Various parasites cause considerable health problems and mortality in farmed salmon and wild salmon alike (see separate chapter). In this section we shall address the environmental impacts of the various forms of treating parasites. We shall concentrate on salmon lice, Lepeophtheirus salmonis, and sea lice, Caligus elongatus, which both belong to the family Caligidae in the class copepods (Copepoda), hereafter called simply lice. Treatments of lice-infested farmed fish can be divided into three main categories, which are usually used in combination: wrasse, delousing baths, and medicated pellets. The first, wrasse, has few environmental drawbacks, but certain limitations on practical use. The two others subject the fish and the marine environment to toxic substances, and must therefore be thoroughly evaluated with a view to environmental impacts. In addition, it was previously common to treat the fish with hydrogen peroxide, which relatively easily breaks down into oxygen and water. The problem, however, is that this treatment only removes the lice from the salmon without necessarily killing them. Thus, the parasites can return to the cages, or worse, infest wild salmon. In Norway, hydrogen peroxide has fallen into complete disuse (Treasurer and Grant, 1997).
Since the spread of salmon lice from fish farms to emigrating wild smolt is reckoned to be a central environmental problem in fish farming, two different environmental problems need to be weighed against each other. For now an important part of the solution to the louse problem is effective chemotherapeutic treatment, which in turn creates another environmental problem, namely, pollution of the marine environment. In the following we shall review documented and assumed environmental impacts of the most common salmon delousing agents, and on the basis of available research findings, give the reader a picture of how the chemicals behave in the environment, especially in view of their toxicity, persistence and health effects. Further, the chapter will describe the potential of biological methods for combating lice using wrasse as well as give an account of how the use of pharmaceuticals can otherwise be curbed. The chapter concludes with a discussion of the difficult balancing act that delousing involves.
Assessing environmental impacts of pharmaceuticals used to combat salmon lice
Assessing the environmental impacts of the various pharmaceuticals used to combat salmon lice is no easy task. There is no standardised method for experimental design and measuring of the substances’ biodegradability, and several experiments with the same substance may therefore yield different half-life periods. It is thus very difficult to compare different substances in respect of environmental characteristics. When pharmaceutical manufacturers apply to have their products approved by the Norwegian Medicines Agency, the agency obtains an environmental assessment of the substance from the Norwegian Pollution Control Authority. The Norwegian Pollution Control Authority gains access to the manufacturer’s environmental documentation and writes up a brief evaluation based on this. Due to a lack of standard procedures for testing and documentation, the Norwegian Pollution Control Authority must in each case use discretion in judging whether the documentation submitted is sufficient, and if not, request additional documentation. In consideration of the manufacturer’s needs for protection against competitors’ possible copying of the actual product or copying the documentation, the Norwegian Pollution Control Authority returns the documentation without disclosing it in any way. Thus, it is completely up to the manufacturers what they want to make public, and as a non-governmental organisation, Bellona is at the mercy of the manufacturers’ disclosure policies in its quest for documentation. In this chapter this may be reflected in the fact that some substances are described in more detail than others. To a certain extent we have had to base our evaluations on secondary sources, such as the Norwegian Pollution Control Authority or Scottish authorities’ evaluation of environmental documentation, as well as presentations from pharmaceutical manufacturers. Recently the new "Environmental Data Act" came into force. Its purpose is to give everyone access to companies’ environmental documentation regarding products, emissions or discharges.
Pharmaceuticals for use against salmon lice in Norway (Norwegian Medicines Control Authority, 2000):
|Classification||Active ingredient||Trade name|
|Pyrethriods||Cypermethrin||Excis vet. (Grampian)|
|Pyrethrum||Pyrethrum extract||Py-sal vet. (Norwegian Pyrethrum)|
|Chitin synthesis inhibitors||Diflubenzuron||Lepsidon vet. (Ewos)|
|Avermectins||Emamectin||Slice vet. (Schering-Plough)|
You will find reviews of the environmental and health documentation of deltamethrin, emamectin and teflubenzuron on these pages.