Many smart friends soak kelp for a long time before cooking to remove the toxic element arsenic. Now, it seems this practice may not be scientific.
First, it must be clarified whether kelp contains "arsenic"? Arsenic is widely present in the environment, plants, and animals in nature. Aquatic organisms, especially marine life, have a strong ability to enrich arsenic. Generally, sea fish contain 1.1 mg/kg of arsenic, lobster 70 mg/kg, and kelp 35-40 mg/kg. Of course, the degree of pollution varies in different sea areas, and so does the arsenic content.
Elemental arsenic is non-toxic, but arsenic compounds such as oxides, salts, and organic compounds are toxic. Arsenic is a trace element in the body and plays a certain role in human cell metabolism, but long-term excessive intake can lead to chronic poisoning. Arsenic in the human body mainly exists in the form of arsenious acid and is mainly excreted through the kidneys and intestines. The normal arsenic content in human blood is 0.0064 mg/100 ml, and urinary arsenic is <0.5 mg/liter. The World Health Organization has provisionally set the maximum allowable daily intake of arsenic at 0.05 mg/kg of body weight.
The common pathways of arsenic contamination in food are: ① pollution from industrial hazardous substances; ② pollution from arsenic-containing pesticides; ③ pollution during food processing; ④ pollution from containers, etc. The arsenic in kelp is mainly caused by seawater pollution. Therefore, from a safety perspective, it is essential to wash kelp thoroughly. After soaking kelp in water, arsenic and arsenic compounds dissolve in the water, and the arsenic content will be greatly reduced. Use plenty of water for soaking, or change the water once or twice. As for the soaking time, it is not absolute and is closely related to the texture and arsenic content of the kelp. If the kelp is tender and has low arsenic content, the soaking time should not be too long; if the texture is hard and the arsenic content is high, the soaking time can be relatively longer. However, since it is difficult to visually determine the amount of arsenic, a soaking time of about 6 hours is generally sufficient. Soaking for too long can also cause water-soluble vitamins, inorganic salts, and other nutrients in the kelp to dissolve in the water, reducing its nutritional value.