La Soil contamination It is a dangerous reality. However, we actually know very little about the real impact in numbers of many man-made chemicals in our soil. There are more than 100.000 different ones. Although many have been studied and have been banned because they are dangerous, they have not disappeared. They are already found in soils where they have reached, most of the time, through uncontrolled spills.

Currently, it is known that the use of pesticides in agriculture It is a common practice carried out in order to increase the productivity of crops. However, it is also known that these substances generally cause problems with environmental and human health. It would be enough to mention the cases of some types of cancer which are known to be linked precisely to the use (and abuse) of certain pesticides.

And yet, they continue to be used. In this context the awareness from childhood It is essential to adopt real changes in commercial and domestic agriculture. exist Beneficial alternatives for crops that do not involve soil contamination, but on the contrary, they contribute to your good health.

En Crickwoo we know it well because earthworm humus is currently the most beneficial alternative in the double objective of achieving more abundant harvests and healthy soils.

The impact of soil contamination

Inorganic fertilizers can be polluting elements, phosphates and nitrates essentially. This is so since both its excess and some low-quality compounds that are cheaper can cause soil contamination. 

The main impact of this pollution is similar to the so-called eutrophication of waters. That is, it causes greater quantities of these basic nutrients to reach aquatic life and are harmful to the living beings of these ecosystems. Is a environmental problems associated with soil contamination since through filtration it reaches aquifers and other aquatic ecosystems.

Another type of soil contamination is linked to its salinization thereof. This occurs, for example, due to the impact of urban solid waste landfills. Also for the use of brackish water for irrigation in coastal areas.

However, many people are unaware of another problem, probably the most important of contaminated soils: that due to heavy metals. This type of contamination can be a consequence of inappropriate discharges, or deposition due to mining operations. Also from the felling and burning practices of tropical forests that leave metals on the surface that were in less superficial layers of the soil. 

The main risk, although not the only one, is that contaminated soils are used for farming. So that heavy metals present in the soil can pass into the plants which are consumed by animals, including livestock, and for people. A type of soil contamination that is very dangerous for humans.

In this dangerous relationship between soil contamination and consumption of contaminated food we are going to focus.

Soil contamination by heavy metals

Metals can reach plants in different ways.

• Directly, by the absorption of these metals from the soil.
• Indirectly, when soils are irrigated with water that contains significant amounts of heavy metals.

Depending on the type of soil, metals can more easily pass into the water used for irrigation. So if it exists filtration, passes into groundwater. And in case of erosion drags, they can also reach surface waters such as rivers, lakes or swamps. In both cases, these waters can be used for irrigation, with the consequent contamination of crop soils.

In this way, the health risk is big. The risk is often forgotten because many of the plants grown for animal and human consumption  such as corn, oats, barley, and beans, they usually tolerate significant amounts of heavy metals. And that hides the real risks to human health. These are none other than the risks derived from their consumption because many of these metals accumulate in the food chain.

This is how the bioaccumulation. That is, heavy metals accumulate in the human body when consuming foods contaminated with them. Arsenic, cadmium, lead and mercury, among others, remain in the body. Thus, they cause increasingly serious damage as their quantity grows and time passes.

To these duly documented risks and problems we must add the impact of many other artificial chemicals still to study. As we noted at the beginning, there are more than 100.000 different ones, some prohibited, others not. However, even the prohibited ones can reach the soil through illegal and uncontrolled discharges.

Fighting soil contamination by heavy metals: a shared responsibility

The responsibility to fight this problem belongs to everyone. Not only in the surveillance and prohibition of heavy metals. Also providing alternatives to improve soil quality and health. And preventing food from polluting areas from reaching the food chain.

At the government level, states have an important job to do in this regard.

The agricultural sector itself can also make changes to levitate the contamination of its soils. And provide beneficial organic fertilizers for their crops and soils, such as organic worm fertilizer.

At a particular level, each person can contribute to the fight against soil pollution, according to the extent of their possibilities. As consumers, choosing local foods and organic agriculture. And through taking care of your own orchards and gardens, avoiding pesticides and choosing biofertilizers beneficial for soils and foods such as organic worm castings.

Soil contaminants that harm health

All mineral elements and some chemicals that enter the roots can be transported to the rest of the plant. The concentration of these substances is usually higher in the roots, but concentrations can also be found in stems, leaves and fruits. Thus, in greater or lesser quantities depending on the type of plant and soil contamination, contaminants reach the edible parts of the plant. 

In plants these minerals penetrate through the roots and in animals through the consumption of the plants that contain them.

The amount of elements and chemicals that a plant can absorb and accumulate depends greatly on each species. That is why, in the same situation, some species are capable of accumulating much more of a certain pollutant than others.

Of the elements considered heavy metals, not all are equally toxic or harmful to health. Elements such as zinc, copper, chromium or iron are necessary for the proper functioning of the human body. They are known as trace elements, because human beings, like other living beings, require very small amounts of them to live. 

But be careful! The amount It is crucial to differentiate between healthy and unhealthy. If they enter the body in high quantities they can be toxic.

Heavy metals that pass from the soil to the human body through food

El zinc is an essential micronutrient, a trace element considered not dangerous for humans. Although its toxicity can increase due to the presence of arsenic, lead and cadmium in vegetables that grow in soil contaminated by them.

Unlike other heavy metals, zinc is usually lost along the food chain rather than accumulating. But excess copper causes damage to the cytoplasmic membrane of both plant and animal cells, which destroys tissues. Thus in people, an excess of zinc can cause Wilson's disease, although poisoning due to these metals is not very common.

Other heavy metals such as arsenic, lead, cadmium or mercury, which may be in quantities higher than those allowed in many soils. They are also capable of being absorbed by plants. And they can be toxic to them even at low concentrations. 

In general, all of them can cause carcinogenic, genotoxic and reproductive effects in people and animals. They can also affect the nervous system. 

Examples of soil contamination and risks to human health.

• Lead can also inhibit blood formation, causing anemia, and can cause kidney damage and hypertension. 
• Mercury can cause coronary heart disease. 
• The toxic effects of cadmium are much more aggressive in the plant world and in herbivores. In our species it can remain in the body for a long time and can accumulate from many years of exposure to low levels. Thus, a well-known case of cadmium poisoning is Itai-Itai disease, recognized in Japan in the 60s. It occurred as a consequence of soil contamination due to the continued dumping of mining waste into the rivers with which they were flooded. the rice fields. This began around 1912. Cadmium was absorbed by rice, so it was ingested by people. This disease was characterized by producing a very painful bone malformation, among many other symptoms.

• Although aluminum also has no known function in organisms, its high levels in some soils cause toxicity in plants. For example, as a consequence of the exploitation of bauxite. If these are consumed by people, they can cause neurotoxic and neurodegenerative effects.

Table 1. Maximum concentrations of metals (mg/kg dry weight) found in plants growing in grass communities at abandoned mine sites in the center of the peninsula, and in forage populations planted in contaminated soils. The values ​​can be compared with those allowed for animal and human health.

Source: https://www.miteco.gob.es/content/dam/miteco/es/calidad-y-evaluacion-ambiental/publicaciones/guiarehabilitacioninstalacionesresiduosminerosabandonadas2019_tcm30-496582.pdf

Soil contamination by other chemicals

It is also worth highlighting the case of the chemical substances that reach the ground in the form of waste. Some are very biodegradable and only last a few weeks in it. But there are those that can take decades, or even centuries, to degrade.

Some stay very attached to mineral particles or organic matter in the soil. But there are others that dissolve easily and therefore can enter the roots of plants with great ease.

Acute poisoning by these compounds is not common. Its effects are rather related to the very important increase in the probability of suffering from cancer, especially the digestive tract. Damage to the reproduction and development of the fetus that can be produced.

Soil contamination and presence of metals in plants that are consumed by animals and people: examples

This type of problem has been and is being studied by our research group in recent years. These are some examples that illustrate these situations that will make you more aware of this environmental and health problem.

A very relevant case is the grasses that grow in waste dumps and adjacent areas of several abandoned mines in Spain. These pastures provide food for both sheep and cattle. Many plants there grow easily despite contamination in the soil and are food for these animals.

So copper, lead or zinc, are incorporated into their animal tissues that feed on those grasses. Animals are able to distribute the metals they ingest to other organs in their body, mainly the liver. But you can also find tbreeds in milk and muscles. And therefore, there may be a risk that these will reach people when consumed as food in the form of milk, cheese or meat. 

Apart from grazing in areas with contaminated soils, another known problem is the use of contaminated soils for food crops of people. In general, and in the same situation, tubers and roots tend to accumulate a greater amount of metals than fruits in other types of plants. For this reason, they are the foods that require the most attention. However, this does not exclude the possibility that other fruits in certain highly contaminated areas may not accumulate large amounts of metals. See the example in table 2.

What can you do about this problem?

To conclude, it is clear that the problem of contaminated crops and use of soil exists. Also, it represents a decrease in people's health through the consumption of these products. It is up to each of us to become aware.

If you are concerned, you can make effective changes in your consumption. And if you have a garden or a domestic orchard or you dedicate yourself to agriculture, value the contribution of worm humus to your floors.