micro-organisms and vertebrates is unknown. The method has not been used to treat sea water.

Deoxygenation

Oxygen deprivation (or deoxygenation) is toxic to a range of fish, invertebrate larvae, and aerobic bacteria but is ineffective against anaerobic bacteria and cyst and spore stages, including dinoflagellate cysts, and would provide only a partial solution to killing the range of aquatic species likely to be found in ballast water.4

Biological Techniques

Whether biological techniques are effective in removing, reducing or altering living organisms in ballast water and sediment remains theoretical. The addition of new species is unlikely to act as a successful control agent against the wide diversity of microbial animal and plant life that may be present in ballast water. The issue of the transport and release of the added species must also be addressed. Using genetically engineered organisms is also unlikely to provide a solution for the ballast water problem in the near future. The committee did not evaluate biological remediation in detail.

Anti-fouling Coatings

The committee did not consider anti-fouling coatings to be suitable for controlling introductions of nonindigenous species because the surfaces of ballast tanks and the organisms that settle on these surfaces represent only a small fraction of the total problem. Ballast water is a suspension of organisms, and the bulk fluid must be treated to prevent introductions of nonindigenous species by discharged ballast. A coating could be formulated that was highly loaded with toxic material and would release lethal concentrations of biocide into the water. However, this coating would have a short lifetime, and the treated ballast water would probably be toxic and require treatment prior to discharge.

New types of surface-active anti-fouling coatings are being introduced into the market in response to environmental concerns over paints containing copper and tin. The surface-active systems are nontoxic and rely on flow velocity to remove loosely attached fouling. These paints do not prevent fouling and are not appropriate for ballast tanks.

4  

 The survival of zebra mussels and Asian clams under conditions of anoxia (oxygen deficiency) has been investigated in the context of research and development aimed at finding environmentally sound methods of controlling zebra mussels (see, for example, Matthews and McMahon, 1995).



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