A Rapid, Sensitive, Seedling-Based Bioassay for the Determination of Toxicity of Solid and Liquid Substrates and Plant Tolerance

Abstract

We have developed a rapid, sensitive, seedling-based bioassay that can be used to evaluate the relative toxicity of solid and liquid media and to evaluate plant tolerance to toxic compounds. Using this method, it is possible to use percent germination, root and shoot growth as parameters. For this bioassay, solid substrate such as soil or acid-washed sand is sandwiched between two layers of microfiber filter paper inside a perforated Petri dish that bathes within a larger reservoir. The addition of distilled water or liquid media to the reservoir causes the liquid to pass through the perforations in the inner dish, through the solid substrate to form a film at the top of the filter paper that covers the substrate. Seeds are placed into the film of solution for germination and subsequent growth. Unlike germinating seeds in soil, the early germination of seeds can easily be observed. A distinction can then be made between seeds that do not germinate and those that do germinate but subsequently cease growth, giving the toxicity bioassay additional sensitivity. Root growth may be monitored as a time-course or measured at the end of the experiment. In addition, visual symptoms of stress such as swelling or coloration can be observed throughout the experiment. While shoot growth is often found to poorly reflect toxicity of media, we have found a good response in this parameter. The bioassay has been used to test relative toxicities of metal-contaminated soils, metal solutions, hydrocarbon-contaminated soils and soil leachates and airborne hydrocarbons accumulated in plant tissues.

Keywords:

• Metals
• hydrocarbons
• leachates
• airborne pollutants
• root and shoot growth
• germination