3.5 FACTORS INFLUENCING THE SEVERITY OF SKIN LESIONS 3.5.1 ‘Phe Characteristics of the Fallout Material The fatloat material was composed inamly of calehumn oxide from coral, with adherent (is sion products, The skin lestongs observedtwere undoubtedly (he resull primarity of beta bandit tron from fallout material deposited on tre skin, with mintnal or no contribution Crom chenmbeal Irritation. “The yaminia dose ¢o the skin was small compared tu Che beta dase, and thus wis relatively untmportant in producing the lesions. 3.5.2 Energy of Beta Particles From available data on the fallout material it has been calculated that 50 to 80 per cent of the beta rays during the exposure pertod were soft with an average energy of about 100 kev. Since 80 microns of tissue pggguces 50 per cent attenuation of such radiation,! the greater portion of energy was sisoaiea in the epithelium which is roughly 40 to 70 microns in thickness. The remaining 20 to 50 per cent of the beta rays were of higher energy, with an average of approximately 600 kev. The latter would penetrate well into the dermasince if takes 800 microns of tissue to produce 50 per cent attenuation.!? In addition, a wide spectrum of gamma energies irradiated the skin. Approximately 10 per cent of the total gamma spectrum was below 80 kev which would be absorbed largely in the superficial layers of the skin. The remainder of the gamma spectrum is distributed between 100 and 1600 kev with a large proportion between 600 and 800 kev. 3.5.3) Physical Dose to the Skin There 18 no practical way to estimate the physical dose tu the areas of skin where Jesions were found, The entire surface of the body of the Rongelap group received approximately 175 r from gamma irradiation derived from fission products distributed on the ground, trees, and buildings. To this 175 r would have to be added the beta component. In view of the high beta to gamma ratio in fission products, one might expect the total beta surface dose to the skin to be large. The maximal skin doses from the plane field of radiation are estimated in chapter 1. To these duses must be added the contribution of the material deposited on the skin. The latter can not be calculated, or estimated biologically with any degree of accuracy. A rough approximation of dose received at the hair follicles can be made as follows: The hair follicles must have received a dose comparable to the known minimal epilating dose of about 400 r for 200 kvp X-rays. Since regrowth of hair occurred, the upper limit of dose at the depth of the hair follicle must not have exceeded the permanent epilating dose of around 700 r of 200 kvp X-ray. 3.5.4 Protective andAggravating Factors The individuals who remained indoors or under the trees showed someprolection as compared to those who were in the open during the period of the fallout. Those who went swimming or bathed were also protected to varying degrees. Small children who went wading developed fewer foot lesions. Clothing, even a single layer of cotton material, offered almost complele protection, as was demonstrated by the fact that lesions developed almost entirely on the exposed parts of the body. Since the lesions predominate in areas where perspiration ig abundant such as folds of the neck, axillae, and antecubital fossae, it seems likely that the abundant perspiration produced “by a hot, humid climate tended to cause the material to concentrate and adhere tu these areas. In addition, the coconut oil hair dressing used by the Marshallese acted as an effective collecting agent for the radioactive material. This was proved since the hair was the most highly contaminated part of the body. The concentration of radioactive material on the hair may have been responsible for the large number of scalp lesions, epilation and the large number and severity of neck lesions in women. 41 ee