Microplastic emission characteristics of stormwater runoff in an urban area: Intra-event variability and influencing factors.

Stormwater runoff is considered a major pathway for land-based microplastic transportation to aquatic environments. By applying time-weighted stormwater sampling at stormwater outlets from industrial and residential catchments, we investigated the emission characteristics and loads (number- and mass-based) of microplastics to aquatic environments through urban stormwater runoff during rainfall events. Microplastics were detected in stormwater runoff from industrial and residential areas in the concentration range of 68-568 n/L and 54-639 n/L, respectively. Polypropylene and polyethylene were found as major polymers accounting for around 60 % of total microplastics. The fragment was the dominant shape of microplastics, and the most common size class was 20-100 µm or 100-200 µm. The microplastic load emitted from industrial and residential areas were estimated to be 1.54-46.1 × 108 and 0.63-28.5 × 108 particles, respectively. The discharge characteristics of microplastics inter- and intra-event were affected by the land-use pattern and rainfall characteristics. The concentration of microplastics did not significantly differ between industrial and residential catchments, but the composition of polymer types reflected the land-use pattern. The microplastics in stormwater were more concentrated when the number of antecedent dry days (ADDs) was higher; the concentration of microplastics was generally peaked in the early stage of runoff and varied according to rainfall intensity during a rainfall event. The contamination level and load of microplastics were heavily affected by the total rainfall depth. Most microplastics were transported in the early stage of runoff (19-37 % of total runoff time), but the proportion of larger and heavier particles increased in the later period of runoff. The microplastic emission via stormwater runoff was significantly higher than that through the discharge of wastewater treatment plant effluent in the same area, implying that stormwater runoff is the dominant pathway for transporting microplastics to aquatic environments.

Capillary flow velocity profile analysis on paper-based microfluidic chips for screening oil types using machine learning.

We conceived a novel approach to screen oil types on a wax-printed paper-based microfluidic platform. Various oil samples spontaneously flowed through a micrometer-scale channel via capillary action while their components were filtered and partitioned. The resulting capillary flow velocity profile fluctuated during the flow, which was used to screen oil types. Raspberry Pi camera captured the video clips, and a custom Python code analyzed them to obtain the capillary flow velocity profiles. 106 velocity profiles (each with 125 frames for 5 s) were recorded from various oil samples to build a training database. Principal component analysis (PCA), support vector machine (SVM), and linear discriminant analysis (LDA) were used to classify the oil types into heavy-to-medium crude, light crude, marine fuel, lubricant, and diesel oils. The second-order polynomial SVM model with PCA as a pre-processing step showed the highest accuracy: 90% in classifying crude oils and 81% in classifying non-crude oils. The assay took less than 30 s from the sample to answer, with 5 s of the capillary action-driven flow. This simple and effective assay will allow rapid preliminary screening of oil types, enable early tracking, and reduce the number of suspect samples to be analyzed by laboratory fingerprinting analysis.

Phenotypic toxicity, oxidative response, and transcriptomic deregulation of the rotifer Brachionus plicatilis exposed to a toxic cocktail of tire-wear particle leachate.

Tire-wear particles (TWPs) are potential source of microplastic (MP) pollution in marine environments. Although the hazardous effects of MPs on marine biota have received considerable attention, the toxicity of TWPs and associated leachates remain poorly understood. Here, to assess the toxicity of TWP leachate and the underlying mechanisms of toxicity, the phenotypic and transcriptomic responses of the rotifer Brachionus plicatilis were assessed with chemistry analysis of a TWP leachate. Although acute toxicity was induced, and a variety of metals and polyaromatic hydrocarbons were detected in the leachate, levels were below the threshold for acute toxicity. The results of particle analysis suggest that the acute toxicity observed in our study is the result of a toxic cocktail of micro- and/or nano-sized TWPs and other additives in TWP leachate. The adverse effects of TWP leachate were associated with differential expression of genes related to cellular processes, stress response, and impaired metabolism, with further oxidative stress responses. Our results imply that TWPs pose a greater threat to marine biota than other plastic particles as they constitute a major source of nano- and microplastics that have synergistic effects with the additives contained in TWP leachate.

Spatial distribution and temporal trends of classical and emerging persistent organic pollutants (POPs) in black-tailed gull (Larus crassirostris) eggs from Korea.

This study monitored the spatiotemporal trends of persistent organic pollutants (POPs) contamination along the Korean coasts using eggs of the black-tailed gull, a resident bird that occupies a high trophic position in the marine food web. Black-tailed gull eggs were collected from three breeding islands located in the western (Seoman-do), southern (Hong-do), and eastern (Dok-do) seas of Korea during 2015-2019, and egg contents were analyzed for classical and emerging POPs. Among the target analytes, levels of emerging POPs such as brominated flame retardants (BFRs) and perfluoroalkyl acids (PFAAs) were significantly higher in eggs from Seoman-do than other islands. Global positioning system tracking data show that seagulls from Seoman-do traveled frequently to two neighboring major cities (Incheon and Seoul), indicating that the accumulation of BFRs and PFAAs in bird eggs is directly affected by the pollution characteristics of urban areas. Overall, the ratios of PFAA and BFR to the total POPs in eggs from the islands increased over time, while the proportion of classical POPs decreased. A shift from classical POPs to BFRs and PFAAs in seagull eggs was identified. Interestingly, perfluorooctanoic acid (PFOA), which exhibits limited bioaccumulation, was detected at higher levels in eggs from Seoman-do, indicating widespread use of PFOA and maternal transfer to seabird eggs. Continuous monitoring of PFAAs in marine environments of Korea is needed. This study demonstrates that monitoring of seabird eggs is effective for detecting spatial and temporal trends of POPs in the marine environment, and provides insights into emerging POPs such as PFAAs.

Determination of anthropogenic organics in dichlomethane extracts of aerosol particulate matter collected from four different locations in China and Republic of Korea by GC-MS and FTICR-MS.

In this study, the hypothesis that particulate matter in east of Korea peninsula would be significantly influenced by particulate matter originated from east of China was evaluated. To test the hypothesis, water-insoluble compounds in particulate matter samples collected from three different locations in Korea and one in China were characterized by atmospheric pressure photoionization (APPI) coupled with Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) and gas chromatography mass spectrometry (GC-MS). Each sample was collected twice, in winter and in spring. The GC-MS data revealed the presence of high levels of polycyclic aromatic hydrocarbons (PAHs), such as benzo[a]anthracene in the samples from Tianjin, China. The sample collected in the winter from Baengnyeong Island, which is the location in Korea that is geographically closest to the east coast of China was also rich in aromatic compounds. Meanwhile, the APPI FTICR-MS data showed that polycondensed PAHs and two- to four-ring PAHs with long alkyl chains were abundant in the winter samples from Tianjin and Baengnyeong Island which stems most likely from coal combustion in the eastern China. In contrast, nonaromatic compounds with a biogenic origin were mostly observed in samples collected from islands located in eastern (Ulleung Island) and southern (Jeju Island) Korea. A principal component analysis by FTICR-MS and GC-MS also showed that the samples from Tianjin and those collected from Baengnyeong Island in the winter are strongly associated with coal combustion, whereas the other samples are mainly influenced by vehicle emissions. Therefore, it is concluded that the atmosphere from east of China has significant influence over atmosphere in west of Korea peninsula.

Sediment quality assessment combining chemical and biological (non)target analysis.

Aquatic sediments act as a storage for diverse mixtures of organic and inorganic contaminants. Nevertheless, most evaluations of contaminated sediments have been limited to the assessment of concentrations of target compounds and lethal effects on some test species. To identify the organic contaminants causing sub-lethal effects of contaminated sediment, this study combined chemical and biological (non)target analysis involving comprehensive two-dimensional gas chromatography coupled with a time-of-flight Mass Spectrometer (GCxGC/ToF-MS) analysis, embryonic malformation and high-throughput sequencing (RNA-seq) analysis on developing flounder. Polycyclic aromatic hydrocarbons were more abundant in the sediment extract of Yeongil Bay (SEY), while Jinhae Bay (SEJ) was contaminated with a large amount of unidentified chemicals. The unidentified chemicals of SEJ included branched alkanes, oxygenated cycloalkanes, heterogeneous hydrocarbons, and other unknown compounds. Percentage of pericardial edema was the highest in embryonic flounder exposed to SEY. Consistent with the morphogenesis results, the expression level of genes related to heart formation including the nkx2.5 and robo1 was greater in embryonic flounder exposed to SEY. In the analyses of differential gene expression profiles (cutoff P < 0.05), by RNA-seq, embryos exposed to SEJ showed changes related to cell differentiation, cell part morphogenesis, neurogenesis, and neuron development. Genes related to neurogenesis and positive regulation of molecular functions variated significantly in embryos exposed to SEY. These results demonstrated the advantages of combining target and non-target analysis to accurately evaluate the major chemical groups causing sediment toxicity. Therefore, this work provided a useful approach to tracking and revealing the causes of toxic effects and identifying potential toxic mechanisms.

Phenotypic and transcriptomic responses of the rotifer Brachionus koreanus by single and combined exposures to nano-sized microplastics and water-accommodated fractions of crude oil.

Sorption of organic pollutants on microplastics can be an alternative uptake route for organic pollutants in aquatic organisms. To assess the combined effects of microplastics and organic pollutants, we employed phenotypic and transcriptomic analyses to the responses of the marine rotifer Brachionus koreanus to environmentally relevant concentrations of nano-sized microplastic (0.05 µm), water-accommodated fractions of crude oil, and binary mixtures thereof. Our multigenerational in vivo experiments revealed more than additive effects on population growth of B. koreanus in response to combined exposure, while a single exposure to nano-sized microplastic did not induce observable adverse effects. Synergistic transcriptome deregulation was consistently associated with dramatically higher numbers of differentially expressed genes, and increased gene expression was associated with combined exposure. The majority of synergistic transcriptional alteration was related to metabolism and transcription, with impaired reproduction resulting from energetic reallocation toward adaptation. As further supported by chemistry analysis for polycyclic aromatic hydrocarbons sorption on microplastic, our findings imply that nano-sized microplastics can synergistically mediate the effects of organic pollutants in aquatic organisms.

Development of a portable oil type classifier using laser-induced fluorescence spectrometer coupled with chemometrics.

Due to the recurrent small spills, oil pollution along coastal regions is still a major environmental issue. Standardized oil fingerprinting techniques are useful for oil spill identifications, but time- and resource-consuming. There have been ongoing needs for simple yet rapid approach for field screening of oil spill. Laser induced fluorescence (LIF) technology can be incorporated into a spectrometer, and with the integration of chemometrics can be consolidated as a potentially useful portable oil type classification device. Using a LIF spectrometer, 775 oil spectra were calibrated into supervised classification models and validated with 162 oil spectra. Reliability of the device to accurately remove background emission from fluorescence spectra was verified. Prediction performance and model robustness were further validated by comparison between commonly used classification models such as partial least square discriminant analysis (PLS-DA) and support vector machine-discriminant analysis (SVM-DA). Robustness in both models were comparable with PLS-DA having a lower number of misclassification (PLS-DA: 5.50%, SVM-DA: 13.8%) while SVM-DA having a lower number of unassigned samples (PLS-DA: 10.9%; SVM-DA: 16 1.39%). This study explicitly demonstrated the development of a new convenient and handy device which can be used as part of the screening process for oil spill fingerprinting.

High-throughput screening of oil fingerprint using FT-IR coupled with chemometrics.

An important element of the oil spill emergency response is the ability to rapidly identify the properties of oil spilled. Chemometrics provides large numbers of multivariate analysis tools that allow for more extensive use of data. Fourier transformed infrared spectroscopy coupled with classification and prediction models such as partial least square (PLS) and PLS-DA (discriminant analysis) allows the rapid identification of oil type and characteristics. By searching for the maximum covariance with the variables of interest, PLS allows the visualization of relations between samples and variables. The framework of this study is based on two main steps: The first is classification of oil and the second is prediction of physicochemical properties. Separated into four main categories: crude, light fuel, heavy fuel, and lubricant, spectrums of 92 oils were calibrated to predict the oil type and physicochemical properties of 26 oils. The predictability and robustness of the model was further validated using weathered oil. The classification and prediction models have accuracy of >95%. Most of the PLS models have root mean square error of calibration and prediction ranging from 0.10-3.07 and 0.3-2.8, respectively. External cross validations using weathered oils showed high prediction accuracy (relative standard deviations <5%). By increasing the number of oil type and samples, this approach is a promising method and can be included as part of the oil spill fingerprinting protocols.

Development and Evaluation of Olive Flounder cyp1a1-Luciferase Assay for Effective Detection of CYP1A-Inducing Contaminants in Coastal Sediments.

Flounders have been widely used as indicator species for monitoring the benthic environment of marine coastal regions owing to their habitat and feeding preferences in or on sandy sediments. Here, a single-step, sensitive, specific, and simple luciferase assay was developed, using the olive flounder cyp1a1 gene, for effective detection of CYP1A-inducing contaminants in coastal sediments. The developed cyp1a1-luciferase assay was highly sensitive to the widely used CYP1A inducers 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), benzo[a]pyrene (B[a]P), and 3,3',4,4',5-pentachlorobiphenyl (PCB 126). In the case of TCDD, significant dose-dependent increases in luciferase activity (0.3-300 ng/L) were detected. The assay was more sensitive to PCB 126 than to B[a]P. The assay also involved the highly sensitive expression of luciferase to extracted mixtures of PCBs and polycyclic aromatic hydrocarbons (PAHs) collected from coastal sediments. PCBs were more capable of cyp1a1 induction in the assay system at small doses than PAHs in environmental samples. Using the cyp1a1-luciferase assay along with water or sediment chemistry will certainly aid in diagnosing CYP1A-inducing contaminants in coastal environments.

Handheld UV fluorescence spectrophotometer device for the classification and analysis of petroleum oil samples.

Oil spills can be environmentally devastating and result in unintended economic and social consequences. An important element of the concerted effort to respond to spills includes the ability to rapidly classify and characterize oil spill samples, preferably on-site. An easy-to-use, handheld sensor is developed and demonstrated in this work, capable of classifying oil spills rapidly on-site. Our device uses the computational power and affordability of a Raspberry Pi microcontroller and a Pi camera, coupled with three ultraviolet light emitting diodes (UV-LEDs), a diffraction grating, and collimation slit, in order to collect a large data set of UV fluorescence fingerprints from various oil samples. Based on a 160-sample (in 5x replicates each with slightly varied dilutions) database this platform is able to classify oil samples into four broad categories: crude oil, heavy fuel oil, light fuel oil, and lubricating oil. The device uses principal component analysis (PCA) to reduce spectral dimensionality (1203 features) and support vector machine (SVM) for classification with 95% accuracy. The device is also able to predict some physiochemical properties, specifically saturate, aromatic, resin, and asphaltene percentages (SARA) based off linear relationships between different principal components (PCs) and the percentages of these residues. Sample preparation for our device is also straightforward and appropriate for field deployment, requiring little more than a Pasteur pipette and not being affected by dilution factors. These properties make our device a valuable field-deployable tool for oil sample analysis.

Rapid recovery of coastal environment and ecosystem to the Hebei Spirit oil spill's impact.

The 2007 Hebei Spirit oil spill (HSOS), the largest in the national history, has negatively impacted the entire environment and ecosystem along the west coast of South Korea. Although many studies have reported the damages and impacts from the HSOS, quantitative assessment evaluating the recovery time and status have not been documented. Here, we first address the recovery timeline of the HSOS, by comprehensive analyses of 10-years accumulated data in quantitative manner. Concentrations of residual oils in seawater, sediments, and oysters rapidly dropped to backgrounds in 16, 75, and 33 months, respectively. Also, damaged benthic communities of intertidal and subtidal areas were fully recovered only after ~6 years. The present results collectively indicated unexpectedly fast recovery of the damaged environment and ecosystem from such a huge oil spill. The high tidal mixing (~9 m tidal height) and intensive human cleanup (~1.2 million volunteers) at the initial cleanup period might have contributed to rapid recovery; cf. 4-5 times faster than the Exxon Valdez oil spill. However, potential risk to human health remains unclear. Thus, it is warranted to conduct more in depth epidemiological studies to address chronic health effects associated with the cleanup volunteers as well as the local residents who have been living nearby the oil spill impacted sites.

Environmental significance of lubricant oil: A systematic study of photooxidation and its consequences.

Lubricant (lube) oil discharge from ships has been widely considered as normal "operational consumption", but is now deemed to be oil pollution. Despite the chronic contamination of the marine environment by lube oil, the number of studies related to its environmental impact, characteristics, and toxicity is limited. This study is the first attempt to investigate the environmental fate of lube oil subjected to photooxidation using in situ mesocosms. A tiered approach using thin-layer chromatography-flame ionization detection (TLC-FID), Fourier-transform infrared spectroscopy (FTIR) and gas chromatography-mass spectrometry (GC-MS) demonstrated compositional changes in lube oil and the water-soluble fraction (WSF). Total polycyclic aromatic hydrocarbons (ΣPAHs) in lube oil after 96 h of photooxidation were measured at 79.8 and 41 µg/g in the control (Con) and exposure (Exp) groups, respectively. Meanwhile, the ΣPAHs concentration in WSF after 96 h was very low, at 0.25 and 0.45 µg/L in Con and Exp, respectively. FTIR and GC-MS helped identify bond changes and photoproducts in WSF. A wide range of photoproducts, including carboxylic acids, esters, anhydrides, aldehydes and ketones, were identified in WSF. Toxic effects of WSF in both the Con and Exp groups obtained after 96 h of photooxidation were evaluated on olive flounder (Paralichthys olivaceus) embryos. Morphological defects, especially tail fin fold defects, were found to be significantly elevated in both the Con and Exp groups, with marginally higher frequency in Exp. The results of this study demonstrate the need for further research on lube oil weathering, including monitoring over prolonged periods of time.

Stability of mechanically and chemically dispersed oil: Effect of particle types on oil dispersion.

Oil spill dispersant (OSD) application is one of the preferred cleanup options to cope with oil spills at sea. OSD, in principle, can enhance biodegradation of oil because of its effectiveness in producing relatively small droplets and dispersing them into the water column. Under turbulent conditions, suspended particulate matter (SPM) which are present naturally in the environment can interact with oil to form aggregates known as oil-SPM aggregates (OSA) which also enhances biodegradation of oil. Despite its high dispersion effectiveness, chemically dispersed oil (CDO) has a tendency to resurface with increasing time which decreases the biodegradation potential. Meanwhile, the presence of SPM prevents recoalescence of dispersed oil which can enhance stability of oil droplets. This study focused on the effects of SPM on the dispersion effectiveness and stability of mechanically dispersed oil (MDO) and CDO. Dispersion tests of MDO and CDO extended to 72 h with and without SPM to see the initial effectiveness and the prolonged stability of dispersed oil. In the presence of SPM, the oil dispersed by MDO increased by 14.8-40.7%, while the resurfacing oil by CDO decreased by 8.7-19.4%. Regardless of SPM type, oil dispersion effectiveness and stability of MDO and CDO were significantly increased. Long-term stability test for 3 months showed that stability of OSA increased as the particle size decreased and particle counts increased.

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

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.

Suspended particles enhance biodegradation of oil in sea.

Biodegradation patterns of oil in four distinct phases were compared over a 14-day series of exposures. The dispersibility and stability of oil droplets in the water column were important factors affecting oil biodegradation. Due to the stability of oil droplets with particle interactions, oil-suspended particulate matter aggregates (OSA) showed a five-fold enhancement in biodegradation compared to non-dispersed oil. The reduction of total petroleum hydrocarbons was highest in OSA (51.45%), followed by chemically dispersed oil (33.5%), oil film (21.6%), and water-accommodated fractions (WAF, 14.3%). Polycyclic aromatic hydrocarbon (PAH) profiles and percentage weathering plots showed that reductions in PAHs in WAF, oil film, and chemically dispersed oil were mainly due to evaporation (41.5-69.5%) and only partially due to biodegradation (7.4-16.3%). However, the reduction of PAHs in OSA was driven more by biodegradation (36.8%) than evaporation (29.7%). The strong PAH-particle interactions in OSA inhibited evaporation of PAHs and enhanced microorganism biodegradation in the water column.

Comparative evaluation of bioremediation techniques on oil contaminated sediments in long-term recovery of benthic community health.

While various bioremediation techniques have been widely used at oil spill sites, the in situ efficiency of such techniques on recovering the benthic communities in intertidal areas has not been quantified. Here, the performance of several bioremediation tools such as emulsifiers, multi-enzyme liquid (MEL), microbes, and rice-straw was evaluated by a 90-days semi-field experiment, particularly targeting recovery of benthic community. Temporal efficiency in the removal of sedimentary total petroleum hydrocarbons (TPH), reduction of residual toxicity, and recovery of bacterial diversity, microalgal growth, and benthic production was comprehensively determined. Concentrations of TPH and amphipod mortality for all treatments rapidly decreased within the first 10 days. In addition, the density of bacteria and microphytobenthos generally increased over time for all treatments, indicating recovery in the benthic community health. However, the recovery of some nitrifying bacteria, such as the class Nitrospinia (which are sensitive to oil components) remained incomplete (13-56%) during 90 days. Combination of microbe treatments showed rapid and effective for recovering the benthic community, but after 90 days, all treatments showed high recovery efficiency. Of consideration, the "no action" treatment showed a similar level of recovery to those of microbe and MEL treatments, indicating that the natural recovery process could prevail in certain situations.

Fate of residual oils during remediation activities after the Wu Yi San oil spill.

In this study, the fate of residual oils was investigated during remediation activities for a year after the Wu Yi San oil spill. Microscope observations showed that relatively large amounts of oil-suspended particulate matter aggregate (OSA) were formed. Negatively buoyant OSA was the dominant form (>95%), followed by neutrally (~5%) and positively buoyant (<1%) forms. To elucidate the dominance of negative buoyancy OSA, physicochemical properties of the mineral and residual oils were identified. Chemical analysis showed that the weathering percentage of residual oils was 43.7 ±â€¯2.59%, which was the driving factor for sedimentation of OSA. As the density of oil increased with weathering stages, the density of OSA also increased simultaneously. These results showed that, during mechanical remediation activities, resurfaced residual oils can form negative buoyancy OSA which tends to sink and transfers oil contaminants from intertidal to benthic environments.

A preliminary study on the role of suspended particulate matter in the bioavailability of oil-derived polycyclic aromatic hydrocarbons to oysters.

Suspended particulate matter (SPM) refers to fine-grained materials that are suspended in water columns. By providing a surface for the adsorption of non-polar organic compounds, SPM is a carrier for persistent and toxic contaminants. A wide range of organic pollutants, including polycyclic aromatic hydrocarbons (PAHs), can be adsorbed onto SPM. The formation of particle-associated PAHs can sequentially increase the potential for exposure to and bioaccumulation by organisms. Until recently, most oil exposure studies were performed using freely dissolved and dispersed forms, and therefore the role of SPM in influencing the bioavailability and bioaccumulation of PAHs has not been considered. This study found that SPM influences the bioavailability of petrogenic PAHs in the water column and their potential for accumulation in oysters. SPM significantly enhanced the water column entrainment of petrogenic PAHs, thus increasing the potentials for uptake by exposed organisms. PAHs in the water column was highest from mechanically dispersed oil (MDO; 2.27 µg/mL) ≥ oil-SPM aggregate (OSA; 1.96 µg/mL) > water accommodated fraction (WAF; 0.19 µg/mL) but the percentage of PAHs accumulated in oysters were highest from WAF (18.3%) > MDO (14.2%) > OSA (9.62%). Despite the high water column available PAHs, oysters exposed to SPM-associated oil accumulated PAHs at half the accumulation efficiency compared with those exposed to PAHs without SPM.

Estimating degree of degradation of spilled oils based on relative abundance of aromatic compounds observed by paper spray ionization mass spectrometry.

Paper spray ionization mass spectrometry (PSI-MS) was applied for the first time to study temporal change of photo-oxidized and weathered oils subjected to degradation. PSI is chosen in this study because it is an optimal ionization technique for the analysis of degraded oils with limited sample quantity and prone to salt and particulate contamination. With PSI-MS, quantitative analysis of oils can be successfully performed with as little as 2 µg of oil sample. In addition, oil solutions containing up to 0.05% sodium chloride were successfully analyzed with PSI-MS. In the PSI-MS spectra of photo-degraded oils, the relative abundance of compounds having double equivalence value (DBE) ≥ 5 increased but those with DBE < 5 decreased in number. The summed abundance ratio of compounds having DBE < 5 and DBE ≥ 5 showed a negative exponential correlation with the duration of UV exposure in laboratory experiments. The same trend was observed from spilled oils obtained from the environment. Therefore, this ratio serves as an effective means to estimate the degree of weathering in spilled oils.