Raw Cork Outperforms Activated Carbon Rivals in Sweeping Estrogens from Water

In a finding that could reshape how water utilities think about low-cost filtration materials, researchers in Portugal and Brazil have shown that ordinary, untreated cork waste from the wine and construction industries can outperform its own carbonized, engineered versions at stripping endocrine-disrupting estrogens from contaminated water. The study, published in Environmental Science and Pollution Research, tackled one of the most stubborn categories of aquatic micropollutants: the natural hormones estrone (E1) and 17β-estradiol (E2), together with the synthetic contraceptive compound 17α-ethinylestradiol (EE2). All three are notorious for interfering with the hormonal systems of fish and other aquatic organisms at vanishingly small concentrations, and all three frequently coexist in the same wastewater streams, where they compete for whatever removal technology is thrown at them.

The research team, led by Bruno M. Exposto of the Polytechnic University of Bragança in Portugal, working with colleagues at the Federal University of Technology of Paraná in Brazil, took a deliberately counterintuitive approach. Rather than assuming that more processing means better performance, they compared raw, in-natura cork with pre- and post-carbonized derivatives of both cork and industrial almond shell residues. The results upended expectations: thermal activation through carbonization proved ineffective, while the humble raw cork, designated CiN in the study, delivered the best overall performance. At 25 degrees Celsius and a modest adsorbent dosage of 1.0 gram per liter, raw cork achieved a cumulative mean removal efficiency of 66.1 percent across the three estrogens simultaneously present in solution.

The numbers behind that headline figure reveal how the three hormones behaved when forced to compete for the same binding sites. The maximum experimental uptake capacities were 3.82 milligrams per gram for estrone, 3.75 milligrams per gram for 17β-estradiol, and a striking 7.23 milligrams per gram for the synthetic estrogen EE2, yielding a combined capacity of 14.79 milligrams per gram. That EE2, the artificial compound used in oral contraceptives, captured nearly twice the capacity of either natural hormone is one of the study’s most consequential observations, and the authors traced it to the molecule’s higher hydrophobicity and a lower activation energy barrier for its uptake. In a real wastewater matrix, where these compounds arrive together rather than one at a time, such competitive dynamics determine whether a treatment actually works.

Understanding the speed and shape of the uptake process was central to the work. The kinetic profiles of all three estrogens were accurately captured by the pseudo-second-order model, a mathematical framework that assumes the rate-limiting step involves chemical interactions between the adsorbate and the binding sites rather than simple diffusion-limited filling. That model predicted an equilibrium time of 440 minutes at 25 degrees Celsius, meaning the system needs roughly seven and a half hours to settle into its final partitioning between water and cork. For engineers designing contact tanks or packed-bed filters, that timescale matters: it defines how long contaminated water must linger against the material before the bulk of the hormone load has been transferred to the solid phase.

Equally important was the equilibrium modeling. Because the three estrogens compete, single-solute isotherm models, which describe one pollutant at a time, cannot capture reality. The team therefore applied the Sheindorf–Rebuhn–Sheintuch (SRS) multicomponent isotherm model, an extension of classical adsorption theory that explicitly accounts for competition between species sharing the same surface. The SRS model successfully simulated the competitive equilibrium data, providing a quantitative handle on how strongly each hormone suppresses the uptake of the others. This kind of validated multicomponent framework is rare and valuable, because most published adsorption studies report only single-contaminant results that dramatically overstate real-world performance.

The researchers also probed how acidity and alkalinity govern the process, and the answer was unambiguous. Highly alkaline media, at pH values of 12 or above, caused a significant decline in uptake capacity, an effect the authors attribute to electrostatic repulsion. At such extreme pH, the ionization states of the estrogen molecules and the cork surface change in ways that make the hormone and the adsorbent repel rather than attract each other. For practical applications, this finding brackets the operating window: the material performs best under the near-neutral conditions typical of most natural and treated waters, but strongly caustic environments would undermine it.

Thermodynamic analysis added another layer of mechanistic clarity. The sequestration process was confirmed to be spontaneous, with a negative standard Gibbs free energy change; exothermic, with a negative standard enthalpy change, meaning it releases heat and proceeds more readily at lower temperatures; and entropically favorable at the solid–liquid interface, with a positive standard entropy change. Taken together, these signatures describe a process that does not need to be driven by external energy input, a property that bodes well for low-cost, passive deployment in treatment trains, particularly in regions where sophisticated infrastructure or reagent supply chains are lacking.

Perhaps the deepest contribution of the study lies in its mechanism analysis. By combining kinetic, thermodynamic, and isotherm evidence, the authors identified a synergistic interplay between two uptake modes. The first is physisorption via pore filling, in which hormone molecules physically lodge inside the porous architecture of the cork. The second, and apparently the more decisive, is chemisorption governed by p-electron donor–acceptor interactions and hydrogen bonding networks. In these interactions, the electron-rich aromatic rings of the estrogen molecules engage with complementary electron-accepting or donating sites on the cork surface, while hydroxyl and carbonyl groups on both partners form hydrogen bonds that lock the hormones in place. Crucially, the team concluded that surface chemistry can play a more decisive role than texturized porosity in sequestering endocrine-disrupting chemicals, a conclusion that directly challenges the industry’s long-standing fixation on maximizing surface area through energy-intensive activation.

That conclusion carries real economic and environmental weight. Conventional activated carbon remains the workhorse adsorbent for micropollutant removal, but its production demands high-temperature processing and, often, chemical activation, both of which carry substantial carbon and cost footprints. Cork and almond shells, by contrast, are abundant agricultural and industrial byproducts. Portugal is among the world’s leading cork producers, and almond processing generates mountains of shell waste annually; the study’s materials were supplied by the companies Amendouro and Corticeira Amorim, underscoring the industrial relevance of the feedstocks. Converting these residues into an effective water-treatment medium without any carbonization step means the adsorbent arrives with a fraction of the embedded energy of conventional alternatives, and the waste stream becomes a resource rather than a disposal problem.

The broader context makes the work timely. Steroid estrogens are on the European Union’s watch list of substances of concern for water intended for human consumption, and monitoring studies across European rivers, including Portuguese estuaries such as the Douro and the Mira, have repeatedly detected estrogenic compounds at biologically active levels. Exposure to these chemicals has been linked to feminization of fish populations and a range of endocrine effects in wildlife, and they resist many conventional treatment steps such as coagulation and standard chlorination. Adsorption onto bio-based materials has emerged as one of the most promising remediation routes, but the field has lacked rigorous multicomponent studies that reflect the competitive reality of mixed contaminants. By delivering validated kinetics, a working multicomponent isotherm model, a full thermodynamic picture, and a coherent mechanistic narrative, all anchored in a material that requires no activation at all, the Bragança and Paraná team has provided both a practical candidate technology and a conceptual correction to the field: when it comes to capturing endocrine disruptors from water, what is on the surface of a sustainable residue may matter far more than how many pores it contains.

Subject of Research: Competitive adsorption of steroid estrogens from water using sustainable cork and almond-shell residues

Article Title: Competitive adsorption of natural and synthetic estrogens onto sustainable almond-shell and cork residues: kinetics, multi-component isotherms, and mechanism analysis

Article References: Exposto, B. M., Gomes, M. C. S., de Menezes, M. L., Brito, P., Queiroz, A., & Ribeiro, A. E. (2026). Competitive adsorption of natural and synthetic estrogens onto sustainable almond-shell and cork residues: kinetics, multi-component isotherms, and mechanism analysis. Environmental Science and Pollution Research. https://doi.org/10.1007/s11356-026-38277-8

Image Credits: AI Generated

DOI: 10.1007/s11356-026-38277-8

Keywords: estrogens, cork, almond shell, adsorption, endocrine-disrupting chemicals, water remediation, multicomponent isotherms, Sheindorf–Rebuhn–Sheintuch model, biomass valorization, p-electron donor–acceptor interactions, hydrogen bonding, wastewater treatment