Soils as source and sink of phosphine

The evolution of free phosphine from soil samples collected from seven different areas in Germany was observed in laboratory experiments. Phosphine emissions increased after additions of manure, glucose, formate, pyrogallol and sulphide, revealing a potential influence of microbial activity on the liberation of phosphine. However, the concentrations decreased as time progressed. Soil samples exposed to phosphine removed the gas according to an exponential relationship. When Fe(III) was added to soil samples, phosphine removal was accelerated. The release of phosphine from soils to the atmosphere was concluded to be dependent on a balance of natural generation and depletion processes. At every time ''matrix-bound'' phosphine, which constitutes a trace of this balance, can be liberated by acid digestion of the soils. (C) 1997 Elsevier Science Ltd.