Vegetables such as celery, beets, spinach and lettuce are often high in nitrates, according to the Agency for Toxic Substances and Disease Registry. Nitrates are also used in meat products, such as sandwich meats and hot dogs, as a preservative and to enhance color. Contaminated water is another dietary source of nitrates.
While vegetables are not the normal source of nitrate toxicity in adults, they provide up to 80 percent of the nitrates in the typical diet, explains the Agency for Toxic Substances and Disease Registry. Parsley, fennel, Chinese cabbage, leeks and endive are also high in nitrate contribution to the diet. Infants and unborn babies are particularly susceptible to nitrate toxicity. While babies require only breast milk or formula before six months, parents should avoid homemade vegetable-based baby foods before three months due to the potential toxic effect. Additionally, parents should avoid using well water that is high in nitrates for preparing baby formula.
In nature, microbial action converts nitrogen-containing organic material into ammonia, notes the Agency for Toxic Substances and Disease Registry. Ammonia breaks down to nitrites and nitrates. However, nitrites are easily oxidized and quickly develop into nitrates. Human and animal waste, along with nitrogen-containing fertilizers, cause nitrogen contamination of the soil. Nitrates are generally water soluble and dissolve in groundwater, which then transports the chemical to vegetables.