late 1800s correspond to the beginning of major urban development of the 
region. For PAH, which have natural sources (e.g., forest fires and 
erosion of coal deposits), a significant increase in concentration was 
observed in sediments dating from the turn of the century. In central 
Puget Sound, maximum concentrations of PAH appear to have occurred 
sometime around the 1950s (Figure 9). These PAH concentrations are 
approximately 2-3 times present day concentrations and over 30 times those 
of the 1880s. Much greater temporal changes are apparent close to PAH 
sources in the industrialized embayments and Eagle Harbor. Decreases 
observed in some areas since the late 1950s probably result from 
improvements in industrial practices and perhaps from the continued 
conversion from coal to oil used for home heating (Bates et al. 1984; 
Barrick and Prahl in press). 
PCBs were used commercially only from the 1930s to the 1970s when 
their use was banned. PCB concentrations in sediments show a 
corresponding pattern (Figure 9). Several metals (e.g., lead, copper, and 
zinc) show increased concentrations over the last century, but again have 
somewhat lower concentrations in recently deposited sediments (Figure 9). 
Conclusions 
Accurate measurements of many toxic chemicals concentrations in the 
environment have been made only in the last several years. Consequently, 
it is difficult to assess the spatial and temporal trends in the 
concentrations of all but a few toxic chemicals. For some chemicals found 
frequently in Puget Sound (e.g., PAH, PCBs, and lead), several lines of 
evidence demonstrate decreasing discharges and sediment concentrations in 
recent years. Improved pollution controls, changes in product usage, and 
the closure of some industries are thought to result in similar reductions 
for other chemicals. Additional data on sources and sediment 
concentrations are required to support this conclusion. Recent increases 
in concentrations may result from discharges associated with new 
industries and more domestic sewage. In general, however, contamination 
by many chemicals was much worse 10-25 years ago. 
Puget Sound as a whole is not highly contaminated in comparison with 
other coastal areas of the United States. Some small areas of the Sound 
are contaminated at levels similar to heavily contaminated areas along the 
East coast and southern California. For particular chemicals, it has been 
possible to identify sediment concentrations at which biological effects 
can be observed. This knowledge of the apparent association of chemical 
contamination and biological effects, although still limited, contributes 
to a growing body of information useful in addressing environmental 
problems in all contaminated coastal areas. These problems arise because 
sediments act not only as a convenient and significant sink for 
contaminants, but also as a source of toxics to organisms that live in or 
feed on surface sediments. 
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