| Objective:The distribution and characteristics of water iodine in Gansu province were studied by analyzing the water iodine level in different regions,different ecological types,different water supply modes and 30-years of change,so as to provide a basis for delimitation iodine deficiency areas and scientific iodine supplementation.Methods:The multi-stage sampling method was adopted.Take the township as sampling unit at the first level,and the administrative villages with the water iodine content?10?g/L as the second level sampling unit.Water sample were collected according to the three water supply modes including unified centralized water supply,partial centralized water supply and dispersed water supply ways.Iodine content of drinking water was detected by the method recommended by the national Iodine Deficiency Disorders reference laboratory.Non-normally distributed measurement data were indicated by median(interquartile range),two independent samples were compared by Mann-Whitney U(Z)test,and multiple independent samples were compared by Kruskal-Wallis H test.Results:(1)8976 water samples were tested in the province,the median water iodine was 2.3?g/L,and the range of iodine level was 0.0~111.4?g/L,water iodine content<10?g/L accounted for 91.1%,8.6%of samples were 10~<50?g/L,0.3%were?50?g/L.A total of 1388 townships were detected,townships of water iodine median<10?g/L accounted for 94.9%,4.8%of townships were 10~<50?g/L,0.3%were 50~<100?g/L,There were no townships of water iodine median?100?g/L.895administrative villages in townships with a median water iodine?10?g/L were detected,429 administrative villages with the median water iodine<10?g/L,accounted for 47.9%.Administrative villages of 10~<50?g/L,50~<100?g/L and?100?g/L accounted for 50.3%,1.2%and 0.6%,respectively.5 administrative villages with water iodine median?100?g/L were Minqin county of Wuwei city.(2)The median water iodine in Desert region,Gobi region,Hilly region,Qinling Gorge region,Grassland Meadow region and Gully region were 4.5?g/L,1.1?g/L,2.5?g/L,1.3?g/L,2.2?g/L,3.8?g/L,respectively.The ratio of water iodine content<10?g/L were 92.2%,96.5%,93.1%,95.6%,99.1%,76.9%,respectively.The median water iodine<10?g/L in the six ecological regions,there was a statistically significant difference in water iodine content between different ecological regions(?~2=1826.310,P<0.05).The water iodine level of Desert region was significantly higher than Gobi region,Hilly region,Qinling Gorge region and Grassland Meadow region(P<0.05).The water iodine level of Gully region was significantly higher than Gobi region,Hilly region,Qinling Gorge region and Grassland Meadow region(P<0.05).There was no statistically significant difference in other ecological regions(all P>0.05).(3)1388 townships were tested in the province,the townships of unified centralized water supply,partial centralized water supply and dispersed water supply accounted for 35.7%,56.3%and 8.0%,respectively.The townships of water iodine median<10?g/L,10~<50?g/L and?50?g/L accounted for 94.9%,4.8%and 0.3%,respectively.895 administrative villages were tested at the second level,the administrative villages of centralized water supply and dispersed water supply accounted for 87.6%and 12.4%.The administrative villages of water iodine median<10?g/L,10~<50?g/L and?50?g/L accounted for 47.9%,50.3%and 1.8%,respectively.Among the different ecological regions,the least dispersed water supply was Desert region,accounting for 10.9%,and the least centralized water supply was Qinling Gorge region,accounting for 0.2%.There was a significant difference of water iodine content in the three water supply modes(?~2=8.923,P<0.05),and the water iodine level distribution was partially concentrated water supply>unified centralized water supply>dispersed water supply(all P<0.05).(4)154 water iodine data of Gansu province in 1985 were collected,the range of iodine level was 0.1~43.0?g/L,and the median value was 3.6?g/L.In 2017,8976water samples were tested,the range of iodine level was 0.0~111.4?g/L,and the total median of water iodine was 2.3?g/L,and the total water iodine content in 2017 was significantly higher than that of 1985(Z=-6.015,P<0.05).The different ecological regions comparison shows that the water iodine level of Hilly region,Qinling Gorge region,Grassland Meadow region and Gully region in 2017 were higher than that of1985(all P<0.05).The water iodine level of Desert region and Gobi region were no significant difference between 2017 and 1987(all P>0.05).Conclusions:(1)Most townships were iodine deficiency areas,and only a few townships were iodine suitable areas.In the townships of iodine suitable,there existed administrative villages with iodine deficiency,iodine excess areas were found in only5 administrative villages of the Minqin county of Wuwei city in Gansu province.There were no iodine excess endemial areas,and the measured range of iodine content varies greatly.(2)Comparative analysis of the six ecological regions shows that the water iodine content was relatively high in Desert region and Gully region,and it were iodine suitable areas,Gobi region,Hilly region,Qinling Gorge region and Grassland Meadow region were iodine deficiency areas.There were no iodine excess areas.(3)The water supply modes of townships and administrative villages were mainly unified centralized water supply and partial centralized water supply ways in Gansu province.Among the different ecological regions,the Desert region was basically concentrated water supply,and Qinling Gorge region was partially concentrated water supply.The water iodine level of different water supply modes shows that partial concentrated water supply>unified centralized water supply>dispersed water supply.(4)Compared with 1985,the iodine deficiency areas decreased in 2017.The water iodine level of Desert region and Gobi region in 2017has not changed,the water iodine level of Hilly region,Qinling Gorge region,Grassland Meadow region and Gully region in 2017 were higher than that of 1985. |
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