BLOOD BROMINE LEVELS 95 The Br concentration in Rongelap lagoon water wassimilar to that of Atlantic ocean water (62.4 ppm and 67.2 ppm, respectively). Rain catchment water on Rongelap had no detectable Br. Intermediate Br values of 2.2, 13.8, and 17.9 ppm were found in three Rongelap wells. The Br concentration in three samples of Rongelap coconut water was 7.0, 6.4, and 5.3 ppm, similar to the 7.0 and 6.8 ppm found in two Florida-grown coconuts. DISCUSSION The mean serum and red cell Br levels of the 20 Marshallese studied were significantly higher than those of the 10 New Yorkers, as well as being higher than levels reported for other populations (1—6). Cross and Smith (8) have suggested that the tissue ratio of Br to Cl is determined physiologically and that elevated ratios indicate excessive Br intake. The mean Br/Clratios of 1.83 for serum and 4.1 for red cells in the Marshallese were higher than the New York ratios (which were arbitrarily set at unity), This finding suggests excessive Br intake by the Marshallese. It is of interest to point out that Rb, which is considered to be a K analog just as Br is considered to be Cl analog, had similar ratio Rb/K in all three populations studied. Tissue Br can be elevated by an increase in the dietary Br intake and also by respiratory and cutaneous exposures (4). Leaded gasoline, which contains organic bromide, is little used on Rongelap, where Br levels were highest, and can be ruled out as a significant Br source. There is no atmospheric pollution with Br-containing dust or industrial fumes. Someresidual fumigant Br may be present on imported U.S. Department of Agriculture foods on Rongelap, but these foods are not supplied on Majuro. Therefore, a local environmental source of Br was suspected. Ocean water has a bromine concentration of 65.0 ppm (12), consistent with the measurements of Atlantic ocean and lagoon water sampled for the present study. There is significant vertical exchange of lagoon and ocean water with the fresh water lens system ofatoll islands (13), and dug wells exhibit different degrees of salinity depending on their depth and placement about the lens. The variable levels of Br detected in well water are consistent with earlier atoll studies of Cl and other elements (unpublished 1972 water quality data from Bikini and Enewetakatolls kindly supplied by C. J. Huxel, U.S. Dept. of the Interior Geological Survey, Honolulu, Hawaii). However, the most important source of drinking water is rain catchment water, samples of which showed no Br present. Another commonly ingested liquid is coconut water, which is used for cooking as well as for drinking. An estimate of the weight of coconut products ingested daily, including coconut water, is 2.4 kg for a man aged 23-50 years of age (14). The Br concentrations measured in coconut water samples would provide an average daily consumption of 17 mg Br solely from coconuts. The acceptable daily intake of Br set by the FAO/WHO is 1 mg/kg body weight (15). It has been suggested that a more appropriate value would be 0.1 mg/kg body wt (16), which would approximate one-third of a Marshallese man’s daily intake of Br from coconuts alone. Br levels in other food supplied were not tested in the present study, but