Investigation on the effect of several parameters involved in the biodegradation of polyethylene (PE) and low-density polyethylene (LDPE) under various seawater environments

Abstract

This work investigates the biodegradation of polyethylene (PE) and low-density polyethylene (LDPE) and the leaching of their harmful additives. Micro/macro-plastics of both types were subjected to different laboratory-controlled conditions for 3 months. Gas Chromatography-Mass Spectroscopy (GC-MS) results revealed that leachate concentrations ranged from 0.40 ± 0.07 μg/L to 96.36 ± 0.11 μg/L. It was concluded that the additives' leaching process was promoted by light. However, light was not the only factor examined; microorganisms, pH, salinity, aeration/mixing and temperature influenced the biodegradation process, too. GC-MS results showed a prodigious impact on the biodegradation process when Pseudomonas aeruginosa was added to the artificial seawater compared to plastics exposed to light/air only. Scanning Electron Microscopy (SEM) micrographs demonstrated a significant alteration in the plastics' morphologies. Similarly, Fourier-Transform Infrared Spectroscopy (FTIR) spectra showed obvious changes in plastics characteristic peaks, especially microplastics. Furthermore, it was shown that PE was more susceptible to degradation/biodegradation than LDPE. Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) findings showed that some toxic metals were present in water samples after experiments, with concentrations above the permissible limits. For instance, bio-augmentation/bio-stimulation experiments showed that the concentrations of Pb, Sr, and Zn were 0.59 mg/L, 70.09 mg/L, and 0.17 mg/L, respectively; values above the permissible limits. It is crucial to emphasise that plastics must be meticulously engineered to avoid environmental and human impacts, originated from their degradation by-products. Furthermore, a holistic approach engaging stakeholders, researchers, policymakers, industries and consumers, is essential to effectively tackle the global challenge of marine plastic pollution.

Keywords: Biodegradation; Halomonas venusta; Leachates; Plastics; Pseudomonas aeruginosa.