Synergistic toxicity of multiple heavy metals is revealed by a biological assay using a nematode and its transgenic derivative

Caenorhabditis elegans, a free-living nematode species, was adopted for a toxicity bioassay of 10 heavy metals. The lethal concentration (LC) of these metals was determined. Based on these data, we conducted pairwise and triple metal combination testing and demonstrated that these heavy metals displayed synergistic killing effects on C. elegans larvae. Drastic increases in mortality rate up to 100% could be observed at low metal concentrations. The results illustrate the complexity of toxicity tests in biological systems and show that physical-chemical monitoring of toxicants may underestimate biohazards in environmental samples. We also demonstrate that a transgenic derivative nematode strain, KC136, carrying a heat shock promoter driven gfp reporter gene could be used to reduce the duration of an assay so that the synergistic effects among toxicants could be revealed. This derivative strain allows rapid and frequent monitoring of environmental hazards, which usually requires the handling of a large number samples. (C) 2002 Elsevier Science B.V. All rights reserved.