instances. As a result, the clay-humic structure contains a 
historical reservoir of many compounds deposited through natural 
or anthropogenic influx. In the present study where no biologi¬ 
cal specimens were preserved, the key to the retrospective anal¬ 
ysis of the past oyster mortality would have to told by the 
sediment composition. 
DISTRIBUTION PATTERNS 
Three factors which may modify the distribution patterns of 
organic distribution in the Chester River as as follows. 
a. The downstream dilution effect . The width of the 
Chester River grows from roughly 0.5 km at Chestertown to 1.6 km 
near the midway region close to Spaniard Point to 5 km at the 
mouth. This suggests that the sediments, behaving as a pollu¬ 
tant sink, may become more dilute in the pollutant as one proceeds 
downstream. In the initial pollution history of a tidal river, 
this would would be more likely than later on when the accumula¬ 
tive pollution may build toward a uniform pollutant concentration. 
b. Uniform recirculation model . The Chester River, as a 
tributary estuary, is moderately stratified into two layers as 
described by Pritchard (1967). The net advective surface water 
flow is in the upstream direction while that in deeper water is 
downstream. Suspended or dissolved matter is dispersed in both 
directions as a result of two processes: (1) diffusion of the 
dissolved solute across the thermocline so that it is spread into 
layers whose net motions are in opposite directions. It is likely 
that the nonpolar plasticizers will quickly (2) sorb onto su¬ 
spended sediment and then settle down to the leptopellic layer on 
the sediment surface, and then either deposit or become resuspend¬ 
ed into a circulation cycle. These circula-processes may cause 
wide mixing, motably upstream as well as downstream. 
c. "Hot spots." As noted in Han's dye tracer experiments 
(1972), a pollution plume is apt to remain intact during the first 
few tidal cycles. That pattern was shown to exhibit selective 
localization effects. This would produce the opportunity for hot 
spots where an elebated concentration of pollutant may deviate 
significantly from the model based on complete mixing. 
PROBLEM STATEMENT 
It seems fundamental that environmental influx of toxic 
pollutants is feasible for study when the pollutant is identified, 
or at least limited to be among a group of candidates. In the 
present study, this line of first approach was blocked from the 
beginning because none of the affected oyster tissue had been 
saved. The circumstances are such that the toxic agent (if there 
was any) may have been introduced, reached toxic levels, and re¬ 
turned afterwards to pretoxic conditions. Although alkyl 
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