phthalate esters is in the dissolved fraction in the water 
column. It is not known at this time if the water phase trans¬ 
port of phthalates out of the system and other environmental 
degradation processes are great enough to preclude further 
buildup of DEIIP in the estuarine sediments. Based on the levels 
of DEHP found in the pond receiving an effluent, further accumu¬ 
lation of phthalates in the estuarine sediments may be possible. 
Additional modeling could address these issues if sediment 
deposition and resuspension calculations were included in a 
modeling frameworks. 
Tin, microorganisms resistant to tin, and microorganisms 
capable of transforming inorganic tin to organotin(s) were 
present at the sites sampled. However, the analysis of tin 
and organotin compounds in Chester River media did not result 
in any data to support or preclude the possibility of oyster 
mortality due to organotin compounds. 
In summary, no significant mortality of oysters was 
observed during the course of this study. However, there are 
indications of chronic stress in the estuarine system based on 
the results of this study. Should mortality be observed again 
at any time in the future, it is recommended that oyster samples 
should be taken immediately, stored, and later analyzed for 
suspected xenobiotics. At the same time, water quality variables 
such as dissolved oxygen, salinity and other environmental 
variables should be observed as soon as possible after the 
mortality is reported. It should be noted that the greater the 
time period between when mortality of organisms is reported, and 
the analytical observations are made, the more difficult it will 
be to evaluate possible cause-and-effect relationships. 
In addition, the acute and chronic effects of phthalate 
esters to estuarine organisms is relatively unknown. Additional 
monitoring of phthalates in this River is recommended as well 
as laboratory aquatic bioassay tests. Monitoring of oyster 
growth and mortality, dissolved oxygen and salinity over a 
several year period is required to determine if the observed 
high mortality has subsided. Such monitoring would help to 
identify causes of chronic stress indicated by reduced growth 
rate of the oysters. 
v 
