Karachi is most industrialized and urbanized city of Pakistan. More than 350 million gallons of wastewater is generated per day by different types of industrial processes and human operations. There are only three wastewater treatment plants in Karachi city working at Haroonabad (TPl), Mahmoodabad (TP2) and Mauripur (TP3), which can treat less than 30% of the total wastewater generated. Sindh Industrial Estate (SITE), Korangi Industrial Area (KIA) and Landhi Industrial Area (LIA) are important industrial sites of Karachi influxing their wastewater indirectly into the Arabian Sea without any treatment. In addition untreated industrial effluents and domestic wastewater from other resources is also being discharged into the Arabian Sea. Therefore, more than 70% of the wastewater goes into the Arabian Sea without any treatment. Major rivers of Punjab discharge their wastewater load into the River Indus, which ultimately discharges its pollution load into the Arabian Sea at Ke Tee Bunder endangering aquatic life and fish. Besides containing other toxicants, this wastewater contains large quantities of heavy/trace metals/metalloids, cyanides, phenols, oils and greases and suspended solids resulting in high values of biological and chemical oxygen demand and low dissolved oxygen threatening aquatic life and as well as fish. It is also suspected that, influx of this untreated wastewater is also making the water quality of the Arabian Sea unfit for recreation purposes at different sea spots like Paradise Point, Hawks Bay, Sand Spit, Keamari, Manora, Clifton and Sea View.
Therefore a study was conducted to determine the performance of wastewater treatment plants (TPI, TP2, TP3), quality of effluents from industrial sites (SIE, LIA and KIA) on the unchecked discharge of wastewater into the Arabian Sea generated in Karachi city and at point of confluence of Arabian Sea with River Indus. Water quality of different sea spots/coastal areas was also monitored to determine their impact on some commercially important edible fish species of River Indus and Arabian Sea. It included analysis of water for physical characteristics (temperature, pH, total dissolved salts, total suspended solids), nutrients (ammonia, nitrate, phosphate), non-metals (cyanide, chloride, sulfate), organic constituents (BOD5, COD, phenols, oil and grease), inorganic constituents (dissolved oxygen, total alkalinity and total hardness), heavy/trace metals/metalloids (zinc, cadmium, copper, arsenic, iron, nickel, lead, chromium) in water. Water samples were collected and analyzed before (influent) and after treatment (effluent) from wastewater treatment plants (TPl, TP2, TP3), three important industrial sites of Karachi (SITE, KIA and LIA), at point of mixing of River Indus with Arabian Sea (Ke Tee Bunder) and different sea spots/coastal areas in Karachi (Paradise Point, Hawks Bay, Sand Spit, Keamari, Manora, Clifton and Sea View). Analysis of heavy/trace metals/metalloids (As, Pb, Cd, Cr, Cu, Ni, Fe and Zn) was also conducted in water. Different species of fish/prawn i. e, Labeo rohita (Rohu), Hilsa ilisha (palla), Pampus aegenteus (Silver pamfret), Sardinelta sindensis (Padam), Kowala Coral (Mitto), Mugil speigleri (Boi), Platycephalus indicus (Kuker), Peneaus lndicus (Prawn Black), Peneaus lndicus Pencillaulus (prawn Red) were collected from point of confluence of River Indus and Arabian Sea at different sea points/coastal areas of Karachi City. Fish and prawn were also analyzed for these metals to determine their level of accumulation. Statistical analysis was conducted using statistical package "SPSS". Different 25 parameters determined for wastewater treatment plants, industrial sites, sea points/coastal areas were analyzed by Analysis of Variance (ANOV A) to determine their significance level. Multivariate Analysis was conducted to determine Least Significant Difference (LSD) performing Post Hoc Test. Relationship between different parameters/variables was calculated to determine the effects of these water quality parameters of three wastewater treatment plants and industrial effluents on these water quality parameters of Arabian Sea.
Principal Component Analysis (PCA) was also applied on experimental results. Multivariate Analysis revealed significant effect of temperature, BOD, COD, cyanide, zinc, cadmium, iron and chromium due to effluents of treatment plants and temperature, TSS, COD, phenol, cyanide, phosphate and copper due to effluents from different industrial areas on these parameters of sea points/coastal areas. It has resulted in deterioration of water quality at different sea points/coastal areas of Karachi.
Analysis of different trace/heavy metals in different fish and prawn species revealed significantly high values of copper, cadmium, nickel, zinc and chromium (at P