Chemical and toxicological properties of coal fly ash - University of ...

Table 21. The LC-50 values, amount of dilution necessary to eliminate mortality, and the initial pH values for extractsgenerated from five fly ashes.Fly ash LC-50 Confidence intervalsa Di lution for zerosample PH i mL/100mL mL/ 1 O0mL percent mortal i tyaThere is a 95 percent probability that the LC-50 falls within the confidenceinterval listed.The results of the LC-50 determinations indicate that W2 was the fly ashextract most toxic to young fathead minnows; it required as much as a1:1000 dilution to eliminate mortality. The I3 ash produced the secondmost toxic extract; the remaining three extracts had similar LC-50 values.The acute toxicity of a leachate should be partly a function of itschemical composition. Simple linear and multiple regression analyses wereused to determine, for each extract, the relationship between the mortalitydata and the chemical data collected during the LC-50 determinations(Tables 22-25) The I8 test solutions were not chemically analyzed. Therange of concentrations for each chemical constituent, the recommendedwater quality level for each chemical constituent, the change in r2 forthe multiple regression, and the r value for the simple linear regressionare listed in each table. In statistical analysis, the values for r andr2 w i l l vary from 0.70). When the results of these statisticalanalyses are considered with the levels of various chemical constituentspresent in the test solutions, the importance of various chemicalconstituents with respect to acute toxicity of a particular fly ash extractcan be assessed.A strong relationship existed between the acute toxicity of the W2 leachateand its pH. Alkaline (pH > 9.2) solutions have been shown to be acutelytoxic to young fathead minnows (Suloway et al., 1981 ). Cairns et al.(1972) described the effects of a fly ash pond spill on a small river andsuggested that the principal lethal agent was the high pH level. Wassermanet al. (1974) reported that runoff from alkaline ash ponds was lethal tocatfish because the increased pH caused the precipitation of ferrichydroxide, which might have clogged the gi l apparatus, causing asphyxiation.