Concentration Ratios As previously indicated, we have developed concentration ratios between food products and soil for each radionuclide (pCi/g wet weight in food per pCi/g dry weight in soil). The mean for the concentration ratios developed from samples collected on the 1376, 90, 239+240 Northern Marshall Islands survey is listed in Table 2 for Pu, and , 3 241 Am. The concentration ratios are developed from soil profiles taken to a depth of 40 cm through the root zone of the plants being sampled. This depth is used, if data are available, because we observe that it encompasses most of the active root zone of the subsistence plants we have studied on Enewetak and Bikini Atolls. A report on the root activity of large, mature coconut and banana trees in other tropical regions showed most of the activity in the 0- to 40-cm depth, with some activity also in the 40- to 60-cm depth, although root activity did vary with age and species.-* The report is consistent with our observations of the physical location of the root zone at Enewetak and Bikini Atolls in the 0- to 40-cm depth. Concentration ratios can be developed equally well for 0- to 10-, 0- to 15- or 0- to 25-cm depths, and in those cases where we were unable to obtain soil samples to a depth of 40 cm, we used the 0- to !0-cm concentration ratios as appropriate. MARINE FOODS, BIRDS, AND COCONUT CRABS The radionuclide concentrations in marine fish, shellfish, and invertebrates are described in detail in Ref. 25, and the summarized radionuclide concentrations in fish and the doses from the marine pathway at each atoll are presented in Ref. 19. radionuclide concentrations in fish and invertebrates for each atoll The average are listed in Appendix A. Some of the data are limited but the radionuclide concentrations in most of the species, which constitute a very small portion of the diet, are quite low. Thus, they have a minimal impact on the overall! dose assessment. Very few bird samples were collected on the survey. However, studies at other atolls indicate that the radionuclide concentrations in birds is very similar to the fish radionuclide concentrations because most of the birds are marine feeders. The combination of the low radionuclide concentration in birds and the low average daily intake make the dose contribution from this pathway very small. Thus, the radionuclide concentrations in birds is assumed to be the same as in the fish at each atoll. 1/