Marine versus Continental Sources of Iodine and Selenium in Rainfall at Two European High-Altitude Locations

The essential elements selenium (Se)
and iodine (I) are often present
in low levels in terrestrial diets, leading to potential deficiencies.
Marine I and Se emissions and subsequent atmospheric wet deposition
has been suggested to be an important source of I and Se to soils
and terrestrial food chains. However, the contribution of recycled
moisture of continental origin to I and Se to precipitation has never
been analyzed. Here we report concentrations and speciation of I and
Se, as well as of bromine (Br), sulfur (S), and DOC-δ13C signatures for weekly collected precipitation samples (in the period
of April 2015 to September 2016) at two high altitude sites, i.e.,
Jungfraujoch (JFJ; Switzerland) and Pic du Midi (PDM; France). Analysis
of precipitation chemistry and moisture sources indicate combined
marine and continental sources of precipitation and Se, I, Br, and
S at both sites. At JFJ, concentrations of I and Se were highest when
continental moisture sources were dominant, indicating important terrestrial
sources for these elements. Furthermore, correlations between investigated
elements and DOC-δ13C, particularly when continental
moisture source contributions were high, indicate a link between these
elements and the source of dissolved organic matter, especially for
I (JFJ and PDM) and Se (JFJ).