Comparative toxicity of six test chemicals to lettuce using two root elongation test methods.

Lettuce (Lactuca sativa L., cv buttercrunch) was used to evaluate and compare the results from two different root elongation phytotoxicity test methods with the same six test substances. Seeds were either germinated in the dark on an inclined filter paper substrate with one end immersed in test solution or germinated in 0.1 strength nutrient solution with a 16 hr light period in a glass bulb mixed and aerated with compressed air. Sodium fluoride, monosodium methanearsonate and monuron reduced lettuce root length at similar concentrations for both methods, while cadmium chloride and 2,4-D root inhibition occurred at concentrations approximately one order of magnitude smaller in the solution culture method than in the substrate method. Two orders of magnitude difference were observed between the two methods for silver nitrate. The results indicate that the solution method is at least as sensitive for all the chemicals tested and much more sensitive for some.