Designing for Non‐Persistence

Under the Pollution Prevention Act of 1990, it is the policy of the United States that pollution should be prevented or reduced at the source whenever possible. One way to accomplish this is to design safer chemicals. Until now, safer has usually meant less toxic, but environmental persistence should also be viewed as integral to product safety. Chemicals that persist in the environment remain potentially available to exert toxic effects and bioaccumulate. This chapter addresses the design of small molecules to minimize persistence, along with tools and models that can assist in this task. One of the great challenges is that over 30 000 chemicals are used in commercial quantities, but very few have experimental data on their environmental behavior. This chapter reviews databases that can be searched for such information, but we also outline a path forward for when the chemical of interest does not have any experimental data. Two general approaches are suggested: (1) identify chemicals that are similar in structure and have persistence data; or (2) use structure–degradation relationships or models to predict degradability. Estimation methods are available for the most important degradation processes: atmospheric oxidation, biodegradation, and hydrolysis. Finally, case studies are used to show how these processes and resources can be used to implement design for non-persistence. The examples also illustrate some of the challenges in designing safer chemicals in the real world, where “green” usually comes only in shades of gray and conflicting demands always lead to compromise. Keywords: persistence; structure–degradability relationships; biodegradation; atmospheric oxidation; hydrolysis; safer chemicals; green chemistry