Superfund Research Program
Mitigation of Chemical and Mixture Effects Through Broad-Acting Sorbents
- Project Summary
The Novel Broad-Acting Sorption Materials for Reducing Bioavailability of Contaminants Project has focused on the development of therapeutic enterosorbents for hazardous Superfund chemicals including: PAHs (benzo[a]pyrene, pyrene, benzo[b]fluoranthene, and naphthalene), industrial solvents (phenol, benzene, toluene, xylene), pesticides (lindane, linuron, diazinon, aldicarb, dinitrophenol, atrazine, 2,4-D, paraquat, glyphosate, AMPA, pentachlorophenol, trichlorophenol, DDT, dieldrin, chlorpyrifos, and trifluralin), PCBs and Aroclors, PFAS, plasticizers (phthalates and bisphenols), and heavy metals (lead, mercury, cadmium, and arsenic). A variety of sorbent materials have been characterized, including purified clays (montmorillonite and talc), amended montmorillonite clays (with carnitine, choline, lecithin, and chlorophyllin), processed sorbent materials (APMs), natural products (chitosan, barley, grass, and psyllium) and activated carbons. To characterize and test the binding efficacy of newly developed sorbents, the research team have conducted equilibrium isothermal analyses and dosimetry studies to derive binding parameters and gain insight into: 1) surface capacities and affinities, 2) potential mechanisms of sorption, 3) thermodynamics of toxin/surface interactions, and 4) estimated dose of sorbent required to maintain chemical threshold limits. Researchers have also used Hydra vulgaris and oysters, in culture, to confirm the safety and predict the efficacy of sorbents. The results showed that APMs and carnitine-/choline-amended montmorillonite clays significantly increased the sorption ability of most materials tested compared to the parent clays. In some cases, APMs were as effective as activated carbon for toxin sorption, which may be due to the enhanced surface area and porosity of both materials. The project-to-field pathway for the development of edible sorbents for first responders, frontline personnel, and vulnerable populations during the course of these studies has been firmly established. Stakeholders for the Project are: 1) TxESI, Inc. (in a partnership with TAMU on APM technology transfer), 2) US Silica, Inc. (manufacturing partner for all APM products), and 3) Halliburton, Inc. (collaboration on toxicant binders and sharing unique clay-based materials). Following a provisional patent for this technology, a worldwide exclusive license was granted to TxESI, Inc. The PCT Notification of Receipt of the provisional patent of Record (PCT/US2019/047356) has been received and patent issue is expected in early 2021.
Computational chemistry studies were introduced to confirm and validate experimental results and predict binding mechanisms for toxin interactions on sorbent surfaces. Computational chemistry strategies were used to characterize and confirm favorable surface interactions between hazardous chemicals and potential binding materials, delineate the fundamental chemical mechanisms of effective sorbents. Overall, such approaches can enhance the screening of potentially hazardous chemicals that can be adsorbed by montmorillonite clays, and aid in the design and discovery of amending compounds that enhance the stability of hazardous chemicals adsorbing to montmorillonite clays. The sorption of toxins (bisphenols, phthalates, PFAS, glyphosate, and paraquat) to parent montmorillonite clays and carnitine-amended clays has been investigated using molecular dynamics simulations based on classical molecular mechanical force interactions. Additionally, minimalistic simulations were used to provide atomistic details on the mechanism of sorption of a series of toxins (naphthalene, phenol, and chlorpyrifos) as well as to delineate between toxins with high affinity and toxins with a minimal affinity (e.g., benzene, toluene, and atrazine) for the parent clay. Overall the research lab’s studies, in collaboration with the Data Science Core, support that computational methods, including minimalistic simulations and models, can be used as predictive tools to screen potential hazardous chemicals that can be adsorbed by montmorillonite clays.
Ongoing work is underway to investigate the sorption of additional toxins to sorbent surfaces. In recent work, the project team have developed a plant-based model to evaluate the efficacy of selected sorbents to sequester (and neutralize) hazardous environmental chemicals in garden soil. Contaminants of concern include metals (arsenic, chromium, lead), PAHs, PFAS, and pesticides (DDT, glyphosate, and dieldrin). In an initial study, dieldrin and glyphosate were investigated due to their persistence in soil and potential for plant uptake. The sorbent materials that were most effective for binding dieldrin and glyphosate were applied to the model. Equilibrium isothermal analyses were conducted to determine if these sorbents would effectively bind dieldrin and glyphosate in garden soil. Initial results have indicated that activated carbon, calcium montmorillonite, and APMs can significantly reduce the bioaccessibility of dieldrin and glyphosate from garden soil. In other plant studies, representative PFAS was spiked in soils and treated with doses of sorbents for different durations. Results showed that nutrient amended clays significantly detoxified PFAS contaminated soils and reduced PFAS residues in plant root and sprout and enhanced plant growth. Ongoing work will determine if the best sorbents or sorbent combinations can reduce plant uptake of these and other pesticides in community gardens, thus impacting human and animal exposure following disasters and floods. Additionally, ongoing work will study protein amendments to montmorillonite clays to improve their efficacy toward toxic metal ions.