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Polyethylene Microplastics Modulate the Copper Adsorption–desorption Processes in Agricultural Soils

Water Air & Soil Pollution 2025
Jonathan Suazo-Hernández, Cecilia Paredes, Lizethly Cáceres-Jensen, Fabio Corradini, Marı́a de la Luz Mora, Humberto Aponte, Pablo Cornejo, Silvia Celletti, Luisella Celi, Antonieta Ruíz

Summary

Batch adsorption experiments showed that adding 1% polyethylene microplastics to two agricultural soils modestly increased copper adsorption capacity while altering desorption behavior in soil-type-dependent ways. This matters because microplastic accumulation in farmland can disrupt heavy metal cycling, potentially increasing bioavailability of toxic metals like copper in crops and the humans and animals that consume them.

Polymers

The accumulation of microplastics (MPs) in terrestrial systems can change the availability of metal(loid)s. The goal of this study was evaluated the effect of 1% (w/w) polyethylene MPs (PE–MPs) on Cu2+ adsorption–desorption processes in two agricultural soils (Andisol: ANDI and Mollisol: MOLL). Batch Cu2+ adsorption–desorption experiments were conducted using AnDI And MOLL soils with and without 1% (w/w) PE–MPs addition. The results revealed, for the very first time, that the adsorption of Cu2+ in both soils with 1% PE–MPs is slightly higher than in the soils without MPs. The adsorption kinetic studies of Cu2+ in soils in the absence And presence of 1% PE–MPs fitted well to the pseudo–second–order model (r2 ≥ 0.940 and ꭓ2 ≤ 14). The Langmuir model described the adsorption isotherms of Cu2+ in both soils in the absence And presence of 1% PE–MPs (r2 ≥ 0.982 and ꭓ2 ≤ 7). According to this model, the maximum adsorption capacity showed the following trend: ANDI + 1% PE–MPs > ANDI > MOLL + 1% PE–MPs > MOLL, reaching values of the order of (mmol kg−1): 51.77 > 48.85 > 39.10 > 37.75, respectively. The Cu2+ desorption percentage showed the following trend MOLL > ANDI + 1% PE–MPs > MOLL + 1% PE–MPs > ANDI, suggesting that Cu2+ desorption from soils by adding 1% PE–MPs was soil type–dependent. This study demonstrated, that PE–MPs could favor the accumulation of Cu2+ in MOLL soils and increase the mobility/availability of Cu2+ in ANDI soils.

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