Recently, a claim has been widely circulating on friends' WeChat Moments, stating that steamer water contains a large amount of nitrite, and that accidentally drinking it can cause cancer. Is this really true? Steamer water refers to the water used to steam buns. According to China's "Sanitary Standard for Drinking Water" (GB5749-2006), the nitrate content in drinking water should be ≤10 mg/L (limited to ≤20 mg/L for groundwater sources), and the nitrite content should be ≤1 mg/L. The presence of trace amounts of nitrates and nitrites in drinking water is permitted.
If water is heated and boiled for a long time or for too long, nitrates can decompose into nitrites, or heavy metals such as lead may remain in the steamer water. Nitrites pose two types of harm to the human body. Firstly, nitrites can oxidize the normal low-iron hemoglobin in human blood, which carries oxygen, into methemoglobin, which cannot bind with oxygen, causing the body to become hypoxic. Secondly, nitrites can cause blood vessels to dilate, leading to a drop in blood pressure; in severe cases, it can cause collapse.
It is worth noting that nitrites themselves are not carcinogenic. They only become carcinogenic when converted into N-nitroso compounds. Therefore, the claim on WeChat that nitrites are a strong carcinogen is pure nonsense.