Letter to the editor

Abstract

The possible effect of the impact of radiation exposures from nuclear testing and Chernobyl fallout on the male to female ratio at birth (M/T) has been questioned in a letter to the editor. Social factors have been mooted as possible causes. However, due to historical timings of availabilities of technologies that permitted antenatal sexing, these factors cannot explain the statistically significant global changes in M/T (involving 94.5% of births studied) which included a uniform reduction in M/T between the early 1950s to the late 1960s, followed by an increase to the mid-1970s, with a subsequent decline. The rise in M/T in the mid-1970s was thus transient and superimposed on an overall declining trend, and occurred shortly after an upsurge of nuclear bomb tests just before 1963, when the Partial Nuclear Test Ban Treaty was signed, prohibiting above-ground atomic bomb testing. The nuclear tests led to a global increase in radiation levels. The increase in background radiation due to atomic tests alone in 1962 and 1963 added approximately an additional 0.11 mSv of exposure per year worldwide (5% of the average background dose from all sources). After 1963, global background radiation levels fell progressively, down to 0.005 mSv per year by the year 2000. The rise and fall of M/T therefore occurred in temporal association with the spike in atomic bomb tests. However, this author also acknowledges that several factors may have played an interacting role in the observed trends, and not only radiation.