56 WORLDWIDE EFFECTS OF ATOMIC WEAPONS SAMPLING AND RESEARCH PROGRAM practical suggestion for computing X(r), the activity level of Sr°° deposited, it seems sensible to weight equally the average activity level in areas within 150 mi of the city and the United States general average of samples. The ingestion function a(t) is to be approximated by a step function a, (#= 1, 2,3), a series of constants, one for each of the six age groups. The parameters to be estimated are the a,’s and f. In the absence of any detailed structure in the model, it appears reasonableto usea leastsquaresfit to estimate the parameters; accordingly we are to minimize: time r. The results of the soil samples and Eisenbud's data, corrected to Sr°° activity in whatever way seems appropriate, will have to form the basis of the estimation of exposure. The ingestion function a(t) is a function of (1) age (metabolism of strontium and diet as influenced by age), (2) the general efficiency of the whole biological and plant process whereby Sr°° goes from the lithosphere into human beings, and (3) the availability of Sr°° to plants, as it is laid down, due to incasementin glass beads, soil fixation, etc. In this general context the sampling should be roughly as follows: 1. In the G sample areas (probably large cities within the areas), collect rib bone samples from autopsies by age groups 0 to 10, 10 to 20, 20 and over. 2. In each age group, for each city, collect roughly 200 gm of bone; randomly sort this into two 100-gm samples. This size of sample will allow one to detect 10 ‘ of a lifetime tolerance dose, assuming that this lifetime dose is luc of Sr” and that five counts per minute will be required to obtain a good determination of the Sr" activity level (two counts per minute assumed as background). 3, In these cities one will, after the analysis of these samples, have a picture of the current levels of Sr°° activity in human bone material as a function of age. (The 100 gm per assay may have to be increased if the current level in human beingsis less than 10° of the tolerance dose. If so, 1000 gm will detect 10° of the tolerance dose, etc. It has been suggested that a few preliminary assays be done to determine just what level we are dealing with. If it is very low, say 10° or 10° of the tolerancedose, the size of the sampling program mayhaveto be revised to save money.) 4, For each grouped sample of 100 gm, one must compute the function X(t) for the city and age group under analysis. The ages of persons in the sample will be used, and in the pooled dose the separate ages should be taken into account, or at least the average age of the bonein the pooled sample. In general it will be best to have complete case histories of the various people in the pooled samples. These should be collected with the Min) >) LeEs(8) — FJ? tal fz=t 57 (i= 1,2,3), where E,,(8) is the calculated exposure for the jth assay sample and Y,; is the observed amountof Sr°° per gram of bone in the 100-gm sample. The exact method for computing F,,(f8) wil! have to be worked out. The Problem of Obtaining Individual Samples The problem of collecting individual samyles has been mentioned earlier. The experience from other sample survevs indicates that great care must be taken in writing out the detailed instructions for the collection of individual samples so that they will be properly collected, labeled, and described. Usually, sampling programs are more successful if everything except the actualcollection of the sample item is done at one central headquarters. For example,in the case of the soil samples it seems reasonable that the following types of things be done: 1. For each city the surrounding area must be delineated and a map of the area obtained; on this map the food-producing soil areas must be delineated (presuming these soils to be the only ones we are interested in because only the Sr°° in these soils represents a human ingestion hazard). 2. Fromthese areas the three samples must be selected in some way. Suppose each sample is to consist of the soil in a volume 1 yd? by 7 in. deep. We have the choice for each sample of pooling 7 smaller samples or of having one sample of the given volume. It would appearbetter to have at least some pooling of smaller-sample volumes, but it is not clear what #7 should be. LherC e ONCCTION N very large, and these must be balanced off against the increased information obtained about the average Sr®° level of soil in the area. In addition there are schemes of sampling intermediately between complete random sampling for all » subsamples and having only one sample 36in. by 36 in.