Conclusions from the results of I 131 surveillance in milk and grass in 1976 and 1977

In 1976 and 1977 numerous 131I determinations have been made on milk and grass samples from the surroundings of some nuclear power plants and from districts far from nuclear plants in Northern Germany. The observed 131I contaminations were a consequence of two nuclear weapons tests on 26/9/1976 and 17/9/1977 in the People's Republic of China. In one case 131I could be detected soon after a release out of a nuclear power plant. On the basis of the numerical values of these measurements a transfer factor grass - milk with a mean value of 1.1 . 10-3 pCi/l / pCi/d intake has been estimated. This mean value is about one power of tenths lower than the value assumed by the German Radiation Protection Commission. The too high value for the transfer grass - milk might be the reason for very high transfer factors of 2,000 to 6,000 m3 air/l milk reported by some authors, but which could not be confirmed by direct measurements. Direct measurements of 131I in air and milk lead only to transfer factors of 200 to 800 m3 air/l milk. These latter values correspond far better with the experience in 131I surveillance measurements. (orig./HP)