It arises from the presence of nitrite (NO₂⁻ anion) in food. This nitrite can:

Nitrite occurs only to a limited extent freely in nature, as it is typically an intermediate stage in the conversion of nitrate. Sources include:

From the figure below, it becomes clear that vegetables and drinking water by far constitute the largest proportion of nitrate intake.

Therefore, it seems important:

    To limit the nitrate content in vegetables wherever possible, particularly in the diet of vulnerable groups (e.g., through limits for dietetic vegetables and baby food). Possible techniques include: reduced nitrogen fertilizer application, supplying plants with ammonium, monitoring and potentially rejecting specific batches, washing processes during food processing, and blending.

    To limit the nitrate content in drinking water. The current limit is 50 mg NO3 per liter (which corresponds to how many ppm of NO3-N?). These limits are generally adhered to. However, there have been and continue to be exceptions:

However, scientific studies clearly show that the life expectancy for groups of people who consume large quantities of vegetables (and fruit) is higher. The classic example is Japanese women, who have a very high average life expectancy despite a very high consumption of vegetables.

The figure below shows an example of the change in soil water concentration after grassland is plowed up.

What is water used for in a private household? Where does this water come from?

The figure above shows that food preparation accounts for only a very small portion of a household's water consumption. Approximately two-thirds of this water comes from groundwater.

My opinion: It is actually absurd to purify 100% of wastewater to drinking water quality in treatment plants when only 3% is used for food purposes.

Further problems associated with nitrogen:

In streams and lakes, phosphate input may lead to eutrophication because it is the nutrient element that limits algal growth. When detergents still contained phosphates, this was the primary cause of eutrophication in rivers and lakes.

Phosphate is supplied in fertilizers with varying solubilities. However, after a relatively short period, this phosphate is precipitated and/or adsorbed onto soil particles. With few exceptions, phosphate therefore can be leached towards groundwater with soil water very slowly. However, it may very well enter surface waters through transport with soil particles (wind and water erosion).

This issue can be addressed by limiting erosion, for example by:

Heavy metals are ubiquitous, meaning they are found everywhere. They are a natural component of both pristine and agriculturally/horticulturally managed soils. From the perspective of food quality and the environment, a clear distinction must be made within heavy metals between:

Nutrient deficiency was likely a contributing cause. This is inferred because the consumption of highly cadmium- contaminated (173 ppm) and zinc-contaminated (57,600 ppm) oysters (Crassostrea gigas) from the Derwent Estuary in Tasmania caused nausea and vomiting; however, there is no evidence there of permanent health damage from eating cadmium-contaminated fish or other seafood. With the exception of some shellfish, seafood generally contains no more cadmium than other foods and therefore does not pose a particular health risk.

Commercial horticulture is characterized by:

This leads, among other things, to minimizing the risk of crop failure, and cost-saving measures are only implemented where costs are high relative to total expenses. The table below illustrates, for example, that fertilization constitutes only a small portion of the total cost. For business management reasons, it is therefore understandable (though not acceptable) that saving on fertilizer is considered a secondary priority, as it increases the risk of crop failure without significantly improving the business outcome.