 the objective of this study was to investigate the impact of long - term pyrene exposure on molting and reproduction in the model estuarine invertebrate , the grass shrimp ( palaemonetes pugio ) . 
 grass shrimp were exposed to measured concentrations of 5.1 , 15.0 , and 63 . 
 4 ppb ( microg / l ) pyrene for 6 weeks , during which time we determined molting and survivorship . at the end of the exposure 
 , we immediately sacrificed some of the shrimp for biomarker ( cyp1a and vitellin ) analyses . 
 the remaining shrimp were used to analyze fecundity and embryo survivorship during an additional 6 weeks after termination of pyrene exposure . 
 male shrimp at the highest pyrene dose ( 63 ppb ) experienced a significant delay in molting and in time until reproduction , and showed elevated ethoxycoumarin o - deethylase ( ecod ) activity immediately after the 6-week exposure period . 
 in contrast , 63 ppb pyrene did not affect these parameters in female shrimp . 
 females produced the same number of eggs per body weight , with high egg viability ( 98 - 100% ) at all exposure levels , but with decreased survival for the offspring of the 63-ppb pyrene - exposed females . 
 in addition , vitellin levels were elevated only in females at 63 ppb pyrene after the 6-week exposure . 
 we hypothesize that the elevated vitellin binds pyrene and keeps it biologically unavailable to adult females , resulting in maternal transfer of pyrene to the embryos . 
 this would account for the lack of effect of pyrene exposure on ecod activity , molting , and reproduction in the adult females , and for reduced survival of their offspring.imagesfigure 1figure 2figure 3 
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