Tetrakis(hydroxymethyl)phosphonium salts: Their properties, hazards and toxicities

Tetrakis(hydroxymethyl)phosphonium chloride (THPC) and sulfate (THPS) are of importance in the textile industry as flame retardants, in the oil industry as scale-removers, as biocides for water systems, in the leather industry as tanning agents, in nanochemistry as reductants and stabilizers of nanoparticles, and as oxygen-scavengers in medical uses. In the majority of cases, THPC and THPS themselves are not chemically active and solely play a role of reservoirs for the more reactive species tris(hydroxymethyl)phosphine (THP) and/or formaldehyde. The contents of THPC/THPS solutions greatly depend on pH, which is now recognized as a key factor, for example, in metal hydrosol preparations, biocidal activity, and ecotoxicity. This review is intended to reveal and explain the complex behavior of THP and (HOCH2)4P+ salts in aqueous solutions, conditions that might lead to potential hazardous compounds such as formaldehyde, hydrogen gas, phosphine PH3, and bis(chloromethyl)ether. Literature data on their toxicities are reviewed.