can also be present in those vegetables. Concentrations of nitrate in vegetables depend on agricultural practices, storage conditions, the temperature and light in which they are grown, and the concentrations of nitrate in the soil, fertilizers, and water used to grow the vegetables (NRC 1981; Hwang et al. 1994).
The concentrations of nitrate and nitrite in cured-meat products depend on the curing process and on the amounts added as preservatives. Concentrations of nitrite in bacon, for example, can be up to 120 ppm, which is the maximum allowed by law (9CFR 318.7B). Nitrate and nitrite are used as preservatives because of their ability to inhibit the growth of Clostridium botulinum (NRC 1981). Improved manufacturing processes have led to a steady decline in the concentrations of nitrate and nitrite in preserved meats (nitrate is now used only rarely).
Dairy products contain low concentrations of nitrate and nitrite in general, rarely exceeding 5 mg/kg in milk (NRC 1981 ).
Nitrate and nitrite can occur in drinking water as a result of human and other activities. The microbial oxidation of ammonia to nitrate and nitrite is the primary nonhuman source. Inorganic fertilizers and human and animal wastes (from livestock operations and septic tanks) are the primary human sources. Nitrate released to soil can enter groundwater or surface water as a result of leaching or runoff. Nitrate concentrations in groundwater are typically less than 10 mg/L but can exceed that in areas of concentrated human sources. Concentrations of nitrate in surface water seldom exceed 1 mg/L except in areas of severe contamination. The nitrite in groundwater and surface water is negligible compared with the nitrate; in oxygenated waters, nitrite is rapidly converted to nitrate (EPA 1990b).