Environmental Health Criteria 214

HUMAN EXPOSURE ASSESSMENT
ready-to-eat foods is the most useful measure for purposes of
dietary exposure assessment.
7.4.1 Duplicate diet surveys
Duplicate diet surveys are particularly useful because they
reflect the range of preparation habits of the study population. These
studies require that respondents save a serving of each meal or
components of each meal and store them until collection by the
research team. Following collection, the food is composited over
predetermined time intervals (e.g., by meal or by day) and analysed
for the target analytes. In duplicate diet studies, logistic and cost
constraints typically require that foods be composited. The principal
disadvantage of composite samples is that they do not allow for
identification of the contribution of individual foods to total
dietary exposure. A high degree of respondent burden is associated
with duplicate diet studies, so they are not conducive to assessing
chronic dietary exposures and may underestimate intake. Such
approaches are only suitable for chemicals that can be analysed
accurately, so direct diet methods are not traditionally used for
assessing food additives exposure, for example. A summary of dietary
exposure assessments for chemical contaminants in food using the
duplicate diet performed worldwide may be found in Thomas et al.
(1997).
There are many indirect methods for estimating exposure to food
chemicals because there are a variety of ways to collect consumption
data, to express residue levels in the foods concerned (for example,
legislative levels, manufacturer or industry use levels, predicted,
proposed or analysed levels or any combination of these) and there are
several approaches which can be used to combine the information to
assess exposure (Rees & Tennant, 1994). Some methods are better than
others, depending on the chemical; for example several countries have
found it useful to assess food additive exposure by using per
capita methods (Ito, 1993). More information on these indirect
methods is given below, but the reader is strongly advised to refer to
more comprehensive documents on dietary survey methodology and dietary
exposure assessment approaches (WHO, 1985a, 1997c; FAO/WHO, 1995a,b,
1996, 1997).
7.4.2 Market basket or total diet surveys
Market basket or total diet surveys utilize food chemical
concentrations measured in ready-to-eat foods prepared in the
laboratory linked to model diets derived from food consumption data
and standard recipe preparation for large populations, households or
individuals. Food products or food groups selected for sampling and
analysis are generally intended to be representative of those most
commonly consumed by the population of interest. Total diet studies
have been carried out since the 1960s in many countries. Market basket
surveys are often employed by regulatory agencies charged with
ensuring and monitoring the safety of a national food supply (FAO/WHO,
1995b). Initially this purpose was to estimate background exposures of
the population to pesticides residues and radioactive contaminants.
The emphasis has shifted from pesticides to toxic metals and more
recently has included a variety of trace elements and organic
contaminants.
For example, the US FDA Total Diet Study (US TDS) is a market
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