A Comprehensive Review
Understand the Main Environmental Issues
1. What is pollution?
Pollution is the contamination of an ecosystem by factors that are harmful for the equilibrium of its biotic or abiotic constituents.
2. Is pollution always caused by humans?
In most cases pollution is caused by human activity. Other species and some abiotic factors however can also pollute an ecosystem. For example, the red tide is created by proliferation of some algae and volcanic dust is a consequence of the internal activity of the planet.
3. Why is waste considered one of the major environmental issues?
The environmental problem concerning waste worsens with industrial development and the global growth of consumption societies in the 20th and 21st centuries, factors that cause the immense volume of residuals produced by mankind in the last decades. The increased waste generation raises the issue about what to do with waste since nature is not able to degrade and resorb with adequate speed and efficiency most of the residuals. Therefore the various kinds of waste accumulate, polluting the environment and creating danger to humans and nature. (The present destination of waste has been public waste depositories where the waste volume is compressed and buried underground, an environmentally risky method. Another method has been incineration, with the grave consequence of causing air pollution.)
4. What are the main types of waste?
The waste can be classified into many types, each of them carrying its own different environmental problem: organic waste, recyclable waste, non recyclable waste, toxic waste, nuclear toxic waste and space waste.
The organic waste is more easily resorbed by nature, but the speed and the geographical concentration of its production due to urbanization generate pollution of rivers, lakes, proliferation of disease vectors and environmental degradation of towns. The recyclable waste is composed of residuals that can be reprocessed, used again by humans, like plastics and metals; the problem regarding recyclable waste is that the separation of such material is not culturally diffused and there is not enough social organization to use them; so the recyclable waste is mixed to other wastes increasing the volume of waste depositories even more. The non recyclable waste is formed of residuals that technology cannot yet recycle, like ceramics, photographic paper, mirrors, cigarettes, plasticized papers, etc; this kind of waste in the future may become recyclable waste and should be separated. The toxic waste includes industrial chemical residuals that are harmful for life and the environment, like contaminated medical waste and the domestic waste containing insecticides and medicines; the toxic waste is one of the major environmental problems since it puts the life of humans and other living beings in danger. The nuclear toxic waste is made of materials that release invisible dangerous radiation for many years; nuclear toxic waste is produced in the extraction of nuclear minerals (like uranium), by nuclear reactors and nuclear plants, in hospitals where Nuclear Medicine is performed and in research centers; although the nuclear waste is often put into armored receptacles the risk of accidents is permanent. Space waste is the waste produced by the activity of humans in space from the second half of the 20th century; it consists of non operating satellites, rocket piece and other equipments that remain orbiting the earth or other celestial bodies or even travelling across space.
non recyclable waste
nuclear toxic waste
5. What is selective waste collection?
Recyclable waste is waste that can be reprocessed and used again. Waste recycling depends on the separation of the recyclable residuals from non recyclable ones and on the classification of the recyclable into plastics, metals, papers, etc. The function of the selective waste collection is to simplify that separation for the waste to be sorted at the point of origin. Selective collection also helps the creation of an environmental conscience in the people that produce the waste.
selective waste collection
6. What is the cost-benefit relationship regarding sewage treatment as a strategy to fight water pollution?
To treat sewage is much cheaper for society. The non treated sewage pollutes rivers, lakes and the sea, being a cause of diseases transmitted through water. For the society the costs of these diseases are much higher than the cost of the sewage treatment.
One of the most economical systems to treat sewage is the aerobic treatment system, reservoirs kept very oxygenated for aerobic bacteria to decompose organic material.
7. What is eutrophication?
Eutrophication is the process of excessive increasing of nutrients, like phosphate and nitrate, in water due to direct deposit of non treated sewage. The nutrients act as fertilizers leading to abnormal proliferation of aquatic algae. With the exaggerated growth of the alga population the number of aerobic bacteria that cause decomposition of organic material also increases. The proliferation of these bacteria depletes the dissolved oxygen killing fishes and other animals. Besides, the lack of oxygen causes the decomposition to be assumed by anaerobic bacteria. Anaerobes multiply and release hydrogen sulfide that makes water improper to other living beings and creates a putrid smell.
8. What is a biodigester?
A biodigester is equipment that produces carbon dioxide, hydrogen sulfide and fuel gases (biogases) like methane from organic material under decomposition (dung, food waste, sugar cane waste, etc.). The biogas is used in heating, as energy for motors and machines and it even has industrial uses. Biodigesters are widely used in public waste depositories and in rural areas. Besides producing biogas the organic waste can be turned into good quality fertilizer.
9. What are the environmental harms caused by mercury pollution? What are the main sources of mercury pollution?
Mercury is a metal that when present in the water of rivers, lakes and seas contaminates fishes, crustaceans, molluscs and other living beings. The mercury accumulates along the food chain and in each following trophic level the amount of the metal within the individuals is higher. When humans eat contaminated animals they also become contaminated and severe nervous system injuries may emerge. The main sources of mercury pollution are gold mining and the use of derived substances in industry and agriculture.
10. Besides mercury which other heavy metals cause toxic pollution?
Examples of other heavy metals that cause toxic pollution are lead, cadmium and chromium.
11. What are persistent organic pollutants (POPs)?
POPs, or persistent organic pollutants, are toxic substances formed from organic compounds. POPs are made in several industrial processes, like the production of PVC, paper whitened by chlorine, herbicides, insecticides and fungicides, and also in the incineration of waste. Examples of POPs are dioxins, furanes, chlordane, DDT, dieldrin, heptachloride, toxaphen and hexachlorbenzene.
POPs are toxic and highly harmful since, like the heavy metals, they are bioaccumulative, i.e., they are not degraded by the body and accumulate even more in each following trophic level of the food chains. In humans POPs can cause cancer and nervous, immune and reproductive impairments.
persistent organic pollutants
12. Is the upward move of warm air good or bad for the dispersion of pollutants?
The upward movement of warm air is a natural method of dispersion of pollutants. The air near the ground is hotter because the sun heats the soil and the soil heats the air nearby. Since it is less dense, the warm air tends to move towards higher and colder strata of the atmosphere. Such movement helps the dispersion of pollutants.
13. Does thermal inversion occur in the winter or in the summer?
Pollutant low altitude thermal inversion occurs in the winter. In this period of the year the sun heats the soil less and the natural upward move of warm air decreases. Therefore the pollutants form a low altitude layer between the cold air layer near the ground and another layer of warmer air above. The pollutant layer over industrial areas or big urban concentrations reduces the penetration of the sun's energy and the air bellow takes an even longer time to warm.
14. Why does thermal inversion increases air pollution? What harm can thermal inversion cause to humans?
Thermal inversion confines at low altitude a layer of pollutants that would have been dispersed by the natural upward move of warm air. The solid particles present in the atmosphere cause health problems, like the exacerbation of asthma and other pulmonary diseases, cough, respiratory unease and ocular discharges; later the pollution can also trigger the appearance of cardiovascular and neoplastic diseases.
15. What is the role of the ozone layer for living beings?
Ozone, O3, is a gas of the atmosphere that filters ultraviolet radiation from the sun disallowing most of that radiation from reaching the surface of the planet. Ultraviolet radiation is harmful for living beings because it is a mutagen and can cause cancer (mainly skin cancer), other DNA mutations and even burns.
16. What are the main chemical compounds that destroy the ozone layer?
The mains chemical compounds that destroy the ozone layer are the CFCs, chlorofluorocarbons, or freons, substances used in the past in refrigerators, airconditioners and spray cans.
Chlorofluorocarbons react with ozone in the high atmosphere releasing molecular oxygen and therefore the amount of ozone in the atmosphere is reduced.
Another substance that destroys the ozone layer is methyl bromide, used in agricultural insecticides.
17. What is nuclear pollution?
Nuclear pollution consists of radiations emitted from atomic nuclei, these radiations are highly injurious to living beings. They can be originated from the extraction of radioactive minerals, nuclear plant reactors, nuclear research centers, hospitals and medical centers that use radioisotopes, nuclear bomb explosions or accidents with transportation, handling or storage of nuclear material. Nuclear materials remain dangerous for many years, contaminating the environment with radiation that can cause cancer, immune impairment, congenital deficiencies, burns and even death. The damage is proportional to the intensity of the exposition to the radiation.
Its persistent feature and high aggression power make nuclear pollution one of the major environmental problems of our time.
18. What is plutonium reprocessing? Why is it a big environmental issue?
Plutonium is the highly radioactive chemical element produced from uranium by nuclear plants. Plutonium can be reprocessed to be used again in nuclear plants or in other destinations, like the making of nuclear bombs. Plutonium reprocessing nowadays, however, is done only in some countries like France, Russia and Britain. The countries that have nuclear plants, like Japan, Australia, etc., send their atomic waste by ship to those plutonium reprocessing centers. Besides the inherent risks of the storage of nuclear waste, plutonium reprocessing brings the risks of the transport of radioactive material across the oceans. The “nuclear ships” often travel near the coast of many countries posing danger to their populations.
19. What is transgenic food?
Transgenic beings are animals, microorganisms and plants that contain recombinant DNA, i.e., genes from other plants, microorganisms or animals artificially inserted into their genetic material. Transgenic beings are made for scientific and economic purposes, in this last case with the intention of improving their commercial features. For example, bacteria that produce human insulin are transgenic beings made by biotechnology. The main targets of the transgenic technology are edible vegetables, like soy, corn, potato and tomato.
20. Why are transgenics considered a threat to the environmental safety?
Transgenics can be dangerous to the entire biosphere since the transfer of genes between species may have immediate and long term unpredictable consequences. The creation of new species by nature is a slow process, dependent on causal mutations and natural selection, a relatively safe process for the ecological equilibrium. It is impossible to know how the fast and artificial introduction of transgenic beings in nature affects ecosystems. Pathogenic agents may be involuntarily created in laboratories, spreading unknown diseases; transgenic species may uncontrollably proliferate destroying ecological interactions that have taken thousands of years to be established; the ingestion of transgenic food also has unpredictable effects.
21. What is biological control?
Biological control is a natural method to control the size of animal, microorganism or plant populations. Biological control is based on the knowledge of inharmonious (negative) ecological interactions between species. Using such knowledge a parasite, competitor or predator species is introduced in an ecosystem in order to attain reduction of the population of another species with which it has inharmonious ecological interaction. The biological control presents the advantage of substituting the use of pesticides and other toxic chemical products in the control of plagues and diseases. It however should be employed with caution under serious previous study to avoid harmful ecological disequilibrium.
A kind of biological control of some species can be done by the introduction of previously sterilized males, that do not generate offspring.
22. What is bioremediation?
Bioremediation is the use of microorganisms, like bacteria, protists and fungi, to degrade noxious substances turning them into non toxic or less toxic substances. Bioremediation employs microorganisms whose metabolism uses contaminants as reagents.
Bioremediation is used, for example, in the decontamination of environments polluted by oil spills. In this process bacteria that use hydrocarbons as substrate for their cellular respiration are employed.
23. What is global warming?
Global warming is the increase in the temperature of the planet due to accumulation of some gases in the atmosphere, especially gases that retain the solar energy reflected by the planet surface. The main gas that causes the global warming is carbon dioxide, CO2, but other gases act as “warming gases” too, like methane, CH4, and nitrous oxide, N2O. The exaggerated increase of carbon dioxide in the atmosphere has been caused by the burning of fossil fuels (mainly oil and coal) in industrial and urban societies and by forest fires. (It is important to note that the natural warming provided by gases of the atmosphere is fundamental for the maintenance of the planet temperature.)
Predictions of studies sponsored by the United Nations stated that the global warming may cause life-threatening transformations to the planet in the near future. Countries that are the biggest emitters of carbon dioxide, like the United States and China, however, systematically ignore the warnings and continue to largely contribute to the danger.
Global warming is one of the most polemic environmental issues today.
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