The stable oxygen isotope ratio of resin extractable phosphate derived from fresh cattle faeces†. (11th April 2018)

• Record Type: Journal Article
• Authors: Granger, Steven J.; Yang, Yuguo; Pfahler, Verena; Hodgson, Chris; Smith, Andrew C.; Le Cocq, Kate; Collins, Adrian L.; Blackwell, Martin S. A.; Howden, Nicholas J. K.
• Is Part Of: Rapid communications in mass spectrometry. Volume 32:Number 9(2018)
• Page Start: 703
• Page End: 710
• Publication Date: 2018-04-11
• Subjects: Mass spectrometry -- Periodicals; 543.65
• DOI: 10.1002/rcm.8092
• Languages: English
• ISSNs: 0951-4198

Abstract

Abstract : Rationale: Phosphorus losses from agriculture pose an environmental threat to watercourses. A new approach using the stable oxygen isotope ratio of oxygen in phosphate (δ 18 OPO4 value) may help elucidate some phosphorus sources and cycling. Accurately determined and isotopically distinct source values are essential for this process. The δ 18 OPO4 values of animal wastes have, up to now, received little attention. Methods: Phosphate (PO4 ) was extracted from cattle faeces using anion resins and the contribution of microbial PO4 was assessed. The δ 18 OPO4 value of the extracted PO4 was measured by precipitating silver phosphate and subsequent analysis on a thermal conversion elemental analyser at 1400°C, with the resultant carbon monoxide being mixed with a helium carrier gas passed through a gas chromatography (GC) column into a mass spectrometer. Faecal water oxygen isotope ratios (δ 18 OH2O values) were determined on a dual‐inlet mass spectrometer through a process of headspace carbon dioxide equilibration with water samples. Results: Microbiological results indicated that much of the extracted PO4 was not derived directly from the gut fauna lysed during the extraction of PO4 from the faeces. Assuming that the faecal δ 18 OH2O values represented cattle body water, the predicted pyrophosphatase equilibrium δ 18 OPO4 (Eδ 18 OPO4 ) values ranged between +17.9 and +19.9‰, while using groundwater δ 18 OH2O values gave a range of +13.1 to +14.0‰. The faecal δ 18 OPO4 values ranged between +13.2 and +15.3‰. Conclusions: The fresh faecal δ 18 OPO4 values were equivalent to those reported elsewhere for agricultural animal slurry. However, they were different from the Eδ 18 OPO4 value calculated from the faecal δ 18 OH2O value. Our results indicate that slurry PO4 is, in the main, derived from animal faeces although an explanation for the observed value range could not be determined.