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Mechanisms of microplastic generation from polymer-coated controlled-release fertilizers (PC-CRFs)
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This study investigated how the plastic coatings on slow-release fertilizers break down and release microplastics into soil. Significantly more microplastic particles were released in soil conditions than in water alone, and wet-dry cycles accelerated the breakdown, meaning agricultural soils receiving these fertilizers may be accumulating substantial amounts of microplastic pollution.
Polymer-coated controlled-release fertilizers (PC-CRFs) are valued for nutrient efficiency, but concerns remain about the long-term impacts of their plastic coatings on soil health. This study investigates the physicochemical characteristics of two commercially available PC-CRFs, type A and B, and their changes during nutrient release. Accelerated nutrient release experiments were conducted for 25 d in ultrapure water (free water) and saturated soil with five wet-dry cycles. Total phosphorus and total nitrogen release were measured, with lower concentrations found in soil column effluent compared to water. Additionally, studying microplastic (MP) release from type A PC-CRFs during nutrient release showed that a significantly greater number of MPs were released in the soil column than in water. The results also indicated a preferential migration of smaller MPs to the deeper layers of the soil column. Microscopic pores and cracks were observed through surface morphology analysis, likely caused by osmotic pressure during nutrient release, potentially contributing to MP generation. Mechanical degradation of the type A PC-CRF microcapsules was assessed through surface wear and shear tests to simulate the forces exerted by soil particles and agricultural machinery. Our results showed that longer surface wear duration increased the number of generated MPs, while higher loading in surface wear experiments resulted in a larger median diameter of the MPs.
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Researchers conducted soil incubation experiments simulating five years of continuous application of three polymer-coated controlled-release fertilizers to characterize microplastic generation from their degrading coating films. The study found that the polymer coating type significantly affected both fertilizer release characteristics and microplastic production, with changes in soil nitrogen fractions and electrical conductivity influencing the rate of membrane shell degradation and subsequent plastic particle release.
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Analysis of slow-release fertilisers coated with polymer shells found that these products can release microplastics into agricultural soils as the coatings degrade. Two major manufacturers' products showed varying polymer compositions and differing abilities to adsorb soil contaminants, raising concerns about MP accumulation from fertiliser use.
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Scientists studied how microplastics from fertilizer coatings break down in soil over more than two years, finding that polyethylene degraded the most (nearly 17% weight loss) while producing secondary microplastic fragments and chemical byproducts. Specific bacteria and fungi colonized the plastic surfaces, forming biofilms that helped break down the material. This research shows that coated fertilizers are a direct source of microplastic pollution in farmland, where the breakdown products could enter crops and groundwater.
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Researchers digging up soil samples found tiny plastic coatings left behind from slow-release fertilizers, the same kind used on farms and lawns, building up in the ground. These plastic bits don't just disappear after the fertilizer does its job; they stick around in the soil, which matters because that's the same dirt growing our food and potentially breaking down into microplastics that can work their way into water and crops we eat.
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This review examines controlled-release fertilizers, which are designed to deliver nutrients to plants gradually, and finds that many use synthetic polymer coatings that can leave microplastic residues in soil. The authors highlight biopolymers made from natural materials like chitosan, cellulose, and starch as promising alternatives that can biodegrade without contributing to plastic pollution. The shift toward biodegradable fertilizer coatings could help reduce a significant but often overlooked source of agricultural microplastic contamination.
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