Cadmium-induced colony disintegration of duckweed (Lemna paucicostata Hegelm.) and as biomarker of phytotoxicity

The toxic effect of cadmium on Lemna paucicostata was investigated with hydroponic culture in a culture facility. Cadmium treatment (0.4–6.4 μmol L−1 Cd) induced L. paucicostata to release daughter fronds from the mother frond before maturity, resulting in colony disintegration. The 8-h and 24-h EC50 values for colony disintegration in L. paucicostata plants were 0.12 and 0.11 mg L−1, respectively. The maximum permissible concentrations (MPCs) were 0.012 and 0.011 mg L−1 accordingly (MPC=10%×EC50). These values were lower than the values of most of these biomarkers in duckweed reported in the literature, suggesting that colony disintegration in L. paucicostata may serve as a sensitive biomarker for the phytotoxicity test. Nutrient concentrations (1/2, 1/10, 1/20, 1/40, and 0-fold concentrations of Hoagland’s solution) and Cd salt form (CdCl2 or CdSO4) did not have a significant effect on colony disintegration. In addition, resistance to Cd stress differed significantly among clones of the plants. Approximately 2% of colonies in the wild population of L. paucicostata were tolerant of cadmium. These results indicate that colony disintegration of L. paucicostata could be used as a sensitive, cost-effective, and valuable biomarker to assess the acute phytotoxicity of cadmium and other heavy metals.