PET-microplastics as a vector for polycyclic aromatic hydrocarbons in a simulated plant rhizosphere zone

The persistence of microplastics (MPs) in the environment is seen as a global hazard. Typically, polycyclic aromatic hydrocarbons (PAHs) and MPs are classified into two separate pollutant groups and the relationships between the two stressors are poorly understood. Wheat is the most important grain in the human food chain. Thus, investigating adsorption and desorption capacity of polyethylene terephthalate (PET), when exposed to PAHs in irrigation water and wheat rhizosphere zone is very important. Adsorption experiments based on Langmuir or Freundlich models were performed to specify the adsorption capacity of PET particles for Naphthalene and Phenanthrene. Besides, desorption experiments were conducted to determine whether MPs in the rhizosphere zone could release previously sorbed Naphthalene and Phenanthrene. For desorption experiments, three scenarios were considered according to different environmental stresses. The results show that, when PET particles were exposed to Naphthalene (18 μg/l) and Phenanthrene (0.11 μg/l), they adsorbed 17.44 and 0.03 μg/l of Naphthalene and Phenanthrene, respectively. PET particles also desorbed the same concentration in all three scenarios (root exudates) for Naphthalene (on average 3.775 μg/l) and Phenanthrene (on average 0.00875 μg/l). This indicates that the change in root exudates content does not affect the desorption capacity of PET for PAHs contaminants. Generally, the results of this study, suggest that PET particles absorbed 96.89% of Naphthalene and 27.27% of Phenanthrene and desorbed 21.65% of adsorbed Naphthalene and 29.17% of adsorbed Phenanthrene in the root exudate. The results show that PET particles can act as a carrier and transport PAHs from any source to the rhizosphere zone.