It’s commonly accepted that the three major types of pollution are: air pollution, land pollution and water pollution. But one can argue, as I often do, that there is only ‘one’ kind of pollution and that is water pollution. This is because each type of pollutant, whether it belong to the air or land tends to end up in the ocean, thus posing a major threat to the health of millions of people, marine animals and plants.

But not all pollutants are equal, and so let’s first examine exactly what’s going into the world’s waters, and here there are four different categories of pollutants:

1— Degradable wastes (urban sewage, agricultural wastes, oil spillages, food and brewing processing wastes) are organic materials that are subject to bacterial attack which is an oxidative process. Since bacteria play an important role in food chain, if the input of wastes increases then organic material accumulates and bacterial activity increases the supply of dissolved oxygen in water. This can, in fact, have a positive impact on both plants and animals.

2 — Dissipating wastes are industrial discharges that very quickly dilute to harmless levels after they enter the water.

3 — Solid wastes are litter such as manmade plastics (polythene bags, fishing gear, nets, rope plastic products), dredging spoil, industrial (china clay and silt wastes), mine tailing, etc.

4 — Conservative wastes are heavy metals, halogenated hydrocarbons and radioactive isotopes. This type of waste is not subject to bacterial attack and do not rapidly (if at all) dilute, and therefore they essentially become permanent additions to the sea and are regarded as a serious threat.

Water pollution due to industrial and sewage waste is affecting both marine and human life

Heavy metal pollution in the ocean is a major problem that directly affects marine life and indirectly affects human health and resources. In seawater, the heavy metals are conventionally considered to be those which exist at concentration of 1mg/kg or less. The most hazardous metals are mercury (Hg), cadmium (Cd) and lead (Pb) from a public health point of view; next on the list are copper (Cu), zinc (Zn), silver (Ag) and chromium (Cr). Over time, such heavy metals accumulate in marine plants and animals, a process known as bioaccumulation. It’s a vicious circle, as marine animals consuming plants or other animals that have accumulated heavy metals also ingest these pollutants and in many cases, these marine animals make their way onto our dining tables. Of these pollutants, mercury is a particularly toxic element that most of us are only exposed to through food, with fish being a major source of methyl mercury exposure. One must point out that while the general population does not face a significant health risk from methyl mercury, certain groups with high fish consumption may attain blood levels associated with a risk of neurological damage to adults. Since there is a risk to the foetus in particular, pregnant women should avoid a high intake of certain fish, such as shark, swordfish and tuna. Naturally, fish taken from polluted fresh / marine waters should be avoided. But that’s not easy to do at all.

Consider that there are above 6,000 industries located in Karachi alone. Apart from the Steel Mill, none of these have a pre-treatment facility and untreated effluents from all these areas drain into municipal sewers, and then into the sea via the Lyari and Malir Rivers. The Lyari River brings an estimated 120 million gallons/day (mgd) of municipal and industrial waste. The Malir River discharges 42mgd into Gizri Creek. Apart from this, another source of contamination is oil waste discharge. Nearly about 20,000 tons/year of oil and oily wastes are received by the Manora Channel and Gizri Creek and about 2,000 tons/year is received from different oil refineries and through the Malir River. Crude oil contains a wide variety of hydrocarbons, as well as other compounds, including metals.

Then there’s the question of sewage, and if we take the example of Karachi, we must note that the existing sewage system was designed for a city of two million. The rapid growth in the population and industrialisation of Karachi over the last 30 years has made this system inadequate. According to the Karachi Water Board and Sewerage Board, Karachi generates about 446mgd of sewage and waste waters from municipal and industrial sources. Again, much of this waste ends up in the sea.

Pakistani scientist and NGOs are working continuously to come up with a solution for this problem, tackling the question of what is and what should be done to reduce or remove the damaging and undesirable effect of these additions to the marine environment. What would be the consequences of not releasing these materials in to the sea and would such consequences be better or worse than the existing situation? To consider this latter question is all the more crucial, because in some cases the cure might be worse than the disease.

Published in Dawn, Sunday Magazine, April 26th, 2015

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