TRITIUM INTAKE BY EXPOSURE TO PLASTIC CASE WATCHES

In recent years tritium has been used in plastic case watches as perma nent light sources on watch dials. To measure the release of tritium t hrough the plastic cases, 82 different waterproofed watches were immer sed in a water bath for 24 h, and the tritium concentration of the wat er was measured, The mean tritium release rate was 24,400 Bq d(-1) ran ging from 110-162,000 Bq d(-1). Parallel measurements were made to det ermine the tritium concentration in the urine of 108 wearers of plasti c case watches, The mean tritium concentration in urine was 197 Bq L(- 1) up to 1,133 Bq L(-1). The whole body dose resulting from exposure t o plastic case watches is negligibly small but given the pathway of sk in absorption, the annual skin dose is 3-4 times higher than the dose limit for the public, Plastic case watches are collector's items and a re often kept with other watches in glass cabinets or other containers , Storage of a large number of such watches in one container causes tr itium to diffuse through the plastic cases and to contaminate watches that did not contain tritium at first, If the container is more or les s airtight, the tritium concentration in the container and the tritium release rate from the watches can reach levels up to 4 MBq d(-1).