Organophosphates, a class of chemicals that includes weapons such as sarin and agricultural pesticides, could pose a unique risk to marine mammals, according to a study in the August 10 issue of Science. Ocean-dwelling animals that trace their ancestry to various land mammals independently acquired mutations in the gene PON1 that render it useless in breaking down the chemicals, researchers found.

“Marine mammals may be at a great disadvantage in the Anthropocene if run-off of this agricultural product [organophosphates] into the marine environment continues,” the study authors write in their paper.

The researchers came upon PON1 while looking for common genetic changes associated with the transition from land to sea. Such an evolution has occurred at least three times, giving rise to today’s whales and dolphins; manatees and dugongs; and walruses and sea lions. Among other adaptations among all the marine...

Meanwhile, all known land animals have held on to PON1, which also turns out to help in breaking down organophosphates. When the researchers tested how organophosphates fared when added to blood samples from different mammals, they found that the chemicals broke down much more quickly in samples from land animals than in those from marine mammals or beavers. 

“People have the impression that mammals are only susceptible to these pesticides at high levels, but marine mammals might be susceptible at low levels,” study coauthor Wynn Meyer of the University of Pittsburgh tells The Atlantic. “We need data on how much these compounds are getting into the environment and accumulating in the animals.” 

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two manatees at the ocean floor

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