Nitrate and Nitrite in Drinking Water (1995) / Chapter Skim
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3 DOSE-RESPONSE ASSESSMENT
3 DOSE-RESPONSE ASSESSMENT
Pages 29-34
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From page 29... ...
METHEMOGLOBINEMIA Very few of the reports of studies performed on nitrate-incluced methemogIobinemia in humans that include dose information involve cases occurring at nitrate concentrations below 50 mg/L, and most cases occurred when bacterial contamination of water supplies was present as well. In some cases, important dietary sources of nitrate (such as spinach)
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From page 30... ...
Of the 306 cases for which additional information was available, 98% occurred in infants aged 3 months old or younger, and 53% of the infants had diarrhea, an indicator of bacterial contamination and a factor associated with endogenous nitrate formation. Dose-response relationships for nitrate exposure and methemogIobin concentrations have been reported in several studies of infants.
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From page 31... ...
The only evidence of a role of nitrite in carcinogenesis comes from studies in which nitrite was administered simulta neously with a nitrosatable amine; in these cases, carcinogenesis can be attributed to the endogenous formation of carcinogenic nitrosamines. Cancer risk associated with endogenous nitrosamine formation is a function of four variables: the amount of nitrite ingested or formed from nitrate, the amount of nitrosatable substances ingested, the rate of in viva nitrosation, and the carcinogenic potency of the resulting nitrosamine.
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From page 32... ...
Therefore, developing dose-response relationships based on human data is not possible. Developmental effects and fetal toxicity have been reported among rats and mice receiving both nitrite and nitrosatable amines, but (as discussed above for cancer)
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From page 33... ...
Reproductive effects attributable to nitrite exposure have been reported in animal bioassays at clo sage s that might have been associated with maternal methemogIobinen~ia. Developmental effects of nitrite that have been reported at lower dosages in rodents appear to result *
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