United States
                    Environmental Protection
Environmental Research
Duluth MN 55804
                    Research and Development
EPA-600/S3-84-008  Feb. 1984
4>EPA          Project  Summary
                    PCBs  in  Saginaw  Bay:
                    Development of  Functional
                    Indices  to  Estimate  Inhibition  of
                    Ecosystem  Fluxes

                    Donald C. McNaught, David Griesmer, Marlene Buzzard, and Michele Kennedy
                     Saginaw  Bay  is among  the most
                    polluted bays in  the Great Lakes. For
                    many years the Large Lakes Research
                    Station of the US EPA has examined
                    many aspects of this ecosystem, from
                    phytoplankton community character-
                    istics to contaminant levels in fishes. As
                    a result, when it became desirable to
                    determine the impact of an organochlo-
                    rine contaminant like PCB, it was not
                    necessary to study the ecosystem in
                    detail. Phytoplankton  species and
                    densities were known, zooplankton
                    species,  densities and feeding  habits
                    had been investigated.
                     This study produced new information
                    on  the two most basic fluxes in any
                    aquatic system, the flow of solar energy
                    into the phytoplankton and the flow of
                    chemical  energy into the zooplankton.
                    The use of phytoplankton gross photo-
                    synthesis to estimate the inhibition by
                    contaminants of the first flux mentioned
                    was developed for marine communities.
                    In comparison, the use of zooplankton
                    ingestion rates to estimate the inhibition
                    by  contaminants of  carbon flow into
                    secondary producers is new and was
                    developed for this investigation.
                     The International Joint Commission's
                    (IJC) Science Advisory  Board and,
                    specifically, the  Ecosystem Function
                    Working Group, is currently examining
                    the use of such measures of functional
                    impairment as water quality indices.
                    Thus, the announcement of the results
                    of this study is timely with regard to
                    ecosystem management in the Great
                     This Project Summary was developed
                    by EPA's Environmental Research
Laboratory-Duluth, Large Lakes Research
Station. Grosse lie. Ml. to announce key
findings of the research project that is
fully documented in a separate report of
the same title (see Project Report ordering
information at back).

  Aquatic ecosystems of the Great Lakes
are threatened by approximately 50,000
chemicals of commerce from the United
States and Canada; at least 2000 may
have adverse biological effects and only
200 have  been studied. Contaminants
such  as chlorinated hydrocarbons are
especially predisposed to concentrate in
food chains because of their partitioning
into  lipids of lower organisms and
because of their later food chain concen-
tration by apex predators. Waters of the
Great Lakes contain 2 to 300 ng I"1 PCB;
this major contaminant is concentrated
about 1 million times in apex predators.
Generally,  PCBs  inhibit  organismic  as
well as ecosystem metabolism and thus
ecosystem productivity. Since the complex
food webs of Lake Huron involve hundreds
of phytoplankton  taxa and tens  of zoo-
plankton taxa, we developed and  utilized
two ecosystem functional indices  for
measuring contaminant inhibition. These
were  measures of the  inhibition (and
sometimes stimulation) of algal  photo-
synthesis and of zooplankton grazing.

  14C-bicarbonate was used to measure
phytoplankton gross photosynthesis. PCB
concentrations of 5-500 ng l~1 above

   control levels were injected into experi-
   mental test samples  of  phytoplankton
   incubated at depth of collection. Inhibition
   of photosynthesis was expressed as a
   percentage decrease relative to control
   values This simple  test is a functional
   (rate  impacted)  index of ecosystem
   inhibition  at  trophic level one (phyto-
   plankton).  In a similar treatment, 14C
   tagged algae, fractionated into nanno-
   plankton and netplankton size ranges
   (<20 /um and >20 //m dia.), were fed to
   zooplankton, and filtering rates  were
   calculated. Then, similar tests  were
   performed  in which experimental con-
   tainers also contained  PCBs Thus, the
   relative  depression of grazing  by  PCBs
   was measured for all major taxa of

     Eight important  conclusions  were
   reached about the Sagmaw Bay ecosystem.
   With regard to phytoplankton photosyn-
   thesis, dichlorobiphenyl was selectively
   more  toxic to nannoplankton than to
   netplankton. This is an important conclu-
   sion, since Great  Lakes food chains are
   based on  small  nannoplankton algae.
   Secondly, dichlorobiphenyl metabolites
   (unspecified) were more toxic to phyto-
   plankton  than the parent isomer. This
   finding suggested problems similar to
   those encountered for  other  man-made
   organics. In addition to selective toxicity
   by  phytoplankton size, we found that
   PCBs inhibited photosynthesis of diatoms
   and green  algae more than  blue-green
   algae; unfortunately, diatoms and small
   greens are the most grazed components
   in this ecosystem. Zooplankton grazing
   was also inhibited by PCB metabolites,
   and especially when detritus was present,
        as it is in most productive waters of the
        Great  Lakes. The above findings were
        based  on exposures to PCBs above
        normal environmental levels encountered
        in Lake Huron.
          Inhibition of algal  photosynthesis by
        ambient levels of PCBs was examined for
        dichlorobiphenyl, hexachlorobiphenyl,
        and purified  metabolites,  including
        hydroxylated PCB and furans. Ambient
        levels  of PCBs inhibited nannoplankton
        productivity.  In  the  hexachlorobiphenyl
        series,  the hydroxylated PCB and furan
        were more  inhibitory to photosynthesis
        than the parent isomer, with a seasonal
        range of inhibition of -2 to -93%. At depth,
        these   same contaminants stimulated
        gross  photosynthesis,  probably  by in-
        creasing algal respiration and net produc-
        tion. This was a totally new result. In the
        dichlorobiphenyl series, the metabolic pro-
        ducts inhibited  photosynthesis in surface
        waters from -6 to -22%, much less than
        the higher chlorinated compound
  Lastly, we compared grazing in westen
Lake Erie to that in Saginaw Bay. In Lak<
Erie,  grazing  as  a control on  alga
populations was almost as effective as ir
oligotrophic Lake Huron, whereas grazinc
was greatly depressed  in Saginaw Bay
Apparently the Lake Erie ecosystem is ir
much  better  condition than that o
Saginaw Bay.
  We conclude that functional ecosysterr
inhibition by such toxic chemicals as PCBs
is  a most serious  problem. Our results
clearly indicate  that levels of PCBs rnusi
be held below 5 ng l~1, and we suggest
this level as an appropriate water qualit\
objective  to  the  IJC.  In  addition, we
suggest that more attention be paid to the
effects of  PCB metabolites  on natural
communities.  It may also be inferrec
that the lack of zooplankton grazing in an
ecosystem  like Saginaw Bay is related to
unknown  inhibitory compounds with  a
mode of action similar or identical to that
of  PCBs.
          Donald C. McNaught (currently with the University of Minnesota, Minneapolis,
            MN 55455), David Griesmer, Marten Buzzard, and Michele Kennedy were with
            the State University of New York, Albany, NY 12222.
          William L. Richardson is the EPA Project Officer (see below).
          The complete report, entitled "PCBs in Saginaw Bay: Development of Functional
            Indices to Estimate Inhibition of Ecosystem Fluxes, "(Order No. PB 84-133 008;
            Cost: $13.00, subject to change) will be available only from:
                  National Technical Information Service
                  5285 Port Royal Road
                  Springfield, VA 22161
                  Telephone: 703-487-4650
          The EPA Project Officer can be contacted at:
                  EPA Large Lakes Research Laboratory
                  Environmental Research Laboratory—Duluth
                  U.S. Environmental Protection Agency
                  9311 Groh Road
                  Grosselle, Ml 48138
                                                                                           •JUS GOVERNMENT PRINTING OFFICE 1984-759-015/7315
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