Presently, aquatic pollution is a worldwide problem specially in the thickly populated areas. Karachi is the ninth populous city of the world and is also the most industrially developed city of Pakistan. A big part of its basin is occupied by alluvials of Malir River. It is, basically, a seasonal river but becomes perennial within the limits of Karachi and serves for the discharge of untreated sewage and industrial effluents through its basin into the Arabian Sea
The basin of Malir River is situated between 24º45’N to 25ºN Lat. And 67º13’E to 67º22’E Long, with a drainage area of 1520 sq. km. Its upstream pari remains dry except during the rainy season. To determine the extent of pollution in Malir River (within Karachi region), water samples were regularly collected from four spots namely Murad Memon Goth (spot 2), Malir City (spot 3), Drigh Road (spot 4) and Qayumabad (spot 5) from May, 1993 to April, 1996. Sporadic water samplings were done at Dumlott (spot 1), a point beyond Karachi, to compare the characteristics of water there
During the study, twenty-nine physico-chemical parameters were estimated in the field and laboratory. Values of all the parameters were found within the range of the observed values of streams and rivers, except total dissolved solids, total alkalinity, sodium, manganese, lead and chromium. However, among all the chemical constituents, quantities of total iron, manganese, lead, chromium and pH were also found beyond the standard values of these factors given by WHO for drinking water.
Both heavy metals (Pb, Cr) and manganese were present in huge quantities, particularly at Malir City and Qayumabad spots, due to the inclusion of sewage and industrial wastes
Data of physico-chemical characteristics of water is grossly polluted at spot 5 and comparatively less at spot 3 and lesser at spots 2 and 4
In addition to study the effects of pollutants on the characteristics of water their effects were also observed on the growth of Oreochromis mossambicus, the most common fish found in Malir River. For this purpose, three growth variables namely length, weight and condition factors were measured in the specimens collected from spot 2 to 5 throughout the study period. The comparative study of the above mentioned growth variables of the said fish in Malir River reveals that pollution has influenced the growth of this fish. Comparatively, condition index of the collected specimens of this fish was best at spot 4, better at spot 2 and worst at 5 in accord with the presence of pollutants at these spots
Present data show that pollution has not only deteriorated the pristine condition of Malir River but is also causing pollution in the Arabian Sea where this river falls finally. Pollution in the rivers is also hazardous to the inhabitants of Karachi due to the danger of mixing of this water with drinking water and consumption of food items, grown with this water. Serious efforts should, therefore, be made by public and private agencies, to control the pollution in this river. Such effects would then result in the increased food production and better health of Karachi’s populace