Iodine content in centralized water supply projects in Gansu Province in 2014

Objective To investigate the scope and distribution of water iodine in centralized water supply projects, and provide a basis for taking appropriate control measures in Gansu Province. Methods Collected 2 copies of water samples of all the different water supply of centralized water supply project water in the province's 87 counties (cities, districts), the source water iodine of all centralized water supply projects was tested by the method of cerium sulfate catalytic spectrophotometry. The relationship between different water types and different iodine levels in deep well water were analyzed. Results Of the total 1 563 centralized water supply projects, the median of water iodine was 6.38 μg/L, the range was 0.00-182.10 μg/L, the rates were 62.0% (969/1 563), 30.1% (471/1 563), 6.9% (108/1 563), 0.5% (7/1 563) and 0.5% (8/1 563) in water iodine level of < 10, 10-< 50, 50-< 100, 100-< 150 and ≥ 150 μg/L. The surface water was 26.7% (418/1 563), the median of water iodine was 4.42 μg/L, the groundwater was 73.3%(1 145/1 563), the median of water iodine was 8.10 μg/L, the iodine content of surface water was lower than that of the groundwater (Z=-10.089, P < 0.01); in surface water, the rate of river, lake, reservoir and other water source was 55.7% (233/418), 7.7% (32/418), 21.5% (90/418) and 15.1% (63/418), and the median was 2.52, 31.10, 6.65 and 5.40 μg/L, the iodine content between surface water and water sources of different water sources was significant different (χ2= 179.976, P < 0.01); in the groundwater, the rate of deep well, shallow well and spring was 55.5% (635/1 145), 41.3% (473/1 145) and 3.2% (37/1 145), and the median was 17.90, 3.66 and 4.18 μg/L, the iodine content in groundwater from different sources was significant different (χ2= 357.346, P < 0.01). Iodine content of different well depth was significantly different (χ2= 288.959, P < 0.01), there was a positive correlation between iodine content and well depth (r= 0.364, P < 0.01). Conclusions Iodine content of the surface water is generally lower in many water types in Gansu, iodine content is higher in deep well, and there is high iodine deep well water in local areas. It is recommended that water iodine be included in the population iodine nutrition assessment index. Key words: Iodine; Centralized water supply; Data collection