We ask a lot of our wastewater treatment plants (WWTPs). We expect them to clean up our sewage, so that the effluent that is returned to our water resources is environmentally benign. A century or more ago, the main goal was to prevent the spread of water-borne diseases, and treatment mainly consisted of dilution. Since that time, our environmental sensibilities have increased, and treatment techniques have been vastly improved to disinfect wastewater and remove pollutants to protect receiving waters. At first those pollutants were primarily limited to nutrients. Now we’re asking WWTPs to remove other things. Any idea what this compound is?

It’s sulfamethoxazole, a sulfonamide antibiotic, one of hundreds (thousands?) of synthetic organic molecules that are part of our wastewater streams. We’d like to remove them before they reach our waterways, because we know that some of these compounds are harmful to aquatic life. But some of these compounds can be difficult to remove, and there is a lot of research looking into the best ways to remove these compounds.

But the idea of “removal” may be misleading. A recent viewpoint in Environmental Science and Technology (Stadler, et al., 2012, v. 46, 10485−10486) makes the point that the disappearance or removal of some of these compounds, including sulfamethoxazole, may not mean that the effluent quality has necessarily improved. These are complex molecules, and breaking them down requires many steps, and transformation products produced in these reactions may “exceed the parent form in both concentration and toxicity” according to the authors. This has long been known for pesticides such as atrazine in groundwater and surface waters (Kolpin et al., 1996, Environ. Sci. Technol., v. 30, 335-340).

The point the authors are making is that we can’t just analyze for the “parent” compounds, because just because we can no longer detect them doesn’t mean that they have broken down into benign components. Risk reduction requires a more holistic understanding of the degradation reactions. This will be tough work.