METHOD

The Method The most frequently used method of data collection for assessing the actual intake of a particular group is the duplicate method. Participants are usually asked to provide a duplicate amount, or a portion, of every food they consumed over the duration of the study. The foods contributed by each participant are composited and analyzed for the presence of the nutrient(s) or contaminant(s) of interest. An estimate of the daily intake is obtained for each participant by multiplying the amount of food consumed daily by the nutrient or contaminant concentration detected in the duplicate portions provided. Examples Miles et al. (1984) used the duplicate method to estimate energy intake and validate estimates of energy intakes of a small group of men and women, while Witschi et al.

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(1985) used the duplicate method to estimate and validate estimates of sodium intakes for high school students. The duplicate portion method was used in the assessment of human exposure to benzo(a)pyrene via food ingestion in the total human environmental exposure study (THEES) (Waldman et al., 1991). Twenty individuals participated in the study and collected duplicate portions of the foods they consumed over three periods of 14 days each. A daily intake of chemical (exposure estimate) was derived for each person, based on the amount of food consumed weekly and the concentration of benzo(a)pyrene in the analyzed foods (composited for the entire week samples). Fujita and Morikawa (1992) used the method to assess regional differences in dietary intake of environmental pollutants in Japan. One-hundred and twenty-seven women in five cities in Japan were asked to collect duplicate samples of all foods eaten during a typical day. The foods consumed by each participant were homogenized and analyzed for the presence of 12 pollutants. Estimates of the average and 90th percentile of the distribution of intake values of each contaminant were derived for the women participating in the study, and regional differences were examined. Advantages, Limitations, and Relation to Other Methods Intake estimates derived by the duplicate method combine the actual amount of foods consumed with the actual amount of nutrient or contaminant detected in ‘‘identical’’ foods. It thus has the advantage of being able to measure directly the actual intake by the subjects included in the study. Unlike most of the other methods discussed in this paper, no surrogate data are used to estimate either the consumption or concentration values. However, because the method is labor intensive and requires a significant amount of commitment on the part of the participants (Urietta et al., 1991), its use is usually restricted to small groups, and the data are usually collected over a short period of time. Thus, the intake estimates derived using the duplicate method are not usually applicable to large populations or long-term intake. The representativeness of the estimates of intake has also been questioned because participants may tend to modify their behavior (Waldman et al., 1991). All the foods in the duplicate diets are usually homogenized and analyzed as composite samples. Foods that contain the chemical or nutrient of interest are mixed with foods that do not contain the chemical or nutrient. This dilution of the compounds of interest may result in final concentrations that are below the limits of detection (Fujita and Morikawa, 1992). Furthermore, with compositing the important sources of the chemical or nutrient cannot be identified. The duplicate method differs from the other methods discussed in this paper in the source and type of data used to estimate total intake. The data are derived from direct ‘‘observation’’ of the individuals under study, and the intake estimates refer to the observed individuals. Unlike other methods discussed in this review, the duplicate method does not attempt to identify the ‘‘source’’ of the contaminant or nutrient. Typically, it does not aim at producing estimates that can be generalized to an entire population. When Should the Duplicate Method Be Used? The duplicate method is useful if estimates of the actual intake of nutrient or food contaminant are needed, for instance, to be correlated with specific health effects or

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specific biological measurements. The duplicate diet method is also useful if it is necessary to identify the individuals with extreme intake levels or if estimates of the intakes of individuals with particular diets or food preparation habits are needed. THE TOTAL DIET STUDY OR MARKET BASKET METHOD

The Method In the Total Diet Study (TDS) method, estimates of the types and amounts of foods typically consumed by the individuals in the population are derived from food consumption surveys of a representative sample of the population. Several samples of each of these foods are collected, prepared in table-ready form, and analyzed for the nutrient(s) or contaminant(s) of interest. The measured concentrations are multiplied by the consumption estimates derived from ‘‘typical diets’’ to estimate the nutrient or contaminant intake by a given population. Examples The Total Diet Study approach has been used by the U.S. Food and Drug Administration (FDA) since 1961. Data from the FDA TDS were used by Anderson et al. (1994) to estimate the intake of several nutrients. Lombardo (1991) combined pesticide concentrations measured in samples of 234 foods from the FDA TDS with food consumption data from typical diets to estimate pesticide intake. The Total Diet Study approach has also been used in Canada. For instance, Mongeau et al. (1989) collected samples from 101 foods in a typical total diet and measured their fiber content. They combined the concentration data with average food consumption estimates from the 1971–1972 Nutrition Canada Survey to estimate the average total fiber intake of the Canadian population. Advantages, Limitations, and Relation to Other Methods The Total Diet Study approach combines concentration estimates of nutrients and contaminants in a ‘‘typical diet’’ to estimates of consumption from these or other diets. The method thus refers to a ‘‘typical’’ consumer, and its results cannot usually be applied to specific individuals or those consumers with very atypical food consumption patterns. In addition, constructing typical diets may be difficult and time consuming (Nutriscan, 1992). Because of the resources required to prepare the foods, only a limited number of foods and samples from each food can be prepared and analyzed; thus, regional, varietal, and other differences that might affect the distribution of nutrient or contaminant concentrations are generally not accounted for in the assessment. Also, since several samples of food are usually mixed and analyzed as a composite, the TDS does identify the individual foods contributing most to the intake (Rees and Tennant, 1994). The TDS methods, however, may be more cost effective than duplicate diet methods (Urietta et al., 1991). Unlike the duplicate method, the TDS approach uses surrogate information about food consumption patterns and concentration levels to derive indirect estimates of nutrient of contaminant intake.

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When Should the Total Diet Study Method Be Used? The Total Diet Study approach can be used to derive a rough estimate of average intake of a population and enables one to determine whether more refined assessments are needed. The TDS can provide data for trend analysis when repeated over time, as in the case of the FDA’s TDS. It can also provide estimates of ‘‘background’’ intake levels, in the event of local contamination. When the dietary habits of specific population subgroups are used to construct a hypothetical diet, the TDS can be used to estimate the intake of these specific subpopulations (Rees and Tennant, 1994). It should not, however, be used to make inferences about the intake distributions of the general population. THE HYPOTHETICAL DIET METHOD

The Method A hypothetical typical diet is defined using data from several sources, and average estimates of food consumption derived from these hypothetical diets are combined with estimates of nutrients or chemical concentrations to estimate dietary intakes. Examples The World Health Organization’s (WHO’s) global diet is based on nine Cultural diets developed using data from the Food and Agriculture Organization (FAO) balance sheets. The global diet was developed using the highest average food consumption for each food from each of the cultural diets (Galal-Gorchev, 1991). The cultural or global diet method attempts to reflect long-term food consumption habits, not dayto-day variations, in order to compare consumption to the Acceptable Daily Intake (ADI) or Recommended Dietary Allowances (RDAs) over a lifetime. Estimates of maximum residue concentrations (MRLs) are combined with food consumption estimates from Cultural or global diets to calculate ‘‘Estimated Maximum Daily Intakes’’ (EMDIs) and ‘‘Theoretical Maximum Daily Intakes’’ (TMDIs) (WHO, 1989). The TMDI and EMDI are calculated as (WHO, 1989) TMDI Å ( Fi 1 Mi , where Fi is the average consumption of food i (kilograms of food per person per day) estimated from the global, cultural, or national diet and Mi is the MRL for food i (milligrams of contaminant per kilogram of food) and EMDI Å ( Fi 1 Ri 1 Pi 1 Ci , where Fi is the average consumption of food i (kilograms of food per person per day) from a specific cultural or national diet, Ri is the residue level in edible portion for food i (milligrams of contaminant per kilogram of food), Pi is a correction factor for commercial processing, and Ci is a correction factor for preparation or cooking. The TMDI and EMDI are then divided by an estimate of average body weight (60 kg) to allow comparison with the ADI, which is expressed in milligrams of pesticide per kilogram of body weight per day.

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The U.S. Department of Agriculture (USDA) Family Food Plans comprise different types of foods that households might buy to provide nutritious diets for household members (Consumer Nutrition Division, 1983). In the plans, amounts of foods are suggested for men, women, and children of various ages, as well as for families of different composition. Average estimates of nutrient content are then combined with the suggested amounts of foods to derive estimates of potential nutrient intake. The Danish Budget Method (Hansen, 1979) estimates additive intake by defining a hypothetical diet based on the assumption that the maximum intake of a food additive is limited by the energy requirement. Advantages, Limitations, and Relation to Other Methods The hypothetical diet approach is useful when limited data are available or when conducting international comparisons or trend assessments. Because of its simplicity, the approach is used for screening purposes, to identify situations where no further assessments are needed, and for situations where a more refined assessment of intake is required. Note that the TMDI and EMDI represent two levels in the exposure assessment process. The TMDI assumes that 100% of the food crop is treated and that all food crops have residues at maximum residue levels. It does not allow for residue dissipation during storage, processing, and cooking and includes inedible portions. On the other hand, although the EMDI still assumes 100% of the food contains residues of the chemical, it does adjust the residue to represent only the edible portion and does adjust for cooking and processing (WHO, 1989). Because the consumption data are derived from hypothetical diets, and because of the assumptions underlying the derivation of the maximum levels, exposure estimates derived using the TMDI or the EMDI methods are primarily used as a screen of the potential exposure of any given population and cannot be used to identify actual problem situations. Like the TDS approach, the hypothetical diet approach derives an estimate of intake based on a ‘‘typical’’ diet. But, unlike the TDS, the hypothetical diet does not necessarily refer to a specific population. Furthermore, while the concentration estimates used in the TDS are derived from analyses of food samples specifically collected and prepared to represent the foods in the typical diet, the concentration estimates for the hypothetical diet approach are usually derived from general monitoring programs, not necessarily designed to collect foods representative of those in the diet used by the hypothetical diet approach. When Should the Hypothetical or Global Diet Method Be Used? The Hypothetical Diet approach can be used to derive rough estimates of intake and enables one to determine whether more refined assessments are needed. It can also provide comparisons across different populations. It should not, however, be used to make inferences about the intake distributions of the general population. Its relative low cost is one of its most attractive features. The method is often used to establish priorities by government regulatory officials. However, the results are sufficiently crude so that priorities may not be appropriately determined without at least EMDI calculations.

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METHODS COMBINING ESTIMATES FROM FOOD CONSUMPTION SURVEYS AND FOOD MONITORING DATA

Dietary intake of the general population and subgroups is assessed using food consumption survey data and surveillance data on residues in foods (Berry, 1992). The consumption and concentration data are collected independently, often for different purposes. Food consumption surveys are usually conducted on representative samples of the population and use dietary recall methods, diaries, or a combination of both. Data collected through the recall method refer either to the amounts of foods consumed over the previous 24 h or to how often the foods have been consumed over the last week, month, or year. Data collected through diaries usually refer to amounts of foods consumed. Depending on the toxicological profile of the contaminant of interest, consumption data for single eating occasions per day or over a longer time interval (e.g., week, month, year) may be needed (Knowles et al., 1991). The data collected through food consumption surveys are used to derive estimates of average consumption, high or extreme consumption, and percent consumers and to derive distributions of consumption levels. These summary estimates or the raw consumption data are combined with residue monitoring or nutrient concentration data to derive intake estimates, as described by Højmark and Møller (1991). Methods Using Single-Point Estimates Estimates of average intake of food contaminants or nutrients are obtained by summing the product of the average consumption estimate for food i, (Ci), for the entire population or for specific population subgroups with the average contaminant or nutrient level in food i, (Ri), to estimate the total intake, I. Therefore I Å ( Ci 1 Ri . When an estimate of particular upper percentiles of the intake distribution from one food is needed, one approach is to multiply the upper percentile of consumption by an estimate of the concentration of the contaminant (Pesticide Safety Directorate, 1994). This method should not be used when an estimate is needed for several foods, since summing the upper intake estimates corresponding to each of these foods leads to a gross overestimate (Pesticide Safety Directorate, 1994). A method for estimating the upper percentiles of intake using only the average consumption estimates and percent consumers data was suggested by Nutriscan (1992). This method is based on the observation that for data from the 1986–1987 Dietary and Nutritional Survey of British Adults, the 97.5th percentile of the distribution of consumption values for a large variety of foods was about three times higher than the average consumption value. Thus, estimates of upper percentiles of consumption can be combined with estimates of contaminant or nutrient concentrations to estimate upper percentiles of intake for specific foods. An extension of this approach was tested by Nutriscan (1992) for intake from several foods and was found to provide valid results for foods that are fairly commonly consumed. Advantages, limitations, and relation to other methods. The advantages and limitations of all methods using concentration data independently collected from consump-

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tion data will be discussed later. We focus here on intake estimate methods using single-point estimates from concentration data independently collected from consumption data. These methods are easy to implement and may be used when estimates of average intake are of interest. If average estimates of consumption and concentration are used, the estimate derived using this method is equal to the average of the estimated distribution of intakes derived using distributional methods (see following sections). However, when these methods are applied using an upper estimate of the contaminant or nutrient concentration distributions, as a single-point estimate, they grossly overestimate the distribution intake values, particularly if intake from more than one food is used in the assessment. In that case, these methods are best used as a screening process to identify the need for a more realistic assessment of the distribution of intake values using distributional methods. Methods Using Distributions of Consumption Values The methods described in this section take into consideration the fact that consumption levels vary from person to person and from day to day. These methods would combine an estimate of the entire consumption distribution with a single estimate of concentration. In the case of several foods, consumption estimates for each of the foods in the assessment are multiplied by the corresponding concentration estimate and summed for each individual. If estimates of a particular upper percentile of the intake distribution are needed, the resulting distribution of total intakes is used to derive the percentile(s) of interest. The U.S. EPA has typically used these methods to estimate intake of acute toxicants. The approach followed by EPA combines estimates of upper percentiles from the distribution of concentration levels with a distribution of daily consumption levels. Advantages, limitations, and relation to other methods. Methods using distributions of consumption values could provide more realistic estimates of intake than those using only single-point estimates. They generate an estimate of the intake distribution and can be used to assess the variability in these intakes, as well as to assess the representativeness of point estimates of intake. They may be more costly than methods using point estimates since they require more data. However, since a single concentration value is used, the approach is equivalent to assuming that all individuals consume foods containing the same amount of nutrient or contaminant. When these methods are applied using an upper estimate of the contaminant or nutrient concentration distributions, as a single-point estimate, they grossly overestimate the distribution intake values, especially if intake from more than one food is used in the assessment. In that case, these methods are best used as a screening process to identify the need for a more realistic assessment of the distribution of intake values using distributional methods. Methods Using Food Frequency and Serving Size Data Another approach, proposed by Beloian (1982), for estimating intake of contaminants combines data from food frequency questionnaires and typical serving size information with residue estimates. The daily intake of contaminants is estimated for each individual using the formula

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∑ (Ei 1 Ci 1 Si) iÅ1

N

,

where Ei is the number of eating occasions for the ith food in N days, Ci is the contaminant concentration in the ith food, Si is the serving size for the specific age group, and N is the number of days of dietary record for each person. Average or typical amounts of foods and concentrations are used. The only variability comes from the number of eating occasions, obtained from food frequency questionnaire surveys. The average contaminant concentration was derived from monitoring programs, and serving size estimates were derived from the 1965 USDA Household Food Consumption Survey. Advantages, limitations, and relation to other methods. Like the previous method, the combination of food frequency and serving size data method uses a distribution of consumption values and thus could provide more realistic estimates of intake than methods using only single-point estimates. The variability in the consumption estimate is derived from the variability in the frequency of consumption of the foods, rather than from the variability in actual amounts consumed since the method uses a single serving size estimate. The method thus assumes that when an individual consumes a given food, he or she consumes a constant amount. The method is useful for deriving average intake estimates (provided average serving sizes and concentration levels are used) and is useful in assessing intakes from infrequently consumed foods. Methods Using Distributional Analyses The methods discussed so far have all used a single estimate of the contaminant or nutrient concentration in each food. However, these concentrations are not constant, and their distributions in foods tends to be skewed to the higher concentrations, with a few extreme values (NRC, 1993). The National Research Council (NRC, 1993) and Petersen et al. (1994) have proposed methods for estimating contaminant intake that use the observed distribution of contaminant concentrations in addition to the distribution of food intakes to estimate the distribution of intake values. In the method proposed by the NRC (1993), the estimate is derived using Monte Carlo simulations. Specifically, each food consumption value is multiplied by observations drawn at random from the distribution of contaminant concentrations, and the resulting distribution constitutes the estimate of the intake distribution. The Joint Distributional Analysis method proposed by Petersen et al. (1994) divides the distributions of contaminant concentrations and food consumption values into intervals, and the resulting multinomial distributions are multiplied to derive an estimate of the intake distribution. In the case of intake from more than one food, both methods were shown to result in similar estimates of the distribution of intake values (Tomerlin et al., 1994). The two distributional methods discussed above combine observed distributions. Alternatively, distributional methods have been used on ‘‘simulated’’ distributions. For instance, Thompson et al. (1992) used Monte Carlo techniques to derive an estimate of the distribution of intake of benzene and benzo(a)pyrene. Parametric distributions (e.g., log-normal and normal) were used to represent the distributions of the various parameters in the model. Finley et al. (1994) proposed several distributions

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that can be used in intake assessments, some based on parametric representations (e.g., normal, log-normal, or triangular distributions). Advantages, limitations, and relation to other methods. The methods using distributional analyses require more data to implement and specialized computer software. They do not make the simplifying assumption that individuals consume the same amounts of foods and that the foods contain the same nutrient or contaminant concentration levels and thus result in more realistic estimates of intake. Furthermore, with the new advances in computer technology, such computations can be performed with relative ease. The quality of the estimates derived from these methods depends on the quality of the data used in the assessment. The representativeness and completeness of the consumption and concentration data are crucial factors. And, in the case of contaminant intake, the treatment of the samples with nondetectable residue levels has a significant impact on the resulting estimate of contaminant intake (Loftus et al., 1992; Petersen, 1993; Tran, 1994). Advantages and Limitations Common to These Methods in Relation to Other Methods In the above sections, we have described the several methods that combine estimates from food consumption surveys and food monitoring data and have reviewed their advantages and limitations. In this section, we review the advantages and limitations that are common to these methods. Methods for assessing intake indirectly through the use of data on nationwide food consumption combined with residue or nutrient concentrations from other food monitoring programs provide a large amount of data about specific populations (Berry, 1992). Unlike the Duplicate Portion or the Total Diet Study methods, the resulting measures of intake can be generalized to entire populations. They could be less costly than other methods because they use available consumption and concentration data. The resulting estimates may, however, not necessarily be representative of actual intakes by specific individuals. As mentioned above, the quality of the estimates derived from these methods depends on the quality of the data used in the assessment. The representativeness and completeness of the consumption and concentration data are crucial factors. When Should Methods Combining Estimates from Food Consumption Surveys and Food Monitoring Data Be Used? Methods combining estimates from food consumption surveys and food monitoring data can be used to derive estimates of the intake of entire populations. Methods using single-point estimates are useful when average intake estimates are needed or when the assessment is used to determine whether it is necessary to conduct a more refined assessment. When realistic estimates of intake are needed, more detailed data (moving from point estimates to entire distributions) need to be used in the estimation. The level of detail required in both the consumption and residue data depends on the purpose of the risk assessment (Rees and Tennant, 1993). CONCLUSION

We have reviewed several methods used for the assessment of total nutrient or contaminant dietary intake. All the methods described in this paper derive estimates

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of intake through combining food consumption data with nutrient and contaminant concentration data. They differ, however, in the source and type of data to be used in the assessment and in the assumptions about the distribution of the consumption and concentration levels. The choice of which method to use should depend on the purpose of the assessment, although it is often guided by the data and resources available. Distributional methods using observed data (including the Duplicate Diet Method) may provide more realistic estimates of the potential intake than those methods using theoretical (parametric) distributions or single-point estimates. However, investing the time and resources to derive the data needed to implement these methods may not be necessary if only an average estimate of intake is required or if the purpose of the assessment is simply to screen for the need for a more elaborate assessment. REFERENCES ANDERSON, D. L., CUNNINGHAM, W. C., AND LINDSTROM, T. R. (1994). Concentrations and intakes of H, B, S, K, Na, Cl, and NaCl in Foods. J. Food Comp. Anal. 7(1/2), 59–82. BELOIAN, A. (1982). Use of a food consumption model to estimate human contaminant intake. Envirn. Monitoring Assessment 2, 115–127. BERRY, M. R. (1992). Strategy for a dietary exposure research program. J. Exp. Anal. Envirn. Epid. Supplement 1, 97–110. Consumer Nutrition Division (1983). USDA Family Food Plans, 1983: Low Cost, Moderate Cost, and Liberal, CND (Adm) 366. Human Nutrition Information Service, USDA, Hyattsville, MD. FINLEY, B., PROCTOR, D., SCOTT, P., HARRINGTON, N., PAUSTENBAUCH, D., AND PRICE, P. (1994). Recommended distributions for exposure factors frequently used in health risk assessment. Risk Anal. 14(4), 533–553. FUJITA, M., AND MORIKAWA, K. (1992). Regional differences in dietary intake of environmental pollutants in Japan. J. Exp. Anal. Envirn. Epid. 2(2), 177–193. GALAL-GORCHEV, H. (1991). WHO international co-operation in exposure studies. In Monitoring Dietary Intakes, ILSI Monograph (Ian Macdonald, Ed.), pp. 231–245. Springer-Verlag, Berlin. HANSEN, S. C. (1974). Conditions for use of food additives based on a budget for acceptable daily intake. J. Food Protec. 42(5), 429–434. HO/ JMARK, J. J., AND MO/ LLER, A. (1991). National surveillance of food and contaminant intake: the Danish experience. In Monitoring Dietary Intakes, ILSI Monograph (Ian Macdonald, Ed.), pp. 117–125. SpringerVerlag, Berlin. KNOWLES, M. E., BELL, J. R., NORMAN, J. A., AND WATSON, D. H. (1991). Surveillance of potentially hazardous chemicals in the United Kingdom. Food Add. Contam. 8(5), 551–564. LOFTUS, M. L., BARRAJ, L. M., AND TOMERLIN, J. R. (1992). Effect of the limit of detection on exposure assessment. J. AOAC Int. 75(5), 911–915. LOMBARDO, P. (1991). Pesticide residues in the United States. In Monitoring Dietary Intakes, ILSI Monograph (Ian Macdonald, Ed.), pp. 183–190. Springer-Verlag, Berlin. MILES, C. W., BROOKS, B., BARNES, R., MARCUS, W., PRATHER, E. S., AND BODWELL, C. E. (1984). Calorie and protein intake and balance of men and women consuming self-selected diets. Am. J. Clin. Nutr. 40 (Suppl.), 1361–1367. As cited in WILLETT, W. (1990). Nutritional Epidemiology. Oxford Univ. Press, New York. MONGEAU, R., BRASSARD, R., AND VERDIER, P. (1989). Measurement of dietary fiber in a Total Diet Study. J. Food Comp. Anal. 2(4), 317–326. National Research Council (NRC) (U.S.) (1993). Pesticides in the Diets of Infants and Children. Natl. Acad. Sci. Press, Washington, DC. Nutriscan (1992). An evaluation of the methodologies for the assessment of exposure to food additives and contaminants in the European community. The O’Reilly Institute, Trinity College, Dublin, Ireland.

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