causes of water pollution and enumerate the microbial population by some of the microbiological tests

1. WATER POLLUTION is defined as the presence in groundwater of toxic chemicals and
biological agents that exceed what is naturally found in the water and may pose a threat to
human health and/or the environment. Additionally, water pollution may consist of chemicals
introduced into the water bodies as a result of various human activities. Any amount of those
chemicals pollutes the water, regardless of the harm they may pose to human health and the
environment.
The chemical and biological agents represent the main causes of water pollution and are
generically referred to as water pollutants.
TYPES OF WATER POLLUTION
There are various types of water pollution based on the various causes of water pollution.
1. Chemical – when various chemicals are the water pollution causes. The following
chemicals are the most common water pollutants: Crude oil and various petroleum
products, Fertilizers, Chlorinated solvents, Antibiotics, Petroleum solvents, per chlorate,
pesticides/insecticides/herbicides
2. Radiological – when radioactive materials are the water pollutant causes.
3. Biological – when various microorganisms (e.g., bacterial species and viruses), worms,
and/or algae occurring in a large number are the water pollution causes. This type of
pollution is caused by decaying organic material in water, animal wastes, as well as
improper disposal of human wastes.
WATER QUALITY TESTS
Various water quality tests are available to detect the number and types of
microorganisms in waters and assist communities in keeping the microbial content of water
supplies at a low level. These tests vary from the more sophisticated tests to the standard
procedures that have been used for decades.
A. The Membrane Filter Technique
• It uses a filtration apparatus and a cellulose filter called a membrane filter.
• A 100-ml sample of water is passed through the filter, and the filter pad is then
transferred to a bacteriological growth medium.
• Bacteria trapped in the filter grow on the medium and form colonies.

2. • By counting the colonies, an estimate can be made of the number of bacteria in the
original 100-ml sample by using the below formula;
B. The Standard Plate Count
• It is generally impractical to test for all pathogenic organisms, but the total number of
bacteria can be calculated.
• In this test, samples of water are diluted in jars containing 99-ml sterile water, and
samples are placed in Petri dishes with nutrient agar or other nutritious medium.
• After incubation, the colony count is taken and multiplied by the dilution factor to obtain
the total number of bacteria per ml of sample.
• Indicator bacteria can be detected to give an estimate of pathogens. The most common
indicator organisms in water bacteriology are the coliform bacteria. These are Gram-
negative rods normally found in the intestine and typified by Escherichia coli. To test for
the presence of coliforms, a standard plate count can be performed, with violet red bile
agar used as the growth medium to encourage proliferation of the coliform bacteria.
Total No. of Colonies
CFU = ---------------------------
Volume filtered

3. C. The Most Probable Number Test (MPN)
• Tubes of lactose broth are inoculated with water samples measuring 10 ml, 1 ml, and 0.1
ml.
• During incubation, coliform organisms produce gas. Depending upon which tubes from
which water samples display gas, an MPN table is consulted and a statistical range of the
number of coliform bacteria is determined.
• The MPN test is very easy to perform and interpret, but it does not determine the exact
number of bacteria as the standard plate count does.
• In order to test for the presence of E. coli in water, a medium called eosin methylene
blue (EMB) agar is used. On this medium, E. coli colonies become green with a metallic
fluorescent sheen.

4. D. The biochemical oxygen demand (BOD)
• The extent of pollution in wastewater can be determined by measuring the biochemical
oxygen demand (BOD).
• The BOD is the amount of oxygen required by the microorganisms during their growth in
wastewater.
• The BOD test is begun by noting the oxygen concentration in a sample of water before
incubation. The water is then incubated in an air-tight, stoppered bottle for a period of
about five days.
• A temperature of between 5° and 20°C is used.
• The oxygen concentration in the water is then noted again, and the difference in the
dissolved oxygen is the BOD.
• A higher BOD indicates presence of a higher amount of organic matter. High BOD
values are found in wastewater from agricultural communities, food processing plants,
and certain industries.
References:
❖ https://www.environmentalpollutioncenters.org/water/
❖ https://www.cliffsnotes.com/study-guides/biology/microbiology/aquatic-
microbiology/water-quality-tests