March 29, 1996
Global Distribution of Organochlorines
Two recent studies show that organochlorine chemicals are
found in measurable concentrations worldwide, even in regions
far removed from sources of pollution. Organochlorines, such
as DDT, PCBs and dioxins, have been linked to a range of
negative health and environmental impacts, including cancer,
birth defects, endocrine disruption and neurological damage,
as well as harm to wildlife.
In a study of the global distribution of 22 potentially
harmful organochlorine compounds, Indiana University
researchers found high concentrations of organochlorines not
only in some developing countries, but also in industrialized
countries where use of many of these compounds is now
restricted. Researchers examined organochlorine residue
concentrations in over 200 tree bark samples from 90 sites
worldwide.
Scientists have long speculated that some organic pollutants
move through the atmosphere from relatively warm regions and
condense at colder, higher latitudes onto vegetation, soil
and bodies of water. This process, also known as the global
distillation effect, could be the reason that high
concentrations of some pollutants are found in the Earth's
Arctic regions. The Indiana University study found that
distribution of relatively volatile organochlorine compounds
such as HCH and lindane demonstrate the global distillation
effect, whereas less volatile organochlorine compounds such
as endosulfan tend to remain in the region of use. However,
as a result of its widespread use, endosulfan was found in
high concentrations in many areas throughout the world.
Low but measurable organochlorine concentrations were found
in tree bark samples from remote regions of the world,
including the Orinoco rain forest in Venezuela and the rain
forests of Ecuador and Belize. Tree bark samples from remote
islands such as the Marshall Islands, Guam, Bermuda and
Tasmania also had low but measurable concentrations of
organochlorine compounds. High concentrations of
organochlorine compounds were measured in tree bark from
Australia, Europe, India, Japan, the Middle East, Russia and
the U.S.
According to the New York Times, a second recent study has
found high levels of organochlorine compounds in black-footed
albatrosses on the Midway islands, a relatively remote atoll
in the North Pacific. Researchers, sponsored by World
Wildlife Fund and the U.S. Environmental Protection Agency,
chose to study Midway because it is considered a pristine
environment. Midway atoll is 3,100 miles from Los Angeles,
2,400 miles from Tokyo and 1,150 miles from Honolulu.
Despite their remote location, albatrosses in the Midway
islands were found to exhibit classic signs of exposure to
organochlorine chemicals, including deformed embryos,
eggshell thinning and a 3% reduction in nest productivity.
Nest productivity measures the rate at which eggs hatch.
Researchers found levels of DDT, PCBs and dioxin-like
compounds in albatross adults, chicks and eggs nearly as
great as levels found in bald eagles from the North American
Great Lakes, according to Dr. James Ludwig, an ecologist on
the research team. Fish-eating birds that nest in the Great
Lakes have suffered embryo deaths and chick deformations such
as crossed bills and club feet due to DDT, PCBs and dioxin-
like compounds in their diet.
Dr. Ludwig states that DDT compounds in Midway albatross eggs
were found at levels just under two parts per million, a
threshold above which further contaminants could cause
adverse population-level effects. Eggshell thinning has been
shown to occur at levels of between two and three parts per
million.
The New York Times reports that contaminants in the birds'
diet probably originate in India, Southeast Asia and Japan.
Dr. Ludwig states that a large DDT plume is being carried by
ocean currents from the coast of Southeast Asia to the north-
central Pacific. He emphasized that this is fresh DDT,
possibly from DDT currently used in mosquito and crop pest
control in Southeast Asia.
Source: Staci. L. Simonich and Ronald A. Hites, "Global
Distribution of Persistent Organochlorine Compounds,"
Science, September 29, 1995; Les Line, "Old Nemesis, DDT,
Reaches Remote Midway Albatrosses," New York Times, March 3,
1996.
Contact: PANNA.
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