Microplastics, which serve as sources and vector transport of organic contaminants in both terrestrial and marine environments, are emerging micropollutants of increasing concerns due to their potential harmful impacts on the environment, biota and human health. Microplastic particles have a higher affinity for hydrophobic organic contaminants due to their high surface area-to-volume ratio, particularly in aqueous conditions. However, recent findings have shown that the concentrations of organic contaminants adsorbed on microplastic surfaces, as well as their fate through vector distribution and ecological risks, are largely influenced by prevailing environmental factors and physicochemical properties in the aquatic environment. Therefore, this review article draws on scientific literature to discuss inherent polymers typically used in plastics and their affinity for different organic contaminants, as well as the compositions, environmental factors, and polymeric properties that influence their variability in sorption capacities. Some of the specific points discussed are (a) an appraisal of microplastic types, composition and their fate and vector transport in the environment; (b) a critical assessment of sorption mechanisms and major polymeric factors influencing organic contaminants-micro (nano) plastics (MNPs) interactions; (c) an evaluation of the sorption capacities of organic chemical contaminants to MNPs in terms of polymeric sorption characteristics including hydrophobicity, Van der Waals forces, π–π bond, electrostatic, and hydrogen bond interactions; and (d) an overview of the sorption mechanisms and dynamics behind microplastics-organic contaminants interactions using kinetic and isothermal models. Furthermore, insights into future areas of research gaps have been highlighted.

Plastic pollution is a fast-rising environmental catastrophe. Microplastics and nanoplastics (MNPs) are ubiquitous components of most aquatic environments, and their burgeoning prevalence is endangering aquatic organisms. Recent studies have documented the entanglement of marine and freshwater biota by plastic litters, particularly ghost fishing gear, resulting in suffocation, drowning, or starving to death. Numerous reports have shown that aquatic organisms readily ingest and accumulate these emerging contaminants in their digestive systems. Given experimental evidence that contaminants-laden MNPs can persist in the gastrointestinal tract for considerable durations, investigations have documented a high probability of lethal and sublethal toxicological effects associated with direct and indirect MNPs ingestions. These include chronic protein modulation, DNA damage, embryotoxicity, gastrointestinal toxicity, genotoxicity, growth inhibition toxicity, histopathotoxicity, liver toxicity, neurotoxicity, oxidative stress, reproductive toxicity, and tissue damage. Today, reports have proven the transfer of MNPs across the aquatic food web to humans. However, the mechanisms of multiple contaminants-laden MNPs-induced toxicities, size-dependent toxicity, and the comprehensive mode-of-action and alterations of digestive, reproductive, and neurological systems’ functionality in marine organisms are still unclear. Thus, this review mainly addresses the prevalence, food web interactions, and toxicity assessment of micro(nano) plastics in marine and freshwater organisms. It summarizes documented studies based on the following broad objectives: (1) the occurrence and prevalence of micro(nano) plastic particles in marine and freshwater environments; (2) the ingestion of MNPs by aquatic biota and the food web exposure routes and bioaccumulation of contaminated MNPs by higher trophic entities; (3) the adsorption and desorption of persistent organic pollutants, metals, and chemical additives on/from micro(nano)plastics; and (4) the probable ecotoxicological effects of micro(nano)plastics ingestion on aquatic biota.

Introduction: The conversion and utilization of agricultural wastes in environmentally friendly processes have transformed these materials into useful rather than waste materials. Aim: This study investigates the adsorption of indigo blue dye from aqueous solution onto coconut shell, a low cost agricultural waste material in a batch process. Materials and Methods: Pulverized coconut shell was chemically modified and characterized using the Fourier Transform Infra Red spectroscopy and Scanning Electron Microscopy. Adsorption process using the chemically modified coconut shell was studied as a function of pH, initial dye concentration, adsorbent dose, and contact time. The adsorption equilibrium data were analyzed with Langmuir, Freundlich and Temkin isotherm models. Results: The results revealed that percentage of the indigo dye adsorbed from aqueous solution varied linearly with the adsorbent dose, concentration and time with maximum percentage dye adsorption of 88.4% at 70 mg dosage, 95.8% at 0.05 mg/L concentration and 90% at 1 hr contact time but varies non-linearly with pH with maximum percentage dye adsorption of 92.9% attained at pH of 5. The adsorption equilibrium data were analyzed with Langmuir, Freundlich and Temkin isotherm models with the Langmuir isotherm having the best fit to the adsorption process with R2 value of 0.998. The experimental data were best described by the pseudo-second order kinetics model. FTIR analyses reveal that the adsorption process was through a chemical interaction of the dye with some functional groups at the surface of the adsorbent Conclusion: The chemically modified coconut shell is an effective adsorbent for the removal of indigo dye from aqueous solution is by chemisorption process with the adsorbent surface energetically homogeneous (n < 1). Keywords: Adsorption, Indigo blue dye, Coconut Shell, Kinetics, Aqueous solution.