Chemicals used in marine fish farms can be broadly divided into two categories:

• hygiene products for disinfection or for environmental control, e.g. antifouling agents for fish cages, and
• medicinal products, divided into chemotherapeutic agents for therapy or prophylaxis of disease which act on the invading organisms, and pharmacological drugs which act on the target animal.

Inevitably when such therapeutants are applied to farmed stocks, a significant proportion will not reach the target species but will enter the environment. Route of entry and potential concentrations will depend on the volumes used and method of application. For example chemicals could enter the marine environment through faeces, uneaten food, or from bath treatments. Greater volumes can be expected for chemicals used in bath treatments, compared to chemicals applied through food.

Sea lice treatments are necessarily toxic medicines which are applied, either as bath treatments or as in-feed treatments. The fate and effects of these chemicals in the environment depend upon their physical and chemicals properties. They may persist in the water column and affect plankton and/or affect the seabed and its benthic fauna.

A Nature Conservancy Council report in 1989 (NCC 1989) identified impacts in the environment from mariculture. This included a consideration of chemical pollution from aquaculture; feed additives, pharmaceuticals and other treatments, e.g. antibiotics, immersion and antifoulant treatments to equipment. The reader is referred to this review for background information. SEPA has recently published a document entitled Regulation and monitoring of marine cage fish farming in Scotland - A procedures manual (SEPA Fish Farming Manual) which details the procedures SEPA will follow in the control of fish farm chemicals and includes EQSs in the water column and the sediments. This document is freely available and should be used as a companion to this manual when considering the impact of fish farm chemicals on European marine sites.

The table below lists the main chemicals used in marine cage fish farming and indicates where standards exist and where further information can be found.

Hydrogen peroxide is administered as a bath treatment for the removal of sea lice by enclosing the cage in a tarpaulin. It is the recommended treatment for the removal of sea lice by SEPA. The Environment Agency is investigating its effects on aquatic organisms.

Dichlorvos is also administered as a bath treatment and EQSs have been proposed for the water column in the form of annual averages and maximum allowable concentrations.

Azamethiphos is an organophosphate that has recently been granted market authorisation by SEPA for use as a bath treatment for the removal of sea lice. EQSs have been proposed by Lewis et al (1998) for the protection of saltwater life in the form of annual averages and maximum allowable concentrations (these are non-statutory). SEPA Policy No. 17 contains short term (3 to 72 hours) EQSs in the form of maximum allowable concentrations. The SEPA Fish Farming Manual explains the application of these EQSs.

Cypermethrin is a synthetic pyrethroid (see Section B20 for general information on synthetic pyrethroid pesticides) that has recently been granted market authorisation by SEPA as a bath treatment for the removal of sea lice. The Environment Agency is currently investigating the effects of cypermethrin on aquatic organisms with a view to deriving EQSs. SEPA Policy No. 30 contains EQSs in the form of short-term maximum allowable concentrations and an annual average. The SEPA Fish Farming Manual explains the application of these EQSs.

Teflubenzuron is the active ingredient of Calcide which is a new in-feed sea lice treatment which has recently been granted limited market authorisation by SEPA. SEPA Policy No. 29 contains EQSs for this chemical in the water column in the form of a short-term (3 hour) maximum allowable concentration and in the sediment in the form of a maximum allowable concentration in surface sediment outside an allowable impact zone and as an average for surface sediment within the zone of impact. The SEPA Fish Farming Manual explains the application of these EQSs.

Ivermectin is an in-feed sea lice treatment and EQSs have been proposed in the water column in the form of annual averages and maximum allowable concentrations (these are non-statutory). SEPA Policy No. 2 deals with the application of ivermectin in fish farming and the SEPA Fish Farm Manual explains the application of the existing standards.

Antimicrobials are used as treatments for diseases. These chemicals can be persistent in seabed sediments and reduce metabolic processes of micro-organisms. Problems caused by a bacterial infection, furunculosis, in the 1980s required the use of substantial quantities of antibiotics which had the potential of causing environmental harm. Reviews, and (where possible) EQSs (although these are not statutory) have been proposed for the protection of saltwater organisms for a number of chemicals used as antimicrobials or disinfectants, namely oxolinic acid, oxytetracycline, malachite green and formaldehyde (Murgatroyd et al 1994; Gendebien et al 1994; Burchmore and Wilkinson 1993; Jerman and Wilkinson 1993). The reader is referred to these studies for further information on the effects of saltwater organisms. However, SEPA has suggested that the industry is no longer dependent on chemical treatments following the introduction of vaccination.

Antifoulant paints which contain toxic chemicals for preventing growth of marine plants and animals are used on fish cage structures and nets. These chemicals will gradually be released to the marine environment. The move to deploy bigger net enclosures is viewed with concern as this involves the use of increased chemical antifoulant coating as the nets are larger and it becomes uneconomical to change them regularly. The washing of antifoulant coated nets also causes concern as the spent washings have been found to contain unacceptably high concentrations of copper and zinc.

Micro-nutrients (e.g. zinc) are added to fish feeds. There are indications of elevated levels in sediments below cages which require further investigation. Anaesthetics and disinfectants are also used, but, according to SEPA, these are not currently perceived to pose a significant environmental risk.

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