American Scientist

To the Editors:

In his interesting “A Short History of Hydrogen Sulfide” (January–February), Roger P. Smith mentions strontium sulfide as a potential source of the hydrogen sulfide in homes where Chinese drywall was installed in South Florida, New Orleans and elsewhere. It’s hard for this retired chemist to conceive that any source of gypsum contains sufficient strontium to generate so large a problem. That’s especially so when a primary raw material is 25 percent sulfur.

Anyone who has ventured into stagnant areas of the many swamps in Florida, for instance, has noted the odor of so-called swamp gas. The origin of this hydrogen sulfide is well known. It comes from the action of anaerobic bacteria on organic material, using the oxygen in sulfate ions for metabolism, reducing sulfur to hydrogen sulfide.

I propose an alternative explanation regarding the drywall. The gypsum there, either intentionally or naturally, likely was contaminated with some proportion of organic material. That contamination in an oxygen-free location, such as the interior of drywall, was then exposed to water, thanks to the high humidity of the subtropics. That mix, at a suitably warm temperature, provides the essential environment for anaerobic bacteria to do their thing.

As a retired chemist, I have no access to a laboratory to conduct simple tests to verify my proposal. I hope someone else will.

Barton Milligan
Fort Lauderdale, FL

Dr. Smith responds:

I am doubly indebted to Dr. Milligan. First he points out the controversy surrounding the assertion that strontium sulfide is the source of hydrogen sulfide in homes damaged by Chinese wallboard. Google “Chinese wallboard” and “strontium sulfide” for a sampling of opinions. Difficulty with the idea that wallboard could contain enough sulfide to account for “so large a problem” is shared by many.

Secondly, Dr. Milligan reminds us of an important source of environmental hydrogen sulfide, namely the reduction of sulfate by anaerobic bacteria, often in swamps. Hence, the origin of the term “swamp gas.” Although he proposes an interesting idea, my question is this: How anaerobic do conditions have to be for those bacteria to do their thing? It comes down to how low the oxygen tension is in the interior of the wallboard? Wallboard must have a certain porosity to let the hydrogen sulfide out, which in turn would allow oxygen to come in.

At least we agree that hydrogen sulfide is the most likely culprit; such accord is a good and sometimes rare thing.