4.2 Water

4.2.1 Water Pollutants

The pollutants which enter water bodies are most commonly contained in effluents derived from a wide range of human activities, as a result of soil erosion, accidental spills or illegal dumping. Nine groups of pollutants in two categories can be identified (JICA/GOK, 1992).

Physico-chemical pollutants:

- Organic residues, such as, sewage, brewery wastes.
- Inert suspensions - soil sediment, mine wastes.
- Toxic wastes - heavy metals, pesticides.
- Fertilizers and detergents.
- Inorganic reducing agents - sulphides, sulphites.
- Petroleum products - waste oil, tanker spills.
- Heat.

Biological pollutants:

- Micro-organism - faecal coliforms, cholera bacilli.
- Macro-organisms - parasitic worms, exotic fish species and aquatic weeds.

4.2.2 Prioritisation of Variables to be Standardised

Priority Uses of Water

Pollution and the consequent water quality degradation interfere with vital and legitimate uses of water, and general environmental health. Some types of water uses are more prone to be affected than others.

Water quality criteria, standards and the related legislation are used as the main administrative means to manage water quality in order to achieve user requirements. The most common national requirement is for drinking water of suitable quality; however, the number and specification of variables standardised have a technical and economic implication on the country. It is, therefore, not practical to standardise all variables at once. Hence, it is necessary to prioritise the variables based on their impact on the water resources and key uses of the water resources, viz., domestic and fishing or sustenance of aquatic life.

In addition, industries such as detergent manufacture, paints, electro-plating, food canning, fish processing, fertilizer and pesticide manufacturing, sulphuric acid plants, fluoride mining, contribute to various types of pollutants including heat, nutrients, heavy metals, acids, and detergents.

4.2.3 Basis of Selection of Variables

Water for drinking and fisheries is accorded top priority. Therefore, the variables to be standardised in order to protect the water resources and enhance environmental health are mentioned below:

Temperature ( °C)

Temperature should be less than 25°C for trout farming areas and below 35°C for other regions. As temperature rises, dissolved oxygen decreases. Higher temperatures increase the solubility of many chemical compounds and may influence the effect of pollutants on aquatic life and also affect palatability of drinking water. Heated effluents cause stratification and lowering of dissolved oxygen. Fish have upper and lower limits for optimal growth. Therefore, changes in temperature regimes alter the distribution and species composition of aquatic communities.

Suspended Solids

It is recommended that water should have less than 30 mg/l whether the suspended solid has or as no oxygen demand. Suspended solids blanket spawning grounds, river bed, plant life and benthic organisms. They restrict fish vision and affect gill action. Water transparency is reduced with resultant decrease in primary production.

Biochemical Oxygen Demand (5-day at 20 °C)

BOD is not a pollutant itself, but is a measure of organic pollution. Waters with BOD levels less than 4 mg/l are deemed clean while those with BOD more than 10 are considered polluted. High BOD concentrations may limit water use for public consumption, fisheries and irrigation.

Heavy metals
Heavy metal concentration should be less than 0.1 mg/l in combination. They adversely affect fish gills and cause asphyxiation. Heavy metal salts are lethal to fish at very low concentrations especially in soft water. Mercury in
particular affects the rate of photosynthesis. At only 1 ppb radioactive carbon can be inhibited by 50%. Organo- mercury fungicides have been shown to halt uptake of carbon at 50ppb. Heavy metals are essential to organisms in trace amounts. At high levels they accumulate in sediments and in aquatic organisms, and are further concentrated in the food chain (biomagnification), hence, they may reach lethal levels.

Lead ( Pb)

Less than 0.1 mg/l: Lead is a toxic material that accumulates in the skeletal structure of man and animals. Pb in blood lowers mental performance, causing damage to children.

Mercury (Hg)
Less than 0.005 mg/l: Mercury from industrial effluents is transformed into methyl mercury which accumulates in fish and presents serious hazard to aquatic life and to humans whose diet is rich in fish.

Silver (Ag)
Less than 0.05 mg/l: Silver, like mercury, accumulates in body tissues and is also toxic to aquatic life.

Chromium (Cr)
Total Chromium should be less than 0.5 mg/l while hexavalent Chromium should be less than 0.05 mg/l. The hexavalent form is more toxic than the trivalent form. Chromium is lethal to fish at very low concentrations.

Zinc (Zn)
Less than 0.5 mg/l: Zinc is relatively non-toxic to man but is acutely and chronically toxic to aquatic organisms, particularly fish. It is widely used in industry and affects the aesthetic quality of drinking water.

Nickel (Ni)

Less than 0.3 mg/l: Any appreciable amount of nickel ions will hinder self purification of a river and it is toxic to some plants at concentrations as low as 0.5 mg/l.

Copper (Cu)
Less than 1.0 mg/l. High concentrations of copper restrict water use for drinking due to taste problems. Very large doses may result in liver damage and at concentrations above 1.0 mg/l it may be toxic to aquatic organisms.

Arsenic (As)
Less than 0.5 mg/l: Arsenic may be acutely or chronically toxic to man.

Cyanides ( CN)
Less than 0.1 mg/l: Cyanide renders tissues incapable of oxygen exchange. Levels more than 0.2 mg/l are known to be lethal to fish.

Sulphide - Hydrogen sulphide (S)

Less than 0.1 mg/l: Hydrogen sulphide is lethal to fish at slightly higher concentrations than those of cyanides.

Free Ammonia (NH 3 )

Less than 0.2 mg/l: The lethal oncentration for a variety of fish species is in the range 0.2 to 2.0 mg/l NH 3 .

Phenolic compounds (Phenol)

Less than 0.001 mg/l: Phenolic substances are toxic to fish and other aquatic organisms and taint flesh of fish at sub- lethal concentrations.
Phenolic substances, if released into water for public supply, will be detected through the characteristic taste of chlorinated phenols even with concentration as low as 0.002 mg/l.

Nitrates (N)

Less than 10 mg/l: Nitrates cause eutrophication of fresh waters and methaemoglobinaemia ("blue baby syndrome") in infants.

Phosphates (P)

Phosphates enrich fresh water environment with plant nutrients resulting in rapid algal growth which affect municipal, industrial and recreational uses.

Floating materials

Foam, oils and greases should be absent as they reduce light transmission thus, reducing photosynthesis rate and consequently reducing the rate of re-aeration and dissolved oxygen content of the receiving water body. Floating
materials are an aesthetic nuisance