Mineral Fertilizer Use and the Environment International Fertilizer Industry Association United Nations Environment Programme

12.1. Human health
12.1.1. Nitrates
Normally drinking water provides from 10 to
30% of the nitrate ingested, the remainder
coming from vegetables, fruit and meat. The
proportion of nitrate converted to nitrite also
varies widely, but about 7% is typical.
Nitrate in drinking water is considered to be a
public health problem because nitrate rapidly
reduces to nitrite in the body. The nitrite oxidizes
the blood haemoglobin which is unable to
transport oxygen to the tissues; this can manifest
itself in babies up to six months old, causing the
blue-baby syndrome. It is normally due to the
conversion by microbes of nitrates into nitrites in
the feeding bottles as a result of defective
hygiene. The occurrence of the syndrome is now
rare, although, for some reason, cases still occur
in Hungary and Romania.
Another concern is that nitrite may react with
compounds in the stomach to produce
N-nitroso compounds, particularly nitrosamines,
which have tested positive in animal
carcinogenicity experiments. Ingested nitrate is
absorbed rather quickly from the upper
gastrointestinal tract and most is subsequently
eliminated in the urine. About 25% of the nitrate
in blood is secreted by salivary glands, and the
microbial flora of the oral cavity reduce some of
it to nitrite.
It is never possible to prove zero risk, but it
should be taken into account that doses of
nitrosamines which have proved carcinogenic in
animals far exceed those to which humans are
exposed. No link to cancer in humans has been
demonstrated.
In fact, there is now evidence that some
nitrate is beneficial. Many pathogens are

---

34
Mineral Fertilizer Use and the Environment
appropriate fertilization, as can the calibre, taste
and flavour of fruits. Potassium improves the
tuber quality of potatoes and the sugar content of
sugarcane. Sulphur increases the protein content
in grain and the oil content of oil-seed crops. And
so on.