Contents lists available at ScienceDirect Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul Review Microplastic particles in the Persian/Arabian Gulf – A review on sampling and identification Saif Uddin a, ⁎ , Scott W. Fowler b,1 , Talat Saeed a a Environment and Life Sciences Research Center, Kuwait Institute for Scientific Research, Kuwait b School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook, NY 11794-5000, USA ARTICLE INFO Keywords: Microplastics Seawater Sediments Biota PET Nylon ABSTRACT Microplastics are ubiquitous, persistent pollutants that are reported in abundance within the marine environ- ment. Their presence in seawater and marine sediments poses a legitimate environmental and ecological concern for toxicity and food chain transfer via marine organisms. Their capability for sorption of other hydrophobic contaminants and the inability of the wastewater treatment plants to completely remove them pose additional risks. This review highlights the methodologies for sampling, sample preparation, and identification used in the Persian/Arabian Gulf region, which is possibly one of the least studied marginal seas with only sixteen papers published on microplastics. The review highlights the several orders of magnitude variations in microplastic concentrations among different studies; e.g. in seawater, only 12 microplastic particles were reported from 40 transects of one km length in Kuwait to 0.71 microplastics m -3 in Qatar. Concentrations in beach sediments also show the significant difference between the northern and southern Gulf coasts, with 13 particles in 24 samples reported in Qatar, and 15 particles within 44 samples across Kuwait, to 3252 ± 2766 particles m -2 from Bandar Abbas, Iran. The biota samples also show similar variances, with only three particles identified from 87 gut samples in Kuwait to 828 particles in 58 samples that include 46 fish and 12 shrimps from Iran. Some extremely high concentrations in biota are also reported from Iran, with concentrations as high as 0.251 parti- cles g -1 of muscle and 0.931 particles g -1 in gills. It is evident that there is no consensus in the Gulf region on the sampling techniques (mesh size of plankton nets and sieves), use of fluidization solutions and very different units used in data reporting such as particles m -3 and particles m -2 in water samples. In sediments units like particles g -1 and particles m -2 have been used, and for biota it is the number of particles present in the sample, while others have quantified data as particles g -1 of tissue. Considering the higher densities of PET, PVC, nylon and polyester than seawater, they are likely to migrate downwards into marine sediments, a transfer process that has not been studied in detail. Thus the review underscores the need to adopt harmonized protocols for mi- croplastic studies in the region, and identifies certain aspects of microplastics that require further study. 1. Introduction Ever since the term ‘microplastic’ was introduced by Thompson et al. (2004), it has generated a great deal of scientific interest due to its abundance, omnipresence and potential impact on marine biota. The scale of the microplastics' issue can be comprehended from the fact that 4.85 trillion particles of a size between 0.33 and 4.75 mm are floating in the world ocean with an approximate mass of 35,540 tons (Eriksen et al., 2014). A significant portion of these microplastic particles lies within the Indian Ocean region, i.e., 1.204 trillion particles with an estimated weight of 7470 tons (Eriksen et al., 2014). Studies have suggested even higher microplastic densities exist in marginal seas and along densely populated coastlines (Derraik, 2002; Eriksen et al., 2014; Seltenrich, 2015). Until recently there were no standardized meth- odologies for sampling and identification of microplastics, and a few studies have proposed adopting harmonized methodologies (Bessa et al., 2019; Frias et al., 2019; Frias et al., 2018; Masura et al., 2015; OSPAR, 2010; Shim et al., 2017; Van Cauwenberghe et al., 2015; Zhang et al., 2019). One such effort of standardization of methodology through profound comparison and evaluation of different approaches was the JPI-Oceans BASEMAN project, an international collaborative study (Bessa et al., 2019; Frias et al., 2018). Although the focus of the project was enabling comparison between various studies in Europe, those protocols are empirical and can be extended globally. https://doi.org/10.1016/j.marpolbul.2020.111100 Received 16 February 2020; Received in revised form 22 March 2020; Accepted 22 March 2020 ⁎ Corresponding author. E-mail address: sdin@kisr.edu.kw (S. Uddin). 1 Present address: Institute Bobby, 8 Allée des Orangers, Cap d'Ail 06320, France. Marine Pollution Bulletin 154 (2020) 111100 Available online 27 March 2020 0025-326X/ © 2020 Elsevier Ltd. All rights reserved. T