Superfund Research Program
Clay Products in Remediation and Intervention Strategies
Clays are well known for their strong sorptive capabilities; however, for environmental remediation applications, the use of clays as fixed-bed filtration media has been limited due to relatively poor hydraulic conductivity. Tim Phillips' team of researchers at the Texas A&M Superfund Basic Research Program studies various chemical treatment processes for clays designed to enhance their sorptive properties and water permeability characteristics. Furthermore, by bonding modified clay particles to quartz or granulated activated carbon substrates, researchers have produced unique, matrix-anchored clays (Claypacs) that have both the sorptive properties of the clay and the water permeability of sand or granular carbon.
Researchers in Dr. Phillips' laboratory use molecular modeling techniques to study and design chemically diverse materials for the sorption and detoxification of hazardous compounds. To develop a Claypac tailored for a specific target chemical, Phillips first characterizes the sorption of the target chemical onto the surfaces of various clay and zeolitic minerals in order to define the structural and functional characteristics which maximize the sorption process. The researchers then delineate a combination of modified clay, bonding agent and substrate matrix to form a Claypac media with optimal particle size, water permeability and sorptive properties. Claypacs are first tested in laboratory bench-scale experiments, followed by scaled-up field studies to evaluate their effectiveness. Removal efficiencies of target chemical contaminants are determined by comparison of treated and untreated water samples via chemical analyses, and rapid in vitro bioassays such as the adult hydra bioassay and the chick embryotoxicity screening test.
Polycyclic aromatic hydrocarbons and pentachlorophenol
Wood-preserving facilities have been identified as a significant source of polycyclic aromatic hydrocarbon (PAH) contamination in soil and groundwater. Common contaminants at these sites include pentachlorophenol (PCP), the most acutely toxic of the chlorinated phenols, and creosote, a complex mixture of more than 400 compounds, 85-90% of which are PAHs. By bonding various organoclays onto quartz as a solid support, Dr. Phillips has developed a Claypac media that is effective in removing many of the toxic contaminants from groundwater at wood-preserving waste sites.
Following initial bench studies, researchers conducted field tests at a former wood-preserving facility in the northwestern United States, which is on the National Priorities List. Prototype filtration columns packed with Claypac composites reduced the contaminant load from the oil-water separator (OWS) effluent stream by 97%. The concentrations of benzo[a]pyrene and PCP were considerably reduced (i.e., >99%). The effectiveness of sorption of PCP from the OWS effluent by the Claypac was confirmed using a PCP-sensitive adult hydra bioassay. Studies were also conducted to compare remediation efficiencies of columns packed with Claypac or granular activated carbon (GAC) with samples of the effluent stream from a bioreactor. Although Claypac columns reduced the majority of contaminants, they were less effective in diminishing the levels of lower molecular weight PAHs. Conversely, GAC was more effective in removing the lower molecular weight PAHs, except for naphthalene and PCP. Laboratory studies utilizing radiolabeled compounds are in progress to determine optimum ratios of Claypac to quartz or GAC substrates for contaminant removal.
Chemoprevention of aflatoxicosis: Aflatoxin-producing molds are ubiquitous in the environment and commonly contaminate food items derived from a variety of grains and oilseeds. Moreover, aflatoxin B1 is a very potent carcinogen and hepatotoxin. Dr. Phillips has developed and patented a practical and effective approach to the problem of aflatoxin contamination of animal feeds - the dietary inclusion of processed calcium montmorillonite clay (NovaSilTM). When ingested in the diet, NovaSilTM acts as an enterosorbent that rapidly and preferentially binds aflatoxins in the gastrointestinal tract of animals, resulting in decreased aflatoxin uptake and bioavailability. NovaSilTM and similar clay-based sorbents are now being used in 10% of animal feeds worldwide to prevent aflatoxicosis. Phillips is optimistic that this same technology may one day be applicable and sustainable for the protection of humans by diminishing aflatoxin exposure and improving human health.
Detection of aflatoxins: In recent studies, nanostructuring methodologies were used to develop various formulations of NovaSilTM clay on the surface of quartz, and these clay/quartz composites were evaluated for their efficacy in the cleanup and analysis of aflatoxin B1 from aqueous solutions and contaminated grain samples. NovaSilTM clay, with high affinity for aflatoxins, was electrostatically anchored as a thin film onto the surface of quartz particles using poly(diallyldimethylammonium chloride), or PDDA. Self-assembly of films was accomplished by the sequential treatment of substrate in aqueous cationic solutions of PDDA and aqueous dispersions of exfoliated clay. Particle sizes and film thickness were controlled experimentally. Aflatoxin B1 sorption studies, using prototypical affinity columns, indicated that clay-based composites can be formulated to offer narrowly defined, reproducible capacity ranges. As a solid phase extraction media, these composites may provide an alternative and cost-effective method for the field-practical cleanup and analysis of aflatoxins from contaminated samples. Studies are ongoing in the Phillips laboratory at Texas A&M University to optimize affinity media for the detection of a variety of aflatoxin congeners, including aflatoxin M1 in urine as a biomarker of human and animal exposure.
Dr. Phillips is also involved in the development and validation of a sorbent technology for the removal of arsenic and other heavy metals from drinking water. This research, funded by an SBRP Small Business Innovation Research (SBIR) grant, is focused on providing a cost-effective remediation strategy for water systems that do not meet the new EPA arsenic Maximum Contaminant Level of 10 parts per billion.
Dr. Phillips' work demonstrates that naturally-occurring and chemically-modified clay minerals can be an integral component of practical strategies leading to decreased exposure to toxins and chemoprevention of toxin-induced disease.
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To learn more about this research, please refer to the following sources:
- Ake CL, Wiles MC, Huebner HJ, McDonald TJ, Cosgriff D, Richardson MB, Donnelly KC, Phillips TD. 2003. Porous organoclay composite for the sorption of polycyclic aromatic hydrocarbons and pentachlorophenol from groundwater. Chemosphere 51(9):835-844. doi:10.1016/S0045-6535(03)00040-7 PMID:12697173
- Bingham AK, Phillips TD, Bauer JE. 2003. Potential for dietary protection against the effects of aflatoxins in animals. J Am Vet Med Assoc 222(5):591-596. doi:10.2460/javma.2003.222.591 PMID:12619837
- Huebner HJ, Phillips TD. 2003. Clay-based affinity probes for selective cleanup and determination of aflatoxin B1 using nanostructured montmorillonite on quartz. J AOAC Int 86(3):534-539. PMID:12852572
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