An Overlooked Entry Pathway of Microplastics into Agricultural Soils from Application of Sludge-Based Fertilizers

Abstract

The widespread application of sewage sludge produced from wastewater treatment plants for agricultural use has been regarded as a primary source of microplastics (MPs) into soils. However, little is known regarding MPs in sludge-based fertilizers and their relevant fate in soils as being applied in agriculture. We comprehensively investigated the abundance, polymer size, type, and morphology of MPs in dewatered sludge, sewage sludge composts, sludge-based fertilizer-amended soils, and earthworms by stereoscopy and micro Fourier transform infrared (μ-FTIR) spectrometry methods. The results clearly showed that the quantity of MPs in soils exhibited a close correlation with the application rate of sludge-based fertilizers. The total abundances of MPs were 545.9 and 87.6 items/kg in soils after annual amendment with 30 (field A) and 15 t/ha (field B) of sludge composts, which is significantly higher than that without compost application (field C, 5.0 items/kg). Correspondingly, MPs were found in earthworms with low quantities of 1.8 and 0.4 items/ individual in fields A and B, respectively, while no MP was detected in field C. We speculate that sludge composts may act as a vehicle of MPs into soils and then enter soil biota and in turn influence the spread of MPs in the environment.

Presence and fate of microplastics in the water sources: focus on the role of wastewater and drinking water treatment plants

“…Information on the effect of the sludge treatment line on MPs is clearly scant and not directly comparable when considering the different sampling and analytical procedures. It is clear how treated sludge could represent another source of MPs to the environment: there are indeed studies that demonstrated how the application of sludge in agriculture and sludge-based fertilizers caused MPs accumulation in soil [97][98][99].…”

Land Application of Biosolids in Europe: Possibilities, Con-Straints and Future Perspectives

“…Sludge applications on soils resulted in increased MP counts in soil samples [14]. However, studies on the fate and spread of MPs in soils after being amended with sludge-based products are lacking [43], thus the true scale of the problem has yet to be assessed. Whether the presence of MPs in agricultural soils has implications for the economy and environmental health is already under discussion [38].…”

Transport and transformation of microplastics and nanoplastics in the soil environment: A critical review

“…The MPs/NPs will enter the soil through sewage irrigation. Studies have shown that the content of MPs/NPs in soil samples is generally less than 320 n kg −1 , but the content of MPs/NPs in soil irrigated with sewage is higher than 7,000 n kg −1 (Zhang et al, 2020a;Zhang et al, 2020a). The concentrations of MPs/NPs in sewage in Ireland, Germany, Russia and Sweden are 4,200-15,800 n m −3 , 1,000-24,000 n m −3 , 627,000 n m −3 and 15,000 n m −3 , respectively (Magnusson & Norén, 2014;Mahon et al, 2017;Mintenig et al, 2017;Talvitie & Heinonen, 2014 (Gao et al, 2020).…”

“…). Zhang et al (2020a), Zhang et al (2020b) Composition and structure Different compositions of MPs release different types of organic pollutants. PS can release monomeric styrene, and PC has the potential to leach bisphenol A.…”