Nitrates in drinking water, angels or demons?

Nitrates in drinking water are the subject of much debate. In France, regulations limit nitrate levels to 50mg/l. But beyond the figures, what is the real impact of nitrates on our health?

Nitrates: definition, sources, benefits and harm

Nitrates are naturally occurring chemical substances, more specifically salts (or esters) of nitric acid containing the NO 3 anion. In simple terms, they are composed of the elements nitrogen (N) and oxygen (O). Nitrates occur naturally in the environment and are also produced by human activities.

Natural origins

Nitrates are naturally present in soil, water and certain foods, particularly green leafy vegetables such as spinach and lettuce. They result from the decomposition of organic matter by bacteria.

For humans, our main sources of nitrates are plant foods: beetroot, lettuce, spinach, potatoes, etc. For example, eating 50g of spinach provides 250mg of nitrate, equivalent to 5 litres of water containing 50mg/l of nitrate.

Their use in agriculture

Nitrates are commonly used as fertilisers (in the form of calcium nitrate, potassium nitrate or ammonium nitrate) in agriculture because they are an excellent source of nitrogen for plants.

But therein lies the rub. It is intensive farming that is going to expose the dark side of nitrate use. Indeed, modern agriculture is a scourge for the environment: all it takes is a heavy rainfall after a fertiliser application to bury the bulk of the fertiliser content in the groundwater.

Nitrate pollution in water

Excess nitrates in water, often due to agricultural run-off, are a major environmental concern. High concentrations of nitrates in water can lead to the proliferation of algae. The overabundance of these algae leads to dead zones where marine life cannot survive due to the lack of oxygen.

For example, the large quantity of nitrate that Brazil is pouring into the Amazon River is endangering the ecosystems of Martinique and Guadeloupe. It's a proven fact, and a real environmental disaster.

On the other hand, the ingestion of this product by the human body, within reasonable limits compared to the intake from vegetables, is in no way dangerous, quite the contrary.

Nitrates, the environment and health: let's not confuse the two!

As we have seen, while an excess of nitrates in a watercourse can trigger a proliferation of green algae harmful to ecosystems, the ingestion of nitrates, in doses comparable to our plant intake, is not harmful. On the contrary, they can be beneficial to our bodies.

The benefits of nitrates

That's why modern science considers nitrates to be friends (not to be confused with nitrite salts, a controversial preservative in charcuterie). But we'll come back to that later).

For example, in the human body, nitrates are converted into nitrites, which can then be transformed into nitric oxide, a molecule that plays a key role in the dilation and relaxation of blood vessels.

In fact, the benefits of nitrates are so well known that they have been turned into medicines, available by prescription! They are used to treat heart failure and high blood pressure, and to help sportspeople breathe easier at altitude and provide oxygen to the muscles.

Finally, they reduce stress and lower blood pressure.

However, it's important to remember that it's all a question of balance: high levels of nitrates can be harmful, particularly for infants, as they can cause a condition called methaemoglobinaemia. But in moderate quantities, they are not necessarily to be avoided.

We refer you to these 2 articles to find out more:

WHO Standards vs French Standards

The World Health Organisation (WHO) limits nitrates to 50mg/l, with no particular specification for children or pregnant women. However, in France, they are perceived as risky for infants under the age of six months. It is therefore essential to highlight this difference in perception.

Nitrates Vs. Nitrites

As we have seen, in reasonable concentrations (which is the case for tap water in France), nitrates in themselves are not directly toxic.

So where does the danger lie?

The risks associated with nitrates (No. 3) are in fact those posed by nitrites (No. 2), which are themselves formed from nitrates through the action of bacteria.

As mentioned above, in the human body, a small quantity of nitrates can be converted into nitrites. These can then react with other compounds to form potentially harmful substances. But it's mainly from a certain diet that the problem is likely to come.

Use of nitrites in food

Nitrites are commonly used as preservatives in the food industry, and come in a variety of forms. Here are some of the most common forms:

Sodium nitrite : It is one of the most commonly used forms in the food industry. It is often added to cooked meats for its ability to prevent bacterial growth and to give meats a pinkish colour. [You can find it on the packaging with the code E250].
Potassium nitrite : Although less common than sodium nitrite, potassium nitrite is sometimes used as an alternative, particularly in organic foods. [You can find them on the packaging with the code E249].
Organic nitrites : Some vegetables, such as lettuce, spinach and beetroot, naturally contain nitrites. When ingested, these nitrites can be converted into nitrosamines in the stomach, especially in the presence of specific amines.

Health risks associated with nitrites

It's important to note that, although nitrites are used to prevent the growth of dangerous bacteria such as botulism, excessive consumption can cause health concerns.

This is because nitrites, once formed, can cause the blood to form 'methaemoglobin', a modified version of haemoglobin that cannot carry oxygen efficiently. As mentioned earlier in this article, this can be particularly problematic in infants, in whom a condition known as 'infant methaemoglobinaemia' can develop.

However, in healthy adults, the acidity of the stomach limits the growth of bacteria, thereby reducing nitrite production. Infants, on the other hand, are more vulnerable because of their young digestive systems. However, if nitrate levels in water do not exceed 50 mg/L, the risk to babies is considered minimal.

How can we reduce our individual exposure to nitrites?

In conclusion, if you want to reduce your exposure to nitrates and nitrites at all costs, you need to look at your consumption of red meat and other cooked meats!

The ANSES (Agence Nationale de Sécurité Sanitaire de l'Alimentation) website recommends 150 grams of charcuterie a week and 500 grams of red meat a week. https://www.anses.fr/fr/content/le-point-sur-les-nitrites-et-les-nitrates-en-10-questions

How to remove nitrates from tap water (even if it's pointless...)

While the presence of nitrates and nitrites in our food is accepted, their presence in our water is often a source of concern.

So you'll find a number of products on the market promising to rid your tap water of the 'nasty' nitrate ion. Let's take a closer look at 2 types of water filter and their effects on your tap water

Filter carafes

Some carafes replace nitrates with sodium ions through the action of their filter.

In fact, you should know that resin-filled balls are inserted into the filters of filter carafes to replace nitrates with sodium ions (table salt, in other words, which is already absorbed in excessive quantities from ultra-processed food!)

Of course, it also reduces calcium (90 %), which is largely bioavailable in water and necessary for our health. For example, it is used to convey commands from the brain to the muscles.

Obviously, these beads, loaded with nitrates, become very difficult to recycle. In fact, they usually aren't, because it would be too expensive.

Read also: Filter carafes: a good idea?

The osmosis unit

Another device in the family of tap water purifiers promises to eliminate nitrates from drinking water: the osmosis unit.

Read also: What is a water osmosis unit used for?

A reverse osmosis unit is a device used to purify water through a process known as reverse osmosis. Reverse osmosis is the process by which water is forced through a semi-permeable membrane to separate and remove impurities, salts and other contaminants from the water.

Nitrate molecules, which are larger than water molecules, are prevented from passing through and are therefore removed from the water. In general, an osmosis unit will remove between 90 % and 99 % of the nitrates present in water.

The result is demineralised (goodbye essential minerals) and nitrate-free water, which is good for your health and whose initial concentration is completely safe and regulated/controlled!

Read also: Calcium / calcium ion in drinking water, the whole truth!

It is therefore crucial to be aware of the impact of the solutions we adopt to purify our water. In the case of filter carafes and osmosis machines, by trying to get rid of a supposedly harmful substance, we are impoverishing the quality of our tap water while at the same time worsening its environmental impact!

Moderation and diversity!

I'll end on a note of common sense: a substance, nitrates, which is beneficial (and essential) for the health provided by our vegetables, can hardly be dangerous when absorbed in liquid form in good water.

To say otherwise would be tantamount to saying that the vitamin C contained in cabbage is good, but that taking a vitamin C tablet would be dangerous...

In (organic) chemistry, it's all a question of quantity. We mustn't overdo anything, but eat healthy and varied products that provide us with the building blocks for our bodies and our immunity.

Cheers!

Nitrates in water: frequently asked questions

What are nitrates and where do they come from?

Nitrates are chemical compounds containing nitrogen and oxygen (NO3). They are naturally present in the environment, particularly in soil, water and certain foods such as green leafy vegetables. Nitrates also come from human activities, such as the use of agricultural fertilisers and discharges from sewage treatment plants.

Are nitrates in tap water dangerous to health?

In general, nitrates in drinking water are not harmful to health when present in regulated quantities (maximum 50 mg/L in France). However, high concentrations can pose risks, particularly for infants, by causing a condition known as methaemoglobinaemia. Nitrates can be beneficial in small quantities because they convert into nitrites and then into nitric oxide, which helps to dilate blood vessels.

What is the difference between nitrates and nitrites?

Nitrates (NO3) are transformed into nitrites (NO2) in the human body. Nitrites can react with other compounds to form potentially harmful substances, such as nitrosamines, which are known carcinogens. Nitrites are often used as preservatives in processed food products. Find out more about nitrites: https://www.anses.fr/fr/content/le-point-sur-les-nitrites-et-les-nitrates-en-10-questions

How do you test tap water for nitrates?

There are several methods for testing nitrates, including colorimetric tests, ion chromatography and spectrophotometry. Colorimetric tests are simple and inexpensive but less accurate, while ion chromatography and spectrophotometry offer greater accuracy but require specialised equipment and trained personnel.

What are the health risks associated with high nitrate consumption?

High nitrate consumption is associated with the risk of methaemoglobinaemia in infants, as well as a potential increase in the risk of certain cancers, such as gastric cancer. There is also evidence that nitrates in excess can contribute to cardiovascular problems.

How can nitrate levels in tap water be reduced?

Domestic water filters, such as reverse osmosis systems, can remove nitrates from tap water. However, these systems can also remove beneficial minerals. Infrastructure improvements, such as updating wastewater treatment plants and adopting sustainable farming practices, can also reduce nitrate levels.

Are nitrates in bottled water regulated?

Yes, in France, nitrate levels in bottled water are also regulated. The maximum authorised concentration is 50 mg/L.

Pascal Nuti - CIO Solable - Passionate about energy, I'm constantly on the lookout for new targets for improvement, exploring cross-disciplinary paths using novel methods.

Article written on 28/08/2023 and updated on 23/06/2024