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(13-05) Rhizotoxicity scores to determine bioavailable amounts of Cd and Cu in soil solutions. Voigt, Astrid*,1,2, Hendershot, William1, Sunahara, Geoffrey2, Sauve, Sebastien3, 1 McGill University-Macdonald Campus, 21 111 Lakeshore, Ste-Anne-de-Bellevue, Quebec, Canada2 Biotechnology Research Institute (CNRC), 6100 Royalmount Avenue, Montreal, Quebec, Canada3 Université de Montréal, C.P. 6128 succur. Centre-ville, Montreal, Quebec, Canada ABSTRACT- We are still not able to predict unambiguously the bioavailable amount of metals in soils. Short-term phytotoxicity tests using higher plants, such as root elongation tests, could be practical to assess the bioavailability of trace metals, such as Cd and Cu in soil solutions and furthermore to link toxicological effects directly to the bioavailable trace element status of soils. A modified procedure of the 2-day root elongation test of lettuce was used to examine the rhizotoxicity of Cd and Cu in synthetic and soil solutions differing in pH, ionic strength and composition. Surface adsorption models that consider the plant root as an adsorbing surface were tested for their ability to predict the rhizotoxicity of metals and hence their bioavailability in solution. Rhizotoxicity scores were related to metal ion activities at the root surface and in the bulk solution. These activities were incorporated into non-linear growth equations for root elongation versus toxic trace metals and alleviating ions. Using RRG (Relative root growth) has allowed us to pool data from growth experiments that were performed under similar conditions. Both metals led to significant inhibitions of root elongation at ion activities that are in the range of what has been reported in the literature for soil solutions when applied in simple media. The toxicity decreased with increasing concentrations of alleviating ions, such as H and Ca. The lettuce root elongation bioassay is sensitive and reproducible at environmentally relevant activities in simple solutions. Rhizotoxicity scores are a useful tool to study processes that are influencing the bioavailability of trace metals in soil solutions. Key words: trace metal, root elongation, rhizotoxicity, soil solution |
