title: Assessment of spatial variation in drinking water iodine and its implications for dietary intake: a new conceptual model for Denmark.
abstract: Iodine is essential for human health. Many countries have therefore introduced universal salt iodising (USI) programmes to ensure adequate intake for the populations. However, little attention has been paid to subnational differences in iodine intake from drinking water caused by naturally occurring spatial variations. To address this issue, we here present the results of a Danish nationwide study of spatial trends of iodine in drinking water and the relevance of these trends for human dietary iodine intake. The data consist of treated drinking water samples from 144 waterworks, representing approx. 45% of the groundwater abstraction for drinking water supply in Denmark. The samples were analysed for iodide, iodate, total iodine (TI) and other major and trace elements. The spatial patterns were investigated with Local Moran's I. TI ranges from <0.2 to 126 μg L(-1) (mean 14.4 μg L(-1), median 11.9 μg L(-1)). Six speciation combinations were found. Half of the samples (n = 71) contain organic iodine; all species were detected in approx. 27% of all samples. The complex spatial variation is attributed both to the geology and the groundwater treatment. TI >40 μg L(-1) originates from postglacial marine and glacial meltwater sand and from Campanian-Maastrichtian chalk aquifers. The estimated drinking water contribution to human intake varies from 0% to >100% of the WHO recommended daily iodine intake for adults and from 0% to approx. 50% for adolescents. The paper presents a new conceptual model based on the observed clustering of high or low drinking-water iodine concentrations, delimiting zones with potentially deficient, excessive or optimal iodine status. Our findings suggest that the present coarse-scale nationwide programme for monitoring the population's iodine status may not offer a sufficiently accurate picture. Local variations in drinking-water iodine should be mapped and incorporated into future adjustment of the monitoring and/or the USI programmes.
authors: Department of Geoscience, Aarhus University, Høegh-Guldbergs Gade 2, DK-8000 Aarhus C, Denmark; Geological Survey of Denmark and Greenland (GEUS), Lyseng Allé 1, DK-8270 Højbjerg, Denmark; Geological Survey of Denmark and Greenland (GEUS), Øster Voldgade 10, DK-1350 Copenhagen K, Denmark. Electronic address: ddv@geo.au.dk.
authors: Denitza Dimitrova
authors: DD
authors: Voutchkova
authors: Geological Survey of Denmark and Greenland (GEUS), Øster Voldgade 10, DK-1350 Copenhagen K, Denmark.
authors: Vibeke
authors: V
authors: Ernstsen
authors: Geological Survey of Denmark and Greenland (GEUS), Lyseng Allé 1, DK-8270 Højbjerg, Denmark.
authors: Birgitte
authors: B
authors: Hansen
authors: Geological Survey of Denmark and Greenland (GEUS), Lyseng Allé 1, DK-8270 Højbjerg, Denmark.
authors: Brian Lyngby
authors: BL
authors: Sørensen
authors: GIS Centre and School of Geography and Archaeology, National University of Ireland, Galway, Ireland.
authors: Chaosheng
authors: C
authors: Zhang
authors: Department of Geoscience, Aarhus University, Høegh-Guldbergs Gade 2, DK-8000 Aarhus C, Denmark.
authors: Søren Munch
authors: SM
authors: Kristiansen
mesh_terms: D000293:Adolescent; D000328:Adult; D003718:Denmark; D060766:Drinking Water / Q000737:chemistry*; D004781:Environmental Exposure / Q000706:statistics & numerical data*; D060587:Groundwater / Q000737:chemistry; D006801:Humans; D007455:Iodine / Q000032:analysis*; D008962:Models, Theoretical; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D060766:Drinking Water; D014874:Water Pollutants, Chemical; D007455:Iodine
keywords: Dietary iodine intake; Iodate; Iodide; Iodine; Local Moran's I