Dietmar Glindemann

Free phosphine from the anaerobic biosphere

The possible liberation of highly toxic and mutagenic phosphine from putrefying media raises the question of its significance as a problem of hygiene. Free phosphine was established by gas chromatography as a universal trace component in gas emitted from the anaerobic biosphere. Sources of phosphine include landfills, compost processing, sewage sludge, animal slurry and river sediments. We detected maximum concentrations in the order of 20 ppb(v/v).

Soils as source and sink of phosphine

Abstract 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.

Phosphine by bio-corrosion of phosphide-rich iron

Phosphine is a toxic agent and part of the phosphorus cycle. A hitherto unknown formation mechanism for phosphine in the environment was investigated. When iron samples containing iron phosphide were incubated in corrosive aquatic media affected by microbial metabolites, phosphine was liberated and measured by gas chromatography. Iron liberates phosphine especially in anoxic aquatic media under the influence of sulfide and an acidic pH. A phosphine-forming mechanism is suggested: Phosphate, an impurity of iron containing minerals, is reduced abioticly to iron phosphide. When iron is exposed to the environment (e.g. as outdoor equipment, scrap, contamination in iron milled food or as iron meteorites) and corrodes, the iron phosphide present in the iron is suspended in the medium and can hydrolyze to phosphine. Phosphine can accumulate to measurable quantities in anoxic microbial media, accelerating corrosion and preserving the phosphine formed from oxidation.

Phosphorus cycling through phosphine in paddy fields.

Phosphine emission fluxes from paddy fields, phosphine ambient levels in air, and the vertical profile of matrix-bound phosphine in soil have been measured throughout the growing season of rice in Beijing, China. It was found that both the seasonal and diurnal emission fluxes and ambient levels fluctuate significantly. During the drainage period, phosphine released from the soil with the highest diurnal average flux on the first period of drainage (approx. 17.7 ng m(-2) h(-1)), whereas its highest ambient level (approx. 250 ng m(-3)) occurred at 06.00 h. During the flooded period, phosphine emission was low, and the peaks of phosphine emissions occurred at midnight. The average flux of PH3 emission for the whole season was found to be approximately 1.78 ng m(-2) h(-1). The mass fraction of matrix-bound phosphine is approximately 0.18 approximately 1.42 x 10(-7) (m/m) part of organic phosphorus or 3.4 approximately 9.2 x 10(-9) (m/m) part of total phosphorus in paddy soil. The amount of phosphine emitted to the atmosphere was only a small fraction of the phosphine that remained in the soil in the matrix-bound form. Soil serves both as the source and the sink of PH3.

Phosphine in the urban air of Beijing and its possible sources

Both as an air pollutant and as a gaseous component of the local phosphorus cycle, phosphine (PH3) was found in the urban air of Beijing. Other possible sources, like paddy fields and water reservoirs, were selected for testing the hypothesis of the biological phosphine formation. Phosphine in the urban air of Beijing was measured in different seasons. In the summertime phosphine levels typically peak in the early morning and then decline towards noon. The maximum concentration at 6.00 am was 65 ng m−3 whilst that at noon was 11 ng m−3. In spring and in wintertime, the phosphine levels in the urban air of Beijing were lowest. A first screening revealed phosphine also in gas and in sediment samples from a paddy field near Beijing, the Beijing Shisanling water reservoir, and the refuse tips Changping of Beijing as well as in the ambient air adjacent to these sampling sites. The maximum phosphine concentrations in these gas samples were 41 (marsh gas, paddy field), 135 (marsh gas, reservoir), 1062 (landfillgas) ng m−3, and in the ambient air samples 146 (air, paddy field), 166 (air, reservoir), and 71 (air, refuse tips) ng m−3. In sediment samples, the highest matrix-bound phosphine levels were 13 (paddy field), and 3.9 (reservoir) ng kg−1. These comparatively high concentrations of the readily oxidizable phosphine in air indicate hitherto unknown but important phosphorus emission sources, which might reduce the biomass growth in Chinese fields and forests by a general phosphorus limitation. Phosphine is also a constituent of the air pollution in China. However, more work has to be done to evaluate the different sources of atmospheric phosphine.

Methylated bismuth in the environment.

Biomethylation of metals and metalloids of Group 14 and 15 metals such as tin, lead and arsenic takes place in the environment, but information about methylated bismuth compds. is rather limited, although bismuth compds. are used widely in alloys, cosmetics and pharmaceutical products. Cryotrapping gas chromatog. and hydride generation gas chromatog. coupled with an ICP-MS as a bismuth-selective detector were used to det. volatile bismuth compds. in landfill and in sewage gas, as well as non-volatile methylated compds. in water and sediment samples. One volatile bismuth compd. could be detd. in gaseous samples; it was identified as Me3Bi (TMB) by element-specific detection (ICP-MS, m/z 209), matching the retention time with a TMB std. The mol. structure was recently confirmed by gas-chromatog. fractionation with MS-ion trap detection (electron impact). Among other volatile metal compds., TMB is a major component in the gases of sewage sludge digesters: concns. of up to 25 mg m-3 have been measured at eight sewage treatment plants. The concn. in landfill gas was approx. one order of magnitude lower. In lab. expts., fermentors contg. an anaerobic culture from a clean pond sludge were mixed with contaminated soil from four different industrial areas. After an incubation time of two weeks at 30 Deg in the dark, TMB was detected in the headspace of all the samples. The volatilization rate of bismuth did not correlate with the total amt. of bismuth in the sediments or with the available fraction after acid digestion following hydride generation. Some evidence was obtained for the occurrence of methylated bismuth compds. in water samples and in sediments.

Balancing phosphine in manure fermentation

The evolution of phosphine gas during the anaerobic batch fermentation of fresh swine manure was detected and correlated to the production of methane and hydrogen sulphide. A close temporal relationship between phosphine liberation and methane formation was found. However, the gaseous phosphine released from manure during fermentation only represents a tiny fraction of the overall phosphine balance. The majority of phosphine is captured in solid manure constituents. This matrix-bound phosphine is eliminated by more than 50% during anaerobic batch-fermentation. Seasonally determined phosphine concentrations in biogas and manure from two large-scale manure treatment plants also revealed net losses of phosphine in fermentation. Consequently, manure has to be considered more as a sink of phosphine rather than a phosphine-generating medium. Furthermore, a close relationship between phosphine in the feed of swine and manure of these swine was observed, implying that phosphine residues in the feed (possibly as a result of grain fumigation) represent an important source of phosphine in manure technologies that is relevant before the faecals of swine enter manure treatment plants.

Effect of free phosphine on anaerobic digestion

Gaseous phosphine was found to inhibit biogas formation during the anaerobic fermentation of swine manure. A logarithmic dose-response correlation was obtained with 50% inhibition at a phosphine concentration of approximately 150 ppm. Anaerobic fermentation of acetate and yeast extract measured by biogas formation were not affected at concentrations up to 1000 ppm. Despite the relative tolerance of anaerobic bacteria, phosphine may obviously inhibit the degradation of manure constituents.

Toxic oxide deposits from the combustion of landfill gas and biogas

Oxide deposits found in combustion systems of landfill gas fired power stations contain relatively high concentrations of elements which form volatile species such as P, As, Sb and Sn. These deposits should be handled with care because of their potential toxicity. By contrast, deposits in biogas system engines were found to contain much lower levels of such elements. The enrichment of these elements can be attributed to a hypothetical multistage process. The elements form volatile species in the landfill body. They are selectively transported as part of the landfill gas into the gas-burning devices. Inside the burners, they are immobilized as nonvolatile oxides.