Friday, December 08, 2006

Antimicrobials: Too Much of a Good Thing?

What do my husband’s armpits, my son’s sandals, my mother’s steak knives and my daughter’s hairbrush all have in common? Antibacterials. They are all impregnated with antibacterial chemicals – well maybe not the armpits, but the underarm deodorant. These days, just about anywhere that is suitable for bacteria is apparently also suitable for antibacterial treatment by manufacturers wishing to attract health-conscious shoppers.

But here’s the rub – antibacterial chemicals are now showing up in the environment – in places they were never meant to be. In water flowing into rivers downstream from sewage treatment plants, in fish, and in treated sewage sludge that is applied to agricultural crops.

Additionally, while it’s clear that the use of antibacterials are beneficial in clinical settings, according to a Food and Drug Administration panel on Nonprescription Drugs there is little or no indication that such additives protect the consumer any better than washing with plain soap and water.

As a one-time teacher of microbiology, I’d always prided myself on having the foresight to stay away from purchasing soap products with antimicrobials. Although to my surprise, there they were in other household I’d purchased including the Teva sandals and the Old Spice Classic with triclosan that I’d bought for my husband.

“[The antibacterials] triclocarban (and triclosan) were introduced in the hay-days of chlorine chemistry, when chemicals like DDT and PCBs were considered safe. Relative to the latter, the antimicrobials are less problematic, but now that PCBs and DDT are banned, the focus has shifted to other chlorinated chemicals like triclocarban and triclosan,” says Dr. Rolf Halden, of Johns Hopkins University.

Recently, Dr. Halden’s group reported in the journal Environmental Science and Technology that the majority of triclocarban that is washed down the drain and into sewage treatment plants ends up in sewage sludge, which in turn may end up on agricultural fields.

His research reveals not only the persistent nature of the chemical (not unlike those other chlorinated chemicals now banned.) It also highlights the high volumes of these chemicals that are used by consumers and released into the environment. Halden’s group estimated that in their study area alone, more than one ton of triclocarban ends up in the environment (and on agricultural land – where it can be taken up by crops) each year!

While Halden is concerned about the release of the chemicals into the environment, Dr. Stuart Levy, the director of the Center for Adaptation Genetics and Drug Resistance at Tufts University, is concerned about the potential for antimicrobials to encourage development of antibiotic or drug resistant microbes.

Development of antibiotic resistance is an important survival mechanism for microbes, and soil microbes in particular. Soil is packed with microbes. They are part of what makes healthy soil healthy. Soil is also a fertile hunting ground for new antibiotics. In fact the first mass-produced antibiotic, penicillin was produced by a soil-dwelling microbe. What better way to stake one’s microscopic claim then to poison one’s neighbors? So soil microbes are constantly battling antibiotics produced by neighboring soil microbes. And in order to “keep up with the Jones’” or at the very least survive the Jones’ constant assaults, bacteria have become adept at developing antibiotic resistance.

The same can be said for the millions of bacteria that live on and in our bodies. When they are constantly exposed to antibiotics, it is possible that some will overcome, and develop antibiotic resistance. This is where the antimicrobials come in.

“We produced the original evidence that triclosan [a chemical simlar in structure to triclocarban] can lead to antibiotic resistance,” said Dr. Levy, “but while resistance to antibacterials has been found among bacteria outside the laboratory, they have not been linked to the use of triclosan.”

“Triclocarban is another antibacterial found in soaps. No one has looked at its mechanisms of action. There is clearly concern about the exposure to both of these antibacterials [causing antibiotic resistance], but in particular triclosan. The other antibacterials of concern are those under the heading of quaternary ammonium compounds like benzalkonium chloride. More and more data are linking resistance to this product with antibiotic resistance.”

So, antibacterials which have the potential to cause antibiotic resistance are released into the environment in huge quantities as a result of consumer use, and an FDA panel has concluded that antimicrobial products appear to be no more protective to consumers than soap and water. Who’s in charge of regulating this stuff?

Antimicrobials are regulated by both the FDA and the Environmental Protection Agency, depending upon their use, and claims made by manufacturers. EPA regulates antimicrobials when they are used as pesticides, for example to reduce odors in my son’s stinky Tevas, but FDA regulates them as drugs when used in something like the bottle of soft-soap that graces the bathroom sink at my daughter’s school. In either case – since triclosan and triclocarban were developed and registered at least thirty years ago, back when persistent chemicals weren’t known to be a problem, and antibiotic resistance hadn’t reared its ugly head – one wonders how today’s research has enlightened the regulators.

“Advances in a number of fields have changed the way we examine and interpret the potential risk of synthetic chemicals,” says Halden. “Many studies conducted in the 1970’s would not pass muster today.”

But there’s hope, according to Stuart Levy, who noted that while “there is no evidence of a change in regulation, there certainly seems to be a greater insight and concern by regulatory agencies like the FDA and EPA. They are both looking more closely at this issue, thanks to the advocacy of scientists and others.”

It’s also worth noting that perhaps not all products present the same risks. “It is presumably more likely that triclosan in a water-solubilizable form [soft-soaps for example] would be more risky than that which has been incorporated into something like a mattress or sneakers,” suggests Levy, who notes that even with these products, the fate of antibacterials is unknown.

So where does that leave us? According to Dr. Bernadette Albanese, a public health expert, “If people spent as much time washing their hands, as they do reading the labels of this stuff, we’d all be better off. Putting antibacterial in soap, towelettes, band-aids is mostly useless. The message should be proper and frequent hand washing, use plain (liquid) soap and paper towels. That is the message the public needs to hear.”

Although I’m not sure I’m ready to give up the microban treated Tevas (have you smelled a well-worn pair of Tevas?) I’ll definitely be reading my consumer products labels more carefully.

1 comment:

Anonymous said...

Thank you for describing the research in plain language.

I am sending a link to your blog to everyone coming to our next PTO meeting on Health and Safety issues.