First, it must be clarified whether kelp contains "arsenic"? Arsenic is widely present in nature, as well as in plants and animals. Aquatic organisms, especially marine life, have a strong ability to concentrate arsenic. Generally, sea fish contain 1.1 mg/kg of arsenic, lobsters 70 mg/kg, and kelp 35-40 mg/kg. Of course, the degree of contamination 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. However, 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 include: ① contamination from industrial hazardous substances; ② contamination from arsenic-containing pesticides; ③ contamination during food processing; and ④ contamination from containers. The arsenic in kelp is mainly caused by seawater pollution. Therefore, from a safety perspective, kelp must be thoroughly washed before consumption. After soaking 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, as it is closely related to the texture and arsenic content of the kelp. Soaking time should not be too long for tender kelp with low arsenic content; for kelp that is hard and has high arsenic content, the soaking time can be relatively longer. However, since the amount of arsenic is difficult to judge with the naked eye, soaking for about 6 hours is generally sufficient. This is because if the soaking time is too long, the nutrients in the kelp, such as water-soluble vitamins and inorganic salts, will also dissolve in the water, reducing its nutritional value.