Digital class 2. Basics – Part 2

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Basics – Part 2


Welcome back to our course! I hope you continue with an interest in learning and discovering new concepts related to the environmental engineering of water and soils. In this session, we will review the classification of soil and water pollutants, their transport mechanisms, and the final destination.

The physical and chemical characteristics of these pollutants will also be reviewed.

I hope that the content of that session is valuable and serves to increase your knowledge.

Go ahead!

Content developement

1.5 Contamination in soil and water systems

1.5.1 Types of pollutants, transportation, and final destination
1.5.2 Physical and chemical characteristics of pollutants

Different causes can contaminate the soil and water; these causes or agents are generically referred to as pollutants.

Pollutant compounds are substances of natural or human origin that, when introduced into a physical environment, cause the alteration of physical, chemical, or biological conditions, making them dangerous, unsafe, or unfit for use.

When we talk about soil contamination, we can differentiate two types, depending on their origin:

Natural or biogenic contamination: It is the contamination that is usually endogenous. This pollution occurs due to the presence in the soil of natural compounds caused by imbalances created by atmospheric depositions and water precipitation.

Anthropogenic pollution: It is the contamination that is entirely exogenous. This is what is usually the product of the hand of man.

We can also classify pollutants, according to their chemical nature, for example:

  1. Chemical contamination: It deals with the pollution generated by those substances of a chemical nature that are created or not by man, which can cause great changes in the soil ecosystem, these being very negative and generally not reversible.
  2. Organic pollutants: They are produced to be used in various human activities and can be classified as follows:

* Pesticides. According to the FAO (Food and Agriculture Organization of the United Nations), a pesticide is “any substance intended to prevent, destroy, attract, repel or combat any pest, including unwanted species of plants or animals, during production, storage, transportation, distribution or storage of food, agricultural products or animal feed ”.

These in turn can be chemically classified as follows:

Persistent organic compounds or POCs, are toxic organic substances that remain in the environment for long periods and, as they do not easily degrade, tend to accumulate and severely damage the biological systems with which they come into contact. 

These pollutants are not only the product of human activity but also biogenic.

In general, terms, if they are anthropogenic, they can be generated by fixed sources, i.e., industrial processes where waste is generated and disposed of during energy production; during the production and use of pesticides for forestry or agricultural use and during the combustion of municipal or domestic waste.

On the other hand, those of a biogenic type can occur during volcanic eruptions or forest fires.

Once these pollutants are released into the atmosphere, they can easily join the food chain and ultimately harm human health.

Polycyclic aromatic hydrocarbons (HPAs or PAHs, for its acronym in English), are an extensive group of more than 100 different chemical substances that are formed during the incomplete combustion of coal, oil, and gasoline, garbage, or other organic substances such as wood, paper, and tobacco; they are usually found in mixtures of more than one compound.

According to the United States Environmental Protection Agency, at least 7 compounds in this group have carcinogenic properties in humans: benz [a] anthracene, benzo [a] pyrene, benzo [b] fluoranthene, benzo [k] fluoranthene, chrysen, dibenz [a, h] anthracene and indeno [1,2,3-cd] pyrene.

Emerging organic compounds are compounds of different origins and chemical nature that have negative impacts on the environment. They are characterized because their presence in the environment in terms of concentration is not considered significant (they are in the ng-µg / L range), however, they tend to accumulate and cause severe damage to ecosystems, for example, loss of biodiversity in aquatic and terrestrial systems.

Fertilizers are organic or inorganic substances that aim to provide nutrients to the soil easily assimilated by plants. The excessive and uncontrolled use of these compounds can lead to potential damage to man and ecosystems, eg, a risk to human health due to nitrates entering plants irrigated with water with a high content of this compound or, environmental risk due to contamination of drinking water or eutrophication of surface waters or infiltration of soluble elements that reach groundwater bodies.

Heavy metals: Heavy metal contamination is a problem that has been increasing mainly due to anthropic activities. Among the main sources of pollution are mining, metallurgy, agriculture, motor vehicles, and the natural contribution to certain aquifers.They are a set of elements that have metallic properties, which include transition metals, some semimetals, lanthanides, and actinides. The most general criterion for its classification is based on the specific density, according to which elements with a density greater than 5 g / cm3 are included in this group.

Mobilization and distribution of pollutants in the environment

The knowledge of the origin and final destination of the pollutants in the environment is important to be able to evaluate the scope and magnitude of the damage to the environment.

Water and terrestrial ecosystems are susceptible to damage due to the incorporation of these pollutants and their interactions with biotic and abiotic components.

The following are the concepts related to the dynamics of mobilization and distribution of pollutants:

  • Toxicity: Property of a substance to be potentially harmful (time and concentration) in a biological system, can be:
    * acute: short term or severe, 
    * chronic: long-term, lethal or sublethal (reversible, irreversible)
  • Bioavailability: Fraction of a substance available to an organism.
  • Bioaccumulation: Process by which polluting compounds are captured by organisms present in ecosystems.
  • Bioconcentration: It is the net accumulation of a contaminant in an organism; it is the result of the accumulation and elimination of the compound.
  • Biomagnification: It is the increase in the concentration of the pollutant in living organisms, as each level of the trophic chain increases.

The following table describes the processes by which pollutants are transported or transformed in the environment.

The detailed knowledge of the nature of the pollutants allows to foresee their behavior in soil and water, the effects on living beings in the matrices that receive them, and in the same way, it allows establishing criteria and guidelines for their treatment, aimed at the reduction of the concentration of these or their eventual elimination.

To understand in more detail the characteristics and properties of the pollutants that affect soil and water, I ask you to read carefully the contents listed below.

Knowledge of the characteristics, properties, and behavior of contaminants in water and soil will allow us to more easily present proposals for the environmental remediation of contaminated soils.

In subsequent sessions, we will make use of this knowledge to harmoniously integrate it into proposals for environmental decontamination.

Finally, as is evident, the resources on the planet are limited, finite, and of crucial importance for the coexistence of living beings.

I invite you to review the concept of planetary boundaries, developed by the Center for Resilience at the University of Stockholm, and discover the 9 environmental aspects categorized as critical, analyze the causes, consequences, and the actions that you should implement to address them.

Now I invite you to reflect on the following:

  • The importance of having a solid knowledge of inorganic and organic chemistry: how does this knowledge facilitate the understanding of the behavior of pollutants in water and soil?
  • Analysis of system interactions: How can the presence of one or more pollutants in any matrix affect the balance in other ecosystems? How can a pollutant transform itself and generate other more or less polluting substances in the environment?
  • Impact on society: What social, economic, cultural, and political factors have favored the excessive use of water and soil resources, and how this has been reverted to society? Is the damage produced observed in the places where the contamination is generated?
  • Costs associated with environmental damage: Is it possible to estimate the economic costs associated with soil and water contamination? Are these costs borne by the pollution generators?


The nature of the pollutants in soil and water are diverse, category by origin, by structure and chemical behavior, and by effects in nature.

Every day, the growing demand for satisfiers has strongly put pressure on water and soil resources, generating invaluable damage to nature and severely modifying the characteristics of environmental matrices, to the extent of putting life on the planet at risk.

In this session, the concepts associated with ecotoxicology were analyzed, as well as the processes by which pollutants are transported and transformed. With these concepts, it is possible to analyze the effect of pollutants on biotic and abiotic components of nature and thus start with a more in-depth study of environmental problems to propose environmental remediation strategies.

Information sources

  • Mathew, BB, Singh, H., Biju, VG, & Krishnamurthy, NB (2017). Classification, source, and effect of environmental pollutants and their biodegradation. Journal of Environmental Pathology, Toxicology and Oncology, 36 (1).
  • Mirsal, IA (2008). Soil pollution. New York, NY: Springer.
  • Lindegaard, C. (1995). Classification of water bodies and pollution. In The Chironomidae (pp. 385-404). Springer, Dordrecht.
  • Ghangrekar, MM, & Chatterjee, P. (2018). Water pollutants classification and its effects on the environment. In Carbon nanotubes for clean water (pp. 11-26). Springer, Cham.