Two Old Chemicals

Two stories in this week’s issue focus on two old chemicals that are back in the news—triclosan and 2,4-dichlorophenoxyacetic acid, which is better known as 2,4-D. The stories illustrate the fact that many useful chemicals follow an interesting and often complex narrative arc over their commercial lifetimes.

In this week’s cover story (see page 10), Senior Editor Jyllian Kemsley probes deeply into the chemistry, toxicology, and environmental impact of triclosan, a widely used antibacterial that was patented in the 1960s. As Kemsley points out, if you’ve ever used a product labeled as antibacterial, chances are you’ve encountered triclosan. It is ubiquitous, found in products ranging from soaps and toothpaste to toys, shoes, and caulking compounds.

Triclosan is in the news because some people think its use should be regulated. “Many scientists question whether triclosan reduces disease enough to be beneficial in the face of concerns about its toxicity. Others are concerned that it may promote drug resistance,” Kemsley writes. “Triclosan is currently the focus of several regulatory efforts, not the least of which is a ban on triclosan-containing soaps and cleaning products passed by Minnesota legislators last month.”

Like so many chemicals we are concerned about today, triclosan originally wore a white hat. Bruce D. Hammock, a toxicology professor at the University of California, Davis, told Kemsley that when triclosan was first used in medical settings as a surgical scrub, “it replaced some really scary compounds. Triclosan is much less toxic, more effective, and more biodegradable” than hexachlorophene and other common biocides of that era.

As Kemsley ably documents, there are a number of areas of concern about triclosan’s toxicity and environmental impact but no real smoking gun. It might disrupt endocrine function. It might promote antibiotic resistance. It might be toxic to some plants and freshwater marine animals. But the data are hardly conclusive.

Just as maddening, it’s not clear that triclosan provides a real benefit. Although it does kill bacteria, reducing bacteria counts is not the same as demonstrating clinical benefit, Kemsley points out. And studies here, too, are inconclusive—which leads some to think that triclosan is overused. “With many of the chemicals I look at, I find it difficult to make a decision about what we should do with them, because there are risks and there are benefits,” Thomas M. Young, a civil and environmental engineer at UC Davis, told Kemsley. Sometimes “it seems like we’re putting chemicals in stuff just for the point of putting chemicals in stuff.”

In contrast to triclosan, 2,4-D was born wearing a black hat. According to Wikipedia, it was first synthesized in 1941 as part of an effort to create chemical warfare agents for use during World War II, although it was never used during the war. Its herbicidal activity was first reported in 1944, and it subsequently revolutionized weed control.

Many studies have shown that 2,4-D is safe when used properly, and it is widely used around the world for weed control. Senior Correspondent Stephen Ritter reports that its use is expected to grow significantly when Dow Chemical, which manufactures the chemical, brings 2,4-D-resistant soybeans and corn to market in 2015 (see page 33). Increased production of 2,4-D would exacerbate an already existing problem: The chemical has a pungent odor that was not being blocked by the packaging Dow had been using.

But chemists are clever people and adept problem solvers. “One day a member of the Dow AgroSciences team who previously worked in the Dow Performance Packaging business recognized that Dow’s Saranex barrier films might provide a solution,” Ritter writes. “These multilayered materials have proved their mettle in a variety of odor-barrier applications.”

Sure enough, the Saranex film—which has as its core Dow’s famous Saran wrap polymer—worked. “As soon as the bulk containers were lined with the new 3-mil-thick barrier film, warehouses reported an immediate improvement in the 2,4-D odor situation,” Ritter reports.

Every chemical has a story to tell. That’s part of what makes our jobs here at C&EN fun.

Thanks for reading.

Views expressed on this page are those of the author and not necessarily those of ACS.