Fall-out Levels Up, Hazards Unchanged

Press, Volume CVI, Issue 31247, 20 December 1966, Page 32

Fall-out Levels Up, Hazards Unchanged

Although fall-out levels in air and rainwater, due to shortlived bomb debris from the French nuclear tests in the Pacific, have increased, the levels of the long-lived fall-out products—-strontium-90 and caesium-137 in rainwater and milk —have changed little from levels in the second three months of this year.

This is stated in the report for July to September on environmental radioactivity in New Zealand, issued by the National Radiation Laboratory of the Health Department in Christchurch.

Summarising measurements made, the report said a distinction was made between the levels of radioactivity due to long-lived radionuclides—of major significance in assessing health hazards—and short-lived radionuclides from the recent French tests. Although the short-lived radionuclides showed increased levels of radioactivity during limited periods, they were of less significance in assessing health hazards. Strontium Level

“The level of strontium-90 in rain during the quarter was less than one fifth of the highest level previously recorded in the first quarter of 1965,” the report states.

“The level of strontium-90 in milk during July-August was about one half of the highest level previously recorded in July-August, 1964, and the level of caesium-137 in milk for the same period was less than half of the highest level previously re-

corded in March-April, 1965.

“The fall-out level in air and rainwater due to the short-lived bomb debris from the French tests, however, have increased during the third quarter, 1966. The average level in air was about four times higher than the level in the second quarter, and in rainwater at Christchurch, the level was about three times higher.” The report stated that the all-station average of stron-tium-90 in New Zealand milk for the 12 months ended August, 1966, was 6.5 per cent of the “cautionary level” for the whole population, or about 3.3 per cent of the “permissible level” for the whole population. The levels were set by the British Medical Research Council, and the report emphasised that their levels referred to continuous lifetime exposure.

Caesium-137 in milk was less than .6 per cent of the permissible level for the whole population. Increases in the radioactivity of air were detected at all measuring stations, the highest levels being recorded at Nandi, Fiji, on September 17, and at Rarotonga on October 9.

Increased radioactivity in rainwater was shown in samples from 12 Pacific islands and from Greymouth and Christchurch. The high-

est levels were at Apia, Samoa, during the week. September 13-20, and at Niue. The report says the highest weekly total beta activity in rainwater occurred at Apia. The level during this week was between four and five times the permissible level for continuous consumption.

“Measurements on subsequent weekly rainwater samples from Apia now make possible the calculation of the average concentration of fission products in rainwater over longer periods,” the report said. For rainwater, the average concentration over the entire collection period—July 1 to November 29—was approximately one third of the maximum permissible concentration for continuous consumption.

The highest monthly average of radioactivity in air was 1.5 per cent of the permissible level for continuous breathing by the entire population.

Referring to iodine-131 in milk, the report said if the highest level measured in New Zealand milk, at Invercargill on October 19 and Wellington on October 24, were maintained over the entire year, this level would be 18 per cent of the acceptable level for any age group. In fact, it was maintained only during a few days.