Temporal and spatial variation characteristics of environmental iodine elements in the Gansu region, China

Objective This study investigates the spatiotemporal variation of iodine concentrations in drinking water and soil across Gansu Province, aiming to generate observational evidence for adjusting iodine deficiency disorder (IDD) prevention strategies, given inherent methodological limitations of historical unpaired cross-sectional surveys. Methods We collected data on water iodine from four surveys (1972, 1985, 2014, and 2017) and soil iodine from two surveys (1985 and 2014) in Gansu Province, along with related information. These data were analyzed to examine trends in iodine levels across different time periods, watersheds, and geomorphological types. Results Water iodine concentrations consistently followed the order: Yellow River > Inland River > Yangtze River at the watershed level, and Longdong > Longzhong > Hexi > Longnan at the regional level, with consistent distribution patterns across both watersheds and regions.Water iodine concentrations exhibited temporal fluctuations across survey rounds, with relatively lower iodine medians observed in recent surveys; these apparent shifts may partly stem from sampling heterogeneity rather than genuine environmental change. However, due to the unpaired sampling design and methodological variability across surveys, these findings should be interpreted as observational patterns rather than definitive causal trends.Soil iodine content in Hexi and Longnan decreased significantly, and soil iodine content in other regions did not change significantly. Conclusions Persistent environmental iodine deficiency was observed across all surveys in Gansu's hydrological systems, with temporal fluctuations that suggest potential changes warranting further investigation.The pronounced reduction of topsoil iodine observed in arid inland basins may indicate possible shifts in biogeochemical cycling, although analytical or sampling artifacts cannot be fully excluded. Critical knowledge gaps persist regarding atmospheric iodine fluxes, necessitating integrated air-water-soil monitoring systems to elucidate complete iodine ecodynamics. Our observational findings underline that future paired-site monitoring, including atmospheric iodine measurements, is required to fully disentangle regional environmental iodine cycling.