Geographical distribution of trace elements (selenium, zinc, iron, copper) and case fatality rate of COVID-19: a national analysis across conterminous USA

Supplementary Information The online version contains supplementary material available at https:// doi. org/ 10. 1007/ s10653-022-01204-0. by Rural-Urban Continuum Code) was considered for adjustment as a confounding factor in the final statistical modeling, as well as other county level variables including population characteristics and socialdemographics. Concentrations of trace elements at the county level were the only data from the National Geochemical Survey. Additional information, such as other parameters of samples that determine the bioavailability of the analyzed elements, was not available. Many other variables (such as food source and details of health care service), which differ among counties, were also not available, which became one obvious limitation of this study. We did not study the incidence rate (i.e., the percentage of cases among the total population) of COVID-19. As a disease of high contagion, the incidence of COVID-19 should be more related to population characteristics (e.g., age, comorbidity) and density, living environment (e.g., urban vs. rural area) and condition, ways of transportation, All authors contributed to the study design and interpretation of the data, and all authors approved the final version of the manuscript submitted for publication. Funding No funding was received for conducting this study. Declarations Conflicts of interest The authors declare that they have no known competing financial interests or personal relationships..