Can nitrates be obtained from clippings?

How can the groundwater be protected from contamination?

The quality of the groundwater in Germany is impaired by nitrate in many places, as the 2016 nitrate report shows, for example. In the period 2012-2014, excessively high nitrate levels were found in the groundwater at over a quarter of the measuring points. Compared to the last assessment period from 2008-2011, the results have not improved.

Even with surface waters such as lakes and rivers and especially in coastal waters, the measurement results for the period 2012 to 2014 do not always correspond to the desired values.

Excessively high nitrate levels in the groundwater are a problem because they can lead to a high level of effort in the treatment of drinking water. Because in Germany more than 70 percent of drinking water is obtained from groundwater. Because nitrate is harmful to health in the human body, the nitrate content in drinking water must be limited.

Too much nitrate can also affect ecosystems through so-called overfertilization. Because nitrate is a nitrogen compound that acts as a nutrient for plants.

How do contaminants get into the groundwater?

In order to consider the causes and consequences of contamination, it is important to consider the entire water cycle.

The earth's water is in a constant cycle that includes surface water as well as groundwater and the atmosphere. The heat radiation of the sun causes water to evaporate and rise - from land surfaces and especially from the large surfaces of the oceans. In higher air layers, where it is colder, the water vapor condenses and clouds form. The water comes back to the surface in the form of rain or snow. On the mainland, the precipitation watered plants and partially evaporated again. It fills surface waters such as lakes, streams and rivers, partially seeps into the ground and feeds the groundwater supplies here. With the rivers, the water strives to the sea, where it evaporates again and thus closes the cycle.

This shows that water is returning to us - at least in part. Strictly speaking, it cannot be "consumed", only used. However, the cycle must not be excessively burdened with impurities, because the possibilities of cleaning in sewage treatment plants and the cleaning performance of water and soil are limited.

Groundwater is also part of the water cycle. Impurities from the surface enter the groundwater through the soil. Impurities from the atmosphere can also get into the water cycle. After evaporation, water is initially free of salts and impurities. But the precipitation washes out air pollutants such as soot, sulfur and nitrogen compounds from the air and carries them into the soil.

Conversely, groundwater feeds springs and rivers, especially in summer. In addition, near-surface groundwater is important as a water source for overlying ecosystems, especially for wet biotopes, for example.

There are layers of soil between surface and groundwater resources that partially cleanse seeping water and hold back the input of substances. But this cleaning ability was overestimated in the past.

Remediation of the groundwater is, if at all, only possible with great effort and over long periods of time and is accordingly expensive. Therefore, in each individual case, it is carefully considered whether a renovation is an option. This can be the case, for example, if contaminants have entered the soil at industrial sites through contaminated sites. If the nitrate pollution is too high, it is trusted that this will decrease over longer periods of time due to the degradation capacity in the soil and in the groundwater and the leaching. That is why consistent preventive care is particularly important.

Where do the contaminants come from?

The main problem with the nitrate content of groundwater is the excessive use of fertilizers in agriculture: Mineral fertilizers and organic fertilizers such as liquid manure are applied to the fields because the nitrogen compounds they contain, such as nitrate and ammonium, promote the growth of plants. The plant nutrients contained in fertilizers also include phosphate.

However, if the absorption capacity of the plants is exhausted, a large part of the nitrogen carried into the soil is converted into nitrate (NO3-) washed out into deeper layers of soil. There it can no longer be absorbed by plants and kept in the cycle of the ecosystem. The nitrate can only be broken down to a very limited extent in the subsurface.

In addition to fertilizers, pesticides and pesticides from agriculture also find their way into the groundwater.

The contamination from agriculture mainly ends up in water bodies,

  • if fertilizer, liquid manure or liquid manure is washed out by unexpected weather events, e.g. rain shortly after fertilization or is applied in excess on fields (more than the plants can absorb),
  • when farmers wash equipment on their farms with which they apply fertilizer, slurry or liquid manure,
  • when pathogens and veterinary medicinal products are washed away from areas fertilized with liquid manure and liquid manure, and
  • when ammonia gases from livestock farming and slurry spreading precipitate on the soil with the rain.

In addition to agriculture, there are other sources from which contamination with a large number of substances can enter the groundwater. For example, further pollution is caused by emissions from industry and traffic, polluted soils at old industrial sites, leaky sewers or accidents with substances hazardous to water.

What do the impurities do?

An oversupply of the nutrients nitrate and phosphorus can lead to so-called eutrophication, the nutrient oversupply of ecosystems. This is also known as overfertilization. The nitrate pollution of the groundwater can also contribute to this, because a not inconsiderable part of the nitrate from the groundwater ends up in lakes, rivers and ultimately in the oceans.

The nutrient load leads, among other things, to excessive growth of algae and plants. The enrichment of nutrients in the estuaries of the rivers is particularly critical, as coastal areas are particularly sensitive to increased nutrient loads.

From a health protection perspective, too, high nitrate levels in drinking water can be problematic. Because nitrate can turn into nitrite (NO2-) being transformed. There it can react with certain protein breakdown products (amines) to form nitrosamines, many of which are considered carcinogenic. Infants can suffocate internally on the nitrite itself ("blue rash" or "methaemoglobinemia"): if nitrite enters the blood, it disrupts the transport of oxygen by destroying the red blood pigment.

However, drinking water is not the only source of nitrates. Since plants meet their nitrogen requirements with nitrate, plant-based foods, especially various types of vegetables, can contain high levels of nitrate. In contrast to drinking water, however, these are not consumed every day for a lifetime.

In addition to the nutrients, there are a number of other residues in the water. For example, drug residues are also detected in surface waters and even in groundwater - mostly in very low concentrations between a few billionths to fractions of a millionth of a gram per liter, also: micrograms per liter (μg / l). Examples are residues from pain killers or X-ray contrast media.

People and animals treated with drugs partially excrete these again. The pharmaceuticals enter the water cycle through the spreading of liquid manure and through sewage treatment plants, in which some of these substances cannot be adequately retained.

Medicines are also released into the wastewater if they are incorrectly disposed of via the toilet or sink.

It is important to protect the water cycle and thus the environment and people from drugs that are difficult to break down in nature. Therefore, never pour medication into the toilet or sink - not even to empty bottles! Medicines are generally to be disposed of in the residual waste. If it is not known whether this will be burned, medicines should be returned to pharmacies.

Although the concentrations of active pharmaceutical ingredients in the environment are classified as low, scientific studies show negative effects for some active ingredients. Hormones, for example, influence the reproduction of fish even in very low concentrations. Even if effects on human health can be ruled out based on current knowledge, the introduction of pharmaceuticals into the environment should be reduced as a precaution.

Does the contamination in the groundwater endanger drinking water?

Because increased amounts of nitrate in water can be harmful to human health, legal limit values ​​must be observed in drinking water. In order to keep the treatment effort within limits, these limit values ​​were also adopted for the groundwater.

According to the Drinking Water Ordinance, the limit value for nitrate in drinking water is 50 mg / l. It was chosen in such a way that the consumption of water in normal quantities does not cause any harmful effects - not even in the case of particularly sensitive babies. The utility companies are obliged to regularly check the quality of the drinking water.

In the period 2012-2014, more than a quarter of the measuring points showed excessively high nitrate levels in the groundwater. But the drinking water is practically unpolluted. The proportion of limit values ​​exceeded has fallen to almost zero.

The water suppliers ensure that the drinking water is clean. Some dilute excessively polluted raw water with unpolluted water. However, more and more suppliers have to technically remove the nitrate from the groundwater because there is too little unpolluted groundwater. It's relatively expensive.

How can the burden be reduced?

When it comes to protecting water, the main aim is to avoid or reduce the input of all kinds of pollution. In addition to nitrate and pharmaceuticals, there are a number of other pollutants, for example heavy metals or mineral oils.

A special example are the protective measures for drinking water: In many areas where drinking water is obtained from groundwater, spring water or surface water, special precautionary measures apply when handling substances hazardous to water. These areas are known as water protection areas. Among other things, there are restrictions on fertilization and no oil stores or pipes may be built.

In agriculture, there are a number of ways to reduce the inputs of nutrients and pollutants into bodies of water. This includes more economical fertilization with nitrogen. Soil protection and measures against erosion are also part of it.

In order to lower heavy metal inputs, on the one hand emissions must be reduced - for example through better exhaust gas cleaning in coal-fired power plants, in industry and in motor vehicles. On the other hand, urban rainwater must be cleaned better. A large part of this wastewater reaches surface waters through rainwater canals or overflows, poorly or not at all.

Consumers can also make a contribution and avoid substances that are hazardous to water or dispose of them properly. For example, no paint residues, gasoline or other solvents should end up in the sewer system. Toxic agents such as pesticides should not be used in the garden, as these can get through the soil into bodies of water. As shown above, old medication can be returned to the pharmacy or disposed of in the residual waste bin.

Particular care should be taken when handling mineral oil. One liter of oil can make 1 million liters of water undrinkable. Therefore, cars should only be washed where the sewage is collected. Used oil must be handed in at collection points.

Additional information

Federal Environment Agency: groundwater

Federal Environment Agency: drinking water 

Federal Environment Agency: Nitrogen - Too much of a good thing

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