Big Question: How can harmful chemicals become less dangerous to the environment? Reducing the production of pollutants is the best answer, but sometimes we can also help lessen the impact of pollutants already released.
At the end of this inquiry, you should be able to answer the following questions:
How does dispersion and dilution decrease the negative effect of pollution on air and water systems?
What is biodegradation?
How are living organisms used to clean up contaminants in water and soil?
What is phytoremediation?
What is photolysis?
Pages 243 to 247 and 250 to 252 in your textbook will help you answer these questions about making harmful chemicals less dangerous in the environment.
Introduction
Harmful Pollutants in the Environment
In an ideal world, there would be
no pollution.
Unfortunately, most human activities produce some harmful chemicals. What is nature’s way of diminishing the negative effects of pollutants being released into the environment?
How do dispersion and dilution decrease the negative effects of pollution on air and water systems? Dispersion is the scattering of a substance away from its source. Smog is a type of air pollution caused by emissions from power plants,
industrial sources, and motor vehicles. On days when the pollution is dispersed by prevailing winds, pollution dissipates.
In large cities such as Los Angeles, London, and Mexico City, smog can be a huge problem. When there is little air movement (dispersion), the air pollution become more concentrated. As a result, it is more difficult for organisms to
breathe. The concentration of oxygen is less in polluted air than in the “normal” atmosphere.
Dilution is the process of mixing polluting substances with large quantities of air or water. Dilution decreases the concentration of the pollutant; however, the pollutant is still present.
In a chemistry lab, leftover acid (with a pH >2) can be poured down the drain with lots of water. The diluted acid is much less likely to react with other chemicals as well as the pipes.
Acids with a pH <2, must be neutralized with a weak base such as limestone or baking soda before it can be poured down the drain safely.
Figure 1 – More than 100 cities in China suffered from severe air pollution on Dec 7, 2013. Masks are worn to help protect people’s lungs from the dust and other particles in smog.
Figure 2 – Many chemicals used outside of industrial processes or chemistry labs have been diluted to safe concentrations.
Watch
Watch the following video carefully, it explains how some chemicals can be broken down in the environment, with emphasis on the process of biodegradation.
Biodegradation
Biodegradation is nature's way of recycling wastes by breaking down organic matter into nutrients that can be used by other organisms. "Degradation" means “decay”, and the "bio" prefix means “life”. Therefore, biodegradation is the process
of living things causing breakdown and decay.
Figure 3 – Water plants are often used in the treatment of waste water and sewage.
Biodegradation is carried out by a huge assortment of bacteria, fungi, insects, worms, and other organisms that eat dead material or unwanted substances and recycle them into new, less harmful forms.
Bio-degraders are of various types, but most of the work is done by
bacteria that give off enzymes that break down the chemicals into forms that can be absorbed
fungi that grow on contaminants and absorb them
algae that can absorb chemicals and change these chemicals into organic molecules
protozoa that use organic molecules for life processes
worms that ingest soil as well as the organic matter in the soil
Biodegradation can occur in the presence of oxygen (aerobic) or without oxygen (anaerobic). Anaerobic degradation occurs at the bottom of landfills where little oxygen is available.
Figure 4 – Through composting, which is an accelerated type of biodegradation, organic wastes are converted to nutrient rich soil.
Figure 5 – Not every piece of biological waste breaks down the same way. Anaerobic bacteria break down substances in location without oxygen, like at the bottom of a landfill.
As you watch the video "What Materials Biodegrade", complete the assessment as indicated on the worksheet.
When you are satisfied with your responses you can check your work by clicking on the "SUGGESTED ANSWERS" button below.
Wait! Don't view the suggested answers first.
This practice work is not for marks, it is meant to help you check your
understanding. Check the answers AFTER doing the questions! Keep the
practice worksheet for study purposes. If you don't understand
something, contact your teacher!
In the case of the Styrofoam, plastic bag, aluminum foil, and glass, there was no degradation – these items are not biodegradable because small organisms, bacteria, and fungi cannot feed on them.
In the case of all the other items, they all were broken down to some degree by organisms in the soil, so they are all biodegradable.
Using Biodegradation for Cleaning Up
How are living organisms used to clean up contaminants found in water and soil? Micro-organisms can be used to remove pollutants from the environment. If small amounts of oil spill in a lake or ocean, natural-occurring bacteria break
down the oil.
A site in Sarnia, Ontario was contaminated with an organic chemical called ethylbenzene. Approximately 400 tonnes of clay soil were dug up and placed in piles, and micro-organisms were added to the piles of soil. Within five months, concentrations
of ethylbenzene dropped from 434 ppm to 25 ppm.
Phytoremediation is the use of plants to clean up contaminants in soil, groundwater, surface water, and air. These plants can remove heavy metals, arsenic, petroleum, DDT, and many other substances from toxic soil.
The prefix "phyto" means “plant” and “remediation” comes from the word remedy, which means “restoring balance”. For example, water lilies can absorb extra nitrates that enter waterways from excess fertilizer. Water lilies are able to cleanse
the water and make it safe for wildlife and humans.
Figure 6 – The brake fern is able to remove arsenic from the soil.
Figure 7 – Alfalfa can be used to absorb spilled petroleum.
Figure 8 – Water lilies can cleanse the water.
Figure 9 – Some plastics slowly break down in sunlight.
Photolysis
The breakdown of chemicals in nature can also occur without the use of plants or bacteria. Photolysis uses sunlight to breakdown chemicals. Photolysis occurs in the conversion of nitrogen dioxide to ground level ozone and in the breakdown
of some plastics to smaller pieces in sunlight.
Photodegradable plastics can break down in sunlight into a fine powder that is easier to dispose of than the original plastic item.
