TBT and related organotins have been found to be very toxic to molluscs in 

 trace quantities because of the characteristics of the physiology of these 

 organisms. To determine nonlethal but detrimental effects, toxicity 

 testing must become more sophisticated and focused on physiological 

 processes. 



Studies are needed to provide more information on: 



o How much of each butyltin species is actually present in the 

 exposure solution at the time the bioassay is conducted? 



o What concentrations of TBT elicit selected responses along the 

 continuum from successfully counteracting the toxin to the 

 complete overwhelming of hemostatic mechanisms? 



o What are the low level physiological effects on molluscs of 

 chronic exposure to TBI extending over the full life cycle of the 

 mollusc? 



o What are the effects on gametogenesis and other aspects of 

 reproductive success in molluscs during chronic exposure to TBT 

 extending over the full life cycle of the mollusc? 



o What are the effects on the calcification mechanism of molluscs 

 during chronic exposure to TBT extending over the full life 

 cycle of the mollusc? 



o What are the mechanisms inducing imposex associated with chronic 

 exposure to TBT extending over the full life cycle of the 

 mollusc? 



o What are the mechanisms inducing suppression of the immune 

 response system due to chronic exposure to TBT over the full life 

 cycle of the mollusc? 



o What is the true no effects level (NO-EL) of TBT in coastal 

 waters with respect to molluscs? With respect to fish? 



o Can the coastal ecosystem response to the toxin (TBT) be 

 adequately represented by toxicity tests on single species? 



o Would mesocosm or microcosm community response to the toxin be 

 representative of the response of the coastal ecosystem to TBI? 



V-8 



