Predicting Abiotic Reduction Rate Constants of Munition Compounds in Soils

Area of Science:

• Environmental Chemistry
• Soil Science
• Chemical Kinetics

Background:

• Munition compounds (MC) pose environmental risks due to their persistence in soil.
• Abiotic reduction is a key process for MC degradation in soil environments.
• Predicting MC reduction kinetics is crucial for effective soil remediation.

Purpose of the Study:

• To develop an empirical poly-parameter linear free energy relationship (LFER) for estimating mass-normalized rate constants of abiotic MC reduction in soil.
• To establish a predictive model for MC reduction kinetics based on thermodynamic properties and soil characteristics.

Main Methods:

• Conducted 131 kinetic experiments using three classes of MC (nitroaromatic, nitramine, azole) and 11 diverse soils.
• Reduced soils with dithionite to achieve varying electron contents.
• Investigated the influence of soil organic carbon and iron content on MC reduction rates.

Main Results:

• Developed an LFER predicting MC reduction rate constants within an order of magnitude using MC's one-electron reduction potential, soil pe, and pH.
• Observed that NTO reduction rates required soil-specific corrections due to its higher reactivity with iron reductants.

Conclusions:

• This is the first model to successfully predict the reduction kinetics of diverse nitro compounds in complex soils using thermodynamic properties.
• The developed LFER can aid in the management and restoration of soils contaminated with munition compounds or other nitro pollutants.