and low consumption levels, as well as the average level of consumption. Pesticide residue levels present in food will also vary, depending on several variables including application practices in different regions, time that has elapsed since application, degradation during transportation and storage of food, and the manner in which food is prepared by the consumer. Thus, both food consumption and pesticide residue data are characterized not by a single value but, rather, by a broad distribution reflecting high, low, and average values.
The variation in food consumption and residue data produces considerable variation in dietary exposure of pesticides by infants and children. This can be represented by a distribution of exposures across individuals within a particular age group. The distribution of dietary exposures is determined by the distribution of food consumption levels and the distribution of pesticide residues in food. If both the distribution of food consumption and the distribution of residue levels are known, statistical methods can be used to infer the distribution of dietary exposures. The process for combining different distributions into one distribution is termed convolution. The statistical convolution methods that can be used for this purpose are discussed later in this chapter.
Since ingestion of pesticides is dependent upon both food consumption and pesticide residue levels in food, it follows that the quality of dietary exposure data is determined by the quality of consumption and residue data. Although food consumption surveys such as the Nationwide Food Consumption Survey (NFCS) provide data on consumption patterns in the population at large, these surveys have generally not targeted infants and children. Hence, they included relatively small sample sizes within the age groups of primary interest for this report. One exception is the 1985–1986 Continuing Surveys of Food Intakes of Individuals (CSFII), which did focus on food consumption patterns of children.
Determination of the distribution of pesticide residues in foods consumed by infants and children is also difficult: only a fraction of all food consumed can be tested for the presence of pesticide residues. Many of the available residue data are based on surveillance studies that because of their focus on potential problem areas may overstate residue levels in the general food supply. The detection limit of residue monitoring methods can also impart uncertainty as to the residue levels actually present on food, especially when many residues are below the limit of detection and the detection limit is relatively high.
Recognizing these data limitations, the committee has included in this chapter several examples to illustrate possible approaches to estimating the distribution of dietary exposure to pesticides for infants and children. Each of these examples is designed to illustrate different aspects of exposure estimation, including the estimation of average daily exposures for use in chronic toxicity risk assessment and the estimation of peak exposures