United States
Environmental Protection
Agency
Environmental Research
Laboratory
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
Lakes.
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).
Introduction
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.
Methodology
14C-bicarbonate was used to measure
phytoplankton gross photosynthesis. PCB
concentrations of 5-500 ng l~1 above
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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
zooplankton.
Conclusions
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
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