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.

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