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Due: 12/2/99 |
Soil Ingestion Study
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Due: 12/2/99 |
Modern soil ingestion studies are conducted to estimate the quantity of soil casually ingested by children and adults. Such estimates are used when assessing the health risk due to chemical contamination of the soil. The amount of soil ingested is estimated using a mass-balance equation. The estimates are formed by measuring the trace element amounts in duplicate food samples, fecal samples, and the concentration of the trace element in soil. The amount of soil ingested is estimated by subtracting from the trace element amount in fecal samples the amount of the trace element in food, and then dividing by the soil concentration. Normally, several trace elements are used in such studies, with trace elements selected that occur rarely in food, are not bioavailable, and occur in large concentrations in soil.
We consider data on Aluminum (Al) from a soil ingestion study conducted in Western Massachusetts on 12 children identified by parents as likely soil ingesters (Calabrese et al. (1997). Soil Ingestion Rates in Children Identified by Parental Observation as Likely High Soil Ingesters, Journal of Soil Contamination, 6:217-279). In this study, duplicate food samples were collected on seven consecutive days, with fecal samples collected for a similar time period, beginning one day after the food collection.
Data are contained in three files: food, fecal, and soil. In these data sets, the consecutive food and fecal days are indicated in the variable F_PID. The variable F_PID has embedded in it the study subject ID, and the day in the study (where the day is coded such that same day code is used for the fecal output and the corresponding food intake for the fecal output). This coding of day was made under the assumption that there is a 24 hour passage time from food to fecal for all subjects. For example, when the day code is 1, the fecal output is the amount of the fecal output on day 1, whereas for the same day code (ie. 1), the food input corresponds to the amount of the trace element ingested in food on day 0. Soil concentrations are in mg/g of soil. Each data set contains a variable named AL0. In the food and fecal data sets, this variable represents an intermediate concentration value, and will not be used. In the soil data set, this variable represents the average concentration of Al in soil, and should be used.
1. Using these data, construct a SAS data set that has estimates of soil ingestion on each study day for each subject. Print a list of these estimates (for each subject), expressing soil ingestion in mg/day.
2. Construct a list of the average daily amount of soil ingested for each subject. Print a list of these averages (in mg/day).
3. Briefly discuss any problems or decisions that you made in completing 1&2, and the rational for your decision.
4. Include a copy of your SAS programs in an appendix.