Microplastic abundance in sludge-treated fields: Variance and estimated half-life

• Published in: The Science of the total environment Vol. 922; p. 171394
• Main Authors: Klemmensen, Nanna D.R., Chand, Rupa, Blanco, María S., Vollertsen, Jes
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 20-04-2024
• Subjects: Agriculture; Biosolid; Microplastic; Soil; μ-FTIR imaging; Soil; Agriculture; μ-FTIR imaging; Microplastic; Biosolid
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2024.171394

This study investigated the abundance of microplastic (MP) in agricultural soil fertilised with sludge, assessing the variation in MP count and estimated mass in three long-term field trials treated excessively with sludge in 2003–2012. Ten samples were taken from each of the three fields with concentrations ranging from 2392 to 48,791 counts kg−1, where over 50 % of the MPs were polyester and acrylic. Due to the considerable variation in concentration, the impact of the number of sub-samples on the predicted measured concentration was estimated applying a Monto Carlo simulation approach. Choosing the number of sampling points is a compromise between acceptable sampling error and available resources. The simulations showed an increasingly high risk of obtaining an outlier when taking less than approx. ten subsamples. When ending fertilisation with sludge, the estimated half-life for the MPs measured by counts was approx. 2.5 years, whereas the half-life for the MP estimated mass was approx. 4 years. Hence, smaller particles seemed to degrade and/or migrate elsewhere the fastest.
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•Soil treated long-term with sludge was analysed for MP using μ-FTIR imaging.•The MP count varied by a magnitude of 20 among the 30 sampling points.•The most detected polymer types were polyester and acrylic, comprising over 50 %.•The importance of sampling size was demonstrated with a Monto Carlo simulation.•It was estimated that MP degrade and/or migrate from the fields over time.