Triphenyl phosphate (TPhP) is an organic compound, easily soluble in benzene, chloroform, ether, acetone and other organic solvents, soluble in ethanol, and insoluble in water. It is used as a plasticizer and flame retardant in a variety of environments and products.
Preparation
Triphenyl phosphate is prepared by the bimolecular nucleophilic substitution reaction of phenol and phosphorus oxychloride.
Purpose
Triphenyl phosphate has been widely used as a flame retardant and plasticizer. It has been used as a flame retardant in a variety of materials, including electronic equipment, PVC, hydraulic fluids, glues, nail polish and casting resins. Its mechanism of action as a flame retardant is as follows: First, triphenyl phosphate forms phosphoric acid during thermal decomposition. It reacts to form pyrophosphoric acid, which when in the condensed phase acts to prevent heat transfer. As one of the most effective flame retardants for certain polymers, triphenyl phosphate is an additive in flame retardants only in the gas phase. The discontinuation of PBDE use several years ago led to an increase in the use of triphenyl phosphate.
Antioxidants
Triphenyl phosphate is also used as a plasticizer in varnishes and hydraulic fluids. Nail polish has been of particular concern as a source of exposure to triphenyl phosphate.
Toxicity
There is limited information indicating that TPhP has significant toxicological effects. Although its impact was initially expected to be small overall, there is growing evidence that the impact may not be so benign. Triphenyl phosphate exhibits low acute toxicity through skin contact or oral administration. However, a growing body of research links triphenyl phosphate exposure to reproductive and developmental toxicity, neurotoxicity, disruption of metabolism, the endocrine system, and genotoxicity. Triphenyl phosphate has also been found to induce significant estrogenic activity. One study found that concentrations above the minimum observable effects were observed in multiple studies of coral grouper, yellow-striped goatfish, and freshwater bass. This suggests that triphenyl phosphate may be present in the environment at high enough concentrations to have deleterious ecological effects. Triphenyl phosphate is considered toxic to aquatic life by the European Chemicals Agency and may have long-term effects.
Contrary to many POPs, triphenyl phosphate has limited affinity for lipids. Still, bioaccumulation of this compound was found to occur at varying levels in fish, with the strongest differences arising based on sex, feeding patterns and metabolic efficiency. However, the reasons and mechanisms that explain triphenyl phosphate accumulating in this manner are unclear.
Environmental diffusion and change
The presence of triphenyl phosphate has been detected in the environment. Other triaryl phosphates are known to volatilize and leach from plastics through hydraulic fluid leaks and, to a lesser extent, into the aquatic environment through the manufacturing process. In particular, triphenyl phosphate has been found to enter the environment from various sources including industrial use (e.g. during manufacturing processes) and through indoor use (e.g. through paints and electronic equipment). Like many other phosphorus-containing flame retardants, triphenyl phosphate has been found widely in sediments, soil, indoor dust and air.
Once in water, triphenyl phosphate has been found to biodegrade relatively quickly under both aerobic and anaerobic conditions, and it does not meet criteria for persistent organic pollutants. However, although the compound is readily biodegradable and does not bioaccumulate, it is easily detectable due to the sheer volume utilized. In 2014, the U.S. Environmental Protection Agency added triphenyl phosphate to its Toxic Substances Control Act work plan list, citing that the compound exhibits acute and chronic aquatic toxicity, moderate bioaccumulation potential, and moderate environmental persistence. However, there is still insufficient information to fully assess the environmental impact of triphenyl phosphate.
