Physical and Chemical Oceanography

A detailed field survey was completed, which investigated the origin of the tarmats found on a remote uninhabited island, Ras Rakan Island, located at the northern tip of Qatar. The focus of this study was to determine the possible origin of the tarmats and to assess their environmental risks. Based on the field observational data it was hypothesized that the tarmats found on Ras Rakan Island must have been deposited by (1) a relatively large oil spill, and (2) an old oil spill. The physical observational data collected from the field surveys indicated that the tarmat contamination was widespread. The tarmats found on Umm Tais Island, Al-Ruwais, Al-Ghariyah, and Fuwairit beaches located on the northern tip of Qatar were similar to those found on Ras Rakan Island beaches. Moreover, all the tarmat samples were highly weathered, blackish, asphalt-like materials. The hopane fingerprints of Ras Rakan Island samples were compared to the fingerprints of the tarmat samples collected from four other northern beaches and the data were identical. Therefore, the tarmats found on Ras Rakan Island likely evolved from the residues deposited by a large, regional-scale oil spill event. Moreover, the hopane fingerprints of all the tarmat samples closely matched the fingerprint of the reference crude from Basrah, an Iraqi town located at the border of Kuwait. Furthermore, the tarmat fingerprints were almost identical to the hopane fingerprints of the Kuwaiti crude oils, which were constructed from the literature data. As the source of the 1991 Gulf War oil spill was Kuwaiti crude oil, our results indicate that the tarmats currently present in northern Qatar beaches have been originated from the 1991 Gulf War oil spill event. The PAH dataset showed these tarmats contain several heavy toxic PAHs including chrysenes, benzo(a)pyerene, and benzo(b)fluoranthene, which are known carcinogenic compounds.

The spatial distribution, chemical composition and weathering pattern of tarmat along the west coast of Qatar has been assessed based on the tarmat samples collected from 12 coastal regions. The range of tarmat distribution is 0-104 gm-1 with an average value of 9.25 gm-1. Though the current tarmat level is thirty-fold lesser than that was found during 1993-1997 (average 290 gm-1), the distribution pattern is similar. The prevailing winds and currents might have dominated the surface drifting of floating oil residues towards the NW coast of Qatar. Chemical and structural properties of tarmats were calculated using ATR-FTIR spectral indices (i.e., aliphatic, aromatic, long chain and carbonyl indices) and some of their features are comparable to that of Iranian crude oil asphaltenes. The aromatic compounds of tarmats are lesser in the NW coast than those found in the northern coast. Carbonyl Index values indicate that tarmat samples from the NW coast are highly weathered than those found in the north and SW coasts. The concentration of hydrocarbons (including aliphatic and aromatic) in tarmat can be used to study the ecological risks on sediment associated biota.

WorldView-3 (WV-3) data used to study the spectral behavior of tarmat deposits and maps the occurrences of tarmats found on the coast of Ras Rakan Island of the northern part of the State of Qatar. The study of laboratory spectra of tar materials shows diagnostic absorptions features at 0.6 and 1.1 µm in the visible and near-infrared (VNIR) and 1.52, 1.73, 2.04, and 2.31 µm in the shortwave infrared (SWIR) region. The mapping of deposits using WV-3 data by decorrelation stretch and Linear Spectral Unmixing (LSU) methods discriminated the tarmats, sandy soil vegetation and sabkha features in a different tone. The capability of WV-3 sensor and the potential of image processing methods were confirmed by the mapping of tar occurrences of the Ras Ushayriq and NE of Al Ruwais. The results were verified through field studies and laboratory analyses of field samples.

The spatial distribution, sources and characteristics of ML from 36 locations spread over 12 beaches along the west coast of Qatar have been assessed. A total of 2376 ML items with varying sizes were found with an average abundance of 1.98 items/m2. The order of abundance of ML along the coast was as follows: plastics (71.4%) > metal (9.3%) > glass (5.1%) > paper (4.4%) > fabric (4.0%) > rubber (3.9%) > processed wood (2.0%). Locations in the south and northwest-north part of the study area had significantly higher concentrations of ML. Surprisingly, nearly 47% of the beached polyethylene terephthalate (PET) bottles were derived from the neighboring countries, and most of them were produced in the last 2 years. Moreover, most of the plastic bottles of neighboring countries were drifted by winds (primarily shamal) and currents to the Qatar coast. Gulf circulation provides evidence to the pathways of ML beached on the Qatar coast. Qatar coast can be negatively impacted by ML originating from fishing activities and PET bottles coming from neighboring countries. The regional organization for the protection of the marine environment (ROPME) in the Gulf countries has adapted the UN 2030 agenda for sustainable development goals (SDG) to mitigate the marine litter pollution to help, restore and preserve the region’s natural environment.

The vertical distribution and characterization of microplastics (MPs) in the beach sediments around the Ras Rakan Island, Qatar have been investigated. The vertical distribution of MPs ranged from 0 to 665 particles/kg with maximum abundance at the surface layer (0–5 cm). The counts of MPs were found to be higher in the western and northern parts of the island. The distribution reflects the degree of past and present anthropogenic impact (including plastic production, usage, mismanaged waste and population growth). Pellets were the dominant MPs in the surface layer, whereas fibers were the most frequently observed MPs in the bottom sediments. Polyethylene (PE), polypropylene (PP), and polyamide (PA) were the most abundant polymer types of MPs in the sediments. The winds, currents, waves and nearshore processes are the main influencing factors for the transportation and deposition of MPs in the Gulf. This is the first study reporting the depth-wise variation of MPs in the Gulf region. The results are useful to inform the historical MP pollution trend in the Gulf. The values of MP concentrations in the surface layer of sediments found in the Ras Rakan Island are higher than those found in the Qatar mainland, and other parts of the Gulf region. Therefore, the regular MP pollution monitoring programs and numerical modeling studies are needed in all the remote islands in the Gulf to assess the risk associated with MP on the biota.

Microplastics (MPs) have been identified and reported in environmental matrices from the poles to equator and from atmosphere to deep ocean. Though the usage of Fourier Transform Infrared (FTIR) spectroscopic techniques in MP research has increased tremendously since 2004, there are still some challenges to be overcome in the area of standardizing the operational protocols for identification and quantification. Therefore, we have reviewed and highlighted the recent advances in FTIR (spectroscopy and chemical imaging) techniques that are used to characterize various polymer types of MPs and to trace their fate and transport in different environmental matrices. Attenuated total reflectance (ATR) technique coupled with FTIR spectroscopy is widely used to characterize the large size MPs, whereas smaller MPs require the use of µFTIR coupled with detector, especially, µFTIR coupled with focal plane array detector facilitates a much faster generation of chemical imaging of MPs by simultaneously scanning several thousand spectra within a single measurement. FTIR technique is also used to study the changes in chemical bond structures (hydroxyl, carbonyl groups and carbon-oxygen) of MPs during various weathering process. Moreover, FTIR method is used to understand the ecological effects of ingested MPs and its associated pollutants and biochemical variations at the cellular level. Following criteria are needed to be considered during data processing, evaluation and identification MPs using FTIR spectroscopy: (i) when we compare/ match an unknown spectrum with literature or a commercial spectral library, it is necessary to check the mode of acquisition of FTIR spectra (acquired the same mode or different modes), (ii) the spectral change caused by weathering and aging, when comparing or matching with the spectral library and (iii) desirable substrate to be used to reduce the spectral interference. Standardization of chemometric techniques, decrease in data processing time, better file handling capabilities of systems are expected to improve FTIR analysis in MP pollution research. Since identification of MP particles < 10 µm using FTIR technique is a challenging task, development of novel additional accessories or proper combination use of existing techniques is needed for future MP research.