Microplastics - An emerging contaminants for algae. Critical review and perspectives

In recent decades, micro- and nanoplastics (MNPs) became persistent contaminants of emerging concern to the environment. These xenobiotic are found in all components of environment, including living organisms. Ubiquitous contamination of aquatic ecosystems with these pollutants is studied worldwide. In aquatic ecosystems, algae are important primary producers providing nutrients for a wide range of species, so they play a fundamental role in maintaining the balance of the marine ecosystem. Thus, the toxic effect of pollutants on algae can have a negative impact on organisms at higher trophic levels. The microplastic toxic effect on algae is studied by many researches, leading to many different conclusions due to different experimental designs. The polymer type is an important parameter, as it influences the growth rate, the photosynthetic pigments content, and the oxidative stress. Polystyrene is considered more toxic than other types of microplastics. Studies show that plastics of a smaller size and with a positive surface charge have a higher toxic effect on algae. MNPs toxicity to algae strongly depends on their concentration, and becomes more severe as its level increase. Moreover, size and concentration of plastic particles influence changes in reactive oxygen species and the enzymatic antioxidant activity. MNPs are also a vector for other environmental pollutants. Effects of pollutant-MNPs complexes are more often found to be antagonistic than synergetic, in consequence of toxic substance adsorption on the MNPs surface and their lower bioavailability to algae. The aim of this review was to summarize effects and impacts of microplastics and coexisting pollutants on algal populations, on the basis of currently available literature.