TWO new toxic chemicals will soon be discharged into lochs in Scotland,
with the permission of the Scottish Environment Protection Agency (SEPA). The
agency is under pressure from salmon farmers who want to douse their fish with
azamethiphos, an organophosphate, and cypermethrin, a synthetic pyrethroid, to
control sea lice.
Sea lice eat away at the flesh of salmon, and the two chemicals are the
latest weapons in the battle to eradicate them. Fish farmers are abandoning the
pesticide used over the past two decades, dichlorvos, which is also highly
toxic, because lice are gaining resistance. All except five of Scotland鈥檚 350
salmon farms are also prevented from using another synthetic pesticide,
ivermectin, because of fears that it will kill farmed shellfish and even
threaten human health (This Week, 7 September 1996, p 4).
The Scottish Salmon Growers鈥� Association expects all its members to apply for
permission to use both new chemicals. David Mackay, director of SEPA鈥檚 northern
region, says that the agency will have no choice but to license the use of
azamethiphos and cypermethrin. The British government鈥檚 Veterinary Medicines
Directorate has already approved azamethiphos for use in fish farms and is
expected to agree a similar licence for cypermethrin soon.
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鈥淚f they have said yes, we can鈥檛 just turn around and say no,鈥� says Mackay.
However, he says that applications to use the pesticides will be dealt with on a
case-by-case basis. 鈥淲e will give permission in the right circumstances but that
will only be a small proportion of farms.鈥�
Scottish salmon farmers say that their competitors are already using the
chemicals. Canada last year gave azamethipos 鈥渆mergency authorisation鈥� to tackle
a plague of lice, but has resisted pressure to approve cypermethrin. Azamethipos
was licensed for use on Norwegian fish farms in 1994, and cypermethrin was given
limited approval last year. But Norway鈥檚 authorities want fish farmers to cut
their use of louse pesticides by 75 per cent in the long term.
Cypermethrin, which acts on the nervous system of invertebrates, is
鈥渆xtremely toxic to crustacea鈥� and has 鈥渁 very bad reputation in freshwater鈥�,
says Mackay. He blames the chemical, which is widely used as a sheep dip, for
wiping out invertebrates along long stretches of Scottish rivers (This Week, 11
January, p 4).
A report prepared by SEPA鈥檚 scientists reveals that tiny concentrations of
azamethiphos, which also attacks the nervous system, kill young lobsters and
herring. Although previous studies suggested 鈥渁n unacceptable environmental risk
to most sea lochs鈥�, the report argues that reductions in dosage, put forward by
Novartis, the pesticide鈥檚 Swiss-based manufacturer, mean that it can now be
given the go-ahead.
Azamethiphos is ten times as toxic as dichlorvos but Novartis is now
proposing to use it at a tenth of the concentration. SEPA says that the company
admits that lice may develop resistance, however, which was the reason for the
鈥渙ptional elevated dose rate鈥� it originally proposed.
SEPA argues that it can police salmon farmers so that they do not exceed
approved doses. But environmentalists fear that farmers will be tempted to
increase the dose as lice become more resistant. SEPA is being 鈥渢otally
unrealistic鈥� in suggesting it can control the risk, argues Ali Ross, marine
consultant to Scottish Wildlife and Countryside Link, a coalition of
conservation groups.
鈥淭his sends totally the wrong message to the industry,鈥� she says. 鈥淚t should
instead be under notice that its release of toxic chemicals has got to end.鈥�