Amounts of 137 Cs in residents of Central Southern England were smaller during 1974-76 than at any time during the previous 17 years, and 17 times lower than those recorded during 1964-65. A simple model has been developed, empirically relating 137 Cs in rainfall during 1957-76 to the ensuing burdens in man, and the results suggest that a slowly-declining reservoir of deposited material from the weapons tests of 1955-63 currently contributes as much dietary contamination as the low levels of recent fall out. 137 Cs burdens are therefore unlikely to decline by more than a factor of 2-3 during the next decade, even in the absence of additional weapons tests. The radiation dose rate from the current (early 1977) average level of 137 Cs in these subjects is however only one percent of that delivered by the body's natural 40 K.

Micbael C Eagle is