Microplastics contaminate organic waste, raising environmental concerns

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A groundbreaking study by Te Whare Wānanga o Waitaha | University of Canterbury (UC) and the Institute of Environmental Science and Research (ESR) has uncovered alarming levels of microplastic contamination in organic wastes and composts applied to land in New Zealand.

The research, published today (15 January) in Water Emerging Contaminants & Nanoplastics, highlights the potential for thousands of microplastic particles per kilogram of organic waste to enter productive soils.

UC Ph.D. candidate Helena Ruffell, who led the study as part of her thesis, analyzed various organic wastes routinely used as fertilizers and soil conditioners or in land remediation. These included biosolids (sewage sludge), vermicompost (worm composting), bulk compost (from curbside collections, large-scale industrial facilities, and small-scale decentralized facilities), and bagged composts from garden centers across New Zealand.

The study detected between 1,100 and 2,700 microplastic particles per kilogram of organic waste.

"Organic wastes are a valuable source of carbon and nutrients for our soils, and diverting these wastes from landfill by applying them onto land is a crucial measure to reduce greenhouse gas emissions and promote the circular economy," says Ruffell, who is due to receive her doctorate in UC's Autumn graduation week in a few months.

"Our findings indicate that these contaminants in organic wastes originate from everyday products such as food packaging, health and beauty products, synthetic textiles, and household goods. These products shed and fragment microplastics, which can then enter wastewater treatment plants and ultimately be released into the environment."

The study also revealed that composts are contaminated with microplastics due to improper disposal of plastics and confusion around biodegradable or compostable plastics.

Despite efforts by councils to prevent plastic contamination in curbside organics collections, conventional and biodegradable plastics such as polylactic acid (PLA) and polybutylene adipate terephthalate (PBAT) were found in mature composts. These plastics had not effectively broken down during the composting process and are likely to accumulate in soils over time.

"Even biodegradable plastics are not breaking down as expected, leading to their accumulation in soils. This raises concerns about the long-term impact of microplastics on soil health and productivity," Ruffell says.

"We urgently need to reduce the use of plastics to prevent microplastic contamination of these valuable organic wastes."

The study, co-supervised by UC Environmental Science professors Sally Gaw and Brett Robinson, and ESR Science Leader Dr. Olga Pantos, underscores the need for further investigation into the potential adverse effects of microplastics in productive soils and calls for improved waste management practices to mitigate a growing environmental issue, Ruffell says.

More information: Helena Ruffell et al, Quantification of microplastics in biowastes including biosolids, compost, and vermicompost destined for land application, Water Emerging Contaminants & Nanoplastics (2025). DOI: 10.20517/wecn.2024.65

Provided by University of Canterbury