Volcanic environments and thyroid disruption - A review focused on As, Hg, and Co

The purpose of this review is to explore the link between volcanic environments and thyroid disruption, with focus on the role played by As, Hg, and Co. Volcanoes are the most well-known source of natural pollution, enriching the environment in hazardous elements. It is estimated that about 10 % of world population lives near active volcanoes (Brown et al., 2015). There is evidence supporting a link between living in volcanic environments and thyroid cancer, but it is likely that other types of thyroid disruption are also exacerbated in the populations inhabiting volcanic areas. Arsenic (As) and mercury (Hg) are elements with toxic properties that are present in volcanic environments. Cobalt (Co), which is also present in these environments, is part of the essential cobalamin vitamin (B₁₂). However, exposure to non-cobalamin Co can pose health risks. The effects of these three elements on the thyroid are understudied. A review of 125 publications retrieved from the Web of Science, PubMed, and Scopus databases, covering year 1955 to present, was performed. The known molecular mechanisms underlying thyroid disruption by these elements are discussed. It was found that thyroid cancer incidence, but also that of hypothyroidism are heightened in populations living in volcanic environments, particularly in Iceland, Hawaii, and Italy. Knowledge gaps regarding (i) thyroid disruption in areas with non-eruptive active volcanism, (ii) the toxic effects of As, Hg, and Co on the thyroid, and (iii) the incidence of hypothyroidism and other thyroid pathologies in volcanic environments are highlighted. The need to monitor the population of volcanic areas in terms of health is accentuated.