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Global Phosphorus Dynamics in Terms of Phosphine ✉ Wanyi Fu1 and Xihui Zhang 1

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Global Phosphorus Dynamics in Terms of Phosphine ✉ Wanyi Fu1 and Xihui Zhang 1 www.nature.com/npjclimatsci PERSPECTIVE OPEN Global phosphorus dynamics in terms of phosphine ✉ Wanyi Fu1 and Xihui Zhang 1 Since the detection of phosphine in the wastewater treatment plants in 1988, more and more investigations revealed that phosphine is closely related to ecological activities on a global scale. Here, we present perspectives on the whole dynamic cycles of phosphorus, particularly in terms of phosphine and its interactions with natural ecosystems, as well as the impacts from human activities. It may conclude that the phosphine-driving cycles of phosphorus depend on the coordination of human activities with natural ecosystems. Most importantly, the extensive recovery of phosphorus in numerous urban wastewater treatment plants may seriously obstruct its global cycles to catch up with the ecological needs in natural ecosystems. Phosphine gas plays an important role in the biogeochemical phosphorus cycle. Phosphorus might be one of the important elements participating in the global climate change together with carbon and nitrogen. npj Climate and Atmospheric Science (2020) 3:51 ; https://doi.org/10.1038/s41612-020-00154-7 INTRODUCTION organic matter (e.g., soil, dust) to form a local phosphate reducing 58 In the millions of years’ evolution of the global natural ecosystem, condition , favoring the production of phosphine. Since the the sustainability of this ecological system formed by many agricultural practice, specifically fertilization with phosphate-rich 1234567890():,; 59 element cycles is self-regulated and complex. Most studies fertilizer, is likely to greatly increase phosphine production , focused on the carbon, nitrogen, and sulfur cycles because the impact of the seasonal agriculture activities on the phosphine phosphorus was considered not to exist in gaseous forms. emission should be analyzed in the future. In addition to the seasonal Actually, as one of the critical elements, phosphorus, is cycling trend, phosphine concentrations in the atmosphere show an obvious 24 in a specific form, i.e., gaseous phosphine (PH3), and getting diurnal trend . That is, atmospheric PH3 levels peak during the early involved actively in ecological interactions. Now phosphorus morning because phosphine accumulates in the night atmosphere might be one of the important elements participating in the and degraded gradually until noon due to the effects of increasing 60 global climate change together with carbon and nitrogen. light intensity that promotes air oxidation . From the detection of free phosphine gas (Fig. 1) and MBP concentrations (Fig. 2) in different environments, it can be OCCURRENCE OF PHOSPHINE concluded that the phosphine levels are seriously impacted by human activities. Generally, the concentrations of phosphine in For a long time, the distribution of phosphorus in the cycle of the urbanized and populated areas, are higher than those in the hydrosphere was thought to be ambiguous and mass-unbalanced, natural ecosystems in rural areas. Glindemann et al. found that the until the detection of phosphine in wastewater treatment plants phosphine concentration in the air above the urban areas (e.g., by Dévai et al. in 19881. With the development of chromatography Berlin, Hamburg, Beijing) is 0.62–157 ng/m3 while 0.04–2.03 ng/m3 techniques and sample pretreatment methods, phosphine has in rural air, indicating emission by concentrated human activ- been shown to exist universally in the environment. A large ities33. Anthropogenic PH production by industry can interfere number of investigations on the global scope of phosphine have 3 – with the natural cycling of PH . For example, the exhaust gas from been conducted all over the world1 55. Phosphine exists 3 the PH fumigation of grain foods in the harbor resulted in high universally in the natural environment with two different forms: 3 atmospheric PH concentrations in Shanghai Harbor28. Besides, free gaseous phosphine and matrix-bound phosphine (MBP). The 3 high PH levels are found in paddy fields and eutrophic former has been detected in marsh gas36, sludge biogas1, upper 3 lakes13,35,36. The increased PH liberating biological activity in troposphere37, and the atmosphere around the world33. MBP has 3 polluted ecosystems with agricultural nutrients, such as the been detected in various types of soils and sediments14,45,50,54, excessive P fertilizer, results in the high PH values59. Unexpect- sewage sludge5, and feces55. It is worth noting that MBP is defined 3 edly high phosphine concentrations were found in air samples as the non-gaseous reduced phosphorus compounds that are from the poles and the main sources were assumed to be the transformed into phosphine gas by acid or alkaline digestion45. penguin colonies, guano, and tundra ecosystem26,61. Thus, MBP does not necessarily refer to the pre-existence of phosphine in the matrix. It generally comprises of phosphine adsorbed by the media, phosphine gas in the interstice, and solid phosphides. FORMATION AND TRANSFORMATION OF PHOSPHINE IN The phosphine concentrations in the atmosphere and the ECOSYSTEMS sediments demonstrate significant seasonal variations24,56,57.The Numerous biological and abiological mechanisms of phosphine phosphine concentrations display higher values in the summertime formation have been proposed in the literature2,20,23,58,62–65. because the high temperature in summer might induce more Significant evidence demonstrates that the production of phos- microbial activity4. Besides, the thunderstorm weather during phine is associated with the microbial reduction of P-containing summer create lightning, which strikes the phosphate-containing substances and most of the results have been summarized in a ✉ 1Tsinghua-Berkeley Shenzhen Institute, Shenzhen 518055, China. email: [email protected] Published in partnership with CECCR at King Abdulaziz University W. Fu and X. Zhang 2 and wetlands35,36,52,53. Non-biological pathways for phosphine formation include corrosion of P-containing metals66, reduction of phosphate by lightning strike67, and mechanochemical reduction of phosphate in minerals65. For example, phosphine is produced when atmospheric lightning strikes the aerosol or soils that contain oxidized forms of phosphorus and chemical reductants58. In previous studies, phosphorus usually is thought not to undergo redox reactions and the removal of phosphorus in water occurs only from adsorption, complexation, and precipitation68. However, the reduction of phosphate to phosphine occurs commonly in wetlands and paddy fields. It is well-established that the formation of phosphine in nature follows thermody- namics in terms of ORP (oxidation-reduction potential) levels59. Anaerobic microorganisms use a sequence of terminal electron acceptors instead of oxygen during their respiration under the anaerobic condition69. With decreasing redox potential, they fi Fig. 1 Survey of the presence of free phosphine in the reduce nitrates to nitrogen or N2O, sulfates to sul des, and 33 62,70 environment. (Urban air : 1. Berlin, 2. Leipzig, 3. East Leipzig, 4. carbonate to methane . Similarly, the production of PH3 occurs Hamburg, 5. Buenos Aires; Rural air33: 6. Leipzig, 7. Hammamet, 8. under the reducing conditions while requires more energy and Israel, 9. Namibia; Pole air7,27,34: 10. Arctic Yellow River station, 11. higher reducibility59. When redox potential falls below −300 mV, Arctic New Oldsson region, 12. Antarctica Milo Peninsula; Freshwater the phosphate may act as an electron receptor and finally get area24,35,36: 13. Lake Taihu (Year 2005), 14. Lake Taihu (Year 2011), 15. 19 28,37,38 reduced to phosphine . Beijing Reservoir; Sea area : 16. Southwest Yellow Sea, 17. Though the thermodynamics of the production of phosphine by Shanghai Harbor, 18. North-Atlantic Sea, 19. North Sea, 20. Southern reduction of phosphate is exergonic71, Bains et al. reported that Ocean; Marsh Wetland13,15,36: 21. Yancheng Reserve, 22. Beijing paddy fields, 23. Jiangsu Paddy fields, 24. Guangzhou paddy fields; the phosphine production from phosphite is thermodynamically 1 39 fi 59 25. Sludge biogas in Hungary ; Landfill gas : 26. Beijing, 27. Berlin, favored in speci c ecosystems . Pasek et al. presented a 28. Belgium). comprehensive review on the redox chemistry in the phosphorus 1234567890():,; biogeochemical cycle and proposed that the source of phosphine in the atmosphere is the reduced P compounds, such as phosphite and hypophosphite72,73. As shown in Fig. 2, high concentration of phosphine is detected in Taihu Lake and paddy fields, where relatively high levels of phosphite in basal sediments are observed as well74,75. Consistently, Sun et al. reported that more phosphine was produced from anaerobic activated sludge with hypophosphite as the inorganic phosphorus source than that with phosphate63. About 10% of the phosphorous in the atmosphere exists as phosphine59,73. Most phosphine is formed in soil, sediments, sludge, or landfill, and prefers to adsorb in the media at a matrix- bound status. Then most phosphine may transform back to phosphates for use by natural plants or microbes76, and the rest may emit from lower layers to surface layers and eventually into the atmosphere. The living plants in wetlands transfer atmospheric oxygen through aerenchyma to the rhizosphere, keeping a high ORP level in their root areas77. The rhizospheric ORP ranges from 130 to Fig. 2 Survey of the presence of matrix-bound phosphine in the 5,40,41 350 mV in daily time, creating an aerobic microenvironment that is environment. (Sludge : 1.
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