Reduced inorganic phosphorus in the natural environment: significance, speciation and determination.

It is commonly assumed that phosphorus occurs almost exclusively in the environment as fully oxidized phosphate (primarily H(2)PO(4)(-) and HPO(4)(2-), where the oxidation state of phosphorus is +V). Recent developments in the field of microbiology and research on the origin of life have suggested a possibly significant role for reduced, inorganic forms of phosphorus in bacterial metabolism and as evolutionary precursors of biological phosphate compounds. Reduced inorganic forms of phosphorus include phosphorus acid (H(3)PO(3), P(+III)), hypophosphorus acid (H(3)PO(2), P(+I)) and various forms of phosphides (P(-III)). Reduced phosphorus has been detected in anaerobic sediments, sewage treatment facilities and in industrial and agricultural processes. Microbiological evidence suggests a significant role for reduced phosphorus species in metabolic processes and raises interesting questions regarding the biogeochemistry of this nutrient in the environment. However, the paucity of data on the presence and cycling of reduced phosphorus compounds in the environment requires attention in order to elucidate the role of these compounds in natural systems. This paper discusses the significance of reduced phosphorus in the natural environment, its speciation and methods of detection.