Spatial-temporal Trend Analyses of Infant Mortality Versus Chernobyl Fallout in Switzerland (1969 - 2024): Analysis of a Dose Response Association at the Canton Level View PDF

Infant mortality is an important global socio-medical health indicator [1]. The dramatic decline in infant mortality in Europe over the course of the last century is attributable to modern medicine – particularly neonatology – as well as to improved hygienic and social conditions. Whilst in Switzerland in the 1950s more than 30 per thousand newborns died in their first year of life, this figure now stands at around 3 per thousand [2]. Infant mortality is linked, among other things, to socio-economic status [3], the density of doctors [4], unemployment [5], income [6], urbanization [7], nitrogen dioxide concentrations in the air [8] and lead contamination in the soil (particularly in agricultural land) [9].

The biological effects of IR have been systematically studied for more than 100 years. Depending on the dose, IR leads to deterministic or stochastic changes at the organism, tissue, cell, and subcellular levels [10]. It has been shown that unborn babies, children and women are especially sensitive to radiation [11-13]. It has also been demonstrated that IR causes cancer and impairs reproduction. In the 1920s, Muller [14] landmark findings on the detrimental genetic effects of IR in Drosophila caused a sensation. In the 1950s, Stewart et al. [12] demonstrated a carcinogenic effect in children whose mothers had been exposed to radiological examination of the pelvis during pregnancy. Even then, it was evident that exposure to low doses of IR in the order of magnitude of natural background radiation [15] posed a significant stochastic cancer risk. However, it was not until the turn of the millennium that the scientifically based linear no-threshold model [11] became generally accepted. It states that the radiation risk is proportional to the dose and that there is no harmless dose of radiation, no matter how low it may be. However, one implausible and illogical dogma prevails, namely that detrimental genetic effects in humans have not been demonstrated for radiological exposures below 1 gray (Gy; 1 Joule/kg) [11]. Contrary to this dogma it is reasonable to assume that eggs, sperm, embryos, fetuses, and infants also experience health detriment under elevated environmental radiation as Schmitz- Feuerhake et al. [16] have aptly demonstrated.

A recent large metanalysis of epidemiological studies in varying settings directly supports excess cancer risks from low-dose IR [17]. Wakeford and Bithell [18] confirmed the harmful effects of medical x-ray examinations of the pregnant mother and pointed at the fact of an almost uniformly raised relative risk for nearly all types of cancer that are most frequent in children. Even a radiation dose of around 10 millisieverts (mSv) leads to a 50% increase in cancer risk up to the age of 15. Interestingly, several recent studies have described natural background radiation as a possible risk factor for childhood cancer [13]. Large-scale, census-based cohort studies are needed to obtain reliable results in this complex area [19]. According to observations from Switzerland [20, 21], natural background IR likely contributes to the risk of leukemia and tumors of the central nervous system in children with a population attributable fraction of about 30%. In addition, Little et al. [22] stated in an extensive review that the large body of data relating to in utero and childhood exposure provides support for the existence of excess cancer and benign neoplasm risk associated with radiation doses < 0.1 Gy), and for certain groups exposed to natural background radiation, to fallout and medical X-rays in utero, at about 0.02 Gy.

Radiation-related reproductive disorders have been studied less extensively than radio-induced carcinogenicity. Nevertheless, an increase in stillbirths [23], perinatal mortality [24], infant mortality [25], congenital malformations [26, 27], reduced birth weight [28], increase in trisomy 21 (Down syndrome) [29] and a distorted sex ratio at birth [30, 31] were observed after radiation exposure from radioactive fallout, whether from atomic bomb explosions or civil nuclear accidents. Causality in relation to radiation health effects is known to be the subject of controversial debate, although Hill’s classic criteria [32] are met, at least to a considerable extent. A broad variety of these reproductive pathologies have enhanced exposure to low doses of IR in common.

Recently an unusual ongoing increase in infant mortality in Switzerland was reported [33]: After the Chernobyl accident in April 1986 the infant mortality proportion increased relative to the prevailing monotone secular downward trend from 1950 to 1986. In this ecological study, which covers more than 6’186’000 live births between 1950 and 2022, nearly 2’000 excess infant deaths were identified between 1987 and 2022. The jump OR in 1987 was 1.175 (1.102, 1.253). Given the radioactive contamination of Switzerland from the Chernobyl accident, which amounted to approximately 3’500 person-Sieverts and was mainly due to Cs-137 [34, 35], we aimed at the evaluation of a possible association of the increased radioactive exposure and the increase of infant mortality after 1986. Therefore, an independent review by the Swiss Tropical and Public Health Institute was commissioned. The results were largely confirmed [36], and the authors recommended a detailed analysis of a possible dose-response relationship to clarify arguments for a causal link. Additionally, the review raised some uncertainty regarding the assumption of the specificity of the estimated and tested change-point point in 1986/1987. However, the specificity was sufficiently demonstrated using three independent statistical methods [36] that this point in time is most likely to capture the greatest jump in infant mortality during the whole period from 1950 to 2022 under discussion. We, therefore, investigated – using appropriate correlation and regression methods – if we could demonstrate whether a low dose or low exposure is associated with a slight increase in infant mortality and whether a high dose or high exposure leads to an escalated infant mortality in the 26 cantons of Switzerland experiencing considerably different Chernobyl fallout.