I heard that sodium nitrate (in Costco turkey bacon, for example) may have catastrophic effects on the body. What is the purpose of the nitrate bond, especially when in contrast with NaCl? Is it a preservative? Are the damages actually not very likely, or are they highly common?
Sodium nitrate (chemical symbol NaNO3) and the related molecule, sodium nitrite (chemical symbol NaNO2) are sometimes used to prevent food poisoning and act as food color enhancers in products like bacon, ham, hot dogs, some lunch meats and smoked fish. The issue is that when heated (as in frying a food), sodium nitrite can form compounds called nitrosamines, many of which are carcinogens (i.e., cause cancer). Most of this evidence, however, stems from animal research. How much nitrosamines cause human cancer is unknown, but most experts feel it’s prudent to limit exposure. This is especially true in pregnant women. Heating these compounds seems to be the issue because these nitrates are found in many healthy foods. For example, nitrates are found in fruits and vegetables. The Center for Disease Control estimates that 70 percent of the nitrates we get in our diet come from vegetables. Vegetables don't cause cancer – they help prevent it! Fortunately, for processed meat lovers, vitamin C stabilizes sodium nitrate. In the US, vitamin C is added to sodium nitrate to reduce nitrosamine formation. If you check the bacon you mentioned, you will probably also see vitamin C (ascorbic acid) or another compound called erythorbic acid listed in the ingredients list. Both reduce nitrosamine formation.
The chemical bonds between sodium nitrate and sodium chloride are different. The bond holding sodium chloride (NaCl) together is called an ionic bond and is formed between two elements that are oppositely charged (Na is positively charged while Cl is negatively charged). In this instance, one element holds the electrons that make up the bond more tightly than the other element. With respect to sodium nitrate, it’s a little more complicated. The Na portion (sodium) is bonded to the nitrate portion via an ionic bond. The nitrate molecule (NO3), however, is actually held together via a covalent bond. A covalent bond occurs when the molecules holding the compound together actually share the electrons that make up the chemical bond. It’s not that the bonds themselves act as a preservative. Rather, the molecule sodium nitrate preserves food by inhibiting food poisoning (botulism).