Unusual response of Whole Effluent Toxicity testing; L/E WWTP,
     Englewood, Colorado.

        The Littleton/Englewood Wastewater Treatment Plant (L/E WWTP)
     monitors it's effluent into the S. Platte River at the south Denver
     border for lethal and sublethal toxicity using the EPA Whole Effluent
     Toxicity (WET) test for both the Fat Head minnow (Promelas pimphales)
     and the water flea (Ceriodaphnia dubia).  The method used is the short
     term chronic WET test; the test has been routinely performed on a
     monthly basis since January 1993.  An indication of a potential
     toxicity problem occurs when a significant difference is observed
     between a control population and any population of organisms tested in
     a solution containing 60% effluent or less.  A single failure triggers
     a series of WET tests to determine if a pattern of toxicity is
     present.  If a pattern of toxicity is present then further
     investigations are required to try and determine the cause of the
     toxicity.

        A significant long term pattern has been observed in the survival
     of the Fat Head minnow (FHM).  During 1995 and 1997 (still continuing)
     a pattern of lethality in the WET test for the FHM is quite
     pronounced.  The characteristics of this lethal effect include

     1. Only the FHM test species is affected; Ceridaphnia are completely
     unaffected.
     2. A dose response is not observed; that is, effluent/control mixed
     water samples are as lethal as 100% effluent.
     (Note: some specimens always survive in all effluent concentrations;
     typically 30-60%).
     3. No potential toxic material has been identified among a large suite
     of potential agents (1995 & 1997).
     4. A bioassay of the invertebrate population of the river indicates no
     toxic effect caused by plant effluent (1995).
     5. Bacteria tests indicate no toxicity.
     6. Filtration with a 0.45 um membrane filter removes the lethal effect
     of the plant effluent on fish survival.
     7. No relation to plant processes or industrial discharges has been
     identified.
     8. Surviving fish usually have same average weight as control fish.
     9. Onset of the effect takes ~3-5 days.
     10.Occurs from Late Spring till Early Fall (1995).


     Request for Help:
     1. Has anybody observed similar results in WET testing using the FHM
     or in natural populations of other fish species?
     2. Any suggestions on what might cause this pattern?  Our observations
     and discussions suggest that the cause is a pathogen and probably a
     bacteria.
     3. Any suggestions on a laboratory that (1) might be interested in
     this problem and (2) is appropriately staffed and experienced to help
     solve this problem in fish pathology/toxicology.

     I appreciate any and all suggestions and comments.


     Philip A. Russell, Environmental Analyst
     L/E WWTP
     Englewood, CO  80110
     USA
     303-762-2611
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