Population exposures to I-131 releases from Hanford Nuclear Reservation and preterm birth,infant mortality,and fetal deaths

Communities surrounding the Hanford Nuclear Reservation in southeastern Washington were exposed to radionuclides, particularly iodine-131, released during the period 1945 to 1951. This study evaluated whether estimated iodine-131 exposures were risk factors for infant mortality, fetal death, and preterm birth in the years of highest releases, 1945 and 1946. Data on births, fetal deaths, and infant deaths, during the period 1940 to 1950, were abstracted from vital records for an eight county area surrounding the Hanford facility. The analysis included 56,320 births, 1,656 infant deaths, and 806 fetal deaths. The Hanford Environmental Dose Reconstruction project provided iodine-131 dose estimates for the 1,102 grid areas in the study area. The grid areas were collapsed into 4 exposure groups using estimated exposure to iodine-131 during 1945. Each birth and death record was assigned to one of the four grid groups based on mother's residence at the time of birth. Comparisons of preterm birth, infant death, and fetal death rates were made among the grid groupings for the primary exposure period (1945 to 1946) and for other years of the study period (i.e., 1940 to 1944 and 1947 to 1950). In the grid group with the highest estimated iodine-131 exposures, the mother's residence during the latter part of pregnancy was associated with preterm birth (OR = 1.74, 95% CI = 1.09-2.72). An association with infant mortality (OR = 1.26, 95% CI = 0.79-1.97) was suggested. No association was found for fetal deaths. This study found that iodine-131 exposure was associated with increased risk of preterm birth. This finding is biologically plausible because other studies have found that: (1) iodine-131 exposure can cause hypothyroidism, and (2) overt or subclinical hypothyroidism during pregnancy can increase a mother's risk of a preterm delivery.