RIVER POLLUTION: CAUSES, POLLUTANTS AND EFFECTS - BIOLOGY - 2024

The river pollution is the alteration or degradation of the natural state of these bodies of water by the introduction of chemical or physical elements that threaten its balance as an ecosystem.

The contamination of these important ecosystems threatens life and the availability of fresh water on the planet. Rivers and their associated ecosystems provide us with the drinking water necessary for our food and for industrial processes, therefore, they are essential for human well-being.

Waste dumping in the Huallaga river in Peru. Source: Averyaudio, from Wikimedia Commons

Fresh water available on Earth is a scarce resource. Only 2.5% of the total water on the planet is fresh water. Of it, about 70% is in the form of glaciers, while the rest appears in the form of groundwater, lakes, rivers, environmental humidity, among others.

In recent decades, global freshwater demand has increased due to population growth and associated factors, such as urbanization, industrialization, increased production, and consumption of food, goods, and services.

Despite the recognized importance of rivers and the scarcity of fresh water sources, they continue to be polluted. It is estimated that, worldwide, every day two billion tons of water are contaminated by two million tons of waste.

Causes

Pollution is a phenomenon of anthropogenic origin that systemically affects rivers and their associated ecosystems. Thus, the polluting causes of these important bodies of water must be interpreted under an ecosystem approach.

In a structural sense, the causes are generated by global patterns of water use, management and disposal, associated with unsustainable lifestyles that prioritize immediate economic variables over environmental and social variables.

For example, it has been estimated that about 250 liters of water are needed to produce one kg of paper. In agriculture 1,500 and 800 liters are required to produce 1 kilogram of wheat or sugar respectively. In metallurgy, 100,000 liters are necessary to produce 1 kilo of aluminum. Can nature supply these demands?

In general, the causes that act on the pollution of rivers and other lotic ecosystems can be outlined in:

• Direct, such as elements, activities and factors that directly affect water.
• Indirect, made up of a set of factors that make possible, favor and magnify the impact of direct causes.

Among the direct causes are the lack of awareness and education about the threat of pollution of ecosystems, weaknesses in legislation and its implementation at different scales, lack of ethics, as well as social inequity.

Urban waste

The main source of river pollution is liquid waste from urban centers, due to sewage / wastewater not properly treated.

Furthermore, surface runoff waters can reach rivers carrying pollutants such as detergents, oils, fats, plastics and other petroleum derivatives.

Industrial waste

Industrial waste, whether solid, liquid or gaseous, is highly polluting if not properly treated. These wastes can potentially contaminate rivers through the industry's sewage / wastewater system.

Another polluting factor is acid rain that occurs as a result of the emission of sulfur and nitrogen oxides. These chemical compounds react with water vapor and lead to acids that are then precipitated by rain.

Acid mining drainage in Centralia, United States. Source: Michael C. Rygel, from Wikimedia Commons

Mining and oil

Mining and oil activities are the most serious causes of river pollution. In open pit gold mining the topsoil is destroyed, thus increasing erosion and runoff.

Also, the water used to wash the alluvial material ends up in the rivers causing heavy pollution, including heavy metals.

One of the most serious cases of contamination by mining occurs when mercury or cyanide is used for gold extraction. Both compounds are highly toxic.

Agricultural activities

Modern agriculture uses a large number of chemicals, such as biocides for pest and disease control or fertilizers.

These chemical products applied directly to the soil or to the foliage of the crops, end up being washed by irrigation water or rain in a high proportion. Depending on the type of soil, the topography of the terrain and the water table, these pollutants frequently end up in rivers.

In some crops such as cotton, high doses of biocides are applied by aerial spraying (fumigation planes). In these cases, the wind can be a transport agent for these chemical products to the rivers.

On the other hand, many biocides are not easily degradable, which is why they remain for a long time, polluting the waters and affecting biodiversity.

Fertilizers affect the potability of the water, by incorporating high levels of nitrogen, phosphorus and potassium.

Intensive livestock farming, poultry and pig farming are sources of river pollution, mainly due to the accumulation of excrement. Intensive pig farming is a highly polluting activity due to the high content of phosphorus and nitrogen in the excreta.

Polluting components

Petroleum derivatives

Oil spills are the most difficult pollution events to remedy due to the accumulation of the oil layer on the water surface and its eventual incorporation into coastal ecosystems, such as mangroves, marshes or swamps. This results in the loss of potability of the water, the death of numerous aquatic species and the alteration of ecosystems.

The hydrocarbons and heavy metals contained in oil harm fish and other animal and plant species that are part of river ecosystems. These damages can be chronic (long-term) or acute (short-term), and can include death.

Oil pollution, Ecuador. Source: Julien Gomba, via Wikimedia Commons

Asphaltene-rich heavy oil spills are very troublesome. Asphaltenes accumulate in the adipose tissue of animals and generate biacumulation.

Detergents

Detergents are not easily biodegradable, so it is difficult to remove them from the aquatic environment. In addition, they contain surfactant compounds that hinder the solubility of oxygen in water, thus causing the death of aquatic fauna.

Agricultural and livestock products

Among the agricultural products that can pollute rivers are biocides (herbicides, insecticides, rodenticides and acaricides) and fertilizers (organic and inorganic). Among the most problematic are chlorinated pesticides and nitrogen and phosphorous fertilizers.

Purines (any organic residue with the ability to ferment) that are generated by agricultural and livestock activities are pollutants in nearby rivers. Among the most polluting and abundant are excreta produced by farm animals.

Pollution from agricultural activities in Wairarapa, New Zealand. Alan Liefting, from Wikimedia Commons

Heavy metals, metalloids and other chemical compounds

Chemical compounds from industrial and mining activities are highly toxic pollutants. These include different heavy metals such as mercury, lead, cadmium, zinc, copper and arsenic.

There are also lighter metals such as aluminum and beryllium that are highly polluting. Other non-metallic elements, such as selenium, can also reach rivers through spills from mining or industrial activities.

Metalloids such as arsenic or antimony are a source of pollution in rivers. They come from the application of pesticides and urban and industrial wastewater.

Organic matter and microorganisms of fecal origin

Various species of disease-causing bacteria, protozoa, and viruses reach river water. The route of arrival is domestic waste and livestock farms without wastewater treatment, which are dumped directly into the riverbeds.

The accumulation of these microorganisms in the water can cause diseases of varying severity.

Effects edit

Drinking water

Rivers are an important source of drinking water for both humans and wildlife. Likewise, in many cases they provide the water required for agricultural and livestock activities.

River pollution disables water for human or animal consumption and in extreme cases makes it equally useless for irrigation water. In addition, the presence of pathogenic microorganisms of fecal origin favors the spread of diseases.

Biodiversity

Water pollution causes the disappearance of species in riparian ecosystems. Both aquatic and riparian species can disappear, as well as animals that consume water from polluted rivers.

Irrigation water

The waters of rivers contaminated with untreated urban waters or from animal husbandry farms are not suitable for irrigation. The same happens with the water of rivers near mining operations or industrial zones.

If contaminated water is used for irrigation, feces and toxic compounds or pathogenic organisms can settle on the epidermis of plants or be absorbed by the roots. Contaminated agricultural products become a health risk if consumed by humans.

tourism

Rivers and associated ecosystems can be economically important tourist areas for residents. The contamination of these diminishes their value and entails economic losses.

Polluted rivers can constitute a health risk due to the presence of pathogenic microorganisms or toxic wastes. Furthermore, it loses its scenic value particularly due to the accumulation of solid waste.

How to avoid river pollution?

Global Actions

The reduction of contamination of surface running water ecosystems is a global goal that can only be achieved if it is possible to structurally change the global patterns of water use, management and disposal associated with unsustainable ways of life.

In a general sense, laws should be strengthened at all levels for environmental protection. In addition, an education should be promoted that in addition to generating awareness, builds the values ​​of respect for nature.

Some national actions

Legislation

A strict legal system is required for the protection of rivers to minimize damage from pollution.

One of the most important aspects that must be regulated is the treatment of sewage. Another aspect of interest in the legislation is to regulate the activities that can be carried out on the banks and in the protection strip of the water courses.

Investigation

The rivers make up basins, which are large areas whose natural or artificial drains converge in a tributary network of a main river. Therefore, they are complex systems that must be studied to propose management plans.

It is necessary to permanently monitor the quality of the water and the functioning of the ecosystem.

Conservation of riparian vegetation

Riparian vegetation participates in nutrient cycling, in environmental sanitation and mitigates the effects of climate change. Therefore, it is important to promote their conservation and protection.

Some local actions

Treatment plants

The main source of river pollution is sewage from urban and industrial centers. To mitigate its effects, the adequate treatment of polluted water is necessary through the installation of treatment plants.

Treatment plants employ various systems depending on the nature of the pollutants. These include the decantation of solid waste, water filtering, chemical decontamination treatment and bioremediation.

Remediation practices

Once a river has been contaminated, remediation measures must be taken. These measures vary depending on the type of contaminant.

One of these measures is mechanical cleaning. For this, the extraction of solid waste thrown into the rivers is carried out using dredging machinery and collection equipment.

Another of the most common practices is phytoremediation. Some species of plants that are efficient in extracting heavy metals from polluted rivers are used. For example, Eichhornia crassipes (water lily) has been used to absorb cadmium and copper. Likewise, the Azolla-Anabaena azollae symbiosystem is used for the bioremediation of rivers contaminated with arsenic and other metalloids.

Some species of bacteria and certain derivatives of fungi are used for the degradation of polluting compounds in rivers (biodegradation). Bacterial species of the Acinetobacter, Pseudomonas and Mycobacterium genera degrade alkanes, monoaromatic and polyaromatic respectively.

References

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