THE EFFECT OF TRIBUTYL TIN (TBT) ON GLUTATHIONE-S-TRANSFERASE (GST) OF THE COMMON GARDEN SNAIL, Helix aspersa.
R Torres and A.Z. Mason, Ph.D. Department of Biological Sciences, 
California State University, Long Beach, CA.

• Tributyl tin self polish copolymer (TBT-SPC) based paints are commercial marine antifoulant coating used to prevent attachment of aquatic organisms such as algae, barnacles and tubeworms to the ship bottoms.

• TBT-SPC based paint allows vessels to maneuver more efficiently and quickly reducing frictional drag, fuel consumption, and air pollution.  TBT-SPC based paints are effective for at least five years because of their ability to be slowly and uniformly released into the aquatic environment.

• Previous studies have shown that TBT causes imposex, a condition whereby the female individuals of certain susceptible marine snails develop a penis and vas deferens causing sterility. 

• The superimposition of male characteristics in afflicted female individuals coincides with an accumulation of physiologically active androgens, including testosterone.

• Two mechanisms have been proposed to account for the observed androgen build up.  (i) TBT inhibits Cytochrome-P450-aromatase, which normally converts testosterone to 17ß-estradiol in females. (ii) TBT may inhibit various transferases, such as GST responsible for elimination of steroids. (See Figure 1a) 

• GST conjugates reduced glutathione (GSH) to a variety of nonpolar compounds, specifically steroids and aryl halides, and thereby facilitate their elimination via urine.   (See Figure 1b). 

• In this study, the specific inhibitory effect of TBT on GST activity was examined.