Contents lists available at ScienceDirect Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman Review Bio-based remediation of petroleum-contaminated saline soils: Challenges, the current state-of-the-art and future prospects Nayer Azam Khoshkholgh Sima a , Ali Ebadi a,∗ , Narges Reiahisamani a , Behnam Rasekh b a Agricultural Biotechnology Research Institute, Agricultural Research, Education and Extension Organization (AREEO), Karaj, Iran b Microbiology and Biotechnology Research Group, Research Institute of Petroleum Industry, Tehran, Iran ARTICLE INFO Keywords: Assisted-phytoremediation Bioaugmentation Biostimulation Halophyte Remediation complexity Rhizodegradation ABSTRACT Exploiting synergism between plants and microbes offers a potential means of remediating soils contaminated with petroleum hydrocarbons (PHCs). Salinity alters the physicochemical characteristics of soils and suppresses the growth of both plants and soil microbes, so the bioremediation of saline soils requires the use of plants and in microbes which can tolerate salinity. This review focuses on the management of PHC-contaminated saline soils, surveying what is currently known with respect to the potential of halophytes (plants adapted to saline en- vironments) acting in concert with synergistic microbes to degrade PHCs. The priority is to identify optimal combinations of halophyte(s) and the bacteria present as endophytes and/or associated with the rhizosphere, and to determine what are the factors which most strongly affect their viability. 1. Introduction The strong dependence of modern economies on fossil fuel has in- creased the frequency of accidental releases of petroleum hydrocarbons (PHCs) - a mixture of alkanes, aromatic hydrocarbons and nitrogen-, oxygen- and sulfur-containing compounds (Cai et al., 2016; Gao et al., 2013)- into the environment (Fatima et al., 2016). Since prolonged exposure to PHCs has adverse effects on the health of humans, animals and plants (Andreolli et al., 2013), sites which have been contaminated by PHC spillage are in urgent need of remediation. Given that con- ventional approaches to dealing with PHC contamination are typically costly, both in money and environmental terms (Li et al., 2016), the possibility of using bioremediation has been promoted as a cheaper and cleaner decontamination method (Gerhardt et al., 2009; Liu et al., 2014). The approach, in its various forms, including biostimulation, bioaugmentation, phytoremediation and microbe-assisted phytor- emediation, aim to accelerate the natural degradation of organic com- pounds; this depends on an optimal choice of agents of degradation and the provision of a suitable environment which can sustain them (Roy et al., 2018). Because many of the major oil-producing sites are located in arid, semi-arid or coastal areas (Al-Mailem et al., 2014; Ebadi et al., 2017), large-scale PHC contamination occurs most commonly in saline soils. Such soils restrict the growth and metabolic activity of many microbial species (Hua et al., 2010), suppress plant growth (Cai et al., 2016; Robson et al., 2004), decrease the solubility of hydrocarbons and oxygen (Fathepure, 2014; Margesin and Schinner, 2001) and reduce the soil porosity (Nouri et al., 2017). In such environments, therefore, it is essential that any proposed bioremediation agent(s) be salinity tolerant, a trait which is expressed by both some plant species (halophytes) and a number of microbial species; these represent the prime candidates for achieving the detoxification of PHCs from saline soils, particularly when used in tandem (Ebadi et al., 2018; Ribeiro et al., 2014). This review addresses the challenges faced in achieving the bior- emediation of PHC-contaminated saline soils, and describes the current state-of-the-art and future prospects with respect to deploying halo- phytes as bioremediants, in particular by exploiting their synergy with rhizosphere microbes and endophytes. 2. Bioremediation of PHCs Contamination of soils with PHCs is a serious problem (Santos et al., 2011) particularly in coastal and estuarine environments (Beazley et al., 2012; Gomes et al., 2018). Taking advantage of the capacity of plants and/or microbes to detoxify, degrade and/or transform PHCs is seen as the most effective and affordable means of dealing with this problem (Erickson et al., 1992); a number of examples of the deploy- ment of this bioremediation strategy have been reported in the litera- ture, covering both terrestrial and marine ecosystems (Wang et al., https://doi.org/10.1016/j.jenvman.2019.109476 Received 9 May 2019; Received in revised form 17 August 2019; Accepted 25 August 2019 ∗ Corresponding author. Agricultural Biotechnology Research Institute, Agricultural Research, Education and Extension Organization (AREEO), P. O. Box: 31535- 1897, Karaj, Iran. E-mail addresses: ksima@abrii.ac.ir (N.A. Khoshkholgh Sima), a.ebadi@abrii.ac.ir (A. Ebadi), nargesreiahisamani@gmail.com (N. Reiahisamani), rasekhb@ripi.ir (B. Rasekh). Journal of Environmental Management 250 (2019) 109476 0301-4797/ © 2019 Elsevier Ltd. All rights reserved. T