Revealing the effect of humic substance compounds on the aged characteristics and release compounds profiles from photodegradation of polyethylene microplastics

Abstract

The aim of this study was to investigate the effect of humic substance compounds (humic acid (HA) and fulvic acid (FA)) on the aged characteristics and release compounds profiles from polyethylene microplastics (PE-MPs). Results showed that HA promoted degree of PE-MPs photodegradation with a higher value of weight loss and oxygen atom and lower average particle size (110 μm), compared with the presence of FA during 15 days of irradiation. Likewise, the needle trap microextraction (HS-NTME) combined with gas chromatography/mass spectrometry (GC/MS) analysis revealed that HA and FA promoted a variety of oxygen-containing products (carboxyl acid, phenols and ketones) and siloxanes additives released from photodegradation of PE-MPs. Moreover, HA was found to have a higher ability to generate free radicals (▪OH and O2–) than FA, which accelerated the photooxidation of PE-MPs and led to the different mechanisms of photodegradation pathway of PE-MPs. These findings not only shed light on how humic substances affect photodegradation process of MPs, but also support further investigation into the possible hazard of MPs when co-existing compounds exist in the aqueous system.

Keywords

• Humic acid
• Fulvic acid
• Microplastics
• Degradation products
• Photooxidation