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Microplastics in Biosolids: Analysis of an Exposure Route of Microplastics to Agricultural Soils

A bundle of various synthetic fibres found within a biosolid sample.

In an attempt to increase the recycling of urban and rural waste, wastewater treatment plants (WWTPs) have developed processes that turn raw sewage sludge into biosolids. Biosolids are used as a field amendment for agricultural fields as they are high in nutrients and organic material. The use of biosolids as a field amendment has become widespread in both Europe and North America. It is estimated that in Canada, WWTPs generate more than 660,000 dry tonnes of biosolids annually.

A PVC fragment found within a biosolid sample

WWTPs have been identified as a source of microplastic contamination to the environment. Plastic particles accumulate at WWTPs through domestic wastewater, stormwater, landfill, and industrial effluents. The majority or microplastics that are discharged from WWTPs are synthetic fibres from clothing and plastic particles primarily from personal care products. Depending on the infrastructure of the WWTP, it has been documented that 7.5% - 99% of microplastics present within influent are deposited in biosolids. With the widespread use of biosolids, it can be seen that they are a significant source of microplastics to terrestrial ecosystems. It is estimated that in North America alone, up to 300,000 tonnes of microplastics are being introduced to the environment via the spreading of biosolids

A microplastic with a hexagonal shape found within a biosolid sample

Quantifying and characterizing the microplastic content of biosolids will be crucial for determining the environmental exposure of microplastics to the biota living within the agricultural soils that they're spread on. This data, as well as data from toxicity testing on soil biota, will aid in performing an assessment of the risk that microplastics have on the ecosystems within agricultural soils.

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