We focus on detoxification and biotransformation processes and 
propose to develop methodologies that can be used to identify 
aquatic ecosystems at risk, to evaluate ecosystem contaminant 
capacity, and to monitor the impact of contaminants from waste 
sites or effluent discharges. 
Let us consider briefly changes in phsiological response 
that fishes and invertebrates may undergo in response to 
increases in environmental stress. These responses may be 
divided into four phases: normal adjustment, which is 
controlled by homeostatic processes; compensation, which is 
maintained without significant cost to the individual; 
breakdown, which occurs at the limit of compensatory processes; 
and finally failure, which is characterized by irreversible 
changes that result in death of the individual (Figure 1). Most 
of the standards and criteria that have been set were based on 
single species tests that used mortality as the endpoint. 
Because concentrations that cause mortality are too high to 
protect populations, standards and criteria were set not from 
these values, but from LC50 values that were multipled by an 
application factor considered to provide the degree of conser¬ 
vatism required. However, what may be more relevant for the 
maintenance of healthy populations in aquatic ecosystems is the 
setting of criteria and standards that are based on knowledge of 
when the limits of compensatory processes are being approached. 
This is critical because when these limits are exceeded, adverse 
effects ensue. 
The organism we chose to study was the bay mussel Mvtilus 
edulis. This species was selected because it appears to have 
evolved compensatory (adaptive) strategies that have resulted in 
the distribution of mussels throughout the world in bays and 
estuarine that have wide fluctuations in environmental condi¬ 
tions. Furthermore, there is an extensive data base on con¬ 
taminant levels in populations from pristine and polluted eco¬ 
systems (Goldberg et. al . 1978), and studies have been performed 
to characterize its morphology (White, 1937) and its physio¬ 
logical and reproductive processes (Bayne et. al . 1976). 
Metal Metabolism 
Let us consider now metal metabolism in aquatic animals. It 
has been well established that many aquatic animals accumulate 
significant metal burdens from metal-contaminated ecosystems. 
Although the biochemical processes associated with metal toxi¬ 
city have not been completely identified, specific effects have 
been demonstrated. Evidence is available indicating that the 
site of toxic action may be enzymes. However, the toxic effects 
on enzymes may be mitigated by the organism's ability to detoxi¬ 
fy metals and eliminate them. It is apparent, then, that an 
understanding of these toxification and detoxification processes 
is required. 
108 
