for National Geographic News
The planet's last river-dwelling finless porpoises are dying in part due to exposure to insecticides and mercury in China, a new study says.
The mammals had already been declining as their natural habitat in and around the Yangtze River deteriorated.
In the new research, scientists also found high concentrations of polychlorinated biphenyls (PCBs) and other pollutants in the organs of porpoises found in central China's Dongting Hu Lake, which is connected to the Yangtze. (See China map.)
However the researchers haven't yet established medically the toxicity level that will kill a porpoise.
"In recent decades the [Yangtze finless porpoise] population decreased sharply each year by approximately 7.3 percent because of human activities on the river, including fishing, pollution, transportation, and dam construction," said study co-author Wang Ding of China's Institute of Hydrobiology.
A recent census turned up just 1,800 porpoises, and Wang warned that "the Yangtze finless porpoise will become extinct within 24 to 94 years if no protective measures are taken."
The baiji, a Chinese freshwater dolphin that also lived in the Yangtze, was declared extinct in December 2007.
Wang and colleagues from the Chinese Academy of Sciences started examining porpoise tissue and organ samples after the animal was declared an endangered species by the World Conservation Union in 1996.
Some contaminants found in tissue samples, such as PCBs, likely originated from industrial wastewater and agricultural pesticides and herbicides, according to Beat Mueller, a geochemist at the Swiss Federal Institute of Aquatic Science and Technology who has tested the waterway.
Wang said that some of the toxic substances were also found in water samples taken in "heavily polluted areas near the sewerage outfalls of a medicine factory and a paper mill around the lake."
Local agriculture and industry, including paper mills and oil refineries, have increased dramatically in the region in the past few decades, Wang said.
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