Artificial radioactivity in the vicinity of St. Marianna University School of Medicine after the Chernobyl reactor accident

Following the Chernobyl reactor accident on April 26, 1986, rain water and atomospheric dust were monitored for their possible contamination by artificial radionuclides on the roof of the building of our medical school from April 30 through June 8, 1986. Radiological monitoring was also performed on cabbages obtained from a nearby field, city water, cow's milk produced in Kanagawa Prefecture and human milk obtained from a volunteer living in Kawasaki. Our campus and the nearby area were exposed to 131I from May 2 through 22 by rainfall and from May 1 through 15 by atomospheric dust. In particular, rain water on May 4 and May 5 contained 7600 pCi (282 Bq)/l and 6000 pCi (222 Bq)/l, respectively. The cabbage specimen obtained on May 7 was contaminated by 131I with 808 pCi/kg wet weight, but another specimen obtained on June 6 was not contaminated by any detectable amounts of 131I. No radioactivity was detected in city water during the period monitored. Cow's milk and human milk contained, as a total of β-radioactivity, 1412 pCi (52 Bq)/l and 915 pCi (34 Bq)/l, respectively. However, parallel determinations on their potassium concentrations revealed that these radioactivities were due entirely to natural 40K. The degree of radiological contamination in and around our campus following the Chernobyl accident was mostly below the action levels above which the governments of several countries involving Japan would take preventive measures against possible radiation damages. Although 131I radioactivities contained in the rain water of the first week of May, 1986 significantly exceeded the action level for this radionuclide, their effects on human health were considered negligible and undetectable in the vicinity of our school. (author)