Mathematical Modeling of RDX and HMX Metabolism in Poplar (Populus deltoides × Populus nigra, DN34) Tissue Culture

ABSTRACT

Three mathematical models were developed based on a fate study as an approach to define transformation pathways of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) within plant cells. [U-¹⁴C]RDX and [U-¹⁴C]HMX were added in Murashige and Skoog (MS) liquid media containing Populus deltoides × P. nigra (DN34) tissue cultures. Radioactivity of samples was analyzed using HPLC, a bio-oxidizer and liquid scintillation counter. Based on information collected, transformation pathways of nitramine compounds were fitted with the raw data obtained and using a modified “green liver” model. Ordinary differential equations were developed and simulations were performed with MicroMath Scientist version 2.0 (MicroMath Inc., St. Louis, MO, USA). The three models, with different sequential transformation processes, were tested in order to support the raw data (model I) and the assumptions of the modified “green liver” model (models II and III). The results showed a high correlation between the collected data and the simulated concentrations for all models. Thus, the simplest model developed (model I) is the best model description of these particular results. The results obtained suggest that the principle of parsimony should be applied. The “green liver”-based models also demonstrated a reliable approach for the investigation of degradation pathways of nitramines within plant cells.

Keywords:

• phytoremediation
• “green liver” concept
• transformation pathways
• hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX)
• octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX)
• ammunition wastes
• modeling.

ACKNOWLEDGEMENTS

We gratefully acknowledge Stephen Duirk, Ph.D. (The University of Iowa, Iowa city, IA) for the assistance with the model calculations and Dr. Sijin Lee, Ph.D. (The University of Iowa) for valuable mathematical advice. This work was partly funded by the W.M. Keck Foundation and conducted as part of the Strategic Environmental Research and Development Program (SERDP) Project. The authors would like to thank CNPq—Conselho Nacional de Desenvolvimento Científico e Tecnológico, of the Ministry for Science and Technology of Brazil.