Growth and Lead Accumulation Capacity of Lemna minor and Spirodela polyrhiza (Lemnaceae): Interactions with Nutrient Enrichment.

A study to understand the biological effects of samples prepared with lead and the effects of lead were conducted on Lemna minor L. and Spirodela polyrhiza (L.) Schleid. This study was intended to test the hypothesis that nutrient enrichment (P, NO(3) (-)-N and SO(4) (2-)) enhances the metal tolerance of floating macrophytes. The plants were exposed to Pb concentrations 0, 1, 5, 10, 25, and 50 mg l(-1) for a period of 1, 3, 5, and 7 days. L. minor accumulated 561 mg g(-1) dry weight (dw) Pb, and S. polyrhiza accumulated 330 mg g(-1) dw Pb after 7 days, whereas in the groups enriched with nutrients, L. minor accumulated 128.7 mg g(-1) Pb and S. polyrhiza accumulated 68.7 mg g(-1) dw Pb after 7 days. Relative growth rates and photosynthetic pigments (chlorophyll a, b, and carotenoid) were measured in L. minor and S. polyrhiza exposed to different Pb concentrations under laboratory conditions. Relative growth rates were negatively correlated with metal exposure, but nutrient addition was found to suppress this effect. Photosynthetic pigment levels were found negatively correlated with metal exposure, and nutrient addition attenuated chlorophyll decrease in response to metal exposure. Metal and nutrient concentration in water decreased throughout the experiments. The study concluded that nutrient enrichment increases the tolerance of L. minor and S. polyrhiza to metals, that L. minor and S. polyrhiza are suitable candidates for the phytoremediation of low-level lead pollution, and that L. minor was more effective in extracting lead than was S. polyrhiza.