Introduction

They are tiny—the size of a person’s fingernail—yet they are having a billion-dollar impact on the North American economy and causing great harm to countless freshwater ecosystems. Zebra mussels (Dreissena polymorpha) and quagga mussels (Dreissena rostriformis bugensis) are highly invasive bivalves native to Eastern Europe. These tiny, freshwater species originated in the Caspian and Black Seas and were transported to North America in ballast water from a cargo ship. First discovered in the Great Lakes in the late 1980s, these mussels have now invaded waterways across the United States, causing numerous ecological impacts and creating operations and maintenance challenges for commercial facilities that draw water from infested lakes and rivers. By the early 1990s facility operators were employing a variety of methods to try and stave off impending damage that could be caused by the ever-expanding mussel colonies. Some methods were labor intensive, some turned out to be completely ineffective and others posed a tremendous risk to the facilities’ employees and the surrounding ecosystem. Without a better alternative, operators had to tolerate these shortcomings. In 2007, however, an exciting scientific breakthrough led to the development of Zequanox®, a naturally derived molluscicide that offered a highly effective AND environmentally compatible control method for these invasive mussels. Presented herein is the story of Zequanox: how it was discovered, how the product was developed, and an overview of the science behind this innovation. This document also summarizes results that demonstrate the efficacy and safety of Zequanox and highlights the product’s many advantages over traditional control options.

A Multibillion Dollar Problem

Zebra and quagga mussels can attach by the millions to one another, forming dense colonies in heavy masses up to a foot thick (U.S. Department of the Interior, U.S. Geological Survey [USGS] 2008). These colonies can clog piping, filters and screens, impeding or preventing the flow of critical cooling or process water. The mussels can also cover system components and mechanical parts, causing system damage and weighing down equipment and infrastructure. These effects can hinder or in some cases shut down operations. Continual attachment of Dreissena can also significantly increase corrosion rates of steel and concrete (Benson and Raikow 2011), leaving equipment and infrastructure vulnerable to failure. Many of the traditional chemical control options, chlorine in particular, exacerbate the increased corrosion and pitting that invasive mussels initiate. Once introduced into a new water body, the population growth of these mussels can be explosive.

Very successful invaders, zebra and quagga mussels thrive in a variety of temperatures, readily find food, reproduce prolifically and rapidly, and lack natural predators. The average female zebra mussel, which is ready to reproduce in its first year of life, can release 30,000 to 40,000 eggs per year. After hatching, the planktonic larvae can not only move great distances in flowing water, but can also easily invade small places in both natural systems and industrial systems that draw from infested waters. Mussel colonies can build up very quickly. It has been reported that these mussels have been able to clog a three-foot-diameter pipe in less than three months (U.S. Department of Energy, National Energy Technology Laboratory [NETL] 2006).

An added challenge is that these mussels can rapidly disperse to other water bodies, primarily by the larval movement and their inadvertent transport by barge and boat traffic, and can survive for many days out of water, factors that have caused the zebra and quagga mussel invasion to spread to many previously uninfested waters throughout the United States. They arrived in Lake Erie in the late 1980s, likely in the ballast water of transoceanic vessels (McMahon, 1996). Dreissenids can survive dry conditions for several days on or in boats, motors, and trailers. They also hitchhike on aquarium plants, such as moss balls available at petand aquarium stores (U.S. Geological Survey, 2021). Zebra mussels were the first to arrive and establish. Where both species exist, quagga mussels frequently replace zebra mussels because they are larger. Since their invasion, zebra mussels have spread to 31 states and quagga mussels to 18 states (U.S. Geological Survey, 2023). Bilge and livewell water of recreational vessels and ballast water of shipping vessels have been the primary vectors of transmission.

There is widespread agreement that zebra and quagga mussels annually cause millions of dollars in additional maintenance expenses in North America. United States Congressional researchers estimated that zebra mussels alone cost the power industry $3.1 billion during 1993–1999. The U.S. Fish and Wildlife Service estimated the economic impact during 2000–2010 at $5 billion. The mounting costs, combined with an ever-expanding geographical area of impact, have increased the need for reliable control methods that are suitable for a variety of industrial and civil applications.

The Need for a New Approach

Enclosed Systems Commercial and public entities facing zebra and quagga mussel infestations have applied a variety of methods when seeking to control mussel populations, including aqueous controls, antifouling coatings, physical removal and mechanical controls. Each of these methods has significant drawbacks.

A common approach to mussel control is aqueous applications of chemicals such as chlorine for enclosed systems such as pipes and bays. Chlorine-based methods using hypochlorite, chlorine gas and chlorine dioxide necessarily involve careful practices to ensure that the chemicals are safely stored, and that employees handling the chemicals are not exposed to hazards and unnecessary risk. In addition, chlorine and other oxidizing chemicals are corrosive to equipment. Chemical treatments are toxic to other aquatic organisms and because of this non-targeted toxicity, facilities using chlorine and other chemical- based molluscicides may be required to deactivate or detoxify the treated water before discharge to meet environmental requirements (NETL 2006). Bisulfate or similar salts are used to help prevent the release of chlorine into the environment and reduce the impact on other aquatic organisms, contributing to salt loading in water bodies. Many molluscicides require the addition of clay to a treated water system to quench or deactivate the chemicals’ toxicity before discharge into the environment. The ultimate fate and transport of the clay-bound molluscicides once discharged is unknown; many of these substances are nonbiodegradable and stay in the ecosystem long after discharge.

An additional disadvantage of using chlorine is that the mussels perceive the chlorinated water as a threat, causing them to shut their valves for so long that very long application times are necessary to achieve results. The formation of harmful by-products is yet another area of concern; when chlorine combines with organic compounds in water, potentially carcinogenic substances such as trihalomethanes, haloacetic acids and dioxins are formed (U.S. Environmental Protection Agency [EPA] 1999; Thornton 2000).

A Biological Breakthrough

The need for a new control method drove extensive research that led to an industry-changing discovery. Faced with the threat of zebra mussels fouling electric power facilities within New York State, a research consortium of New York State’s electric power generation companies contracted with New York State Museum Field Research Laboratory in 1991 for the screening of bacteria as potential biological control agents. The use of microbial, natural product compounds already had a clear record of commercial success and environmental safety in the control of invertebrate pests in North America, as well as globally (Rodgers 1993). Extensive laboratory screening trials of more than 700 bacterial strains identified a North American isolate, strain CL145A of Pseudomonas fluorescens, to be lethal to zebra and quagga mussels (Molloy 2002). Pseudomonas fluorescens is worldwide in distribution and is present in all North American water bodies. In nature, it is a harmless bacterial species that is found protecting the roots of plants from diseases.

Bringing the Solution to Market

In 2007 Marrone Bio Innovations (MBI) entered into a commercial partnership with the New York State Museum to bring this naturally occurring soil microorganism to market for the control of zebra and quagga mussels. The result was Zequanox—the industry’s first environmentally compatible molluscicide.

The EPA registered Zequanox on July 29, 2011 and it is now registered in all states except Hawaii and In Canada for pipe use. Beginning in 2009, MBI in cooperation with the U.S. Bureau of Reclamation (Reclamation) conducted field trials of Zequanox under a Cooperative Research and Development Agreement (CRADA). The product was tested at Reclamation’s Davis Dam on the lower Colorado River, where supply lines were heavily infested. MBI also teamed with Ontario Power Generation of Ontario, Canada, to perform testing at the DeCew II Generating Station Facility. Ontario Power Generation, which had a 20-year history of chlorine control that had reached its maximum optimization potential and wanted to help bring a more sustainable mussel control solution to the market, assisted MBI in its commercial development of Zequanox (Van Oostrom, Peterson-Murray and Dow 2010).