快猫短视频

THE Inuit people of northern Canada have a use for almost every part of the
hundreds of beluga and narwhal whales that they catch every year in the seas and
estuaries of the Arctic. Perhaps their favourite bit is muktuk, the skin and
surface fat, which is eaten fried or raw. This traditional diet provides the
Inuit whalers, their families and neighbours with ample supplies of protein and
the fatty acids that prevent heart disease. But it鈥檚 not as healthy as it once
was. In recent years every slice of muktuk has come dosed with toxic additives:
polychlorinated biphenyls (PCBs) concentrated in the blubber, and mercury in the
skin.

鈥淓at about 10 grams of muktuk鈥攖hat鈥檚 a piece the size of a sugar
cube鈥攁nd you鈥檝e had the maximum weekly intake of PCBs as recommended by
the Canadian health authorities. But many people here regularly eat a hundred
times that,鈥� says Norm Snow, a biologist from England. Snow is head of the Game
Council in Inuvik, a whaling community of 3000 people near the mouth of the
Mackenzie River.

Another local gourmet dish is the livers of ringed seals. Rich in vitamin A,
they also contain mercury at levels from 20 to 200 times health guidelines, as
well as large amounts of cadmium. Caribou kidneys contain cadmium, seal blubber
packs a punch with dioxins and hexachlorocyclohexanes (HCHs), and many lake fish
are tainted with the insecticide toxaphene.

Blown in from the tropics

These chemicals are some of the most poisonous substances on the planet and
many of them have been banned in Canada for two decades. The Arctic coast of
Canada has neither polluting chemicals factories nor pesticide-happy farmers. So
where have the poisons come from? The source is many thousands of kilometres to
the south, says Snow. They have invaded the waters and ecosystems of the high
Arctic by long-distance transport in the air through a process called 鈥済lobal
distillation鈥�. They evaporate from soils as far away as the tropics, ride the
winds north, then condense out in the cold air of the Arctic as toxic snow and
rain.

Using computer models of the atmosphere, Frank Wania of the University of
Toronto has studied the mechanisms that bring these heavy metals and persistent
organic pollutants (POPs) to the Arctic. There is, he says a 鈥渟ystematic
transfer of these chemicals from warmer to colder areas鈥�. The region鈥檚
environment attracts and holds volatile compounds that travel on the winds and
condense out at temperatures between freezing point and 鈥�50 掳C. These
include some PCBs鈥攐ily synthetic compounds once used widely as insulators
in electrical equipment鈥擧CHs, toxaphene, and other pesticides such as
chlordane. DDT and some similar compounds tend to condense out at warmer
temperatures in mid-latitudes, and are not concentrated in the Arctic in the
same way as PCBs and HCHs. Other POPs, such as naphthalene, are too volatile to
condense anywhere, even at the poles.

Spring鈥檚 toxic flush

Contaminants released in the tropics can reach the Arctic surprisingly fast.
鈥淗ighly volatile chemicals can get from India, say, to the Arctic in five days,鈥�
says Wania. Others may take their time, falling to the ground and re-evaporating
many times before completing their northward journey. Less volatile compounds
often arrive bound to aerosol particles, and even within snowflakes. If so, says
Dennis Gregor of the Center for Groundwater Research at the University of
Waterloo in Ontario, they can produce a 鈥渇lush鈥� of toxins in rivers when the
snows melt in early summer, just when biological activity is most intense.

A striking display of this global distillation is Wania鈥檚 plot of alpha-HCH
concentrations recorded in seawater in the western Pacific
(
see Diagram p 27).
Although the tropics are the major source of this chemical, the concentration
there is fairly small. But at higher latitude the concentration rises, and in
the Canadian north it reaches a hundred times the tropical level. Wania believes
the distillation process is temperature-specific enough to perform a crude
fractionation. In effect, the Earth鈥檚 atmosphere functions like a giant oil
refinery, separating out different compounds at different latitudes, according
to the temperatures at which they condense.

Those compounds that reach the high Arctic tend to be concentrated most
because these coldest regions occupy only a very small fraction of the Earth鈥檚
surface. And once they have arrived, natural decomposition happens much more
slowly in Arctic conditions. Often, the primary breakdown mechanism for POPs is
through oxidation by the highly reactive hydroxyl radical in the atmosphere.
But, says Wania, hydroxyl is scarce in the Arctic air because solar radiation is
needed to produce it. As a result, 鈥渃hemicals that might survive for only a few
days in the tropics before being destroyed, will last for a year or more in the
Arctic air鈥�.

This silent invasion of the Inuit world forms a central element of an
800-page report, State of the Arctic Environment, to be unveiled next
week at an international science symposium on Arctic environmental pollution in
Troms, northern Norway. It was written by environmental scientists from eight
Arctic nations who made up the Arctic Monitoring and Assessment Programme, which
was launched by ministers from the Arctic nations in 1991. The report will call
for action to halt the spread of heavy metals and POPs such as PCBs and
pesticides鈥攄emands that will be discussed by Arctic ministers in nearby
Alta later in the month.

The scientific detective story that led to those calls began with Eric
Dewailly of Laval University in Quebec City, who stumbled on the Arctic poisons
by chance. 鈥淚 was researching PCBs in the breast milk of mothers in southern
Quebec in the mid-1980s,鈥� he explains. 鈥淲e wanted to find some pristine milk as
a control and persuaded some Inuit mothers to provide some samples. The data
that came back from the lab shocked us.鈥� These mothers had five times the
quantity of PCBs in their milk compared to women further south. Later studies
also found high levels of toxaphene and chlordane in their milk.

Around the same time, Harriet Kuhnlein of McGill University in Montreal was
studying children in a tiny Inuit whaling community on Broughton Island in
northeastern Canada, and discovered that almost two-thirds had blood-PCB levels
above health guidelines. Blubber from the tusked narwhal whales in Baffin Bay
was the main source. 鈥淭he more traditional their way of life the more
contamination they had,鈥� says Dewailly.

Such findings triggered a six-year CAN$25 million (拢11 million)
research programme on northern contaminants, which ended in March this year. It
has uncovered a similar story across the rest of the Canadian north. The latest
evidence comes from a study organised in 1995 by the government of the North
West Territories (NWT). Samples of blood taken from Inuit women from the
Kitikmeot region of the NWT and their babies鈥� umbilical cords during childbirth
revealed that 39 per cent exceeded the Canadian guideline limit for PCBs of 5
parts per million (ppm).

In northern Quebec and Labrador, 75 per cent of women exceed this limit, says
Dewailly. And in Greenland, where Dewailly says 鈥渢hey eat more narwhal and
beluga than anywhere else鈥�, the figure is 95 per cent. Older people have the
highest accumulations. Men are worse affected than women because lactation
drains some of the poison from nursing mothers鈥攁lbeit at the cost of
passing it on to their children.

Health researchers agree that regular toxic tuck-ins are the reason why a
majority of Inuit adults in northern Canada and Greenland often have
concentrations of PCBs, toxaphene and chlordane that are many times higher than
safety levels set by Canadian health authorities. But there has been little
research into the effects of these chemicals on the people who consume them.
This, says Walker, is partly because the Inuit have grown hostile to researchers
from the south taking samples of their body fluids, asking questions and
disappearing.

Dewailly, who is pioneering better relations between the Inuit and southern
scientists, adds that the small numbers of people in the Inuit communities make
epidemiological studies very hard. But he is about to start the first such
study, modelled on a pioneering investigation in the Lake Michigan region by
Sandra and Joseph Jacobson of Wayne State University in Detroit. The Jacobsons
tracked children born to women who ate contaminated fish from the lake, and last
September they reported that 11-year-olds who had been exposed to PCBs when they
were in the womb had a lower IQ, poor memory, shortened attention span and
difficulties learning to read.

In the Arctic, more is known about the effects of contamination on animals
than on humans. A recent Greenpeace report on Arctic poisons devoted seven pages
to wildlife and one to humans鈥攁nd put a polar bear on the cover. In fact,
polar bears occupy a similar position in the Arctic ecosystem to humans, eating
seals and whales, supplemented by fish and some land mammals. According to
Dewailly, their contamination with PCBs shows a rising trend from southwest to
northeast, with the lowest concentrations in Alaska and the highest in eastern
Greenland and the islands of Svalbard, north of Norway. Old male bears on
Svalbard have up to 90 ppm of PCBs in their body fat.

Where the chemicals go

Despite the growing scale of long-range contamination of the Arctic, tracking
it remains a low research priority, even among Arctic nations. 鈥淭here is only a
handful of us looking at this,鈥� says Terry Bidleman of the government agency
Environment Canada. And what they look for, he admits, is rather hit and miss.
However, there is some good news. Developed countries are manufacturing much
less of many POPs than they used to. Manufacture of PCBs has been banned in
North America since 1980. Some of the most harmful substances are being phased
out in the tropics, too. While DDT continues to be deployed in the battle
against malaria, it is used much less than it was. Manufacture of toxaphene,
once the pesticide of choice for the world鈥檚 cotton fields, with over a million
tonnes a year used in the southern states of the US alone, has now ceased
worldwide. And chlordane, widely used in the US until the late 1980s to control
termites, is now banned because of its carcinogenic and neurotoxic
properties.

But, even as concentrations of these chemicals are falling in the regions
where they are made and used, levels in the Arctic 鈥渟ink鈥� may continue to rise
for several decades. Residues left behind in the soils of the source regions
gradually evaporate and move north. Derek Muir of the Freshwater Institute
points out that there has been no reduction in concentrations of DDT and PCBs in
Arctic waters, whales or seals. He reported in 1995 that lake sediments in
southern Canada had peak PCB concentrations in layers deposited in the 1960s and
1970s, when national PCB use was high. In the high Arctic, by contrast,
concentrations are continuing to rise today.

The story of HCHs is more complicated. There are three forms, or isomers, of
this widely used pesticide: alpha, beta and gamma. The crude manufactured form,
known as technical HCH, contains all three. But modern manufacturers make a
mixture, called lindane, that is predominantly gamma-HCH. The fingerprint of the
changeover can be seen in the Arctic, says Bidleman. Unlike PCBs, which linger
in the environment long after their production has ceased, alpha-HCH
concentrations in Arctic waters fell after China switched to making lindane in
1983, and again in the early 1990s when Russia banned technical HCH and India
stopped spraying it on food crops. However, gamma-HCH is reaching the Arctic at
record rates.

Faced with this continuing toxic fallout, the Inuit have a fundamental
problem. Should they eat their traditional foods or not? Their leaders are
extremely sensitive to any suggestion that food from the land or sea might be
unsafe. 鈥淚 want to reassure people that traditional food is still preferable to
store food,鈥� says Nellie Cournoyea, a former NWT premier and health minister,
now back home in Inuvik.

Jody Walker, of the NWT government鈥檚 health department, says that the
benefits are cultural as well as nutritional. Most Inuit today have forsaken
igloos for village settlements with clinics, schools, stores and airstrips. But
hunting remains an essential part of life. 鈥淧eople here can鈥檛 just replace
country food with store food,鈥� says Bill Carpenter of the M茅tis nation in
the NWT. 鈥淚n the far north, we estimate it would cost families $10 000 a
year to live on store food, and they would eat much less well.鈥� Walker鈥檚 boss,
NWT鈥檚 deputy minister of health Dave Ramsden, says: 鈥淚f we start a stampede away
from eating beluga or caribou we will have lost the people鈥檚 culture.鈥�

Government warning

But such sentiments leave officials open to the charge that they are
downplaying evidence of dangerous poisons. When in 1995 two out of every five
mothers in Kitikmeot were found to have worrying PCB levels in their blood, the
federal government issued a statement advising that, to protect fetuses, 鈥渨omen
of child-bearing age eat less contaminated tissues鈥濃�攆or instance caribou
meat, which is low in fat-soluble POPs. But in the NWT capital, Yellowknife,
Walker continued to distribute a leaflet extolling the nutritional benefits of
PCB-rich muktuk and blubber without mentioning the contaminant risks. 鈥淪erve
beluga muktuk with rice, vegetables and a glass of milk for a healthy meal,鈥� it
suggests. I asked Julia Ogina, a health official in the 300-strong community of
Holman on Victoria Island, what advice she gives to mothers worried about
poisoning their babies by eating blubber during pregnancy. 鈥淚鈥檇 say you are
catering for two. You should eat more,鈥� she replied.

Walker stresses that 鈥渇or the general population, the benefits of continuing
to eat a traditional diet far outweigh the small known risks鈥�. Russel Shearer,
head of the contaminants programme at the federal Department of Indian Affairs
and Northern Development in Ottawa, agrees. But he warns that 鈥渢here could be a
lot more to these risks than we know now, including perhaps the cumulative
effects of different toxins. Things may look different in ten years鈥� time.鈥�

Long before then Shearer hopes that tough international action will have
stopped the poisoning of the Arctic. According to David Stone, chairman of the
scientists writing the State of the Arctic Environment report, 鈥淎rctic
contamination is now driving international negotiations to toughen controls on
POPs and heavy metals鈥�. The negotiations are well under way.

But whatever happens, many more poisons are undoubtedly already on their way
north. An estimated million tonnes of PCBs alone have been released into the
environment in the past 60 years says Bideleman, 鈥渆ven if all further emissions
stopped tomorrow, we have no idea how long it would be before things start to
improve in the Arctic. Global distillation can continue for decades after you
turn off the tap.鈥�