increases f locculation and precipitation of suspended materials and 

 solids. Harris and Cleary (1987) have found in the English river Tanar 

 that the percent TBT adsorbed to particles exhibited a maximum which 

 corresponded with the location of the turbidity maximum. The circulation 

 patterns of the partially stratified estuary will tend to accumulate 

 particulate bound TBT at the salinity interface, which may be well 

 upstream from where concentrations of boats are moored. In this situation 

 estuarine physical processes would act to transport TBT upstream to the 

 turbidity maximum for deposition [see Figure 4.5 from Harris and Cleary 

 (1987) ] . In this case the sediment serves primarily as a sink and the TBT 

 is removed and isolated from the water column by continued sedimentation. 



Studies of Chesapeake Bay sediment sorption coefficents have been 

 conducted by Uhger et al. (1987). Table 4.16 summarizes the relationships 

 that Uhger et al. (1987) observed between sediment types and sorption 

 coefficients for TBT. Table 4.17 summarizes partitioning coefficients of 

 butyltin compounds between sediments and water reported by Stang and 

 Seligman (1987) . These studies have found that significant amounts of TBT 

 may be associated with particulate material or sediments in coastal plain 

 type estuaries. They have also observed that the sorption process is 

 reversible suggesting that contaminated sediments may well act as sources 

 for TBT to redissolve into the water column. Sorption to sediments 

 decrease with increasing salinity (see Figure 4.5, fr om Harris and Cleary, 

 1987) . Therefore, salinity changes and sediment types must be considered 

 when estimating the effects of dredging of contaminated sediments or TBT 

 transport and bioavailability. 



IV-36 



