Canada States Its Position on the MPN Method


By Wendy Laursen 2016-07-07 17:39:03

The Government of Canada has stated its support for the use of the most probably number (MPN) method for determining the efficacy of ballast water treatment systems.

The MPN method evaluates the ability of an organism to reproduce and hence its ability to colonize a new environment. As such, it does not provide a result equivalent to that of the U.S. Coast Guard’s preferred method - vital staining.

The U.S. Coast Guard decided to reject the MPN method in December last year. Since then, equipment manufacturers Trojan Marinex and DESMI Ocean Guard have submitted appeals, and the Chamber of Shipping of America has issued a letter of support for the MPN method.

The science behind vital staining was called into question earlier this year. In a presentation at the IMO GloBallast Forum in March, Dr Hugh L. MacIntyre concluded that the vital stain method is seriously flawed and unable to accurately classify phytoplankton as either live or dead.

DNV GL is of the position that the MPN method is the most relevant method and is a reliable way of evaluating the performance of UV technologies. The method has been validated to a greater extent than most of the methods described in the Environmental Technology Verification (ETV) Protocol (prescriptive guidance incorporated by reference to U.S. regulation), and UV technologies are commonly accepted in other water treatment industries. 

Disinfecting water while ensuring acute kill of the organisms (instead of the ability to reproduce) will require a much more conservative dosage, implying higher power consumption (three to five times) by the UV lamps compared to most systems designed today, says DNV GL.

With the Ballast Water Management Convention inching closer to ratification, the U.S. Coast Guard’s decision has drawn criticism from the International Chamber of Shipping and INTERTANKO who assert that the decision negatively impacts treatment systems based on UV and “halves the number of systems shipowners can select from if they wish to operate globally.” This is expected to create substantial equipment supply issues, should the Convention come into force soon.

Trojan Marinex remains optomistic about a solution. “Coupled with Canada’s strong support of the MPN method, we are encouraged by the good progress being made at the IMO in adopting a definition of “viable” that continues to allow the use of reproductive measurement methods, such as the MPN method. We are also very encouraged by the strong interest that U.S. Congress is showing to help resolve the MPN matter with the U.S. Coast Guard,” says Mark Kustermans, Market Manager for UV system manufacturer Trojan Marinex.

The Canadian Government’s response

In responding to an inquiry by Water Canada the government stated its clear support for UV systems and the MPN method: 

“The Government of Canada supports effective ballast water management standards to reduce the risk of introducing invasive species. Canada’s Ballast Water Control and Management Regulations were established in 2006 and require that international ships manage their ballast water. Four management methods are permitted: ballast water exchange, treatment using a ballast water management system, transfer to a reception facility or retention on board the ship.

“In 2010, Canada signed on to the International Convention for the Control and Management of Ships’ Ballast Water and Sediments, 2004, which will further reduce the risk of aquatic species invasions compared to Canada’s current regulations. After it enters into force, this Convention will require ships to comply with a standard limiting the number of viable organisms that can be discharged in ballast water. As it will not be possible to use ballast water exchange to meet this standard, most ships are expected to use BWMS in order to comply.

“The function of ballast water management systems is to reduce the number of viable organisms in ballast water, preventing species invasions when ballast water is moved between locations. While many ballast water management systems are designed to kill or remove aquatic organisms, some ultra-violet light-based systems are designed to remove or cause irreparable genetic damage to organisms, preventing them from becoming established in new locations by eliminating their ability to reproduce. An organism that cannot reproduce will not be able to establish itself in a new location and will not be able to trigger a species invasion. Canada supports the type-approval of ballast water management systems that make use of UV light as one of a suite of processes appropriate for the treatment of ballast water.

“The [MPN] Serial Dilution Culture-Most Probable Number method (SDC-MPN) has been used to measure viability by determining if organisms are capable of reproduction. This method can be used in the assessment of any ballast water management system to measure there productive capability of organisms remaining after treatment. Canada supports the use of the SDC-MPN method as one of a suite of methods appropriate for assessing BWMS.

“Canada is calling for U.S. legislators and U.S. federal and state administrations to maximize compatibility between the implementation of U.S. requirements and the Convention. Transport Canada officials also work closely with their counterparts at the U.S. Coast Guard and the Environmental Protection Agency towards this goal. These discussions occur bilaterally under the Canada-U.S. Great Lakes Water Quality Agreement, as well as multilaterally through the International Maritime Organization.”