Effect of Single and Paired Metal Inputs in Soil on a Stress-Inducible Transgenic Nematode

Abstract.

A toxicity test using a transgenic strain of the free-living soil nematode Caenorhabditis elegans carrying a stress-inducible β-galactosidase reporter has been adapted for use in soil biomonitoring. High concentrations (250 μg · g⁻¹) of cadmium are required to induce the stress response in worms exposed to Lufa 2.2 soil. Even at relatively high concentrations, the response to copper and zinc additions alone is minimal, yet combinations of cadmium and copper in the test soil induce a larger response than with cadmium alone at the same concentration. In contrast, the addition of both zinc and cadmium induces a lower response than cadmium additions alone. Analysis of the interstitial water suggests that there is preferential occupation by copper of sorption sites in the soil, allowing more cadmium to remain in solution. Conversely, cadmium and zinc would appear to interact similarly with the soil constituents, resulting in an increase of both metals in solution with increased additions to the soil. Aquatic tests mimic the results of the soil test, so it is not increased cadmium availability alone that causes an increased stress response when both cadmium and copper are present. The presence of other metals could reduce the amount of cadmium available, which may be one factor in the zinc moderation of the stress response to cadmium. Intracellular mechanisms may also contribute to the copper enhancement of the stress response to cadmium.