Salinity appears to have an effect on the rate at which TBT is debutylated 

 to dibutyltin and monobutyltin. Most evidence points to the microalgae 

 and bacteria as agents for debutylating TBT. Differences in species 

 composition of the phytoplankton between fresh and salt water are 

 sufficient to account for the difference in degradation rates observed by 

 Maguire et al. (1986). The diatoms appear to be the principal 

 marine/estuarine microphytes debutylating TBT in salt water. 



Boating activity correlates with variations in the concentration of TBT 

 observed in coastal waters (Hall et al., 1986; Grovhoug et al . , 1986; 

 Seligman et al., 1986). The Navy's baseline study demonstrated that 

 recreational boat mooring facilities and also drydock and ship painting 

 facilities were associated with higher water column concentrations of 

 organotin (Grovhoug etal., 1986). Huggett (1986) observed high butyltin 

 concentrations in the Elizabeth River shortly after the launching of a 

 freshly painted commercial ship. The extreme variability in the 

 Elizabeth River was found to be associated with intermittent discharges 



(Seligman et al., 1987). However, in Baltimore Harbor, which does not 

 have major ship repair and painting facilities, TBT concentrations are 

 more closely associated with recreational boating facilities than with 

 commercial shipping (Hall et al., 1986). The EPA/Gulf Breeze Lab Study 



(1987) found a linear relationship between recreational boat density and 

 mean TBT concentrations (Johnson et al, 1987) . In addition to boat 

 density, a strong seasonal effect has been observed with peak 

 concentrations of TBT occurring in May and June in the Chesapeake Bay, 

 during the peak period of launching newly painted recreational boats for 

 the beginning of boating season. 



4.6.3 Measured Environmental Concentrations of TBT 



Concentrations of TBT have been measured in Chesapeake Bay by Huggett 

 (1986), Hall et al. (1986), Grovhoug et al. (1986), Seligman et al. 

 (1987), and the EPA Gulf Breeze Laboratory (Johnson et al., 1987). 

 Huggett (1986) employed a Grignard reaction to derivatize the organotin, 

 gas chromatography to separate the organotin into TBT and DBT species, and 

 quantification by mass spectrometer. The level of detection is given as 1 

 part per trillion (see Unger et al., 1986 for protocols). Sampling was 

 conducted once every two weeks from January 1986 through September 1986. 

 Results are summarized in Table 4.20. The Hall et al. (1986) study was 

 conducted at marina sites in the Severn River, West River, South River, 

 Chester River, Patapsco, Choptank and Potomac Rivers and in the Chesapeake 

 and Delaware Canals. Data was collected on the number of boats kept in 

 marinas adjacent to sampling locations. The results permitted an 

 estimation of the relationship between boat density and water quality with 

 respect to tributyltin concentrations. The study used the borohydride 

 derivatization method developed and in current use by the National Bureau 

 of Standards. The NBS method uses GC for separation and guantification. 

 Atomic Absorption Spectroscopy was used to quantify the chemical species. 

 Only the TBT concentrations are given in Table 4.20. Each of the 8 

 stations was sampled once a month from July 1985 to June 1986. The limits 

 of detection were given as 20 to 30 ng/1 of TBT. 



IV-44 



