The EPA is also employing the Dynamic Estuarine Model in the 

 Elizabeth River and Hampton Roads portion of Chesapeake Bay (EPA, 1987) . 

 The impacts of recreational boating activity, commercial shipping and 

 military ship traffic are being simulated by assumptions regarding several 

 loading levels caused by boating and shipping activity in the area. Ihese 

 estimated concentrations are expected to help EPA make its final 

 regulatory decision regarding continued registration of TBT biocides in 

 antifouling paint (EPA, 1987) . 



Seligman et al. (1987) have reported on the results of a series of Dynamic 

 Es tuar ine modeling runs to investigate the environmental concentrations of 

 TBT resulting from paint releases from drydocks in the Hampton Roads and 

 Elizabeth River areas. The comparison of model estimates with observed 

 concentrations in this area show generally good agreement except for 

 intermittent higher measured concentrations than the model has predicted, 

 suggesting that estimates of releases from drydock operations may be too 

 low. The authors suggest that improved drydock cleanup procedures would 

 reduce this discrepancy. 



4.10 AIJIERNATTVES TO ORGANOTIN ANTIPOUIING PAINTS 



There is not a product on the market which matches the performance of 

 tributyltin as an antifoulant (Porter, 1980; Schatzberg, 1987) . There are 

 other antifouling chemicals. The primary alternative is copper, usually 

 copper oxide. Research is being conducted on alternatives to organotin 

 antifouling paints, however, useful results have not been clearly 

 demonstrated. The three main areas being investigated are: 

 (1) alternative toxins, (2) non-toxic compounds, and (3) disruption of the 

 successional stages of the development of the fouling communities. There 

 are also specific, or selective biocides being investigated. These 

 selective biocides are likely to be employed as an addition to rather than 

 a replacement for either organotin or copper. Neither organotin nor 

 copper controls all potential fouling organisms. Copper works well 

 against calcarious fouling organisms such as barnacles but not well 

 against algae, bacteria or some bryozoans. Organotin is repellant or 

 toxic to a wider range of species but does not work as well against algae 

 (Atherton et al., 1979; Callow et al., 1978). 



The ideal antifouling material must be able to prevent the attachment of 

 any members of the phylogenetic spectrum from bacteria to chordates 

 (tunicates) without being toxic to any of them. The ideal antifouling 

 material should adhere to all man made surfaces, be highly resistant to 

 abrasion, non-soluble in sea water and not inactivated by contact with 

 chemicals in aqueous solution, should remain effective indefinitely, be 

 inexpensive, and easy to apply. In the absence of the ideal substance, 

 research is progressing on the development of alternative toxins and 

 non-toxic alternatives. 



IV-51 



