Ingested nitrate is readily absorbed from the upper part of the small intestine and rapidly distributed throughout the body. About 25 % are recirculated in the saliva, and 20 % of what is contained in it is converted into nitrite by the microflora buccale. If the pH of the stomach is high (eg., In infants when stomach acid is low), reducing bacteria proliferate and nitrate is converted to nitrite.

In my opinion, nitrates in drinking water are acting with threshold effect. I invite you to visit the ATSDR toxicological profile of nitrates.

http://www.atsdr.cdc.gov/toxfaqs/tf.asp?id=1186&tid=258#

Information from the Integrated Risk Information System US EPA

http://www.epa.gov/iris/subst/0076.htm

Other information from ATSDR

Http://www.ext.colostate.edu/pubs/crops/00517.html

http://psep.cce.cornell.edu/facts-slides-self/facts/nit-heef-grw85.aspx

There was a good plenary session on this topic at the international nitrogen conference in New Delhi 2010. Also check out European nitrogen assessment. Sometimes thresholds are based on ecology or statistical analysis!!!! So you will need to look at why thresholds exist in different regions first.

Hi Tatiana! Babies who drink water bottles which contain water with high concentrations of nitrate can develop a methemoglobinemia, also called blue baby syndrome. I send you this file in french for more information.

I send you this file also for a review of the literature.

Can you tell me where the metabolism of nitrate is doing in the organisme.

Ingested nitrate is readily absorbed from the upper part of the small intestine and rapidly distributed throughout the body. About 25 % are recirculated in the saliva, and 20 % of what is contained in it is converted into nitrite by the microflora buccale. If the pH of the stomach is high (eg., In infants when stomach acid is low), reducing bacteria proliferate and nitrate is converted to nitrite.

In my opinion Nitrates are considered as a substance acting with a threshold effect. Which is 50 mg/L for European Union. Attached, please find the European Union standards for drinking water. In the same document, you will also find the threshold value for Nitrites.

Hello,

Remember that regulatory limits for nitrates are sometimes in units of nitrate as the nitrogen; e.g., U.S. EPA limit is 10 ppm as Nitrate-Nitrogen where as EU limit is 50 ppm as the Nitrate ion.

Regarding thresholds in drinking water sources, this might be covered in the following references:

Fewtrell L (2004) Drinking-water nitrate, methemoglobinemia, and global burden of disease: A discussion. Environ Health Perspect 112:1371-1374 (should be free online).

Bryan NS, Loscalzo J (Eds.) 2011. Nitrite and Nitrate in Human Health and Disease. Springer, New York Dordrecht Heidelberg London. pp 139-153. (may be in google books)

Not only does nitrates have a threshold effect, in risk assessment there is a vulnerable population. The Blue baby syndrome has been mentioned by contributors to this post, infants and children are more vulnerable to this nutrient in water than adults are.

Thanks to everyone. But what i mean is : in risk assessment, i don't see threshold for carcinogenic substances. But nitrates in drinking water could be carcinogenic and act with threshold. How can you explain that?

Find attached herewith a publication that reports no obvious correlation of increasing levels of nitrate in water with all types of cancers.

I think its important to note that when it comes to ingested nitrogenous compounds nitrate is a lesser carcinogenic concern than nitrites (the reduced form of nitrates) and the most prominent of them is sodium nitrite gotten from cooked meat.

Thank you Azubuike for paper.

The maximum permissible limit for nitrate (NO3) is 45 mg/L

Dear Charles,

I send you one paper to related your question.

Thaks