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Chemical Reaction: Down the Drain

By: Steve Herman
Posted: August 26, 2008, from the October 2007 issue of GCI Magazine.

“The struggle to save the global environment is in one way much more difficult than the struggle to vanquish Hitler, for this time the war is with ourselves. We are the enemy, just as we have only ourselves as allies.” —Al Gore

Once upon a time, the safety of personal care products and fragrances implied one of three things: the products’ effect on the skin, around the eyes or if ingested. A chemical in a shampoo was less likely to be an irritation problem because it was in a rinse-off product. Now, however, there exists a heightened awareness that the shampoo goes down the drain, and, therefore, new issues in safety include environmental considerations. For a formulating chemist, an understanding of the environmental fate of chemicals is a key to designing products for a better world.

Though computer models have limitations and shortcomings, they are a useful tool for evaluating chemicals without expensive and tedious laboratory work, and, despite limitations, are too valuable to be dismissed. I will look at two programs linked through the U.S. Environmental Protection Agency (EPA) Web site (www.epa.gov): the PRT profiler and EPI Suite.

The Programs

The surfactants in a shampoo, for example, cannot be analyzed by computer modeling because they are water-soluble mixtures, a dual property that disrupts the algorithm. Likewise, any botanicals or natural products cannot be checked. For illustrative purposes, we will examine propylene glycol, a single chemical of simple structure present in numerous personal care products.

The PBT (persistence, bioaccumulation and toxicity) profiler site begins with pages of disclaimers. It is, after all, a model, and does not produce rock solid data. Very conservative correction factors are applied, as is customary to many regulatory results. PBT is calculated online when a Chemical Abstract Service (CAS) number is entered. Every chemical has at least one CAS number—and often multiple numbers since there is considerable duplication. The CAS number of propylene glycol is 57-55-6.