Nitrates and Nitrites in Food and Vegetables

Capture33Why not have a salad for breakfast, especially when it contains Mom and Dad’s home-grown lettuce? Because they either use no fertilizer or in the odd year composted manure, it’s lower in nitrates ( I measured about 250 ppm, relatively low for lettuce). Fresh manure can contaminate it with both nitrates and bacteria, while most synthetic fertilizer will also increase the concentration of the ion. Other vegetables and fruits known to be high in nitrates include spinach and strawberries. Here’s more on why nitrates can be harmful and what foods contain them.

  1. Why worry about nitrates (NO3) and nitrites NO2?

Here’s the latest health effect summary(italicized) from the Environmental Protection Agency

A)                 Excessive levels of nitrate in drinking water have caused serious illness and sometimes death. The serious illness in infants is due to the conversion of nitrate to nitrite by the body, which can interfere with the oxygen-carrying capacity of the child’s blood. This can be an acute condition in which health deteriorates rapidly over a period of days. Symptoms include shortness of breath and blueness of the skin.

One author (Martijn Katan ) who is a nutritionist argued here (http://ajcn.nutrition.org/content/90/1/11.full#ref-3) that what’s being described above (methemoglobinemia ) is actually caused by bacterial contamination and subsequent production of nitrogen monoxide. But that was one conclusion from an experiment in the 1950s. Meanwhile, reputable medical sources (such as http://www.nlm.nih.gov/medlineplus/ency/article/000562.htm) point out that nitrites and nitrates can cause methemoglobinemia , and it can also be brought about by a host of other compounds according to several sources that show up in Google Scholar under “causes of  methemoglobinemia”.

B)                 Drinking water levels which are considered “safe” for short-term exposures: For a 10-kg (22 lb.) child consuming 1 liter of water per day, a ten-day exposure to 10 mg/L total nitrate/nitrite.

C)                  Chronic: Effects of chronic exposure to high levels of nitrate/nitrite include diuresis, increased starchy deposits and hemorrhaging of the spleen.

D)        Cancer: There is inadequate evidence to state whether or not nitrates or nitrites have the potential to cause cancer from lifetime exposures in drinking water.

So it is still a possibility given that their presence and impact can combine with that of known carcinogens in the environment. Nitrates and nitrites are not themselves carcinogenic but they can form cancer-causing nitrosamines in the gut.

  1. What foods are sources of nitrates and nitrites?

Bacon particularly along with cold cuts and hot dogs have nitrites added to them either in the form of sodium nitrite or celery salt. But erythorbic and ascorbic acids are also added to prevent nitrosamine formation. Meanwhile spinach, especially, and lettuce can also have concentrations of nitrate that can be as high as those of bacon. But it depends on how they’re grown! If they are grown with composted manure, legume-enriched soil or with no fertilizer at all, these vegetables will have safe levels of nitrates. What elevates their concentration is liquid synthetic nitrates, some other nitrogen fertilizers and fresh manure, especially that of chickens. It should also be noted that outer leaves of lettuce have more nitrates than the inner leaves, since they have more time to concentrate them.

3. What happens to nitrites in processed meats?

Nitrites from cold cuts that have been rendered red by the addition of nitrites (hot dogs that  are made from byproducts are pale in color without nitrite) can form nitrosamines . Certain antioxidants added along with nitrites are supposed to prevent this. It works in most cases except in fried bacon, cured meats and salami, which contain between 2 and 11 ppb of nitrosamines(specifically, N-nitrosodimethylamine). Interestingly the nitrosamines in raw fish are volatile and do not show up in the analyses of cooked fish.

4. Can Excess Nitrates from Fruits and vegetables End Up As Nitrosamines?

Salivary glands and microbes in saliva are capable of converting some nitrates to nitrites, which subsequently, under the stomach’s acidic conditions can end up as nitrosamines. Some nitrites end up as nitrogen monoxide, which can have beneficial effects.

Another factor to consider is the serving size of cured meats and salami relative to that of a salad. Four slices of a cold cut has twice the mass of a serving of lettuce. So even if the compared foods contain an equal concentration of nitrites/nitrates, eating treated meat would expose you to twice the amount. Add lettuce to the cold cuts and that amount rises further.

Sources:

http://www.agroecology.org/documents/Joji/leafnitrate.pdf

J Sci Food Agric. 2014 Mar 15; 94(4):773-8.

http://ajcn.nutrition.org/content/90/1/11.full#ref-3

http://www.nlm.nih.gov/medlineplus/ency/article/000562.htm

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2 thoughts on “Nitrates and Nitrites in Food and Vegetables

  1. This morning I just analyzed some of my own home grown parsley, which definitely was not fertilized with any manure(composted or otherwise) or synthetics. I obtained a value of 140 ppm of nitrate(mg per kg of fresh parsley), plus or minus 20% (large uncertainty comes from the fact that I used color strips; 3.47 g in 100 ml of distilled boiling water for 10 minutes, leading to a 5 ppm solution) This is far lower than the average of 1070 ppm found in commercially grown parsley. (see http://www.medwelljournals.com/fulltext/?doi=javaa.2010.2013.2016) My value for commercially grown spinach was 2500 ppm,plus or minus 20% (large uncertainty comes from the fact that I used color strips; 20.34 g in 200 ml of distilled boiling water for 10 minutes, leading to a 250 ppm solution). The 2500 ppm result was comparable to that of the literature average of 2170 ppm. http://www.agroecology.org/documents/Joji/leafnitrate.pdf

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  2. A strawberry farmer in Laval, Quebec told me that they use liquid fertilizer to get the seedlings going. The following year no additives are used when the plants bear fruit. I could tell that at least the first part was true because next to the field where we had picked ripe strawberries, there was indeed a fruitless field with young plants that had been recently fertilized. The concentration of nitrate in the strawberries was 224 ppm +/- 20% . A range of 30 to 320 ppm is reported in the literature.

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