BANGKOK — Pollution in the Mekong River is putting the rare Irrawaddy dolphin in danger of disappearing from Cambodia and Laos, according to a study by an environmental group released Thursday.
A Cambodian government official, however, rejected the finding and demanded that the group apologize.
The World Wide Fund For Nature Cambodia said it has documented 88 deaths in the past six years of the Irrawaddy dolphin or Orcaella brevirostris along a 118-mile (190-kilometer) stretch of the Mekong River.
The Irrawaddy dolphin, which is related to orcas or killer whales, frequents large rivers, estuaries, and freshwater lagoons in South and Southeast Asia. The population in the Mekong is now believed to include as few as 64 members, the WWF said, down from 80 to 100 just three years ago.
Researchers from WWF Cambodia said they found levels of the pesticide DDT in the bodies of dead dolphin calves from the Mekong that were 10 times higher than in a similar population in India, plus environmental contaminants such as PCBs. They also found mercury, a toxin used in gold mining that can compromise the immune system of marine animals, they said.
The group said it was investigating the source of the pollutants, noting that many young calves died of bacterial diseases that only occur when immune systems are damaged. Many had black and blue lesions on their necks.
"These pollutants are widely distributed in the environment, and so the source of this pollution may involve several countries through which the Mekong River flows," said Verne Dove, the report's author and a veterinarian with WWF Cambodia.
Touch Sieng Tana, chairman of the Cambodian-run Commission for Mekong Dolphin Conservation, dismissed the findings and said there is no mercury, DDT or PCBs in the Mekong. He called on the WWF to apologize for suggesting that the Mekong was polluted.
"If the Mekong River is full of pollution, then all the Cambodians who use that water and drink it would have died," he said. "The WWF statement aims to destroy Cambodia and cause fear to foreigners who want to visit Cambodia."
Scientists do not know exactly how many Irrawaddy dolphins remain in the world _ researchers recently found a population of nearly 6,000 near Bangladesh's mangrove forests _ but the species is listed as "vulnerable" on the IUCN Red List of Threatened Species. The Mekong River subpopulation has been listed as "critically endangered" since 2004.
Brian Smith, an Irrawaddy dolphin expert with the Wildlife Conservation Society, said the findings were surprising given that until now, the biggest threats facing the dolphins have been thought to be fishing, collisions with boats and habitat loss. He cautioned that more research needs to be done to establish a link between the deaths and pollution.
However, he said the extremely low survivorship of calves on the Mekong _ and the fact that many carcasses were found with lesions _ suggests that disease combined with pollutants documented in the WWF study "may indeed be an important factor threatening the population."
Seng Teak, WWF Cambodia's country director, urged Mekong River countries to develop a coordinated program to protect the dolphins that reduces pollutants at their source.
Two years ago, Cambodia launched a $700,000 plan with the World Tourism Organization to reduce threats from fishing by boosting tourism in areas known to have dolphin populations. Authorities have said the program was successful in increasing awareness among villagers and persuading some to abandon fishing for tourism jobs.
Associated Press writer Sopheng Cheang contributed to this report from Phnom Penh, Cambodia.
(This version CORRECTS that study was released Thursday, not Friday)