Food supply, Habitat destruction and Pollution

Learning objectives

At the end of this unit, you should be able to:

- describe the negative impacts to an ecosystem of large-scale monocultures of crop plants and of intensive livestock production
- discuss the social, environmental and economic implications of providing sufficient tood for an increasing human global population
- state the reasons that lead to habitat destruction
- explain the undesirable effects of deforestation on the environment
- explain the problems that contribute to famine including unequal distribution of food, drought and flooding, increasing population and poverty
- state the sources and effects of pollution of land and water (rivers, lakes and sea) by chemical waste, discarded rubbish, untreated sewage and fertilisers
- describe the undesirable effects of water pollution by sewage and chemical waste (pesticides and herbicides), with reference to eutrophication
- describe the overuse and dangers of fertilisers on the land (e.g. nitrates)
- discuss alternatives to the use of large amounts of industrially produced fertilisers
- state the causes and effects of acid rain on the environment and the measures that might be taken to reduce its incidence
- discuss the effects of non-biodegradable plastics on the environment, in both aquatic and terrestrial ecosystems.

 Monoculture
Monoculture is the growing of the same crop on the same piece of land every season, year after year. Modern farming techniques produce abnormal ecosystems, such as large fields with only one species of crop plant. When one species is cultivated to the exclusion of all others, it is described as monoculture.
Monoculture produces a potentially unstable ecosystem. It is unstable because all the plants are usually all the same strain or identical clones. They are all equally resistant, or Susceptible, to any particular pest. A pest will rapidly colonise the whole field and destroy most of the crop. Careless use of pesticides may make this more likely. This is because when the pest is killed, so too are many of its enemies. For example, you might spray your plants to kill greenfly, but this will also kill the ladybird beetles that eat the greenfly. If you do this on a field of crops, the field will have no natural pest killers. The pest could return before its natural enemies do. If it does, there will be a population explosion and the crop will be lost. The only way to control this is to use even more pesticide. Monoculture is currently the cheapest way to produce food and so we cannot blame farmers for this practice. People demand large quantities of cheap food and monoculture provides it.

# The social, environmental and economic implications of providing sufficient food for an increasing human global population
An increasing global population means more resources are needed to meet the increasing demand. At the most basic level, people need uncontaminated food, clean and safe water supplies, shelter, clothing and good health. Resources are also required to make all the things that we use in our daily lives.

 Consequences of resource exploitation
  There are socio-economic Consequences:
- As sources of energy are depleted, prices rise, for example, an increase in your water and electricity bill. This could mean the elderly and those with low incomes are unable to afford energy to meet their basic needs.
- The gap between the rich and poor becomes more evident.
- Funding is needed for research into alternative energy, and there are increased costs for exploration and extractionof existing energy sources.
There are environmental consequences:
- Increased carbon emissions cause global warming. This causes climate change and a rise in sea levels due to melting ice caps.
- Air pollution from the burning of fossil fuels and car exhausts increases, as countries industrialise and exploit resources.
- Ecosystems, such as forests and oceans, are under threat as Namibia exploits resources tor development and due to overfishing.
 There are political consequences:
- There is a need for international cooperation, such as global agreements like the Kyoto Protocol, to reduce carbon emissions, and a need for stimulating green investment to meet the agreed emission target in a cost-effective way.
- There can be loss of public support for governments as domestic water bills and electricity rise. People are forced to change their lifestyle, which is unpopular.

 Sustainable use of resources
 The world's natural resources have contlicting demands upon them and can be difficult to manage.
The conflicting demands for resources are:
- The environment should be preserved.
- Resources need to be retained tor future generations to enjoy.
- Humans need to continue to make and do the things that allow them to live comfortably.
- Low-income developing countries need to develop through exploiting their resources.
- There should be a better balance between the consumption of those resources between low-income developing countries and middle-income developing countries.

To conserve natural resources for future generations, sustainable management of the natural environment is necessary. Alternative resources might be developed in order to ease the strain on finite resources. However, alternative resources can be expensive and take time to develop. Existing resources could be used more efficiently to prevent fin resources being used up so quickly.

Ways to Iimit the damage caused by humans to the environment include:
 Sustainable resource management:
This helps ensure that the use of resources does not cause an imbalance in the environment. Increasingly, sustainable practices
are being encouraged to preserve animal and plant life for the benefit of future
generations. An example of sustainable development is eco-tourism. Tourists are able to enjoy areas of natural beauty without causing over-development that might harm the environment.
 Recycling resources reduces waste:
Used cans, bottles, paper and cardboard can be recycled and reduce the need to use extra resources.
 Limiting carbon emissions generated from industrial and domestic use of Fuels:
This can assist in reducing pollution levels and limit environmental problems, Such as global warming and acid rain. Some nations, including the UK, signed the kyoto Protocol to say that they will try to reduce carbon emissions.
Resource substitution:
This  is another sustainable way in which resources can be managed. Renewable resources can be used instead of finite resources. Electric power can be produced with a renewable source such as tidal, wind or solar power, instead of fossil fues.

# Habitat destruction
A habitat is the natural place where plants, animals, or other organisms live, it is a place they call home. This is the living area necessary for an ecosystem to remain healthy. Destruction means to change something so much that it can no longer exist as it once was. So, when we put the two definitions together we get: habitat + destruction = a home to species that has been changed to the point that it no longer exists. There are many types of habitat destruction that can change entire ecosystems. Habitat destruction can even wipe out an entire species. Habitat destruction occurs when enough change has happened to an area that it can no longer support the natural wildlife. This change can be in many forms, including destruction, fragmentation, and degradation. But no matter how it happens, the plants, animals, and other organisms whose habitat has been destroyed no longer havea home.
Causes of habitat destruction
Picture a bulldozer pushing its way through the woods, creating flat open land so that a wooded area can be turned into a subdivision or office building. As the bulldozer is knocking down trees, it is also crushing grasses and packing the ground super tight. The bulldozer is not only killing the trees and other plants that it is running over, but it is killing the living area of multiple species. This is just one example of habitat destruction, known simply as destruction. Destruction is instant and the species have little to no time to adapt. The animals must move if they are to survive at all. Plants must adapt to the newly compacted land or find a way to disperse their seeds elsewhere.
Another example of instant destruction to habitats is when humans fill in wetlands. We fill in wetlands usually to construct other buildings, such as work spaces or houses. Sometimes it is the law that if you are filling in a wetland in one area, then you must create a new wetland area somewhere else. However, wetlands are home to some of the most diverse ecosystems and many species are destroyed in this process. Mowing fields and cutting trees are other examples of instant habitat destruction.
When roads or dams are created, the habitat is altered, but not completely destroyed. This type of habitat destruction is called fragmentation. Fragmentation is when the habitat is broken up into pieces or fragments. A road could cut the area of the habitat in half with the result that a species has a lack of options with which to mate. This type of destruction can also cause a lack of resources, such as food. Migratory species need a place to rest when they are moving from one area to another. When the land or water is shrunk down due to roads or dams, then their options for resting areas are limited. Fragmentation is not as instant as destruction, but it can be fatal to many species. Look at the image of a wetland near the Ugab River, this is home to frogs, water lilies, birds and insects. If a road was put in the middle of the wetland, it might split theseorganisms. Some organisms may migrate to other areas. The road alters the habitat for the organisms. They have decisions to make and sometimes the choices are slim and dangerous.
Like destruction and fragmentation, degradation can also cause habitat destruction. This type of destruction is not always as easy to see as destruction and fragmentation. Instead, degradation is when a habitat becomes polluted or is invaded by a non-native species, otherwise known as an invasive species. Degradation is when something interrupts the ecosystem process and starts a chain reaction to the point that the habitat can no longer support wildlife. Human-made causes of habitat destruction include construction of both previously undeveloped areas, as well as new construction on the fringe of developed areas. Deforestation for construction can have a huge impact on many different animal species. A wetland area may be filled in to build a structure or road on. A field may be moved To make the area more esthetically pleasing, or to purposely discourage the presence of wildlife from a developed area.
Agriculture is another human-made cause of habitat destruction. Again, land cut clear of trees or natural grassland mowed to provide farmland can destroy the habitat of mammals, insects, or birds. In addition, efforts to irrigate farmland and provide water for farm animals can impact habitat, either by taking water from an area, or adding water to an area that was previously dry. Global warming is a process that human activity has contributed to. Burning fossil fuels anddeforestation have both contributed to increased carbon dioxide in the atmosphere. The increased carbon dioxide in the atmosphere keeps solar heat in the atmosphere. Global warming is an important cause of habitat destruction for polar bears, as the sea ice of the Arctic Ocean is melting. The sea ice platforms are retreating, making it more difficult for the polar bears to swim from shore to ice. This interferes with their ability to successfully hunt seals. Polar bears are likely just the tip of the iceberg with regard to the species that will be affected by global warming. Fire is another culprit that can fall under human-made or natural causes of habitat destruction. Human error or intent can result in forest fires. Lightning strikes can also result in serious fires. Either way, the end result can be devastating to species that live in grasslands or forests that are damaged by fire. Natural disasters can be causes of habitat destruction. Examples of natural disasters that can be devastating include earthquakes, floods, and tornadoes. Earthquakes can physically move the land, and may be associated with subsequent tsunamis. Floods can destroy the vegetation and cause erosion of the land. Tornadoes can physically rip trees out of the ground and crush vegetation with debris that is strewn about. There are some ways we can try to reduce causes of habitat destruction, including attempting to minimally impact an area with new construction, by using existing addition, promoting the use of renewable energy sources and finding alternatives to deforestation may help slow down the effects of global warming. Unfortunately, there are some causes of habitat destruction that are out of our control. Efforts to mitigate farmland instead of creating new farmland, and being extremely cautious with fire. In destruction can be attempted by planting trees and plants native to a specific area where there has been destruction.

 The undesirable effects of deforestation on the environment
Deforestation is the cutting down of large numbers of trees. Trees are removed to clear the land for crops because growing food is more profitable than growing trees. Trees are sometimes destroyed by uncontrolled fires caused by people in rural areas clearing landfor growing crops. Burning trees is easier than cutting them down! Hunters sometimes burn large areas of trees to chase animals out of the forest so that they are easier to kill. Trees are also cut down to provide wood for cooking, heating, making furniture and for building materials. The grazing of livestock in forest areas prevents young trees from growing, because the animals eat the young tree seedlings and trample them.
 Deforestation can result in:
- the destruction of habitats, leading to the extinction of many species of plants and animals.
- a reduction in the rate at which carbon dioxide is removed from the atmosphere during photosynthesis.
- an increase in the level of carbon dioxide in the atmosphere as a result of the burning of the trees.

 Modern technology and food production
Only about 30% of the land on Earth can be used for food production. The other 70% is unsuitable, for example, it may be too dry or too steep. Crops are grown on only about half of the land that could be used for food production, the rest is either used for growing trees or grazing animals. In many countries, the amount of food produced by an area of land can be increased by the use of:
- fertilisers to increase crop yields.
- pesticides to control disease.
- machinery to bring land under control.
- using varieties of plants and animals that are resistant to disease and give greater yields.
There are advantages and disadvantages of using modern technology in food production, as listed below.
Use of fertilisers
Advantage
By using fertilisers, bigger and better crops can be grown on a piece of land; without fertilisers, the crops would be smaller and more likely to be affected by disease.
Disadvantage
Fertilisers can be expensive; careless use and overuse of fertilisers can cause pollution of land and water, living organisms in rivers and lakes are affected and often killed.
Use of pesticides
Advantage
Pesticides kill insects, fungi and other pests, which would seriously damage the crop and afftect crop yields.
Disadvantage
Pesticides can be expensive; overuse of pesticides can cause the pests to become resistant so they are no longer killed by the pesticide, pesticides are poisonous if the pest is eaten by birds, then the birds are affected by the pesticide and may die.
Use of machinery, such as ploughs and tractors
Advantage
Machines can be used to turn over the soil, plant new seeds and collect crops, time is saved and human labour is used more efficiently as fewer agricultural Workers are needed and people can be trained to do other work.
Disadvantage
This can involve huge costs in purchasing the machineny, spare parts and fuel; technical knowledge is required to maintain the machinery and fit spare parts.

Overuse of fertilisers
Fertilisers are important to ensure a good crop. But the nitrates in the fertilisers are very soluble. Any nitrates put onto the soil and not immediately taken up by plants can be washed away. This is called leaching. The leached fertilisers may be washed into rivers, streams and dams.
Nitrates stimulate the growth of water plants and algae, which causes considerable damage. For example, the algae grow so much that the water looks green and thick. This, in turn blocks out sunlight for the plants growing lower down in the water and so the plants die. This process is called eutrophication. This happens whenever plant nutrients or organic wastes, such as faeces from livestock, get into water sources. Eutrophication can also be caused by untreated sewage and waste from factories producing foodstuffs. Figure above shows the effect of high concentrations of fertilisers in water. As you can see in Figure above, bacteria respire and use up a large amount of oxygen when they decompose the plants that have died. Large populations of bacteria result in the reduction of the amount of oxygen in water. Fish and other animals that need oxygen are killed.

 Preventing problems caused by overuse of fertilisers
 Many of the problems resulting from the overuse of fertilisers can be overcome if fertilisers are used sensibly and carefully. It is important to follow some simple guidelines:
- Apply the correct amount of fertiliser; never over-fertilise the land.
- Do not apply fertiliser during wet weather, if it is likely to be washed away.
- Use manure and other natural fertilisers as much as possible.
 Organic fertilisers
Organic fertilisers are not human-made, but they are made naturally. Examples are  manure, blood and bones, guano, compost and kelp products. Organic fertilisers contain lower levels of nutrients and might take longer than inorganic fertilisers to be absorbed, as they generally have to be destroyed first. However, organic fertilisers increase the organic component of the soil. This improves the physical structure of the soil, which in turn increases the soil's water-holding capacity. The nutrients also tend to be released slower than those of inorganic fertilisers, decreasing their contribution to water pollution.
 Manure
Manure is a solid waste product from animals that is widely used as an organic fertiliser in agriculture. It contains high levels of nitrogen, phosphorus, potassium and other nutrients. Manure decomposes over time through bacterial and microbial action, and in the process releases these nutrients into the soil. This slow release mechanism is a great benefit to farmers as it limits the leaching of nutrients into the ground water, making it available to plants over a longer period of time. Manure also adds organic matter to the soil, increasing the quality of the soil itself. Plants can only absorb nutrients that are dissolved in water. When manure decomposes, the nitrogen compounds are converted to a form that is soluble in water, for example, nitrates (NO₃). The nitrates are dissolved in the moisture in the soil and plants are then able to absorb the nitrogen compounds through their root system.
 Lime
Agricultural lime, or crushed limestone, can be used as an alternative fertiliser. Lime increases the pH of the soil, making the soil less acidic and more soluble for nitrogen, potassium and phosphorus compounds. These nutrients will therefore be more readily available for absorption by plants.
 Crop rotation
Crop rotation is a farming method that is used to manage the nutrients in soil naturally when the same crop is grown repeatedly in the same place, it eventually depletes the soil of specific nutrients. with crop rotation, one type of crop that depletes the soil of a particular kind of nutrient is rotated with another type of crop that replaces the depleted nutrient. For example, legumes, like beans or peas, have nodules on their roots that contain nitrogen-fixing bacteria. When the same crop is planted from year to year, only one single group of minerals is continuously taken from the soil. The soil becomes poor and is easily blown or washed away. However, if three or four different crops are grown in rotation, the farmer benefits in several ways:
- The structure of the soil is improved.
- The chances of infectious diseases that can enter the crop through the soil are reduced; for example, if you plant tomatoes year after year in the same field, fungal diseases that cause wilting will increase.
- The nitrate content of the soil is replaced by leguminous crops because their root nodules contain nitrogen-fixing bacteria.
- Crop rotation improves yield and saves on the use of pesticides and fertilisers.

 Irrigation
Over-irrigation causes soil erosion that washes away important minerals. When irrigated water evaporates, it leaves behind salts that poison the soil. This causes the soil to lose its fertility. Soil fertility is the soil's capacity to produce a high yield of crops. Farmers use more water to irrigate their crops. As a result, they pay a high price for equipment and water.

Land and water pollution
Pollution is the addition of substances to the environment that may be harmful to living organisms. Population growth and a higher standard of living cause more waste to be produced. It this waste is not handled correctly, it leads to pollution.
Land pollution
In order to improve the yield from their land, most farmers spray their crops with chemicals called herbicides and pesticides.
Pesticides and herbicides
- Pesticides are chemicals used to kill pests. A pest is any animal that has a negative effect on human activities, for example, caterpillars and locusts eat plants, and some fungi cause a number of blight and wilt diseases. Pests also compete for resources and they carry diseases to the plants, such as viruses.
- Herbicides are chemicals used to kill weeds, which are plants growing in the wrong place.
The advantages of using pesticides and herbicides include the following:
- They reduce crop loses.
- They control the spread of diseases.
- They increase food production.
 Wide-spectrum pesticides
Many pesticides and herbicides are described as wide-spectrum or non-specific. Wide-spectrum and non-specific means that the pesticide or herbicide might kill a wide variety of organisms, especially harmless or even beneficial species, such as birds. Some wide-spectrum herbicides kill all green plants. On the other hand, some pesticides are very specific. Some just kill a specific species of insect, or a particular virus.
Persistent pesticides and the food chain
Pesticides may become more concentrated as they move along a food chain. For example one of the first insecticides to be widely used in the 1950s and 19605 was DDT. DDT is soluble in water and fat and has a very long active life. It is stored in the fat tissues of animals and people, and becomes more concentrated in each successive organisms it is passed along a food chain (biomagnification). Figure below shows how DDT becomes concentrated in the food chain. You can see in Figure below how DDT builds up in the bodies of the larger animals as they feed on many smaller animals. At these higher concentrations, the pesticide may become harmful to other organisms. Persistent pesticides, such as DDT, can be washed into streams and rivers. They may be carried in the water and do much harm far from where they were applied DDT has now been banned in most developed countries because it cannot be broken down easily. However, tens of thousands of tonnes of DDT are now used in southern Africa annually, mostly to control malaria mosquitoes in the north of the region.

 Ways to reduce the amount of pesticide used
 We can, however, make improvements and make economies:
- The farmer could benefit from more specific pesticides that just kill the pest.
- An alternative may be to apply the pesticide only at the right time.
- It is only worth spraying when pests reach a certain number. It may then be possible to kill pests just as efficiently, but with less pesticide.
It is common practice to spray the crop each season with the appropriate pesticide. This is done whether the pest is present or not. This guarantees crop yields. Nevertheless, pesticide is wasted during the times that the pest is not present. Pest numbers, particularly of aphids, can be forecast. Then the pesticide can be applied at the right time.

 Water pollution
Water pollution is caused by the discharge of harmful substances into rivers, lakes and seas. Fertilisers are used by tarmers to increase their crop yield, supplying extra minerals to their plants so they grow better. However, these minerals can run off into watenways and lead to a process called eutrophication. This involves the over-growth of algae and ultimately leads to oxygen depletion from the water and the death of invertebrates and fish. This causes food chains within the ecosystem to collapse. Sewage may also pollute waterways. Sewage consists mostly of waste water from the kitchen, bathroom and toilet. It Contains human urine and faeces, which may contain bacteria, parasites and other disease-causing organisms. Improper sewage disposal is a major cause of water pollution. If raw sewage is discharged into rivers and lakes, or allowed to soak into ground water near sources of drinking water, then drinking water can become contaminated. There are two major problems which can occur - disease and eutrophication:
- Diseases may be transmitted when a person swims in or drinks contaminated water, or eats food that has come into contact with it. Diseases such as cholera, typhoid and dysentery are spread in this way.
- Untreated sewage also causes eutrophication, similar to the problem caused by nitrate-containing fertilisers, which was discussed earlier. These problems can be avoided If the raw sewage is treated before it is allowed into the environment.
Waterways can also be polluted by toxic chemicals from industries and mining.

Air pollution and acid rain
 Sulphur dioxide and air pollution
With the increase in population and urbanisation, there is an increased demand for energy, in the form of wood, electricity and petrol. The gas, sulphur dioxide, is produced whenever coal, gas or oil is burnt. Large amounts of sulphur dioxide are formed at power stations, where large quantities of fossil fuels are burnt to generate electricity. Some other industries also burn large amounts of these fuels. Sulphur dioxide is a dangerous pollutant of the atmosphere. It is very harmful to plants as it is taken into their leaves through their stomata. The leaf cells are killed, and the leaves may drop off. If a lot of the leaves are damaged, the plant may die. Sulphur dioxide may also be harmful to people. People living near industries that burn a lot of fuel may breathe in air containing small amounts of sulphur dioxide. If they go on doing this for a long time, they are more likely to get colds, bronchitis, and asthma attacks. In some countries, the levels of sulphur dioxide in towns and cities are now much lower than they used to be. Clean Air Acts have prevented people from having coal fires and have made sure that factory chimneys are very tall. The sulphur dioxide is therefore lifted high into the atmosphere to be carried away by the wind. In countries without a Clean Air Act, levels of sulphur dioxide are still unacceptably high.
Carbon dioxide
One other major source of air pollution in the world is carbon dioxide. You will remember from our study of photosynthesis how vital carbon dioxide is to life on Earth. Overproduction of carbon dioxide as a result of industrialisation is, however, becoming a problem. Scientists think that carbon dioxide is contributing towards the greenhouse effect.
Acid rain
When fossil fuels, such as coal and oil, are burnt, they release the following gases
- sulphur dioxide (SO₂)
- carbon dioxide (CO₂)
- nitrogen oxides (NO₂)
These gases dissolve in water to form weak acids. Sulphur dioxide reacts with water to form sulphurous acid (H₂SO₃), which then reacts with oxygen in the atmosphere and forms sulphuric acid (H₂SO₄). Other gases, such as nitrogen oxides, can also form acids. This happens high in the atmosphere and the acid may be carried for hundreds of kilometres before it falls to the ground as acid rain. 'Normal' rain is slightly acid anyway, because some carbon dioxide dissolves in it and forms a very weak acid called carbonic acid (H₂CO₄). Similar processes happen with the nitrogen oxides, forming nitric acid. Normal rain has a pH of around 5 or 6. Rain with sulphuric acid in it can sometimes have a pH as low as 2 to 3, the same as vinegar! Acid rain is widespread. It can fall on a forest or lake many hundreds of kilometres away from the source. Often the people who suffer from it are in a different country from where the rain is produced. The major contributors to acid rain are electricity power plants, industrial boilers and smelting plants.
The effects of acid rain
Acid rain:
- damages buildings and statues, especially those made of marble and limestone; the acid dissolves the limestone and causes it to crumble away.
- corrodes metals and causes them to rust.
- reduces the productivity of farmland and forests.
When the acid rain seeps into the soil, it washes out important ions like calcium, magnesium and aluminium. One of the effects of acid rain is to cause the soil to release poisonous metals, which are absorbed by trees. These metal ions might also leach out to rivers and lakes, and killfish and other freshwater organisms. Acid rain can also make the water itself more acidic, so that animals and plants cannot survive.
 Ways to reduce acid rain
Various countries have laid down strict rules on how much sulphur dioxide and nitrogen oxides are permitted to be released into the air. Methods employed in restricting output Or these gases are, however, very expensive and result in an increase in costs. For example, in electricity-generating plants, waste gases can be passed through scrubbers that remove sulphur dioxide. Car exhausts can be fitted with catalytic converters to convert the gases to less harmful products.In the long term, we can reduce acid rain by burning less coal, oil and gas. We will have to do this anyway, because these reserves will not last forever. We will also have to use alternative forms of enerqy, such as nuclear, wind or solar power.
 Pollution caused by nuclear fall-out, plastics and inorganic waste
Nuclear fall-out
The average nuclear power station produces no acid rain gases or carbon dioxiIde, or even smoke. The average coal-fired power station releases more radioactivity into the air than is released from the average nuclear power station. So why is there so much fuss about nuclear power? There is the potential for catastrophic damage if there is a nuclear accident furthermore, nuclear power stations require more safety features and higher technology they also need somewhere to dump waste. This waste remains dangerous for thousands of years. The biggest threat to safety is from airborne particles of radioactive material. This material eventually settles as nuclear fall-out many hundreds or thousands of kilometres from the source. A nuclear reactor at Chernobyl, in the Ukraine, exploded in 1986. Most of Europe had measurable amounts of the radioactive tall-out from Chernobyl. Even now, large areas of land near Chernobyl are uninhabitable. Radioactive fall-out contains elements such as plutonium, iodine, cobalt, and strontium. These elements are radioactive and they may be absorbed by the body. For instance, strontium is deposited in the bones. This strontium then irradiates nearby tissue. Radioactivity is carcinogenic. Most of the other problems with radiation sickness are treatable to some degree. But even after the initial sickness is over, there is an increased danger that some form of cancer will occur. This remains asa lifetime of increased risk.
 Non-biodegradable plastics
Non-biodegradable plastic does not break down. Many plastics are still non-biodegradable, although research has now resulted in some biodegradable plastics, which can be treated and their components returned to the system. Decomposers, such as bacteria and fung are unable to break down plastics. Plastics cannot be digested. Because of this, many organisms have been found within large amounts of plastic in their guts, which may block the gut. Another problem is that many marine organisms have been found choked or strangled in nylon line and pieces of nylon fishing net.Plastics are so resilient that they may be carried long distances. Foam polystyrene granules are often found on beaches around South Africa. They are even found on beaches of mid-oceanic islands. Plastic bottles and containers are afloat all over the oceans of the world. The rate of breakdown of plastic is much lower than the rate at which it is produced. Consequently, more and more plastic will appear in the environment. Plastics are difficult to recycle. There are so many different types of plastics and they are difficult to sort for recycling. They can be destroyed by burning, but they produce large amounts of poisonous smoke and gases. Plastics could be made biodegradable if biodegradable filler material, such as starch or fine sawdust, were added. Then, as the filler biodegrades, the plastic would also disintegrate.

Inorganic wastes
Many industries and mines produce large quantities of waste substances that contain inorganic chemicals, such as lead, arsenic and mercury. If any of these substances get into rivers, lakes or dams, they act as pollutants. They are highly toxic and can cause serious health problems, even death. This build-up of toxic substances in organisms as a result of long-term exposure to toxic waste is called bioaccumulation. These substances are also taken into the bodies of bacteria and microscopic animals and plants. From here they enter food chains and may be absorbed by humans who eat fish or shelfish taken from polluted water.

 The End, Posted By Miss Elisabeth N.