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

摘要

Since the first arrival of the zebra mussel (Dreissena polymorpha) to Ireland in the earlyud1990’s, there has been a rapid secondary spread of these highly invasive mussels withinudmany Irish freshwater systems suitable for their establishment. This has resulted inuddirect invasive impacts to infested lakes, rivers and canals, both to the freshwater biotaudand to man-made infrastructure. The availability of an effective, yet environmentallyudbenign, mussel control product to replace those currently used, such as chlorine andudother biocides is particularly needed to mitigate mussel fouling impacts in drinkingudwater plants and other infested facilities.udZequanox® is a selective control product for dreissenids, i.e. zebra and quaggaud(D.rostriformis bugensis) mussels. It is a natural biocide, with the active ingredientudbeing dead Pseudomonas fluorescens CL145A cells; a patented strain of a naturallyudoccurring soil bacterium, which works by disrupting the mussels’ digestive system. Thisudproduct was developed in the USA, and has been tested and used in a number of NorthudAmerican trials, with the aim of commercialising a cross-continental, effective andudregulatory compliant control product.udResearch outputs from this thesis were utilised in the Zequanox regulatory applicationudfor commercial use within Europe. Ecotoxicology trials were carried out on nine speciesudfound commonly in Irish ecosystems. Results indicated that Zequanox does notudnegatively affect eight of these organisms at concentrations and treatment lengthsudrequired to get a >80% zebra mussel kill.udField trials were carried out to demonstrate the effectiveness of Zequanox in industryudand open water and to monitor water quality during and after treatment. These includeduda biobox trial at a drinking water treatment plant and an open water trial in a canal. Bothudtrials achieved high levels of zebra mussel mortality (up to 81%) and provided insightsudinto practical application techniques.udAdditional laboratory assays were undertaken to determine the exact responseudrelationship of juvenile zebra mussels to Zequanox. The results showed that juvenileudmortality, on both experimental and control plates, are decreased with reduced handling,udwith subsequent recommendations given for future juvenile treatment and countingudprocedures in the field.udAfter the two field trials (drinking water treatment plant and canal) were undertaken, itudwas apparent that mortality rates after treatment were lower in Ireland and also tookudlonger to occur than similar trials carried out in North America. It was suspected that theudhigher water temperatures during North American trials (>25C) meant that the zebraudmussels were more metabolically active and therefore ingested more product. A numberudof comparative studies commenced to evaluate the effect of Zequanox on NorthudAmerican zebra mussels versus European zebra mussels. The results of this studyudshowed that under the same temperature regimes mortality is similar. North Americanudmussels were found to ingest more product in the initial eight hours, however by 24udhours, product concentration was similarly low for both mussel groups. The results ofudthis trial allowed for industry recommendations to be made regarding the timing ofudtreatments in Europe.udIn conclusion this research has bridged the gap between the use of Zequanox in Europeudand North America, showing there is potential for Zequanox to control zebra mussels inudEurope not only in industry but also in open water. This study has also demonstratedudZequanox’s potential to replace chlorine as the traditionally used control method,udthereby reducing the environmental impact of mussel control on freshwater ecosystems.