1,2,3-trichloropropane (TCP) is a contaminant of Department of Defense concern mainly due to its use in solvent formulations for paint and varnish removal, cleaning and degreasing, etc. Compared with other chlorinated solvents, TCP is similarly mobile, exceptionally persistent, and relatively toxic, suggesting that TCP will pose cleanup challenges that are similar, but in some respects more difficult. While TCP is characteristically recalcitrant to abiotic (and biotic) degradation pathways, potentially beneficial transformations of TCP are possible by hydrolysis, elimination, reduction, and oxidation. The objective of this project was to provide a detailed, quantitative characterization of these pathways of TCP degradation in water or soil.
The kinetics and products of abiotic hydrolysis, elimination, reduction, and oxidation of TCP were determined in batch and column experiments, as a function of environmentally relevant conditions including temperature, pH, and concentrations of likely co-contaminants such as other chlorinated solvents. The specific systems investigated include: (1) homogeneous solutions: deionized water with and without buffers, aqueous sulfide, and groundwater samples from representative sites; (2) reducing heterogeneous systems: Fe(0) (including bimetallic combinations with palladium or nickel), magnetite, goethite reduced by dithionite, and iron sulfide with particle sizes ranging from millimeters to nanometers; and (3) soluble chemical oxidants: hydrogen peroxide with various catalysts [aquo Fe(II), chelated Fe(II), and Fe(0)], ozone (with and without hydrogen peroxide), persulfate (with and without thermal activation), and permanganate. In addition, efforts on reduction of TCP with zero-valent zinc (ZVZ) were conducted during the final year of the study.
Hydrolysis of TCP under ambient conditions of pH and temperature is negligible, but base-catalyzed hydrolysis becomes favorable at high pH and temperature, such as under conditions of in situ thermal remediation. Oxidation of TCP is less favorable than it is with many contaminants and is negligible with mild/specific oxidants like permanganate. However, the stronger oxidants involved in some in situ chemical oxidation processes—especially hydroxyl and sulfate radicals—do oxidize TCP. Reduction of TCP under the mild conditions involved in natural attenuation is negligible, and the treatments used in conventional forms of in situ chemical reduction, such as granular zero-valent iron (ZVI), give only slow dechlorination. More rapid degradation of TCP was obtained by reduction with nano ZVI, palladized nano ZVI, and ZVZ. The potential for remediation of TCP with ZVZ was investigated in batch and column experiments because this combination might prove to be a novel solution to a distinctive problem.
This research provided the data necessary to make quantitative estimates of natural attenuation rates and to perform design/scaling calculations for engineered remediation technologies to address TCP. While the focus of this project was on abiotic degradation, the results will be useful for understanding the biodegradation of TCP where both processes occur by related reaction pathways.