SYAMA S. VEERINAL AND NICK C. PARKER, Texas Cooperative Fish and Wildlife Research Unit, Texas Tech University, Lubbock, Texas 79409-2120, USA

CLIFFORD B. FEDLER, Department of Civil Engineering, Texas Tech University, Box 41023, Lubbock, Texas 79409-1023, USA

Toxicity testing with aquatic biota has become an accepted practice for determining the potential toxicity of waste water and other effluents that may be discharged to the Nation’s water resources. Similarly, runoff reaching playas and lakes from agricultural lands treated with sludge, can also be tested to evaluate its effect on the flora and fauna. These tests can be indirectly used to identify the toxic effects of effluent and runoff on the survival and reproduction of fish populations. However, organisms that are selected for toxicity tests should be easily cultured, have a short life cycle, and be representative of local populations. The fresh water invertebrate currently used in toxicity tests is a micro crustacean, Ceriodaphnia dubia. Two separate batches of bioassay experiments were performed at Texas Tech University, utilizing soil samples treated with sludge and sludge samples from a municipal waste water treatment plant. Results of the toxicity test with soil samples indicated that the No-Observed-Effect-Concentration and the Lowest-Observed-Effect-Concentration for survival were, respectively, 80% and 100% concentrations (P<0.05) for soil samples treated with 16 tons/acre of sludge. For soil samples treated with 0 and 8 tons/acre of sludge, the survival rates of Ceriodaphnia dubia were not significantly (P<0.05) affected at any concentration. Reproduction was suppressed by 25% when Ceriodaphnia were exposed to 10.9% concentration of soil treated with sludge at 16 tons/acre. A 50% suppression of reproduction occurred when Ceriodaphnia were exposed to 50% concentration of soil treated with sludge at 16 tons/acre. With a sludge application rate of 8 tons/acre, the reproduction was suppressed significantly (P<0.05) by 25%, at a treatment concentration of 60%. Neither 25% nor the 50% Inhibition Concentrations were significantly (P<0.05) affected in the treatment involving the sludge application rate of 0 tons/acre. It is inferred from this experiment that, runoff from soil treated with 16 tons/acre seems to have an effect on the reproduction and survival of cladocerans. Experiments utilizing both wet and dry sludge samples from a waste water treatment facility indicated that, the No-Observed-Effect-Concentration and the Lowest-Observed-Effect-Concentration for survival were respectively, 80% and 100% concentrations of the sludge. Reproduction data indicated that the 25%-Inhibition Concentration was 40.3% for the wet sludge and 19.2% for the dry sludge, whereas the 50%-Inhibition Concentration on reproduction was 54.2% for the wet and 92.5% for the dry sludge. This indicated, that the inhibition of reproduction by the wet sludge was caused by the anaerobic conditions of the sludge, whereas in the dry sludge it may have been caused by dissolved metals present in the sludge.