PESTICIDES that are rapidly replacing hazardous organophosphates in sheep
dips across Britain are decimating invertebrates in rivers, say government
ecologists.
Up to a half of all sheep farmers in Britain are thought to have switched to
dipping their animals in synthetic pyrethroids in the past two years. This has
followed growing fears about the health effects on farm workers of exposure to
organophosphates, also known as OPs.
鈥淧yrethroids are undoubtedly safer for farmers than the conventional OPs, but
we estimate they are at least a hundred times more toxic in the aquatic
environment than OPs, especially to invertebrates,鈥� says Donny Morrison of the
Scottish Environmental Protection Agency (SEPA).
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Synthetic pyrethroids are chemically similar to the toxin pyrethrum, which is
found in the flowers of a species of African chrysanthemum. They were first
manufactured in the 1970s to protect crops from aphids, and act against insects鈥�
nervous systems. Unlike conventional pesticides, they do not persist in the
environment and are largely nontoxic to mammals.
Farmers dip sheep in tanks of pesticides to prevent sheep scab, caused by
skin mites, and to protect the wool against lice and ticks. Because pyrethroids
pose little threat to people, says Morrison, farmers get the impression that
they are safe. 鈥淭hey have become careless about disposing of the dip.鈥�
Roger Cook, director of the National Office for Animal Health, a veterinary
drugs industry group, agrees that the pesticides must be disposed of carefully:
鈥淩ight from the start, pyrethroids have always been seen as particularly
hazardous to the aquatic environment.鈥�
In rivers, pyrethroids are stealthy killers. Because they degrade within a
few days, they leave little behind鈥攁part from a distinctive pattern of
invertebrate death.
Neither the SEPA nor the Environment Agency, which covers England and Wales,
has collated data on the number of cases of pyrethroid pollution. But the
problem is clearly escalating. 鈥淲e have probably had as many cases of pollution
from sheep dip in the past year as in the previous 10 years,鈥� says Morrison.
鈥淧robably we are missing many incidents,鈥� adds Ray Prigg, a senior ecologist
with the Environment Agency鈥檚 northwest region. 鈥淢ost cases only kill
invertebrates, and by and large the public only notice and report pollution when
they see dead fish in a river.鈥�
鈥淭he problem first came seriously to our attention in April 1996,鈥� says
Prigg. 鈥淲e found that virtually all the invertebrate fauna, especially mayflies,
stoneflies and freshwater shrimps, had disappeared from 30 kilometres of the
river Caldew near Carlisle.鈥�
Prigg鈥檚 staff only recognised the likely cause of the die-offs after hearing
at a conference about Scotland鈥檚 problems with pyrethroids. Further incidents of
pollution followed last summer.
快猫短视频s were initially surprised that pyrethroids, which have been used in
Britain for two decades, had suddenly become a killer. One possible reason is
the growing use of a pyrethroid called cypermethrin, which both the SEPA and the
Environment Agency believe is more toxic. But the adoption of pyrethroids by
sheep farmers seems to be the most likely cause. 鈥淚t seems that only with their
use as sheep dip have pyrethroids begun to reach the aquatic environment,鈥� says
Prigg.
Government guidance allows farmers to pour waste dip into holes or onto
fields where it will biodegrade. The latter is adequate for OPs. But Prigg says
that pyrethroids are so toxic that 鈥渋f dipped sheep drip while grazing near
streams, that can provide the few nanograms of pesticide per litre of water
required to kill freshwater shrimps鈥�.
The pollution incidents have brought fresh demands from the SEPA and the
Environment Agency for the government to tighten rules on sheep dipping. Two
years ago, the National Rivers Authority, the Environment Agency鈥檚 predecessor,
called for a ban on pouring waste dip into holes in the ground and for new rules
to keep sheep dipping away from rivers.
But 快猫短视频 has learned that plans drawn up by the Scotland
and Northern Ireland Forum for Environmental Research, a coordinating group for
government agencies, to commission research into treating dip waste to make it
more environmentally friendly have recently been dropped because no funds could
be found.
