Ballast water: Living Versus Viable

By Rear Adm. Paul Thomas, assistant commandant for prevention policy, U.S. Coast Guard

In the last blog, I compared the U.S. regulations with the IMO Ballast Water Management Convention. Here I will address the confusion about using living or viable terminology in the standard, and I will discuss the challenges with determining viability.

Living versus viable

The ballast water discharge standard in the IMO Convention is phrased in terms of “viable” organisms; specifically, discharged ballast water must contain no more than 10 “viable” organisms per cubic meter or cubic milliliter, depending on the size class of organisms. The IMO G8 guidelines for approval of ballast water management systems, or BWMS, specify that for the purposes of approving BWMS, “viable” is defined as “living”. It goes on to state that viability is determined through a live/dead judgment. Therefore, the U.S. interpretation of these guidelines has always been that “non-viable” means dead.

The ballast water discharge standard in the Coast Guard regulation is the same as the IMO Convention but is phrased in terms of the maximum allowable number of “living” organisms per cubic meter or cubic milliliter of ballast water. Accordingly, the U.S. type-approval procedures specify a method for determining the number of “living” organisms. 

Modern techniques currently exist to make this live/dead judgment reliably and with a high degree of accuracy. The U.S. Coast Guard’s 2012 ballast water discharge standards final rule and the Environmental Protection Agency’s environmental technology verification, or ETV, protocols are designed to establish that organisms are dead, by measuring enzymatic activity and motility.

In response to the Coast Guard’s 2009 notice of proposed rulemaking, one commenter recommended that the Coast Guard rephrase the discharge standard in terms of “viable” organisms to be consistent with the Convention. In the preamble to the 2012 final rule, the Coast Guard rejected that recommendation due to the technical difficulties associated with determining viability.

The difficulties of determining viability 

Despite the wording in the G8 guidelines regarding the live/dead judgment, some Flag Administrations have been using reproductive ability tests to determine viability of organisms when approving BWMS.

Theoretically, one would assess viability by culturing each of the unique organisms found in a sample of ballast water to determine if they can reproduce after treatment. This raises several technical challenges, the most important being that it may not be possible to culture all of the types of organisms found in ballast water; simply put, we do not yet know how to consistently induce them to reproduce in the laboratory. 

In addition many organisms cannot be induced to reproduce under laboratory conditions but may be able to reproduce in natural environments. Finally, it is not clear that organisms rendered nonviable will remain so over time. It has been shown that some organisms have repair mechanisms that can undo damage caused by ultra-violet radiation and thus restore the ability to reproduce.

Most probable number method 

Some administrations have type-approved ultraviolet light, or UV, systems on the basis of the most probable number, or MPN, method, which is used to determine the viability of organisms rather than making the live/dead judgment. For all the reasons discussed above regarding the difficultly of determining viability and because the U.S. discharge standard is expressed in terms of living organisms, the MPN method is not incorporated into the U.S. type-approval procedures.

However, manufacturers are able to submit a request for an equivalent alternative to the U.S. type-approval procedures under 46 CFR 162.060-10.b.1 of the final rule. Several manufacturers of UV systems that rely on the MPN method to demonstrate efficacy of their systems have submitted requests of equivalency under this section. Many of these manufacturers do not believe the systems will pass the “live/dead” criteria required by the final rule. We are currently evaluating these requests and expect to rule on them in the near future.