One important link in the strontium-90 food chain is the pathway through plants. The significance of the amount of strontium-90 uptake by plants relates to its transport and final deposition in the bones of humans. There are many complicated mechanisms concerned in the soil-plant relationship which are still to be evaluated. These, when they are worked out, will make possible the determination of the ultimate significance of a particular level of soil contamination at a particular time. The strontium/calcium ratio for plant root uptake in nutrient solutions is 1.0. The U.S. Department of Agriculture studies0/» how- ever, indicate that in American soils the average uptake departs from this experimental value. Menzel has calculated a factor of ky = 0.36 on the basis of _ tSe/ee) plant kr * Sr/Ca) soil The available calcium in the soil determines the amount of strontium-90 taken up by the plant. Menzel has shown that over a range of 0.7 to 48 milli-equivalents of calcium per 100 gms of soil, the strontium-90 uptake wasinversely proportional to the amount | of calciumpresent. = Some experiments have been conducted which relate uptake of strontium-90 by plants to soil depth distribution of this contaminant. Here root depth is the critical parameter. The over-all significance of this principle will depend upon calculations relating actual depth ‘of contamination to root’ depths for various food crops. The total problem, however, has not yet reached a degree of sophistication which would render such analysis fruitful. The SUNSHINE Project data contain correlated sets of alfalfa and soil samples from the Chicago milk shed, analyzed for strontium-90. 4o/ Menzel, R.G. and Brown, I.C., Leaching of Fall-out and Plant Uptake of Fall-out. March-April 19953. Bi-monthly Report, U.S. Dept. of Agriculture, 104