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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - PHOSPHOTRAC (Speciation, sources, and fate of atmospheric organic phosphorus over the Mediterranean Sea: A missing piece of the P cycle?)

Teaser

Summary

Phosphorus affects primary productivity in large areas of oceanic ecosystems. The main source of externally supplied nutrients in many marine ecosystems is the atmosphere. As the ocean is an important sink of atmospheric CO2, P through productivity limitation can indirectly affect global warming by removing more CO2 from the atmosphere. The importance of organic P as a potential pool of bioavailable P in the atmosphere is not widely recognized. The only available data in the literature are the atmospheric measurements of Phosphate and total P, while there are almost no data about the organic P, especially over the Mediterranean Sea (MS).
Studies in the east MS reveal that it is highly depleted in P relative to N. Now, it is well known that the atmosphere is an important P path for the area. Indeed, the atmosphere is the dominant nutrient path for PO43- in the eastern MS compared with the riverine inputs at 60%. Orthophosphate is the most soluble form of inorganic P and can be consumed by organisms, which convert it in organic or other inorganic forms. The organic P pool contains unknown compounds that may also be bioavailable for some microorganisms.
The main goal of Phosphotrac was to identify those organic P compounds, defining their role to the biogeochemical cycle of P over the MS. The specific objectives of the project were:
â€¢ Identification of atmospheric organic P sources by the chemical characterization of atmospheric organic P fraction over the MS and the chemical analysis of specific tracers, followed by a statistical analysis of the acquired data (WP1)
â€¢ Estimation of atmospheric P deposition fluxes and the study of the influence of atmospheric acidity to organic P pool solubility by the implementation of atmospheric transport model TM4-ECPL, coupled with the thermodynamic model ISORROPIA-II (WP2)
â€¢ Assessment of the biogeochemical role of atmospheric organic P in the MS marine ecosystem (WP3)

Work performed

Total Suspended atmospheric Particles (TSP) were collected in eastern Med. (Crete, N=77) and West Med. (Luminy Campus, N=25) by using high-volume air sampler. The TSP particles were analysed initially for Total Phosphorus (TP), Phosphate and condensed inorganic P (the pyro-, meta- and other inorganic polyphosphates forms), according to the protocol described in Violaki et al., (2018). Total Organic-P was calculated by subtracting all inorganic forms of P from TP. The results are depicted in Table. 1 (Fig.1a) for both the West and East Med. Almost 30% of TP is attributed to organic forms of P in the atmosphere of the MS. However, the higher average concentration of organic-P was observed in E. Med., as in the sampling period were recorded more dust events from the Sahara comparing with W. Med.
The aerosols samples (TSP) were analysed for organic P compounds of biological origin (e.g. phospholipids, ATP-like compounds, phytic acid, nucleic acids) and of anthropogenic origin (e.g. OPEs, organophosphorus pesticides, and degradation products of chemical weapons), by liquid chromatography coupled to mass spectrometry at the time of flight mode (Q-TOF-LC/MS) after optimization of the analytical protocols for the matrix of the aerosol samples. Regarding the anthropogenic atmospheric organic P, important role played the OPEs compounds following by organophosphorus pesticides, while degradation products of chemical weapons were not detected. Five pesticides were found in 27 samples in East Med. The most abundant were chlorpyrifos-e (n=9) with an average concentration of 0.24Â±0.38 pmol/m3 and Phosmet (n=10) with an average concentration 0.24Â±0.45 pmol/m3; Diazinon was detected in 4 samples with average concentration 0.07Â±0.00 pmol/m3. Less abundant but with higher concentration was the chlorpyrifos-me (n=3) with average concentration 0.91Â±0.93 pmol/m3. Ethoprophos was detected only in one sample (0.002 pmol/m3), Malathion was not detected. The average contribution of organophosphate pesticides in atmospheric organic P detected in this study was 0.2%.
The organophosphorus flame retardants and plasticizers (OPEs) are widely employed in industrial applications and household products. Some OPEs have been reported to be persistent in the environment and to bio-accumulate in the food chain. In addition, some halogenated OPEs have been found to exhibit various toxic effects. During this study were analysed six different OPEs compounds: TCPP(mix isomers), TCPP, TDCP, TnBP, TPhP, EHDP. In Table 2 (Fig. 1a) are presented the average atmospheric concentrations of OPEs measured during this study. It is remarkable that all OPEs compound presented high concentrations in West Med., especially the most potentially hazardous (TCPP, TCEP, TDCP). The percentage contribution of OPEs in atmospheric organic-P over West Med. was 9%, while over East was just 0.5%.
The atmospheric organic P compounds of biological origin detected during PHOSPHOTRAC were the phospholipids: phosphatidylcholine (PC), Phosphatidylglycerol (PG) and phosphatidylethanolamine (PE) and ATP-like compounds. Phytic acid was not detected. PC is usually the most abundant phospholipid in animals and plants, often amounting to almost 50% of the total complex lipids, while it is less often found in prokaryotic cells. Preliminary results on phospholipids showed that PC was the predominant phospholipid with an average concentration of 14.1Â±47.2 pmol/m3, following by PG with an average concentration of 2.3Â±10.2 pmol/m3, with contribution to TP of 2% and 0.2%, respectively. Negligible was the contribution of PE. It is remarkable that during a dust event the concentration levels of PC and PG were increased 20 and 30 times, respectively, suggesting that the high number of cells delivered by the dust contribute significantly to the atmospheric organic P pool (Fig.1). Furthermore, the ATP-like compounds analysed were ATP (Adenosine TriPhosphate) which is a key molecule of the energetic cell met

Final results

This research provides valuable societal-economic impact information regarding the impact of organic pesticides and OPEs on the Mediterranean environment (atmosphere and sea) in terms of abundance (WP1) and degradation (WP3) establishing a link between the atmosphere and sea on the transport of these compounds. Further, the identification of such compounds may help to use them as potential environmental pollution tracers to verify the use of pesticides in specific areas. This will probably help the creation of compound-specific sensors to track the presence of such molecules in the air and better monitor the air quality. PHOSPHOTRAC also provided improved analytical protocols which will benefit the research for new environmental tracers (scientific impact). As a perspective, our results may have an impact beyond the proposed research in that they help the construction of models, which will set threshold concentration values for pesticides or OPEs in order to prevent a potential level of risk in the marine ecosystem(s).
The URL below is the one of the team at AMU.