Results of a thyroid monitoring survey carried out on workers exposed to 125I in São Paulo, Brazil.

The thyroids of 30 workers performing routine 125I labelling in several laboratories of the city of São Paulo have been monitored about once every 2-3 mo from November 1985 to October 1986. Twenty-five of them presented a significant radioactivity (in our detection system greater than 62 Bq), but none reached the maximum permissible thyroid burden. The maximum measured thyroid contamination is 24 kBq (650 nCi). The uptakes were determined by comparison with a standard curve obtained by placing various calibrated standard sources of 125I in a thyroid neck phantom. The paper also describes the set up of quality controlled counting conditions, with high sensitivity, precision, accuracy and stable detector efficiency, by adaptation of an old equipment to this purpose. Calculated 125I effective half-lives for five individuals ranged between 31.7 and 47.0 d, the average being 39.4 +/- 6.1 d.