Scientists identify key vectors of toxicity in marine mammals

A gray whale that strayed into Tokyo Bay during the Golden Week holiday period early last month found its sudden fame cut short when it was strangled by a fixed shore net.

The whale, which was only 1 or 2 years old, was on its way to the Arctic Ocean to join other whales who head there at that time of the year for the rich feeding grounds. However, it might not have fared better if it had reached the Arctic Ocean, as the ocean is becoming increasingly polluted with toxic chemicals.

Marine biologists are finding high concentrations of DDT, polychlorinated biphenyls (PCBs) and dioxins in the carcasses of whales, seals and polar bears.

These chemicals affect the immunity and reproductive powers of these creatures to the extent of threatening the continuity of some species, experts warn.

Prof. Shinsuke Tanabe of Ehime University's Center for Marine Environmental Studies says agrochemicals, which are used widely across developing countries in Asia, are mainly to blame for the pollution of the Arctic Ocean.

Many of the agrochemicals banned in developed countries are still legal in developing countries. They are highly volatile and about 90 percent of chemicals used on agricultural land end up in the air, Tanabe said.

In a landmark study, Tanabe identified four key methods by which sea mammals become affected by toxic materials.

In the first, toxic chemicals that have dissolved in cold water become vaporous once the temperature rises and return to a liquid state when the temperature falls. Alternating their physical states in this way, the toxins travel 10,000 kilometers from South Asia to the Arctic Circle and end up in the food chain.

Once ingested, the chemicals become trapped in the thick layers of fatty tissues in sea mammals such as dolphins and whales.

In the third method, chemicals are transmitted from mother to child during breast-feeding.

Last, sea mammals, unlike land mammals, lack mechanisms to break down enzymes.

Tanabe's discovery of these four vectors has been hailed by experts around the world. In the United States, his thesis on the discovery was named one of the 10 most frequently quoted academic papers about environmental studies and ecology last year.

At home, he was awarded by the Japan Society for Environmental Chemistry last year.

Tanabe's study was reflected in the 2001 Stockholm Convention on Persistent Organic Pollutants.

Tanabe said the key to success in his study was field work and team work.

A sea mammal found in the Arctic Ocean, for instance, would be dissected by up to 50 laboratory technicians, who would make detailed measurements and could detect even minute traces of toxins.

The results were then analyzed by experts in such fields such as ecology, environmental studies and toxicology.

Tanabe's laboratory contains 400,000 samples kept in freezers of sea mammals from all over the world, making him the envy of his peers, many of whom propose joint studies with him.

But as much as he is successful, the noted environmental researcher said he felt sad as the high demand for him and his studies reflected the seriousness of environmental pollution.

In addition to traveling to the Arctic Circle, Tanabe pointed out that toxic chemicals used in developing countries in other parts of Asia are also polluting the Sea of Japan, raising the density of DDT to a high level.

Tanabe said part of his strategy for cleaning up the Arctic Ocean and the Sea of Japan is to educate students from developing countries so that when they return home, they will share their knowledge on the safe way of handling agrochemicals.

Commenting on the need to clean up the world, Tanabe pointed out that while the European Union is to implement new regulation governing toxic materials in products in July 2006, the Japanese governments and corporations--as usual--are content to follow the lead of Europe and the United States and conform to their environmental standards rather than formulate their own.

When it comes to the environment, Japan has fine academics such as Tanabe, but the country never steps up to assume a leadership role as the government lacks an overall strategy for preventing pollution.

That reminds me, sadly, of the strayed whale that lost its way. I can only hope this country will not end up following that whale's sad fate.

Asaba is a senior writer of The Yomiuri Shimbun.

Source: www.yomiuri.co.jp