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Migration of toxic organics contained in the water-soluble fraction (WSF) of land-applied hazardous wastes poses the most serious threat to groundwater resources. Wastes containing toxic organics that are potentially leachable must be applied to the land at a rate that will allow attenuation of such constituents before their migration from the treatment zone can occur.
A toxicity reduction (TR) test system is being proposed that will serve to determine whether and to what extent attenuation of WSF organic constituents, including both parent compounds and intermediate transformation products, will occur in a well-managed land treatment system.
The test system employs reduction of acute toxicity exerted by WSF organics over time as the measurement criteria. Four sample sets of selected waste-soil combinations are prepared in duplicate for extraction with deionized water (DW) at 14-day intervals during a 42-day experimental period. Acute toxicity of each DW extract is determined by using a bacterial bioluminescence assay. Dose-response curves for each loading rate and subsequent time interval are compared with those of previous sample sets. The waste is predicted to be a candidate for land treatment if a significant reduction of acute toxicity exists during the experiment period at any of the loading rates tested. The maximum acceptable initial loading rate (MAIL) for waste application is predicted from these data. The predicted MAIL rate is the highest rate tested in which toxicity reduction for the waste-soil DW extract progresses steadily during the experimental period with the Day-42 EC50 approaching or exceeding 100 percent. (The EC50 is defined as the effective concentration of the DW extract that causes a 50% decrease in bacterial light output.) The higher the EC50 the lower the toxic effect; therefore, a 42-day EC50 approaching 100% signifies toxicity reduction in a waste-soil DW extract.
The TR procedure currently is being used by the EPA's Hazardous Waste Land Treatment Research Program to assist in evaluating land treatability potential for a variety of organic hazardous wastes. The most extensive use of the procedure to date has involved evaluation of land treatability for oily wastes from different sources within a refinery: i.e., lagoon bottom sludge, API separator sludge, slop oil emulsion solids, and dissolved air flotation unit skimmings. Additional evaluation tests have been conducted by using wastes from the wood preserving and paint industries. Results from these evaluation tests indicate the potential usefulness of the TR procedure as one of the initial tests conducted in a laboratory screening test sequence for predicting the land treatability potential of organic hazardous wastes.
toxicity, tests, bioassay, treatability, land treatment, hazardous wastes, screening
Research biologist, U. S. Environmental Protection Agency, Kerr Environmental Research Laboratory, Ada, OK
Microbiologist, Beckman Instruments, Inc., Carlsbad, CA