TOXICITY OF ALUM SLUDGE EXTRACTS TO A FRESH-WATER ALGA, PROTOZOAN, FISH, AND MARINE BACTERIUM

Alum sludges from ten water treatment plants throughout North America were subjected to a battery of toxicity tests which included the S. ca pricornutum growth test, the fathead minnow survival and growth test, a protozoan mortality test, and the Microtox(R) test. S. capricornutum was more sensitive than any other test species to sludge extracts. Al gal growth inhibition was observed in extracts obtained at pH 5 but ge nerally not in circumneutral solutions. Alum sludge extracts prepared with natural receiving waters were toxic to S. capri cornutum at all e xtract pH levels tested if receiving water hardness was less than 35 m g CaCO3/L. These results indicate that water-soluble constituents from alum sludges discharged into receiving waters may affect algal growth .