SECTION 2 
CONCLUSIONS 
EVALUATION OF BIOTOXICITY 
Since there was no significant mortality in our experimental 
oysters, there was no strong indication that the causative factor 
for oysterkills in the Chester River was in operation during our 
studies. 
Fouling organisms died off in July and August at five sta¬ 
tions upriver from Corsica Neck. Since this accompanied dieoff 
of oysters in previous years, the phenomenon which is responsible 
for oyster dieoff might have occurred but in a mild form. 
Despite reasonable growth in the oysters planted in Chester River, 
the growth rate during the period of fouling community dieoff was 
significantly lower than that of controls placed in the Patuxent 
River. The phenomenon this year may have been so mild that the 
main effect in the oysters was a reduction in new growth. 
The beginning of dieoff of the fouling community correlated 
with a fishkill. The fishkill originated well above Morgan Creek. 
The two phenomena may be unrelated as the fishkill may be bacte¬ 
rial in origin and species-specific since only carp and catfishes 
were noted dying. 
Experiments with fish and crayfish in Radcliff Creek and 
Morgan Creek do not find any indication that either creek con¬ 
tains the sole source of the cause of oyster mortality within its 
drainage; however, the lack of significant mortality during the 
study period makes these results inconclusive. 
PHTHALATE ESTERS AND RELATED CHEMICALS 
The Chester River sediments taken from the vicinity of the 
oyster mortality zone, as well as farther downstream, show no 
evidence that Tenneco discharges are causally linked to the past 
oyster mortality. Oysters are now grown with apparent health in 
regions where the alkyl phthalates should be similar in concen¬ 
tration to those presently measured in the vicinity of the oyster 
mortality. Since the concentration history has not been measured, 
the study cannot rule out the possibility of a past causal re¬ 
lationship. 
5 
