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Soil pollution

Soils, like the entire natural environment, may become polluted. Due to their sorptive properties, soils absorb a lot of chemical substances that penetrate into them in the form of:

• solids – ashes, plastics;

• liquids – wastewater discharged into water reservoirs and entering soil together with water;

• gases – harmful gases absorbed by the soil or first dissolved by water, and then entering soil together with water;

We talk about soil pollution when chemical substances occur in it in quantities exceeding their typical content and cause changes in soil properties that do not allow for its normal use.

The main sources of soil pollution caused by human activity:

• industrial – mining, energy, metallurgical, steel, chemical, construction industry;

• agricultural – too intensive fertilization, excessive use of pesticides;

• municipal – sewage and solid waste;

• communication – toxic substances and heavy metals contained in the vehicle exhaust, salt, which is sprinkled on ice‑covered road surfaces.

Pesticides

PesticidespesticidesPesticides are chemical compounds used, among others, for:

• plant protection against pests (insecticides) and fungi (fungicides),

• plant disease control (bactericides),

• weed removal (herbicidesherbicidesherbicides).

Pesticides spread in the environment through air and water, but they also remain in the soil. Due to the their exceptionally long shelf‑life, toxicity and high biological activity, pesticides pose a serious threat to the natural environment.

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Zdjęcie przedstawia samolot, który dokonuje oprysk na mszyce.

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Zdjęce przedstawia pole zaorane po, którym jedzie traktor dokonujący oprysk na stonkę ziemniaczaną.

Pollutants of petroleum origin

When the significant amounts of hydrocarbons which originate, among others, from petroleum and the products of its processing, i.e. gasoline, diesel oil, get into the soil, they can cause its exclusion from biological activity for the period of 10 -15 years. Soil supersaturation with these products destroys soil and plant microorganisms and causes oxygen deficiency.

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Ilustracja przedstawia budynek stacji benzynowej. Na stacji pod dachem znajdują się dystrybutory paliwa, za nimi znajduje się budynek ze sklepem. Po bokach stacji na parkingu stoją samochody.

Inorganic salts

An excess of nitrates in the soil reduces the resistance of plants to diseases and pests. Overfertilization of plants may be the cause of their physiological diseases. High‑grade mineral fertilizers used in excessive amounts may in many cases be more harmful than a shortage of nutrients in the soil. The plants grown in the soil contaminated with nitrates may also be harmful to consumers. In certain conditions, nitrates accumulated in the tissues of plants may undergo conversion to nitrites, which have carcinogenic properties (they promote cancer development).

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Grafika przedstawia doswiadczenie: pierwsze do warzywa dodajemy 2-3 krople roztworu nitanolu, drugie do warzywa dodajemy 2-3 krople kwasu solnego.Obserwuj kolor.

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Ilustracja pokazuje doswiadczenie: Jeśli wokół punktu zwilżania próbki nie ma różowo-czerwonego koloru, co wskazuje na obecność dużej ilości azotanów, posypać próbkę wiórami magnezowymi i obserwować zmiany koloru.

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Ilustracja pokazuje, iż jony azotanowe (III) powodują, że próbka zmienia kolor na czerwony, a jony azotanowe (V) na jasnofioletowy.

Nitrogen needed for plant growth is taken up by plants in the nitrate $\text{N}{\text{O}}_{\text{3}}^{-}$ or ammonium form ${\text{NH}}_{\text{4}}^{\text{+}}$. However, it may also occur in the soil in the form of nitrites which are toxic to many plants. Not all vegetables accumulate nitrates and nitrites equally. These compounds are accumulated to a high extent by, for example: radish, beets, parsley, to a lesser extent – carrot, celery, potato and onion.

This pollution may lead to a significant reduction in plant resistance to diseases and pests. Plants grown in soils polluted with nitrates and nitrites contain an excess of these substances and have a negative impact on the health of consumers. Excess nitrates can be converted to nitrites, which contribute to the formation of very toxic compounds exerting carcinogenic activity. Processes of this type may occur, for example, when storing vegetables containing excessive amounts of nitrates.

Task 2

Formulate a research question and hypothesis before doing the experiment “Testing the effect of soil salinity on plant growth”

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Zapisz swoje obserwacje i wnioski.

Zapisz swoje obserwacje i wnioski.

Analysis of the experiment: “Testing the effect of soil salinity on plant growth”

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Research question

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Hypothesis

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Zdjęcie przedstawia drzewa na poboczu, których liście zmieniły kolor z zielonego na żółty, a powodem było posypywanie dróg solą w sezonie zimowym.

Excessive concentration of salt in the soil solution makes it difficult or impossible for the plants to take up water. The degree of salinity depends on the amount of water in the soil. The negative reaction of plants to excess salt is their wilting, and at higher concentrations – dieback (halophytes are an exception). Salinity is caused by: chlorides, sulfates, sodium and potassium carbonates.
The effects of excessive salinity in Poland may be observed on the leaves of roadside trees in June and July.

Heavy metals

Heavy metals – lead $\text{Pb}$, copper $\text{Cu}$, mercury $\text{Hg}$, cadmium $\text{Cd}$ – are another group of the chemical pollutants of soil. Over 90% of the total content of cadmium, copper, zinc and lead in soils comes from anthropogenic sources. A particularly high content of heavy metals in the soil was found in the areas adjacent to steel mills, galvanizing plants and mines.
Heavy metals polluting the soil accumulate in the tissues of plants and cause irreversible changes in their organisms. They are also toxic to consumers (they can cause many diseases, including cancer).

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Ilustracja przedstawia mapę geograficzną na której jest ukazane zanieczyszczenie gleby metalami ciężkimi w Polsce. Na mapie przedstawionych jest sześć poziomów zanieczyszczeń. Największe zanieczyszczenia oznaczone kolorem czerwonym znajdują się na śląsku w okolicach Katowic. Nieco mniejsze ale również silne zanieczyszczenia oznaczone kolorem jasno czerwonym znajdują się również w okolicach Śląska w nieco dalszej odległości od Katowic niż pierwsza grupa zanieczyszczeń. Ta sama sytuacja dotyczy trzeciej grupy zanieczyszczeń oznaczonych kolorem różowym. Zanieczyszczenie średniego stopnia oznaczone kolorem mocno żółtym znajdują się w okolicach Krakowa, Wrocławia, Opola, Kielc, Katowic, pomiędzy Warszawą, a Łodzią oraz ponad Bydgoszczą. Podobnie wygląda sytuacja z zanieczyszczeniami oznaczonymi kolorem jasno żółtym. Natomiast zanieczyszczenia najsłabsze oznaczone kolorem zielonym znajdują się w różnym nasileniu rozmieszczone po terenie całej Polski.

Summary

• The chemical sources of soil pollution include, among others, hydrocarbons and their derivatives, chemical fertilizers, pesticides, heavy metals.

• Contaminated soil is unsuitable for cultivation as harmful substances enter the consumer's organisms along with the plants grown.

Keywords

herbicides, pesticides

Glossary