Microplastics as carriers of toxic pollutants: Source, transport, and toxicological effects.

Microplastic pollution has emerged as a new environmental concern due to our reliance on plastic. Recent years have seen an upward trend in scholarly interest in the topic of microplastics carrying contaminants; however, the available review studies have largely focused on specific aspects of this issue, such as sorption, transport, and toxicological effects. Consequently, this review synthesizes the state-of-the-art knowledge on these topics by presenting key findings to guide better policy action toward microplastic management. Microplastics have been reported to absorb pollutants such as persistent organic pollutants, heavy metals, and antibiotics, leading to their bioaccumulation in marine and terrestrial ecosystems. Hydrophobic interactions are found to be the predominant sorption mechanism, especially for organic pollutants, although electrostatic forces, van der Waals forces, hydrogen bonding, and pi-pi interactions are also noteworthy. This review reveals that physicochemical properties of microplastics, such as size, structure, and functional groups, and environmental compartment properties, such as pH, temperature, and salinity, influence the sorption of pollutants by microplastic. It has been found that microplastics influence the growth and metabolism of organisms. Inadequate methods for collection and analysis of environmental samples, lack of replication of real-world settings in laboratories, and a lack of understanding of the sorption mechanism and toxicity of microplastics impede current microplastic research. Therefore, future research should focus on filling in these knowledge gaps.

Waste plastics pyrolytic oil is a source of diesel fuel: A recent review on diesel engine performance, emissions, and combustion characteristics.

Most waste plastics can be converted into automobile fuel through the pyrolysis process. Plastic pyrolysis oil (PPO) has a heating value comparable with commercial diesel. The properties of PPOs depend on parameters such the plastic and pyrolysis reactor types, temperature, reaction time, heating rate, etc. This study reviews the performance, emissions, and combustion characteristic of diesel engines fuelled with neat PPO, PPO and diesel blends, and PPO with oxygenated additives. PPO has higher viscosity and density, higher sulphur content, lower flash point, lower cetane index and an unpleasant odour. PPO displays a higher delay in ignition during the premixed combustion phase. The literatures reported that diesel engines can run with PPO without any modification to the engine. This paper reveals that the brake specific fuel consumption can be lowered by 17.88 % by using neat PPO in the engine. Brake thermal efficiency can be reduced by 17.26 % while blends of PPO and diesel are used. Some studies say NOx emission can be reduced up to 63.02 %, however, others indicate that it can be increased up to 44.06 % compared to diesel when PPO is used in engines. The highest reduction in CO2 emission was found to be 47.47 % using blends of PPO and diesel; conversely, the highest increase was documented as 13.04 % when only PPO is used as fuel. In summary, PPO has very high potential as a substitute for commercial diesel fuel through further research and by improving its properties through post-treatment processing such as distillation and hydrotreatment.