Analysis Method Of Iodine In Drinking Water And Urine And Its Significance On Human Iodine Nutritional Status Assessment

Iodine is an essential trace element of human, more than 90% of the iodine intake by urine excretion, and urinary iodine is the most widely used human iodine nutritional status measure target. Water is an important way of human iodine intake,which was considered as accounting for about 10% of the body iodine intake traditionally. National standard methods(WST 107-2006) and(GBT 5750.5-2006)use arsenic cerium catalytic spectrophotometry(S-K method) analysis iodine content in urine and drinking water, but this method has some disadvantages, it will influence the scientific assessment of human body’s iodine nutritional status.In this paper, main conclusions are as follows:(1) Urine samples will be diluted 10 times which use ICP-MS as analysis instrument, Rh(103) as internal standard and ultrapure water as thinner. And this way will get the bset standard deviation and sample added recovery rate, hence it can get more accurate urinary iodine value.(2) S-K method is used to analysis the urinary iodine content lower than the ICP-MS method on average 46.2%. The two methods differences of urinary iodine test values may be due to the following reasons: 1. In S-K method, organic iodine digestion is not completely; 2. In digestion process, the urinary organic iodine may have volatilization.(3) Compared with ICP-MS method, urinary iodine content value is lower which is analyzed by the S-K method the WHO recommended, however urinary iodine as the most widely used indicators of the human body iodine nutritional status,inaccurate analysis will influence the scientific assessment of iodine nutritional status, and the partition interval value from iodine deficiency to excess through the urinary iodine value analyzes by S-K method WHO recommended should be review.This may seriously hampered the science formulation and correct execution of iodine intervention policy.(4) Compared with ICP-MS method, iodine content value in tap water, water source and atmospheric precipitation is lower which is analyzed by the S-K method.A large number of sample analysis results indicated that organic iodine in water accounts for a considerable part of total iodine, and this conclusion is confirmed by HPLC-ICP-MS. From theoretical analysis and practical experiments S-K method cannot analyze the total iodine in water samples.(5) The iodine in ground water samples which were supplied by countryside drilling wells is natural iodine, this one is generally thought to have a better biological availability. The direct drinking water samples were collected in natural state which were used in this experiment have 26.9% to 100%(average 59.27%)iodine that cannon be detected by S-K method, so in our country which drink the untreated natural water, the beneficial iodine intake is underestimated.(6) The iodine in tap water samples which were supplied by water distribution system have 72.6% to 100% iodine that cannon be detected by S-K method. This part of iodine may be organic iodine and may be not the beneficial one to human body. It should be iodine disinfection by-products, its toxicity is much higher than other disinfection byproducts, and belong to the material of "mutagens, teratogens and carcinogens". This type of organic iodine cannot be analyzed by the Standard examination methods for drinking water – Normal parameters, but along with the gradually increased kinds of drinking water quality index, this kind of material will soon become an important focus areas of drinking water safety, so the traditional national standard method underestimates its harmfulness to human body, in the future, this analysis method will not be recommended when establish analysis method of iodine in drinking water.