EFFECT OF BRINE BLOWDOWN DISCHARGE FROM A DESAL/POWER PLANT ON MARINE LIFE 1

High salinity, temperature and metal ions of corrosion origin constitute the principal environmental pollutants present in the brine effluent discharge from the Desal/Power Plant in Al-Jubail. The dilution and disposal procedures employed in the plant to minimize the effects of desal brine blowdown are discussed. Data collected on initial salinity - temperature characters of the desal blowdown and after its dilution and passage along the open canal suggest that the brine disposal procedure employed are effective in keeping the pollutants at levels close to that of the receiving water body. Algal bioassys were conducted to evaluate the effect of heavy metals on marine phyto- plankton community. A mixed population of diatoms comprised of Nitzschia closterium, N.seriata and Chaetoceros lorenzianus, isolated from the intake seawater were used in the toxicity studies. The heavy metals selected for the studies were copper, chromium, iron and nickel - the main products of corrosion of metallic construction materials. Copper has been found to have the maximum growth inhibitory effect (~ 64% growth reduction at 40 ug/l) on diatoms grown in unenriched seawater. Chromium and iron were far less toxic and nickel was not toxic up to a concentration of 200 ug/l. In fact the presence of nickel in the culture medium stimulated algal growth. Composition of the culture medium on copper toxicity was also examined. Substantially higher toxicity of copper in unenriched seawater compared to that observed in modified f medium proved that the presence of nutrients acting as chelators and adsorbents in the f medium, significantly reduced the growth inhibitory effect of copper. Similarly, exposure of diatoms to combination of the four metals resulted in substantial amelioration of copper toxicity. In the light of the present results, the need to study biological effects of metal ions in presence of other chemicals and metals to determine safety levels for the ecosystem under consideration is discussed.