In an article in Environmental Science and Technology, Rebecca Renner reports on accumulating evidence that perflourinated chemicals--widely used in many consumer and industrial products--may represent a serious environmental threat to wildlife and people.
Most troubling:
- exposure to PFOS (perfluoro-octane sulfonate) is ubiquitous, found in human and wildlife tissues around the world.
- PFOS
is remarkably persistent. For example, PFOS does not show the
slightest sign of degradation when boiled in nitric
acid for an hour. - PFOS is known to be toxic in laboratory animals (rats, mice, monkeys) at levels close to the range already found in animals and people in the real world.
The sense one gets in reading this article and related materials about PFOS is that this is a repeat of a story told all too often in the age of synthetic chemicals. Without adequate testing, we assumed that a chemical was safe and let it go into global production. Now four decades later, only after PFOS has been allowed to contaminate a significant percentage of living organisms around the world, we're starting to get a sense almost by accident that it represents a real danger.
The best known use of PFOS is in the fabric protector, Scotchgard. Its manufacturer, 3M, announced in May 2000 that it was withdrawing Scotchgard and related products from the market because of preliminary indications of both persistence and toxicity.
PFOS is just one of a family of related perflourinated compounds, in which the normal carbon-hydrogen bonds of organic chemicals are replaced with carbon-flourine bonds. As a class, these compounds are highly resistant to degradation and poorly known toxicologically. The astounding persistence of perflourinated compounds is due to the strength of the carbon-flourine bond. Thermodynamically, the C-F bond is one of the strongest known in chemistry.
An important distinction between PFOS and its relatives compared to other persistent organic pollutants is that perfluorinated compounds don't accumulate in fat but instead in the liver the gall blader. This may be one reason why toxicologists missed finding pervasive PFOS contamination for so long: they didn't expect bioaccumulation outside of fatty tissue. PFOS doesn't accumulate in fat because it is lipophobic... indeed one of the principal uses of PFOS, in Scotchgard, is specifically because PFOS repels fat and grease. That's one reason why it works as a fabric protector.
PFOS and related chemicals are not endocrine disrupters in the traditional sense of binding with hormone receptors or affecting synthesis or metabolism of hormones, at least as far as current understanding indicates [not all appropriate testing has been undertaken]. Instead, in a fashion analogous to the way that a hormone disruptors bind with hormone receptors, PFOS binds with certain blood proteins. Quoting a scientist, biochemist Brad Upham from Michigan State University, Renner writes:
| "Compounds like PFOS are chemically inert, and since they don't react with DNA, the accepted assumption is that they aren't toxic," he says. But their structures fit like keys into some of the body's natural locks that control a variety of processes." |
This mechanism of action reinforces the argument that many if not all of the body's natural chemical systems for communication are vulnerable to disruption by contaminants [More...]