Xiaomei. Li

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

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.

Evaluation of the Capability of Aggregated Oil Sands Mine Tailings: Biological Indicators

An experiment was initiated in 1997 in northeast Alberta at the Syncrude Canada Ltd. Mildred Lake site to field test an innovative technique for reclamation of oil sand mine tailings. This technique was used to create an aggregated soil material from oil sand tailings. A plant community was successfully established on the soil material created by this technique. However, whether the site would be capable of supporting a self-sustainable ecosystem for the long-term remained a challenging issue. We evaluated the capability of these aggregated oil sand tailings by using biological indicators of the abundance and diversity of soil microbial biomass. Soil respiration rates and soil microbial biomass measurements were used to assess the abundance and activities of soil microbial communities. The ability of soil microbial biomass to utilize a diverse range of carbon substrates was used to assess the diversity of soil microbial communities. Soil biological activity increased with increasing growth of plant biomass and over time. Increasing the amount of peat moss or muskeg incorporated into the soil during reclamation resulted in higher organic carbon and nitrogen content and caused an increase in abundance and diversity of soil microbial biomass. These results indicate that measurements of soil respiration and substrate utilization by soil microbial communities may be used as biological indicators for assessing the capability of reclaimed soils.

PHYSIOLOGICAL TESTS TO MEASURE IMPACTS OF GASEOUS POLYCYCLIC AROMATIC HYDROCARBONS (PAHs) ON CULTIVATED PLANTS

Polycyclic aromatic hydrocarbons (PAHs) are important airborne pollutants that accumulate at increased concentrations in vegetation surrounding PAH emitters such as smelters, roadways, runways, oil and gas operations. Terrestrial plants are at risk of injury from potentially toxic PAHs. The objective of this study was to measure the effects of gaseous PAHs on performance of crop plants using a combination of destructive and non-destructive methods. Experiments were carried out in a gas exposure system on five crop species: canola, barley, field pea, alfalfa and lettuce. Plants were exposed to naphthalene and creosote (a substance containing 90% PAHs) at two developmental stages (7 and 21 days old). Chlorophyll fluorescence was measured daily using a portable screening chlorophyll fluorometer and compared with readings taken from control plants. At the end of the experiments, chlorophyll content in leaves was measured using a portable chlorophyll meter. A rapid, sensitive seedling-based bioassay was used to evaluate the relative toxicity of water-extracts from plants exposed to PAHs. Our results suggest that measurements of photosynthetic parameters of plants exposed to gaseous PAHs using portable devices accurately reflect detrimental effects of these compounds. The bioassay used in these experiments allowed for the indirect determination of the accumulation of PAHs in/on plant tissues. Simple, non-destructive physiological measurements and bioassays are practical diagnostic tools for the monitoring of PAH exposure and injury.