Here is some information on Nitrite poisoning:
The following information on nitrite toxicity is from "GRAS (Generally Recognized as Safe) Food Ingredients: Nitrates and Nitrites (Including Nitrosamines)," 1972. This report was prepared for the U.S. Food and Drug Administration (FDA) by Battele-Columbus Laboratories and Department of Commerce, Springfield, VA 22151.
According to this source, the fatal dose of potassium nitrate for adult humans is in the range of 30 to 35 grams consumed as a single dose; the fatal dose of sodium nitrite is in the range of 22 to 23 milligrams per kilogram of body weight. Lower doses of sodium or potassium nitrate or sodium nitrite have caused acute methemoglobinemia (when hemoglobin loses its ability to carry oxygen), particularly in infants, resulting from conversion of nitrate to nitrite after consumption. There is no confirmable evidence in the literature on the carcinogenicity (cancer-causing capacity) of nitrate as such.
It has been reported that people normally consume more nitrates from their vegetable intake than from the cured meat products they eat. Spinach, beets, radishes, celery, and cabbages are among the vegetables that generally contain very high concentrations of nitrates (J. Food Sci., 52:1632). The nitrate content of vegetables is affected by maturity, soil conditions, fertilizer, variety, etc. It has been estimated that 10 percent of the human exposure to nitrite in the digestive tract comes from cured meats and 90 percent comes from vegetables and other sources. Nitrates can be reduced to nitrites by certain microorganisms present in foods and in the gastrointestinal tract. This has resulted in nitrite toxicity in infants fed vegetables with a high nitrate level. No evidence currently exists implicating nitrite itself as a carcinogen.
To obtain 22 milligrams of sodium nitrite per kilogram of body weight (a lethal dose), a 154-pound adult would have to consume, at once, 18.57 pounds of cured meat product containing 200 ppm sodium nitrite (because nitrite is rapidly converted to nitric oxide during the curing process, the 18.57 pound figure should be tripled at least). Even if a person could eat that amount of cured meat, salt, not nitrite, probably would be the toxic factor.