Assessment and utilisation of Zequanox for zebra mussel (Dreissena polymorpha) control in Irish waters

Abstract

Since the first arrival of the zebra mussel (Dreissena polymorpha) to Ireland in the early 1990’s, there has been a rapid secondary spread of these highly invasive mussels within many Irish freshwater systems suitable for their establishment. This has resulted in direct invasive impacts to infested lakes, rivers and canals, both to the freshwater biota and to man-made infrastructure. The availability of an effective, yet environmentally benign, mussel control product to replace those currently used, such as chlorine and other biocides is particularly needed to mitigate mussel fouling impacts in drinking water plants and other infested facilities. Zequanox® is a selective control product for dreissenids, i.e. zebra and quagga (D.rostriformis bugensis) mussels. It is a natural biocide, with the active ingredient being dead Pseudomonas fluorescens CL145A cells; a patented strain of a naturally occurring soil bacterium, which works by disrupting the mussels’ digestive system. This product was developed in the USA, and has been tested and used in a number of North American trials, with the aim of commercialising a cross-continental, effective and regulatory compliant control product. Research outputs from this thesis were utilised in the Zequanox regulatory application for commercial use within Europe. Ecotoxicology trials were carried out on nine species found commonly in Irish ecosystems. Results indicated that Zequanox does not negatively affect eight of these organisms at concentrations and treatment lengths required to get a >80% zebra mussel kill. Field trials were carried out to demonstrate the effectiveness of Zequanox in industry and open water and to monitor water quality during and after treatment. These included a biobox trial at a drinking water treatment plant and an open water trial in a canal. Both trials achieved high levels of zebra mussel mortality (up to 81%) and provided insights into practical application techniques. Additional laboratory assays were undertaken to determine the exact response relationship of juvenile zebra mussels to Zequanox. The results showed that juvenile mortality, on both experimental and control plates, are decreased with reduced handling, with subsequent recommendations given for future juvenile treatment and counting procedures in the field. After the two field trials (drinking water treatment plant and canal) were undertaken, it was apparent that mortality rates after treatment were lower in Ireland and also took longer to occur than similar trials carried out in North America. It was suspected that the higher water temperatures during North American trials (>25C) meant that the zebra mussels were more metabolically active and therefore ingested more product. A number of comparative studies commenced to evaluate the effect of Zequanox on North American zebra mussels versus European zebra mussels. The results of this study showed that under the same temperature regimes mortality is similar. North American mussels were found to ingest more product in the initial eight hours, however by 24 hours, product concentration was similarly low for both mussel groups. The results of this trial allowed for industry recommendations to be made regarding the timing of treatments in Europe. In conclusion this research has bridged the gap between the use of Zequanox in Europe and North America, showing there is potential for Zequanox to control zebra mussels in Europe not only in industry but also in open water. This study has also demonstrated Zequanox’s potential to replace chlorine as the traditionally used control method, thereby reducing the environmental impact of mussel control on freshwater ecosystems.