Laboratory Hood Culture of Terrestrial Plants for Investigations Involving Highly Toxic Materials.

Field investigations suffer from an inability to adequately control inherently unstable ambient variables. Toxicity testing conducted under controlled environmental conditions allow investigations to focus on factors that directly affect critical parameters. Normal plant physiological responses must be sustained to obtain results applicable to the field. We successfully sustained healthy living plants within laboratory hood constraints, and safely disseminated highly toxic compounds onto mature leaves of intact plants. Traditional plant culture in growth chambers or greenhouses typically involves balancing heat loads with chilling units too cumbersome for most laboratory hoods. Recent technological advances in blue light-emitting diodes (LED) now permit delivery of high-quality photosynthetically active radiation (PAR) in sufficient quantity to maintain physiology and sustain extended culture of healthy plants. We installed an array of modern LEDs to provide PAR in a laboratory surety hood. Conditions were: PAR illumination 300–350 μmoles cm² sec^-1, 16h-light/8h-dark; 22°C±2; RH 50%±10; airflow 1.5mph±0.09. We selected Echinochloa crus-galli (grass) for method development and subsequent research. Grass is the most prevalent higher plant worldwide, and natural distribution of E. crus-galli is one of the largest. We constructed stands with adjustable rings to hold soil containers in fixed positions, with petri dishes below each container for bottom-up irrigation. Individual leaves were secured in horizontal positions within rings by lengths of cellulose-acetate tape folded onto itself, then placed across the leaf surface, and tape ends were then secured. This prevented leaf damage by tape removal, yet ensured that disseminated compound contacted the leaf surface at points intended, and identified those locations for further investigation. Critical parameters successfully established were: characterization of droplet-spread, distribution within leaves as a function of time, coefficient of wash-off, Effective Half-Life, Contact Transfer from contaminated foliage. Results comport with those from field studies, thus allowing standardized comparisons among compounds, plant effects, and corresponding hazards.