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Background The use of agricultural waste as a low-cost adsorbent for the removal of hazardous methylene blue (MB) from aqueous solution was investigated. In this research, the potentiality of using black nano olive stones (black NOS) and green nano olive stones (green NOS) for MB adsorption was conducted. Methods Various remediation parameters such as initial MB concentration, pH, and temperature were investigated. Thermodynamic study was carried out to determine the homogeneity of the adsorbent and spontaneity of the adsorption process. Different physical and chemical characterizations were studied using scanning electron microscopy (SEM), Fourier transform infrared (FTIR), Brunauer-Emmett-Teller (BET) surface area, pore radius and pore volume. Results It was found that NOS exhibits an acidic nature, however the highest MB removal efficiency was recorded at pH 10; reaching up to 71%. The negative value of the heat of the adsorption process (ΔH°) indicated the reaction followed an exothermic pathway while the negative value of Gibbs adsorption (ΔG°) further suggested its spontaneous nature. The results indicated that the Freundlich model described well the adsorption process with 99.5% correlation coefficient for green NOS. FTIR was used to analyze functional groups on the adsorbents' surfaces that could play vital roles in the remediation process. SEM analysis revealed that the adsorbents comprised of abundant spherical deep cavities and porous nature. Conclusion The result obtained successfully demonstrated the potential of using black and green NOS as suitable adsorbents for the removal of MB from water.

The Exclusive Economic Zone (EEZ) of Qatar is affected by extreme dust and extensive industrialization, making it an ideal location to examine influences of coastal processes on biological activity, which greatly affects marine biogeochemical cycling. In this study, the influence of dust on the trace element composition of plankton and how distance from shore effects elemental concentrations in marine plankton was investigated. Samples were collected using net tows with mesh sizes of 50 (bulkplankton) and 200 (zooplankton) mm size-fractions in 2012 and 2014 to examine temporal and spatial variabilities. The samples were strong acid digested and analyzed using ICP-OES. Trace metal clean techniques were used. The biogenic concentrations of trace metals were determined by correcting the bulk analyses for the lithogenic contribution using aluminum content of Qatari dust as a lithogenic tracer. The relative trace metal composition of plankton from EEZ of Qatar is Fe > Zn ≈ Cu > V ≈ Ni ≈ Cr ≈ As ≈ Mo > Cd ≈ Co. Small and large size planktonic compositions were similar, except for Ba, Mn, Pb, Mo which were higher in zooplankton than bulkplankton. It was not clear if the variability was due to differences in biology, proximity to the coast or interannual effects. The geochemical and statistical analysis suggested that the concentrations of Al, Fe, Cr, Co, Mn, Ni, Pb, Li in net-tow plankton samples were mostly of lithogenic (dust) and Cd, Cu, Mo, Zn, Ca are most likely of biogenic/anthropogenic origin. The excess concentrations relative to average dust from Qatar for most elements (except Cd) decreased with distance from shore. This may be due to contamination or uncertainties with the lithogenic correction or due to our sampling locations in a marginal sea, dominated by dust input. This is an aspect of this study that warrants more research.

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The ubiquitous microplastic (MP) pollution is an emerging environmental issue in the marine environment. In this study, historical accumulation trends of MPs in the beach sediments around the Ras Rakan Island of Qatar have been established. The vertical distribution of MPs ranged from 0 to 665 particles/kg with maximum abundance at the surface layer (0–5 cm). Pellets were the dominant type of MPs in the surface sediments, whereas fibers were dominant in the bottom sediments. The polymer composition of MPs was identified using Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy. Polyethylene (PE), polypropylene (PP), polyamide (PA), polyethylene terephthalate (PET), polyvinyl chloride (PVC) and Polystyrene (EPS) were the abundant polymers present in the sediments. High MP concentrations were found in the western and northern parts of the island. The prevailing winds, waves, tides and currents are the forces responsible for the distribution and transport of MPs from the offshore to the island and further to vertical re-distribution as time progresses. The level of MP pollution along the Coast of Ras Rakan Island was higher than that found on the coast of mainland Qatar. This informs that remote islands should also be considered for MP pollution monitoring to assess the risk associated with MP on the biota.