Biodegradable microplastics adsorb more Cd than conventional microplastic and biofilms enhance their adsorption

Area of Science:

• Environmental Science
• Materials Science
• Soil Science

Background:

• Conventional polyethylene (PE) mulch contributes to plastic pollution and soil microplastic (MP) accumulation.
• Biodegradable polylactic acid (PLA) mulch is a potential alternative to reduce environmental plastic burden.
• Soil contaminants like cadmium (Cd) can adsorb onto MPs, influencing their environmental fate.

Purpose of the Study:

• To investigate the effect of natural weathering and biofilm formation on the adsorption properties of PLA and PE microplastics (MPs).
• To compare the cadmium (Cd) adsorption capacity of pristine and weathered PLA and PE MPs, with and without biofilms.

Main Methods:

• PLA and PE mulches were exposed outdoors for 16 months to simulate natural weathering.
• Microplastics (MPs) were generated from weathered and pristine mulches.
• Biofilm presence and chemical changes (oxygen-containing functional groups) on MPs were analyzed.
• Cadmium (Cd) adsorption experiments were conducted on MPs with and without biofilms.

Main Results:

• Biofilms developed on weathered PLA and PE MPs.
• Weathered MPs showed increased oxygen-containing functional groups.
• Pristine PLA MPs exhibited higher Cd adsorption than pristine PE MPs due to chemistry, not surface area.
• Weathered MPs adsorbed more Cd, but this increase was attributed to the biofilm, as adsorption returned to pristine levels after biofilm removal.

Conclusions:

• Biofilm formation on weathered microplastics (MPs) significantly enhances the adsorption of cadmium (Cd).
• The chemical changes on the plastic surface due to weathering play a lesser role in Cd adsorption compared to the biofilm.
• Understanding biofilm-MP interactions is crucial for assessing the environmental impact of microplastics in soil.