Radioiodine in the Biosphere during 1968

Abstract

THE northern and southern hemispheres were contaminated with iodine-131 during 1968. Most of the contamination correlated with announced tests of nuclear weapons in the atmosphere, but some additions of ¹³¹I have not been accounted for. Thyroid glands have been collected continuously in various parts of the world for the past 16 yr, and at regular intervals between ten and twenty fresh glands have been preserved in paraformaldehyde and received at this laboratory within 2–8 days of slaughter. The gamma emission between 0.30 and 0.40 MeV has been measured with a coefficient variability of ±20 per cent for radioactivity less than 0.6 pCi/g and ±5 per cent for activity more than 1.5 pCi/g. The total weight of non-goitrous bovine thyroids averaged 15.8 g and the ovine glands 1.7 g. The bovine thyroids from Colombia were, on average, 490 per cent larger than those from areas free from goitre and the sheep from New Zealand had thyroids 50 per cent larger than the other sheep. The average concentration of ¹³¹I was expressed as pCi/g of thyroid and the accumulated data are shown in Fig. 1.