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Environment & Health

Question
7 out of 72
 

Nitrates in excess of ------- may cause infantile methemoglobinemia: (AIIMS Nov 09)



A 15 mg/L
B 25 mg/L

C 35 mg/L
D 45 mg/L

Ans. D 45 mg/L Ref: Park; 22nd edi, pg – 671

a. Nitrate and nitrite: Nitrate and nitrite are naturally occurring ions that are part of the nitrogen cycle. Naturally occurring nitrate level in surface and ground water are generally a few milligrams per litre. In many ground waters, an increase of nitrate level has been observed owing to the intensification of farming practice. In some countries, up to "10 per cent of the population may be exposed to nitrate levels in drinking water of above 50 mg/litre.

b. In general, vegetables are the main source of nitrate intake when levels in drinking water is below 10 mg/litre. When nitrate level in drinking water exceeds 50 mg/litre, drinking water will become the main source of total nitrate intake. The guideline value for nitrate in drinking water is solely to prevent methamoglobinaemia, which depends upon the conversion of nitrate into nitrite. Bottle-fed infants of less than 3 months of age are most susceptible.

c. The guideline value should not be expressed on the basis of nitrate-nitrogen but on the basis of nitrate itself, which is the chemical entity of concern to health and the guideline value for nitrate is 50 mg/litre.

As a result of recent evidence of the presence of nitrite in some water supplies, it was concluded that a guideline value of 3 mg/litre for nitrite should be proposed.

Environment & Health Flashcard List

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