Synergy in Science: Determining the Effective Half-Life of a Chemical Warfare Agent on Plant Foliage.

Methods for investigating Chemical Warfare Agent (CWA)–Plant Interactions have successfully been developed using live plant species, necessary in order to maintain plant physiological responses and obtain results applicable to CWA-contaminated battlefields. Pioneering research was undertaken, sustaining living plants within mandatory surety hood constraints and disseminating CWA onto individual mature leaves of the foliage of intact living plants. The primary plant species selected for method development and initial research is the grass Echinochloa crus-galli. Grass is the most prevalent type of higher plant worldwide, and the natural distribution of E. crus-galli is one of the largest. Traditional plant culture under controlled measurable environmental conditions outside of surety hoods typically involves balancing heat loads with large chilling units too cumbersome for functioning surety hoods. Because physiologically healthy living plants are required in order to investigate and record critical parameters for the effects of CWA–plant interaction, we installed and tested a system of light-emitting diodes (LED) within the surety hood in order to supply high-quality photosynthetically active radiation (PAR). The experimentally determined Effective Half-Life of VX [O-Ethyl-S-(2-diisoproylaminoethyl) methyl phosphonothiolate] on grass leaves (illumination >250 umoles cm² sec^-1, 16h-light/8h-dark; 21ºC; relative humidity >45%) is 72h (95% CI 46-98), calculated using the statistical Logistic Gompertz Model which provided the best fit to observed experimental data. Effective Half-Life is a measure of the net effect of all factors affecting CWA persistence, including evaporation, transformation, and fixation. Additional critical parameters under investigation include the coefficient of wash-off from measured rainfall, distribution of CWA on and within leaves as a function of time, and Contact Transfer (exposure) of CWA from contaminated foliar surfaces onto Army Combat Uniform (ACU). Results of these investigations provide critical parameter input for predictive models, direct experimental determinations for comparison of predictive model outcomes, plus information for decision-making affecting Soldiers on CWA contaminated Battlefields.