'Pollutants' in whale blubber are naturally produced
Sea creatures make chemicals similar to those spewed out by human factories.
Noxious chemicals found in whale blubber may not be entirely artificial, research shows. Some of the compounds, which resemble the environmentally polluting chemicals we create as flame retardants, may be produced by sponges and other sea creatures.
Scientists have known for years that certain artificial chemicals in the environment can accumulate in animals, especially in predators that eat other contaminated animals. Such tenacious molecules, called halogenated organic compounds, include the toxic pesticide DDT.
Recently, a group of similar compounds was identified in marine animals, but its source was not known. Were these methoxylated polybrominated diphenyl ethers (MeO-PBDEs) the natural products of slow, soft marine creatures, such as sponges? One sponge in the Indian Ocean had been shown to produce a MeO-PBDE, perhaps to deter predators or parasites.
Or were they derived from discarded flame retardants, slightly altered by some biological process on the way? Unaltered flame-retardant molecules have been found in animal and fish tissues, including human breast milk.
Chris Reddy, of the Woods Hole Oceanographic Institution in Massachusetts, sought to answer this question by looking at the different isotopes of carbon in the molecules. MeO-PBDE that had been produced by plants or animals would contain a consistent percentage of radioactive carbon-14, which is present at low levels throughout the ocean.
If, on the other hand, the MeO-PBDE were artificial, it would have been made out of carbons from petroleum that was so old that all the carbon-14 would long since have decayed. "We call it a 'dead or alive' approach," says Reddy.
The idea was simple, but the task was anything but. Reddy's colleague Emma Teuten spent months working with a smelly 10-kilogram sample of blubber from a fatally beached True's beaked whale (Mesoplodon mirus). "I cut the skin off, and diced it and blended it, which gave something the consistency of a strawberry smoothie," she recalls. Then she burned off the fat with acid and isolated small amounts of MeO-PBDEs from it.
Carbon-14 was present in levels consistent with the surrounding ocean, the researchers report in Science1. This suggests that the MeO-PBDE was a natural creation, and Reddy's team suggests that it accumulated in the whale after it ate some unknown creature, perhaps a squid, that had in turn gobbled up the organic creator of the chemicals.
The researchers' sample size is admittedly small: just one whale, which was probably ill. But marine-mammal toxicologist Paul Ross, of Canada's Institute of Ocean Sciences in Sidney, British Columbia, is impressed. "It seems quite clear," he says.
Reddy says there are larger implications. "We can start to think about how humans and animals and plants have evolved over millions of years. We've only manufactured these compounds since the 1930s. The way we respond to these compounds might have been programmed over many generations." It might explain, he suggests, why some enzymes in the natural world can break down these kinds of molecules.
But the producers of flame retardants and other nasty chemicals are by no means off the hook. Although it is not clear whether MeO-PBDEs are toxic, many similar compounds are dangerous. "We might be adding to an already very complicated soup of chemicals with our own chemicals," says Ross. In the whale that was studied, the compounds of interest were less abundant than their nastier artificial cousins.
- Teuten E., Xu L. & Reddy C. Science 307, 917 (2005).