A team of scientists has discovered that the crystal structure of naturally occurring iron minerals plays a crucial role in breaking down harmful chemical additives released from plastics. The findings could improve predictions of how these pollutants behave in the environment and guide strategies for reducing their long-term risks.
The study, published in Environmental and Biogeochemical Processes, examined how three types of iron oxyhydroxide nanominerals, goethite, akaganeite, and lepidocrocite, catalyze the breakdown of organophosphate esters (OPEs). OPEs are widely used as flame retardants and plasticizers but have been increasingly detected in air, water, and soil. Many of these compounds are known or suspected endocrine disruptors that can interfere with human and animal hormones.
"Plastic additives like OPEs are designed to improve materials but end up as invisible pollutants that persist in the environment," said corresponding author Prof. Chuanjia Jiang from Nankai University. "Our research shows that the tiny details of mineral structure can determine how quickly and efficiently these compounds are broken down."
Using a model compound called p-nitrophenyl phosphate, the researchers tested how efficiently each iron mineral promoted hydrolysis, a reaction that splits chemical bonds with water. The experiments revealed that all three minerals could accelerate OPE degradation under typical environmental conditions, but their effectiveness varied with crystal structure. Lepidocrocite showed the fastest reaction rate, followed by akaganeite and goethite.
Further analysis revealed that the difference arises from two competing factors: how strongly the pollutants attach to the mineral surface and how reactive the surface sites are once adsorption occurs. Akaganeite bound the pollutants most tightly, but lepidocrocite had the most chemically active sites that promoted faster bond breaking. Advanced spectroscopy and computer simulations confirmed that lepidocrocite's surface iron atoms create stronger electric fields that pull electrons from the pollutant's phosphorus atom, making it more vulnerable to attack by water molecules.
"This crystal-dependent behavior explains why some forms of the same mineral can be much more effective catalysts than others," Jiang said. "It also highlights the need to consider nanoscale structure when assessing the environmental fate of pollutants."
Because iron oxides are abundant in soils and sediments, these findings have broad implications for understanding how microplastics and their additives transform over time. As plastics weather into micro- and nanoplastics, their additives can leach out and interact with mineral surfaces, influencing both their degradation rates and potential toxicity. The study's insights into mineral reactivity could help scientists design better remediation materials and refine models of contaminant persistence in natural systems.
The researchers note that in real-world environments, minerals can interact with natural organic matter, ions, or even change their crystal form, which may alter their catalytic abilities. Future work will explore how these complex conditions affect the breakdown of OPEs and other emerging pollutants.
The study was supported by the National Natural Science Foundation of China, the Tianjin Municipal Science and Technology Bureau, and Rice University in the United States. The collaborative team included scientists from Nankai University, Ankang University, and Rice University.
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Journal reference: Pei X, Liang Z, Chen Z, Duan L, Jiang C, et al. 2025. Crystalline phase-dependent hydrolysis of organophosphate esters by iron oxyhydroxides: implications for nanomineral-mediated transformation of plastic additives. Environmental and Biogeochemical Processes 1: e007 https://www.maxapress.com/article/doi/10.48130/ebp-0025-0008
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About the Journal:
Environmental and Biogeochemical Processes is a multidisciplinary platform for communicating advances in fundamental and applied research on the interactions and processes involving the cycling of elements and compounds between the biological, geological, and chemical components of the environment.
