The most common definition of pollution states that it is the transfer of pollutants (liquids, solids or gasses) to the air, soil and water, and also the presence of microbial germs that come from the waste products of different human activities.
Pollutants can be understood as toxic substances that reach certain concentrations in the environment, altering the relatively stable conditions of ecosystems and damaging the living or non-living components, whether by limiting their development or ca, using their death.
Pollutants are classified as natural or artificial, according to their origin. The former are not produced by man and correspond to the planet’s own phenomena, such as volcanic eruptions, which expel ash, carbon dioxide (CO2), sulfur, nitrogen (N), carbon monoxide (CO), hydrochloric acid (HCl) and hydrofluoric acid (HF).
Other natural pollutants are solid waste left by volcanic lava, gasses emitted from fires caused by electrical storms and the residue that comes from the erosion of rocks rich in heavy metals. In the last case, the heavy metals include high concentrations of nickel (Ni), chromium (Cr) and magnesium (Mg) whose accumulation creates soils that are toxic for plant development.
Artificial pollutants are those that originate from human activities (urban or rural) such as industry, transportation, agriculture and cattle farming. Among the most harmful substances of this kind we find plastics, detergents, pesticides, herbicides, fertilizers and large quantities of household and industrial waste. The serious problem of these elements is that, in addition to being produced in large quantities, they don’t decompose easily once thrown away, which make their accumulation rate very high. This is mainly due to the fact that the detritivorous organisms (they eat the remains of other organisms) of natural ecosystems don’t decompose artificial compounds.
All pollutants are classified according to the physical state in which they are released into the environment.
There are gaseous, liquid and solid toxic substances. The gasses, which affect the atmosphere, are CO2, CO, sulfur dioxides (SO2), volatile organic compounds, such as methane (CH4), nitrogen oxides (NOx), ozone (O3) and chlorous acid (CIO2), among others. Several of these pollutants have been grouped under the name of greenhouses gasses due to the fact that they contribute to the phenomenon known as the greenhouse effect (review chapter on Climate Change).
Among liquids – which mainly affect rivers, lakes and seas – we find sewer water (household and industrial), oils, solvents, and petroleum and its derivatives. Solids include elements such as plastic, glass and heavy metals (some of which are radioactive) and whose main damaging effect can be noted in soil.
Solid and liquid toxic agents mainly affect soil, although they are also present in the atmosphere and in the sea.
Causes of pollution
As previously indicated, pollutants can be natural or artificial. The latter are a product of human activities. Next, we will mention some actions that create artificial toxic substances.
– Burning of fossil fuels: fossil fuels are petroleum, natural gas, and carbon and its derivatives, such as gasoline and kerosene. These are burned in internal combustion engines that move vehicles, thermo electrical energy generators and other machines present in industrial processes and heating systems.
When these actions are carried out, diverse pollutants such as CO2, CO, NOx and SO2 are released into the atmosphere.
In addition, the burning of fossil fuels promotes the production of ozone in the lower level of the atmosphere.
– Industrial activities: aside from the toxic gasses which are released into the atmosphere, such as CO2, CO, NOx and SO2, some industries produce many other pollutants. For example, refrigerator and electrical component factories release chlorofluorocarbon (CFC) compounds, heavy metals (such as lead and mercury), acids, solvents and sewer water into the environment. CFCs in particular are very harmful, as they gradually destroy the ozone layer that protects life from ultraviolet rays.
– Agriculture: large extensions of cultivated lands almost always use pesticides (chemical substances which are used to combat plagues), herbicides (chemical products which are used to kill weeds) and fertilizers (chemical substances which provide nutrients that promote plant growth) that contaminate the soil, air and water of these zones. In addition, there are some crops that promote the emission of gasses that can have harmful effects. For example, rice crops generate greenhouse gasses due to the fact that the zones in which they are grown flood constantly, promoting the decomposition of organic material, from which methane, one of the main greenhouse gasses, is released.
– Cattle farming: many foods consumed by man come from cows, pigs, sheep and goats. These animals need extensive areas of pastureland and land for cultivating products for fodder (such as alfalfa and corn). For the latter, highly pollutant substances are used, such as fertilizers and pesticides. What’s more, cattle produce large quantities of urine and excrement that increase the concentration of nutrients in soil, which can be harmful for ecosystems.
