First Measurements on Triple Oxygen Isotopes of Dissolved Inorganic Phosphate in the Hydrosphere

Abstract

Although dissolved inorganic phosphate (DIP) is an important nutrient in the hydrosphere, it is difficult to quantitatively clarify the dynamics of DIP in the hydrosphere using the δ18O value of DIP as a tracer. In this study, we quantified the triple oxygen isotopic compositions (Δ′17O) of DIP relative to VSMOW with the reference line with a slope of 0.528 as an additional tracer to clarify the sources and dynamics of DIP in the hydrosphere. We found significant variation in the Δ′17O values of riverine DIP in urban areas, ranging from −107 × 10–6 to +3 × 10–6, while those of DIP in the effluents from wastewater treatment plants (WWTP) and DIP extracted from the chemical fertilizers showed −56 ± 5 × 10–6 (1SD) and −98 ± 5 × 10–6, respectively. We conclude that both the DIP supplied directly from the artificial loads (the WWTP effluent and chemical fertilizers) showing 17O-depleted Δ′17O values and the DIP turned over via the aquatic biosphere showing 17O-enriched Δ′17O values similar to ambient H2O were the major sources of riverine DIP. High-precision determination of the Δ′17O value of DIP can contribute to quantitative clarification of the dynamics of DIP in the hydrosphere.

Oxygen isotope ratios of phosphates in the soil‐plant system: Limitations and future developments

“…Microbial intracellular water can comprise significant fractions of atmospheric oxygen, presenting a distinct mass-independent 17 O anomaly, that is passed onto the respective inorganic and organic phosphorus compounds (Herwartz, 2021). Similarly, atmospheric O 2 carries 17 O anomalies that have been traced in various geological materials (Pack, 2021) and more recently in the hydrosphere (Sambuichi et al, 2023). This 17 O anomaly could also persist in phosphate from ash derived from biomass burning (e.g., wildfires) because phosphate exchanges with air O 2 at elevated temperatures (Bigio & Angert, 2018;Liang & Blake, 2006b).…”

Oxygen Isotope Analysis of Nanomole Phosphate Using PO3– Fragment in ESI-Orbitrap-MS

“…In the mass spectrum for a 50:50 μM mixed solution of phosphate and sulfate, we observed that the relative signal intensity of 1 H 2 P 16 O 4 − was only 37% of that of 1 H 32 S 16 O 4 − under source fragmentation with 0 V (Figure 4A). Since 1 H 32 S 16 When source fragmentation energy was set to 40 V to achieve condition where almost all H 2 PO 4 − ions were converted into PO 3 − ions, the generated SO 3 − ion signal was only half of that of the PO 3 − ion in intensity (Figure 4B). Note that the 32 S 16 O 3 − (m/z = 80) ions do not interfere with the P 16 O 3 − ions (m/z = 79), and the PO 3 − ions become the predominant species in the Orbitrap analyzer.…”

“…Since 1 H 32 S 16 When source fragmentation energy was set to 40 V to achieve condition where almost all H 2 PO 4 − ions were converted into PO 3 − ions, the generated SO 3 − ion signal was only half of that of the PO 3 − ion in intensity (Figure 4B). Note that the 32 S 16 O 3 − (m/z = 80) ions do not interfere with the P 16 O 3 − ions (m/z = 79), and the PO 3 − ions become the predominant species in the Orbitrap analyzer. Consequently, we think that the higher PO 3 − fraction in the Orbitrap analyzer results in a higher shot-noise limit precision and better phosphate δ 18 O reproducibility.…”

“…The data acquisition for each collision energy had a duration of 1 min. We normalized the signal intensity of three major ions recorded in 1 min to 1, including PO 2 When introducing 50 μM NaH 2 PO 4 solution to the ESI-Orbitrap-MS, we observed both the PO 3 − fragment (m/z = 79 for P16 O 3 − ) and H 2 PO 4 − (m/z = 97 for 1 H 2 P 16 O 4 − ) in the mass spectrum. We interpreted the PO 3 − fragment as the result of dissociation of H 2 PO 4 − , which is consistent with what had been reported in-source fragmentation in various ESI sourced mass spectrometers.…”

“…− , P17 O16 O 2 − , and P18 O16 O 2 − , respectively) generated by source fragmentation; and (3) using PO 3 − fragment ions generated by higher-energy collisional dissociation (HCD). − m/z = 99).…”