LAUSR

Cadmium is a toxic, bioaccumulating, non-essential, and highly persistent metal, making up 0.1 parts per million (ppm) of the Earth’s crust, with ubiquitous exposure to the population [1]. No significant deposits of cadmium-containing ores are known, though it is commonly associated with zinc, lead, and copper in the forms of complex oxides, sulfides and carbonates [2]. Historically, its exposure has been proportional to its occurrence in the environment. As a trace element, exposure was limited. However, the use of cadmium in manufacturing has increased sharply over the last century and has significantly altered the exposure risk for this otherwise rare element [3]. Dietary sources are the most common route for non-occupationally exposed individuals, with cigarette smoke doubling the amount found in the body [4]. The estimated biological half-life of this metal is 10–30 years with a fraction of the inhaled or ingested amount sequestered, primarily in the kidneys, liver, and muscle [5]. At present, there is no evidence that humans have developed any specialized system to handle this non-essential element, compounding any potential risk associated with exposure. Rather, cadmium uptake, transport, and absorption are linked to metal transporters whose primary function is for physiologically essential metals, such as calcium, iron and zinc [6]. Recently, a decline in urinary cadmium levels has been reported from sequential, national, cross-sectional populationbased data (i.e. National Health and Nutritional Exposure Study). This decline has been attributed to a reduction of smoking prevalence but not to a reduction in dietary sources [7]. In contrast, the prevalence of cadmium exposure in the U.S. adult population remains high at over 90% [8]. Consequently, even a small increase in its exposure can result in a large number of women affected. Among workers, several industries, such as the nickel-cadmium battery industry, pigment manufacturing, zinc/cadmium refining, and lead smelting, have been identified as places for increased exposure, commonly from inhalation [9]. The International Agency for Research on Cancer (IARC) designated cadmium as ‘carcinogenic to humans’ (group 1) primarily based on an increased lung cancer risk among occupationally exposed workers [2]. Data from non-occupationally exposed populations suggests that its exposure may increase the risk of kidney cancer, prostate cancer, and female breast cancers, as well as other adverse effects [10]. Most recently, higher levels have been implicated in elevating the risk of endometrial cancer [11], though risk for gynecological cancers needs further exploration.