I was recently asked by an old friend of mine whether I knew anything about the potential hazards of something I had never heard of called galaxolide. This, I quickly learned, is not an electrolyte replacement drink for sport-conscious extra-terrestrials. Galaxolide, it turns out, is a major player in the fragrance industry, one of a group of synthetic chemicals known generically as artificial musk. And it has a lot of environmental scientists worried.
To understand synthetic musk, it's probably best to start with the real thing. Natural musks are intensely aromatic biochemicals produced by a fairly short list of animals along with a few plant wannabes. At the top of that list, and the father of all musks, is that of the male musk deer. Musk deer include multiple species, but are limited in the wild to various areas of Asia, including mountainous regions ranging from China to the Hindu-Kush.
For millennia, musk has been valued as a key fragrance component in perfumes and in traditional medicinal agents. This has been good for purveyors of pricey potions, but bad for the Mr. Deer, given that the preferred method to obtain the musk organ (situated neatly next to the male deer's private parts) has been to slaughter its owner. Moreover, modernization not only increased the demand for musk but also the efficiency of killing its bearer, endangering the survival of the musk deer. Although various other animals have been found to produce musk as well (hint: muskrat; musk-shrew, and the big-boy, the musk-ox), none has been as valued as that of the deer.
Enter synthetic musk. Much like the early manmade dyestuffs, the first generation of synthetic musk chemicals was inadequate to the task and has been replaced by chemically more sophisticated creations. Indeed, as with the advanced dye chemicals on the 19th century, these synthetic musk chemicals have multi-ring structures, generically classified as polycyclic hydrocarbons. That is the first thing that starts to put environmental scientists on edge, since polycyclic chemicals (especially ones incorporating a benzene ring as galaxolide does) have a long track record of raising biological havoc. The chemical polycyclic dyes, for example, were shown more than 100 years ago to cause cancer of the bladder.
Galaxolide, however, raises questions that go beyond such generic considerations. The friend that asked me about it had a professional interest. His research career has been based on several decades studying bad breath, but he has recently segued into body odors (http://www.tau.ac.il/~melros/welcome.html). To try to get down to specifics in addressing his query, the first thing that I did was to check the public database of the U.S. National Institutes of Health, PubMed (http://www.ncbi.nlm.nih.gov/pubmed/).
Even after a cursory review of the updated medical-scientific literature on the subject, it becomes abundantly clear that galaxolide does indeed give cause for concern. First of all, it is nearly ubiquitous, not only detectable in water supplies in a number of locations sampled, but also being the most abundant synthetic musk chemical among those analyzed. Moreover, not only is galaxolide persistent in the environment, it also appears to bio-accumulate in some species, its concentration increasing up the food chain. This is a particularly nasty attribute to have in a pollutant, for example, being one of the hallmarks of DDT. We are not just talking about fish, here. Galaxolide is detectable in humans and in at least one study has been shown to correlate with fragrance and cosmetic use (don't bother to look for it on labels, though). Unfortunately, this can be said of a number of modern synthetic chemicals: common, persistent, and detectable in people.
Galaxolide has one other key attribute, though. In specialized biological testing of the sort not required prior to the widespread commercial release of consumer products, this synthetic musk displays the potential to interfere with estrogen hormonal function. Of course, maybe this shouldn't be surprising of a chemical mimic of a substance that naturally plays a role in the mating practices of certain mammals (biologists are still not exactly sure of the details when it comes to the musk deer). A classmate of mine from college had a hunting-critical bumper-sticker on his truck that read, "Arm the Deer." Maybe nature did.