Macro- and microplastics in composts from municipal solid waste industrial composting Plants in Uganda

Area of Science:

• Environmental Science
• Soil Science
• Polymer Science

Background:

• Organic fertilizers can introduce plastics into the environment.
• Limited data exists on plastic contamination in Sub-Saharan African biowaste composts due to minimal source separation in waste collection.

Purpose of the Study:

• To assess macro- and microplastic contamination in composts from two municipal solid waste composting facilities in Uganda.
• To quantify the plastic load introduced into agricultural soils via this compost.

Main Methods:

• Composts from two Ugandan facilities were sampled monthly over four months.
• Samples were sieved into various size fractions to analyze macroplastics (>5 mm) and microplastics (<5 mm).
• Dominant polymer types and microplastic shapes were identified.

Main Results:

• Composts showed heavy macro- and microplastic contamination, with levels exceeding prior studies.
• Average microplastic concentrations were approximately 49,000 ± 7,000 and 62,000 ± 6,000 items/kg dry weight.
• The 0.212-0.6 mm compost fraction had the highest microplastic contamination; polyethylene and polypropylene were the most common polymers.

Conclusions:

• Ugandan biowaste composts are a significant source of plastic pollution in agricultural soils.
• Plastic input via compost can range from kilograms of macroplastics to billions of microplastic items per hectare.
• Compost quality is influenced by facility operations, feedstock, and local population density.