NITRATES AND NITRITES (硝酸盐和亚硝酸盐）

NITRATES AND NITRITES CAS # 84145-82-4, 14797-65-0 Division of Toxicology and Environmental Medicine ToxFAQsTM January 2011 This fact sheet answers the most frequently asked health questions (FAQs) about nitrates and nitrites. For more information, call the ATSDR Information Center at 1-800-232-4636. This fact sheet is one in a series of summaries about hazardous substances and their health effects. It is important you understand this information because these substances may harm you. The effects of exposure to any hazardous substance depend on the dose, the duration, how you are exposed, personal traits and habits, and whether other chemicals are present. HIGHLIGHTS: Nitrates and nitrites occur in soil, in water, and in some foods. They are naturally occurring inorganic nitrogen ions. Nitrates are a natural part of the human diet. When drinking water or eating food from areas containing nitrogen-based fertilizers, people could be exposed to high nitrate and nitrite levels. The most serious health condition caused by high nitrate or nitrite exposure is acute acquired methemoglobinemia. Infants younger than 4 months of age exposed to high levels of nitrates/nitrites are especially prone to acute acquired methemoglobinemia, which is described more fully in this fact sheet in the section entitled "How can nitrates and nitrites affect my health?" What are nitrates and nitrites? How can nitrates and nitrites affect my health? Nitrate (NO -3 ) and nitrite (NO - 2 ) are inorganic ions that occur Excessive nitrate or nitrite exposure can result in acute naturally and are part of the nitrogen cycle. Nitrates (e.g., acquired methemoglobinemia, a serious health potassium nitrate and ammonium nitrate) are common condition. ingredients of fertilizer that contains nitrogen. Hemoglobin in blood carries oxygen from the lungs to tissues and helps carry carbon dioxide back to the lungs. What happens to nitrates and nitrites when they Hemoglobin in blood contains iron normally found in the enter the environment? Fe 2+ (ferrous) state. But excessive nitrates or nitrites can alter the iron in hemoglobin to the Fe3+ (ferric) state. This ‘ Nitrite oxidizes easily into nitrate. Nitrate thus more forms methemoglobin, an abnormal form of hemoglobin. Asfrequently occurs in groundwater and surface water. methemoglobin forms, the blood loses its ability to carry oxygen ‘ Nitrate-containing compounds in the soil are generally to tissues (anoxia). soluble, which means they dissolve easily in water. Nitrates Methemoglobinemia is actually an excess of methemoglobin inthus flow easily into groundwater. the blood. Methemoglobinemia can cause cyanosis (blue skin) ‘ Nitrates and nitrites both occur in soil and water. of limbs/trunk, weakness, and rapid heart rate. If Microbes break down animal and human organic wastes in methemoglobinemia progresses in severity, central nervous soil and water. T his breakdown process converts wastes system depression can occur, as can headache, dizziness, into ammonia, which then oxidizes into nitrite and nitrate. fatigue, dif ficulty in breathing, and nausea. Finally, severe methemoglobinemia can cause lethargy, brief loss of How might I be exposed to nitrates and nitrites? consciousness, irregular heartbeat, shock, convulsions, ‘ You might be exposed to nitrates and nitrites as normal coma, and even death. In fact, methemoglobin levels greater parts of a human diet. Vegetables such as cauliflower, than 50% are potentially fatal (Nathan et al. 1977). spinach, collard greens, broccoli, beets, and root vegetables Nitrate and nitrite medications may cause hypotension (low have naturally greater nitrate content than do other plant blood pressure). But ingestion of nitrates and nitrites in foods. food and water does not commonly result in hypotension. ‘ You may be exposed to high amounts of nitrates/nitrites Maternal exposure to environmental nitrates and nitrites may from soil and water contaminated by runoff from nitrogen- increase the risk of pregnancy complications such as anemia, containing fertilizers (e.g., potassium nitrate and ammonium abortion, premature labor, or preeclampsia. nitrate). ‘ You may be exposed to nitrates/nitrites from contaminated foodstuffs, from certain medications, and from certain inhalants that give off nitrite fumes. U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES, Public Health Service Agency for Toxic Substances and Disease Registry NITRATES AND NITRITES Page 2 CAS # 84145-82-4, 14797-65-0 ToxFAQsTM Internet address is http://www.atsdr.cdc.gov/toxfaq.html Methemoglobinemia can also occur from other causes. ‘ If you have well water that comes from areas that contain Exposure to oxidizing drugs or chemicals, systemic acidosis large amounts of nitrogen-containing fertilizers, you should (a generalized, abnormal increase in body fluid acidity), monitor the water closely. diarrhea, or some genetic disorders such as infant cyanosis (bluish discoloration of skin and mucus membranes) shortly Is there a medical test to determine whether I’ve after birth can all result in methemoglobinemia. been exposed to nitrates and nitrites? No routine medical tests are available to determine nitrate How likely are nitrates and nitrites to cause cancer? and nitrite levels. The Department of Health and Human Services (DHHS), the Routine blood tests are available to detect International Agency for Research on Cancer (IARC), and methemoglobinemia. But these tests cannot tell whether the the Environmental Protection Agency (EPA) have not high methemoglobin levels were caused by nitrates or nitrites. classified nitrates and nitrites as to their human carcinogenicity. Has the federal government made recommendations Still, a metabolic pathway is available for nitrites to react with molecules in organisms to form N-nitroso compounds, some to protect human health? The U.S. EP A has set an enforceable standard called a of which may cause cancer. maximum contaminant level (MCL) for nitrates at 10 ppm and for nitrites at 1 ppm in drinking water. Public How can nitrates and nitrites affect children? water supplies meeting certain criteria must follow these In some infants, fetal methemoglobinemia can be a significant regulations. problem. An infant's highly alkaline gastrointestinal system The U.S. EP A has set a reference dose (RfD) for nitrate of favors the growth of nitrate-reducing bacteria, particularly in 1.6 mg nitrate nitrogen/kg body weight per day (equivalent the stomach and especially after ingestion of contaminated to about 7.0 mg nitrate ion/kg body weight per day). water. This can lead to conversion of nitrates into high levels The U.S. EPA has set an RfD of 0.l mg nitrite of nitrites. These can change the hemoglobin in blood to nitrogen/kg body weight per day (equivalent to 0.33 mg methemoglobin. An adult stomach, however, is typically nitrite ion/kg body weight per day). too acidic to allow for significant bacterial growth that would convert nitrates to nitrites. Infants younger than 4 months of age are prone to nitrite References Agency for Toxic Substances and Disease Registry exposure, especially infants who ingest formula diluted with (ATSDR). 2007. Case Studies in Environmental Medicine, water from nitrate-contaminated rural domestic wells. A Nitrate/Nitrite Toxicity. portion of hemoglobin in young infants is still in the form of Atlanta, GA: U.S. Department of Public Health and Human Services, Public Health Service. fetal hemoglobin. Nitrites can more readily generate met- hemoglobin from oxidized fetal hemoglobin than from adult Agency for Toxic Substances and Disease Registry hemoglobin. Thus, infants less than 4 months of age, and (ATSDR). 2004. Interaction Profile for: cyanide, fluoride, especially premature infants, are particularly susceptible to nitrate, and uranium. Atlanta, GA: U.S. Department of Public such exposure. Health and Human Services, Public Health Service. At or near the 30th week of pregnancy, an expectant mother and her fetus might be more sensitive to toxicity from nitrites Nathan DM; Siegel AJ, Bunn HF . 1977. Acute or nitrates. methemoglobinemia and hemolytic anemia with phenazopyridine. Arch Intern Med:137(11):1636-1638. How can families reduce the risk of exposure to nitrates and nitrites? ‘ You should avoid exposure to water, soil, or food contaminated with high levels of nitrates and nitrites. Where can I get more information? For more information, contact the Agency for Toxic Substances and Disease Registry, Division of Toxicology and Environmental Medicine, 1600 Clifton Road NE, Mailstop F-62, Atlanta, GA 30333. Phone: 1-800-232-4636, FAX: 770-488-4178. ToxFAQs Internet address via WWW is http://www.atsdr.cdc.gov/toxfaq.html. ATSDR can tell you where to find occupational and environmental health clinics. Their specialists can recognize, evaluate, and treat illnesses resulting from exposure to hazardous substances. You can also contact your community or state health or environmental quality department if you have any more questions or concerns. Federal Recycling Pr ogram Printed on Recycled Paper