On-Site Critical Life-Stage Bioassay with the Fathead Minnow, Pimephales promelas, on Effluent from the Wastewater Treatment Facilities of Austin, Minn.

An on-site, flow-through, critical life-stage bioassay was conducted challenging the fathead minnow with treated effluent from the City of Austin, Minn., wastewater treatment facilities. Using U.S. Environmental Protection Agency (EPA) methodology modified by Union Carbide Environmental Services (UCES) and the Minnesota Pollution Control Agency (MPCA), effluent effect data were obtained for (a) egg hatchability, (b) fry survival, (c) fry growth, and (d) fry deformities. The data were used to estimate the maximum acceptable effluent concentration (MAEC) range, expressed as percent effluent and ammonia concentration. Statistical analyses (P = 0.05) indicated an MAEC range of 18 to 32 percent treated effluent. The corresponding un-ionized and total ammonia concentrations were, respectively, 0.2 to 0.3 mg/litre and 2.3 to 3.2 mg/litre.

In light of the current EPA water quality criterion of 0.02 mg/litre un-ionized ammonia, the results suggest that in situ studies of this type might be useful in establishing more realistic discharge requirements.