Detection of phosphine: new aspects of the phosphorus cycle in the hydrosphere

Abstract

The role of phosphorus in limiting organic matter production and in causing eutrophication has been in the forefront of hydrobiological research during the past 30–50 yr^1–7. Comparing the cycles of major biogenic elements, it is evident that, with the exception of phosphorus, each of them contains gaseous substances (for example, CO₂, CH₄, O₂, N₂, NH₃, H₂S and volatile organic sulphur compounds) which, because of their gaseous state, can leave aquatic systems^8–16. We examined the phosphorus cycle of open-air sewage treatment plants and a deficit (∼30–45%) in the phosphorus mass balance was found which cannot be explained by knowledge based on earlier research on this cycle of the hydrosphere. By developing special sampling and analytical methods, we have shown that gases released from the sewage treatment plants and from the sediments of shallow (1–2 m deep) waters contain a reduced, gaseous phosphorus compound: phosphine. According to our measurements and calculations, about 5g of phosphorus per day was released as phosphine from an Imhoff tank settling 2,000 m³ per day of raw sewage. Under laboratory conditions, it was also demonstrated that phosphine is released by bacterial reduction from a medium containing inorganic phosphorus. The phosphorus content of the medium decreases by nearly one half. Our results on the metabolic importance of phosphine formation and release suggest that ∼25–50% of the phosphorus deficit in open-air sewage treatment plants can be explained by the release of phosphine into the atmosphere. These results change our understanding of the aquatic phosphorus cycle; former ideas about the phosphorus budget should be revised.