The concentrations of many chemicals have been determined in sediments 
from many parts of the Sound. For some chemicals the concentrations vary 
dramatically from place to place. The mixtures of chemicals also vary 
from place to place, dependent upon local sources. 
Since the sediments are a repository for many contaminants, they also can 
be regarded as a source of contaminant exposure for many biota. Comparing 
the values in figures 1 and 2, it is apparent that some contaminants 
(e.g., PCBs) may be passed from environmental media such as the sediments 
to the biota and become more concentrated from lower to higher trophic 
(feeding) levels. Other chemicals (e.g., aromatic hydrocarbons) are 
apparently metabolized successfully and do not accumulate to a significant 
degree in upper trophic level biota. 
Because of these differences in the way toxic chemicals behave, various 
biological organisms would be expected to be exposed to differing mixtures 
and concentrations of contaminants. Any single biological test of the 
effects of contaminants in the Sound may not be indicative of how other 
tests with other organisms may react. Therefore, a wide variety of tests 
have been performed by various researchers in the area. Some have shown 
trends very consistent with trends in contamination; others have not. 
Some are probably responsive to only some of the chemicals found in the 
Sound. Others may be responsive to chemicals not detected in routine 
analytical procedures. The following is a brief summary of some of the 
more important biological indications of pollution measured in Puget 
Sound. 
Overview of Biological Data 
Water bioassays. 
Oyster larvae bioassays . Table 1 summarizes the three main biological 
tests of water quality performed in the Sound. Data also exist for 
plankton community studies and effluent bioassays. 
The microscopic drifting larvae of oysters are very sensitive to 
pollutants and changes in natural water properties such as temperature. 
The larvae of the Japanese oyster were used extensively in the 1960s and 
1970s in bioassays of water samples collected near and away from the 
discharges of pulp mills. These discharges proved to be very toxic to the 
larvae, possibly explaining, in part, the demise of the native Olympic 
oyster population in Puget Sound. All the mills around Puget Sound now 
treat their effluents and have significantly decreased the total volume of 
pollutants discharged. Curiously, the oyster larvae bioassay was also 
found to be highly sensitive to a naturally occurring organism, Cerati urn . 
Cerati urn is a single-cell drifting plant that, for some reason, seems to 
kill oyster larvae. 
Up to 100% mortality among oyster larvae exposed to some samples of water 
from the south Sound inlets has been recorded as recently as 1977. 
Usually less than 5% mortality occurred in tests of samples from the 
30 
