DEVELOPMENT OF A PLANT BIOASSAY TO ASSESS TOXICITY OF CHEMICAL STRESSORS TO EMERGENT MACROPHYTES

A static renewal bioassay has been proposed to evaluate the effects of chemical stressors on the growth of emergent macrophytes. Bioassay me thods were developed using Oryza sativa L. (domestic rice) as the test species and boron as the test compound. After culturing O. sativa in a natural sediment for 2 weeks, the plants were continuously exposed t o various concentrations of boron dissolved in the dilution water. At the end of the exposure period the plants were evaluated. Endpoints in cluded visual observations, dry weight, residue, and chlorophyll conce ntration in the leaf tissue. Dose-response relationships were establis hed for each endpoint; however, dry weight appears to be the least sen sitive endpoint. Exposure duration also significantly influenced toxic values. The bioassay procedure was then used to screen several other emergent macrophytes for toxicity to boron. Visual observations and re sidue indicated treatment differences for each of these species; howev er, dry weight and chlorophyll concentration did not confirm the diffe rences. Oryza sativa plants exposed to water naturally contaminated wi th boron accumulated similar concentrations of boron in their leaf tis sue as plants exposed to laboratory-prepared solutions of boron. Based on the data presented here, this bioassay appears to be useful in eva luating the potential toxicity of chemical stressors to emergent macro phytes.