Nitrate and Nitrite in Drinking Water (1995) / Chapter Skim
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2 HAZARD IDENTIFICATION
2 HAZARD IDENTIFICATION
Pages 13-28
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From page 13... ...
Hazard identification _ This chapter summarizes the qualitative aspects of the health | effects Ion own to be associated with nitrate and nitrite exposure. METHEMOGLOBINEMIA The primary adverse health effect associates!
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From page 14... ...
studied newborns hospitalized for acute diarrhea and found no correlation between ingestion of food or water containing high concentrations of nitrate or nitrite and methemogIobinemia; they concluded that endogenous synthesis of nitrite resulting from diarrhea was the principal cause of infantile methemogIobinemia. Thus, diarrhea apparently can be a major cause of infant methemogIobinemia unrelated to the nitrate content of food and water (endogenous synthesis is discusser!
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From page 15... ...
CANCER Nitrate and nitrite have been tested for carcinogenicity in laboratory animals, and epidemiologic studies of human cancer rates among populations with high nitrate or nitrite exposure concentrations have been performed. In general, nitrate and nitrite are not carcinogenic in laboratory animals when administered in the absence of nitrosatable amines.
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From page 16... ...
The increases are thought to result from the formation of nitrosamines in the stomach. Nitrosamine formation from nitrite and nitrosatable amines is of concern because nitrosamines are potent mutagens and carcinogens at various sites and in various species of laboratory animals (Peso et al.
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From page 17... ...
Nitrosamine formation from nitrite and nitrosatable amines is discussed further in Chapter 4. There are several reasons why nitrosamine formation and consequent cancer risk among laboratory animals receiving nitrite and nitrosatable amines might not be relevant to similar human exposures.
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From page 18... ...
The latter study found that nitrate concentrations in saliva were higher in exposed worIcers than in controls. In both studies, however, neither overall cancer mortality nor mortality for any particular cancer site was statistically significantly higher among the exposed populations than in controls.
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From page 19... ...
States and Canada. Increased nitrate intake was associated with a decrease in the risk of primitive neuroectodermal tumors, whereas there was no association between nitrate or nitrite intake and astrocytoma risk.
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From page 20... ...
The case-control studies of nitrate exposure and cancer risk thus show either no association or an inverse correlation. Negative associations are Wildly to be a result of the fact that vegetables are the primary dietary source of nitrate; diets rich in vegetables have consistently been shown to be associated with lower cancer risk (NRC 1989~.
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From page 21... ...
(1984) reported a positive association between gastric-cancer incidence and drinking-water nitrate concentrations in Italy, but this stucly did not control for other important risk factors for gastric cancer, such as age, diet, alcohol consumption, and occupation.
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From page 22... ...
Finally, the epidemiologic studies that have been conducted to date suffer from a variety of limitations, such as lack of historic exposure measurements, small sample size, and confounding by concomitant exposures. It is lilcely that considering nitrate or nitrite exposure without also considering exposure to nitrosatable amines is not adequate to determine cancer risk.
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From page 23... ...
uit and vegetable intakes will also have a relatively lower intalce of ascorbic acid and other vegetable-derived antioxidants. the proportion of Americans consuming the recommended five servings of fruits and vegetables per day is less than 20% (Lanza et al., 19~37)
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From page 24... ...
and ICammerer and Siliart ~ ~ 993) studied the reproductive and developmental effects of nitrate in female rabbits and reported no effects on reproductive performance, fertility, litter size, or weight at birth or at weaning in association with nitrate at 250 or 500 mg/L of clrinIcing water (about 9 or ~ ~ m~lcg-clay)
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From page 25... ...
~ ~ 987) , who noted anemia and reduced weight gain among the pups of clams supplied with drinIcing water containing nitrite at 145 or 200 mg/Icg-day during gestation and 275 or 340 mgllcg-clay during lactation.
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From page 26... ...
Results of both studies indicate that the toxic effects observed were due to nitrosamine formation. Extrapolating the results to humans must be approached with caution for the same reasons that the relevance of the carcinogenicity bioassays discussed must be questioned: the gastric acidity of humans favors nitrosamine formation but that of rodents does not, and the doses used were often much higher than those encounterer!
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From page 27... ...
~ 989~. An increase in the risk of birth defects was reported in South Australia among women consuming groundwater containing nitrate at 5- ~ 5 my, compared with women consuming rainwater containing nitrate at less than 5 mg/L (Scragg et al.
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From page 28... ...
Now ~ Name iN Do ~ and at doses that overlap with dosages that cause methemogIohi ~ 1~.
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