SYLLABUS REFERENCE

[E1] identify pollutants in the environment;
[E2] discuss the causes of water … pollution;
[E3] describe the effects of pollutants on human beings and the environment;
[E4] explain the methods of controlling pollution;
[E5] describe the water cycle;
[E6] describe simple ways of purifying water in the home;
[E7] describe the process of testing water for bacteria;
[E8] describe processes involved in large scale water purification;
[E9] discuss the impact of human activities on water supplies;
[E10] explain why contaminated water is detrimental to human beings.

WATER SUPPLY IN THE CARIBBEAN

A growing human population leads to an increased demand for water. Meeting that demand with a safe supply of water has become a social problem.

A large proportion of that demand comes from industry, which uses enormous quantities of water. In the Caribbean, paper making, steel manufacture and agriculture lead the industrial sector in the use of water.

Water security is a major problem for the Caribbean.

Less than 17% of Caribbean homes are connected to a public sewage system.
The demand for clean water is increasing but rainfall is decreasing.
Waste water is not recycled.
Attempts to provide drinking water by desalination of seawater is problematic. This is because large quantities of energy are consumed by desalination plants, and the waste product (brine) is a form of pollution when returned to the ocean.
Drinking water may easily become polluted by humans with chemicals and disease organisms. Purification of water is often needed.

THE WATER CYCLE

The water cycle outlines how water moves and recycles through the environment.

Precipitation: (I)

Water that falls from the air as rain, sleet, snow, or hailstones. It falls onto an area of land called the catchment region.

Surface run-off:

This is water from rain, snowmelt and other sources that flows over the land's surface. This water may flow into lakes, streams, and rivers, before eventually passing out into the sea.

As the run-off water flows over the ground, it picks up contaminants such as the phosphates and organic matter. The run-off passes directly into streams and rivers and may cause erosion, creating debris that silts up the water courses.

Run-off lowers the water table because the water does not enter the groundwater, making droughts worse for farmers and others who depend on water wells.

Filtration:

Some of the water soaks into the ground passing between the soil particles to reach the non-porous rock, developing a water table. From here, it flows underground, possibly breaking out to the surface again, before also entering the sea.

This decreases in built-up areas, as the water runs off artificial surfaces into streams, lakes, rivers, and drains.

Evaporation:

Water in the oceans, rivers, lakes and in soils changes state from liquid to a gas (water vapour). It is this water which rises to form clouds.

Both plants and animals produce water in the process of respiration. Water from animals is exhaled or lost from the body's surface into the air. For example, evaporation of sweat from humans.

Transpiration: (II)

Much of the water is absorbed by plants travels to the leaves where it evaporates. The water vapour diffuses out of the leaves through stomata (small holes in the surfaces of the leaves).

Respiration: (IV)

This is a chemical process which produces water, some of which is excreted from plants and animals.

Condensation:

Water vapour rises in the atmosphere and changes state to form liquid water in the clouds.

In countries with colder climates, where snow and ice form, freezing and melting are also involved in the water cycle.

Sources of Potable Water

Rainwater can drain through the soil deep underground into porous (permeable) rock such as limestone, sand or gravel. Groundwater can accumulate in spaces in the porous rock where is lies on top of non-porous (impermeable) rock, such as clay.

Surface Wells

There are not very deep. They can be dug into porous rock to the water that has entered the rock from nearby.

Aquifer

This is an underground layer of porous rock that collects this groundwater and holds it like a sponge.

Water which moves underground through the rock in this way is filtered, thereby removing most of the contaminants. Much of the water that is used in the Caribbean and elsewhere in the world is obtained by drilling deep wells into aquifers.

Artesian Wells

These wells release water under pressure. They are caused by rock formations that are shaped like a bowl. The water will gush through once a hole is made at the bottom of the bowl formation.

Well water used for drinking should be tested periodically. Faeces and urine can be detected by analyzing the water for ammonium compounds.

Water Testing

No matter the source of water, it will always be contaminated to some degree. It is therefore important to carry out testing of the water, especially for bacterial load.

The bacteria may be present in such low numbers, that they cannot be detected without some form of biological or chemical test.

One such test is growing bacterial colonies on agar plates.

You will need:

Drinking water samples

These samples can be taken from different water sources such as household taps, wells and stand pipes.
Samples should be refrigerated till one is ready to conduct the test.
All samples should be treated as if they contain harmful microorganisms!!

Petri dishes containing sterile nutrient agar jelly

What is Agar?

This is a powder to which nutrients such as glucose are added. Nutrient agar is dissolved in water and sterilised in an autoclave. It is then poured into sterile plastic Petri dishes.

Growing Bacterial Colonies on Agar

After the agar is added to the Petri dishes, a known volume of the water sample being tested is mixed with it before it solidifies.
The dish is sealed with transparent sticky tape, turned upside down and incubated in a warm place for 24 hours.
If bacteria are present, colonies will grow on the agar. Each colony develops from one bacterium or one bacterial spore.
These colonies can be counted and the number of bacteria per cm³ of water can be calculated.

If water is found to be unsafe to drink, it can be boiled or treated with water purification tablets. These tablets contain chlorine that forms hypochlorous acid (HClO) and oxygen, which kills bacteria.

One teaspoon of household bleach added to a liter of water is an effective purifier. It functions the same as the water purification tablets.

Small-scale or Domestic Purification of Water

There are several simple ways of purifying water so it is fit to drink:

Boil the water for 5-10 minutes to kill all the pathogens. This method will not remove chemical pollutants.
Use purification tablets containing chlorine or iodine to kill bacteria and destroy viruses, but these do not kill protozoa or remove chemicals. Add the tablet (as directed on the pack) and leave for 30 minutes to four hours before drinking.
Use bleach. Add four drops of bleach to one litre of water, shake or stir, and leave for 30 minutes. Bleach which has passed its expiry data may not be effective.
Use the Sun. Fill a clear, smooth plastic bottle wtih water, seal with the screw cap, shake it and lie the bottle on its side in bright sunlight. The WHO suggests using a black surface under the bottle and leaving the bottle for six hours if sunny or 24 hours if cloudy.
Filtration. If the water has particles in it, they can be removed by passing them through a finely woven fabric or filter paper (even coffee filters).

Clay pots can also be used as filters. Place a clean clay pot over another container and pour water into it. Sediment and bacteria will remain in the clay pot. However, viruses and chemicals will pass through it.

Large-scale Purification of Water

Step 1

Water is extracted from rivers, lakes and boreholes (wells). Constructing dams can make artificial lakes or reservoirs. Water may flow to the waterworks by gravity or pumps may be used.

Step 2

The water enters the water purification plant via screens. First coarse screens, which removes any debris such as leaves, twigs and plastic bottles. Next are fine screens, which remove suspended solids.

Step 3

The water flows into sedimentation tanks, where particles of soil fall to the base and are removed. Sunlight and air help to destroy bacteria at this stage. Within this reservoir, protozoa (which feed on bacteria) are in turn eaten by crustacean and insect larvae, who themselves fall prey to fish. Such food chains help to purify the water.

Step 4

Water leaves the reservoir through additional screens called micro-strainers. These have very fine meshwork, which is capable of removing plankton from the water.

Step 5

The water then passes to a settling tank where it is coagulated to help settle the particles. Colloidal particles are clumped together by the addition of a coagulant. Mechanical stirrers rapidly mix this coagulant with the water. The clumps formed are removed (as a form of sludge) by the process of sedimentation. Fine bubbles of air may be used to help the rise of sludge to the surface prior to its removal.

This aeration helps with the aerobic decomposition in water polluted with organic matter. The oxygen also removes carbon dioxide, which reduces the acidity of the water. The oxygen also converts any iron and manganese present to insoluble hydroxides.

The resulting gelatinous coagulant waste is formed into a filter cake for disposal.

Step 6

Water then passes through filtration tanks filled with sand - called slow sand filters. These filters have sand particles that become coated with a jelly-like film, secreted by microorganisms, which traps bacteria.

They can, however, get clogged easily and have to be cleared more frequently.

Layers of activated carbon are used in some filters. Coarser sand and stones in the lower layers help the water to flow.

Step 7

Water moves into a chlorination plant. The water is then treated with chlorine or ozone to kill bacteria.

Sometimes, flourides are added to drinking water to reduce the incidence of tooth decay in places where there is little naturally occurring fluoride in the water.

Step 8

The water is tested for purity and then pumped through pipes to water storage tanks and on to domestic and commercial customers.

WATER POLLUTION

This is the contamination of fresh water by pollutants so that it is no longer suitable for our needs. These needs include drinking, cooking & washing, as well as tourism, fishing and transport.

These pollutants usually come from human activities.

Since rivers in the Caribbean are so short, most of the pollution that accumulates there quickly gets transferred into the sea and coastal waters.

In the Caribbean, water pollutants are destroying mangrove swamps, a natural habitat for many organisms, such as birds, crabs, fish and oysters. In the same way, valuable coral reefs are under threat from pollutants.

Farming, discharge of waste water, shipping, overfishing and tourism are the main human activities that produce these pollutants, causing damage.

Where waste management is not well controlled, water courses and coastlines become polluted with plastic waste, - especially plastic bottles - styrotex food containers, fishing gear, and car tyres. Where these objects collect and block water courses, flooding may occur.

The Impact of Human Activities on Water Supplies

Humans take too much water from the environment for domestic, industrial and agricultural use. Much of this is wasted.
Pollutants enter water supplies and it is expensive to treat the water to remove them.
Drainage from farmland and from built-up areas reduces water that percolates through the soil to the water table.
Runoff from artificial surfaces, such as roads, contributes to flooding.
Deforestation reduces the amount of water absorbed by plants, so contributing to flooding and reducing the volume of water transpired into the atmosphere.
Dams and reservoirs secure water supplies for people, although they can use cause environmental problems, such as providing breeding grounds for disease vectors.
Development, especially for housing and tourist accommodation, causes destruction of wetlands, which are a valuable source of water.

TYPES OF POLLUTANTS

Industrial Chemical Wastes

Two of the worst offending industries for water pollution are food processors and paper manufacturers. They discharge large quantities of organic matter into water, which reduces oxygen content (See Sewage and Detergents).

Some industries release toxic metals, such as mercury and lead, which are especially poisonous to fish.

Polychlorinated biphenyls (PCBs) & heavy metals are absorbed by small organisms such as plankton. These chemicals then pass down the food chain & accumulate at each trophic level. By the time it reaches top predators, the concentration is high enough to negatively effect physiology, often reducing fertility.

Disposal of electronic equipment, such as old computers, is a major problem, because of the mercury and lead they contain. Specialised industrial plants are required for their disposal.

Thermal pollution

This is caused by power stations and manufacturing industries that use water as a coolant. It happens when water that has been warmed is returned to the environment, heating up a pond, lake, stream or ocean. In some cases, cold water is discharged into warmer seas. This is also a form of thermal pollution.

Gases are less soluble in warm water, so this decreases the oxygen supply to organisms for respiration.

Solutions

Many countries have laws to prevent disposal of hazardous materials into the environment, and inspectors make checks to ensure proper procedures are followed.

Sewage

Sewage is made up of faeces and urine mixed together with domestic waste water (from sink, showers, and baths).

It is a highly dangerous pollutant, mainly due to high concentrations of pathogens. Water that is contaminated with sewage spreads diseases such as typhoid, cholera, dysentery, and gastroenteritis.

Sewage treatment rates in the Caribbean are low and marine pollution from untreated sewage has been identified as a significant risk to the economy.

Effect of Sewage on an Aquatic Ecosystem

The discharge of sewage into a body of water, such as a stream or river, immediately raises the organic content of the water.
Bacteria in the water and sewage decompose the organic material, using up the oxygen in the water as they respire, and contributing to eutrophication.
The suspended solids in the sewage make the water cloudy.

Light cannot pass to plants in the ecosystem, and so photosynthesis stops.

With no photosynthesis and no oxygen, plants and animals cannot live in such water. Therefore many species die off.
Away from the source of pollution, when the microorganisms have consumed the organic matter, slow recovery of the environment occurs. Plants are able to grow and the oxygen is replenished.

Detergents

These chemicals provide a rich sources of mineral salts such as phosphates, and so cause eutrophication.

They have both domestic and industrial sources. Factories may discharge detergent so that a mass of foam forms on the surface of the water. Foam makes a barrier that slows down the entry of oxygen into the water, so organisms cannot respire.

EUTROPHICATION

This is the excessive growth of water plants such as water weeds and water hyacinth, as well as floating algae. Excessive algal growth is referred to as an 'bloom'.

This massive plant growth occurs when additional plant nutrients are washed into the water. Mainly nitrates and phosphates, which enter the water bodies in one or more of the following ways:

fertilisers, which are a rich source of mineral nutrients especially nitrates, get leached from the soil into nearby streams
bacteria decomposes organic matter in sewage and other sources, which releases a wide variety of mineral salts.
the detergents from sewage and industrial wastes are particularly rich in phosphates.

Eutrophication is particularly a problem or inland waterways, such as rivers and ponds.

It tends to lead to the following sequence of events, with very negative consequences:

The algal bloom and/or excessive plant growth prevents sunlight reaching other plants below. They then die, leading to a drop in the oxygen being produced and released into the water.
Bacteria decompose the dead plants, using up even more oxygen as they respire.
Eventually, there is not enough oxygen in the water to sustain larger organisms such as fish. This leads to fish kills.
Eventually all the living organisms in the water die by suffocation.

Preventing Eutrophication

Install improved agricultural drainage systems
Avoid the use of fertilisers and manures close to water sources. This can reduce leaching and run-off
Leave a wide strip of deep-rooted plants along the margins of ditches, streams and lakes. They would help to absorb and filter run-off. This can also be cheaper than using expensive drainage systems.
Gardeners in both urban and rural areas should avoid the use of phosphate fertilisers. They should also prevent their garden waste from entering storm drains, which would then carry the organic material into the waterways.
In gardens and cities, instead of planting and continually mowing short grass near waterways, developers should plant wildflowers, tall ornamental grasses, shrubs and trees. These plants absorb and filter run-off that contains nutrients and dislodged soil, as well as provide habitats for wildlife.

(Spilled) Oil

Ships and offshore oil rigs are the main sources of this pollutant. As a result of shipping and industrial accidents, oil is sometimes spilled into the sea and floats on the surface of the water. It produces oil slicks.

Cruise ships, container ships, oil tankers, and oil exploration are responsible for oil spillage in the Caribbean.

These slicks causes environmental damage to coral reefs, sea grass communities and beaches. The most prominent victims tend to be sea birds that become coated in oil.

Other negative impacts include the following:

The oil often blocks the gills and other respiratory organs of animals
Lack of oxygen in the water and organ damage prevents respiration and causes death
The oil may stick to the feathers of birds and prevents flight. The oil has to be removed by detergent or the animals die
Spilled oil frequently gets washed up onto beaches, fouling the shoreline and destroying the wide variety of life in this habitat.
Cleaning up oil-contaminated beaches is an expensive and time-consuming operation.

Pesticides

These are chemicals used to kill pests of various forms, from weeds to rodents. There are several types:

Herbicides: used to kill weeds that compete for space and nutrients with crop plants
Insecticides: used to kill insects that eat crops (caterpillars, beetles, aphids) and transmit disease (mosquitoes, houseflies).
Fungicides: used to treat fungal crop diseases
Rodenticides: used to kill vermin, such as rats and mice.

A major problem with pesticides is that they kill harmless and important organisms, along with the pests. This can lead to the extinction of useful organisms, such as pollinators.

For example, the numbers of ladybugs that eat aphids have been drastically reduced in the Caribbean due to the aggressive use of insecticides.

They are all soluble in water and can be washed into waterways. From there, they can enter the food chains and accumulate as they are passed from one organism to another.

For example, DDT washes off the land into fresh water, and is picked up by aquatic plants. However, since it accumulates in body fat, so it passes from prey to predator, and high levels are found in top carnivores.

Humans accumulate DDT in their bodies as well. In humans it may cause babies to be born prematurely and it can be a carcinogen. Bioaccumulation of DDT that reaches humans is quite common in places where DDT has been used to destroy mosquito larvae in water for dengue control.

Solution

The use of DDT has been banned in most countries. However, it is relatively cheap and mosquitoes have become resistant to some of the newer pesticides. Therefore, particularly in some African countries, it is still used.

The wide use of pesticides has caused resistance to develop in some species. For example, rats that are resistant to the pesticide warfarin are a major problem in several areas, such as large cities like New York.

CASE STUDY - Chlordecone

This chemical, Chlordecone, is known in the US as Kepone. It is a chlorinated chemical, similar to DDT. It was recognized as hazardous in 1972 but was only banned in 1975 after several hundred workers were contaminated at a factory in Hopewell, Virginia. Their symptoms included nervous tremors, slurred speech, short-term memory loss and low sperm counts.

However, in Guadeloupe and Martinique, it was used for two decades before being banned in 1993. It was sprayed in plantations to kill borers (weevils) that attack banana plants. Chlordecone unfortunately breaks down very slowly and now large areas of soil on these islands are contaminated, as well as the rivers and coastal waters.

A study in 2013 to 2014 found that, among adults in Martinique, 95% had chlordecone in their blood, while the figure for Guadeloupe was 93%.

Fortunately, the pesticide does not contaminate bananas and drinking water, as it can be filtered out with carbon filters, as part of the water treatment process.

The authorities are trying to keep the chemical out of the food chain, but it is difficult, as much produce comes from smallholders and is sold at the roadside without controls.

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CSEC Biology Notes

WATER CYCLE, WATER TREATMENT & WATER POLLUTION [CSEC HSB]