- 63 same in 1960 through 1969 for both the ICRP and the FRC, namely, 5 rems/yr to the bone for occupational workers, and 1/30 of this limit or 0.17 rem/yr for \ : a suitable sample of the exposed people in the general population. To derive an MPC value for water (the ICRP has no milk standards) the ICRP considered the known (in 1960) data on the extent to which strontium-90 taken into the ’ body with water could, through the metabolic chain,make its way to the bone. This is how the value of 33 pCi of strontium-90 per liter of water was de- rived - i. e., by dividing by 30 the ICRP value of 1 x 107° uci/om? for occupational workers. As better metabolic information is developed one would expect the derived MPC value to change and indeed this is what happened. In 1962 the ICRP changed its MPC for water to 4 x 1076 uci/em, a factor of four higher than the 1960 value. . a“ ~ While adhering to the same primary standard of 0.17 rad/yr to the bone _ Marrow, the FRC used a different model for relating the concentration of strontium-90 in the milk to the dose within the skeletal tissue. Using this new technique of relating to the strontium-90/caleium ratio the daily intake, averaged over a year, was determined to be 600 pci strontium-90/em of calcium. However, FRC found no operational justification for releasing this much strontium-90 to the environment under normal operating conditions and therefore reduced its average daily intake value to 200 pCi/day . Question 12D According to the Federal Radiation Council, allradiation is potentially harmful, and every effort should be made to keep doses as far | as possible below even the "acceptable" levels, since they already represent