Low Radioactivity Reaches N.Z.

Press, Volume CVI, Issue 31124, 29 July 1966, Page 1

Low Radioactivity Reaches N.Z.

Traces of bomb debris from the first French nuclear test at Mururoa atoll began to arrive in New Zealand towards the end of last week, Mr G. E. Roth, director of the National Radiation Laboratory of the Department of Health, said in Christchurch yesterday.

The time of the appearance of these traces of radio activity and their very low levels confirmed that the debris had only reached New Zealand after having circled the Southern Hemisphere, Mr Roth said.

Air filters showed that radioactivity in the air increased in Auckland on July 20, and in Wellington and

Christchurch on July 22 and 23. The level of radioactivity had remained unchanged until then, but began to show a very slight increase after that. Mr Roth sain rain-water collections made at Greymouth and Christchurch showed the first slight rise in the week ending July 22 and 23 respectively. Rain-water collected in Tarawa, Funaafuti and Suva showed the first indications of a rise in fallout levels in weekly collections ending between July 8 and 11.

Radio-iodine first appeared in Auckland and New Plymouth milk samples on July 22. Mr Roth said the highest values measured were obtained from New Plymouth milk on July 25. The milk contained 29 picocuries of radio-iodine in one litre; Auckland milk of the same date contained 13 picocuries. The safe average level set by the United Kingdom Medical Research Council for the continuous intake of radioiodine in milk is 130 picocuries a litre. The council said that an acceptable radiation dose to the thyroid “would not be exceeded in any age group of the population unless the average concentration of

iodine 131 in milk of 130 picocuries a litre was exceeded over a period of one year, or higher concentrations for correspondingly shorter times. “The level has been set to provide a margin of safety for the section of the population in the group in which the dose rate would be highest namely infants up to one; considerably lower radiation doses would be received by older children and adults consuming the same milk.” The levels at Auckland and New Plymouth were about one-fourth and one-tenth of the levels permitted for continuous ingestion by children under one, Mr Roth said. ONLY MILK SAMPLES “These are the only milk samples showing traces of radioactivity from the tests,” Mr Roth said. “Samples of the thyroids of animals slaughtered in the Canterbury area show evidence of radio-iodine but so far no radio-iodine has been detected in the milk of any centres other than Auckland and New Plymouth.” Mr Roth said radio-iodine decayed very rapidly. It lost half its radioactivity every eight days. Level of radioiodine contamination would fall off rapidly unless the radio-iodine was continuously replenished.