After soaking dried kelp for at least 24 hours, the iodine content in kelp silk is very high, which is very beneficial to health. However, most of the dried kelp we bought in the sales market is due to seawater pollution and high arsenic content, so we should be more careful when eating it. Arsenic and arsenic compounds are generally harmful and can cause subacute and diffuse arsenic poisoning. Therefore, countries all over the world have strict requirements on the composition of arsenic when formulating food quality standards.

In China, the arsenic content in food and grain should not exceed 0.7 mg/kg; Vegetable oil shall not exceed 0.1mg/kg; Sauce, soy sauce, chicken essence, edible salt and cold food shall not exceed 0.5mg/kg. The World Health Organization (WHO) requires the daily allowable intake of arsenic to be 0.05 mg/kg of static body weight. The arsenic content of dried kelp has already greatly exceeded the above standards.

After soaking for 5- 10 hour, the arsenic content in dried kelp still reached 5 mg/kg. After soaking for 24 hours, its arsenic content can reach the standard of taking test. Therefore, before we eat dried kelp at home, we'd better soak it for a while and change the water in the fish tank frequently.

After long-term soaking, the nutritional components of kelp were destroyed to some extent. Among them, vitamin b2 1 and nicotinic acid can damage some of them. Nutritional elements and mannitol with dietotherapy effect are more harmful; Iodine can also cause some harm. However, this will not have a great impact on the nutritional components of kelp. Because of the high iodine content in kelp silk, even if some of it is damaged, it can still fully supplement the body; Mannitol is a drug for treating brain edema and Japanese encephalitis, but it has little effect on people who are physically and mentally healthy.