Elsevier

Chemosphere

Volume 237, December 2019, 124346
Chemosphere

Molecular level determination of water accommodated fraction with embryonic developmental toxicity generated by photooxidation of spilled oil

https://doi.org/10.1016/j.chemosphere.2019.124346Get rights and content

Highlights

  • Molecules generated by photooxidation and contributing to toxicity were identified.

  • Polar compounds detected by UHR-MS were increased x 4 in 5 day of photooxidation.

  • Toxicity was greatly increased as oils were photodegraded under natural sunlight.

Abstract

In this study, developmental toxicity was increased as the oil was further degraded under natural sunlight. Detailed chemical composition of the degraded oils was examined by use of gas chromatography (GC) and (−) electrospray ionization ultrahigh resolution mass spectrometry (UHR-MS). Baseline toxicities were estimated based on chemical activities of polycyclic aromatic hydrocarbons, and it was obvious that the predicted chemical activities can not explain increased toxicity alone. However, the ultrahigh resolution mass spectral abundance of polar compounds including O3 and O4 class compounds was significantly increased as the photodegradation proceeded. Further examination of double bond equivalence values of the compounds showed that polar compounds with both non-aromatic and aromatic polar structures were increased. Statistical analysis indicates that the increased toxicity can be well explained by the increased polar compounds. Therefore, the oxygenated compounds identified in this study can play an important role in toxicity of degraded oils.

Introduction

Despite the ongoing effort to reduce the usage of fossil fuels, petroleum is still one of the most important energy sources for heating, transportation, and electricity generation. It is also an important source for polymers that are heavily used in modern society. Therefore, petroleum is extracted on a large scale and constantly transported throughout the world. This increases the risk of large- and small-scale oil spills. As vividly evidenced by the Deepwater Horizon oil leak, such spills significantly endanger the environment (White et al., 2012; Yim et al., 2012).

A number of studies have proven the toxic effect of spilled oils on marine lives (Neff et al., 2000; Fisher et al., 2016). The spilled oils can be degraded and transformed into different forms, including the water-accommodated fraction (WAF) and water-soluble fraction (WSF). The toxicity of these photo-oxidized products is well documented (Lee, 2003; González et al., 2009; Khursigara et al., 2017). The toxicity of crude oil has been attributed to the aromatic compounds in it (Incardona et al., 2013; Esbaugh et al., 2016). For example, Carls et al. reported damages to fish embryos from dissolved PAHs (Carls et al., 2008), and Esbaugh et al. explained the toxicity of oil based on three-ring PAHs (Esbaugh et al., 2016).

However, a number of reports suggest that there are limitations in explaining the toxicity of weathered oil by aromatic compounds alone. Barron et al. observed that highly toxic oils could have low aromatic contents (Barron et al., 1999). Saco-Álvarez reported that hydroxyl PAHs such as pyrenol and phenanthrol were more toxic than the original oils (Saco-Álvarez et al., 2008). Neff et al. found that the toxicity of WAF in some oils was higher than prediction based on the concentrations of aromatic compounds, and suggested that the unresolved complex mixture and polar compounds could contribute to the toxicity (Neff et al., 2000). Bellas et al. observed the differences in toxicity between fresh and weathered fuels that could not be explained by the aromatic hydrogen content, and concluded that the formation of oxidized compounds plays an important role in the toxicity to the larvae of sea urchins Paracentrotus lividus (Bellas et al., 2013). In addition, the toxicity of Canadian oil sands has been attributed to naphthenic acid (Bartlett et al., 2017).

From these previous studies, it is clear that polar compounds generated during the weathering process can play an important role in the toxicity of spilled oils. However, the exact role of polar compounds in the degraded oils’ toxicity has not been known. One of the reasons for the lack of information can be attributed to the fact that molecular-level information of these polar compounds is scarce (Bartlett et al., 2017). Of the few studies directly connecting the toxicity to the molecular level analysis of the polar compounds, Melbye et al. found that the toxicity of degraded oil was mainly attributed to the most polar fraction, which was rich in sulfoxide compounds based on GC and comprehensive 2D GC-MS analyses (Melbye et al., 2009).

However, GC is limited in identifying polar compounds, and the ultrahigh resolution mass spectrometry (UHR-MS) technique can expand our knowledge about those compounds. UHR-MS has played an important role in characterizing complex mixtures such as crude oils and natural organic matter at the molecular level (Cho et al., 2015; Kim et al., 2019). Negative mode electrospray ionization ((−) ESI) coupled to UHR-MS has been widely used to study polar compounds generated during the weathering process of oils (Hughey et al., 2007; Islam et al., 2013, 2015, 2016; Vaughan et al., 2016).

In this study, the toxicity of water-accommodated fraction from an oil spill was examined, and (−) ESI UHR-MS and GC-MS were applied to identify these compounds at the molecular level. As far as we know, this is the first study combining the comprehensive analysis of PAHs and polar oxygenated compounds using GC-MS and UHR-MS and the evaluation of their toxicity.

Section snippets

Sample preparation

On April 3, 2014, an oil spill occurred in the Jangmok Bay, Geoje, Korea. The spiller is not known, but the spilled oil was determined to be diesel oil, based on GC-MS analysis data. The carbon range in the collected spilled oil was C9–C30, typical of diesel oil (Fig. S1). Pictures of the oil sampling site are provided in Supporting Information (Fig. S2). The spilled oil and seawater were sampled and transferred to 2 L glass bottles with a stopcock on the bottom. The reservoir bottles were

Identifying the major degradation process

Biodegradation and photo-oxidation were expected as major oil weathering processes in this study. To identify the biodegradation, the ratio of n-heptadecane to pristane or n-octadecane to phytane were calculated (Table S2). The decrease in these values have been used to determine the onset of biodegradation of petroleum hydrocarbons (Miget et al., 1969; Prince and Walters, 2016). There were no significant changes for 5 days of exposure, hence the effects of biodegradation are not considered in

Conclusions

In this work, comprehensive study was performed on molecular level identification of compounds in photodegraded oils and evaluation of their embryonic developmental toxicity. Molecular level identification of polar compounds generated by the photooxidation of spilled oil was performed by FT-ICR MS. The abundance of identified polar oxygenated compound was significantly increased through the photooxidation of spilled oil. The concentration of PAHs in seawater were measured by GC-MS and baseline

Declarations of interest

None.

Acknowledgment

The authors acknowledge support by the Ministry of Oceans and Fisheries under the project ‘Oil Spill Environmental Impact Assessment and Environmental Restoration (PM60090)’, by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2017R1A2B3003455), and by the Korea Basic Science Institute (KBSI) National Research Facilities & Equipment Center (NFEC) grant funded by the Korea government (Ministry of Education) (

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    Comprehensive study was performed on molecular level identification of compounds in photodegraded oils and evaluation of their embryonic developmental toxicity. Ultrahigh resolution mass spectral abundance of polar oxygenated compounds and embryonic developmental toxicity were increased as oils were further photodegraded under natural sunlight. Partial least squares regression analysis supported the correlation between the abundance of the observed compounds and the toxicity. This work can contribute to improove our understanding on the toxic potency of spilled oil based on detailed chemical information.

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