The Distribution, Fate, and Effects of Propylene Glycol Substances in the Environment

The family of synthetic organic substances known as “propylene glycols” consists of the 1,2-propanediol substance (monopropylene glycol, MPG) and its dimer (dipropylene glycol, DPG), trimer (tripropylene glycol, TPG) and tetramer (tetrapropylene glycol, TePG) forms. The formal identities of these substances are summarized in Table 1. Collectively, these substances are produced on a scale of approximately three million metric tons per year, and are among the most important group of synthetic organic chemicals in commerce today (Chinn and Kumamoto 2011). Produced and used globally, the propylene glycol (PG) substances have functional properties that enable their application in the manufacture of polyester resins and their formulation into functional fluids (e.g., anti-freeze, aircraft anti-icing and de-icing fluids), cosmetics, pharmaceuticals, personal care products, pesticides, liquid detergents, paints and coatings, and foods used for human and animal consumption. The PG substances also have more minor uses as a humectant for tobacco, plasticizers, and solvents used in fragrance, agricultural and ink formulations. Considering the sheer volume consumed in these broad and dispersive applications, a variety of scenarios can be envisioned for their emission to the environment. Thus, there is a need to understand the potential hazards of and exposures associated with the manufacture, transport, use and disposal of products containing or manufactured from the PG substances.