In a submission to the Scottish Office and
the Scottish Environmental Protection Agency (SEPA), members of SWCL* set
out a detailed case against the use of ivermectin. It highlights its acute
toxicity to a range of marine life, its persistence in the environment and its
potential to accumulate in organisms and even humans. The group argues that the
environmental assessment produced for the chemical is too limited and fails to
address the longer term and wider ecological implications or the impact on other
sea users such as shellfish farmers and fishermen.
SEPA claims that the consents will be tightly controlled
during a two year trial, although the illegal use of ivermectin has occurred
unchecked for up to seven years. Criticising this position Michael Scott, Chair
of SWCL said: "Clearly SEPA has been under great pressure from the
industry to permit the use of this chemical but the hasty decision to consent
ivermectin represents an abrogation of SEPA's responsibilities."
The UK government's Strategy for Sustainable Development
emphasises the extreme caution needed in the control of chemicals like
ivermectin, highlighting the uncertainties inherent in predicting the effects of
long term, low-level exposure. The Strategy demands a full assessment of the
environmental, health and economic implications, including consideration of
chemical or non-chemical alternatives. The SWCL group does not believe that SEPA
has fulfilled these requirements.
On the consent to release ivermectin, Michael Scott
concludes: "Rather than requiring the industry to reduce its harmful
discharges and operate in a more environmentally responsible manner, SEPA's
decision will put the health of the environment, the livelihoods of others and
even human safety at risk."
According to the Scottish Environment News, Steve
Sankey, head of policy for the RSPB in Scotland said that the RSPB would have
liked the precautionary principle to be applied in a stronger way, and the
chemical not to have been given permission until more research had been done.
The Scottish paper the West Highland Free Press quoted
William Crowe, of the Scottish Salmon Growers Association, who said he was
confident salmon would not contain ivermectin when they went to market, and that
shell fish would have no residue either. He said that even if ivermectin was
applied to the whole of the 70,000 tonnes of salmon produced in Scotland, the
amount of the chemical would be equivalent to two 2kg bags of sugar.
However, the Veterinary Medicines Directorate's
non-statutory surveillance scheme results for the period January-December 1994
show that a total of 41 out of 409 samples of salmon analysed contained residues
of ivermectin in the range 2-30 µg/kg. It was not thought that this represented
a consumer hazard. For the period January-December 1995, 11 samples out of 359
were flagged as above the Action Level. According to SWCL, only one prosecution
has occurred for illegal use of ivermectin.
Toxicity
Ivermectin's use for the treatment of sea lice (Lepeohtheirus
salmonis and Caligus elongata) reflects its toxicity to a range of
marine invertebrates. Ivermectin is administered in the salmon feed. It enters
the marine environment via uneaten food pellets or excreta and is expected to
concentrate mainly in the sediment. Benthic (bottom living) organisms are likely
to be exposed to the highest concentrations of ivermectin. The marine annelid Arenicola
marina is highly sensitive, with lethal effects occurring at levels below
the predicted sedimentary concentration beneath salmon farms. The potential
effects on the function of sediment workers that break down the waste deposits
under salmon cages have serious implications both for the local ecosystem and
the health of the farmed salmon.
Persistence: The research to date has not established the persistence of ivermectin in sediments, although researchers concluded that the half-life is well in excess of 100 days. Persistence is also likely to be affected by the build up of ivermectin as a result of repeated treatments.
Bioaccumulation and environmental fate: Ivermectin can bioaccumulate in the mussel Mytilus edulis 752 fold over six days of exposure, although no adverse effect was reported in this robust species. The Association of Scottish Shellfish Growers say there is a risk that bioaccumulation will exceed danger levels when fat reserves are mobilised in times of poor feeding.
As ivermectin binds to surfaces such as phytoplankton and other particulate matter it is unlikely to be taken up by filter feeders and be biomagnified through the food chain. Alternatively it can enter the food chain through wild fish and other organisms scavenging directly on uneaten salmon feed. There is little data on the chronic effects of ivermectin on aquatic invertebrates, or its fate in the environment.
Conditions of consent
The conditions proposed by SEPA for the use of
ivermectin do not provide adequate safeguards to overcome the lack of knowledge
of the effects of this chemical.
Shellfish exclusion zone
SEPA has recommended a two nautical mile exclusion
zone around shellfish farms, which reinforces the concerns over ivermectin's
potential to affect aquatic life and potentially also human health through
residues in wild fish and shellfish.
SEPA has received letters from shellfish farmers and
fishermen groups expressing extreme concern about the potential ecological
impact of ivermectin, the impact on their livelihood, and consumer confidence in
their food products.
Regulation and enforcement
SEPA states that the use of ivermectin will be subject
to strict conditions. But the inadequate regulation and monitoring of discharges
from Scottish salmon farms has allowed the illegal use of ivermectin to continue
for seven years. SEPA has stated that consent for ivermectin will be reviewed
after two years. However SWCL remains sceptical of the capacity to detect
adverse effects over this period. It also questions the likelihood of withdrawal
of consents once the industry's dependence has been established.
Conclusion
SWCL considers that SEPA has a responsibility to
require stricter environmental standards from the salmon farming industry. In
particular it argues that SEPA must address the growth and intensification of
salmon production of which the sea lice problem is a symptom. The group regards
SEPA's handling of ivermectin as an important test-case for the future
regulation of discharges from fish farms.
* The SWCL marine working group comprises: Marine Conservation Society; Royal Society for the Protection of Birds, Scottish Trust for Underwater Archaeology, Scottish Wildlife Trust, World Wide Fund for Nature Scotland, The appeal is also supported by Friends of the Earth Scotland.
Alison Ross is a consultant to SWCL.
[This
article first appeared in Pesticides News No. 34,
December 1996, page 3]