C8- and C9-Alkylphenols and Ethoxylates: I. Identity, Physical Characterization, and Biodegradation Pathways Analysis

C8- and C9-alkylphenols (AP) and their ethoxylates (APE) are widely used commercial products mainly used in industrial applications, in the formulation of crop protection chemicals, and in industrial and household cleaners. These compounds have been the subject of considerable regulatory scrutiny regarding their potential to pose environmental risks. Recent regulatory focus on these compounds has included an assessment of their potential to meet criteria for persistent, bioaccumulative, and toxic compounds (PBTs). To facilitate the evaluation of the environmental behavior of APE and an assessment of their PBT characteristics, a review of the physical-chemical properties and environmental degradation pathways was performed. The most widely used commercial APE are highly water soluble and non-volatile. Nonylphenol (NP) and octylphenol (OP) are relatively low solubility compounds that are more hydrophilic and volatile than the ethoxylates. Properties of ethoxylate degradation intermediates such as APE1,2 are between values for the commercial APE and the AP building blocks in terms of solubility and partitioning characteristics and are non-volatile at ambient temperatures. The ether carboxylate intermediates are ionic in neutral water solution; hence, they are non-volatile and less prone to partitioning to organic matter. Under aerobic conditions, commercial APE undergo rapid degradation to short chain ethoxylates and ether carboxylates, which in turn degrade ultimately to carbon dioxide and water. Under anaerobic conditions, APE degrade more slowly, and may result in some accumulation of AP. Degradation half-lives and the potential for these compounds to bioaccumulate will be examined in a companion article.