There are localized "hotspots" of elevated metal levels, 
just as there are for organic compounds, particularly around 
industrial areas like the Baltimore Harbor area and the 
Elizabeth River-Hampton Roads area. 
Potential Impact 
I would like to address the potential for toxic effects. Do 
we have a problem in the Chesapeake Bay? This is a very dif¬ 
ficult question to answer definitively. There are many physi¬ 
cal, chemical, and biological factors that must be considered 
before this question can be answered. 
We cannot predict impacts of toxic compounds to an estuary 
by running one or even a series of single-species bioassays 
under laboratory conditions; the natural ecosystem is far too 
complex to be so simply described. Organisms interact with one 
another and with the fluid in which they live. These 
interactions are not simplistic ones, nor can they be ignored. 
I heartily endorse Bob Huggett's suggestion that biologists and 
geochemists work more closely together in coming years to 
discover important cause-and-effect relationships. 
Toxic metals have complex geochemistries and are present in 
a variety of different chemical forms, only some of which are 
biologically available and therefore toxic. In addition, 
inorganic compounds, like organic compounds, can be taken up by 
biota and can be further transformed. These transformations 
often yield compounds that have widely differing toxicity than 
the parent compound. 
There are indications that elevated metal levels within the 
Chesapeake Bay are exerting sub-lethal influences on the eco¬ 
system. We find high levels of metals in the organisms them¬ 
selves, and we also see altered species composition and reduced 
species diversity in some areas. 
As an example, many species of phytoplankton are sensitive 
to low concentrations of arsenate, concentrations found in some 
areas of the Bay, while other species tolerate concentrations 
two orders of magnitude higher (Table 5). In the event of arse¬ 
nate loading, for example, the sensitive species drop out of a 
community, leaving only the resistant species behind. Although 
difficult to detect, this type of impact may be extremely sig¬ 
nificant to the ecosystem as a whole, because phytoplankton form 
the base of the food chain and such alterations can affect the 
feeding of higher trophic levels. 
These are very complex problems; problems that will take 
some time to answer. 
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