Altered sex ratio at birth after installation of a tap-water supply system in an arseniasis-endemic area in southwestern Taiwan

Sex ratio at birth (SRB) is a simple, noninvasive way to monitor population reproductive health. Some metals might function as endocrine-disrupting chemicals (EDCs) with known estrogenic or androgenic effects and were reported to potentially influence SRBs. The metal arsenic (As) is a major risk factor for blackfoot disease (BFD), a peripheral vascular disease, endemic to southwest Taiwan for more than 50 years attributed to residents' consumption of local artesian well water, which contained high levels of this metal. In the early 1960s, a tap water supply system was implemented in BFD-endemic areas. By the mid-1970s, individuals residing in the areas had stopped using artesian well water for drinking or cooking. The aim of this study was to investigate the effects of long-term exposure to As in drinking water on the SRBs. Annual numbers of male and female births were obtained from Taiwan's Department of Household Registration, Ministry of Interior Affairs. Sex ratios at birth were calculated for BFD-endemic areas for the years from 1947 to 2024. Compared to the entire Taiwan, the BFE-endemic area displayed an odds ratio (OR) of 0.9966 (95% CI = 0.9804-1.013) for producing a male child between 1947 and 1980. However, from 1980 onwards, the OR for having a boy was significantly increased in the areas (OR = 1.0311, 95% CI = 1.0114-1.0512) compared to the time residents imbibed water from artesian well water containing high amounts of As (1947-1980). These findings provide increasing evidence that As exposure produced changes in SRBs in Taiwan.